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DIRECTORATE GENERAL FOR ENERGY (DG XVII)
LAYMAN'S HANDBOOK
ON HOW TO DEVELOP A SMALL HYDRO SITE
(Second Edition)
June 1998
t:UROPEAN COMMISION
AUTHOR
Celso Penche
Dr Ingeniero de Minas (U.Politecnica de Madrid)
Introduction
This handbook, an updated version of the original "Layman's Handbook on how to develop a Small Hydro Site",
published by the Commission in 1993, has been written, in the frame of the ALTENER programme, under
contract with the Commission of the European Communities (Directorate General for Energy, DG XVII). It has
not been designed to replace professional expertise but it is hoped it is comprehensive enough to advise
laymen on all necessary procedures that should be followed to develop a site. However its content includes
enough technical information, so a non-specialist engineer would be able to produce a primary feasibility report.
Hydraulic engineering is based on the principles of fluid mechanics. However until now there does not exist,
and probably never will, a general methodology for the mathematical analysis of the movement of the fluids.
Based on the large amount of accumulated experience there exists many empirical relationships to achieve
practical engineering solutions with the movement of the water, the fluid that concerns hydroelectricity. Chapter
2, based on part of the original chapter 5 -written by Eric Wilson is devoted to this subject.
All hydroelectric generation depends on falling water. The first step to develop a site must address the
availability of an adequate water supply. Chapter 3 is entirely devoted to this subject, and particularly to
comment on the European Atlas of Small Scale Hydropower Potential, developed by the Institute of
Hydrology in the UK, on behalf of ESHA and with the financial aid of the DG XVII.
Experience shows that many small hydro plants have failed because they were poorly designed, built or
operated. Most of these failures seepage under the weir, open channel slides-occurred through a lack of
proper geological studies of the site. Chapter 4 incorporates guidelines on such studies.
Hydraulic structures and ancillaries represent almost fifty per cent of the investment cost. If poorly designed
they will require such high maintenance costs that the investment will become unprofitable. Chapter 5 is
devoted to these structures.
Turbines transform the potential energy of water to mechanical rotational energy, which in turn is transformed
into electrical energy in the generators. Chapter 6 is devoted to the study of turbines and generators and to the
devices employed to control them.
Although since the publication of the first edition of the Layman's Handbook many sites have been developed in
the E.U, the installed capacity would be greater if the administrative procedures to authorise the use of water
had been simpler. Many hundreds of authorisation requests are pending approval, mainly because of
supposed conflict with the environment. Chapter 7, "Environmental impact and its mitigation", intends to provide
a few guidelines to help the designer to propose mitigating measures that can be easily agreed with the
licensing authorities. The various papers presented to HIDROENERGIA and more specifically to the European
Workshop on THERMIE "Strategies to overcome the environmental burden of small hydro and wind energies"
that was held at Vitoria in October 1996, constitute the basis of this chapter.
An investor decides to develop a small hydro site in order to obtain a reasonable profit. To do that his decision
should be based on sound economic principles. Chapter 8 shows how the financial mathematics can help to
calculate the cost of the kWh produced annually, and to compare different possible alternatives for the scheme.
Chapter 9 reviews the administrative procedures and buy-back tariffs nowadays in force. Unfortunately the
trend toward deregulation of the electricity market makes the situation very volatile, preventing accurate
reporting of the market from an institutional viewpoint.
Acknowledgements
Although based on the original version, the handbook has been entirely rewritten. The original chapter 5 has
been split in two: chapter 2, a fundamental treatment of engineering hydraulics, and chapter 3 devoted
exclusively to the water resource and to the possibilities offered by the European Atlas of Small Scale
Hydropower Potential. The Institute of Hydrology (IH) in the UK. on behalf of ESHA, has developed this
computer program, with the financial aid of the DG XVII, as a tool to enable potential investors to define the
hydrological potential, for any ungauged site within the European Union. We acknowledge the co-operation of
IH, and more specifically of Gwyn Rees and Karen Kraker, by allowing us to reproduce entire paragraphs of the
"Technical Reference and User Guide" of the Atlas.
Two well known experts, Bryan Leyland from Australia and Freddy lsambert from France, presented to
HIDROENERGIA 95 two papers, dealing with the topic "lessons from failures", describing several schemes
that, due to a lack of adequate geological studies, failed outrageously during its operation. On the base of
these experiences a new chapter, Chapter 4, devoted to the technologies employed to study the site in depth,
was introduced. This chapter has been almost entirely written by Alberto Foyo, Professor of Ground Engineer-
ing at the E. T. S. I. C. C. P, Polytechnic Cantabria University.
Other sources of inspiration in the composition of the handbook were "Micro Hydropower Source" by R.
lnversin (NRCA 1986). the volume 4 of the "Engineering Guidelines for Planning and Designing Hydroelectric
Developments" (ASCE 1990) and "Hydraulic Engineering Systems" (N.C.Hwang and C.E. Hita 1987). The
authorisation by lnversin to reproduce the Appendix X of his book, dealing with the physical description of the
waterhammer phenomena, is much appreciated. We appreciate the spirit of collaboration of the authors of
hydraulic papers; all of them gave their authorisation to reproduce their papers-
We should thank Eric Wilson for his efforts to correct the English text, both for style and content. If any errors
are still present it will be unquestionably the fault of the author.
And finally our acknowledgement to President Henri Baguenier, who solicited the support of the DG XVII to
commission the writing of the handbook and to facilitate the relationship with the ALTENER Committee.
Celso Penche
June 1988.
X Manual de pequena hidraulica
Table of Contents
1.1ntroduction
1. 0 A free fuel resource potentially everlasting ................................................................................................. 15
1.1 Definition of small hydropower .................................................................................................................... 16
1.2 Site configurations .. .. .. . .. .. ... .. .. .. .. . .. . .. . . .. .. . .. . . .. .. .. .. .. . . . . . .. .. .. .. .. .. . . .. . .. .. .. .. . . . . .. . . .. . .. .. .. .. .. . .. .. .. .. .. .. .. . .. . .. .. . .. . . .. .. .. 16
1.2. 1 Run-of-river schemes .. .. . .. .. .. .. .. .. .. .. . .. . . .. .. .. .. .. .. .. .. .. .. . .. .. .. . .. .. . .. . .. .. .. . . .. .. .. . .. .. . .. .. .. . .. .. .. .. .. .. .. . .. . .. .. .. .. . .. .. .. 17
1.2.2 Schemes with the powerhouse at the base of a dam .......................................................................... 19
1.2.3 Schemes integrated with an irrigation canal ........................................................................................ 20
1.2.4 Schemes integrated in a water abstraction system ............................................................................. 21
1.3 Planning a small hydropower scheme ......................................................................................................... 22
2. Fundamentals of Hydraulic Engineering
2.0 Introduction................................................... . ........................................................................................... 25
2.1 Water flow in pipes ...................................................................................................................................... 25
2.1.1 Los of head due to friction ................................................................................................................... 27
2.1.2 Loss of head due to turbulence ........................................................................................................... 36
2.1.2.1 Trash rack (or screen) losses ......................................................................................................... 36
2.1.2.2 Loss of head by sudden contraction or expansion ......................................................................... 37
2.1.2.3 Loss of head in bends .................................................................................................................... 39
2.1.2.4 Loss of head through valves .......................................................................................................... 40
2.1 .3 Transient flow ...................................................................................................................................... 41
2.2 Water flow in open channels ....................................................................................................................... 44
2.2.1 Clasification of open channel flows ..................................................................................................... 44
2.3.2 Uniform flow in open channels ........................................................................................................... 45
2.2.3 Principles of energy in open channel flows ......................................................................................... 46
2.3 Computer programs .................................................................................................................................... 51
Bibliography ....................................................................................................................................................... 53
3 The water resource and its potential
3.0 Introduction .................................................................................................................................................. 55
3.2 Evaluating streamflows by discharge measurements ................................................................................ 57
3.2.1 Velocity-area method ................................................................................................................................ 57
3.2.1.1 Measuring the cross-sectional area ................................................................................................ 59
3.2.1.2 Measuring the velocity .................................................................................................................... 59
3.2.3 Weir method ........................................................................................................................................ 64
3.2.4 Slope-area method . . .. ... .. . . . . .. .. .. .. .. .. . . .. . . . .. .. .. .. .. . . .. . . .. . . . . . .. . . .. .. . . ........................................................... 65
3.3 Streamflow characteristics ........................................................................................................................... 66
3.3.1 Hydrograph ......................................................................................................................................... 66
3.3.2 Flow Duration Curves (FDC) ............................................................................................................... 66
3.3.3 Standardised FDC curves ................................................................................................................... 68
3.3.4 Evaluating streamflows at ungauged sites .......................................................................................... 68
3.3.5 European Atlas of Small Scale Hydropower Resources ...................................................................... 70
3.3.6 FDC's for particular months or other periods ....................................................................................... 72
3.3.7 Water pressure or 'head' ..................................................................................................................... 72
3.3.7.1 Measurement of gross head ........................................................................................................... 72
3.3.7.2 Estimation of net head .................................................................................................................... 72
3.4 Residual, reserved or compensation flow .................................................................................................... 74
3.5 Estimation of plant capacity and energy output ........................................................................................... 75
3.5.1 How the head varies with the flow and its influence on the turbine capacity ....................................... 78
3.5.2 Another methodology to compute power and annual energy output ................................................... 79
3.5.3 Peaking operation ............................................................................................................................... 80
3.6 Firm energy ................................................................................................................................................. 81
Bibliography ............................................................................................................................................... 83
xi
4. Site evaluation methodologies
4.0 Introduction .................................................................................................................................................. 85
4.1 Cartography ................................................................................................................................................. 85
4.2 Geotechnical studies ................................................................................................................................... 86
4.2.1 Methodologies to be used ................................................................................................................... 87
Photogeology ......................................................................................................................................... 87
Geomorphologic maps ........................................................................................................................... 87
Laboratory analysis ................................................................................................................................ 87
Geophysical studies ............................................................................................................................... 87
Structural geological analysis ................................................................................................................. 87
Direct investigations. Borehole drilling .................................................................................................... 87
4.2.2 Methodologies. The study of a practical case ..................................................................................... 88
4.2.2.1 The weir ......................................................................................................................................... 88
4.2.2.2 The open channel ........................................................................................................................... 90
4.2.2.3 The channel in tunnel. .................................................................................................................... 92
4.2.2.4 The powerhouse ............................................................................................................................. 94
4.3 Learning from failures .................................................................................................................................. 96
Ruahihi canal failure (New Zealand) ..................................................................................................... 97
La Marea canal failure (Spain) ............................................................................................................... 99
Seepage under a weir (France) ............................................................................................................ 100
The hydraulic canal in a low-head 2 MW scheme ................................................................................ 101
5. Hydraulic structures
5.1 Structures for storage and water intake ..................................................................................................... 103
5.1.1 Dams ................................................................................................................................................. 103
5.1.2 Weirs ................................................................................................................................................. 103
5.1.2.1 Devices to raise the water leveL ................................................................................................... 105
5.1.3 Spillways ........................................................................................................................................... 108
5.1.4 Energy dissipators .............................................................................................................................. 111
5.1.5 Low level outlets ................................................................................................................................. 111
5.1.6 River diversion during construction .................................................................................................. 111
5.2 Waterways .................................................................................................................................................. 112
5.2.1 Intake structures ................................................................................................................................. 112
5.2.1.1 Water intake types ......................................................................................................................... 113
5.2.1.21ntake location ............................................................................................................................... 115
5.2.2 Power intake ....................................................................................................................................... 116
5.2.3 Mechanical equipment ....................................................................................................................... 119
5.2.3.1 Debris management in intakes ...................................................................................................... 119
5.2.3.2 Sediment management in intakes ................................................................................................ 124
5.2.3.3 Gates and valves .......................................................................................................................... 126
5.2.4 Open channels .................................................................................................................................. 129
5.2.4.1 Design and dimensioning ............................................................................................................. 129
5.2.4.2 Circumventing obstacles .............................................................................................................. 137
5.2.5 Penstocks ......................................................................................................................................... 137
5.2.5.1 Arrangement and material selection for penstocks ....................................................................... 137
5.2.5.2 Hydraulic design and structural requirements .............................................................................. 141
Penstock diameter ................................................................................................................................ 141
Wall thickness ...................................................................................................................................... 144
5.2.5.3 Saddles, supporting blocks and expansion joints ........................................................................ 151
5.2.6 Tailraces ............................................................................................................................................ 151
xii Manual de pequena hidraulica
6 Electromechanical equipment
6.0 Powerhouse .............................................................................................................................................. 153
6.1 Hydraulic turbines ...................................................................................................................................... 155
6.1.1 Classification criteria ......................................................................................................................... 157
6.1.1.1 On the basis of the flow regime in the turbine .............................................................................. 157
6.1.1.1.1 Impulse turbines ...................................................................................................................... 157
Pelton turbines ..................................................................................................................................... 157
Turgo turbines ...................................................................................................................................... 158
Cross-flow turbines . . . .. .. .. .. .. .. ... .. .. .. . .. .. .. .. .. . .. .. . . .. .. .. .. . . . . . . .... .. .. .. .. . . . . . .. .. . .. .. . . . . .. . . .. .. . . . . . .. .. . .. .. .. .. .. .. . .. .. . .. .. 158
6.1.1.1.2 Reaction turbines .................................................................................................................... 159
Francis turbines .................................................................................................................................... 163
Kaplan and propeller turbines .............................................................................................................. 163
Pumps working as turbines .................................................................................................................. 163
6.1.1.2 On the basis of the specific speed ................................................................................................ 164
6.1.2 Turbine selection criteria ................................................................................................................... 170
6.1.3 Turbine efficiency .............................................................................................................................. 177
6.1.4 Turbine performance characteristics ................................................................................................. 179
6.1.5 Turbine performance under new site conditions ................................................................................ 180
6.2 Speed increasers ...................................................................................................................................... 183
6.2.1 Speed increaser types ....................................................................................................................... 183
Parallel-shaft ........................................................................................................................................ 183
Bevel gears: ......................................................................................................................................... 183
Epicycloidal: ......................................................................................................................................... 184
6.2.2 Speed increaser design ..................................................................................................................... 184
6.2.3 Speed increaser maintenance ........................................................................................................... 185
6.3 Generators ................................................................................................................................................ 185
6.3.1 Generator configurations ................................................................................................................... 187
6.3.2 Exciters ............................................................................................................................................. 187
6.3.3 Voltage regulation and synchronisation ............................................................................................ 188
6.3.3.1 Asynchronous generators ............................................................................................................ 188
6.3.3.2 Synchronous generators ............................................................................................................. 188
6.4 Turbine control .......................................................................................................................................... 189
6.4 .1 Speed Governors . .. .. . .. .. .. . .. . . . .. .. . . . .. .. . . . . . . .. .. .. .. . .. . . .. . .. .. .. .. . . . . . .. .. .. . . . .. .. .. .. .. .. .. . .. . . . . .. .. .. . . . .. . .. .. .. . .. . . . . .. . . . .. 189
6.5 Switchgear equipment .......................................................................................................................... 192
6.6 Automatic control ....................................................................................................................................... 194
6. 7 Ancillary electrical equipment .................................................................................................................... 195
6. 7.1 Plant service transformer .................................................................................................................. 195
6.7.2 DC control power supply ................................................................................................................... 195
6. 7.3 Headwater and tailwater recorders .................................................................................................... 195
6.7.4 Outdoor substation ............................................................................................................................ 197
6.8 Examples ................................................................................................................................................... 197
Bibliography ........................................................................................................................................... 200
7. Environmental impact and its mitigation
7.0 Introduction ................................................................................................................................................ 201
7.1 Burdens and impacts identification ............................................................................................................ 202
7.2 Impacts in the construction phase ............................................................................................................. 203
7.2.1 Reservoirs ......................................................................................................................................... 204
7.2.2 Water intakes, open canals, penstocks, tailraces, etc ....................................................................... 204
xiii
7.3 Impacts arising from the operation of the scheme ..................................................................................... 205
7.3.1 Sonic impacts .................................................................................................................................... 205
7.3.2 Landscape impact ............................................................................................................................. 206
7.3.3 Biological impacts .............................................................................................................................. 214
7 .3.4 Archaeological and cultural objects ................................................................................................... 232
7.4 Impacts from transmission lines ................................................................................................................ 233
7.4.1 Visual impact ..................................................................................................................................... 233
7.4.2 Health impact .................................................................................................................................... 234
7.4.3 Birds collisions ................................................................................................................................... 234
7.5 Conclusions ............................................................................................................................................... 234
8 Economic Analysis
8.0 Introduction ................................................................................................................................................ 237
8.1 Basic considerations ................................................................................................................................. 237
8.2 Financial mathematics ............................................................................................................................... 240
8.3 Methods of economic evaluation ............................................................................................................... 242
8.3.1 Static methods (which do not take the opportunity cost into consideration) ...................................... 242
8.3.2 Dynamic methods .............................................................................................................................. 243
8.3.3 Examples .......................................................................................................................................... 245
8.4 Financial analysis of some European schemes ......................................................................................... 248
9. Administrative procedures
9.0 Introduction ................................................................................................................................................ 253
9.1 Economic issues ....................................................................................................................................... 253
9.3 How to support renewable energy under deregulation* ............................................................................. 256
9.5.1 Set asides ......................................................................................................................................... 256
9.2.2 Emission Taxes, Caps and Credits .................................................................................................... 258
9.2.3 Green pricing ..................................................................................................................................... 258
9.2.4 Imposed tariffs ................................................................................................................................... 259
9.2.5. Miscellaneous ................................................................................................................................... 259
9.3 Technical aspects ...................................................................................................................................... 260
9.4 Procedural issues ...................................................................................................................................... 261
9.5 Environmental constraints ......................................................................................................................... 263
GLOSSARY .................................................................................................................................................... 265
xiv Manual de pequena hidraulica
1. Introduction
1.0 A free fuel resource potentially everlasting.
Following the United Nations Conference in Rio on the Environment and
Development, the European Union committed itself to stabilising its carbon dioxide
(C02 ) emissions, primarily responsible for the greenhouse effect, at 1990 levels
by the year 2000.Ciearly Europe will not be able to achieve this ambitious target
without considerable promotion of energy efficiency and a major increase in •'le
development of renewable energy sources. The European Commission is well
aware of this fact and one of the AL TENER objectives is to double, from now to
the year 2010, the electricity generated by renewable resources.
From the beginning of electricity production hydropower has been, and still is
today, the first renewable source used to generate electricity. Nowadays
hydropower electricity in the European Union -both large and small scale -
represents according to the White Paper, 13% of the total electricity generated,
so reducing the C02 emissions by more than 67 million tons a year. But whereas
the conventional hydro requires the flooding of large areas of land, with consequent
serious environmental and social costs, the properly designed small hydro schemes
(less than 10 MW installed capacity) are easily integrated into local ecosystems.
Small hydro is the largest contributor of electricity from renewable energy sources,
both at European and world level. At world level. it is estimated there is an installed
capacity of 47.000 MW, with a potential -technical and economical-close to
180.000 MW. At European level, the installed capacity is about 9.500 MW, and
the EC objective for the year 2010 is to reach 14.000 MW..
The large majority of small hydro plants are «run-of-river» schemes, meaning
simply that the turbine generates when the water is available and provided by
the river. When the river dries up and the flow falls below some predetermined
amount, the generation ceases. This means. of course, that small independent
schemes may not always be able to supply energy, unless they are so sized that
there is always enough water.
This problem can be overcome in two ways. The first is by using any existing
lakes or reservoir storage upstream. The second is by interconnecting the plant
with the electricity supplier's network. This has the advantage of allowing automatic
control and governing of the frequency of the electricity but the disadvantage of
having to sell the energy to the utility company at its price -the 'buy-back' rate-,
which can be too low. In recent years, in most of the member states, the rate has
been fixed by national governments, who, conscious of the environmental benefits
of renewables, have been making provision for increasing the "buy-back" rates.
Portugal, Spain and Germany have proved that reasonable "buy-back" rates are
essential to increase the generation of electricity with renewables.
With the announced deregulation of the European electricity market, the small
producers will be in a weak position to negotiate the purchase of their electricity
by the utilities. But national governments cannot dispense with renewables in
their effort to curb C02 emissions, and must found ways, perhaps similar to the
British NFFO to support generation by renewables.
16 Layman's Guidebook
1.1 Definition of small hydropower
There is no consensus in EU member states on the definition of small hydropower:
Some countries like Portugal, Spain, Ireland, and now, Greece and Belgium, accept
10 MW as the upper limit for installed capacity. In Italy the limit is fixed at 3 MW
(plants with larger installed power should sell their electricity at lower prices); in
France the limit was established at 8 MW and UK favour 5 MW. Hereunder will be
considered as small any scheme with an installed capacity of 10 MW or less. This
figure is adopted by five member states, ESHA, the European Commission and
UNIPEDE (International Union of Producers and Distributors of Electricity).
1.2 Site configurations
The objective of a hydro power scheme is to convert the potential energy of a
mass of water, flowing in a stream with a certain fall (termed the ''head"), into
electric energy at the lower end of the scheme, where the powerhouse is located.
The power of the scheme is proportional to the flow and to the head.
According to the head, schemes can be classified in three categories:
• High head: 100-m and above
• Medium head: 30 -100 m
• Low head: 2-30m
ELEVATION
tunnel
PLANT
figure 1.1 High head scheme
Chapter 1 . Introduction
These ranges are are not rigid but are merely means of categorising sites.
Schemes can also be defined as
• Run-of-river schemes
• Schemes with the powerhouse located at the base of a dam
• Schemes integrated on an canal or in a water supply pipe
17
1.2.1 Run-of-river schemes
In the «run-of-river» schemes the turbine generates electricity as and when the
water is available and provided by the river. When the river dries up and the flow
falls below some predetermined amount-the minimum technical flow of the turbine
equipping the plant-, generation ceases.
Medium and high head schemes use weirs to divert water to the intake, from
where it is conveyed to the turbines, via a pressure pipe or penstock. Penstocks are
expensive and consequently this design is usually uneconomic. An alternative (figure
1.1) is to convey the water by a low-slope canal, running alongside the river, to the
pressure intake or forebay, and then in a short penstock to the turbines. If the
topography and morphology of the terrain does not permit the easy layout of a canal,
a low-pressure pipe, with larger latitude in slopes, can be an economical option. At
the outlet of the turbines, the water is discharged to the river, via the tailrace.
Occasionally a small reservoir, storing enough water to operate only on peak
hours, when "buy-back" rates are higher, can be created by the weir, or a similarly
sized pond can be built in the forebay, using the possibilities provided by geotex-
tiles.
Low head schemes are typically built in river valleys. Two technological options
can be selected. Either the water is diverted to a power intake with a short penstock
(figure 1.2), as in the high head schemes, or the head is created by a small dam,
provided with sector gates and an integrated intake (figure 1.3), powerhouse and
figure 1.2
elevation
~sector gate
PLANT
flow
------+
gate gear
+ ~
gate
river bottom
ELEVATION
generator
SECTION A-A
figure 1.3
trashrack cleaner
55
Chapter I. Introduction 19
figure 1.4
fish ladder.
1.2.2 Schemes with the powerhouse at the base of a dam
A small hydropower scheme cannot afford a large reservoir to operate the plant
when it is most convenient: the cost of a relatively large dam and its hydraulic
appurtenances would be too high to make it economically viable. But if the reservoir
has already been built for other purposes flood control, irrigation network, water
abstraction for a big city, recreation area, etc, -it may be possible to generate
electricity using the discharge compatible with its fundamental usage or the
ecological flow of the reservoir.
The main question is how to link headwater and tailwater by a waterway and how to
fit the turbine in this waterway. If the dam already has a bottom outlet, as in figure
1.4, the solution is clear. Otherwise. provided the dam is not too high, a siphon
intake can be installed. Integral siphon intakes (figure 1 ,5) provide an elegant solution
in schemes with heads up to 10 meters and for units of no more than 1.000 kW,
although there are examples of siphon intakes with an installed power up to 11 MW
(Sweden) and heads up to 30,5 meters (USA). The turbine can be located either on
~
aspiration ---~-----'------...
figure 1.5
siphon intake
20 Layman's Guidebook
SECTION
Bypass
PLANT
figure 1.6
top of the dam or on the downstream side. The unit can be delivered pre-packaged
to the works. and installed without major modifications of the dam.
1.2.3 Schemes integrated with an irrigation canal
Two types of schemes can be designed to exploit irrigation canal falls:
• The canal is enlarged to the required extent. to accommodate the intake, the
power station, the tailrace and the lateral bypass. Figure 1.6 shows a scheme
of this kind, with a submerged powerhouse equipped with a right angle drive
Kaplan turbine. To ensure the water supply for irrigation, the scheme should
include a lateral bypass, as in the figure, in case of shutdown of the turbine.
This kind of scheme must be designed at the same time as the canal, because
the widening of the canal in full operation is an expensive option.
• If the canal already exists, a scheme like the one shown in figure 1. 7 is a suitable
option. The canal should be slightly enlarged to include the intake and the
figure 1.7
Chapter 1. Introduction 21
spillway. To reduce the with of the intake to a minimum, an elongated spillway
should be installed. From the intake, a penstock running along the canal brings
the water under pressure to the turbine. The water, once through the turbine , is
returned to the river via a short tailrace. As generally, fish are not present in
canals , fishpasses are unnecessary.
1.2.4 Schemes integrated in a water abstraction system
The drinking water is supplied to a city by conveying the water from a headwater
reservoir via a pressure pipe. Usually in this type of installation, the dissipation of
energy at the lower end of the pipe at the entrance to the Water Treatment Plant is
achieved through the use of special valves. The fitting of a turbine at the end of the
pipe, to convert this otherwise lost energy to electricity, is an attractive option ,
rovided that waterhammer that wou ld endan er the i e is avoided .
reservoir
figure 1.8
industries
compensation
storage
• • • • • • • • • • • • • • •
• • • • • • • • • •
• • • • • • • • • • •
22 Layman's Guidebook
Waterhammer overpressures are especially critical when the turbine is fitted on
an old pressure pipe.
To ensure the water supply at all times, a system of bypass valves should be
installed. In some water supply systems the turbine discharges to an open air
pound. The control system maintains automatically, and unattended, the level of
the pound. In case mechanical shutdown or load rejection closes the turbine, the
valve of the main bypass can also maintain the level of the pound automatically.
Occasionally if the main bypass valve is out-of-operation and overpressure occurs,
an ancillary bypass valve is rapidly opened by a counterweight and is subsequently
closed. All the closing and opening operations of these valves however must be
slow enough to keep pressure variations within acceptable limits.
The control system has to be more complex in those systems where the turbine
outlet is subjecto the counter-pressure of the network, as is shown in figure 1.8.
1.3 Planning a small hydropower scheme
The definitive project of a scheme comes as the result of a complex and iterative
process, where, always having in view the environmental impact, the different
technological options are compared from an economic viewpoint.
Although is not easy to provide a detailed guide on how to evaluate a scheme, it
is possible to describe the fundamental steps to be followed, before deciding if
one should proceed to a detailed feasibility study or not. A list of the studies that
should be undertaken:
• Topography and geomorphology of the site.
• Evaluation of the water resource and its generating potential
• Site selection and basic layout
• Hydraulic turbines and generators and their control
• Environmental impact assessment and mitigation measures
• Economic evaluation of the project and financing potential
• Institutional framework and administrative procedures to attain the authorisations
The water flowing along natural and man-made canals, conducted by low and
high-pressure pipes, spilling over weir crests, and moving the turbines, involves
the application offundamental engineering principles in fluid mechanics. In Chapter
2 those principles are reviewed together with the shortcuts arising from the
experience accumulated from centuries of hydraulic systems construction.
To decide if a scheme will be viable it is necessary to begin by evaluating the
water resource existing at the site. The energy potential of the scheme is
proportional to the product of the flow and the head. The gross head can usually
be considered as constant, but the flow varies over the year. To select the most
appropriate hydraulic equipment, estimate its potential and calculate the annual
energy output, a flow-duration curve is most useful. A single measurement of
instantaneous flow in a stream has little value. Measuring the gross head requires
a straightforward survey. The results obtained by using a surveyor's level and
Chapter I. Introduction 23
staff is accurate enough, but the recent advances in electronic surveying equipment
make the topographic work much simpler and faster. To produce a flow-duration
curve on a gauged site has no mystery; to produce such a curve at an ungauged
site requires a deeper knowledge of the hydrology. In Chapter 3 various methods
for measuring the quantity of water flowing in a stream are analysed and hydrologic
models to calculate the flow regime at ungauged sites are discussed .. Fortunately,
new computer package programs will ease that task and in Chapter 3 one of
these programs (HydrA) is presented.
Chapter 4 presents the techniques-orto-photography, RES, GIS, geomorphology,
geotectonics, etc-used nowadays for site evaluation, preventing potential future
failures. Some of these failures are analysed and conclusions about how they
might have been avoided are explained.
In Chapter 5 the basic layouts are developed and the hydraulic structures, such
as weirs, canals, spillways, intakes and penstocks, studied in detail.
Chapter 6 deals with the electromechanical equipment used to convert the potential
energy of the mass of water to electricity. Turbines themselves are not studied in
detail, but attention is focused on turbine configurations, specifically for low head
schemes, and on the process of turbine selection, with emphasis on specific
speed criteria. Since small hydro schemes are nowadays unattended, the control
systems, based on personal computers, are reviewed.
Environmental Impact Assessment is required to attain authorisation to use the
water. Although several recent studies have shown that small hydropower having
no emissions nor producing toxic wastes, does not contribute to climatic change,
designers should implement all necessary measures to mitigate local ecological
impacts. Chapter 7 analyses those impacts and mitigating measures.
Chapter 8 reviews techniques, which can be applied in the economical evaluation
of a scheme. Various methodologies of economic analyses are described and
illustrated with tables showing the cash flows generated by the schemes.
Institutional frameworks and administrative procedures in various UE member-
states are reviewed. Unfortunately the recent electricity industry's deregulation
make itimpossible to detail a situation that was fairly clear few years ago, when
ESHA produced in December 1994 and under contract with the E. C., Directorate
General for Energy, DGXVII, the report" Small Hydropower. General Framework
for Legislation and Authorisation Procedures in the European Union"
24 Layman's Guidebook
2. Fundamentals of Hydraulic Engineering
2.0 Introduction
Hydraulic engineering is based on the principles of fluid mechanics, although
many empirical relationships are applied to achieve practical engineering solutions.
Until now there does not exist, and probably never will, a general methodology for
the mathematical analysis of the movement of fluids. Based on the large amount
of accumulated experience, certainly there are particular solutions to specific
problems. Experience that goes back as far as 2500 years ago, when a massive
irrigation system, that is still operative, was built in Siechuan, China, and to the
Roman Empire's builders of the aqueducts.
2.1 Water flow in pipes
The energy in the water flowing in a closed conduit of circular cross section,
under a certain pressure, is given by Bernoulli's equation:
P, v2
H = h + -1 + -1-(2.1) I I I r ""g
Where H 1 is the total energy, h 1 is the elevation head, P1 the pressure, y the
specific weight of water, V 1 the velocity of the water and g the gravitational
acceleration. The total energy at point 1 is then the algebraic sum of the potential
energy h1 , the pressure energy P/y , and the kinetic energy V//2g.
If water is allowed to flow very slowly in a long, straight, glass pipe of small bore into
which a fine stream of coloured water is introduced at the entrance to the pipe, the
coloured water appeared as a straight line all along the pipe, indicating laminar flow.
The water flows in laminae, like concentric thin walled concentric pipes. The outer
virtual pipe adheres to the wall of the real pipe, while each of the inner ones moves
at a slightly higher speed, which reaches a maximum value near the centre of the
pipe. The velocity distribution has the form of a paraboloid of revolution and the
average velocity (figure 2.1) is 50% of the maximum centre line velocity.
If the flow rate is gradually increased, a moment is reached when the thread of
colour suddenly breaks up and mixes with the surrounding water. The particles
close to the wall mix up with the ones in the midstream, moving at a higher speed,
and slow them. At that moment the flow becomes turbulent, and the velocity
distribution curve is much flatter. Osborne Reynolds, near the end of last century,
performing this carefully prepared experiment found that the transition from lami-
nar flow to turbulent flow depends, not only on the velocity, but also on the pipe
diameter and the viscosity of the fluid, and can be described by the ratio of the
inertia force to the viscous force, This ratio, known nowadays as the Reynolds
number, can be expressed, in the case of a circular pipe, by the equation:
D V
N R = v (2.2)
where 0 (m) is the pipe diameter, Vis the average water velocity (m/s), and v is
the kinematic viscosity of the fluid (m 2/s) ..
26 Layman's Guidebook
\\\\\\\\\\\\\\\\\1\\\\\\\\\\\\\\\\\\\\\\
'
laminar flow
r
V =2V
v
turbulent flow
figure 2.1
Experimentally has been found that for flows in circular pipes the critical Reynolds
number is about 2000. In fact this transition does not always happen at exactly
NR=2000 but varies with the experimental conditions, Therefore there is more
than a transition point, what exists is a transition range.
Example 2.1
A 60-mm diameter circular pipe carries water at 20°C. Calculate the largest
flow-rate for which laminar flow can be expected
The kinematic viscosity of water at 20°C is u = 1 x 10·6 m 2 /s.
Accepting a conservative value for NR = 2000
V=2000 I (10 6 x0,06) = 0.033 m/s
Q = AV = /4x 0.06 2 x 0,033 = 3.73 x 10·4 m3/s = 0,3731/s
Water loses energy as it flows through a pipe, fundamentally due to:
1. friction against the pipe wall
2. viscous dissipation as a consequence of the internal friction of flow
The friction against the pipe wall depends on the wall material roughness and the
velocity gradient nearby the wall. Velocity gradient, as can be seen in figure 2.1,
is higher in turbulent flow than in laminar flow. Therefore as the Reynolds number
increases, the friction loss will also increase. At the same time, at higher turbulence
there is a more intensive particle mixing action, and hence a higher viscous
dissipation. Consequently the energy losses in pipe flow increase with the Reynolds
number and with the wall pipe roughness.
It can be verified that for water flowing between two sections, a certain amount of
energy h1 is lost
(2.3)
due mainly to the friction of the water against the pipe wall, and secondarily to the
Chapter 2. Fundamentals of Hydraulic Engineering
v:
2g
P,
'f
~ --
h,
figure 2.2
27
h,
_E._
r
h,
internal friction of the flow. In figure 2.2, HGL is the hydraulic gradient line and
EGL the energy gradient line. If the pipe cross section is constant, V 1 = V 2 and
both lines will be parallel. The question is, how h1 can be evaluated?
2.1.1 Los of head due to friction
Darcy and Weisbach, applying the principle of conservation of mass to a control
volume-a certain volume of fluid in a pipe, between two sections perpendicular
to its axis -derived the following equation, valid for incompressible and steady
flows, travelling through pipes:
( L) v 2
h = t'--
t D Ia -.,., (2.4)
where f, friction factor, is a dimensionless number, L the length of pipe in m, D the
pipe diameter in m, V the average velocity in m/s and g the gravitational
acceleration (9.81 m/s 2 ).
In a laminar flow f can be calculated directly by the equation
t' = 64J1 = 64
pVD NR (2.5)
According to equation (2.5) the friction factor fin a laminar flow is independent of
the wall roughness and inversely proportional to the Reynolds number. The fact
that, apparently, f decreases when NR increases, does not mean that increasing
the velocity decreases the friction losses. Substituting f in equation (2.4) by its
value in (2.5), gives:
64J1 L V 2 32J1LV h, =--X-X-= " (26) pVD D 2g pgD-.
28 Layman's Guidebook
showing that the specific head loss, in laminar flow, is proportional to V and
inversely proportional to 0 2 •
When the flow is practically turbulent (NR>>2000), the friction factor become less
dependent on the Reynolds number and more dependent on the relative roughness
height e/0, where "e" represents the average roughness height of irregularities
on the pipe wall and 0 the pipe diameter. Some values of the roughness height
"e", are provided in table 2.1
Table 2.1 Roughness height "e", for various commercial pipes
Pipe material
Polyethylene
Fiberglas with epoxy
Seamless commercial steel (new)
Seamless commercial steel (light rust)
Seamless commercial steel (galvanised)
Welded steel
Cast iron (enamel coated)
Asbestos cement
Wood stave
Concrete (steel forms, with smooth joints)
e(mm)
0,003
0,003
0,025
0,250
0,150
0,600
0,120
0,025
0,600
0,180
It is well known that, even in turbulent flows, immediately next to the wall pipe there
exists a very thin layer of flow referred to as the laminar sublayer. When~ increases,
the sublayer's thickness diminishes. Whenever the roughness height "e" is resolutely
lower than the sublayer thickness the pipe is considered hydraulically smooth
In a hydraulically smooth pipe flow the friction factor fis not affected by the surface
roughness of the pipe, and for this case Von Karman, developed the following
equation for the friction factor f
_1_=2lo (NRfl] fl g 2.51 (2.7)
At high Reynolds numbers, the sublayer thickness becomes very small and the
friction factor f becomes independent of NR and depends only on the relative
roughness height. In this case the pipe is a hydraulically rough pipe, and Von
Karman found that the friction factor f
)J 2 log(3.7 ~) (2.8)
In between these two extreme cases, the pipe behaves neither completely smooth nor
completely rough. Colebrook and White devised the following equation for this case:
21 (
Yo 2.51 l -og --+-----,= ~ 3.7 Nufl (2.9)
Chapter 2. Fundamentals of Hydraulic Engineering
... , ..., (""'"}
~ C• o
:"J 0 .-;
. "' I ..
. •· i ~ ~.
~.
:-I
• I
~ . .
~
¥ .. ..,
-~
·~;
_J
J:. ••••
~ ....
•• ; II
.0
3 : ~
'=" :....:·
ci
'I
"'; !:-··~.a•.I·Jtirlf•• .-..•,, ~r.1 ::. ~
.r: :'(1 I" ~ ..... p, [,..' g '-' •:.J 1_,
.:11 1.(1
•:-1 ~:,.: gs H c:: 0 ~ E:; .._-;., oc c
~
......... r~·
... ---...
•:j"l .,.. ,.., '-' c
8 ~. 8 r:5 g ~ "'!;'
·-= t:l c. 0 c c
r
:.._.;:....__~-. ·-~
: r-~
• I' I
~····L :[L
~~: L::
I ..
• I I .
; j. I I ........ ~ ~
L: :: . I .L -._. ..J.I--'--1 ...&.-J'----1--'-; ' ~ flo" I c~ 8 Cl o:.J
("i c
:.:1 e. r-. ~ Y.-.. '<"' ·=; ..._, ·==· ·=-~ ...: =':'• L-~ C• .:;: c ·-
u;; :2; oL""I
~
-=· c...::
..... ·=·
29
i::.-
-~
\)I
~
~·,
'I]"
:'•) .. c: .::
O:··
·::o
·~
' o:::J
r...
!:!! -::::·
....
30 Layman's Guidebook
Formulae 2.7 and 2.9 are difficult to solve by hand, prompting Moody to prepare
his well-known chart "Friction factors for pipe flow" (figure 2.3)
Looking to the chart it shows four different flow zones:
1. a laminar flow zone (shaded area in the diagram) where f is a linear function of
NR (equation 2.5)
2. a badly defined critical zone (shaded area)
3. a transition zone, starting with the smooth pipes (equation 2.7) and finishing in
the dashed line where, in between, f depends both of NR and e/D (equation 2.9)
4. a complete turbulence zone where f depends exclusively of e/0 (equation 2.8)
Example 2.2
Calculate, using the Moody chart, the friction loss in a 900-mm diameter
welded steel pipe along a length of 500 m, conveying a flow of 2.3 m3/s
The average water velocity is 4Q /rr 0 2 = 1.886 m/s
From the table 2.1, e = 0.6 mm and therefore e/D = 0.6/900 0.000617
NR=DV/u =(0.9x1.886)/1.31=1.3x106 (u=1.3110-6)
In the Moody chart for e/D 0.00062 and NR = 1.3*1 06 we found f=0.019
From equation (2.4)
h 1 0.019x 500 x 1.
8862
=l.9lm
0.9 2 X 9.81
Those not fond of nomographs can use an electronic spreadsheet to deri-
ve a = JlTi from equation 2. 9
[
e/D 2.51 l a=-2loa --+--a. 0 3.7 NR
As the variable is on both sides of the equation an iterative calculation is needed.
We use an Excel97 spreadsheet (figure 2.4) to do it. In figure 2.5 there is a list of
the formulae that should be introduced on each cell. Once introduced the formulae
Example 2.4 Steel pipe
Q 1.2 m 0 /S f alpha alpha
D 900 mm 0.025 6.32455532 7.43162852
v 1.8863 m/s 7.43162852 7.42203156
L 500 m 7.42203156 7.42211430
Nr 1,300,000 7.42211430 7.42211359
e 0.6 7.42211359 7.42211359
e/D 6.6667E-04 7.42211359 7.42211359
f 0.0182
un 1.31 E-06
hf 1.8289 m
figure 2.4
Chapter 2. Fundamentals of Hydraulic Engineering 31
B3
C3
m
E3
F3
G3
B4
C..J.
D4
E4
F..J.
G4
85
cs
D5
FS
G5
86
C6
Do
F6
q
1.2
m'1s
f
alpha
alpha
D
900
mm
0.025
and the data, the sheet should look as in figure 2.4. In this case we guessed a
value of 0,025 for f, equivalent to a=6.3245. In the spreadsheet it can be seen
how the value of alpha is converging to the final value of n=7.4221136, that
automatically gives the final value for f = 0.0182 and a head loss hf'=1.829 m.
In Internet there are two home pages, one corresponding to the PENNSTATE
University, Department of Mechanical Engineering, and the other AeMES
Department, University of Florida, each having an online computer program to
calculate the friction factor f, by introducing the Reynolds number and the
Roughness parameter. It is much faster than the two above-mentioned methods
G6 -2*L0G(SCS913.7+2.51/SCS7*F6)
B7 Nr
C7 1.3E..-06
F7 +G6
G7 -2*LOG($CS9 3.7~2.5l!SCS7*F7)
B8 e
C8 0.6
F8 +G7
GR -2*LOG('bCS9!3.h2.51iSCS7*F8)
B9 e 1D
+I 1SQRT(E4) ('9 +C8.C4
-2 *LOG(SC$9·3. 7+ 2.5l!SCS7*F4 l F9 +G8
v G9 -2*LOG($CS913.7+ 2.51/SCS7*F9)
+..J.*C3•(C4'1 000Y'2''Pl 810 f
tiTS CIO +I 1G9''2
.,-(i4 811 nu
-2*L0G(SCS9i3 7--c 2.51tSCS7*F5) Cll 1.31*10\-6
L 812 hf
500 Cl2 +C I O*C6/C 4* I OOO*C5 1 2!(2*9.81 J
m Dl2 ITl
+GS
figure 2.5
32 Layman's Guidebook
and more precise than the Moody Chart. The Internet addresses are, respectively
http:l/viminal.me.psu.edu/-cjmbala/Courses/ME033/me033.htm
http:l/grumpy.aero.yfl.edu/gasdynamjcs/colebrook.htm
Applying both online computer programs to the data of example 2.2 the answer was
respectively f=0.01787 and f=0.01823, both complete up to 1 0 decimals. Observe
that the second value is practically identical to the one attained with the spreadsheet.
The formula (2.9) can be used to-solve almost any kind of problem with flows in
close pipes. For example, if you want to know what is the maximum water velocity
flowing in a pipe of diameter D and length L, without surpassing a friction head loss
hr you only need to use an independent variable !l
1 t' ~.' J1 =2 1 v"R (2.10)
Substituting NR by its value in (2.2) and f by its value in (2.4) becomes
(2.11)
where all the parameters are known. Once !l is computed, f is derived from
(2.1 0) and substituted in (2.9) to attain:
N11 =-2..[iiilog(e/D + 2~] (2.12)
3.7 v2J1
An equation that makes it possible to plot the NR evolution with !l for different
values of e/0, as shown in figure 2.6, a variation of the Moody Chart where NR
can be estimated directly.
Example2.3
Estimate the flowrate of water at 10°C that will cause a friction headloss
of 2m per km in a welded steel pipe, 1.5 m in diameter.
Substitute values in equation (2.12), with e/0=0.6/1500 = 4x10 4 ,
after computing !l .
-2~2x3.86xl0 10 JoJ·.4 xl0-
4
+ 251 ]=2.19xl01
' ~ 3.7 ~2x3.86xl0 10
v N 11 v = 2.19xl.31
D 1.5
l.9l3m/ s; Q 3.38 m 3 Is
Also based on the Colebrook-White equation there exists some other nomographs,
to compute the friction head loss on a pipe, given a certain flow and a certain pipe
Chapter 2. Fundamentals of Hydraulic Engineering 33
10
10
10
10
N
10
10
1 o' 1 o' 10 10 10 10 10 10 10 10 " 10
)1
figure 2.6
diameter, with a certain roughness coefficient such as the one shown in the next
page and published by courtesy of Hydraulic Research, Wallingford U.K..
Empirical formulae
Over the years many empirical formulae, based on accumulated experience, have
been developed. They are, in general, not based on sound physical principles
and even, occasionally, lack dimensional coherence, but are intuitively based on
the belief that the friction on a closed full pipe is:
1. Independent of the water pressure
2. Linearly proportional to its length
3. Inversely proportional to a certain power of its diameter
4. Proportional to a certain exponent of the water velocity
5. In turbulent flows it is influenced by the wall roughness
One of these formulae, widely used to estimate the flow in open channels, but
also applicable to closed pipes, is that developed by Manning
lA 5 '5 1 c
Q = , ' (2.13)
ll p-'
Where n is the Manning roughness coefficient, Pis the wetted perimeter (m), A is
cross-sectional area of the pipe (m 2 ) and S is the hydraulic gradient or headless
by linear meter.
Applying the above formulae to a full closed circular cross section pipe:
5=10.2~'~,2p2 (2.14)
D'·-·-·-·
In Table 2.2 the Manning coefficient n for several commercial pipes:
34
lit .....
E -:::..
> ~ ...,
1:1' :;
;:r.
Layman's Guidebook
Discharge Q (1/s) for pipes nowing full
.,.. ~ ~ -.:-, "TT. ~-~ ; -~~~r·~·~·~~~~-~~~--?r.~~~-~~~,~~~~yw~·~·-~~,~~~
I~
I j
I o
<·t
~ ..
Ll,f.
o.o..
".,
(11,-
~~·
L ... ::;~
~ ~ll!i .. ,
~
"'
~ ~ ...,
"' -~ <:--:. "" ., . .. t"o ~ j! '!; ~ ....
c, .:.., c. '=' "":: r;:.
Diamater D (m)
ks = 0·03 mm
.... -.... .... ..
E
0
0
'I""
~ .... e -~
0
0 .....
Chapter 2. Fundamentals of Hydraulic Engineering
Table 2.2 Manning coefficient n for several commercial pipes
Kind of pipe
Welded steel
Polyethylene (PE)
PVC
Asbestos cement
Ductile iron
Cast iron
Wood-stave (new)
Concrete (steel forms smooth finish)
n
0.012
0.009
0.009
0.011
0.015
0.014
0.012
0.014
35
In example 2.4 and more specifically in example 2.5 the results attained applying
the Colebrook-White equation and the Manning formulae can be compared.
Example 2.4
Using the parameters in example 2.2 compute the friction headless
applying the Manning formulae
Accepting n=0.012 for welded steel pipe
h 1 = 10.29x0.~~~=' x 1.2=' = 0_00374 L 0.9 ...
Whereby for L=500 m, h1 =1.87 m, slightly inferior to the value estimated with
the Moody chart and slightly higher than the value estimated with the
spreadsheet.
Example 2.5
Compute, using the Colebrook equation and the Manning formulae, the
friction headless on a welded pipe 500 m long, of respectively 500 mm,
800 mm, 1200 mm, and 1500 mm diameter, under a 4 m/s average flow
velocity.
D (mm) 500 800 1200 1500
Q(m*3*/s) 0.785 2.011 4.524 7.069
V (m/s) 4 4 4 4
L (m) 500 500 500 500
Applying Colebrook-White
e(mm) 0.6 0.6 0.6 0.6
h1 (m) 17.23 9.53 5.73 4.35
Applying Manning
n 0.012 0.012 0.012 0.012
h1 (m) 18.40 9.85 5.73 4.26
It can be observed that the solutions provided by the Manning formula doesn't
differ much from those offered by the Colebrook equation, except in the smaller
36 Layman's Guidebook
diameters, where the head loss provided by Manning is higher than that provided
by Colebrook.
In North America for pipes larger than 5 em diameter and flow velocities under 3
m/s the Hazen-Williams formulae is used:
h./ 6.87 ~ ( . .:_·)I.X5
D 116, ( C (2.15)
where Vis the flow velocity (m/s), D the diameter (m), L the pipe length (m) and C
the Hazen-Williams coefficient such as shown in Table 2.3
Table 2.3 Hazen-Williams coefficients
Pipe type
Asbestos cement
Cast iron
New
10 years
20 years
30 years
Concrete
Cast on site -steel forms
Cast on site -wood forms
Centrifugal cast
Steel
Brush tar and asphalt
New uncoated
Riveted
Wood-stave (new)
Plastic pipes
c
140
130
107-113
89-100
75 90
140
120
135
150
150
110
120
135-140
2.1.2 Loss of head due to turbulence
Water flowing through a pipe system, with entrances, bends, sudden contraction
and enlargements of pipes, racks, valves and other accessories experiences, in
addition to the friction loss, a loss due to the inner viscosity. This loss also depends
of the velocity and is expressed by an experimental coefficient K multiplying the
kinetic energy v2/2g.
2.1.2.1 Trash rack (or screen) losses
A screen or grill is always required at the entrance of a pressure pipe. The flow of
water through the rack also gives rise to a head loss. Though usually small, it can
be calculated by a formula due to Kirchmer (see figure 2. 7)
h, ~K,(iJ (~}n$ (2.16)
where the parameters are identified in figure 2.7.
Chapter 2. Fundamentals of Hydraulic Engineering
k=2.4 1.8 1.8 1.7 1.0 0.8
H= headless (mm)
t = bar thickness (mm)
b =width between bars (mm)
V. =approach velocity (m/s)
g = gravitational constant
<!> = angle of inclination from horizonta
figure 2.7
37
If the grill is not perpendicular but makes an angle ~ with the water flow (~ will
have a maximum value of 90° for a grill located in the sidewall of a canal), there
will be an extra head loss, as by the equation
v2
h =-(-1 sin/3
f3 2 (T
b
2.1.2.2 Loss of head by sudden contraction or expansion
When the pipe has a sudden contraction there is a loss of head due to the increase
in velocity of the water flow and to the turbulence.
1.0
0.8
0.6
K
0.4
0.2
0
V=average velocity in smaller pipe
--...........
"""
~udde
_/ -
r---to~ t r---~
0.2
Su den e~pansi n
/ I
~ v[ to ~
" ~ contr actio~ ' "' ---r--"' -" ~
""" l'o...
I
0.4 diD 0.6
figure 2.8
0.8
............ ....._
1.0
38
0.7
0.6
0.5
0.4
K'
0.3
0.2
0.1
Layman's Guidebook
difusser coefficient K' ..
I .....--
! ~~ ~ '
I
v
I I I
1/
10 20
/.
/ i
'
I
30 40
Difusser angle ex
figure 2.9
!
I
50 60
The flow path is so complex that. at least for the time being, it is impossible to
provide a mathematical analysis of the phenomenon. The head loss is estimated
multiplying the kinetic energy in the smaller pipe, by a coefficient Kc that varies
with the indes of contraction d/0
h=K ~ (' v:)
( ( 2g (2.17)
For an index up to diD = 0. 76, Kc approximately follows the formula
Kc = 0.42(1-d2/02 ) (2.18)
Over this ratio. Kc is substituted by Kex' the coefficient used for sudden expansion.
In sudden expansion the loss of head can be derived from the momentum
consideration, and is given by
(2.19)
where V 1 is the water velocity in the smaller pipe. Figure 2.8 is a graphic
representation of the Kc and Kex values as a function of d/0.
The head loss can be reduced by using a gradual pipe transition, known as
confuser for contraction or difuser-for expansion.
Chapter 2. Fundamentals of Hydraulic Engineering 39
l_L_ L 4__
Ke=O.B Ke=0.5 Ke=0.2 Ke=0.04
I I I I
a) b) c)
figure 2.10
d)
In the confuser the head loss varies with the confuser angle as it is shown in
Table 2.3 where K'c values are experimental:
Table 2.3 K' c for different confuser angles
Angle K'
0.02
0.04
0.07
In the diffuser the analysis of the phenomenon is more complex. Figure 2.9 shows
the experimentally found values of Kex for different diffuser angles. The head loss
is given by:
(2.20)
A submerged pipe discharging in a reservoir is an extreme case of sudden
expansion, where V 2 , given the size of the reservoir, compared with the pipe, can
be considered as zero, and the loss V/12g.
An entrance to the pipe is, otherwise, an extreme case of sudden contraction.
Figure 2.10 shows the value of the Ke coefficient that multiplies the kinetic energy
V2 /2g in the pipe.
2.1.2.3 Loss of head in bends
Pipe flow in a bend, experiences an increase of pressure along the outer wall and
a decrease of pressure along the inner wall. This pressure unbalance causes a
secondary current such as shown in the figure 2.11. Both movements together-
the longitudinal flow and the secondary current-produces a spiral flow that, at a
length of around 100 diameters, is dissipated by viscous friction.
The head loss produced in these circumstances depends on the radius of the
bend and on the diameter of the pipe. Furthermore, in view of the secondary
circulation, there is a secondary friction loss, dependent of the relative roughness
e/d. Figure 2.11, taken from reference 3 gives the value of Kb for different values
of the ratio R/d and various relative roughness e/d. There is also a general
agreement that, in seamless steel pipes, the loss in bends with angles under 90°,
is almost proportional to the bend angle.
40
external wall
(high pressure) 1.0
0.8
Layman's Guidebook
------------------,.,.,.---separation
,. ---0.6
external wall
internal wall
(low pressure)
Kb
0.4
0.3.
0.2
0.1
0.08 '---..1.-__L_....J..._.L......~I!.-I!!!!!:..._j
1 1.5 2
figure 2.11
3
r/d
4 5 6 7 8 910
The problem is extremely complex when successive bends are placed one after
another, close enough to prevent the flow from becoming stabilised at the end of
the bend. Fortunately this is hardly ever the case on a small hydro scheme.
2.1.2.4 Loss of head through valves
Valves or gates are used in small hydro scheme to isolate a component from the
rest. so they are either entirely closed or entirely open. Flow regulation is assigned
to the distributor vanes or to the needle valves of the turbine.
The loss of head produced by the water flowing through an open valve depends
on the type and manufacture of the valve. Figure 2.12 shows the value of Kv for
different kind of valves.
Gate valve Butterfly Globe Check valve
Kv=0,2 Kv=0,6 Kv=0,05 Kv=1,0
figure 2,12
Chapter 2. Fundamentals of Hydraulic Engineering 41
2.1.3 Transient flow
In steady flows, where discharge is assumed to remain constant with time, the
operating pressure at any point along a penstock is equivalent to the head of
water above that point. If a sudden change of flow occur, for instance when the
plant operator, or the governor system, open or close the gates too rapidly, the
sudden change in the water velocity can cause dangerous high and low pressures.
This pressure wave is known as waterhammer and its effects can be dramatic:
the penstock can burst from overpressure or collapse if the pressures are reduced
below ambient. Although being transitory the surge pressure induced by the
waterhammer phenomenon can be of a magnitude several times greater than the
static pressure due to the head. According to Newton's second law of motion, the
force developed in the penstock, by the sudden change in velocity, will be
dV F = m-(2.21)
dt
If the velocity of the water column could be reduced to zero the resulting force
would become infinite. Fortunately this is not possible in practice; a mechanical
valve requires some time for total closure; the pipe walls are not perfectly rigid
and the water column under large pressures is not incompressible.
The following description, reproduced with the permission of the author, Allen R,
Irvine, from Appendix F of his "Micro-Hydropower Sourcebook", is one of the best
physical explanations of the phenomenon. Figure 2,13 illustrates how a velocity
change caused by an instantaneous closure of a gate at the end of a pipe creates
pressure waves travelling within the pipe.
Initially, water flows at some velocity «V0 » as shown in (a). When the gate is
closed, the water flowing within the pipe has a tendency to continue flowing
because of its momentum. Because it is physically prevented from so doing, it
«piles up» behind the gate; the kinetic energy of the element of water nearest the
gate is converted to pressure energy, which slightly compresses the water and
expands the circumference of the pipe at this point (b). This action is repeated by
the following elements of water (c), and the wave front of increased pressure
travels the length of the pipe until the velocity of the water «V0 » is destroyed, the
water is compressed, and the pipe is expanded its entire length (d). At this point,
the water's kinetic energy has all been converted to strain energy of the water
(under increased compression) and strain energy of the pipe (under increased
tension).
Because the water in the reservoir remains under normal static pressure but the
water in the pipe is now under a higher pressure, the flow reverses and is forced
back into the reservoir again with velocity «V0 » (e). As the water under compression
starts flowing back, the pressure in the pipe is reduced to normal static pressure.
A pressure «unloading» wave then travels down the pipe toward the gate (f) until
all the strain energy is converted back into kinetic energy (g). However, unlike
case (a), the water is now flowing in the opposite direction and because of its
momentum, the water again tries to maintain this velocity. In so doing, it stretches
the element of water nearest the gate, reducing the pressure there and contracting
the pipe (h). This happens with successive elements of water and a negative
42
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(j)
(I)
gate
I
.. v-v. [
.. V""V, --------~~--:~·····~
~v v:=-y n
~ y_() ~--~~--------1
_Ss._.·. _;;=..:-+::::::liEir!l "========~:r
~v=-.v-,---.. -.. -.------~~~~
•'%! p > P, (positive surge)
D p = P, (static pressure, function of depth onl
D P < P. (negative pressure)
With authorisation of A.R. lnversin
author of "Micro-Hydropower Sourcebook."
figure 2.13
Layman's Guidebook
pressure wave propagates back to the reservoir (i) until
the entire pipe is under compression and water under
reduced pressure 0). This negative pressure wave would
have the same absolute magnitude as the initial positive
pressure wave if it were assumed that friction losses do
not exist. The velocity then returns to zero but the lower
pressure in the pipe compared to that in the reservoir
forces water to flow back into the pipe (k). The pressure
surge travels back toward the gate (e) until the entire cycle
is complete and a second cycle commences (b). The
velocity with which the pressure front moves is a function
of the speed of sound in water modified by the elastic
characteristics of the pipe material
In reality, the penstock pipe is usually inclined but the
effect remains the same, with the surge pressure at each
point along the pipe adding to or subtracting from the
static pressure at that point. Also, the damping effect of
friction within the pipe causes the kinetic energy of the
flow to dissipate gradually and the amplitude of the
pressure oscillations to decrease with time.
Although some valves close almost instantaneously,
closure usually takes at least several seconds. Still, if
the valve is closed before the initial pressure surge returns
to the gate end of the pipeline (g), the pressure peak will
remain unchanged -all the kinetic energy contained in
the water near the gate will eventually be converted to
strain energy and result in the same peak pressure as if
the gate were closed instantaneously. However, if the
gate has been closed only partially by the time the initial
pressure surge returns to the gate (g), not all the kinetic
energy will have been converted to strain energy and the
pressure peak will be lower. If the gate then continues
closing, the positive pressure surge, which it would then
create, will be reduced somewhat by the negative
pressure (h) surge which originated when the gate
originally began closing. Consequently, if the gate opens
or closes in more time than that required for the pressure
surge to travel to the reservoir and back to the gate, peak
surge pressures are reduced. This time is called the
critical time, T c· and is equal to
Tc = 2L /c (2.22)
where c is the wave velocity. The wave velocity, or speed
of sound, in water is approximately 1420 m/s. However,
the wave velocity in a pipe -the speed with which the
pressure surge travels along the pipe-is a function of both
the elastic characteristics of water and the pipe material.
An expression for the wave velocity is:
Chapter 2. Fundamentals of Hydraulic Engineering
c Kx 10 3
l+KD
Er
where K bulk modulus of water 2.2x1 09 N/m 2
D =internal pipe diameter (m)
E = modulus of elasticity of pipe material (N/m 2)
t =wall thickness (mm)
43
(2.23)
If the valve is already closed, when the pressure wave is on its way back, (time
lower than the critical one T), all the kinetic energy of the water will be converted
on an overpressure, and its value in meters of water column, will be
p C~r
g (2.24)
where ~ is the change of water velocity.
However, if t is greater than Tc, then the pressure wave reaches the valve before
the valve is completely closed, and the overpressure will not develop fully, because
the reflected negative wave arriving at the valve will compensate for the pressure
rise. In this case the maximum overpressure may be calculated by the Allievi
formula:
where P3 is the gross head and
N = ( pLf~~J:::
Prl
where p = water density (kg/m 3 }
V0 =water velocity (m/s)
L =total pipe length (m)
P0 =static pressure (m column of water)
t =closure time (s)
(2.25)
(2.26)
The total pressure experienced by the penstock will be P = P 0 + ~P .
In chapter 6, several examples related to penstock design will clarify the above
physical concepts.
For a more rigorous approach it would be necessary to take into consideration
not only the fluid and pipe material elasticity, as above, but also the hydraulic
losses. The mathematical approach is rather cumbersome and requires the use
of computers. For interested readers Chaudry, Fox and Parmakian, among others,
give calculation m)ethods, together with some worked examples.
44 Layman's Guidebook
2.2 Water flow in open channels
Contrary to what happen in closed pipes, where the water fills the entire pipe, in
an open canal there is always a free surface. Normally, the free water surface is
subject to the atmospheric pressure, commonly referred to as the zero pressure
reference, and usually considered as constant along the full length of the canal.
In a way this fact, by dropping the pressure term, facilitates the analysis, but at
the same time introduces a new dilemma, because a priori the shape of the surface
is unknown. The depth of water changes with the flow conditions, and in unsteady
flows its estimation is a part of the problem.
Any kind of canal, even a straight one, has a three-dimensional distribution of velocities.
A well-established principle in fluid mechanics is that any particle in contact with a
solid stationary border has a zero velocity. Figure 2.14 illustrates the iso-velocity lines
in channels of different profile. The mathematical approach is based on the theory of
the boundary layer; the engineering approach is to deal with the average velocity V.
2.2.1 Clasification of open channel flows
Under the time criterion a channel flow is considered steady when the discharge
and the water depth at any section of the stretch does not change with time. and
unsteady when one or both of them changes with time.
Based on the space criterion, an open channel flow is said to be uniform if the
discharge and the water depth at any section of the stretch do not change with
time, and is said to be varied when the discharge and the water depth change
along its length. The flow could be varied steady if the unidimensional approach
can be applied and varied unsteady if not. Figure 2.15 represents different kind of
flows: steady, varied steady (GV), and varied unsteady (RV)
As in the fully closed pipe flows, channel flows also follow the Bernoulli equation
and consequently formula (2.1) is valid. The amount of energy loss when water
flows from section 1 to section 2 is indicated by hl'
\. /
triangular channel trapezoidal channel
shallow ditch natural watercourse
fi ure 2.14
Chapter 2. Fundamentals of Hydraulic Engineering 45
steady uniform flow unsteady uniform flow
RV GV RV GV RV GV RV
~~~------·~ ~--~--~-~-----.~ ~---+1------------·
GV = gradually varied
RV = rapidly varied
2.3.2 Uniform flow in open channels
weir with
spillway
figure 2.15
By definition a flow is considered uniform when
1. The water depth, water area. and the velocity in every cross section of the
channel are constant
2. The energy gradient line, the free surface line and the bottom channel line are
parallel to each other.
Based on these concepts Chezy found that
V ::: C~ R~;S, (2.27)
where: C =
R, =
se
Chezy's resistance factor
Hydraulic radius of the channel cross-section
Channel bottom line slope
Many attempts had been made to determine the value of C. Manning, using the
results of his own experiments and those of others, derived the following empirical
relation:
(2.28)
where n is the well-known Manning's roughness coefficient (see Chapter 5).
Substituting C from (2.27) into (2.28) we have the Manning formula for uniform
flows:
46 Layman's Guidebook
(2.29)
or alternatively
(2.30)
The parameter ARh 213 has been defined as the section factor and is given, for
various channel sections, in table 2.4. The formula is entirely empirical and the n
coefficient is not dimensionless, so the formulae given here are only valid in S.l.
units. Furthermore the formulae are only applicable to channels with a flat bottom.
The analysis of natural watercourses is more complex and the above formulae
can only be applied as first approximations.
From (2.30) it may be deduced that for a channel with a certain cross-section
area A and a given slope S the discharge increases by increasing the hydraulic
radius. That means the hydraulic radius is an efficiency index. As the hydraulic
radius is the quotient of the area A and the wetted perimeter P, the most efficient
section will be the one with the minimum wetted perimeter.
Among all cross-sectional areas, the semicircle is the one, which has the minimum
wetted perimeter for a given area. Unfortunately such a channel, with a semicircular
cross section is expensive to build and difficult to maintain, and so is only used in
small section channels built with prefabricated elements. Putting aside the
semicircular section, the most efficient trapezoidal section is a half hexagon. The
most commonly used channel section in small hydro schemes is the rectangular
section, easy to build, waterproof and maintain.
In chapter 6 the selection of the channel section is considered from the construction
viewpoint, balancing efficiency, land excavation volumes, construction methods, etc
2.2.3 Principles of energy in open channel flows
Uniform flows in open channels are mostly steady and unsteady uniform flows
are rather rare. If the flow lines are parallel and we take the free surface of the
water as the reference plane, the summation of the elevation energy "h" and the
pressure energy P/y is constant and equal to the water depth. In practice most of
the uniform flows and a large part of the varied steady flows are parallel. On a
channel with a sensibly constant reasonable slope (figure 2.16 a), the pressure
head at any submerged point is equal to the vertical distance measured from the
free surface to the point (depth of water). The stress distribution is typically trian-
gular. Nevertheless if the water is flowing over a convex path, such as a spillway,
the centrifugal flow acts in an opposite direction to the gravity, and the stress
distribution is distorted and looks like figure 2.16 b): the pressure energy is given
by the difference between the depth and the centrifugal acceleration of the water
mv2 /r, being r the radius of curvature of the convex path. lfthe path is concave the
acceleration force is added to the depth and the stress distribution looks like in
figure 2.16 c). Consequently the resulting pressure head, for water flows along a
straight line, a convex path and a concave path is respectively
Chapter 2. Fundamentals of Hydraulic Engineering 47
a)
yv gr
yv'/gr
1
c)
figure 2.16
p
-=v(a); y .
p
y
vc p vc
v-v-(b); -=v+v-(c) · ·rg y · ·rg (2.31)
where y is the specific weight of water, y the depth measured from the free water
surface to the point, V the water velocity at that point and r the radius of curvature
of the curved flow path.
The specific energy in a channel section or energy head measured with respect
to the bottom of the channel at the section is
E v" r+a-. 7v -o
(2.32)
where a is a coefficient that take into account the actual velocity distribution in the
particular channel section, whose average velocity is V. The coefficient can vary
from a minimum of 1 ,05 -for a very uniform distribution-to 1.20 for a highly uneven
distribution. Nevertheless in a preliminary approach it can be used a = 1. a
reasonable value when the slope is under 0.018 (a <1 01 ). Equation 2.32 becomes
E (2.33)
A channel section with a water area A and a discharge Q, will have a specific
energy
E=v+£_ . " A" Lg -(2.34)
Equation (2.34) shows that given a discharge Q, the specific energy at a given
section, is a function of the depth of the flow only.
When the depth of flow y is plotted, for a certain discharge Q, against the specific
energy E, a specific energy curve, with two limiting boundaries, like the one
represented in figure 2.17 is obtained. The lower limit, AC, is asymptotic to the
48
T
Layman's Guidebook
horizontal axis and the upper, AB, to the line E=y. The vertex point A on the specific
energy curve represents the depth y at which the discharge Q can be delivered
through the section at a minimum energy. For every point over the axis E, greater
than A, there are two possible water depths. At the smaller depth the discharge is
delivered at a higher velocity-and hence at a higher specific energy -a flow known
as supercritical flow. At the larger depth the discharge is delivered at a smaller
velocity but also with a higher specific energy, a flow known as subcritical flow.
In the critical state the specific energy is a minimum, and its value can therefore
be computed by equating the first derivative of the specific energy (equation 2.36)
with respect to "y "to zero.
dE Qd4
-=--+1=0 (2 35) (~' &4' 0· .
The differential water area near the free surface, dA/dy = T, where T is the top
width of the channel section (see figure 2.17).
By definition Y=_i
T (2.36)
The parameter Y is known as the "hydraulic depth" of the section, and it plays a
big role in the studying the flow of water in a channel.
Substituting in equation (2.37) dA/dy by T and AfT by Y:
Q 3 dA Q 2 T V 2 1 V ----= ---=--=I·--= 1
aA 3 d,· aA 2 A a Y ' r;;y 6 ~ b b "\16 1
y
/
I
I
I
I
I
\
\
/
/
/
/
(2.37)
/
1
', Q >Q
. ---------~1~ -~ --~--:..--_--..;t.. __ _;, ___ .:.:::....---'_:,::' ....... ::::: ....... :::C==-. ___ ..,. E
figure 2.17
Chapter 2. Fundamentals of Hydraulic Engineering 49
v
The quantity ..[iY is dimensionless and known as the Froude number.
When NF= 1 as in equation (2.37), the flow is in the critical state; the flow is in the
supercritical state when NF<1 and in the subcritical state when NF>1. Figure 2.17
can be analysed in this way. The AB line represents the supercritical flows, and
the AC the subcritical ones.
As shown in figure 2.17, a family of similar curves can be drawn for the same
section and different discharges Q. For higher discharges the curve moves to the
right and for lower discharges to the left.
The second term of equation (2.37) can be written:
= YA (2.38)
g
In a rectangular channel Y = y and A=by; equation (2.38) may be rewritten
0 2
-y'b'-
g
In the critical state y = Yc being Yc the critical depth and
F =~~' =>~
b vg (2.39)
where q=Q/b is the discharge per unit width of the channel.
Table 2.4 shows the geometric characteristics of different channel profiles and
Table 2.5, taken from Straub (1982) the empirical formulae used to estimate Yc' in
non-rectangular channel.
Example 2.6
In a trapezoidal section channel where b=6 m and z = 2, compute the
critical depth flow for a discharge of 17 m3/s.
From table 2.5 If= a 0 2/g = 29.46 for a=1
The solution is valid provided 0.1 < Q/b2 < 0.4; as q/b 2 0.19 it is valid
b 0.86m
30;:
The estimation of the critical depth, and the supercritical and subcritical ones,
permits the profile of the free surface to be determined, in cases such as a sudden
increase in the slope of a channel to be connected to another; for to spillway
design profiles:/g the free surface behind a gate etc. Nevertheless in most cases
the designer should make use of empirical formulae based on past experience.
50 Layman's Guidebook
Table 2.4 Geometrical properties of typical open channels
T T
·~ K!5r I tl
VI
~-v\-1 --
1,. .. b
l ')
Area A by (b+zy)y -( <t>-sen<t>) D-g
Wetted perimeter P b+2y h+2y..JI+::::. l/2¢D
Top width of section T b b+2zy 2~r(D-y)
hl· (h+.::r)r ±( 1_se;<t> )D Hydraulic radius R --h+2y~l+::2 h+2l'
(h+::y}F i[~-";"]o Hydraulic depth D y h+2::y sen-
2
[(h+::y)yf .fi(e-sene( , ,
Section factor by15 D-
.,jb + 2.:y 32...}sen /c ()
Table 2.5 (Straub 1982) 'I'= a. Q 2/g
T T ... ..
ID YI YI
(;r, ( ~ rc·· b ( LO,l_ )~o :5
0,8) _0.7'bL'-' 30z . do __ ,
Chapter 2. Fundamentals of Hydraulic Engineering 51
2.3 Computer prog~ams
There are quite a few computer programs that help to solve all kind of problems
with open channels. We will simply refer to the Flow Pro 2.0, from Professional
Software for Engineering Applications (PSA), a shareware that can be found in
INTERNET, at the address http·\\www prosoftapps com for an evaluation copy.
The first step in computing a water surface profile is to select the Channel Type.
You can do this by clicking the Channel Type menu and selecting Trapezoidal,
Circular, Ushaped or Elongated Circular. The program title will reflect your
selection, and the input fields will change accordingly.
Once a channel type has been selected and all of the required inputs have been
entered, you can compute the water surface profile by selecting Compute from
the ToolsiWater Surface Profile menu. Flow Pro will compute the profile along
with the normal and critical depths, the profile and flow types. The water surface
profile grid will contain the tabulated data, which can be saved and imported into
any spreadsheet for further analysis.
Flow Pro will classify the type of flow in a water surface profile. The flow type will be
classified as either subcritical or supercritical. The profile computations start at the
downstream end of the channel for subcritical flow, and the upstream end for
supercritical flow. This is due to the location of the control depth for each type of flow.
For subcritical flow, the control depth is typically critical depth at the downstream
end of a free discharging outfall or the height over a downstream weir. Supercritical
flow has an upstream control depth such as the depth of flow under a gate. The
·~ •m}, ~:o!jl
t..W • 4~/! ' "' f.~ ,: .a ... -! ~~
L .• !~J ,~,,, *·1 '
t.m -~ ·+ 42Bl
• l.!lll' t • ;: ······t:a· ~:::"" s ,~
. . tl.\fb ~·m .. ~
"'!'.& 7'!i1 ' tfir4 . ' ZB t iifi •'
j~J·~\ --~~!• ~--?,~. i .«.~( ...
figure 2,18
• • • • • • • •
• • • • • • • • • • • • •
52 Layman's Guidebook
water surface profile grid data will start the computations at zero, and continue
until normal or critical depth is reached or until the channel ends. It is important to
note the type of flow, so the direction the calculations proceed in the channel is
understood.
Flow Pro will continue to calculate the profile along the length of the channel until
the depth reaches normal or critical depth or the channel ends (whichever occurs
first).
Figure 2.18 shows the dialog box with the depth, flow rate, slope and roughness
of a certain canal, with the required inputs and the computed results.
Chapter 2. Fundamentals of Hydraulic Engineering 53
Bibliography
1. N.H. C. Hwang y Carlos Hita, "Fundamentals of Hydraulic Engineering Systems",
Prentice Hall Inc. Englewood Cliffs, New Jersey 1987
2. F.H. White, "Fluid Mechanics", MacGraw-Hill Inc. USA
3. A. Piqueras, "Evacuaci6n de Broza", ESHA Info n° 9 verano 1993
4. L. Allievi, The theory ofwaterhammer, Transactions ASME 1929
5. H. Chaudry. Applied Hydraulic Transients, Van Nostrand Reinhold Co. 1979
6. V.L. Streeter y E. B. Wylie, Hydraukic Transients, McGraw-Hill Book Co., New
York 1967
7. J. Parmakian. Waterhammer analysis. Dower Publications, New York 1963
8. R.H. French, "Hidraulica de canales abiertos" McGraw-Hillflnteramericana de
Mexico, 1988
9. V.T. Chow, Open Channel Hydraulics, McGraw-Hill Book Co., New York 1959
Otra bibliograffa sabre el tema del capitulo:
H.W.King y E. F. Brater, Handbook of HYdraulics, McGraw-Hill Book Co., New
York 1963
R. Silvester, Specific Energy and Force Equations in Open-Channel Flow,
Water Power March 1961
V.L. Streeter y E. B. Wylie, Fluid Mechanics, McGraw-Hill Book Co., New York
1975
54 Layman's Guidebook
3 The water resource and its potential
3.0 Introduction
All hydroelectric generation depends on falling water. Streamflow is the fuel of a
hydropower plant and without it, generation ceases. Accordingly, the study of any
potential hydroelectric scheme must first of all address the availability of an
adequate water supply. For an ungauged watercourse, where observations of
discharge over a long period are not available involves the science of hydrology;
the study of rainfall and streamflow, the measurement of drainage basins,
catchment areas, evapotranspiration and surface geology.
Figure 3.1 illustrates how the water by flowing from point A to point B, regardless
of the path B along the watercourse, an open canal or a penstock 8 it loses
energy according to the equation:
P= QHy
Where P is the power in kW lost by the water, Q the flow in m 3/s, H9 the gross
head in m andy the specific weight of water, being the product of its mass and the
gravitational acceleration (9.81 kN/m3 ).
The water can follow the riverbed, losing the power through friction and turbulence.
Or it can flow from A to B through a pipe with a turbine at its lower end. The water
would lose the same amount of power, in pipe friction, turbulence in the inlet, bends,
valves, etc and in pushing its way through the turbine. In the later case it is the
power lost in pushing through the turbine that will be converted by it to mechanical
energy and then, by rotating the generator, to electricity. It can be seen that the
objective of a good design is to minimise the amount of power lost between A and 8,
so the maximum amount of power may be available to rotate the generator.
figure 3.1.
56 Layman's Guidebook
Therefore to estimate the water potential one needs to know the variation of the
discharge throughout the year and how large is the gross available head. In the
best circumstances the hydrologic authorities would have installed a gauging
station, in the stretch of stream under consideration, and streamflow time series
data would have been gathered regularly over several years.
Unfortunately, is rather unusual that regular gaugings have been carried out in
the stretch of river where the development of a small hydro scheme is proposed.
If that happen to be true it will suffice to make use of one of the several approaches,
explained later, to estimate the long-term average annual flow and the flow duration
curve for the stretch in question.
Whatsoever, the first step to take is to look out for streamflow time series, in the
stretch of river in question, if possible, or if not, in other stretches of the same
river or in another similar nearby river, that permit to reconstitute the time series
of the referred stretch of river.
3.1 Streamflow records
There is a United Nations organisation, the «World Meteorological Organisation»,
with a hydrologic information service (INFOHYDRO) whose objective is to provide
information regarding:
• National and international (governmental and non-governmental) organisations,
• Institutions and agencies dealing with hydrology;
• Hydrological and related activities of these bodies;
• Principal international river and lake basins of the world;
• Networks of hydrological observing stations of countries -numbers of stations
and duration of records;
• National hydrological data banks-status of collection, processing and archiving
of data;
• International data banks related to hydrology and water resources.
INFOHYDRO includes a Manual and a computerised data
The INFOHYDRO Manual contains information concerning the entire INFOHYDRO
and its operation. It also contains all hydrological information available at present
in INFOHYDRO. Thus, the Manual comprises in a single volume comprehensive
information on the Hydrological Services of the countries of the world and their
data-collection activities. Chapter IV of the INFOHYDRO manual contains tables
giving the numbers of observing stations maintained by the countries of the world
as follows:
• Precipitation
• Evaporation
• Discharge
• Stage (water level)
• Sediment and water quality
• Groundwater
The INFOHYDRO Manual may also be purchased from WMO at a price of chf
132. Request WMO No. 683, INFOHYDRO Manual, (Operational Hydrology
Report No. 28).
Chapter 3. The water resource and its potential 57
stage=H+B
level zero
figure 3.2
stage measurement in a gauging station
The INFOHYDRO is a computerised database. and data can also be supplied on
diskette. Requests should be addressed to:
The Secretary-General
World Meteorological Organization
41, Avenue Giuseppe Motta
P.O. Box 2300
CH-1211 GENEVA 2
Switzerland
Telephone: (+41 22) 730 81 11
Facsimile: (+41 22) 734 23 26
Cable: METEOMOND GENEVE
Telex: 23 260 OMM CH
3.2 Evaluating streamflows by discharge measurements
If appropriate streamflow time series cannot be found, and there is time. the
discharge may be directly measured for at least a year -a single measurement of
instantaneous flow in a watercourse is of little use. To measure the discharge
several methods are available:
3.2.1 Velocity-area method
This is a conventional method for medium to large rivers, involving the measure-
ment of the cross-sectional area of the river and the mean velocity of the water
through it: it is a useful approach for determining the streamflow with a minimum
effort. An appropriate point must be selected on a relatively straight, smoothly
flowing portion of the river to be gauged (figure 3.2). The river at this point should
have a uniform width, and the area well defined and clean.
As discharge varies, the top water level (termed the stage of the river) rises and
falls. The stage is observed daily at the same time each day, on a board -marked
with metres and centimetres, in the style of a levelling staff-with the discharges.
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
58
120m
1 10 HI
1 0~ m
0 97 IYl
(I 80 Ill
0 60 IYl
. Layman's Guidebook
Figure 3.3 shows a suitable marking system. In modern gauging stations, instead
of a board, that requires regular observations, any one of several water-level
measurement sensors available, which automatically register the stage, may be
used. Periodic discharge measurements from the lowest to the highest are made
over a time period of several months, to calibrate the stage observations or
recordings .
I
'U ro
Q)
.s:::.
H
'
H
H
'
discharge
figure 3.4
rating curve
Chapter 3. The water resource and its potential 59
The correlation stage-discharge is called a rating curve (figure 3.4) and permits
the estimation of the river discharge by reading the river stage. To draw this curve,
both the stage and the discharge must be simultaneously read. It is strongly
recommended to begin measuring the low flows, and use the data to start to draw
a curve that correlates the flows and the 'n' Manning coefficient. Later on the
method of the river slope (section 3.3.4) can be used to estimate the high flows,
often impossible to measure with the other methods.
The rating curve (figure 3.4) is represented by
Q = a(H+B)"
Where a and n = constants
H = river stage as measured or recorded
B = correction factor to get the actual level
(3.1)
To compute B (see figure 3.2) the data corresponding to two discharges should
be noted, such as
0 1 = a(H 1 +B)"
0 2 = a(H 2 +B)"
By measuring a third point, corresponding to a discharge Q3 and a stage H3
Q, =~Q1 Qc_ =a(H, +B)" =~a(H 1 +B)" xa(Hc_ +B)"
consequently:
B= H~-H 1 H,
HI+ H2 -2H3
and therefore
(3.2)
There are ISO recommendations 2·3 for the correct use of this technique.
3.2.1.1 Measuring the cross-sectional area
To compute the cross-sectional area of a natural watercourse it should be divided
into a series of trapezoids (figure 3.5). Measuring the trapezoid sides, by marked
rules, such as figure 3.5 illustrates, the cross-section would be given by
5 = h X hi + /z, + .... +h"
11
(3.3)
3.2.1.2 Measuring the velocity
Since the velocity both across the flow and vertically through it is not constant, it
is necessary to measure the water velocity at a number of points to obtain a
mean value. There are several ways of doing this, two of which are discussed
below.
By a floater
A floating object, which is largely, submerged B for instance a wood plug or a
partially filled bottle B is located in the centre of the streamflow. The timet (seconds)
elapsed to traverse a certain length L (m) is recorded. The surface speed (m/s)
60
staff
b
Layman's Guidebook
s = b h + ...... +h
n
figure 3.5 measurement of cross-section
would be the quotient of the length Land the timet. To estimate the average flow
speed, the above value must be multiplied by a correction factor, that may vary
between 0.60 and 0.85 depending on the watercourse depth and their bottom
and riverbank roughness (0.75 is a well accepted value)
By a propeller current-meter
A current-meter is a fluid-velocity-measuring instrument. A small propeller rotates
about a horizontal shaft, which is kept parallel to the streamlines by tail fins. The
instrument is ballasted to keep it as nearly as possible directly below the observer.
Another version of the instrument has a circlet of small conical cups disposed
horizontally about the suspension axis. (figure 3.6)
Each revolution of the propeller is recorded electrically through a cable to the
observer and the number of revolutions is counted by the observer, or automatically,
over a short period (say 1 or 2 minutes). These observations are converted into
a) caps current-meter
figure 3.6
current-meters
..
b) propeller current-meter
Chapter 3. The water resource and its potential 61
water velocities from a calibration curve for the instrument. By moving the meter
vertically and horizontally to a series of positions whose co-ordinates in the cross-
section are determined, a complete velocity map of the cross-section can be
drawn and the discharge through it calculated.
In the case of medium to large rivers observations are made by lowering the
meter from a bridge, though if the bridge is not a single-span one there will be
divergence and convergence of the streamlines caused by the piers, which can
cause considerable errors. In many instances, however the gauging site, which
should be in as straight and uniform a reach of a river as is possible, will have no
bridge and if it is deep and in flood, a cable to hold some stable boat must be
provided, together with a lighter measuring cable to determine horizontal position
in the cross-section.
Since the drag on a boat with at least two occupants and suspended current-
meter is considerable, a securely fastened cable should be used. The presence of
suitable large trees at a particular site often necessitates its choice for this reason.
Alternatively, for very large rivers, cableways are sometime used to suspend the
meter, either from a manned cable car or directly from the cable car, the instrument
in this latter case being positioned by auxiliary cables from the riverbanks.
Depths should always be measured at the time of velocity observation since a
profile can change appreciably during flood discharges. Observers should also
remember such elementary rules as to observe the stage before and after the
discharge measurement, and to observe the water slope by accurate levelling to
pegs at the water level as far upstream and downstream of the gauging site as is
practicable, up to (say) 500m in each direction.
As water velocities increase in high floods the ballasted current meter will be
increasingly swept downstream on an inclined cable. The position of a meter in
these circumstances can be found reasonably accurately if the cable angle is
measured. Ballast can be increased but only within limits. Rods can be used to
suspend the meters but a rigid structure in the boat will then be required to handle
the rods, calling for a stable platform on a catamaran-type of craft. Rod vibration
and bending are common in deep rivers unless diameters exceed 500m, in which
case the whole apparatus is getting very heavy and unmanageable.
By electro-magnetic current-meter
An electro-magnetic (e/m) current-meter is an electrical induction-measurement
instrument, with no moving parts, mounted in a totally enclosed streamlined probe. The
probe can be mounted on rods and held at various depths or suspended on a cable.
The elm meter has the advantages of being smaller and having a wider
measurement range than the propeller meters. It is particularly useful at very low
velocities when propeller meters become erratic. Its sensitivity and lower
vulnerability to fouling from weeds and debris make it attractive for use in heavily
polluted or weedy streams.
Each unit is provided with a surface control box with a digital display and dry-cell
batteries. A set of stainless steel wading rods is also standard equipment. Latest
models have built-in battery-charger circuitry.
62 Layman's Guidebook
figure 3.7
It will be appreciated that since each river is unique, each will require careful
assessment of its width, depth, likely flood velocities, cable-support facilities,
availability of bridges, boats, etc. before a discharge measurement programme is
started.
The discharge at the cross-section is best obtained by plotting each velocity
observation on a cross-section of the gauging site with an exaggerated vertical
scale. lsovels or contours of equal velocity are then drawn and the included
areas measured by a planimeter. A typical cross-section, so treated, is shown in
figure 3.7 a). Alternatively, the river may be subdivided vertically into sections
and the mean velocity of each section applied to its area, as in figure 3.7 b) In
this method the cross-sectional area of any one section should not exceed 10
per cent of the total cross-sectional area.
A check should always be made using the slope-area method of section 3.3.4
and a value obtained for Manning's n. In this way a knowledge of then values of
the river at various stages will be built up, which may prove most valuable in
extending the discharge rating curve subsequently.
To ensure uniformity in the techniques of current-meter gauging ISO has published
various recommendations 12 :3
3.2.2 Dilution methods.
Dilution gauging is particularly suited to small turbulent streams where depths
and flows are inappropriate for current metering and flow structures would be
unnecessarily expensive. The method involves the injection of a chemical into the
stream and the sampling of the water some distance downstream after complete
mixing of the chemical in the water has occurred. The chemical can either be added
by constant-rate injection until the sampling downstream reveals a constant
Chapter 3. The water resource and its potential 63
c'.
T
~c'(t) t-
figure 3.8
concentration level, or administered in a single dose as quickly as possible, known
as gulp injection. In this case samples over a period of time disclose the
concentration-time correlation. In both cases the concentration of chemical in the
samples is used to compute the dilution, and hence. the discharge of the stream
can be obtained. Analysis of the samples is by an automated colorimetric procedure
that estimates the concentration of very small amounts of the chromium compound
by comparison with a sample of the injection solution. The equipment is expensive
and specialised 4 •
Nowadays the above methods have been substituted by the method developed by
Littlewood 7 requiring simple and relatively cheap equipment. The method depends
on the electrical conductivity of solutions of common salt (NaCI) in the stream water
and is a version of the relative-dilution gauging method of Aastad and Sognens.9
The discharge is measured by gradually discharging a known volume (V) of a
strong salt solution (c,) into the stream at a known rate (q), and measuring, at
short intervals, the change in conductivity of the water at the downstream end of
the mixing length. In that way it is possible to plot a conductivity-time curve, along
a timeT as in figure 3.8. The average of the ordinates of this curve represents the
average of the difference in conductivity, between the salt solutions and the
streamwater, upstream the injection point. If a small volume, v, of the particular
strong solution is added to a large volume V* of the streamwater, and the differences
in conductivity E..c* are measured, the discharge will be then given by the equation:
where V
T
v
V*
Llc*
Llc'
v v' Llc' Q = -X X-=--(3 5) T v Lld .
volume of injection solution
=duration of solute wave (s)
= volume of the strong solution added to a larger
=volume of streamwater
=change in conductivity (ohm') consequence of the dilution of v in V*
ordinate's average curve conductivity-time
64
rectangular notch
Q=1.8(L-0,2h)h''
triangular notch (90°)
Q=1,4h''
3.2.3 Weir method
----+ v<0,15 m/s
+--->4h ---+1
figure 3.9
Layman's Guidebook
If the watercourse being developed is reasonably small (say< 4 m3/s) then it may
be possible to build a temporary weir. This is a low wall or dam across the stream
to be gauged with a notch through which all the water may be channelled. Many
investigations have established accurate formulae for the discharge through such
notches. A simple linear measurement of the difference in level between the
upstream water surface and the bottom of the notch is sufficient to quantify the
discharge. However it is important to measure the water surface level some
distance back from the weir (at least four times the depth over the base of the
notch) and to keep the notch free of sediment and the edge sharp.
Several types of notch can be used-rectangular, vee or trapezoidal. The V-notch
is most accurate at very low discharges but the rectangular or trapezoidal are
capable of a much wider range of flows. The actual notches may be metal plates
or planed hardwood with sharp edges, built to the dimensions of figure 3.9.
Flumes can be used similarly, where a stream is channelled through a particular
geometrically-shaped regular channel section for some distance before entering a
length of different cross-section, usually made so by side contraction or steps in the
bed.
In most cases of small-hydro development, such structures are too expensive
and adequate flow data can be derived by simpler methods. Appropriate guidance
and formulae may be found in references 10 · 11 · 12-13-14.15.
Chapter 3. The water resource and its potential 65
:
' I
.~ '1
~ J ':) ~' ~
~ I
! I
z
I fl I ~ ~ ' """ '~ ~
I r~ I In! 1 r 11 , lr 5 \{ ~
I ~~I ~ ~ v I v \1
Oct Nm Dec Jan Feh Mar Apr May Jun Jul
figure 3.10
3.2.4 Slope-area method
This method depends on hydraulic principles and is useful for high flows where
other methods are impractical. It presupposes that it is practical to drive in pegs or
make other temporary elevation marks at water-surface level at the time of the flow
measurement, upstream and downstream of the discharge-measuring site. These
marks can subsequently be used to establish the water slope (S). Cross-sectional
measurements will yield the area (A) and hydraulic radius of the section (R). Once
known these parameters the discharge is computed by the Manning formula
Q= AR2 ~S~ 2
(3.6)
II
This method is sometimes criticised because of its dependence on the value of n.
Since n for natural streams is about 0.035, an error inn of 0.001 gives an error in
discharge of 3 per cent. This objection may be partially met by plotting n against
stage for all measured discharges, so that the choice of n for high stages is not
arbitrary but is taken from such a plot. If a high flood slope can be measured, then
this method may well be the best one for such flows. Typical values of Manning's
n for watercourses are given Table 3.1
66 Layman's Guidebook
Table 3.1 Typical values of Manning's n for watercourses.
Watercourses n
Natural stream channels flowing smoothly in clean conditions 0.030
Standard natural stream or river in stable conditions 0.035
River with shallows and meanders and noticeable aquatic growth 0.045
River or stream with rods and stones, shallows and weedy 0.060
3.3 Streamflow characteristics
3.3.1 Hydrograph
A programme of stream gauging at a particular site over a period of years will
provide a table of stream discharges, which to be of any use has to be organised
into a usable form.
One way of doing this is to plot them sequentially in the form of a hydrograph,
which shows discharge against time, in chronological order (see figure 3.1 0)
3.3.2 Flow Duration Curves (FDC)
Another way of organising discharge data is by plotting a f)ow duration curve (FOG),
that shows for a particular point on a river the proportion of time during which the
discharge there equals or exceeds certain values. It can be obtained from the
hydrograph by organising the data by magnitude instead of chronologically. If the
individual daily flows for one year are organised in categories:-e.g
Flows of 8.0 m3/s and greater
Flows of 7.0 m3 /s and greater
Flows of 6.5 m3 /s and greater
Flows of 5.5 m3/s and greater
Flows of 5.0 m3/s and greater
Flows of 4.5 m3/s and greater
Flows of 3.0 m3/s and greater
Flows of 2.0 m3 /s and greater
Flows of 1.5 m3/s and greater
Flows of 1.0 m3/s and greater
Flows of 0.35 m3/s and greater
No of days % of the year
41
54
61
80
90
100
142
183
215
256
365
11.23
14.90
16.80
21.80
24.66
27.50
39.00
50.00
58.90
70.00
100.00
then a graph like figure 3.11 will be obtained, which represents the ordinates of
figure 3.10 arranged in order of magnitude instead of chronologically.
Nowadays, when most gauging stations are computerised, the easiest way to
derive a FDC is to transpose the digital data to a spreadsheet, sorting them in
descending order, and by hand or by using a simple macro, classify the data as in
the above table. Once done, the same spreadsheet, using its graphic building
capability will draw the curve FDC (such as has been draw figure 3.11 ).
Chapter 3. The water resource and its potential 67
FDC
4
1':'
c~ ;;;
()
O'X.
f.1fc[('{~f11 l irrw
figure 3.11
For many rivers the ratio of peak to minimum discharges may be two or more
orders of magnitude and FDCs for points on them are often more conveniently
drawn with the ordinate (Q) to a logarithmic scale, and a normal probability scale
used for the frequency axis. On such a graph, if the logarithms of the discharges
are normally distributed, then the FDC plots as a straight line. Figure 3.12
represents figure 3.11 with the vertical axis in logarithmic scale.
figure 3. 12
6R
I :..;::
... .1'-
~~
:;;
~
Layman's Guidebook
:-_ : :---.. -
------------
:>'I
3.3.3 Standardised FDC curves
FOGs for different rivers can be compared when presented in this more compact
way, by standardising them. The discharges are divided firstly by the contributing
catchment area and secondly by weighted average annual rainfall over the
catchment. The resulting discharges, in m3/s or litres/s, per unit area, per unit
annual rainfall (typically m 3/s/km 2/m) can then be compared directly. Figure 3.13
shows twenty FOGs corresponding to catchment areas of different geological
composition, drawn to a double logarithmic scale.
Another method for standardising FOGs is to express Q in terms of Q/Qm, where
Qm is the mean flow. The use of such a non-dimensional ordinate allows all
rivers, large and small, to be compared on the same graph. If sufficient records
are available from neighbouring rivers of similar topographical character in a si-
milar climate. these methods can be very useful.
3.3.4 Evaluating streamflows at ungauged sites
When there are no flow records at a particular location it is necessary to proceed
from first principles. Rainfall data are normally available from national agencies
on an annual-average basis, but often only on a fairly small scale. Attempts should
always be made to find local records, which will indicate seasonal variation. Failing
that, a standard rain gauge should be installed in the catchment area, immediately
studies are considered. Even one year's records will help in the production of a
synthesised FOG.
The first step then is to estimate the mean annual flow Qm (also referred to as AOF
or average daily flow). In UK the mean flow is estimated using a catchment water
balance methodology: the long term average annual catchment runoff can be
Chapter 3. The water resource and its potential 69
assumed to be equal to the difference between standard average annual rainfall
(SAAR) and actual evaporation (AE). Catchment values of SAAR and potential
evaporation are estimated from the rainfall and potential evaporation (PE) maps.
Actual evaporation is estimated from potential evaporation using a scaling factor
«r» where r increases with SAAR and hence increasing water availability. For
catchments with annual average rainfall in excess of 850mm /year, it is assumed
that actual evaporation is equal to potential. This relationship between SAAR is
given by
r = 0.00061 x SAAR+ 0.475
r = 1.0
Actual evaporation is calculated using
for SAAR < 850 mm
for SAAR ;o: 850 mm
AE = r x PE
The average runoff depth (AARD in millimetres) over the catchment area (AREA
in km 2 ) is converted to mean flow in m3s-1 by:
Qm = (AARD x AREA) /31536
In other countries it may need modification, using similar methods. For instance,
in Spain, the water balance methodology does not yield feasible results, whereat
the equation to represent mean flow is given by a modified empirical equation:
The meanflow over catchment is then:
Q = Runoff x AREA x 3.17 x 1 0 85
m
where Qm is given in m 3s·1 , the runoff in mm and the AREA in km 2
Although the mean annual flow gives an idea of a stream's power potential, a
firmer knowledge of the stream's flow regime, as obtained from a flow duration
curve is needed. The flow duration curve depends on the type of soil on which the
rain falls. If it is very permeable (sand) the infiltration capacity will be high and the
groundwater will be a large proportion of flow in the streams. If it is impermeable
(rock) the opposite will be the case. The catchments of high permeability and
large groundwater contributions will therefore tend to have more regular discharges
with less fluctuating flow than rocky catchments, where the variations will be great
and will reflect the incidence of rainfall to a much greater extent.
In UK, for instance, the soils have been categorised into 29 discrete groups to
represent different physical properties and the hydrological response of soils.
The classification system is referred to as the Hydrology Of Soil Types (HOST)
classification. By measuring the areas of each of these categories, within the
catchment area, as a proport1on of the whole, the BFI (Base Flow Index) can be
computed. Knowing the BFI of the catchment, a standardised FDC can be selected
from figure 3.13. Multiplying the ordinates of the selected FDC by the catchment
Qm the particular flow duration curve of the site is obtained
In Spain, the distribution of the soils has been identified from the Soil Map of the
European Communities (CEC, 1985) which is based on the FAO/UNESCO Soil
Classification of the World. Nineteen soils are represented within the gauged
catchments considered in the study.
70 Layman's Guidebook
3.3.5 European Atlas of Small Scale Hydropower Resources
::;Itt?
~ ., • dut.; .' t Tn:;>
=lo,·-·
Although using the above methodology is a rather lengthy process, the flow regime
of the site, represented by the FDC, can be easily estimated. To aid local authorities,
water resource planners and potential investors, to asses the feasibility of
developing small hydro schemes anywhere in the European Union, the Institute
of Hydrology in the UK, has developed the European Atlas of Small Scale
Hydropower Potential. The Atlas has been developed on behalf of the European
Small Hydropower Association (ESHA) with the financial aid of the E.C, DGXVII
in the frame of the AL TENER Programme.
The Atlas, which is presented as a menu driven Microsoft Windows TM compatible
software package, incorporates methods for deriving flow duration curves at
ungauged sites and standard engineering methods for using these curves to
estimate the hydropower generation potential for the commercial turbine types.
To estimate the hydro potential of a site the Atlas proceeds as follows:
1 estimation of the catchment characteristics for the site, including catchment area,
average rainfall, average potential evaporation and appropriate low flow statistic;
2 estimation of the flow regime within the catchment, represented by the flow
duration curve, using above catchment characteristics:
H·,.·:,1r~r,et" ~ :; "€':: 33 • 3-:.u~e -... ,·,t::er ~ · •;
d !.,t ;JI.I~: l!)(i~ ::1 . ;: 12 -:1 t·h:!l.l ··~
.. : ....... :~ii:"~·~·:;j'j;;,;:~ .. t·.i'~'i(,-:~ .......... .
: a!·•..;(JIIII:': . ;:; ilf n !'·:! '! :
:'\1 :.•L:...:a:l.:lh!rt i1 :.:1-1 l• :.•!::i.:IL ~!! :"tJ..:"i-.
~·r::.l:.:~at:llr.~· lr:n ·~!! :~:r.o:: :·lei',
!'I !'I .::. .. :
n:·, '1:"1
f,f, . '.
Lfl o;;c
-:n ;:;t_:
.. 10::. :'!J
.· 0(1 I_: I;
~· ~:;t Gl~
... ,,,,
.•. ._1:.,.1 .::.1·:
:· :jr) .'!I:
:~· :i:1 ·''~
:· 17 1G
~· nn c
~ ,
~
\
\
\
.................................. \
\
\
\
\
figure 3.14
:: =. ~€'I'll:!:..;
.;)·c.; .:·-:a-:-e
~...:: :"'' ::'·::..3 ::-.: :~·--
Chapter 3. The water resource and its potential 71
3 estimation of power potential for a range of suitable turbines based on the
estimated flow duration curve
To accomplish the task the user is required to define the catchment boundary.
The estimation of the catchment characteristics then proceeds by the program:
1. Calculating the catchment area;
2. Transposing the catchment boundary onto thematic catchment characteristic
maps to estimate catchment average values of annual average rainfall, potential
evaporation and the fractional extent of individual soil units;
3. Estimating the mean flow using a water balance model incorporating the
parameters thus determined.
4. Calculation of a standardised low flow statistic using the appropriate relationship
between flow and soil characteristics (assigned to hydrological response units
as appropriate).
Graphical and tabular output may be obtained at each stage in the estimation
procedure within the software. Figure 3.14 shows the flow duration curve of a site
in UK. The box at the upper right is used to obtain the probability of exceedence
for an absolute or relative flow, just as the flow corresponding to a certain
exceedence.
Site: Hydrometric area 33. Gauge number 015
Run Date I Time: 12 Septembre 1995 at 15:57
Mean I Prov Rtd Flow : 1.66 m'lsec Gross Hydraulic Head: 10.00 m
Residual Flow: 0.95 m /sec Net Hydraulic Head: 9.30 m
Rated Flow: 0.71 m'lsec
Applicable Gross Annual Net Annual Maximum Rated Minimu
Turbines Average Average Power Output Capacity Operational
Output Output Output
Propeller 159.2 151.3 56.7 54.4 1.41
Cross Flow 165.5 157.2 51.8 48.5 1.06
Kaplan 180.4 171.4 57.8 54.1 1.09
MWh MWh kW kW m'lsec
Flow Regime Results File: c:\hydra\data\demo.ftt
Plot Power I Flow Graphs [] Plot Flow-Duration Curve: I[] II'!!!~ I lif@~ I
figure 3.15
72 Layman's Guidebook
The flow duration curve, in conjunction with user defined head and design flow
parameters, is used to calculate energy and power output, which can potentially
be anticipated at the site. Figure 3.15 shows a power potential report where gross
and net average annual output and rated capacity for various possible turbines
are clearly indicated.
The computer program is easy to operate and yields very interesting results. The
package in its different modules permits the modification of the input data, coming
from the previous module.
3.3.6 FDC's for particular months or other periods
It is always important to know when, during the year, water will be available for
generation. This is required when considering the economics of schemes in those
networks where tariffs, paid by utilities to independent producers, vary with the
season of the year and time of day.
FDCs can be produced for particular periods of time as well as for particular
years or periods of record. Indeed, it is standard practice to prepare FDCs for six
"winter" months and six "summer" months. This can be taken further, to obtain
FDCs for individual months, if so desired. It is simply a matter of extracting the
flow records for a particular month from each year of record and treating these
data as the whole population. If sufficient flow records for this process do not
exist, then the rainfall record can be used.
3.3.7 Water pressure or 'head'
3.3. 7.1 Measurement of gross head
The gross head is the vertical distance that the water falls through in generating
power, i.e. between the upper and lower water surface levels.
Field measurements of gross head are usually carried out using surveying
techniques. The precision required in the measurement will impose the methods
to be employed.
In the past the best way to measure it was by levelling with a surveyor's level and
staff, but the process was slow. Accurate measurements were made by a tachometer
or less accurately by a clinometer or Abney level. Nowadays with digital theodolites,
the electronic digital levels and especially with the electronic total stations the job
has been simplified. The modern electronic digital levels provides an automatic
display of height and distance within about 4 seconds with a height measurement
accuracy of 0.4 mm, and the internal memory makes it possible to store approximately
2,400 data points. Surveying by Global Positioning Systems (GPS) is already
practised and a handheld GPS receiver is ideal for field positioning, and rough
mapping.
3.3.7.2 Estimation of net head
Having established the gross head available it is necessary to allow for the losses
arising from trash racks, pipe friction, bends and valves. In addition to these losses,
Chapter 3. The water resource and its potential
., 18m ..
figure 3.16
73
85
l •
certain types of turbines must be set to discharge to the atmosphere above the
flood level of the tail water (the lower surface level). The gross head minus the
sum of all the losses equals the net head, which is what is available to drive the
turbine. Example 3.1 will help to clarify the situation
Example 3.1
Figure 3.16 shows the pipe layout in a small hydropower scheme. The
nominal discharge is 3 m 3/s and the gross head 85 m. The penstock has
1.1 m diameter in the first length and 0.90 min the second one. The radius
of curvature of the bend is four times the diameter of the pipe. At the
entrance of the intake there is a trash rack inclined 60° with the horizontal.
The rack is made of stainless steel flat bars, 12 mm thick and the width
between bars is 70 mm. Estimate the total head loss.
According to experience the velocity at the entrance of the rack should be
between 0.25 m/s and 1.0 m/s. The required trash rack area is estimated by the
formula:
s ll t )Q l --------
Kl t+h v 0 scna
where S is the area in m2 , t the bar thickness (mm), b the distance between
bars (mm), Q the discharge (m 3/s), vc the water velocity at the entrance and K1
a coefficient which, if the trashrack has an automatic cleaner, is equal to 0.80.
Assuming v0 = 1 m/s, 8=5.07 m2 • For practical reasons a 6m2 trashrack may be
specified, corresponding to a v 0 0.85 m/s, which is acceptable.
The head loss traversing the trashrack, as computed from the Kirschner equation
h, :::::: 2.4(g 13 4
')
0·8::; 0.007 111
70) .. x9.81
74 Layman's Guidebook
The friction losses in the first penstock length are a function of the water velocity,
3.16m/s.
The entrance to the pipe has a bad design and coefficient K. = 0.8 figure 2.11)
The head loss in the first length according to Manning's equation is:
h 1 o,29 x o:~I?:: x 3 2 = o,oo 8 108 I,f >.~ .•
The headless coefficient in the first bend is Kb = 0.085 (one half of the
corresponding loss of a 90° bend); in the second 1\, = 0.12 and in the third
Kb =0.14
The taper pipe, with an angle of 30°, gives a loss in the contraction he= 0.02 m
(for a ratio of diameters 0.8 and a water velocity in the smaller pipe 4.72 m/s)
The friction headless in the second length is computed in the same way as the
first one, and accordingly h/65 = 0.0234 (water velocity in second span is 4.72 m/
s)
The coefficient of headless in the gate valve is Kv= 0.15.
Therefore the friction headless are estimated as
0.008 X 108 + 0.0234 X 65 = 2.385 m
The turbulence headless will be as follows:
In the trashrack 0.007 m
In the pipe entrance 0.8 x 0.508 0.406 m
In the first bend 0.085x0.508 0.043 m
In the second bend 0.12x1.135 0.136 m
In the third bend 0.14x1.135 0.159 m
In the confusor 0.02x1.135 0.023 m
In the gate valve 0.15x1.135 0.170 m
The total head loss is equal to 2.385 m friction loss plus 1.375 m turbulence
loss, giving a net head of 81.24 m. This represents a loss of power of 4.42%
which is reasonable. Improving the pipe entrance the loss coefficient will diminish
by almost 39 em.
3.4 Residual, reserved or compensation flow
An uncontrolled abstraction of water from a watercourse, to pass it through a
turbine, even if it is returned to the stream close to the intake, could lead to sections
of the watercourse being left almost dry with serious results for aquatic life.
To avoid this happening, permission to divert water through a hydro turbine or a
licence to abstract from a river or stream will almost always specify that a certain
residual flow should remain. The residual flow is sometimes called other names,
depending on the country, or authority responsible.
It is in the interest of the hydro-power developer to keep the residual flow as small
as is acceptable to the licensing authority, since in seasons of low flow. its release
may mean generation being stopped if there is insufficient discharge to provide
both it and minimum turbine discharge. On the other hand the lack of flowing
water can endanger the life of the aquatic biota. In Chapter 7 the subject will be
treated in depth from an environmental viewpoint.
Chapter 3 The water resource and its potential 75
8 i I \ !'"-"~"~"'~w
\, 6
\._
4 mJan flov. ""'
I
j
ffr IDm
cauda
lliTil
minim
rr ~
2
........... ............ '-·~ .... ............ '-·,·,, ··., ··, '-,
'· 0
0% 20% 40% 60% 80% 100%
% of time flow is equalled or exceeded
reserved flow 111111111 useful area
figure 3.17
3.5 Estimation of plant capacity and energy output
The FDC provides a means of selecting the right design discharge and taking into
account the reserved flow and the minimum technical turbine flow, estimate the
plant capacity and the average annual energy output.
Figure 3.17 illustrates the FDC of the site it is intended to evaluate. Usually the
design flow is assumed to be, in a first approach, the difference between the
mean annual flow and the reserved flow. In actual practice is strongly
recommended to evaluate the plant for other design flows in order to choose, the
one that yields the best results. Once the design flow is defined (Q'"-0,85 ), and
the net head estimated, suitable turbine types must be identified. The suitable
turbines are those for which the design flow and head plot within the operational
envelopes (figure 3.18). Figure 3.17 shows the useable region of the flow duration
curve. Every selected turbine has a minimum technical flow (with a lower discharge
the turbine either cannot operate or has a very low efficiency) and its efficiency is
a function of the operating discharge.
The gross average annual energy (E in kWh) is a function
Where:
Qmediar
Hn
Ylturbine
E = fn (Qmediac' Hn' Ylturbine' Tlgenerator' T\ gearbox' Tltransformer' y,h)
= flow in m3/s for incremental steps on the flow duration curve
= specified net head
turbine efficiency, a function of Qmedian
76
1000
I
500 f
300 l
200 I _,-.
E
"? I ('!)
~ .:::. 11):)
~l,S
2 I
50
30
20
10
5
3
0
··i:t:.;~l;];
Pelton <-ua,<o-1
v.f it-~
--
Turgo
l(:, ... ,
U,.
·'frtfo..
0.2 0,5
f.·:-j17'H::I~
--Petor
Layman's Guidebook
3 4 5 6 7 8 910 20 30 50 1 0{1
Chapter 3. The water resource and its potential 77
>. u c
Q) ·u :=:
Q)
Q) c :e
.2
0,9
0,8 0,824
0,7 0,721
0,6
0,54
0,5
20 30 40 50 60 70 80 90 100
%design flow
figure 3.19
llgenerator = generator efficiency
llgearbox = gearbox efficiency
lltransformer = transformer efficiency
h = number of hours for which the specified flow occurs.
The software package uses a procedure to calculate the energy. It divides the useable
area into vertical 5% incremental strips starting from the origin. The final strip will
intersect the FDC at Qmm or O,eserved which ever is larger. For each strip Qmedian is
calculated, the corresponding llturbine value is defined for the corresponding efficiency
curve and the energy contribution of the strip is calculated using the equation:
L1E = W.Qmedian·H. llturbine· llgenerator·llgearbox· lltransformer· Y · h
where
W =strip width= 0.05 for all strips except the last one that should be calculated
h = number of hours in a year
y =specific weight of the water (9.81 KNm·3 )
The gross average energy is then the sum of the energy contribution for each strip.
The capacity of each turbine (kW) it will be given by the product of their design flow
(m 3/s), net head (m), turbine efficiency(%), and specific weight of the water (kNm·3).
In Chapter 6 can be seen the curves of turbine efficiency against flow for the
commercial turbines. Table 3.1 gives the minimum technical flow for different types
of turbines, as a percentage of the design flow.
78 Layman's Guidebook
Table 3.1 Minimum technical flow of turbines
Turbine type
Franc1s sptral
Francis open flume
Semi Kaplan
Kaplan
Cross flow
Pelton
Turgo
Propeller
Q~n 3
30
15
15
15
10
10
65
The European Atlas of Small Scale Hydropower Potential includes a module
to compute both the installed capacity and annual energy output of every
appropriate turbine, and prepare a complete report on the results. Anyone can
estimate both power and energy output by hand, simply by calculating areas, but
it is tedious work that can be shortened with the aid of the software package
3.5.1 How the head varies with the flow and its influence on the turbine
capacity
In medium and high head schemes the head can be considered constant, because
the variations in the upper or lower surface levels it is very small compared with the
value of the head. In low head schemes, when the flow increases over the value of
the rated flow the water surface level, both in the intake and in the tailrace, also
increases but at different rates, so that the head can considerably increase or decrease.
If a turbine operate with a bigger flow than the design flow Qd, under a head H1
smaller than the rated head Hd , the flow admitted by the turbine will be:
O-QHEt -~-d H
"
(3.7)
Headwater elevation versus spillway discharge is easy to compute. According to
the spillway theory,
where Q = Discharge over spillway
C = Spillway discharge coefficient
L = Length of the spillway crest
H = height of the water surface level above the spillway crest
(3.8)
The value of C depends on spillway shape, and may be found in hydraulic
reference books.
Headwater level is normally kept at spillway crest level when all the river discharge
passes through the turbines. When the river discharge exceeds maximum turbine
discharge, equation (3.8) is applied to the excess flow, which passes over the
spillway. In this case measuring the head on the spillway crest we have at the
same time the level of the intake water surface and the river discharge (it suffices
to add the discharge going through the turbine).
Chapter 3. The water resource and its potential 79
7
6
5 i51
Ql
a. I
]:.
4
3
nominal flow 14m -nominal head 6,45 m
i I
I .. ! 100
• .......... • ----...... .... • • .............. ' .... • ···--1 • : , .... • .. ............. 600
r-./ .. ........ r-···-·! • .... .......... • ... • 500
• • ' i
' • .... • ... .... i •
• .... .. • •
400
• .... .... • • • • • ' ' . • • • •
' ' • • • •
f • • • • r
0 10 20
'
i
30
discharge m' /seg
figure 3.20
.... --
40
----1--300
200
100
I
50 60
The tailrace level is more difficult to estimate. The Hydrologic Engineering Center ·
(HE C) of the US Army Corp of Engineers, has developed a computer program, HEC-
HMS, that can be usefull for that purpose. It can be downloaded, free of charge from
INTERNET, http://www.hec.usace.army.millsoftware/software_distrib/hec-hms/
hechmsprogram.html
Figure 3.20 shows how the head varies with the flow in a real case and its influence
on the power delivered at different river discharges.
3.5.2 Another methodology to compute power and annual energy output
If the European Atlas software package is not available, the use of an electronic
spreadsheet, with a model such as the one shown in Table 3.2 is suggested,
especially in low head schemes where the flow passing through the turbine is a
function of the nominal head and the actual head, corresponding at this flow.
The discharge passing through the turbine would be the river discharge, less the
reserved flow, except if it exceeds maximum turbine discharge or other constraints
on turbine discharge are encountered. If the head is smaller than the rated head,
the discharge admitted by the turbine will be given by the equation:
Ql = Qd~ HI I H,, (3.9)
80
River discharge (m3/s)
Nominal head (m)
Rated flow (m3/s)
Head (m)
Flow through the turbine (m3/s)
Global plant efficiency!(%)
Power (kW)
Delta T (%)
E (GWh)
Annual energv outnut !GWhl
Layman's Guidebook
where the suffix 'i' indicate the parameters corresponding to the point i in the FDC
and the suffix 'd' the design parameters. The power P in kW will be given by the
product of 0, H, 11 (global efficiency in%) and 0.0981. The energy output by the
power multiplied by L1 T and the total number of hours in the year, less 5% downtime.
'Downtime' is the time when the plant is unavailable through malfunction,
maintenance or shortage of water.
In table 3.2 the «River discharge» shows the river discharge less the reserved
flow. After some iterative calculations, it was decided to have as design flow, the
corresponding to the 50% exceedence-46m3 /s-with a rated head 6.45 m. The
curve head-river discharge is reflected in line 4 (Head), and the flow going trhough
the turbine is shown in line 5, function of river discharge and net head. The turbine,
a double regulated Kaplan, will have an installed power of 2.450 kW. The calculation
procedure is clearly explicited in the table.
Table 3.2
10% 20% 30% 40% 50% 60% 70% 80% 85% 90% 95% 100%
70.00 60.67 53.7X 49.33 46.00 43.5~ 40.78 37.97 36.33 34.70 3~.70 26.30
6,45
46.00
4.50 4.95 SAO 6.10 6.45 6.55 6.60 6.62 (l.63 6.64 6.65 6.66
3X.42 40.30 42.09 44.73 46.00 43.52 40.7X 37.97 36.33 34.70 32.70 2h.30
O.R3 O.X3 O.X3 O.X4 O.X4 O.X4 O.X4 O.X4 O.X4 O.X4 O.X3 O.X2
IAOX 1.624 I.X51 2.24'! 2445 2.349 2.21 X 2.071 1.9X5 I.XR7 1.771 1.40'1
(()O'o I 0° o I <r~ o lmo I 0" o 1 o·~~o IO"o 5%) 5°o sol) SC' o
1.262 1446 1.706 1.953 1.995 1.900 1.7X5 X44 X06 761 662
15.118
3.5.3 Peaking operation
Electricity prices at peak hours are substantially higher than in off-peak hours,
hence the interest in providing an extended forebay or pound, big enough to
store the water necessary to operate, preferably in peak hours. To compute this
volume considering that:
OR =river flow (m 3/s)
0 0 =rated flow (m 3/s)
OP =flow in peak hours (m 3/s)
0 0 P =flow in off-peak hours (m 3/s)
tP = daily peak hours
t0 P = daily off-peak hours (24 -tp)
ores = reserved flow (m 3/s)
Otm•n = minimum technical flow of turbines (m 3/s)
H =head
The needed storage volume V will be given by:
VR = 3.600 tp(Qp -(QR -Q,J)
Chapter 3. The water resource and its potential 81
3.6 Firm energy
If the pound should be refilled in off-peak hours
tr(Qr (QR -Q,J)<t 0 P(QR -Q,cJthence
( Q ) top-tr Q R -rc> ___:__.;_
t.,
the flow available to operate in off-peak hours will be:
24(QR-0rcs)-tp0P Q Q~ > . lop mm
A run-of-river scheme cannot, in general, guarantee a firm energy. On the contrary
a group of small hydro run-of-river schemes, located in different basins of a country
possibly can, because the low flow seasons may not occur at the same time.
If a small hydro scheme has been developed to supply energy to an isolated
area, the rated flow should be the one corresponding in the FDC to the exceedence
probability of, at least, 90%. But even in these conditions the electricity supply
cannot be guaranteed 90% of the time, because the FDC is related to the long
term and does not necessarily apply in dry years.
82 Layman's Guidebook
Chapter 3. The water resource and its potential 83
Bibliography
1. Jose Llamas, "Hidrologfa General. Principios y Aplicaciones". Servicio Edito-
rial de Ia Universidad del Pais Vasco, 1933.
2. ISO 1100-1 :1996 Measurement of liquid flow in open channels -Part 1: Esta-
blishment and operation of a gauging station
3. ISO/DIS 1100-2 Measurement of liquid flow in open channels --Part 2:
Determination of the stage-discharge relation (Revision of ISO 1100-2: 1982)
4. ISO 2537:1988 Liquid flow measurement in open channels--Rotating element
current-meters
5. ISO 955-1:1994 Measurement of liquid flow in open channels--Tracer dilution
methods for the measurement of steady flow-Part 1 :General
6 ISO 3846:1989 Liquid flow measurement in open channels by weirs and flumes
-Rectangular broad-crested weirs.
7 ISO 3847:1977: Liquid flow measurement in open channels by weirs and flumes
-End-depth method for estimation of flow in rectangular channels with a free
overfall
8 ISO 4359-1983 Liquid flow measurement in open channels: Rectangular,
trapezoidal and U-shaped flumes
9 ISO 4360:1984 Liquid flow measurement in open channels by weirs and flumes
--Triangular profile weirs
10 ISO 4362:1992 Measurement of liquid flow in open channels --Trapezoidal
profil
84 Layman's Guidebook
4. Site evaluation methodologies
4.0 Introduction.
4.1 Cartography
Adequate head and flow are necessary requirements for hydro generation.
Consequently site selection is conditioned by the existence of both requirements.
For the flow, chapter 3 lists the addresses of the international and national
organisations where stream data are recorded, underlining the availability of
specialised databases. With the European Atlas of Small Scale Hydropower
Resources, by introducing the catchment geographic definition, the mean flow and
the Flow Duration Curve for any specific site may be estimated. If the scheme is
located in a country where databases for the Atlas do not exist, one of the
methodologies detailed in the chapter 3 may help to get the required results.
The gross head may be rapidly estimated, either by field surveying or by using the
GPSs (Global Positioning System) or by ortophotographic techniques. With the
aid of the engineering hydraulic principles brought out in chapter 2 the net head
may be computed. Flow and head estimation should no longer be a problem.
Nevertheless, the selection of the most appropriate technical solution for the site
will be the result of a lengthy, iterative process, where the topography and the
environmental sensibility of the site. are most important. That is why a thorough
knowledge of the scheme is needed to avoid dangerous failures in the operation
of the plant. Surveying technologies are undergoing a revolutionary change, and
the use of the technologies mentioned above may greatly assist in scheme design
and reduce its cost.
In the industrialised countries maps to the required scale are usually available.
The E.U. territory has been or is being digitised, and cartography at scale as
large as 1:5 000 is already available. On the other hand, in the developing countries,
the developer will be fortunate if he can find maps at 1 :25 000.
Aerial photographs of topography, can be substituted for maps if they cannot be
found at the required scale. However aerial photographs are unlike maps in one
important respect. A map has a uniform or controlled variable scale -the latter
being dependent on the choice of map projection. The aerial photograph, on the
other hand, does not have a constant or uniformly changing scale. Aside from lens
imperfections, which for all practical purposes can be considered negligible, two
major factors are responsible for variations in the scale of a photograph: the
topographical relief -land, no matter how flat, is never horizontal-and the tilt of the
optical axis of the camera.
Modern cameras remove distortion resulting from their axial tilt. Furthermore aerial
photographs can be viewed stereoscopically or in three dimensions. The stereoscopic
effect enables the geologist to identify rock types. determine geologic structures,
and detecting slope instability and the engineer gather data necessary for dam,
open channels and penstock construction.
86 Layman's Guidebook
Depending on the required accuracy, the digitised photographs can be geocoded
(tied to a coordinate system and map projection) and orthorectified. Distortion from
the camera lens is removed by using ground control points from maps, survey data
or client's GPS vectors. This is a very cost-effective way to orthorectify aerial
photographs. Resolutions of 30 em to one metre can be expected with digital
ortophotos. Both hard copy and digital ortophotos in diskettes can be produced.
With those maps is possible to locate the intake, trace the open channel and the
penstock and locate the powerhouse, with precision enough for the feasibility
studies and even for the phase of bidding. With stereoscopic photographs geologic
problems can often be spotted, specially those concerning slope stability, that
can cause dangerous situations.
4.2 Geotechnical studies
Frequently, the need to proceed with detailed geological studies of the site is
underestimated. In many cases with regrettable consequences -seepage under
the weir, open channel slides etc.
Fortunately in the E.U. member states and in many other countries all over the
world, good geological maps permit estimates, in a first approach, of the security
of the dam foundations, the stability of the slopes and the permeability of the
terrain. However sometimes this general information should be complemented
with fieldwork of drilling and sampling.
Hydraulic structures should be founded on level foundations, with adequate side
slopes and top widths, not subject to stability problems. There are a good number
of slope stability computer programs, ranging from a simple two-dimensional
approach to the sophisticated three-dimensional, full colour graphic analysis. The
catalogue of failures, especially in channel design is so large that a minimum
geomorphologic study of the terrain should be recommended for the first phase
of the project. The problem is especially acute in high mountain schemes, where
the construction may be in the weathered surface zone, affected by different
geomorphologic features such as soil creep, solifluction, rotational and planar
soil slides and rock falls.
The weir and its corresponding reservoir can be affected by the instability of the
superficial formations that can be present within its zone of influence, but at the
same time the pond itself can affect these same formations. If the weir has to be
founded on a unconsolidated ground the variation of water level can generate
instability on the reservoir's wetted slopes.
Along the open channel many geomorphologic features can adversely affect its
selected line which, together with a steep slope of the terrain, may lead to potential
instability. Colluvial formations, product of the surface mechanical weathering of
the rock masses, and solifluction processes, very active in high mountain
environments where the subsoil is seasonally or perennially wet, are some of the
features that can compromise channel stability. Drainage treatments, bench
constructions and gunite treatments, among many others, may be recommended.
Chapter 4. Site evaluation methodologies 87
At the end of the canal the forebay acts as a mini-reservoir for the penstock.
Frequently, authorities require that all the water retaining embankment sections
undergo stability analysis regardless of their configuration.
The layout of the penstock, usually placed on a steep slope, poses problems
both for its anchoring blocks and because its visual impact.
Deep in the valley, frequently built on an old river terrace, the powerhouse
foundation poses problems that marly times only can be solved by using techniques
as up today as the jet grouting (see 4.2.2.4).
4.2.1 Methodologies to be used
Within geological science, there is a wide spectrum of geomorphologic techniques
that can be used including the following most common ones:
Photogeology.
As mentioned above photogrammetry -at scales from 1:10 000 to 1 :5 000
allows the geologist to identify rock types, determine geologic structures, and
detect slope instability.
Geomorphologic maps
The result of photogrammetric analysis complemented with the results of the
field survey must be combined on a Geomorphologic Map. This map, based on a
topographic one, drawn at a scale between 1:10 000 and 1 :5 000, duly classified
using simple symbols, should show all the surface formations affecting the
proposed hydraulic structures.
Laboratory analysis
Traditional laboratory tests such as soil grading and classification, and tri-axial
consolidation facilitate the surface formation classification, to be included in the
above mentioned map.
Geophysical studies
A geophysical investigation either electric or seismic by refraction will contribute
to a better knowledge of the superficial formation's thickness, the location of the
landslide sections, the internal water circulation, and the volumetric importance
of potential unstable formations.
Structural geological analysis
Although not properly a geomorphologic technology it can help to solve problems in
the catchment area and in those cases where hydraulic conduits must be tunnels in
rock massifs. The stability of the rock and seepage in the foundation of hydraulic
structures are problems that can be solved by this methodology, avoiding dramatic
incidents during thE operation.
Direct investigations. Borehole drilling
This is uncommon for small hydro scheme development. However when the
dam or weir has to be founded in unconsolidated strata. a drilling programme,
foli 1wed by laboratory tests on the samples extracted is essential. Some of these
recommended tests are:
88 Layman's Guidebook
Weir
figure 4.1
• Permeability tests in boreholes, such as Lugeon or Low Pressure Test, to defi-
ne the water circulation in the foundation.
• Laboratory tests to determine the compression strength of the samples to de-
fine their consolidations characteristics.
Complementing the above tests a geophysical refraction seismic essay to define
the modulus of dynamic deformation of the rocky massif in depth can be
recommended in the case of high dams ..
4.2.2 Methodologies. The study of a practical case.
4.2.2.1 The weir
A short report on the geomorphologic techniques used in the Cordifianes
scheme, a high mountain scheme located in the Central Massif of Picos de
Europa (Leon, Spain) will help to demonstrate the scope of the above mentioned
studies. Figure 4.1 is a schematic representation of the site, which includes:
• A gravity weir 11.5 meters high over foundations
• A reservoir with a storage capacity of 60 000 m3
• An open channel2475 m long (776 mare in tunnel)
• A forebay at the end of the tunnel
• A 1.4 m diameter penstock, 650 m long with a 190 m drop
• A powerhouse
International regulations require that if there is a potential for direct shear failure
or whenever sliding is possible along joints or faults, rock foundations must be
analysed for stability. When necessary additional rock excavation may be required
or the rock mass must be anchored.
Figure 4.2 shows the weir location and illustrates the entirely different structures
of both slopes: the left one, steeper, follows the nearly vertically bedded slate
Chapter 4. Site evaluation methodologies 89
(" .. ;. -·· _ _,
....... ·· ... .........
Coluviall formation
Alluvial terrace Carboniferous slates
0!!!!!!!!!!!!!!!!!!!!!!!!2iiiii0iiiiii=40 rn
figure 4. 2
formation; the right one less steep is associated to a colluvial formation.
Figure 4.3 shows the geological complexity of the colluvial formation. The borehole
drilling B-1 illustrates the existence of an alluvial terrace under the colluvial formation.
Each formation behaves in a different way to the requirements of the weir foundation.
Alluvial terrace
Alluvial silts
Colluvial formation
Carboniferous slates
w,..
Sondeo B-1
• ,~, Colluvial formation
[
Carboniferous slates
figure4.3.
• • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • •
90
Tunnel
4.2.2.2 The open channel
Photo 4.1
Layman's Guidebook
River Cares
0 2S SOm
• Terrain's sample points
a) General inestability b) Scars
c) Alluvium of rocks d) Solifluxi6n
figure 4.4 .
Figure 4 .4 shows a geomorphologic scheme of the channel trace. Two large
independent unstable zones (band c) can be seen in the right side of the river .
Photographs 4.1 and 4.2 show a general view of the right-side slope and the local
instabilities generated during the excavation works, just as a detail of one of these
instabilities . Photograph 4.3 shows one of the existing sliding scarps before the
beginning of the works .
Chapter 4. Site evaluation methodologies 91
Photo 4.2
Photo 4.3
The foundation of the channel should meet two requirements :
• must be stable. Channels are rigid structures and do not permit deformations.
• should be permeable. Channels do not support thrusts or uplift pressures.
The geologic studies should aim to avoid settlements in the channel and to provide
adequate drainage to hinder the thrust and uplift stresses . The study should conclude
with a recommendation to guarantee the stability and suppress the uplift pressures.
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
92 Layman's Guidebook
4.2.2.3 The channel in tunnel.
The tunnel construction must comply with the following requirements:
• The excavation will be conditioned by the geologic formations that must traverse,
either a rock massif or a superficial formation .
• The tunnel, being a hydraulic channel should be stable and watertight
Consequently the geologic formations existing in the massif to be traversed must
be known in detail.
Photograph 4.4 shows a view of the Cordirianes colluvium, under which the tunnel
runs from the point marked in figure 4.4 with the word "tunnel". Figure 4.5 shows
-- -- - - -- -- -- ------- - ---- - ---- -- --------- - ---- --- --- --- --- - --- --- ---
I&] Colluvial formation
F : : :1 Underlying limestones
fi ure 4.5
Chapter 4. Site evaluation methodologies 93
l. Canal in tunnel
2. Injected concrete
3. Coluviall formation
4. Drain
5. Detail of the draining pipe
figure 4.6
a schematic cut of the tunnel under the colluvium and figure 4.6 illustrates the
concrete lining conforming the final section of the canal.
The excavation works were extremely difficult due to the large variety and
heterogeneity of the blocks, which varied in size from simple stones to blocks of
several cubic meters. The use of large explosive charges was out of place here.
Excavation by tunnelling machines unfeasible. The excavation had to proceed
meter by meter using small explosive charges to reduce the size of the blocks
which could not be handled (Photograph 4.5).
The concrete lining was also difficult. Zone 2 in figure 4.6 was filled by injecting
grout. In fact this injection not only filled the empty space but also enclosed the
supporting structure and reinforced the loose terrain around the tunnel. This
terrain is very permeable so to avoid lateral pressures or uplift pressures a draining
system was put in place.
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
94
Photo 4.5
Photo 4.7
Layman's Guidebook
The construction of tunnels through rocky massifs should take into
account two important geologic characteristics:
• The lithologic variation along its trace, that can decisively influence
the construction method to be used .
• The structural stability of the massif along the trace. Even if the
massif is lithologically coherent the distribution of the potential
discontinuities -stratification planes, joints, fissures -will be far
from homogeneous. Once aga in the knowledge of all those
discontinuities must be based on a detailed structural geological
study. ·
As well as the relatively small discontinuities referred above , the
designer should also deal with the large tectonic discontinuities -large
bendings, faults , invert faults-that not only affect the work itself but
also the future operation of the canal.
Figure 4 . 7 shows a thrust fault, present in the La Rienda tunnel, second
part of the tunnel of Cordirianes, close to the forebay built right at the
end of the tunnel. Due to the strains and deformations supported in the
past by this mass of rocks , the rocks origina ll y sound were completely
altered. Its response to the excavation was of course very different
from the response of the rest of the massif. Only by knowing in time the
presence of this fault could the tunnel be excavated without unexpected
incidents. Figure 4 .8 shows in greater detail how the tunnel was ·
excavated through the fault zone. As photographs 4 .6 and 4. 7 illustrate,
the supporting structure during the tunnel construction was very d ifferent
in this area to the one used in the rest of the work .
4.2.2.4 The powerhouse
Due to the presence of large and heavy equipment units the powemouse
stability must be completely secured. Settlements cannot be accepted
in the powerhouse . If the geologic condition of the ground cannot
guarantee the stability of the foundation it must be strengthened .
Chapter 4. Site evaluation methodologies 95
Sierra de La Rienda
Fault area
Collapse
Coluviall
Limestone
Fault area
~ Water surges
figure 4.7
If the powerhouse is founded on rock, the excavation work will eliminate the su-
perficial weathered layer, leaving a sound rock foundation. If the powerhouse is
to be located on fluvial terraces near the riverbanks which do not offer a good
foundation then the ground must be reconditioned.
The traditional cement grouting presents some difficulties and in any case its results
never will be satisfactory when the terrain is as heterogenous and permeable as
exists in fluvial terraces. A new injection technique, jet grouting, can guarantee the
96 Layman's Guidebook
Alluvium Basement
~ Substratum of rocks D Injection curtain
figure 4.9
terrain consolidation, replacing alluvial sediments by an injected curtain. The
technique, widely used by the DOE (Department of Energy of the U.S) to cut the
seepage in the underground storage reservoir for toxic wastes, is however very
expensive at present. Figure 4.9 illustrates the results of the jet-grouting operation
which was performed to reinforce the terrain supporting the powerhouse.
4.3 Learning from failures
Two well-known experts, Bryan Leyland of Australia and Freddy lsambert from
France, presented to HIDROENERGIA95 Conference, that was held at Milan,
two independent papers dealing with the topic "lessons from failures". Mr Leyland
quoting Mr Winston Churchill -"he who ignores history is doomed to repeat it"-
claims that if one does not want to repeat the mistakes of others, the reasons for
their failures must studied and understood. And according to Mr lssambert "case
studies have shown that a number of small hydro plants have failed because they
were poorly designed, built or operated". The authors presented, with the aid of
graphics and photographs, several examples of schemes that failed in the
commissioning of the plant or later in the operation, and produces considerable
loss of money and dramatic delays.
Professor Mosony wrote in ESHA Info no. 15, "a fair and open discussion about
failures is indispensable in order to learn from failures and, consequently to avoid
Chapter 4. Site evaluation methodologies 97
figure 4.9
their repetition". And quoting Marcus Tullius Ciceron (106-43 BC) "Every human
being can make a mistake. but only the idiot persists in repeating his mistake".From
the accounts of failures reported at HIDROENERGIA. together with more than 50
others described in the ASCE publication "Lessons Learned from the Design.
Construction and Operation of Hydroelectric Facilities", of which 28 of them concern
schemes of less than 10 MW capacity. those have been selected for discussion
below. They demonstrate the importance of studying in depth. the stability of
canals and the effects of uplift pressure on hydraulic structures.
Ruahihi canal failure {New Zealand)
As shown in figure 4.10 the scheme had a 2000 m canal laid along a side slope.
leading to 750 m of concrete and steel penstocks. The canal was excavated in soft
ignimbrite (debris from a volcanic explosion) and lined with a type of volcanic clay.
The brown ash dried and cracked during construction but due to its unusual
characteristics, the cracks did not seal when the canal was filled. So water leaked
into the ignimbrite below. When these leaks appeared perforated pipes were driven
in to drain the bottom of the slope. This hid the problem and also made it worse
because the leaking water caused caverns to form in the fill.
On the day after the scheme was officially opened, a large section of the canal
suddenly collapsed. Photograph 4.8 illustrates the magnitude of the catastrophe.
Many options were examined and finally it was decided that the only viable option
was to replace the failed section of canal with 1100 m of pipes. This increased the
length of the penstocks from 750 m to 1850 m and required that water hammer
pressures have to be reduced because the original concrete pipes could only
withstand a very limited overpressure.
• • • 98 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Photo 4.8
Photo 4.9
Layman's Guidebook
It was necessary to modify the relief valves and the inlet valves so that there
would only be a 3% pressure rise under the worst conditions. A surge chamber
was not an option because the ground could not take the extra weight. Fortunately
the turbine manufacturer was very cooperative and had faith in the ability of his
relief valves to limit the pressure rise to 3%, which they did. The refurbishment
was completed ahead of time and under budget.
The lessons learned were:
• the characteristics of volcanic materials are highly variable and often
undesirable;
• when a canal leaks, be sure the problem is fully understood before repairs
commence;
• when the alternative is to abandon a failed scheme, consider the seemingly
impossible -there may not be a lot to lose!
Chapter 4. Site evaluation methodologies 99
La Marea canal failure (Spain)
The La Marea scheme has a spiral Francis turbine of 1 100 kW installed capacity for
a discharge of 1.3 m3/s and a 100-m head. As shown in figure 4.11 the scheme
includes a small weir for the water intake, provided with a ladder fish pass. From the
intake a rectangular canal built in reinforced concrete (3 x 2m section) is followed
by another 600 m long canal in tunnel. At the outlet of the tunnel a reservoir was
built to store water for peak operation. The reservoir was built by compressing a mix
of sand and clay, and unfortunately proved to be insufficiently watertight. From the
reservoir another canal, built with prefabricated sections of concrete with thin steel
plates between, brings the water to the forebay, located 100-m above the
powerhouse.
The canal lays on a steep slope on strongly weathered sandstone. Heavy rain
was pouring over the canal both during its construction and during its
commissioning. Immediately after opening the intake gate, the reservoir was filled
and the water began to seep into the terrain. The wetted sandstone could not
resist the shear stresses and a landslide broke the reservoir embankment
(photograph 4.9), and large masses of material reached the river, and through
the river, the seacoast. The reservoir was replaced by a construction in reinforced
concrete which, up to the present, has served no useful purpose. Later on, the
second section of the canal -the prefabricated reach-started to leak. The terrain
became saturated and, unable to resist the shear stresses, failed in a rotational
slide. About 200 m of canal were replaced by a low-pressure welded steel pipe
that up to now has been performing adequately. The pipe runs under a daily
storage pound, waterproofed by a thermo-welded plastic sheet, and ends in the
fore bay.
The lessons learned were:
• Weathered sandstone gives bad results against landslide, specially on slopes
with an angle over 35° to the horizontal.
• Hydraulic canals should be built to guarantee their waterproofness; alternatively a
draining system should be dE:\'ised so the water leakage can not affect the terrain.
• The replacement of an open canal by a low pressure pipe on a steep slope may
figure 4.10
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
100 Layman's Guidebook
figure 4.11
be the best option, because it will be watertight and because its anchorage on
the slope will require only a few strong points .
Seepage under a weir (France)
This case concerns a small weir, which is the structure furthest upstream of a 600 kW
project comprising a buried culvert, a penstock and a powerhouse. The operating
personnel had noticed minor leakage at the downstream toe of the dam. The small
reservoir was emptied, and a trench was excavated so that the contact between the
structure and the foundation could be examined. It was then revealed that a conduit
had formed between the upstream and the downstream faces of the weir (photo
4.11 ), which was actually founded on permeable deposits without a cutoff trench. The
weir in this condition would have eventually failed by undermining the foundation .
The key issues to learn from this case were the lack of a geomorphologic survey
and inadequate supervision of the design and construction of the weir .
Chapter 4. Site evaluation methodologies 101
Photo 4.11
Photo 4.12
The hydraulic canal in a low-head 2 MW scheme
The hydraulic canal - 5 m wide and 500 m long -goes along the river and close
to it. The river was known to experience frequent flash floods . On one particular
day, a flood occurred which was later calculated to be a 100 year event. When
the flood occurred, the turbines were stopped and all the gates closed . The
headrace channel had been almost emptied by leakage, and the channel was
destroyed by uplift pressure (photo 4.12).
In this case the key technical issues were : hydraulics , structural stability .and
design.
• • • • • • • • • • • • • • • • • • • • •
• • • • • • • •• • • • ••
102 Layman's Guidebook
There are other cases that could be described to show the effects of misjudgment
during either the design or the construction phase. Such case studies show the
number and diversity of parameters that can cause failures. It is also unfortunately
evident that design, construction and site supervision are often carried out by
companies which may offer lower costs, but have little experience of hydraulic
works.
5. Hydraulic structures
5.1 Structures for storage and water intake
5.1.1 Dams
5.1.2 Weirs
The dam is a fundamental element in conventional hydraulic schemes, where it is
used to create a reservoir to store water and to develop head. In relatively flat
terrain, a dam, by increasing the level of the water surface, can develop the head
necessary to generate the required energy. The dam can also be used to store,
during high flow seasons the water required to generate energy in dry seasons.
Notwithstanding this, due to the high cost of dams and their appurtenances, they
are seldom used in small hydro schemes.
figure 5.1
If a scheme is connected to an isolated net, and if the topography is favourable, a
dam can be built to store excess water when the flow is high or the demand low to
make it available at times of low flow or increased demand.
Where a reservoir is built for other purposes -irrigation, water supply to a city,
flood regulation, etc-it can be used by constructing a plant at the base of the dam
to generate energy as an additional benefit.
The large majority of small hydro schemes are of the run-of-river type, where
electricity is generated from discharges larger than the minimum required to
operate the turbine. In these schemes a low diversion structure is built on the
streambed to divert the required flow whilst the rest of the water continues to
overflow it. When the scheme is large enough this diversion structure becomes a
small dam, commonly known as a weir, whose role is not to store the water but to
increase the level of the water surface so the flow can enter into the intake.
Weirs should be constructed on rock and in their simplest version consist of a few
boulders placed across the stream (figure 5.1 ). When the rock is deep, excavation
is needed, and a sill constructed of gabions-steel mesh baskets filled with stones-
can be used (figure 5.2).
In larger structures the weir may be a small earth dam, with an impervious core
..k pens toe
upstream water level
7
streambed
go 1ons
figure 5.2
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
104
Photo 5.1
Layman's Guidebook
flgura 5.3
figure 5.4
which extends well into the impervious foundation, located in the central portion of
the dam. (Figure 5 .3). This core is generally constructed of compacted dayey mate-
rial. If this material is not available in the site a properly welded geotextiles sheet must
cover the upstream embankment to provide the required waterproofing (figure 5.4)
If clayey material doesn't exist in the site but sand and gravel are easily found,
the construction of a concrete dam can be considered . If the stream is subjected
to sudden floods that require the construction of large spillways, very expensive
to build in an earth dam, concrete dams, where the spillways is easily integrated
(photo 5.1) may be advisable . However if the scheme is located on a seismic
area , rigid structures such as concrete dams should be avoided, and earth dams
are more suitable. In very cold climates the required precautions to be taken
with the freshly poured concrete can be so costly that the construction of a con-
crete dam is not feasible .
According to the ICOLD (International Committee of Large Dams) a dam is
considered "small" when its height, measured from its foundation level to the
crest, does not exceed15 m , the crest length is less than 500 m and the stored
water is less than1 million cubic meters. These parameters are important, because
of the complicated administrative procedures associated with the construction of
large dams. The great majority of small dams in small hydro schemes are of the ·
gravity type , commonly founded on solid rock and where their stability is due to
their own weight. If a dam is less than 10 m high it can be built on earth foundations,
but allowable stresses must not be exceeded and the possibility of piping due to
Chapter 5. Hydraulic structures 105
seepage under the dam minimised, through the use of aprons or cut-offs. For the
foundation it will be necessary to know the shear strength, compressive strength
and Poisson's ratio.
The dam must be stable for all possible loading conditions (figure 5.5): hydrostatic
forces on the upstream and downstream faces; hydrostatic uplift acting under
the base of the dam; forces due to silt deposited in the reservoir and in contact
with the dam; earthquakes forces that are assumed to act both horizontally and
vertically through the centre of gravity of the dam (if the dam is located in a
seismically active zone); earthquake forces induced by the relative movements
of the dam and reservoir etc.
Since the dam must be safe from overturning under all possible load conditions
therefore the contact stress between the foundation and the dam must be greater
than zero at all points. To assure this condition the resultant of all horizontal and
vertical forces -included the weight of the dam-must pass through the middle
one-third of the base. The upstream face is usually vertical whereas the
downstream face has a constant inclination. It is also necessary to guarantee
that the dam doesn't slide, so the static friction coefficient -all the horizontal forces
divided by all the vertical ones-must remain between 0.6 and 0.75.
5.1.2.1 Devices to raise the water level.
To raise the water level slightly behind the weir to ensure adequate depth of water
at the intake, without endangering the flooding of the upstream terrain, flashboards
may be installed on the crest of the weir (photo 5.2). The flashboards are commonly
made of wood and supported by steel pins embedded in steel sockets -pipes cut
down to size-in the spillway crest (figure 5.6 a). The flashboards have to be
removed by hand during flood flows so that high water levels do not flood the
upstream terrain, an operation that in such circumstances is very difficult. The
articulated flashboard illustrated in figure 5.6.b is somewhat easier to remove.
H _______. a IL__P/3 __1.--_..c.___~!:-~
Fr---+
Ullllllllllllllllllllllllll]
ju
fi ure 5.5
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
106 Layman's Guidebook
a) b)
flashboard with embedded articulated flashboard with
supports strut
figure 5.6
Photo 5.2
In low head schemes with integral intake and powerhouse -see figure 1.3-the
best way to increase the head without risking upstream flooding, is the sector
gate. A hydraulic system or an electric motor opens the gate, so that the water
passes underneath .
In large installations, but also sometimes in small ones , it is advisable to place
fusegates, such as those supplied by Hydroplus1• In the event" of a major flood,
when the water reaches a pre-set level, one or more of the fusegates -basically
hinged structures-will tilt to increase the section of the spillway (photo 5.3) .
Another method, capable of remote control, is the inflatable weir, which employs
a reinforced rubber bladder instead of concrete, steel or wood flashboards. This
offers an alternative to more conventional methods of weir construction, with the ·
inherent advantages of low initial cost, simple operation and minimal maintenance .
In effect, inflatable weirs are flexible gates in the form of a reinforced, sheet-
rubber bladder inflated by air or water, anchored to a concrete foundation (figure
5 .7) by anchor bolts embedded into the foundation. Like any other gate, the
inflatable weir needs a mechanism by which it is opened and closed. The weir is
raised when filled with water or air under pressure. An air compressor or a water
pump is .connected, via a pipe, to the rubber bladder. When the bladder is filled
the gate is raised (photo 5.4 ); when it is deflated the weir lies flat on its founda-
tion, in a fully opened position. The system becomes economic when the width of
the weir is large in relation to the. height
When the management and operational safety of the system is rather critical, the
use of inflatable weirs can give substantial advantages over conventional systems .
An electronic sensor monitors the upstream water level and the inner pressure of
the bladder. A microprocessor maintains a constant level in the intake entrance
by making small changes in the inner pressure of the bladder. To avoid flooding
land, a similar device can regulate the inflatable weir regulated to correspond to a
pre-set upstream water level.
Chapter 5. Hydraulic structures 107
Photo 5.3
Inflatable gate control systems can be designed to fully deflate the bladder
automatically in rivers prone to sudden water flow surges. On a typical weir, two
meters high and thirty meters wide, this can be done in less than thirty minutes.
Photo 5.5 illustrates a new type of inflatable weir -patented by Obermeyer Hydro-
where the sheet rubber incorporates a steel panel that behaves as a flash board, which
is quickly and easily manageable in the event of sudden floods. By controlling the
pressure in the rubber blade the steel panels may be more or less inclined, varying the
level ofthe water surface . The system incorporates an additional advantage: the rubber
blade is always protected against boulders carried during flood flows; buoyancy cau-
ses heavy boulders to loos'e a portion of their weight in water, making it easier for the
flood flow to carry them downstream. The free space betWeen panels or between pa-
nel and the buttress are dosed by a synthetic rubber flap anchored to one of the panels'!.
Photo 5.4
flow ...
fig ure 5.7
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • •• • • • •
• •
108
Photo 5.5
5.1.3 Spillways
Photo 5.6
Layman 's Guidebook
In the south of Europe, with a clear difference between dry and wet season flows ,
flood flows can have catastrophic effects on whatever structure is built in the
stream . To avoid damage the excess water must be safely discharged over the
dam or weir. For this reason carefully designed overflow passages are incorporated
in dams as part of the structure. These passages are known as "spillways". Due
to the high velocities of the spilling water, some form of energy dissipation is
usually provided at the base of the spillway .
Chapter 5. Hydraulic structures 109
Photo 5.7
il
{TTTTTTT1 ... 7 ...
. ....... ~
figure 5.8
The commonest type of spillway is the overflow gravity type (photo 5.6). Basically
it is an open channel with a steep slope and with a rounded crest at its entry. To
minimise the pressure on the surface of the spillway the profile of the crest should
follow the same curve as the underside of the free-falling water nappe overflowing
a sharp crest weir. This trajectory varies with the head, so the crest profile is the
right one only for the design head H •. If H>H. negative pressure zones tend to
develop along the profile and cavitation may occur. Recent work suggests that
fortunately, separation will not occur until H>3 H. The U.S. Waterways Experi-
mental Station3 has provided a set of profiles that have been found to agree with
actual prototype measurements.
The discharge may be calculated by the equation
Q=CLHJI2 (5 .1)
where C is the coefficient of discharge, Lis the length of the spillway
crest and H is the static head. The coefficient of discharge C is
determined by scale model tests; its value normally ranges between
1.66 for broad crested weirs to 2 .2 for a weir designed with the
optimum profile, when the head equals the design head.
In some small hydropower schemes -e.g . small scheme in an irrigation
canal-there is not enough space to locate a conventional spillway. In
these cases, U shaped (figure 5.8 and photo 5. 7) or labyrinth weirs
(figure 5.9) should help to obtain a higher discharge in the available
length.
Alternatively where space available for the spillway is limited, a siphon
spillway or a shaft spillway may be used. Both solutions help to keep
the upstream water level within narrow limits. A siphon spillway is
basically a curved enclosed duct as illustrated in Fig 5.10 4 • When the
water level rises above the elbow of the siphon the water begins to
flow, down the conduit just as in an overflow spillway, but it is when it
rises further that the siphon is primed and increases the discharge
considerably. Usually siphons are primed when the water level reaches
or passes the level of the crown , but there are designs where priming
occurs when the upstream level has risen only to about one third of
the throat height.
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
110 Layman's Guidebook
t
t
figure 5.9
If badly designed, the siphon process can become unstable. At the beginning the
siphon discharges in a gravity mode, but when the siphon is primed the discharge
suddenly increases. Consequently the reservoir level drops, the siphon is de-
primed and the discharge is reduced. The level of the reservoir increases anew
until the siphon primes again, and the cycle of events is repeated indefinitely,
causing severe surges and stoppages. Multiple siphons with differential crest
heights or aerated siphons can be the solution to this problem.
When the siphon is primed the flow through a siphon spillway is governed, as in
penstocks, by Bernoulli's equation. Assuming that the velocity of water in the
conduit is the same at the inlet and outlet, the head loss may be calculated from
the formulae in Chapter 2, paragraph 2.2.1.
If the pressure at the crown of the siphon drops below the vapour pressure, the
water vaporises forming a large number of small vapour cavities which entrained
in the flow condense again into liquid in a zone of higher pressure. This
phenomenon is known as cavitation and it can be extremely damaging. To avoid
it, the distance between the crown of the siphon and the maximum level at the
reservoir, depending on height above sea level and prevailing barometric pressure,
vacuum breaker ---.....
siphon spillway
figure 5.10
Chapter 5. Hydraulic stmctures
vertical shaft
horizontal shaft
figure 5.11
5.1.4 Energy dissipators
I 11
shaft spillway into a canal
figure 5.12
should normally not exceed 5 m. Further details on this
kind of spillway can be found in the literature6 •
Shaft or "glory hole" spillways are rarely used in small scale-
hydro. As illustrated in Fig 5.11 a shaft spillway incorporates
a funnel-shaped inlet to increase the length of the crest, a
flared transition which conforms to the shape of the nappe as
in the overflow spillway though it is sometimes stepped to
ensure aeration. a vertical shaft and an outlet tunnel that
sometimes has a slight positive slope to ensure that at the
end it never flows full. Figure 5.12, reproduced from lnversin 5
illustrates a shaft installed to evacuate the excess water in a
channel, where a side-spillway could generate a landslide by
saturating the terrain. The US Bureau of Reclamation reports
(USBR) 6 .7 describe the design principles for these spillways.
The discharge from a spillway outlet is usually supercritical and so may produce
severe erosion at the toe of the dam, especially if the streambed is of silt or clay.
To avoid such damage, a transition structure known as a stilling basin must be
constructed to induce the formation of a hydraulic jump, where the water flow
changes from supercritical to subcritical. The USBR has published a set of curves
to be used in the design of stilling basins8 .
5.1.5 Low level outlets
Low level outlets in small hydropower schemes are used to perform, together or
independently, the downstream release and the evacuation of the reservoir, either in
an emergency or to permit dam maintenance. In general a low level-conduit with a
cone valve at the exit or a sliding gate at the inlet is enough to perform both functions.
At the exit, if the flow is supercritical, the provision of energy dissipaters should be
considered.
5.1.6 River diversion during construction
In small hydropower schemes the construction may be completed, in some ca-
ses, within the dry season, but in many others, diversion arrangements will be
necessary. Suitable diversion structures include the following:
112
5.2 Waterways
Gabions with geotextiles on the upstream faces
Earth dikes with riprap protection
Inflatable weirs
Sheetpile diversion dams
Layman's Guidebook
The techniques of their construction and their practical use require the advice of
specialised engineers.
5.2.1 Intake structures
The Glossary of Hydropower Terms -1989 defines the intake as "a structure to
divert water into a conduit leading to the power plant". Following the ASCE
Committee on Hydropower lntakes 11 , the water intake in this handbook is defined
as a structure to divert water to a waterway -not specifying what type of waterway:
a power channel or a pressure conduit-and reserving the word forebay or power
intake, to those intakes directly supplying water to the turbine, via a penstock.
A water intake must be able to divert the required amount of water into the power
canal or into the penstock without producing a negative impact on the local
environment and with the minimum possible headloss. The intake serves as a
transition between a stream that can vary from a trickle to a raging torrent, and a
controlled flow of water both in quality and quantity. Its design, based on geological,
hydraulic, structural and economic considerations, requires special care to avoid
unnecessary maintenance and operational problems that cannot be easily
remedied and would have to be tolerated for the life of the project.
A water intake designer should take three criteria into consideration:
• Hydraulic and structural criteria common to all kind of intakes
• Operational criteria-e.g. percentage of diverted flow, trash handling, sediment
exclusion, etc-that vary from intake to intake
• Environmental criteria -fish diversion systems, fishpasses-characteristics of
each project.
Even if every year new ideas for intake design are proposed -advances in
modelling, new construction materials, etc-the fundamental hydraulic and structural
design concepts have not changed much in many years, and are not likely to
change in the future. Over the years, many intakes have been designed; vast
quantities of trash have been removed; and large amounts of sediments have
been sluiced. From all that accumulated experience we now know what works
and what does not work, and this experience together with fundamental hydraulic
principles, the designer can develop better and effective intakes, precluding future
incidents.
Chapter 5. Hydraulic structures
5.2.1.1 Water intake types
__/(
trash rack
figure 5.13
intakes
113
The first thing for the designer to do is to decide what
kind of intake the scheme needs. Notwithstanding the
large variety of existing intakes, these can be classified
according to the following criteria:
The intake supplies water directly to the turbine via a
penstock (figure 5.1 ). This is what is known as power
intake or forebay.
• The intake supplies water to other waterways -power
canal, flume, tunnel, etc-that usually end in a power
intake (figure 1.1 Chapter 1 ). This is known as a
conveyance intake
• The scheme doesn't have any conventional intake,
but make use of other devices, like siphon intakes
or "french intakes" that will be described later.
In multipurpose reservoirs -built for irrigation, drinking water
abstraction, flood regulation, etc-the water can be
withdrawn through towers with multiple level ports,
permitting selective withdrawal from the reservoir's vertical
strata (figure 5.13) or through bottom outlets (figure 5.14)
The siphon intake (figure 5.15) renders intake gates
unnecessary, and the inlet valves (provided each unit
has its own conduit) may also be eliminated, reducing
the total cost by 25-40 per cent, and reducing the silt
intake. The water flow to the turbine can be shut off
more quickly than in a gated intake, which is beneficial
in a runaway condition. Photo 5.8 shows a siphon
intake built on an existing dam, with very small civil
works. The siphon can be made of steel, or alternatively
in countries where the procurement of fabricated steel
is difficult, in reinforced concrete, with the critical
sections lined in steel.
figure 5.14
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
114
Photo 5,8
Layman's Guidebook
The "french" or drop intake (figure 5.16) is essentially a canal built in the stream~
bed, stretching across it and covered by a trashrack with a slope greater than the
streambed slope. The trashrack bars are oriented in the direction of the streamflow.
Photo 5.9 shows a drop intake installed in a mountain stream in Asturias (Spain). In
France EDF has improved this type of intake, placing the bars as cantileversto avoid
the accumulation of small stones commonly entrained by the water (figure 5.17)
The Coanda type screen is an advanced concept of the drop intake, incorporating the
"Coanda effect", well known in the ore separation industry, to separate fish and debris
from clean water. Essentially it consists of a weir with a downward sloping profiled
surface of stainless steel wire screen mesh on the downstream side and a flow collection
channel below the mesh -as in the drop intake . The mesh wires are held horizontal -
unlike the drop intake-and are of triangular section to provide an expanding water
passage . Water. drops through the mesh with debris and fish carried off the base of the
screen . The screen is capable of removing 90% of the solids as small as 0.5 mm , so a
beginning of the open canal
figure 5.16 figure 5.17
Chapter 5. Hydraulic structures 115
Photo 5.9
5.2.1.2 Intake location
Photo 5.10
silt basin and sediment ejection system can be omitted. The intake (photo 5.1 0) is
patented by AQUA SHEAR and distributed by DULAS 11 in Europe.
The location of the intake depends on a number of factors, such as submergence,
geotechnical conditions, environmental considerations -especially those related
to fish life-sediment exclusion and ice formation -where necessary.
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
116
Photo 5.11
5.2.2 Power in take
Layman's Guidebook
The orientation of the intake entrance to the flow is a crucial factor in minimising
debris accumulation on the trashrack , a source of future maintenance problems
and plant stoppages. The best disposition9 of the intake is with the screen at right
angles to the spillway (figure 5.1) so, that in flood seasons the flow entrains the
debris over its crest. The intake should not be located in an area of still water, far
from the spillway, because the eddy currents common in such waters will entrain
and accumulate trash at the entrance. If for any reason the intake entrance should
be parallel to the spillway, it is preferable to locate it close to the spillway so the
operator can push the trash away to be carried away by the spillway flow. (See
photo 5.11 in a dry season where all the water went through the turbine)
The water intake should be equipped with a trashrack to minimise the amount of
debris and sediment carried by the incoming water; a settling basin where the
flow velocity is reduced, to remove all particles over 0.2 mm; a sluicing system to
flush the deposited silt, sand, gravel and pebbles with a minimum of water loss;
and a spillway to divert the excess water. Spillways have been already considered
in depth in 5 .1.3, as other components will be later .
The power intake is a variant of the conventional intake, usually located at the
end of a power canal, although sometimes it can replace it. Because it has to
supply water to a pressure conduit -the penstock-its hydraulic requirements are
more stringent that those of a conveyance intake .
In small hydropower schemes , even in high head ones , water intakes are hori -
zontal , followed by a curve to an inclined or vertical penstock. The design depends
on whether the horizontal intake is a component of a high head or a low head
scheme. In low head schemes a good hydraulic design -often more costly than a
less efficient one-makes sense, because the head loss through the intake is
Chapter 5. Hydraulic structures 117
comparatively large related to the gross head. In high head schemes, the value
of the energy lost in the intake will be small relatively to the total head and the
cost of increasing the intake size to provide a lower intake velocity and a better
profile may not be justified.
In a power intake several components need consideration:
• Approach walls to the trash rack designed to minimise flow separation and head
losses
• Transition from rectangular cross section to a circular one to meet the entrance
to the penstock
• Piers to support mechanical equipment including trash racks, and service gates
• Guide vanes to distribute flow uniformly
• Vortex suppression devices
The velocity profile decisively influences the trashrack efficiency. The velocity
along the intake may vary, from 0.8-1.0 m/sec through the trashrack to 3-5 m/
sec in the penstock. A good profile will achieve a uniform acceleration of the flow,
minimising head losses. A sudden acceleration or deceleration of the flow
generates additional turbulence with flow separation and increases the head
losses. Unfortunately a constant acceleration with low head losses requires a
complex and lengthy intake, which is expensive. A trade-off between cost and
efficiency should be achieved. The maximum acceptable velocity dictates the
penstock diameter; a reasonable velocity of the flow approaching the trashrack
provides the dimensions of the rectangular section.
The research department of "Energy, Mines and Resources" of Canada 10
commissioned a study of entrance loss coefficients for small, low-head intake
structures to establishing guide lines for selecting optimum intakes geometries.
The results showed that economic benefits increase with progressively smoother
intake geometries having multiplane roof transition planes prepared from flat
formwork. In addition, it was found that cost savings from shorter and more compact
intakes were significantly higher than the corresponding disbenefits from increased
head losses.
The analyses of cost/benefits recommend the design of a compact intake -it
appeared that the length of the intake was unlikely to be the major factor
contributing to the overall loss coefficient-with a sloping roof and converging
walls (figure 5.18, alternative 2 in the study). The K coefficient of this transition
profile was 0.19. The head loss (m) in the intake is given by
6h = 0.19 v2 /2g (5.2)
where vis the velocity in the penstock (m/sec).
A well-designed intake should not only minimise head losses but also perclude
vorticity. Vorticity should be avoided because it interferes with the good perfor-
mance of turbines -especially bulb and pit turbines. Vortices may effectively:
• Produce non-uniform flow conditions
• Introduce air into the flow, with unfavourable results on the turbines: vibration,
cavitation, unbalanced loads, etc.
• Increase head losses and decrease efficiency
• Draw trash into the intake
118
PLANT
j_
5,09
I_ SECTION ~r-2.78 _J
4,01
5,86
figure 5.18
Layman's Guidebook
('\1 q
(all measurements in metres
The criteria to avoid vorticity are not well defined, and there is not a single formula
that adequately takes into consideration the possible factors affecting it. According
to the ASCE Committee on Hydropower Intakes, disturbances, which introduce
non-uniform velocity, can initiate vortices. These include:
• Asymmetrical approach conditions
• Inadequate submergence
• Flow separation and eddy formation
• Approach velocities greater than 0.65 m/sec
• Abrupt changes in flow direction
Lack of sufficient submergence and asymmetrical approach seem to be the
commonest causes of vortex formation. An asymmetric approach (figure 5.19 a)
is more prone to vortex formation than a symmetrical one (figure 5.19b). Providing
the inlet to the penstock is deep enough, and the flow undisturbed vortex formation
is unlikely.
According to Gulliver, Rindels and Liblom (1986) of St. Anthony Falls hydraulic
laboratories, vortices need not be expected provided (figure 5.19)
Chapter 5. Hydraulic structures
h
a) b)
s
c)
figure 5.19
v
S > 0. 7 D and N F = Jiii < 0. 5
aD b
119
r
d)
(5.3)
After applying the above recommendations, if there is still vortex formation at the
plant and it is impossible to increase the submergence of the penstock entrance
or increase its diameter-the situation can be improved by a floating raft which
disrupts the angular movement of the water near the surface (figure 5.19 d)
5.2.3 Mechanical equipment
5.2.3.1 Debris management in intakes
One of the major functions of the intake is to minimise the amount of debris and
sediment carried by the incoming water, so trash racks are placed at the entrance
to the intake to prevent the ingress of floating debris and large stones. A trashrack
is made up of one or more panels, fabricated from a series of evenly spaced
parallel metal bars. If the watercourse, in the flood season, entrains large debris,
it is convenient to install, in front of the ordinary grill, a special one, with removable
and widely spaced bars -from 100 mm to 300 mm between bars-to reduce the
work of the automatic trash rack cleaning equipment
Trashracks are fabricated with stainless steel or plastic bars. Since the plastic
bars can be made in airfoil sections, less turbulence and lower head losses result.
The bar spacing varies from a clear width of 12 mm for small high head Pelton
turbines to a maximum of 150 mm for large propeller ones. The trash rack should
• • • • • • • • • • • •
•
• • • • • • • • • • •
•
120
Photo 5.12
Photo 5.13
Layman's Guidebook
have a net area -the total area less the bars frontal area-so that the water
velocity does not exceed 0. 75 m/s on small intakes, or 1.5 m/s on larger intakes,
to avoid attracting floating debris to the trash rack. Trash racks can be either bolted
to the support frame with stainless steel bolts or slid into vertical slots, to be
removed and replaced by stoplogs when closure for maintenance or repair is
needed. In large trashracks it must be assumed that the grill may be clogged and
the supporting structure must be designed to resist the total water pressure exerted
over the whole area without excessive deformation .
Chapter 5. Hydraulic structures
trash pass s over
the radial te
radial gates
spillway
(reproduced from ASCE publication)
figure 5.20
anchor
block
121
When the river entrains heavy debris, floating booms may be located ahead of
the trash racks. The simplest boom consists of a series of floating pieces of timber
connected end to end with cables or chains. However modem booms are built
with prefabricated sections of steel and plastic (photos 5.12 and 5.13) supported
by steel cables. Their location is critical, because their inward bowed configuration
does not lend itself to a self-cleaning action during flood flows. Figure 5.20 -
reproduced from reference 11-shows a rather complex trash boom layout designed
for a dual-purpose: preventing boats passing over the spillway and protecting the
adjacent intake. A section of the boom is hinged at one end of the fixed section so
that winches can handle the other end to let the trash pass downstream over the
spillway, when large quantities are passing.
The trashrack is designed so the approach velocity (V0 ) remains between 0.60 m/s
and 1.50 m/s. The total surface of the screen will be given by the equation:
s-1 (b+a)Q 1
- K
1
-a-1<
1
sina: (5.4)
Where: S =Total area of the submerged part of the screen
Q = Rated flow
V0 =Approach velocity
b =Bar width
a = Space between bars
122 Layman's Guidebook
K1 =Coefficient related to the partial clogging of the screen:
no automatic raker 0.20-0.30;
automatic raker with hourly programmer 0.40-0.60;
automatic raker plus differential pressure sensor 0.80-0.85
a = Angle of the screen with the horizontal
For computing head losses in clean trash racks, the Kirscmer formula, detailed in
Chapter 2, section 2.2.2.1, is commonly used. This formula is only valid when the
Drain
Trash rack
figure 5.21
Chapter 5. Hydraulic structures 123
Drive unit
~--...
trash rack
figure 5.22
flow approachs the screen at right angles. Otherwise the head losses increase
with the angle, and can be up to 18 times the value computed by the Kirchsmer
formula. The additional head loss can be computed by the formula
(5.5)
where h" is the head loss in m, a angle between the flow and the perpendicular to
the screen (a max = 90° for screens located in the sidewall of a canal) and V0 and
g there are the same values as in the Kirschmer formula. If the flow is not perpen-
dicular to the screen it is preferable to use round bars instead of profiled wire.
Anyhow it is more important to keep the screen free of clogging because the
head loss computed by the above formulae is insignificant when compared with
the headloss arising from a partial clogging of the screen.
The trashrack should be removable for repair and maintenance and provided with
facilities to clean it. To facilitate the hand cleaning of the trashrack it should be
inclined at an angle 30° from the horizontal although steeper angles are often used.
Trashracks can be cleaned by hand up to 4 meters depth. A horizontal platform
above high-water level should be provided to facilitate the operation. On unattended
plants operated by remote control, mechanical rakers are used. The mechanical
raker can be designed to be operated either on a timed basis or on a head differential
basis. The latter uses a sensor to detect the drop in head across the trash rack. An
accumulation of trash on the trash rack creates an increased differential head across
the trashrack. The raker begins when a predetermined differential head is reached.
The raker in figure 5.21 is operated through oleo-hydraulic cylinders. The
secondary cylinder pushes out or retracts the raker, which rides on a hinged
arm. The raker pushes out in its way down to the bottom of the screen and then
retracts to travel up along the screen. The raker itself is a series of prongs
protruding from a polyamide block that moves along the spaces between bars.
The trash is conveyed to the top to be dumped on a conduit or on to a conveyor.
Intake
flow
If dumped into a conduit a small water pump delivers
enough water to wash the trash along the canal. The
problem of trash disposal must be solved case by case.
bearing in mind that a trash raker can remove large
amount of debris.
When the trashrack is very long the trash raker described
above is assembled on a carriage that can move on rails
along the intake. Automatic control can be programmed
to pass along the supporting structures without human
aid. Using telescopic hydraulic cylinders the raker can
reach down to 10m deep, which combined with the almost
limitless horizontal movement. makes it possible to clean
large surface screens (photo 5.14).
A less common type is represented in figure 5.22. A
hydraulic driven chain system pulls some steel fingers
through the trashrack. The fingers. at the upper travel
position dump the collected trash to a conveyor belt for
• • • • • • • • • • • • • • • • • • • • • • • • • • • •
124
trash rack
figure 5.23
Layman's Guidebook
Photo 5.14
automatic removal
The figure 5.23 illustrates a very particular raker located at the entrance of a
siphon intake in "Le Pouzin" reservoir 12 • Initially no automatic raker was foreseen
because the screen was located very close to the spillway and the plant was
attended. The bars were placed horizontally and it was assumed that the flow
would deal with the trash easily. However it was observed that the trashrack was
clogged too often and a special horizontal raker was designed. The raker begins
its cleaning movement upstream and moves downstream so the spillway flow
contributes to cleaning it. An electrically-propelled carriage moves the raker and
the approach action is provided by an endless screw.
5.2.3.2 Sediment management in intakes
Location of intakes, as detailed in 5.2.1.2 is particularly important in this respect.
Open channels have a tendency to deposit sediments on the inner sides of bends,
but when the intake is located at the outer side of the bend floodwaters may damage
it. To overcome this problem, the best solution is to locate the intake structure in a
relatively straight section of the river. Design of an intake for sediment exclusion can
be adverse for other purposes such as fish protection. For example limiting the
velocity at the screen approach to permit small fish to escape can result in deposition
of sediments, up to actually blocking the entrance. Locating the intake entrance on
a non-eroding bedrock streambed would prevent entrance of the sediment but the
Chapter 5. Hydraulic structures
submergence depth
y:=-=--wale• •mface
• -flow
excavation and deposition area
'-::-:-:----:---
sill freeboard depth
figure 5.24
125
construction costs will be increased. Figure 5.24 shows the invert of the intake sill
raised above the river bottom to reduce the inclusion of bed load and heavy suspen-
ded materials near the bottom. The intake sill is kept off the river bottom to avoid the
sliding of the sediment along the bed. Using the spillway to entrain the sediments
that otherwise would cumulate in front of the intake is a good management technique.
When significant quantities of suspended sediments are expected to enter the in-
take large-size particles must be removed, using a sediment-excluding structure.
The sediment-trap can be located immediately downstream of the intake, where the
flow velocity is reduced. Well designed it should be able to remove all particles over
0.2 mm and a considerable portion of those between 0.1 and 0.2 mm. Such a struc-
ture is essential for heads over 100m. A good example of a sediment-trap with an
appropriate purging system and sufficient deceleration is shown in Fig 5.25.
Recently new sediment sluicing system which minimises the sluicing time and
the wasted water has appeared in the market. One of these, the SSSS (Serpent
Sediment Sluicing System) has been described in detail in the issue 9 -spring/
summer 1993-of ESHA Info.
PLANT t sediments outfall
___.,..
to the forebay
SECTION
figure 5.25
• • • • • • • • • • • • • • • •
•
• • • • • • • • • • • • • • • • • •
126 Layman 's Guidebook
5.2.3.3 Gates and valves
In every small hydropower scheme some components, for one reason or another
hand wheel -maintenance or repair to avoid the runaway speed on a shutdown turbine, etc-
figure 5.26
Photo 5.15
should be temporary isolated. Some of the gates and valves suited to the intakes
for small hydro systems include the following:
* Stoplogs made up of horizontally placed timbers
* Sliding gates of cast iron, steel, plastic or timber
* Flap gates with or without counterweights
*Globe, rotary, sleeve-type, butterfly and sphere valves
Almost without exception the power intake will incorporate some type of control gate
or valve as a guard system located upstream of the turbine and which can be closed
to allow the dewatering of the water conduit. This gate must be designed so it can be
closed against the maximum turbine flow in case of power failure, and it should be
able to open partially, under maximum head, to allow the conduit to be filled.
For low pressure the simplest type of gate is a stop log; timbers placed horizontally
and supported at each end in grooves. Stoplogs cannot control the flow and are
used only to stop it. If flow must be stopped completely, such as when a repair is
needed downstream, the use of two parallel sets of stoplogs is recommended .
They should be separated by about 15 em, so that clay can be packed in between.
Gates and valves control the flow through power conduits. Gates of the sliding type
are generally used to control the flow through open canals or other low-pressure
applications. This is the type of flow control used on conveyance intake structures
where, if necessary, the flow can be stopped completely to allow dewatering of the
conduit. Cast iron sliding-type gates are those mostly used for openings of less than
two square meters. For bigger openings fabricated steel sliding gates are cheaper
and more flexible. Gates of the sliding type are seldom used in penstocks because
they take too long to close. The stopper slides between two guides inside the gate .
Chapter 5. Hydraulic strUctures
Photo 5.16
I
\
\ --
tigvre 5.27
127
When used in a high-pressure conduit the water pressure
that force the stopper against its seat makes the valve
difficult to operate. This difficulty is overcome with a wedge-
shaped stopper (figure 5.26), so that the seal is broken
over the whole face as soon as it rises even a small distance.
To provide a good seal around a sliding gate different kinds
of rubber seals are used13 • They can be made of natural
rubber, styrene-butadiene or chloroprene compounds. The
seal path is located adjacent to the roller path.
Small sliding gates controlling the flow can be raised by
using either a wheel-and-axle mechanism (Photo 5.15),
a hydraulic cylinder (Photo 5 .16) or an electric actuator
on a screw thread .
In butterfly valves a lens shaped disk mounted on a shaft
turns to close the gap (figure 5.27). Under pressure each
side of the disk is submitted to the same pressure, so the
valve is easy to manoeuvre and closes rapidly. Butterfly
valves are used as the guard valves for turbines and as
regulating valves. Is easy to understand that when used
for regulation their efficiency is rather low because the
shaped disk remains in the flow and causes turbulence.
Butterfly valves are simple, rugged and uncomplicated
and can be operated manually or hydraulically. Photo 5.17
shows a large butterfly valve being assembled in a
powerhouse and photo 5.18 shows a butterfly valve,
hydraulically operated, with an ancillary opening system
and a counterweight, at the entrance to a small Francis
turbine.
-'
figure 5.28
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
128
Photo 5.17
Photo 5.18
Layman's Guidebook
Globe and rotary valves (figure 5.28) have lower head losses than the slide and
butterfly gate valves and are also commonly used in spite of their higher price .
The radial gates (figure 5.29), conceptually different, are a method of forming a
moveable overflow crest and allow a close control of headwater and tailwater. In
photo 5.19 it can be seen the housing of the sector on a concrete pier. The radial
gate is operated by raising or lowering to allow water to pass beneath the gate
plate. The curved plate that forms the upstream face is concentric with the trunnions
of the gate. The trunnions are anchored in the piers and carry the full hydrostatic
Chapter 5. Hydraulic structures 129
Photo 5.19
5.2.4 Open channels
load. Because the hydrostatic load passes through the trunnions, the lifting force
required by the hoisting mechanism is minimised. The head losses in gates and
valves are relatively high, especially when are operated as regulating devices.
For further details refer to Chapter 2, Section 2.2.4 and the enclosed bibliography.
5.2.4.1 Design and dimensioning
The flow conveyed by a canal is a function of its cross-sectional profile, its slope,
and its roughness. Natural channels are normally very irregular in shape, and
their surface roughness changes with distance and time. The application of
hydraulic theory to natural channels is more complex than for artificial channels
where the cross-section is regular in shape and the surface roughness of the
construction materials-earth, concrete, steel or wood-is well documented, so
that the application of hydraulic theories yields reasonably accurate results.
Table 2.4, Chapter 2, illustrates the fundamental geometric properties of different
channel sections.
In small hydropower schemes the flow in the channels is in general in the rough
turbulent zone and the Manning equation can be applied
· AR213Sltz A5t3sltz
Q=---(5.6)
n
where n is Manning's coefficient, which in the case of artificial lined channels may
be estimated with reasonable accuracy, and S is the hydraulic gradient, which
normally is the bed slope. Alternatively
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
130
CJJ
CJJ
:
I
SECTION
PLANT
figure 5.29
Layman's Guidebook
I
J I
l
I
Chapter 5. Hydraulic structures 131
(5.7)
Equation 5.7 applies when metric or S.l. units are used. To use Imperial or English
units the equation must be modified to
where Q is in fP/s; A in ft2 and P in ft. n has the same value as before
Table 5.1 Typical values of Manning's n.
Type of Channel
Excavated earth channels
Clean
Gravelly
Weedy
Stony, cobbles (or natural streams)
Artificially lined channels
Brass
Steel, smooth
Steel, painted
Cast iron
Concrete, well finished
Concrete, unfinished
Planed wood
Clay tile
Brickwork
Asphalt
Corrugated metal
Rubble masonry
Manning's n
0.022
0.025
0.030
0.035
0.011
0.012
0.014
0.013
0.012
0.014
0.012
0.014
0.015
0.016
0.022
0.025
Equation 5.7 shows that for the same cross-sectional area A, and channel slope
S, the channel with a larger hydraulic radius R, delivers a larger discharge. That
means that for a given cross-sectional area, the section with the least wetted
perimeter is the most efficient hydraulically. Semicircular sections are consequently
the most efficient. A semicircular section however, unless built with prefabricated
materials, is expensive to build and difficult to maintain. The most efficient
trapezoidal section is the half hexagon, whose side slope is 1 v. 0.577 h. Strictly
this is only true if the water level reaches the level of the top of the bank. Actual
dimensions have to include a certain freeboard (vertical distance between the
designed water surface and the top of the channel bank) to prevent water level
fluctuations overspilling the banks. Minimum freeboard for lined canals is about
10 em, and for unlined canals this should be about one third of the designed
water depth with a minimum of fifteen centimetres. One way to prevent overflow
of the canal is to provide spillways at appropriate intervals: any excess water is
conveyed, via the spillway, to an existing streambed or to a gully.
132 Layman's Guidebook
It should be noted that the best hydraulic section does not necessarily have the
lowest excavation cost. If the canal is unlined, the maximum side slope is set by
the slope at which the material will permanently stand under water. Clay slopes
may stand at 1 vertical, 3/4 horizontal, whereas sandy soils must have flatter
slopes (1 vert., 2 hoz.)
Table 5.2 defines for the most common canal sections the optimum profile as a
function of the water depth y, together with the parameters identifying the profile.
Table 5.2
Channel Area Wetter Hydraulic Top Water
section perimeter radius width depth
A p R T d
Trapezoid:
half hexagon 1.73 y 2 3.46 y 0.500 y 2.31 y 0.750 y
Rectangle:
half square 2 y2 4y 0.500 y 2y y
Triangle:
half square y2 2.83 y 0.354 y 2y 0.500 y
Semicircle 0.5 rty2 rty 0.500 y 2y 0.250 rty
In conventional hydropower schemes and in some of the small ones, especially
those located in wide valleys, when the channels must transport large discharges,
these are built according to figure 5.30. According to this profile, the excavated
ground is used to build the embankments, not only up to the designed height but
to provide the freeboard, the extra height necessary to foresee the height increase
produced by a sudden gate closing, waves or the excess arising in the canal itself
under heavy storms.
These embankment channels although easy to construct are difficult to maintain,
due to wall erosion and aquatic plant growth. The velocity of water in these unlined
canals should be kept above a minimum value to prevent sedimentation and aquatic
plant growth, but below a maximum value to prevent erosion. In earth canals, if the
water temperature approaches 20°C, a minimum speed of 0.7 m/s is necessary to
prevent plant growth. If the canal is unlined and built in sandy soil, the velocity should
be limited to 0.4-0.6 m/s. Concrete-lined canals may have clear water velocities up
to 10 m/s without danger. Even if the water contains sand, gravel or stones, velocities
up to 4 m/s are acceptable. To keep silt in suspension after the intake, the flow
velocity should be at least 0.3-0.5 m/s.
The wall-side slope in rock can be practically vertical, in hardened clay %:1 whereas
if it has been build in sandy ground should not exceed 2:1.
In high mountain schemes the canal is usually built in reinforced concrete, so
much so that environmental legislation may require it to be covered and
Chapter 5. Hydraulic structures 133
Photo 5.20
..
0.:25
~·
F""
14 D .,j
figure 5.30
315
2 65
5 .0'8
A
~488
figure 5.31
. ~
0
0
N
0
M
N
revegetated. Figure 5.31 shows the schematic seCtion of a rectangular reinforced
concrete canal in the Cordirianes scheme, referred to in chapter 4 and photo 5.20
shows the same canal not yet covered with the concrete slab that would serve as
a basis for new ground and new vegetation .. Sometimes to ensure that no seepage
will occur, the canal is lined with geotextile sheets, to prevent landslides consequent
on the wetting of clayey material.
As is shown in the following examples , once the canal profile has been selected
it is easy to compute its maximum discharge,
• • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • •
134 Layman's Guidebook
Example 5.1
Assuming a flow depth of 1 m, a channel base width of 1.5 m. and side
slopes of 2 vert: 1 hoz, a bed slope of 0.001 and a Manning's coefficient of
0.015, determine the discharge (Q), the mean velocity (V).
According to Table 2.4 for b=1.5 x=1/2 and y=1
A=( 1.5+0.5x I )xI =2m": P= 1.5+ 2x~ 1 +0.5c =3. 736m
Applying 5.6 for A=2 and P=3.736
Example 5.2
Determine the slope knowing the discharge and the canal's dimensions.
Assuming a canal paved with smooth cement surface (n=0.011 ), a channel
base of 2m, side slopes with inclination 1v:2h and a uniform water depth
of 1.2 m, determine the bed slope for a discharge of 17.5 m3/s.
Applying the formulae of table 2.4 and equation 5.6
S = ( 17.5 X 0.011 , )c = 0 _002
5.28x0.717c'
When the canal section, the slope and discharge are known and the depth "d" is
required, equation 5.6 -nor any other -does not provide a direct answer so
iterative calculations must be used.
Example 5.3
A trapezoidal open channel has a bottom width of 3 m and side slopes
with inclination 1.5:1. The channel is lined with unfinished concrete. The
channel is laid on a slope of 0.0016 and the discharge is 21 m3/s. Calculate
the depth
According to 5.6 the section factor
A=(b+zy)y = (3 + 1.5y)y P=b+2y(1+z2 )05 = 3+3.6y
Compute the factor section for different values of y, up to find one approaching
closely 6.825:
For y = 1.5 m A=7.875, R=0.937, AR213 =7.539
For y = 1.4 m A=7.140, R=0.887. AR213 =6.593
For y = 1.43 m A=7.357, R=0.902, AR 213 =6.869
According to the above results the normal depth is slightly under 1.43. Using
the software program FlowPro 2.0, mentioned in chapter 2 it would be
instantaneously calculated, as shown in the enclosed captured screen: a depth
of 1.425, with A=2.868, P=8.139, R=0.900 and a section factor 6.826
Summarising, the design of fabricated channels is a simple process requiring the
following steps:
Chapter 5. Hydraulic structures
F#>w Ptawil ~-e lh#'~k hat&, -em f~;wfeye lhece~cyped'pqt.t
cooee. It tril a1tt1 ~,., ttJe< ~}i. areav lf.'ell$d ;pejW!i!lh!H, >m& h}ldlwk tadu4,
De~ I~~' s~ j·Ra~j'·il)~'
St:~et!heo::~~.
Fitl\'W~~. m '·:Yt:
wld:h .. tn
Mmrc'rN:
flo!tom t~P':'
Si~ thr;e
, •..
1:601F
r, "'
De;:th m r.425
Ve~:R'ify •. titl>: pc:,~.EB'!f!!"'P.'Z'"' --
t;;ea, wt2 v.:.\23
'M\d.~Jj petimek~L m ~e.. ~J':e3S':!:"~ --
Hydi¢tilCt~t, w: ~Ji(l[l
135
o Estimate the coefficient n from table 5.1
o Compute the form factor AR 213 =nQ/S 112 with the known parameters in second
term
o If optimum section is required apply values in table 5.2. Otherwise use values
in table 2.4
o Check if the velocity is high enough to form deposit or aquatic flora
o Check the Froude number NF to determine if it is a subcritical or a supercritical
flow
o Define the required freeboard
Example 5.4
Design a trapezoidal channel for an 11 m 3/s discharge. The channel will
be lined with well-finished concrete and the slope 0.001
Step 1. Manning n = 0.012
Step 2. Compute form factor
J\R 2n nQ O.Cl12xll 4 .1 74 ..JS .Jo.OOl
Step 3. Not intended to find the optimum section.
Step 4.Assuming a bottom width of 6 m and side slopes with inclination 2:1
compute the depth d by iteration as in example 5.3
d = 0.87 m A= 6.734 m2
Step 5. Compute the velocity
V=11/6.734=1.63m/s OK
Step 6. Total channel height. The tables of the US Bureau of Reclamation (USA)
recommend a freeboard of 0.37 m.
Needles to say that the FlowPro software would provide all this in one shot.
• • • • • • • • •
• • • • • • •• • • • • • •
•• • • • • • • • • • • • • • • • •
136
Photo 5.21
Photo 5.22
Layman 's Guidebook
To ensure that the channel never overflows endangering the slope stability, and
in addition to provide a generous freeboard, a lateral spillway (as in Photo 5.21)
should be provided .
Before definitely deciding the channel route, a geologist should carefully study
the geomorphology of the terrain. Take into consideration the accidents detailed
in Chapter 4, section 4.4. The photo 5.22 shows clearly how uplift can easily ruin
a power channel, 6 m wide and 500 m long, in a 2 MW scheme. On one particular
day, a flood occurred which was later calculated to be a 100 year event. At the
time the flood occurred, the head race channel had been empty, and uplift
pressures became a reality, so the channel was destroyed .
Chapter 5. Hydraulic structures 137
Photo 5.23
5.2.4.2 Circumventing obstacles
5.2.5 Penstocks
Along the alignment of a canal obstacles may be encountered, and to bypass.
them it will be necessary to go over, around or under them.
The crossing of a stream or a ravine requires the provision of a flume, a kind of
prolongation of the canal, with the same slope, supported on concrete or steel
piles or spanning as a bridge. Steel pipes are often the best solution , because a
pipe may be used as the chord of a truss, fabricated in the field. The only potential
problem is the difficulty of removing sediment deposited when the canal is full of
still water. Photo 5.23 shows a flume of this type in China.
Inverted siphons can also solve the problem. An inverted siphon consists of an
inlet and an outlet structure connected by a pipe. The diameter calculation follows
the same rules as for penstocks , which are analysed later ..
5.2.5.1 Arrangement and material selection for penstocks.
Conveying water from the intake to the powerhouse -the purpose of a penstock-
may not appear a difficult task, considering the familiarity of water pipes. However
deciding the most economical arrangement for a penstock is not so simple .
Penstocks can be installed over or under the ground, depending on factors such
as the nature of th e ground itself, the penstock mat erial , the ambient te mperature s
and the environmental requirements.
A flexible and small diameter PVC penstock for instance, can be laid on the ground ,
following its outline with a minimum of grade preparation. Otherwise larger penstocks
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
138
support
block
figure 5.32
Layman's Guidebook
must be buried, provided there is a minimum of rock excavation. The sand and gravel
surrounding the pipe provides good insulation, and eliminates anchor blocks and
expansion joints. Buried penstocks must be carefully painted and wrapped to protect
the exterior from corrosion, but provided the protective coating is not damaged when
installed, further maintenance should be minimal. From the environmental point of
view the solution is optimal because the ground can be returned to its original condition,
and the penstock does not constitute a barrier to the movement of wildlife.
A penstock installed above ground can be designed with or without expansion joints.
Variations in temperature are especially important if the turbine does not function
continuously, or when the penstock is dewatered for repair, resulting in thermal
expansion or contraction. Usually the penstock is built in straight or nearly straight
lines, with concrete anchor blocks at each bend and with an expansion joint between
each set of anchors (Fig 5.32). The anchor blocks must resist the thrust of the penstock
plus the frictional forces caused by its expansion and contraction, so when possible
they should be founded on rock. If, due to the nature of the ground, the anchor blocks
require large volumes of concrete, thus becoming rather expensive, an alternative
solution is to eliminate every second anchor block and all the expansion joints, leaving
the alternate bends free to move slightly. In this case it is desirable to lay the straight
sections of the penstock in steel saddles, made to fit the contour of the pipe and
generally covering 120 degrees of the invert (Fig 5.33). The saddles can be made
from steel plates and shapes, with graphite asbestos sheet packing placed between
saddle and pipe to reduce friction forces. The movement can be accommodated with
expansion joints, or by designing the pipe layout with bends free to move.
If a pipeline system using spigot and socket joints with 0-ring gaskets is chosen,
then expansion and contraction is accommodated in the joints.
Today there is a wide choice of materials for penstocks. For the larger heads and
diameters, fabricated welded steel is probably the best option. Nevertheless spiral
machine-welded steel pipes should be considered, due to their lower price, if they
are available in the required sizes. For high heads, steel or ductile iron pipes are
preferred. but at medium and low heads steel becomes less competitive, because
the internal and external corrosion protection layers do not decrease with the wall
thickness and because there is a minimum wall thickness for the pipe to be handled.
For smaller diameters, there is a choice between manufactured steel pipe, supplied
with spigot and socket joints and rubber "0" gaskets, which eliminates field welding,
Chapter 5. Hydraulic structures 139
support blocks
SECTION B-B
SECTION A-A SECTION C -C by the expansion joint
figure 5.33
or with welded-on flanges, bolted on site (Fig 5.34 ); plain spun or pre-stressed
concrete; ductile iron spigot and socket pipes with gaskets; cement-asbestos:
glass-reinforced plastic (GRP); PVC or polyethylene (PE) plastic pipes. Plastic
pipe 14 is a very attractive solution for medium heads-a PVC pipe of 0.4 m diameter
can be used up to a maximum head of 200 meters -because it is often cheaper,
lighter and more easily handled than steel and does not need protection against
corrosion. PVC 15 pipes are easy to install because of the spigot and socket joints
provided with "0" ring gaskets. PVC pipes are usually installed underground with
a minimum cover of one meter. Due to their low resistance to UV radiation they
cannot be used on the surface unless painted coated or wrapped. The minimum
radius of curvature of a PVC pipe is relatively large -1 00 times the pipe diameter
and its coefficient of thermal expansion is five times higher that for steel. They
are also rather brittle and unsuited to rocky ground.
Pipes of PE 16 high molecular weight polyethylene-can be laid on top of the ground
and can accommodate bends of 20-40 times the pipe diameter -for sharper bends,
special factory fittings are required-. PE pipe floats on water and can be dragged by
cable in long sections but must be joined in the field by fusion welding, requiring a
special machine. PE pipes can withstand pipeline freeze-up without damage, but
for the time being, may be not available in sizes over 300 mm diameter.
Concrete penstocks, both pre-stressed with high tensile wires or steel reinforced,·
featuring an interior steel jacket to prevent leaks, and furnished with rubber gasket
spigot and socket joints constitute another solution. Unfortunately their heavy
140
Material
Welded steel
Polyethylene
Polyvinyl chloride (PVC)
Asbestos cement
Cast iron
Ductile iron
Layman's Guidebook
spigot and socket flanges
sleeve
figure 5.34
weight makes transportation and handling costly, but they are not affected by
corrosion.
In less developed countries, pressure creosoted wood-stave, steel-banded pipe is
an alternative that can be used in diameters up to 5.5 meters and heads of up to 50
meters-which may be increased up to 120 meters for a diameter of 1.5 meters. The
advantages include flexibility to conform to ground settlement, ease of laying on the
ground with almost no grade preparation, no requirement of expansion joints and no
necessity for concrete supports or corrosion protection. Wood stave pipe is assembled
from individual staves and steel bands or hoops that allow it to be easily transported
even over difficult terrain. Disadvantages include leakage, particularly in the filling
operations, the need to keep the pipe full of water when repairing the turbine, and
considerable maintenance such as spray coating with tar every five years.
Table 5.4 Materials used in pressure pipes
Young's modulus
of elasticity
E (N/m 2 )E9
206
0.55
2.75
n.a
78.5
16.7
Coefficient of
linear expansion
a (m/m °C)E6
12
140
54
8.1
10
11
Ultimate
tensile strength
(N/m')E6
400
5
13
n.a
140
340
n
0.012
0.009
0.009
0.011
0.014
0.015
Chapter 5. Hydraulic structures 141
Table 5.4 shows the main properties of the above materials1718 . Some of these
properties are typical only; particularly the values of the Hazen Williams coefficient
which depends on the surface condition of the pipe.
5.2.5.2 Hydraulic design and structural requirements
A penstock is characterised by materials, diameter, wall thickness and type of joint.
• the material is selected according to the ground conditions, accessibility, weight,
jointing system and cost.
• the diameter is selected to reduce frictional losses within the penstock to an
acceptable level
• the wall thickness is selected to resist the maximum internal hydraulic pressure,
including transient surge pressure that will occur.
Penstock diameter.
The diameter is selected as the result of a trade-off between penstock cost and
power losses. The power available from the flow Q and head H is given by the
equation:
p = QHytl
where Q is the discharge in m3/s, H the net head in m, y the specific weight of
water in kN/m3 and 11 the overall efficiency.
The net head equals the gross head minus the sum of all losses, including the
friction and turbulence losses in the penstock, that are approximately proportional
to the square of the velocity of the water in the pipe. To convey a certain flow, a
small diameter penstock will need a higher water velocity than a larger-diameter
one, and therefore the losses will be greater. Selecting a diameter as small as
possible will minimise the penstock cost but the energy losses will be larger and
vice versa. Chapter 2 details the friction loss calculations, putting special emphasis
on the graphic representation of the Colebrook equations -the Moody diagram
and the Wallingford charts-and on the Manning's formula. In this chapter the
above principles are used and some examples will facilitate their application in
real cases.
A simple criterion for diameter selection is to limit the head loss to a certain
percentage. Loss in power of 4% is usually acceptable. A more rigorous approach
is to select several possible diameters, computing power and annual energy. The
present value of this energy loss over the life of the plant is calculated and plotted
for each diameter (Figure 5.35). In the other side the cost of the pipe for each
diameter is also calculated and plotted. Both curves are added graphically and
the optimum diameter would be that closest to the theoretical optimum.
Actually the main head loss in a pressure pipe are friction losses; the head losses
due to turbulence passing through the trash rack, in the entrance to the pipe, in bends,
expansions, contractions and valves are minor losses. Consequently a first approach
will suffice to compute the friction losses, using for example the Manning equation
I 0 1
1, 11-Q-- = I 0.3 ---:-:;-:;-:;-( 5. 8) L D'·'-'-'
142
minimum cost
---..----;--_/
loss of energy
cost (Ce)
extra cost of pipe
v (Ct)
total cost (CT)
optimum diameter
figure 5.35
Layman's Guidebook
l
j
r
Ct
1
C=Ct + Ce
Examining equation (5.8) it can be seen that dividing the diameter by two the
losses are multiplied by 40. From equation (5.8)
D ~ ( l0.3::Q' L )"'"' (5.9)
If we limit h; at 4H/1 00, D can be computed knowing Q, n and L, by the equation
{) ~ 2.69( n'~' L )"'"' (5.10)
Example 5.5
A scheme has a gross head of 85 m, a discharge of 3 m3 /s, and a 173-m
long penstock in welded steel. Calculate the diameter so the power losses
due to friction do not surpass 4%.
( 0 \0.11'70
l3-x0.01 x173j According to (5.10) D = 2.69
85
= 0.88m
We select a 1-m steel welded pipe and compute all the losses in the next example
Chapter 5. Hydraulic structures
18m
143
Example 5.6
Compute the friction and turbulence head losses in a scheme as the
illustrated in figure 5.36. The rated discharge is 3m3/sand the gross head
85 m. The steel welded penstock diameter 1.0 m. The radius of curvature
of the bends are four times the diameter. At the entrance of the power
intake there is a trashrack with a total surface of 6m2 , inclined 60° regarding
the horizontal. The bars are 12-mm thick stainless steel bars, and the
distance between bars 70-mm.
The flow velocity approaching the screen is according to (5.4) with K1=1
70+12 1 I ~~ = 3x x-x--= 0.7m/s
70 6 0.866
The head loss through the trashrack is given by the Kilchner formula
(
12)"-' 07 2
h 1 = 2.4 X - X . X 0.866 = 0.0049 m
70 2 X 9.81
The head loss at the inlet of the penstock (a bad design) is given in figure 2.11,
Chapter 2: K=0.08. The velocity in the penstock is 3.82 m/s, so the head loss
at the inlet:
he= 0.08 X 3.82 2 /(2 X 9.81) = 0.06 m
figure 5.36
85 m
15m •
144 Layman's Guidebook
The gross head at the beginning of the penstock is therefore
85-0.005-0.06=84.935 m
The friction loss in the penstock, according Manning equation (2.15)
I = I 0.3 X 0.0 I i~ X 3
2
173 = 2 30 z1 _ ]'" x . m 1.0' ·'-'
The Kb coefficient for the first bend is 0.05 (28% of the corresponding to a 90°
bend as in 2.2.23). The coefficient for the second bend Kb=0.085 and for the
third bend Kb =0.12. The head losses in the three bends amount to
(0.05 + 0.085 + 0.12) X 3.82 2/(2 X 9.81) = 0.19 m.
The head loss in the gate valve 0.15 x 3.822 /(2 x 9.81) = 0.11 m
Summarising: head loss in trashrack plus pipe inlet: 0.065 m
head loss in three bends and valve : 0.30 m
head loss by friction in the penstock: 2.30 m
Total head loss: 2.665 m equivalent to 3.14% of the gross power.
Wall thickness
The wall thickness required depends on the pipe material, its ultimate tensile
strength (and yield), the pipe diameter and the operating pressure. In steady
flows-discharge is assumed to remain constant with time-the operating pressure
at any point along a penstock is equivalent to the head of water above that point.
The wall thickness in this case is computed by the equation:
PID e = 2 () (5.11)
where e =Wall thickness in mm
P1= Hydrostatic pressure in kN/mm 2
D = Internal pipe diameter in mm
a,= Allowable tensile strength in kN/mm 2
In steel pipes the above equation is modified by
~D e= +e,
2CJ I k I
where es= extra thickness to allow for corrosion
k,= weld efficiency
k,= 1 for seamless pipes
k,= 0.9 for xray inspected welds
k,= 1.0 for xray inspected welds and stress relieved
a,= allowable tensile stress (1400 kN/mm 2 )
(5.12)
The pipe should be rigid enough to be handled without danger of deformation in the
field. ASME recommends a minimum thickness in mm equivalent to 2.5 times the
diameter in metres plus 1.2 mm. Other organisations recommend as minimum
thickness tm,n =(0+508)/400, where all dimensions are in mm.
In high head schemes it can be convenient to use penstock of uniform diameter
but with different thicknesses as a function of the hydrostatic pressures.
Chapter 5. Hydraulic structures 145
A certain area of the penstock can remain under the Energy Gradient Line (page 13)
and collapse by sub-atmospheric pressure. The collapsing depression will be given by
P,_. = 882500 X (; r (5.13)
where e and D are respectively the wall thickness and diameter of the pipe in
mm.
This negative pressure can be avoided by installing an aeration pipe with a
diameter in em given by
d 747J g,
..;P,_
provided ~ s 0.49 kgN I mm2
; otherwise d 8.94-JQ
(5.14)
Sudden changes of flow can occur when the plant operator or the governing
system opens or closes the gates rapidly. Occasionally the flow may even be
stopped suddenly due to full load rejection, or simply because an obstruction
become lodged in the nozzle of a Pelton turbine jet. A sudden change of flow rate
in a penstock may involve a great mass of water moving inside the penstock. The
pressure wave which occurs with a sudden change in the water's velocity is known
as waterhammer; and although transitory, can cause dangerously high and low
pressures whose effects can be dramatic: the penstock can burst from
overpressure or collapse if the pressures are reduced below ambient. The surge
pressures induced by the waterhammer phenomenon can be of a magnitude
several times greater than the static pressure due to the head, and must be
considered in calculating the wall thickness of the penstock.
Detailed information on the waterhammer phenomenon can be found in texts on
hydraulics'920 , but sufficient information has been given in Chapter 2, section
2.2.3. Some examples will show the application of the recommended formulae.
As explained in chapter 2, the pressure wave speed c (m/s) depends on the
elasticity of the water and pipe material according to the formula
c 10 3 K
KD 1+--
Et
where K = bulk modulus of water 2.1 x1 09 N/m2
E = modulus of elasticity of pipe material (N/m2 )
D =pipe diameter (mm)
t =wall thickness (mm)
(5.15)
The time taken for the pressure wave to reach the valve on its return, after sudden
closure is known as the critical time
T= 2Lic (5.16)
146 Layman's Guidebook
For instantaneous closure-the pressure wave reaches the valve after its closure-
the increase in pressure, in metres of water column, due to the pressure wave is
p (5.17) g
where t.v is the velocity change
Examples 6.4 and 6.5 show that surge pressures in steel pipes are more than
three times greater than in PVC, due to the greater stiffness of the steel.
Example 5.7
Calculate the pressure wave velocity, for instant closure, in a steel
penstock 400mm-dia and 4mm-wall thickness
Applying 5.15
b) The same for a PVC pipe 400mm dia. 14 mm wall thickness
2.1 X 10" --')OS ;"' c= 9 _,_m"s
1 + x 10 x400
2.75xl x14
Example 5.8
What is the surge pressure, in the case of instant valve closure, in the two
penstocks of example 5.7, if the initial flow velocity is 1.6 m/s?
a) steel penstock:
p = 1024 x 4 = 417 m
' 9.8
b) PVC penstock:
123m
As the example 5.8 shows, the surge pressure in the steel pipe is three times
higher than in the PVC pipe, due to the greater rigidity of the steel
If the change in velocity occurs in more than ten times the critical time T, little or
no overpressure will be generated and the phenomenon may be ignored. In
between. if T>2Lic, P swill not develop fully, because the reflected negative wave
arriving at the valve will compensate for the pressure rise. In these cases the
Allievi formula may compute the maximum overpressure:
Chapter 5. Hydraulic stmctures 147
(5.18)
where P 0 is the hydrostatic pressure due to the head and
N (Lr;,l:: (5.19)
.gP0 t
where: V 0 =water velocity in m/s
L =total penstock length (m)
P 0 = gross hydrostatic pressure (m)
t = closing time (s)
The total pressure experienced by the penstock is P = P0 +~P
The next example illustrates the application of the Allie vi formula, when the closure
time is at least twice but less than 10 times the critical time.
Example 5.9
Calculate the wall thickness in the penstock analysed in example 5.6 if
the valve closure time is 3 seconds.
Summarising the data, Gross head : 84.935 m
Rated discharge: 3 m3/s
Internal pipe diameter 1.0 m
Total pipe length: 173m
Estimating in a first approach at 5 mm the wall thickness to compute the wave
speed c
c:::::
") I X I 0'' .... = 836.7 m/ s
I+ 2.1 X 10 9
X 1000
x5
The closure time is bigger than the critical one (0.41 s) but smaller than 10
times its value. so the Allievi formula can be applied.
The water velocity in the pipe is 3.82 m/s
4x3 V-3.82 m/ s -n x I.O'
N would be computed for a gross head in the pipe of 84.935 m
N (. 3.82 X 1 73 Y 0.0 70
9.81 X 84.935 X 3)
and therefore
II,. 84.935[ O.~? ± 0.07
2
]-") 6 . 0.07+
4
-+~5. 5m, 19.58 m
14R Layman's Guidebook
The total pressure would be 84.935+25.65 = 110.585 tf/m 2 = 11.06 kN/mm 2
It requires a wall thickness .
e = 11.06x 1000 +I= 4.95 mm
2 X 1400
That agrees with the initial estimation and covers the specs for handling the
pipes in the field (tmm =2.5x1 +1.2=3.7 mm)
To compute the air vent pipe diameter:
( 5 )' ' P = 882500 --= 0.11 kN I mm-
' 1000
And the diameter d = 7.47Ik = 22.46 em
The waterhammer problem becomes acute in long pipes, when the open channel
is substituted by a pressure pipe all along the trace. For a rigorous approach it is
necessary to take into consideration not only the elasticity of fluid and pipe mate-
rial, as above, but also the hydraulic losses and the closure time of the valve. The
mathematical approach is cumbersome and requires the use of a computer
program. For interested readers, Chaudry 19 , Rich 20 , and Streeter and Wylie 21
give some calculation methods together with a certain number of worked examples.
To determine the minimum pipe thickness required at any point along the penstock
two waterhammer hypotheses should be taken into consideration: normal
waterhammer and emergency waterhammer. Normal waterhammer occurs when
the turbine shuts down under governor control. Under these conditions, the
overpressure in the penstock can reach 25% of the gross head, in the case of
Pelton turbines, and from 25% to 50% in the case of reaction turbines -depending
on the governor time constants-The turbine manufacturer's advice should be
taken into consideration. Emergency waterhammer, caused for example by an
obstruction in the needle valve of a Pelton turbine, or a malfunction of the turbine
control system, must be calculated according to equation (5.17).
In steel penstocks, the compounded stresses -static plus transitory-are a function both
of the ultimate tensile and yield strength. In the case of normal waterhammer, the
combined stress should be under 60% of the yield strength and 38% of the ultimate
tensile strength. In the case of emergency waterhammer, the combined stress should
be under 96% of the yield strength and 61% of the ultimate tensile strength.
Commercial pipes are often rated according to the maximum working pressure under
which they are designed to operate. The pressure rating of a pipe already includes
a safety factor, and sometimes may include an allowance for surge pressures. Safety
factors and surge pressure allowances depends on the standard being used.
If the scheme is liable to surge pressure waves a device to reduce its effects must
be considered. The simplest one is the surge tower, a sort of large tube, connected
at its base to the penstock and open to the atmosphere. The fundamental action of
a surge tower is to reduce the length of the column of water by placing a free water
Chapter 5. Hydraulic structures 149
L = L + L . ' '
L
H
figure 5.37
surface closer to the turbine (figure 5.37}. Some authors21 consider that the surge
tower is unnecessary ifthe pipe length is inferior to 5 times the gross head. It is also
convenient to take into account the water acceleration constant to in the pipe
VL
t" = H g
where L =length of penstock (m},
V flow velocity (m/s) and
H = net head (m).
10
0
-10
time (sec)
-20
figure 5.38
• • • • • • • • •
• • • • • • • • • • •
• • • • • • • • • • • • • • • •
• •
150
Photo 5.24
Layman 's Guidebook
If th is inferior to 3 seconds the surge tower is unnecessary but if surpass 6 seconds,
either a surge tower or another correcting device must be installed to avoid strong
oscillations in the turbine controller.
With the valve open and a steady flow in the penstock, the level of the water in
the tower will correspond to the pressure in the penstock -equivalent to the net
head. When by a sudden closure of the valve the pressure in the penstock rises
abruptly, the water in the penstock tends to flow into the tower, raising the level of
the water above the level in the intake . The level in the tower then begins to fall as
the water flows from the tower into the penstock, until a minimum level is reached .
The flow then reverses and the level in the tower rise again and so on. Fig 5.38
shows a graph plotting the surge height versus time. The maximum height
corresponds to the overpressure in the penstock due to the waterhammer. The
throttling introduced by a restricted orifice will reduce the surge amplitude by 20
to 30 per cent. The time ~ plays an important role in the design of the turbine
regulation system . In a badly designed system, the governor and the tower surge
can interact, generating speed regulation problems too severe for the governor to
cope with .
In instances, when the closure time of the turbine valves must be rapid, a relief
valve placed in parallel with the turbine, such that it opens as the turbine wicket
gates close, can be convenient. This has the effect of slowing down the flow changes
in the penstock. In the ESHA NEWS issue of spring 1991 there is a description of
such a valve. Photo 5.24 shows the water jet getting out of the open valve .
Chapter 5. Hydraulic structures 151
5.2.5.3 Saddles, supporting blocks and expansion joints
5.2.6 Tailraces
The saddles are designed to support the weight of the penstock full of water, but
not to resist significant longitudinal forces. The vertical component of the weight
to be supported, in kN, has a value of
F1=(Wr + Ww )LcosF
where Wr =weight of pipe per meter (kN/m)
W" =weight of water per meter of pipe (kN/m)
L = length of pipe between mid points of each span (m)
<1> = angle of pipe with horizontal
The design of support rings is based on the elastic theory of thin cylindrical shells.
The pipe shell is subject to beam and hoop stresses, and the loads are transmitted
to the support ring by shear. If penstocks are continuously supported at a number
of points, the bending moment at any point of penstock may be calculated assuming
that it is a continuous beam, and using the corresponding equation. The rings are
welded to the pipe shell with two full length fillet welds and are tied together with
diaphragm plates
The span between supports L is determined by the value of the maximum
permissible deflection L/65 000. Therefore the maximum length between supports
is given by the equation
~(D+O.OI47)4 -o 4
L = 182.61 X-=----------p
where D =internal diameter (m) and P =unit weight of the pipe full of water (kg/
m)
After passing through the turbine the water returns to the river trough a short
canal called a tailrace. Impulse turbines can have relatively high exit velocities,
so the tailrace should be designed to ensure that the powerhouse would not be
undermined. Protection with rock riprap or concrete aprons should be provided
between the powerhouse and the stream. The design should also ensure that
during relatively high flows the water in the tailrace does not rise so far that it
interferes with the turbine runner. With a reaction turbine the level of the water in
the tailrace influences the operation of the turbine and more specifically the onset
of cavitation. This level also determines the available net head and in low head
systems may have a decisive influence on the economic results.
Bibliography
Layman's Guidebook
1. J.L. Brennac. "Les Hauses Hydroplus", ESHA Info no 9 verano 1993
2. Para mas informacion acudir a Ia pagina de 1 NTERNET
http://www.obermeyerhydro.com
3. H.C. Huang and C.E. Hita, «Hydraulic Engineering Systems» Prentice Hall
Inc., Englewood Cliffs, New Jersey 1987
4. British Hydrodynamic Research Association «Proceedings of the
Symposium on the Design and Operation of Siphon Spillways», London
1975
5. Allen R.lnversin, <<Micro-Hydopower Sourcebook», NRECA International
Foundation, Washington, D.C.
6. USSR Design of Small Dams 3rd ed, Denver, Colorado, 1987
7. USSR, Design of Small Canal Structures, Denver, Colorado, 1978a.
8. USSR, Hydraulic Design of Spillways and Energy Dissipators. Washington
DC, 1964
9.T. Moore. «TLC for small hydro: good design means fewer headaches»,
HydroReview/April1988.
10. T.P. Tung y otros, «Evaluation of Alternative Intake Configuration for
Small Hydro». Aetas de HIDROENERGIA 93. Munich.
11 ASCE, Committee on Intakes, Guidelines for the Design of Intakes for
Hydroelectric Plants, 1995
12. G. Munet y J.M. Compas «PCH de recuperation d'energie au barrage de
«Le Pouzin>>».Actas de HIDROENERGIA 93, Munich
13. «Rubber seals for steel hydraulic gates, G.Schmausser & G.Hartl, Water
Power & Dam Construction September 1988
14 ISO 161-1-1996 Thermoplastic pipes for conveyance of fluids-Nominal
outside diameters and nominal pressures --Part 1 :Metric series
15 ISO 3606-1976 Unplasticized polyvinyl chloride (PVC) pipes. Tolerances
on outside diameters and wall thickness
16 ISO 3607-1977 Polyethylene (PE) pipes. Tolerances on outside diameters
and wall thickness
17 ISO 3609-1977 Polypropylene (PP) pipes. Tolerances on outside
diameters and wall thickness
18 ISO 4065-1996 Thermoplastic pipes --Universal wall thickness table
19 H.Chaudry «Applied Hydraulic Transients» Van Nostrand Reinhold
Company, 1979.
20 J.Parmakian, «Waterhammer Analyses», Dover Publications, Inc, New
York, 1963
21 Electrobras (Centrais Electricas Brasileiras S.A.) Manual de Minicentrais
Hidreletricas
6 Electromechanical equipment
6.0 Powerhouse
In a small hydropower scheme the role of the powerhouse is to protect from the
weather hardships the electromechanical equipment that convert the potential
energy of water into electricity. The number, type and power of the turbo-generators,
their configuration, the scheme head and the geomorphology of the site controls
the shape and size of the building.
Fig. 6.1 is a schematic view of an integral intake indoor powerhouse suitable for
low head schemes. The substructure is part of the weir and embodies the power
intake with its trashrack, the vertical axis open flume Francis turbine coupled to
the generator, the draught tube and the tailrace. The control equipment and the
outlet transformers are located in the generator forebay.
In some cases the whole superstructure is dispensed with, or reduced to enclose
only the switchgear and control equipment Integrating turbine and generator in a
single waterproofed unit that can be installed directly in the waterway means that
a conventional powerhouse is not required. Figure 6.2 and Photo 6.1 shows a
submerged Flygt turbine with a sliding cylinder as control gate and with no
protection for the equipment. Siphon units provide an elegant solution in schemes
with heads under 10 meters and for units of less than 1000 kW installed. Photo
6.2 shows a recent installation in France with the electromechanical equipment
simply protected by a steel plate.
Otherwise to mitigate the environmental impact the powerhouse can be entirely
submerged (see chapter 1, figure 1.6). In that way the level of sound is sensibly
reduced and the visual impact is nil.
:urtune
• • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • • • •
154
Photo 6.1
Layman 's Guidebook
figure 6.2
In low-head schemes the number of Kaplan turbine configurations is very large
(pit, inS, right angle, etc.) as shown in figures 6.18 to 6.25. In medium and high
head schemes powerhouses are more conventional (figure 6.3) with an entrance
for the penstock and a tailrace. This kind of powerhouse is sometimes located in
a cave, either natural or excavated for the purpose .
The powerhouse can also be at the base of an existing dam, where the water
arrives via an existing bottom outlet or an intake tower. Figure 1.4 in chapter 1
illustrates such a configuration .
Chapter 6. Electromechanical equipment 155
Photo 6.2
6.1 Hydraulic turbines
Photo 6.3
The purpose of a hydraulic turbine is to transform the water potential energy to
mechanical rotational energy. Although this handbook does not define guidelines
for the design of turbines (a · role reserved for the turbine manufacturers) it is
appropriate to provide a few criteria to guide the choice of the right turbine for a
particular application and even to provide appropriate formulae to determine its
main dimensions. These criteria and formulae are based on the work undertaken
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • •
•
• • • • • • • • • • • • • • • • •
156
Photo 6.4
Layman's Guidebook
generator
penstock
figure 6.3
by Siervo and Lugaresi, Austerre and Verdehan1, Giraud and Beslin 2 , Belhaj3,
Gordon and others, which provide a series of formulae by analysing the
characteristics of installed turbines. It is necessary to emphasize however that no
advice is comparable to that provided by the manufacturer, and every developer
should refer to him from the beginning of the development project.
Chapter 6. Electromechanical equipment 157
Needle valve
fiaure 6.4
6.1.1 Classification criteria
6.1.1.1 On the basis of the flow regime in the turbine
The potential energy in the water is converted into mechanical energy in the
turbine, by one of two fundamental and basically different mechanisms:
• The water pressure can apply a force on the face of the runner blades, which
decreases as it proceeds through the turbine. Turbines that operate in this way
are called reaction turbines. The turbine casing, with the runner fully immersed
in water, must be strong enough to withstand the operating pressure.
• The water pressure is converted into kinetic energy before entering the runner.
The kinetic energy is in the form of a high-speed jet that strikes the buckets,
mounted on the periphery of the runner. Turbines that operate in this way are
called impulse turbines. As the water after striking the buckets falls into the tail
water with little remaining energy, the casing can be light and serves the purpose
of preventing splashing.
6.1.1.1.1 Impulse turbines
Pelton turbines
Pelton turbines are impulse turbines where one or more jets impinge on a wheel
carrying on its periphery a large number of buckets. Each jet issues through a
nozzle with a needle (or spear) valve to control the flow (figure 6.4). They are only
used for relatively high heads. The axes of the nozzles are in the plane of the
.---------------------, runner (figure 6.5). To stop the turbine-e.g. when the turbine
figure 6.5
approaches the runaway speed due to load rejection-the jet
(see figure 6.4) may be deflected by a plate so that it does
not impinge on the buckets. In this way the needle valve can
be closed very slowly, so that overpressure surge in the
pipeline is kept to an acceptable minimum.
Any kinetic energy leaving the runner is lost and so the buckets
are designed to keep exit velocities to a minimum. The turbine
casing only needs to protect the surroundings against water
splashing and therefore can be very light.
158 Layman's Guidebook
Turgo turbines
Runner blades
figure 6.6
The Turgo turbine can operate under a head in the
range of 30-300 m. Like the Pelton it is an impulse
turbine, but its buckets are shaped differently and the
jet of water strikes the plane of its runner at an angle
of 20°. Water enters the runner through one side of
the runner disk and emerges from the other (Fig 6.6).
(Compare this scheme with the one in Fig.6.5
corresponding to a Pelton turbine). Whereas the
volume of water a Pelton turbine can admit is limited
because the water leaving each bucket interferes with
the adjacent ones, the Turgo runner does not present
this problem. The resulting higher runner speed of
the Turgo makes direct coupling of turbine and gener-
ator more likely, improving its overall efficiency and
decreasing maintenance cost.
Cross-flow turbines
This impulse turbine, also known as Banki-Michell in remembrance of its inventors
and Ossberger after a company which has been making it for more than 50 years,
is used for a wide range of heads overlapping those of Kaplan, Francis and Pelton.
It can operate with discharges between 20 litres/sec and 1 0 m3/sec and heads
between 1 and 200 m.
Water (figure 6. 7) enters the turbine, directed by one or more guide-vanes located
in a transition piece upstream of the runner, and through the first stage of the
runner which runs full with a small degree of reaction. Flow leaving the first stage
attempt to crosses the open centre of the turbine. As the flow enters the second
stage, a compromise direction is achieved which causes significant shock losses.
The runner is built from two or more parallel disks connected near their rims by a series
<:hs tnb uto r
Chapter 6. Electromechanical equipment 159
Photo 6.5
Photo 6.6
of curved blades). Their efficiency lower than conventional turbines, but remains at
practically the same level for a wide range of flows and heads (typically about 80% ).
6.1.1.1.2 Reaction turbines
Francis turbines.
Francis turbines are radial flow reaction turbines , with fixed runner blades and
adjustable guide vanes, used for medium heads. In the high speed Francis the
admission is always radial but the outlet is axial. Photograph 6.4 shows a hori-
zontal axis Francis turbine.
• • • • • • • • • • • • • • • • • • •
• • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
160 Layman's Guidebook
Photo 6.7
\
figure 6.9
The water proceeds through the turbine as if it was enclosed in a closed conduit
pipe, moving from a fixed component, the distributor, to a moving one, the runner,
without being at any time in contact with the atmosphere. Figure 6.8 shows a
vertical section of a horizontal axis machine. The figure illustrates how the guide
vanes, whose mission is to control the discharge going into the runner, rotate
around their axes, by connecting rods attached to a large ring that synchronise
the movement off all vanes. It must should be emphasized that the size of the
· spiral casing contrasts with the lightness of a Pelton casing. In the photo 6.7 the
rotating ring and the attached links that operate the guide vanes can be seen .
Figure 6.9 schematically shows the adjustable vanes and their mechanism, both
in open and closed position . As can be seen the wicket gates can be used to shut
off the flow to the turbine in emergency situations, although their use does not
preclude the installation of a butterfly valve at the entrance to the turbine .
Francis turbines can be set in an open flume or attached to a penstock. For small
heads and power open flumes are commonly employed. Steel spiral casings are
used for higher heads, designing the casing so that the tangential velocity of the
water is constant along the consecutive sections around the circumference . As
shown in figure 6.8 this implies a changing cross-sectional area of the casing .
Figure 6.10 shows a Francis runner in perspective from the outlet end . Small
runners are usually made in aluminium bronze castings. Large runners are
fabricated from curved stainless steel plates, welded to a cast steel hub .
Chapter 6. Electromechanical equipment
!
l
1 l,
161
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
162
fi[J!ItlJ -6.10
Layman's Guidebook
In reaction turbines, to reduce the kinetic energy still remaining in the water
leaving the runner a draft tube or diffuser stands between the turbine and the tail
race. A well-designed draft tube allows, within certain limits, the turbine to be
installed above the tailwater elevation without losing any head. As the kinetic
energy is proportional to the square ofthe velocity one ofthe draft tube objectives
is to reduce the outlet velocity. An efficient draft tube would have a conical section
but the angle cannot be too large, otherwise flow separation will occur. The
optimum angle is 7° but to reduce the draft tube length, and therefore its cost,
sometimes angles are increased up to 15°. Draft tubes are particularly important
in high-speed turbines, where water leaves the runner at very high speeds.
In horizontal axis machines the spiral casing must be well anchored in the
foundation to prevent vibration that would reduce the range of discharges
accepted by the turbine.
Figure 6.11
Chapter 6. Electromechanical equipment 163
Photo 6.8
Kaplan and propeller turbines
Kaplan and propeller turbines are axial-flow reaction turbines, generally used for
low heads. The Kaplan turbine has adjustable runner blades and may or may not
have adjustable guide-vanes If both blades and guide-vanes are adjustable it is
described as "double-regulated". If the guide-vanes are fixed it is "single-regulated".
Unregulated propeller turbines. are used when both flow and head remain practi-
cally constant
The double-regulated Kaplan, illustrated in figure 6.11 is a vertical axis machine
with a scroll case and a radial wicket-gate configuration as shown in photo 6.8.
The flow enters radially inward and makes a right angle turn before entering the
runner in an axial direction. The control system is designed so that the variation
in blade angle is coupled with the guide-vanes setting in order to obtain the best
efficiency over a wide range of flows. The blades can rotate
r-------------------, with the turbine in operation, through links connected to a ver-
flow
tical rod sliding inside the hollow turbine axis.
Bulb units are derived from Kaplan turbines, with the generator
contained in a waterproofed bulb submerged in the flow. Figu-
re 6.12 illustrates a turbine where the generator (and gearbox if
required) cooled by pressurised air is lodged in the bulb. Only
the electric cables, duly protected, leave the bulb .
Pumps working as turbines
Standard centrifugal pumps may be operated as turbines by
directing flow through them from pump outlet to inlet. Since they
figure 6.12 have no flow regulation they can operate only under relatively
...__ ________________ _. constant head and discharge6 ·
• • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • •
164 Layman's Guidebook
6.1.1.2 On the basis of the specific speed
The large majority of hydraulic structures -spillways, energy dissipaters at the
outlet of a hydraulic structure, the reduction of energy losses at the water intake,
etc.-are designed and built on the basis of the results obtained from preliminary
model studies. The behaviour of these models are based on the principles of
hydraulic similitude, including dimensional analysis, by which is meant the analysis
of the physical quantities involved in the static and dynamic behaviour of water
flow in a hydraulic structure. The turbine design does not constitute an exception
and actually turbine manufacturers make use of scaled models. The problem of
similarity in this case can be summarised as follows: "Given test data on the
performance characteristics of a certain type of turbine under certain operating
conditions, can the performance characteristic of a geometrically similar machine,
under different operating conditions be predicted?" If there is a positive answer to
this question the theory of similitude will provide a scientific criterion for cataloguing
turbines, that will prove very useful in the process of selection of the turbine best
adapted to the conditions of the scheme ..
Effectively the answer is positive provided that model and prototype are:
• Geometrically similar
• Have the same volumetric coefficient as defined by Q I A.J2gH
To be geometrically similar the model will be a reduction of the prototype by
maintaining a fixed ratio for all homogeneous lengths. The physical quantities
involved in geometric similarity are length, I, area A and volume V. If the lengths
ratio is k, the area ratio will be k2 and the volume ratio k3 • For the model and
prototype to have the same volumetric coefficient it will be necessary that:
2 <>Jl A ( lJ )
1
: , -'"'-x - -k-
Q' 2gl/' A' H'
The power ratio between model and prototype will be:
( lf )'' '
P' IJ'Q' = \ H' k-
where P= power (kW)
But as v = .J2gH
The ratio of the angular velocities will be
II
n'
vIr v r' = x-v'lr' v' r
Substituting in (6.2) the value k obtained from (6.3)
!_ = ( !!_)' :(!!_)" 2 11 ,: = (!!_)' :(!i_)c
P' \ H' H' 11-11' 11
(6.1)
(6.2)
(6.3)
(6.4)
Chapter 6. Electromechanical equipment 165
If the model tests had been done with a head H' of 1 metre and a discharge Q'
such that the generated power is 1 kW, and assuming that the model runner has
turned at n' = ns rpm, equation (6.4) would be rewritten:
JP
11,=11 (6.5)
ns is known as specific speed. Any turbine, with identical geometric proportions,
even if the sizes are different, will have the same specific speed. If the model had
been refined to get the optimum ~~.,araulic efficiency, all turbines with the same
specific speed will also have an optimum efficiency.
Substituting in eq. (6.4) P/P' by HQ/H'Q':
:.~. (~.J't~lHQ=Ht:r
and hence if H'=1 and n'=n q
(6.6)
Some manufacturers define the specific speed nq of a turbine as the speed of a
unit of the series of such magnitude that it delivers unit discharge at unit head.
The specific speed such as has been defined by eq (6.5) and (6.6) is not a
dimensionless parameter and therefore its value varies with the kind of units
employed in its calculation. The dimensionless parameter is the specific speed
Ns given by the equation:
' O.~P/p N = -, (gHf 4
where n is the angular velocity and p the water density
In this handbook ns is always expressed in S.l. units with the kilowatt as power
unit and is equivalent to 166 Ns. If ns were calculated with the horsepower as
power unit it would correspond to 193.1 N5 •
Figure 6.13 shows four different designs of reaction runners and their
corresponding specific speeds, optimised from the efficiency viewpoint. It can be
seen that the runner evolves to reconcile with the scheme conditions. A Francis
slow runner will be used in high head schemes, where a high-speed runner would
run at an excessive speed. As the runner evolves with the specific speed it reaches
a point where the lower ring that keep the runner blades together generates too
high a friction, so from there on the ring is abandoned and the blades are built as
cantilevers. From that the Kaplan, propeller and Bulb turbines. used in low head
schemes, with specific speeds as high as 1200 were evolved.
In general turbine manufacturers specify the specific speed of their turbines. A
large number of statistic studies undertaken by De Siervo and Lugaresi4 , Lugaresi
166 Layman's Guidebook
and Massa5 , Schweiger and Gregory6 , Gordon 7 , Lindestrom, Kpordze and others,
on a large number of schemes has established a correlation, for each type of
turbine, ofthe specific speed and the net head. Hereunder some ofthe correlation
formulae graphically represented in figure 6.14.
Pelton (1 jet)
Francis
Kaplan
Cross-flow
Propeller
Bulb
n = 85.49/ H0243
s
n = 3763/ H0854
s
n = 2283/ H0486
s
n =513.25/H0505
s
n = 2702/ H05
s
n = 1520.26/ H02837
s
(Siervo and Lugaresi, 1978)
(Schweiger and Gregory, 1989)
(Schweiger and Gregory, 1989)
(Kpordze and Warnick, 1983)
(USBR, 1976)
(Kpordze and Warnick, 1983)
Once the specific speed is known the fundamental dimensions of the turbine can
be easily estimated.
In one jet Pelton turbines, the specific speed may fluctuate between 12, for a
2000 m head and 26, for a 100 m head. By increasing the number of jets the
specific speed increases as the square root of the number of jets. So then the
specific speed of a four jets Pelton (only exceptionally they have more than six
jets, and then only in vertical axis turbines) is twice the specific speed of one jet
Pelton. In any case the specific speed of a Pelton exceeds 60 rpm.
The diameter of the circumference tangent to the jets is known as the Pelton
diameter. The velocity vch leaving the nozzle, assuming a coefficient of losses of
0.97 is given by
,.ch =0.97 J2Kff (6.7)
D
~ r::-i .cJi=BO
slow Y-:o~
~ -~-n.=200
c~+ VTV-
1 P. I 1m1 o=300
normal
c v
fast
ultrafast T o=514
fi ilre 6.13
Chapter 6. Electromechanical equipment
c:
-o
J1fl 10
If ~ 10
a.
1/)
(,)
<;::
'(3
Q) a.
IJ)
10
1
'
;
I
. I I "%--=•. ""· . !illh
" .. .. r-.: ...
"' ···I:IE I ...
r...........
,.
K pi n
1 ........ ~ I
I
I "s ..
I
'
trtt tlt1± rossn< w
~··
...
10
~-
i
I I
I
net head H
figure 6.14
' '
~--elton ......
i
100
167
I
i
I
'
'
-
!
~
I
1000
It can be easily demonstrated from a theoretical approach that the tangential
speed V0 corresponding to the optimum efficiency is one half the jet speed vch.
Actually the optimum efficiency is obtained by a velocity slightly lower {0.47 V,).
If we know the runner speed its diameter can be estimated by the following equations:
V = nDn = 0 47r 0,456~2zH " 60 ' cit ~
60 X 0,456~2gH .[ij {6.8) D 38,567-
lr/1 11
D is defined as the diameter of the circle describing the buckets centre line.
The jet discharge -in one jet turbine the total discharge-is given by the cross-
sectional area multiplied by the jet velocity:
Q 4
\'
I where d is the diameter of the jet, so then
J
(6.9)
If Q is not known. as the power is P=8.33QH
168
~ B
bi
M
N
I
I
I
I
I
I
I
I
AI
I
c.> 0,67
D
figure 6.15
d.= I
p
28.(>7 H'i 2
Layman's Guidebook
X
v > 0,67
The diamete~ d1 is the jet diameter and not the nozzle-opening diameter. This diameter
varies with the nozzle design, but is accepted that a good nozzle produces such a
"vena contracta" that the ratio of the square of both diameters -jet and nozzle-is
close to 0.6. The jet diameter would be then 0.775d.. The ratio 'nozzle diameter/0
diameter' necessary to obtain a good efficiency mu~t lie between 0.12 and 0.06.
The diameter of a Turgo runner is one half the diameter of a Pelton for the same
power, so its specific speed will be double. In a cross-flow turbine, as the length
of the runner accepts very large discharges even with small diameters the specific
speed can reach the 1 000 rpm.
Francis turbines cover a wide range of specific speeds, going from the 60
corresponding to a slow Francis to the 400 that may attain the high speed Francis.
The slow runners are used in schemes with up to 350 m head, whereas the fast
ones are used with heads of only 30 m. According to research undertaken by
Schweiger and GregoryB on low power turbines, the specific speeds of turbines
under 2 MW are sensibly lower than those corresponding to bigger turbines.
Figure 6.15 shows schematically in the upper part of the graphic the runner of a
Francis turbine and the entrance velocity triangles for slow, medium and high-speed
Chapter 6. Electromechanical equipment 169
1.4· i
I ..,..-:
1.2 :../ .. I i/
1.0 /
/ ! v
0.8 L. ................ -----' ······ -----
0 ......... ------v --.0 0.61 / ; >
0.4' / v ! h/D
i ... -------
0.2; .,.,. ... ; ---·-I . i -oo .._.--
10 200 300 4 0 500
'1 rpm
figure 6.16
runners in the bottom. The absolute velocity C0 is the vectorial sum of the moving
frame velocity V0 and the relative velocity We. The absolute velocity C0 has a radial
COmponent CmO perpendiCUlar tO the turbine aXiS, and a tangential CuO that in the
scheme of figure 6.15 would be perpendicular to the drawing plan. Multiplying cmO by
the outlet section of the distributor -right-angled with it-will give the turbine discharge.
When the projection of the absolute velocity C 0 over the moving frame velocity V 0
is bigger than V 0 the runner is an slow one; If both are of the same order the
runner is a normal one and if is smaller is a fast one.
With the aid of figure 6. 16 the coefficient of the entrance velocity V00 , the coefficient
of the exit velocity V05 , and the ratio b/D (respectively height of distributor and
internal diameter of distributor) can be estimated in function of the specific speed
ns. The moving frame velocity V 0 is given by
V = v ~laH ll lie -o
and the runner diameter 0 0 by
lr/1
(6.11)
and the exit diameter Ds by
60v11 , .J2iii (6.12)
lrll
whenever the turbine axis does not cross the diffuser. If it does it would be
necessary to enlarge the diameter to compensate by the loss of section caused
by the axis, a section easy to compute in function of the turbine torque.
170 Layman's Guidebook
The Kaplan turbines exhibit much higher specific speeds: 325 for a 45-m head
and 954 for a 5-m head. Nowadays these turbines, in the range of power used in
small hydro plants, are standardised, using a certain number of common
components with the objective of decreasing their cost price. Some manufactu-
res can supply all possible configurations by using only 6 runner diameters -1.8,
2.0, 2.2, 2.5, 2.8 and 3.2 metres-, three turbine axis diameters per runner, three
distributor configurations, and three different speed increasers.
In the preliminary project phase the runner diameter can be calculated by the
formula (D and H in m and Q in m3/sec)
D ~ (6.13).
6.1.2 Turbine selection criteria
The type, geometry and dimensions of the turbine will be fundamentally conditioned
by the following criteria:
• Net head
• Range of discharges through the turbine
• Rotational speed
• Cavitation problems
• Cost
Net head
The gross head is the vertical distance, between the water surface level at the
intake and at the tailrace for reaction turbines and the nozzle level for impulse
turbines. Once the gross head is known, the net head can be computed by simply
subtracting the losses along its path, as in example 5.6.
The first criterion to take into account in the turbine's selection is the net head. Table
6.1 specifies for each turbine type its range of operating heads. The table shows
some overlapping, so that for a certain head several types of turbines can be used.
Table 6.1 Range of heads
Turbine type
Kaplan and Propeller
Francis
Pelton
Micheii-Banki
Turgo
Head range in metres
2 < H <40
10< H <350
50< H <1300
3 < H < 250
50< H < 250
The selection is particularly critical in low-head schemes, where to be profitable
large discharges must be handled. When contemplating schemes with a head
between 2 and 5 m, and a discharge between 10 and 100 ffil/sec, runners with
1.6-3.2 metres diameter are required, coupled through a speed increaser to an
asynchronous generator. The hydraulic conduits in general and water intakes in
particular are very large and require very large civil works, with a cost that generally
exceeds the cost of the electromechanical equipment.
Chapter 6. Electromechanical equipment
verti~ Kaplan (/( $(W'Mi-KapG;m
figure 6.11
siphon !Jrwerted semi-Kaplan
flguro 6..19
~!-Kaplan ~ ~ !lli'fango!'Mfi'l
figuR' 6.18
figure 6 .10
171
• • • • • • • • • • • • • • • • •
• • • • • • • • • • • •
• • • •• • • • • • •
• • •
• • • • • • • • • • • • • • •
172
figure 6.24
Layman's Guidebook
5lr~ ..................
... -~ •• ~-w•ww~~mu.
4 ,50i
f~gure 6.13
figure 6.25
In order to reduce the overall cost (civil works plus equipment) and more specifically
the cost of the civil works, several configurations, nowadays considered as classic,
have been devised 9 • All of them include the only turbine type available for this job
-the Kaplan-in a double or a single regulated version .
The selection criteria for such turbines are well known:
• Range of discharges
• Net head
• Geomorphology of the terrain
• Environmental requirements (both visual and sonic)
• Labour cost
The configurations differ by how the flow goes through the turbine (axial, radial,
or mixed) the turbine closing system (gate or siphon), the speed increaser type
(parallel gears, right angle drive, epicycloidal gears) .
For those interested in low-head schemes please read the paper presented by J.
Fonkenell to HIDROENERGIA 91 11 dealing with selection of configurations,
enclosing diagrams with relative costs to facilitate the appropriate choice ..
Chapter 6. Electromechanical equipment 173
Configuration Flow Closing Speed
system increaser
Vertical Kaplan Radial Guide-vanes Parallel 6.17
Vertical semi-Kaplan siphon Radial Siphon Parallel 6.18
Inverse semi-Kaplan siphon Radial Siphon Parallel 6.19
Inclined semi-Kaplan siphon Axial Siphon Epicycloidal 6.20
Kaplan S Axial Gate valve Parallel 6.21
Kaplan S right angle drive Axial Gate valve Epicycloidal 6.22
Kaplan inclined right angle Axial Gate valve Conical 6.23
Semi-Kaplan in pit Axial Gate valve Epicycloidal 6.24
Siphons are reliable, economic, and prevent runaway turbine speed, but are very
noisy. Underground powerhouses are best to mitigate the visual and sonic impact,
but are only viable with an S, a right angle drive or a pit configuration.
The right angle drive configuration permits the use of a standard generator turning
at 1500 rpm, reliable, compact and cheap, by using a double step speed increaser
-planetary gears followed by a conical gear-. The S configuration is becoming very
popular although has the disadvantage that the turbine axis has to cross either the
entrance or the outlet pipe with consequent head loss. A recent study shows that, in
a 4 m head scheme with a 24 m3/sec discharge, the right angle drive configuration
offered an overall efficiency 3% -5% higher than the S configuration.
The pit configuration has the advantage of easy access to all the equipment
components. in particular the coupling of turbine and speed increaser, the speed
increaser itself and the generator, facilitating inspection, maintenance and repair.
The hydraulic conduits are simplified and gives a higher specific volume.
Since the double regulated turbine has a minimum practical discharge close to
20% of the rated discharge whereas in a single regulated it is close to 40%,
whenever a scheme has to cope with flows as low as 40% of the nominal one, the
double regulated turbine should be selected.
As a turbine can only accept discharges between the nominal and the practical
minimum, it may be advantageous to install several smaller turbines instead of a
one large. The turbines would be sequentially started, so all of the turbines in
operation except one will operate at their nominal discharges and therefore will
exhibit a higher efficiency. Using two or three smaller turbines will mean a lower
unit weight and volume and will facilitate transport and assembly on the site. The
rotational speed of a turbine is inversely proportional to its diameter, so its torque
will be lower and the speed increaser smaller and more reliable. The use of several
turbines instead of one large one with the same total power, will result in a lower
ratio kilograms of turbine/cubic meter of operating flow, although the ratio
equipment cost I cubic meter of operating flow will be larger.
Increasing the number of turbines decreases the diameter of their runners,
andconsequently the support components in the powerhouse will be smaller and
lighter. As the water conduits are identical the formwork, usually rather sophisticated,
174 Layman's Guidebook
can be reused several times decreasing its influence in the concrete cost.
Notwithstanding this, generally more turbine means more generators, more controls,
higher costs.
Discharge
A single value of the flow has no significance. It is necessary to know the flow
regime, commonly represented by the Flow Duration Curve (FDC) 12 as explained
in chapter 3, sections 3.3 and 3.6.
The rated flow and net head determine the set of turbine types applicable to the
site and the flow environment. Suitable turbines are those for which the given
rated flow and net head plot within the operational envelopes (figure 6.26). A
point defined as above by the flow and the head will usually plot within several of
these envelopes. All of those turbines are appropriate for the job, and it will be
necessary to compute installed power and electricity output against costs before
taking a decision. It should be remembered that the envelopes vary from
manufacturer to manufacturer and they should be considered only as a guide.
Specific speed
The specific speed constitutes a reliable criterion for the selection of the turbine,
without any doubt more precise than the conventional enveloping curves, just
mentioned.
If we wish to produce electricity in a scheme with 100-m net head, using a 800
kW turbine directly coupled to a standard 1500-rpm generator we should begin
by computing the specific speed according equation (6.5}.
II = lSOoJ80o = 134
s 100'>
With this specific speed the only possible selection is a Francis turbine. Otherwise
if we accept the possibility of using a speed increaser with a ratio up to 1.3, the
turbine itself could turn from 500 to 1500 rpm, corresponding respectively to specific
speeds of 45 and 134. In those conditions it could be possible to select, in addition
to the Francis, a Turgo, a cross-flow or a 2 jet Pelton. The spectrum of appropriate
turbines has been considerably enlarged by the presence of the speed increaser.
If we intend to install a 1500 kW turbine in a 400 m head scheme, directly coupled
to a 1000 rpm generator, we will begin computing the specific speed ns:
n = n.fP = 100~ = 21.65
' 400 --~
which indicates as the only option a 1 jet Pelton, with a diameter D, computed by
equation (6.8):
D = 38,567J4QO =O,nm
1000
Chapter 6. Electromechanical equipment
'00(1
I
5(10 I
3CIO I
200 ~ - -r-----......
100 I Turgo
7,.,....,.
1·. vc.: ,. ,~··/
-~1..,.,
so l'-
30
20
10
2
0.2 OS
----
Vr::prl>1r-!i.~ql;~n Hub;.
~r.;,rofi
Pr:·::f,;:Jr
1Jrqr-
0¥i'f:l M<;'l~:l
175
50
Figure 6. 26
176 Layman's Guidebook
Cavitation
When the hydrodynamic pressure in a liquid flow falls below the vapour pressure
of the liquid, there is a formation of the vapour phase. This phenomenon induces
the formation of small individual bubbles that are carried out of the low-pressure
region by the flow and collapse in regions of higher pressure. The formation of
these bubbles and their subsequent collapse gives rise to what is called cavitation.
Experience shows that these collapsing bubbles create very high impulse
pressures accompanied by substantial noise (in fact a turbine undergoing cavitation
sounds as though gravel is passing through it). The repetitive action of such
pressure waves close to the liquid-solid boundary results in pitting ofthe material.
With time this pitting degenerates into cracks formed between the pits and the
metal is spa lied from the surface. In a relatively short time the turbine is severely
damaged and will require to be shut-off and repaired-if possible.
Experience shows that there is a coefficient, called Thoma's sigma cr1 , which
defines precisely enough under which parameters cavitation takes place. This
coefficient is given by the equation
crT= Hsv/ H (6.13)
where Hsv is the net positive suction head and H the net head of the scheme.
According to figure 6.27
Where: Hsv
Hatm
H vap
z
v.
H
Hsv:: Hate1 Z-Hvap + V/ /2g + H, (6.14)
is the net positive suction head
is the atmospheric pressure head
is the water vapour pressure
is the elevation above the tailwater surface of the critical location
is the average velocity in the tailrace
is the head loss in the draft tube
Neglecting the draft-tube losses and the exit velocity head loss, Thoma's sigma
will be given by
crr=(Hatm-Hvap-z)/H (6.15)
To avoid cavitation the turbine should be installed at least at a height over the
tailrace water level zp given by the equation:
zr =Hatm -Hvap -cr 1 H (6.16)
The Thoma's sigma is usually obtained by a model test, and it is a value furnished
by the turbine manufacturer. Notwithstanding the above mentioned statistic studies
also relates Thoma's sigma with the specific speed. Thereunder are specified the
equation giving 6T as a function of ns for the Francis and Kaplan turbines:
Francis:
Kaplan:
cr = 7 54x10·5 xn 1.4 1
T . s
crT= 6.40x10·5 xn 5
146
(6.17)
(6.18)
It must be remarked that Hvap decreases with the altitude, from roughly 10.3 mat
the sea level to 6.6 mat 3000 m above sea level. So then a Francis turbine with
a specific speed of 150, working under a 100 m head (with a corresponding 61 =
0.088), that in a plant at sea level, will require a setting:
z = 10.3-0.09-0.088 x 100 = 1.41 m
installed in a plant at 2000 m above the sea level will require
z = 8.1 0.09-0.088 x 100 = -0.79 m
a setting requiring a heavy excavation
Chapter 6. Electromechanical equipment 177
Rotational speed
According to (6.5) the rotational speed of a turbine is a function of its specific
speed, and of the scheme power and net head. In the small hydro schemes
standard generators should be installed when possible, so in the turbine selection
it must be borne in mind that the turbine, either coupled directly or through a
speed increaser, should reach the synchronous speed, as given in table 6.2
Table 6.2 Generator synchronisation speed (rpm)
Number Frequency Number Frequency
of poles 50 Hz 60Hz of poles 50 Hz 60Hz
2 3000 3600 16 375 450
4 1500 1800 18 333 400
6 1000 1200 20 300 360
8 750 900 22 272 327
10 600 720 24 250 300
12 500 600 26 231 277
14 428 540 28 214 257
Runaway speed
Each runner profile is characterised by a maximum runaway speed. This is the
speed, which the unit can theoretically attain when the hydraulic power is at its
maximum and the electrical load has become disconnected. Depending on the
type of turbine, it can attain 2 or 3 times the nominal speed. Table 6.3 shows this
ratio for conventional and unconventional turbines
It must be remembered that the cost of both generator and gearbox may be
increased when the runaway speed is higher, since they must be designed to
withstand it.
Turbine type
Kaplan single regulated
Kaplan double regulated
Francis
Pelton
Cross-flow
Turgo
6.1.3 Turbine efficiency
Table 6.3
Normal speed n (rpm) Runaway speed nmax/n
75-100
75-150
500-1500
500-1500
60-1000
600-1000
2.0-2.4
2.8-3.2
1.8-2.2
1.8-2.0
1.8-2.0
2
The efficiency guaranteed by turbine manufacturers is that which may be verified
in accordance with the "International Code for the field acceptance tests of hydraulic
turbines" (publication IEC-141) or, if applied, in accordance with the "International
Code for model acceptance tests" (publication IEC-193). It is defined as the ratio
of power supplied by the turbine (mechanical power transmitted by the turbine
shaft) to the absorbed power (hydraulic power equivalent to the measured
discharge under the net head).
178
energy loss
in penstock
figure 6.27
Layman's Guidebook
It is to be noted that for impulse turbines (Pelton, Turgo and Cross-Flow), the head is
measured at the point of impact of the jet. which is always above the downstream
water level. This effectively amounts to a reduction of the head. The difference is not
negligible for low-head schemes, when comparing the performance of impulse
turbines with those of reaction turbines that use the entire available head.
Due to the head losses generated in reaction turbines the runner only uses a head
H" lower than the net head H" , such as defined in figure 6.27. These losses are
essentially friction losses in the spiral case, guide-vanes and runner blades plus
velocity head losses in the draft tube. The draft-tube or diffuser is designed to recover
the biggest possible fraction of the velocity head generated by the velocity of the
water leaving the blades. This loss is particularly critical in the high specific speed
runners, where it may reach up to 50% of the net head (whereas in the slow Francis
runner it rarely exceeds 3%-4% ). The head used by the runner is in fact the equivalent
to the net head diminished by the kinetic energy dissipated in the draft-tube, quantified
by the expression ve /2g, where ve is the average velocity of the water leaving the
draft-tube. To reduce the velocity the draft tube is commonly designed with a conical
section. Small divergence angles require long, and consequently costly, diffusers.
but otherwise the angle cannot exceed about 7° without danger of flow separation.
Trying to find equilibrium between flow separation and cost some designers increase
the angle up to about 15°. The draft-tube design has such implications on the turbine
operation that it is strongly recommended to leave it to the turbine manufacturer or
at least fabricate it under his advice and drawings.
At present no IEC code defines the net head across a cross-flow turbine or its
efficiency. Care must be taken in comparing reaction turbine efficiencies with
cross-flow efficiencies 11 . Anyhow cross-flow peak efficiencies calculated from
the net head definition given by the IEC code for impulse turbines, reach a ceiling
slightly over 80%, but retain this efficiency value under discharges as low as a
sixth of the maximum.
Fig 6.28 indicates the mean efficiency guaranteed by manufacturers for several
types of turbine. To estimate the overall efficiency the turbine efficiency must be
Chapter 6. Electromechanical equipment 179
1IXI%-l
i ..,.t~--······"····~_·::~:·::.;_.''''J~;~~t-~~;·
I .~/ /• ··· .. cm~.r ···:. ----. -··:7::>""~----................ ---·-··-·····-.. :. -
i1:': t • tl ,/ i m!.+·--·--i-:?·<--;r:: .......................... ·---·------·-----·-····--··
t> I /t ' .
ll ... t ·trf -----··--··----_-------·--·-··------·--·••1
:11~---··-·······~·--·-·-··:····:····--=:J
JO'Iio m. ... ""' WI!. -~ 1(n. eo'~~!> 110'4 t!IO'Ii.
%nominal flow
fi gure6.28
multiplied by the efficiencies of the speed increaser (if used) and the alternator.
A turbine is designed to operate at or near its best efficiency point, usually at 80
per cent of the maximum flow rate, and as flow deviates from that particular
discharge so does the turbine's hydraulic efficiency.
Double regulated Kaplan and Pelton turbines can operate satisfactorily over a
wide range of flow -upwards from about one fifth of rated discharge. Single
regulated Kaplans have acceptable efficiency upward from one third and Francis
turbines from one half of rated discharge. Below 40% of the rated discharge,
Francis turbines may show instability resulting in vibration or mechanical shock.
Propeller turbines with fixed guide vanes and blades can operate satisfactorily
only over a very limited range close to their rated discharge. It should be noted
that with single-regulated propeller turbines the efficiency is generally better when
it is the runner that is adjustable.
6.1.4 Turbine performance characteristics
Turbine manufacturers use scaled models to obtain different curves correlating
their characteristics.
Torque-velocity characteristic
This graphically represents the correlation between the rotational speed and the
turbine torque for different admission degrees. According to figure 6.29 the torque,
for the same admission degree, decreases linearly with the rotational speed. The
maximum torque corresponds to a null speed, hence the high starting torque of
hydraulic turbines . The speed corresponding to the point where the curve cut the
horizontal axis is called runaway speed.
• • • • • • • • • • • • • • • • • • • • • •
• • • •• • • • • • • • • •
180
Torque (m Kg)
a=admision degree
Velocity (rpm)
Power-velocity characteristic
Layman's Guidebook
P, kW
4 v. regime ~
4 v. runaway
H=constant
----~~%
"-------!;i;=->J%
~
n
rpm
figure 6.30
This represents graphically how under a given head the power evolves, at different
degrees of admission, with the velocity. The parabolic curves (figure 6.30) cut
the horizontal axis in two different points, corresponding respectively to the null
speed and the runaway speed.
Flow-velocity characteristic
This practically linear (figure 6.31) representing the flow admitted by the turbine
at different speeds, under a constant head, and a variable admission degree. In
the Pelton turbines the straight lines are almost horizontal; drooping in the slow
Francis (when the speed increases the turbines accept less and less flow), and
ascendant in the fast Francis.
Turbine performance
In the flow-velocity plane, by connecting the points that have the same efficiency,
iso-efficiency curves are obtained (figure 6.32), that look like contour lines on a
topographic map, Compounding these curves with the power as the third axis,
they will form a sort of "hill", the so called "hill charts".
6.1.5 Turbine performance under new site conditions
When rehabilitating a site there are many occasions when, the turbine being
a=100%
Q a=100% Q
H=ct
H=ct
n Francis slow Pelton Francis normal Francis fast and propeller
Chapter 6. Electromechanical equipment 181
Q
Q
N n
figure 6.32
irreparable, an existing second hand turbine with rating parameters somewhat
similar to the site parameters can be installed.
It is well known that the flow, speed, and power output for any turbine are site
specific and are functions of the net head under which the turbine operates.
According to the similarity laws, a turbine manufactured to operate under certain
design parameters, characterised by the suffix 1, will show different characteristics
operating under the new parameters, characterised by the suffix 2. The flow "Q"
like the flow through an orifice is proportional to H:
Qc .j}i; .j}i;
- = ru therefore Q" = Ql ru Ql VHI -..yHI
The speed "n" of a turbine is proportional to the flow velocity within the turbine so:
11 c ..[H; ..[H; - = ru therefore nc = 111 ru
11 1 VHI ..yHI
182 Layman's Guidebook
When the turbine installed at the site is run at "n 2 " speed, the power output "P" is
proportional to the product of head and flow:
p(.H")'1 IH
I
The turbine shaft is designed to transmit a certain torque (T) directly proportional
runner
blades
blade regulation
m.ech ni
speed increaser
turbine axis
wicket gates
figure 6.33
Chapter 6. Electromechanical equipment
to the power and inversely proportionally to the turbine speed.
(~J(ZJ ~: T, P, Ill ....;;;...-_--
~ ~ nc
As the torque is proportional to the cube of the shaft diameter
I H, ~~ 3
d,=dl --.J ,_ , \ H,
183
It can be deduced that if the shaft of the proposed turbine is adequately
dimensioned, it will be adequate for the new site provided the head is smaller
than the head for which the turbine was designed. The same reasoning can be
applied to every turbine component wicket-gates, blades, seals etc. The speed
increaser will also have to be checked. If the new head is slightly lower than the
original, both turbine and speed increaser can be used without difficulties. If the
head is slightly higher, both the speed increaser and the generator should be
checked to verify that they could handle the increased power. If the new head is
significantly higher than the original one, the torque shaft should be checked and
probably reinforced, but the generator could remain unchanged if the speed
increaser has been modified so it runs at the proper speed. lfthe new turbine is a
reaction turbine its setting also needs to be recalculated.
6.2 Speed increasers
When the turbine and the generator operate at the same speed and can be placed
so that their shafts are in line, direct coupling is the right solution; virtually no
power losses are incurred and maintenance is minimal. Turbine manufactures
will recommend the type of coupling to be used, either rigid or flexible although a
flexible coupling that can tolerate certain misalignment is usually recommended.
In many instances, particularly in the lowest power range, turbines run at less
than 400 rpm, requiring a speed increaser to meet the 1 000-1 500 rpm of stan-
dard alternators. In the range of powers contemplated in small hydro schemes
this solution is always more economical than the use of a custom made alterna-
tor.
6.2.1 Speed increaser types
Speed increasers according to the gears used in their constructionare classified as
Parallel-shaft
using helicoid gears set on parallel axis and are especially attractive for medium
power applications. Figure 6.33 shows a vertical configuration, coupled to aver-
tical Kaplan turbine.
Bevel gears:
commonly limited to low power applications using spiral bevel gears for a 90°
drive. Figure 6.34 shows a two-phased speed increaser: the first is a planetary
gearbox and the second a bevel gear drive.
• • •• • • • • • • •
• • • •
• • •
• • • • • • • • • • • • • • •
184
Photo 6.9
Layman's Guidebook
generator 1500 rpm
powerhouse fl o or
figure 6.34
Epicycloidal:
extremely compact and specially adequate for turbines over
2 MW capacity .
6.2.2 Speed increaser design
The gearbox should be designed to ensure, under the most
unfavourable conditions, the correct alignment of its
components. They are usually fabricated in welded steel
with heavy stiffeners to resist the turbine torque without
apparent deformation .
A lack of synchronism, a full load rejection, or any other
accident in the system can generate very high critical
stresses on the gears . To protect gears against these
exceptional strains the speed increaser should incorporate
a torque limiter, so that the connector breaks when there
is an abnormal force .
Chapter 6. Electromechanical equipment 185
To ensure the required level of reliability good lubrication is essential. It is very
important that the quality, volume, viscosity and temperature of the oil always
stay within specifications. A double lubrication system with two pumps and two oil
filters would contribute to the system reliability.
Speed increasers are designed according to international standards (AGMA 2001,
888 or DIN 3990) using very conservative design criteria. These criteria conflict with
the need to reduce costs, but no cost savings are possible or recommended without
a thorough analysis of the fatigue strains, and a careful shaving of the heat treated
gears, a satisfactory stress relieving of the welded boxes, all of which are essential to
ensure the durability of a speed increaser. Metallurgical factors including knowledge
of the respective advantages and disadvantages of hard casing or nitruring of gears
are also essential to optimise the speed increaser.
Selection of journal bearings is also crucial. Under 1 MW the use of roller bearings
is acceptable, but for a higher power it becomes difficult to find roller bearings capable
of sustaining their role for the required life of the increaser. That is why from 1 MW
onwards designers prefer to use hydrodynamic lubricated bearings that present the
following advantages:
• The life of the roller bearings is limited by fatigue whereas the hydrodynamic
bearings have a practical unlimited life.
• Hydrodynamic bearings permit a certain oil contamination, whereas roller
bearings do not.
6.2.3 Speed increaser maintenance
6.3 Generators
At least 70% of speed increaser malfunctioning is due to the poor quality or to the
lack of the lubricant oil. Frequently the oil filters clog or water enters the lubrication
circuit. Maintenance should be scheduled either based on predetermined periods
of time or -better by periodic analysis of the lubricant to check that it meets
specifications.
Speed increasers substantially increase the noise in the powerhouse and require
careful maintenance as their friction losses can exceed 2% of the outlet power,
so other alternatives have been investigated. Figure 6.35 shows a successful
application of a flat belt as speed increaser. In smaller plants the use of V belts
are also becoming popular.
Generators transform mechanical energy into electrical energy. Although most
early hydroelectric systems were of the direct current variety to match early
commercial electrical systems, nowadays only three-phase alternating current
generators are used in normal practice. Depending on the characteristics of the
network supplied, the producer can choose between:
• Synchronous generators equipped with a DC excitation system (rotating or
static) associated with a voltage regulator, to provide voltage, frequency and
phase angle control before the generator is connected to the grid and supply
186
sliding gate
at belt
figure 6.35
Layman's Guidebook
alternator
sliding
gate
the reactive energy required by the power system when the generator is tied
into the grid. Synchronous generators can run isolated from the grid and pro-
duce power since excitation is not grid-dependent
• Asynchronous generators are simple squirrel-cage induction motors with no
possibility of voltage regulation and running at a speed directly related to system
frequency. They draw their excitation current from the grid, absorbing reactive
energy by their own magnetism. Adding a bank of capacitors can compensate for
the absorbed reactive energy. They cannot generate when disconnected from
the grid because are incapable of providing their own excitation current.
Synchronous generators are more expensive than asynchronous generators and
are used in power systems where the output of the generator represents a substan-
tial proportion of the power system load. Asynchronous generators are cheaper
and are used in large grids where their output is an insignificant proportion of the
power system load. Their efficiency is 2 to 4 per cent lower than the efficiency of
synchronous generators over the entire operating range. In general, when the
power exceeds 5000 kVA a synchronous generator is installed.
Recently, variable-speed constant-frequency systems (VSG), in which turbine speed
is permitted to fluctuate widely, while the voltage and frequency are kept constant
and undistorted, have entered the market. This system can even "synchronise" the
unit to the grid before it starts rotating. The key to the system is the use of a series-
resonant converter in conjunction with a double feed machine 12 . Unfortunately its
cost price is still rather high and the maximum available power too low.
The working voltage of the generator varies with its power. The standard generation
voltages are 380 V or 430 V up to 1400 kVA and at 6000/6600 for bigger installed
Chapter 6 . Electromechanical equipment 187
power. Generation at 380 V or 430 V allows the use of standard distributor
transformers as outlet transformers and the use of the generated current to feed ·
into the plant power system. Generating at medium voltage requires an
independent transformer MT/LT to supply the plant services .
6.3.1 Generator configurations
6.3.2 Exciters
Generators can be manufactured with horizontal or vertical axis, independently
of the turbine configuration. Figure 6.36 shows a vertical axis Kaplan turbine
turning at 214 rpm directly coupled to a custom made 28 poles alternator. Photo
6.9 shows the same type of turbine coupled to a standard generator through a
parallel gear speed increaser. A flywheel is frequently used to smooth-out speed
variations and assists the turbine control.
Another criterion characterising generators is how their bearings are positioned.
For example it is common practice to install a generator with extra-reinforced
bearings supporting the cantilevered runner of a Francis turbine . In that way the
turbine axis does not need to cross the draft tube so improving the overall efficiency.
The same solution is frequently used with Pelton turbines .
When these generators are small, they have an open cooling system, but for
larger units it is recommended to use a closed cooling circuit provided with air-
water heat exchangers.
The exciting current for the synchronous generator can be supplied by a small
DC generator, known as the exciter, to be driven from the main shaft. The power
absorbed by this de generator amounts to 0.5% - 1.0% of the total generator
power. Nowadays a static exciter usually replaces the DC generator, but there
are still many rotating exciters .in operation.
• • • • • • • • • • • • • • • • • •
• • • • • • • • • • • •
188 Layman's Guidebook
Rotating exciters.
The field coils of both the main generator and the exciter generator are usually
mounted on the main shaft In larger generators a pilot exciter is also used. The
pilot exciter can be started from its residual magnetic field and it then supplies the
exciting current to the main exciter, which in turn supplies the exciting current for
the rotor of the generator. In such way the current regulation takes place in the
smaller machine.
Brushless exciters
A small generator has its field coils on the stator and generates AC current in the
rotor windings. A solid state rectifier rotates with the shaft, converting the AC
output from the small generator into the DC which is the supplied to the rotating
field coils ofthe main generator without the need of brushes. The voltage regulation
is achieved by controlling the current in the field coils of the small generator.
Static exciters
The exciting current is taken out, via a transformer, from the output terminals of the
main generator. This AC current is then rectified in a solid state rectifier and injected
in the generator field coils. When the generator is started there is no current flowing
through the generator field coils. The residual magnetic field, aided if needed by a
battery, permits generation to start to be then stabilised when the voltage at the
generator terminals reaches a preset value. This equipment is easy to maintain has
a good efficiency and the response to the generator voltage oscillations is very good.
6.3.3 Voltage regulation and synchronisation
6.3.3.1 Asynchronous generators
An asynchronous generator needs to absorb a certain power from the three-
phase mains supply to ensure its magnetisation even, if in theory, the generator
can receive its reactive power from a separate source such as a bank of capacitors.
The mains supply defines the frequency of the stator rotating flux and hence the
synchronous speed above which the rotor shaft must be driven.
On start-up, the turbine is accelerated up to 90-95% of the synchronous speed of
the generator, when a velocity relay close the main line switch. The generator
passes immediately to hyper-synchronism and the driving and resisting torque
are balanced in the area of stable operation.
6.3.3.2 Synchronous generators
The synchronous generator is started before connecting it to the mains by the
turbine rotation. By gradually accelerating the turbine the generator is synchronised
with the mains, regulating the voltage, frequency and rotating sense, When the
generator reaches a velocity close to synchronous, the exciter regulates its field
coils current so the generator voltage is identical to the mains voltage.
When the synchronous generator is connected to an isolated net, the voltage
controller maintains a predefined constant voltage, independent of the load. If it is
connected to the main supply, the controller maintains the reactive power at a
predefined level.
Chapter 6. Electromechanical equipment 189
6.4 Turbine control
Turbines are designed for a certain net head and discharge. Any deviation from
these parameters must be compensated for, by opening or closing control devices
such as the wicket-vanes or gate valves to keep constant, either the outlet power,
the level of the water surface in the intake or the turbine discharge.
In schemes connected to an isolated net, the parameter to be controlled is the
runner speed, which control the frequency. The generator becomes overloaded
and the turbine slows-down. In this case there are basically two approaches to
control the runner speed: either by controlling the water flow to the turbine or by
keeping the water flow constant and adjusting the electric load by an electric
ballast load connected to the generator terminals.
In the first approach, speed (frequency) regulation is normally accomplished
through flow control; once a gate opening is calculated, the actuator gives the
necessary instruction to the servomotor, which results in an extension or retraction
of the servo's rod. To ensure that the rod actually reaches the calculated position,
feedback is provided to the electronic actuator. These devices are called "speed
governors"
In the second approach it is assumed that, at full load, constant head and flow,
the turbine will operate at design speed, so maintaining full load from the generator;
this will run at a constant speed. If the load decreases the turbine will tend to
increase its speed. An electronic sensor, measuring the frequency, detects the
deviation and a reliable and inexpensive electronic load governor, switches on
preset resistances and so maintains the system frequency accurately.
The controllers that follow the first approach do not have any power limit. The
Electronic Load Governors, working according to the second approach rarely
exceeds 1 00 kW capacity.
6.4.1 Speed Governors
A governor is a combination of devices and mechanisms, which detect speed
deviation and convert it into a change in servomotor position. A speed-sensing
element detects the deviation from the set point; this deviation signal is converted
and amplified to excite an actuator. hydraulic or electric, that controls the water
flow to the turbine. In a Francis turbine, where to reduce the water flow you need
to rotate the wicket-gates a powerful governor is required to overcome the hydraulic
and frictional forces and to maintain the wicket-gates in a partially closed position
or to close them completely.
Several types of governors are available varying from purely mechanical to mechanical-
hydraulic to electrohydraulic. The purely mechanical governor is used with fairly small
turbines, because its control valve is easy to operate and does not requires a big
effort. These governors use a flyball mass mechanism driven by the turbine shaft.
The output from this device -the flyball axis descends or ascends according to the
turbine speed-directly drive the valve located at the entrance to the turbine.
190
servomotor
cylinder
Layman's Guidebook
flywheels
manual mechanism
pilot valve
~
.a. to the
T servomotor
figure 6.37
The most commonly-used type is the oil-pressure governor (Fig 6.37) that also
uses a flyball mechanism lighter and more precise than that used in a purely
mechanical governor. When the turbine is overloaded, the flyballs slowdown, the
balls drop, and the sleeve of the pilot valve rises to open access to the upper
chamber of the servomotor. The oil under pressure enters the upper chamber of
the servomotor to rotate the wicket-gates mechanism and increase the flow, and
consequently the rotational speed and the frequency.
In an electrohydraulic governor a sensor located on the generator shaft
continuously senses the turbine speed. The input is fed into a summing junction,
where it is compared to a speed reference. If the speed sensor signal differs from
the reference signal, it emits an error signal (positive or negative) that, once
amplified, is sent to the servomotor so this can act in the required sense. In
general the actuator is powered by a hydraulic power unit (photo 6.1 0) consisting
of a sump for oil storage, an electric motor operated pump to supply high pressure
oil to the system, an accumulator where the oil under pressure is stored, oil con-
trol valves and a hydraulic cylinder. All these regulation systems, as have been
described, operate by continuously adjusting back and forth the wicket-gates
position. To provide quick and stable adjustment of the wicket-gates, and/or of
the runner blades, with the least amount of over or under speed deviations during
system changes a further device is needed. In oil pressure governors, as may be
seen in figure 6.37, this is achieved by interposing a "dash pot" that delays the
opening of the pilot valve. In electrohydraulic governors the degree of sophistication
is much greater, so that the adjustment can be proportional, integral and derivative
(PID) giving a minimum variation in the controlling process.
An asynchronous generator connected to a large net, from which it takes its reactive
power to generate its own magnetism, does not need any controller, because its
frequency is controlled by the mains. Notwithstanding this, when the generator is
Chapter 6 . Electromechanical equipment 191
disconnected from the mains the turbine accelerates up to runaway speed with
inherent danger for the generator and the speed increaser, if one is used. In such a
case it is necessary to interrupt the water flow, rapidly enough to prevent the turbine
accelerating, but at the same time minimising any waterhammer effect in the penstock .
To ensure the control of the turbine speed by regulating the water flow , a certain
inertia of the rotating components is required . Additional inertia can be provided
by a flywheel on the turbine or generator shaft. When the main switch disconnects
the generator the power excess accelerates the flywheel; later, when the switch
reconnects the load, the deceleration of this inertia flywheel supplies additional
power that helps to minimise speed variation. The basic equation of the rotating
system is the following :
JdQ =T-T.
d t I L
where : J = moment of inertia of the rotating components
Q = angular velocity
T1 = torque of turbine
T L = torque due to load
When T1 is equal to TL , dQ/dt = 0 and n =constant, so the operation is steady.
When T1 is greater or smaller than TL , n is not constant and the governor must
intervene so that the turbine output matches the generator load. But it should not
be forgotten that the control of the water flow introduces a new factor: the speed
variations on the water column formed by the waterways.
The flywheel effect of the rotating components is stabilising whereas the water
column effect is destabilising. The start-up time of the rotating system , the time
required to accelerate the unit from zero rotational speed to operating speed is
given by
• • • • • • • • • • • • • • •
• • • • • • • • • • • •
192 Layman's Guidebook
5086P
where the rotating inertia of the unit is given by the weight of all rotating parts
multiplied by the square of the radius of gyration: WR2 , Pis the rated power in kW
and n the turbine speed (rpm)
The water starting time, needed to accelerate the water column from zero velocity
to some other velocity V, at a constant head H is given by:
T=lJV sr.
"f!f!
where H =gross head across the turbine (m)
L =length of water column (m)
V =velocity of the water (m/s)
g =gravitational constant (9.81 m s·2 )
To achieve good regulation is necessary that T miT w > 4. Realistic water starting
times do not exceed 2.5 sec. If it is larger, modification of the water conduits must
be considered-either by decreasing the velocity or the length of the conduits by
installing a surge tank. The possibility of adding a flywheel to the generator to
increase the inertia rotating parts can also considered. It should be noted that an
increase of the inertia of the rotating parts will improve the waterhammer effect
and decrease the runaway speed.
6.5 Switchgear equipment
In many countries the electricity supply regulations place a statutory obligation on
the electric utilities to maintain the safety and quality of electricity supply within
defined limits. The independent producer must operate his plant in such a way that
the utility is able to fulfil its obligations. Therefore various associated electrical devices
are required inside the powerhouse for the safety and protection of the equipment.
Switchgear must be installed to control the generators and to interface them with
the grid or with an isolated load. It must provide protection for the generators,
main transformer and station service transformer. The generator breaker, either
air, magnetic or vacuum operated, is used to connect or disconnect the generator
from the power grid. Instrument transformers, both power transformers (PTs) and
current transformers (CTs) are used to transform high voltages and currents down
to more manageable levels for metering. The generator control equipment is used
to control the generator voltage, power factor and circuit breakers.
The asynchronous generator protection must include, among other devices: a
reverse-power relay giving protection against motoring; differential current relays
against internal faults in the generator stator winding; a ground-fault relay providing
system backup as well as generator ground-fault protection, etc. The power
transformer protection includes an instantaneous over-current relay and a timed
over-current relay to protect the main transformer when a fault is detected in the
bus system or an internal fault in the main power transformer occurs.
Chapter 6. Electromechanical equipment
voltage control
g:-3
exciter 3
transmission line
generator
switch
figure 6.39
outlet
transformer
plant
transformer
193
loads
194 Layman's Guidebook
The independent producer is responsible for earthing arrangements within his
installation. The independent producer's earthing arrangement must be designed
in consultation with the public utility. The earthing arrangement will be dependent
on the number of units in use and the independent producer's own system
configuration and method of operation.
Metering equipment must be installed at the point of supply to record measure-
ments to the requirements of the electric utility.
Figure 6.38 shows a single-line diagram corresponding to a power plant with a
single unit. In the high voltage side there is a line circuit breaker and a line
disconnection switch -combined with a grounding switch-to disconnect the power
generating unit and main transformer from the transmission line. Metering is
achieved through the corresponding P.T and C.T. A generator circuit breaker is
included as an extra protection for the generator unit. A transformer provides
energy for the operation of intake gates, shutoff valves, servomotors, oil
compressors etc. in the station service.
Greater complexity may be expected in multiunit stations where flexibility and
continuity of service are important.
6.6 Automatic control
Small hydro schemes are normally unattended and operated through an automatic
control system. Because not all power plants are alike, it is almost impossible to
determine the extent of automation that should be included in a given system, but
some requirements are of general application 13 :
a) All equipment must be provided with manual controls and meters totally
independent of the programmable controller to be used only for initial start up
and for maintenance procedures.
b) The system must include the necessary relays and devices to detect malfunc-
tioning of a serious nature and then act to bring the unit or the entire plant to a
safe de-energised condition.
c) Relevant operational data of the plant should be collected and made readily
available for making operating decisions, and stored in a database for later
evaluation of plant performance.
d) An intelligent control system should be included to allow for full plant operation
in an unattended environment.
e) It must be possible to access the control system from a remote location and
override any automatic decisions.
f) The system should be able to communicate with similar units, up and downstream,
for the purpose of optimising operating procedures.
g) Fault anticipation constitutes an enhancement to the control system. Using an expert
system, fed with baseline operational data, it is possible to anticipate faults before
they occur and take corrective action so that the fault does not occur.
The system must be configured by modules. An analogue-to-digital conversion
module for measurement of water level, wicket-gate position, blade angles,
instantaneous power output, temperatures, etc. A digital-to-analogue converter
Chapter 6. Electromechanical equipment 195
module to drive hydraulic valves, chart recorders, etc. A counter module to count
generated kWh pulses, rain gauge pulses, flow pulses, etc. and a "smart" teleme-
try module providing the interface for offsite communications, via dial-up telephone
lines or radio link. This modular system approach is well suited to the widely
varying requirements encountered in hydropower control, and permits both
hardware and software to be standardised. Cost reduction can be realised through
the use of a standard system; modular software allows for easy maintenance.
Automatic control systems can significantly reduce the cost of energy production
by reducing maintenance and increasing reliability, while running the turbines
more efficiently and producing more energy from the available water.
With the tremendous development of desktop computers, their prices are now
very low. Many manufacturers supply standardised data acquisition systems. New
and cheap peripheral equipment, such as hard disks, PCMCIA cards for portable
computers, the "watch-dogs-to monitor and replace control equipment in the
event of failure is available and is easy to integrate at low price.
The new programming techniques -Visual Basic, Delphi etc-assist the writing of
software using well-established routines; the GUI interfaces, that every body knows
thanks to the Windows applications; everything has contributed to erase the old
aura of mystery that surrounded the automatic control applications.
6.7 Ancillary electrical equipment
6. 7.1 Plant service transformer
Electrical consumption including lighting and station mechanical auxiliaries
may require from 1 to 3 percent of the plant capacity; the higher percentage
applies to micro hydro (less than 500 kW). The service transformer must be
designed to take these intermittent loads into account. If possible, two
alternative supplies, with automatic changeover, should be used to ensure
service in an unattended plant.
6.7.2 DC control power supply
Plants larger than 500 kW capacity, especially if they are remotely controlled,
require a DC system with a battery charger, station batteries and a DC distribution
panel. The ampere-hour capacity must be such that, on loss of charging current,
full control is ensured for as long as it may be required to take corrective action.
6.7.3 Headwater and tailwater recorders
In a hydro plant provisions should be made to record both the headwater and
tailwater. The simplest way is to fix securely in the stream a board marked with
meters and centimetres in the style of a levelling staff but someone must physically
observe and record the measurements. In powerhouses provided with automatic
control the best solution is to use transducers connected to the computer via the
data acquisition equipment 14 .
• • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • •
196
Photo 6.11
a)
/
/ sensor
sumergible
/
b)
/
figura 6.39
Layman's Guidebook
c)
sensor
sumergible
/
Nowadays measuring units -a sensor-records the measurement variable and
converts it into a signal that is transmitted to the processing unit. The measurement
sensor must always be installed at the measurement site, where the level has to
be measured -usually subject to rough environmental conditions and of difficult
access -whereas the processing unit is usually separated and placed in a well
protected environment easily accessible for operation and service.
There is a wide range of sensors each one using a variety of measuring principles.
It must be realised that a level measurement cannot determine the level for the
forebay, unless the measurement site had been selected in such a way that it
represents the whole forebay. According to the Bernoulli principle, a change in the
flow rate always causes a change in the height of the water level. If the measurement
site is located in the inflow or outflow structures, the measurement will give false
Chapter 6. Electromechanical equipment 197
results. The level sensor can transmit the signal by using the hydrostatic method
(figure 6.39 a) or the pneumatic (bubble) method (figure 6.39 b). In the first method
care should be taken so all the tubes for pressure transmission are dimensioned
and laid in such way that cannot be obstructed and no air can accumulate within
them 17 . In the second, the sensor orifice is located lower than the corresponding
level at the start of the measurement, and that no water can penetrate and collect
in the lines. In the solution shown in figure 6.39 a) floating material can damage
the instrument. The best solution is the concealed assembly of all parts together
within the wall as shown in figure 6.39 b) and c).
6.7.4 Outdoor substation
6.8 Examples
The so-called water-to-wire system usually includes the substation. A line breaker
must separate the plant including the step-up transformer from the grid in case of
faults in the power plant. PTs and CTs for kWh and kW metering are normally
mounted at the substation, at the connecting link between the plant-out conductors
and the take-off line to the grid (Photo 6.1 0). In areas with very high environmental
sensitivity the substation is enclosed in the powerhouse, and the transmission
cables, leave it along the penstock.
Lightning arrestors for protection against line surges or lightning strikes are usually
mounted in the substation structure.
Two examples will help to better understand the concepts exposed in this chapter
and particularly the use of the specific speed tool.
Example 6.1
Select a turbine to equip a 200-m head scheme with a nominal flow of 1.5
m3/sec. The powerhouse is located at an altitude of 1000 m over the sea
level.
Assuming an overall efficiency at the design point of 85% the installed power
will be: P = QHgll = 1.5 X 200 X 9.81 X 0.85 = 2500 kW
According to figure 6.26 the plot of head and flow falls into the envelopes of a
Francis and a Pelton turbine. The turbine speed is given as a function of ns by:
..J2500 n, = 11 2005 4 = 0.0665 11
If we select a Pelton with a rotational speed of 375 rpm, to be coupled via a
speed increaser with a ratio 2/1 to a 750-rpm generator, its specific speed will
be 24.93, inside, although at the limit, of the Pelton's specific speed range.
The jet velocity would be
V1 = 0.97~2gH = 0.97.J2 x9.81 x200 = 60.76 m I sec
198
The tangential speed; V0 = 0.47V = 28.56 m/sec
The Pelton diameter according to (B.8)
Layman's Guidebook
D = 60 Vo 60 x 28 ·56 1.45 m a wheel of a reasonable diameter
nn 375n
If we select a Francis to be directly coupled to a generator running at 1500 rpm,
ns = 99.75
From the curves of figure 6.16 V0e =0.69 and the inlet diameter will be
60x 0.69 x .J2 x 9.81 x200
D 0 = 0.572 m and V0 = 0.49 so the diameter
1500n •
60xQ49x.J2x9B1x200
1500n
According to eq. (6.17)
0.391 m
(J 1 7.54 X lO-S X n:AI = 0.0496 m
and according to eq. (6.16) = = 9.2-0.09-0.0496 x 200 = -0.81 m
a setting that requires important excavation.
If we have selected a Francis running at 1000 rpm we would have had:
ns= 65.5, voe= 0.60, vos=0.373, Do= 0.79 m, OS 0.446 m, crT= 0.027 and
z= 3.62 m which does not need excavation, and is the best of all three
alternatives.
Example 6.2
We want to rehabilitate a 100-m scheme. The turbine is badly damaged,
but there is an offer for an almost new Francis turbine that had been
operating under the following operating parameters: H =120m, P = 1000
kW, n = 750 rpm, and n = 0.90. Compute the nominal discharge when
installed in the above scheme, its nominal power and the turbine speed.
The specific speed of the new turbine is given by:
n = n..JP 750.Ji000 = 59.72
' 1
and the rated discharge under those parameters
QJ = __!L --1 000 1 0.944 m· is
H 1rr7 120 x 9.81 x o.9o
Using the similarity equations computed in 6.1.5 which can be applied because
the diameter remains always constant So:
Chapter 6. Electromechanical equipment 199
[H; -~00 -n, = n 1 ,.-;;-:; 7::>0 -.-= 68.) rpm -v H1 120
[H; ~00 . Qc q ~ = 0.944 -= 0.862 m' I sec -v HI 120
P., = P
11 ~ = 1000 685 : = 762 kW 1 n' 750'
200 Layman's Guidebook
Bibliography
P.T. Than Hline & P.Wibulswas,"Feasibility of using small centrifugal pumps as
turbines". Renewable Energy Review Journal; Vol9, No.1 June 1987
2 Societe Hydrotechnique de France, "Design, Construction, Commissioning
and Operation Guide", May 1985
3 Schweiger & Gregory, "Developments in the design of water turbines", Water
Power & Dam Construction, May 1989
3 F. de Siervo & A. Lugaresi, "Modern trends in selecting and designing Francis
turbines", Water Power & Dam Construction, August 1976
4 H.Giraud & M.Beslin, "Optimisation d'avant-project d'une usine de basse chute",
Symposium A.I.R.H. 1968, Laussane
5 L. Austerre & J.de Verdehan, "Evolution du poid et du prix des turbines en
fonction des progres techniques", Compte rendu des cinquiemes journees de
l'hydraulique, 1958, La Houille Blanche
6 T.Belhaj, "Optimisation d'avant-project d'une centrale hydroelectrique au til de
l'eau" Symposium Maroc/CEE Marrackech 1989
7 Pe Than Line & P.Wibulswas, "The feasibility of using small centrifugal pumps
as turbines", Renewable Energy Review Journal, Vol 9, N°.1, June 1987
8 R. Hothersall, "Turbine selection under 1 MW. Cross-flow or conventional
turbine?" Hydro Review, February 1987
9 Gordon "A new approach to turbine speed", Water Power & Dam Construction
, August 1990
10 Seldon and Logan, "Variable speed pump/turbines", Hydro Review, August
1989
11 J.Cross & J.Burnet,"The development and use of an integrated databasesystem
for management and performance analysis of multiple automated hydroelectric
sites", Third International Conference on Small Hydro, Cancun, Mexico 1988.
12 J.L.Gordon "Powerhouse concrete quantity estimates", Canadian Journal Of
Civil Engineering, June 1983
7. Environmental impact and its mitigation
7.0 Introduction
Following the recommendations of the United Nations Conference in Rio on Envi-
ronment and Development, the European Union committed itself to stabilising its
carbon dioxide (C02 ) emissions, primarily responsible for the greenhouse effect. at
1990 levels by the year 2000. Clearly Europe will not be able to achieve this ambi-
tious target without a major increase in the development of renewable energy sources.
Renewable energy can make a significant contribution to C02 emissions reduc-
tion. The European Commission, through the ALTENER programme, proposed
as indicative objectives by 2005 to increase the contribution of renewable energy
sources from its current level of 4% in 1991 to 8% of primary energy consump-
tion and to duplicate the electricity produced by renewable sources. For small
hydropower this objective will require the European Union to increase the aver-
age annual renewable electricity production from 30 TWh to 60 TWh., and the
development of 9 000 MW in new schemes. The achievement of this objective
will imply an annual reduction of 180 million tonnes of C02 emissions.
However under present trends the above objective will not be attained so long as
the administrative procedures to authorise the use of water are not accelerated.
Hundreds, if not thousands, of authorisation requests are pending approval, the
delay being caused mainly by supposed conflict with the environment. Some envi-
ronmental agencies seem to justify -or at least excuse-this blockade on the grounds
of the low capacity of the small plants. Something is basically wrong when, to attain
the AL TENER objectives contemplated, in small hydro alone, the duplication of the
already existing 9 000 MW (the equivalent to nine last generation nuclear plants)
will be required. It seems to be forgotten that by definition renewable energies are
decentralised, and that for the time being only small hydro power plants and the
wind turbines can significantly contribute to renewable electricity production.
At the same time it should be accepted that, although through having no emis-
sions of carbon dioxide and other pollutants. electricity production in small hydro
plants is environmentally rewarding, the fact is that due to their location in sensi-
tive areas, local impacts are not always negligible. The significant global advan-
tages of small hydropower must not prevent the identification of burdens and
impacts at local level nor the taking of necessary mitigation actions.
On the other hand because of their economic relevance, thermal plants are
authorised at very high administrative levels, although some of their impacts can-
not be mitigated at present. A small hydropower scheme producing impacts that
almost always can be mitigated is considered at lower administrative levels, where
the influence of pressure groups-angling associations, ecologists, etc.-is greater.
It is not difficult to identify the impacts, but to decide which mitigation measures
should be undertaken it is not easy, because these are usually dictated by subjec-
tive arguments. It is therefore strongly recommended to establish a permanent
dialogue with the environmental authorities as a very first step in the design phase.
Even if this negotiation must be considered on a project by project basis it would
be convenient to provide a few guidelines that will help the designer to propose
mitigating measures that can easily be agreed with the licensing authorities.
202 Layman's Guidebook
7.1 Burdens and impacts identification
Impacts of hydropower schemes are highly location and technology specific. A high
mountain diversion scheme, being situated in a highly sensitive area is more likely
to generate impact that an integral low-head scheme in a valley. The upgrading and
extension of existing facilities, which will be given priority in Europe, generates im-
pacts that are quite different from an entirely new scheme. Diversion projects in
mountains use the large change in elevation of a river as it flows downstream. The
tailwater from the power plant then reenters the river, and entire areas of the river
may be bypassed by a large volume of water, when the plant is in operation.
Given below is an exhaustive description of possible impacts, based on European
studies 1 dealing with externalities, and made by groups of experts that perform
Environmental Impact Assessments. However is not certain that all or most of this
list of descriptions will be applicable to a specific project. In the list are identified the
event, persons or things affected, impact and priority at local and national levels.
Event Persons or Impact Priority
things affected
Electricity generation
During construction
Road construction
and road traffic general public noise low
accidents low
emissions low
wildlife noise disturbance low
collision's accidents medium
forest better access medium
future production loss medium
Accidents workers minor injuries medium
major injuries high
death high
Jobs created general public locally high
national medium
In operation
Flow alteration Fish loss of habitat high
Plants loss of habitat medium
Birds loss of habitat medium
Wildlife loss of habitat medium
Water quality contaminant dilution low
General public loss of waterfalls high
loss of recrea-
tional activities: medium
Aesthetic effects medium
Excessive noise workers On health medium
general public on health medium
Dams and damning Agriculture loss of grazing area high
Forestry loss future production high
Chapter 7. Environmental impact 203
Event Persons or Impact Priority
things affected
Aquatic ecosystem change of habitat high
General public local clime change negligible
global clime change
by methane not proven
Water quality eutrophication low
Cultural and
archeologic. effects loss of objects high
Electricity Transmission
On the construction
Accidents workers minor injuries medium
workers major injuries high
workers death high
Jobs created and
increased income General public local and national
employment benefits high
On the operation
Physical presence Forestry lost future production low
General public visual intrusion medium
Birds injury, death medium
Electromagnetic fields General public cancers
nonexistent
Accidents General public major injuries negligible
Death negligible
Accidents on
maintenance of
transmission lines Workers Minor injuries negligible
Major injuries negligible
Death negligible
Jobs created and
increased local income General public local and national
employment benefits medium
7.2 Impacts in the construction phase
Schemes of the diversion type, those using a multipurpose reservoir, and those
inserted on an irrigation canal or in a water supply system produce very different
impacts from one another, both from a quantitative and qualitative viewpoint. The
schemes making use of a multipurpose dam practically do not generate unfavourable
impacts, since it is understood that when the dam was built the necessary mitigating
measures were already incorporated, and in any case the addition of a powerhouse
located in its base shall not alter the ecological system. Schemes integrated in an
irrigation canal or in a water supply pipe system will not introduce new impacts over
those generated when the canal and the pipe system were developed. On the other
hand. diversion schemes present very particular aspects that need to be analysed.
204
7.2.1 Reservoirs
Layman's Guidebook
The impacts generated by the construction of a dam and the creation of the ad-
joining reservoir include, in addition to the loss of ground, the construction and
opening of construction roads, working platforms, excavation works, blasting and
even -depending of the dam size-concrete manufacturing plants. Other non-
negligible impacts are the barrier effect and the alteration of flow consequent to a
river regulation that did not exist before.
Otherwise the impacts generated by the construction of a dam do not differ from
those induced by a large scale infrastructure, whose effects and mitigating mea-
sures are well known.
7.2.2 Water intakes, open canals, penstocks, tailraces, etc.
The impacts generated by the construction of these structures are well known and
have been described in table 7.1: e.g. noise affecting the life of the animals; danger
of erosion due to the loss of vegetation consequent to the excavation work and
affecting the turbidity of the water; downstream sediment deposition, etc. To miti-
gate such impacts it is strongly recommended that the excavation work should be
undertaken in the dry season and the disturbed ground restored as soon as pos-
sible. In any case these impacts are always transitory and do not constitute a seri-
ous obstacle to the administrative authorisation procedure.
In view of its protective role against riverine erosion is wise to restore and rein-
force the river bank vegetation, that may have been damaged during construc-
tion of the hydraulic structures. It should be noted that the ground should be
revegetated with indigenous species, better adapted to the local conditions.
The impact assessment study should take count of the effects of jettisoning exca-
vated material in the stream, and the unfavourable consequences of a men living
during the construction period in an area usually uninhabited. This impact which
may be negative if the scheme is located in a natural park, would be positive in a
non-sensitive area by increasing the level of its activity. Vehicle emissions, exca-
vation dust, the high noise level and other minor burdens contribute to damage
the environment, when the scheme is located in sensitive areas. To mitigate the
above impacts the traffic operation must be carefully planned to eliminate unnec-
essary movements and to keep all traffic to a minimum.
On the positive side it should be noted that the increase in the level of activity in
an area usually economically depressed, by using local manpower and small
local subcontractors during the construction phase is to be welcomed.
Chapter 7. Environmental impact 205
7.3 Impacts arising from the operation of the scheme
7.3.1 Sonic impacts
The allowable level of noise depends on the local population or on isolated houses
near to the powerhouse. The noise comes mainly from the turbines and, when
used, from the speed increasers. Nowadays noise inside the powerhouse can
be reduced, if necessary, to levels of the order of 70 dBA and to be almost
imperceptible outside.
Concerning sonic impact the Fiskeby2 power plant in Norrkoping, Sweden, is an
example to be followed. The scheme owner wanted a maximum internal sound
level of 80 dBA inside the powerhouse at full operation. The maximum allowed
external sound level, at night, was set at 40 dBA in the surroundings of some
houses located about 100 metres away.
To reach these levels of noise it was decided that all the components -turbines,
speed increasers. asynchronous generators-were bought in one package from one
well-known supplier. The purchase contract specified the level of noise to be at-
tained in full operation leaving the necessary measures to fulfil the demands to the
manufacturer. The supplier adopted the following measures: very small tolerances
in the gear manufacturing; sound insulating blankets over the turbine casing; water
cooling instead of air cooling of the generator and a careful design of ancillary com-
ponents. As well as the usual thermal insulation, the building was provided with
acoustic insulation. As a consequence the attained level of noise varied between 66
dBA and 74 dBA, some 20 dBA lower than the average Swedish powerhouses.
Having a single supplier, the issue of responsibility was eliminated .
The external noise level reduction was obtained by vibration insulation of the pow-
erhouse walls and roof. The principle for the vibration reduction system was to let
the base slab, concrete waterways and pillars for the overhead crane be excited by
vibration from the turbine units. The other parts of the building such as supporting
concrete roof beams and precast concrete elements in the walls were supported by
special rubber elements designed with spring constants giving maximum noise re-
duction. For the roof beams special composite spring-rubber supporting bearings
(Trelleborg Novimbra SA W300) were chosen. A similar solution was chosen for the
precast wall components. Once built, the sound emission from the powerhouse
could not be detected from the other noise sources as traffic, sound from the water
in the stream, etc. at the closest domestic building
The underground powerhouse of Cavaticcio3 , located about 200 m from the Pi-
azza Maggiore, the historical heart of Bologna, has also merits in this respect. An
acoustic impact study undertaken on Italian schemes showed an average inter-
nal level of about 85-dbA. The level of noise in the vicinity of the houses near the
proposed powerhouse was 69 dbA by day and 50 dbA by night. The regulations
in force required that these values could not increase by more than 5 dbA during
the day and 3 dbA during the night. The measures carried out to fulfil the require-
ments were similar to those undertaken in Fiskeby:
• Insulation of the machine hall, the most noisy room, from the adjacent rooms by
means of double walls with different mass. with a layer of glass wool in between.
206 Layman's Guidebook
• Soundproofing doors
• Floors floating on 15 mm thick glass wool carpets
• False ceiling with noise deadening characteristics
• Heavy trapdoors to the ground floor, fitted with soundproof counter trapdoors
and neoprene sealing gaskets.
• Vibration damping joints between fans and ventilation ducts
• Low air velocity (4 m/sec) ducts
• Two silencers at the top and rear of the ventilation plant
• Inlet and outlet stacks equipped with noise traps
• Air ducts built with a material in sandwich (concrete, glass wool, perforated
bricks and plaster)
• Turbine rotating components dynamic balanced
• Water-cooled brushless synchronous generator
• Precision manufactured gears in the speed increaser
• Turbine casings and speed increaser casings strongly stiffened to avoid reso-
nance and vibrations
• Anchoring of the turbine by special anti-shrinking concrete to ensure the mono-
lithic condition between hydro unit and foundation block
• Turbine ballasting with large masses of concrete to reduce to a minimum the
vibration's amplitude
The underground ventilation has three main purposes: dehumidification of the
rooms to ensure a correct operation and maintenance of the equipment, fresh air
supply for the workers, removal of the heat generated by the various plant com-
ponents. Even with the maximum air volume circulation estimated at 7000 m3/
hour the air velocity in the air ducts never exceeds 4 m/sec.
It is true that the two above examples are very particular ones but they are included
here to show that everything is possible if it is considered necessary and the project
profitability admits a significant increase of the investment. It is also true that both
examples concern low head schemes implying the use of speed increasers; a high
mountain diversion scheme would permit the direct coupling of turbine and genera-
tor, so eliminating the component responsible for most of the vibrations.
7.3.2 Landscape impact
The quality of visual aspects is important to the public, who are increasingly reluc-
tant to accept changes taking place in their visual environment. A new condominium
in our neighborhood, an artificial beach built with sand coming from a submarine bed
-such things are rejected by a part of the population, even if, in many ways they
improve the environment including landscaping. The problem is particularly .acute in
the high mountain hydropower schemes or in schemes located in an urban area with
remarkable historical character. This concern is frequently manifested in the form of
public comments and even of legal challenges to those developers seeking to change
a well-loved landscape by developing a hydropower facility.
Each of the components that comprise a hydro scheme-powerhouse, weir, spill-
way, penstock, intake, tailrace, substation and transmission lines-has potential
to create a change in the visual impact of the site by introducing contrasting
forms, lines, colour or textures. The design, location, and appearance of any one
feature may well determine the level of public acceptance for the entire scheme.
Chapter 7. Environmental impact 207
Photo 7.1
Most of these components, even the largest, may be screened from view through
the use of landform and vegetation. Painted in non-cont rasting colours and tex-
tures to obtain non-reflecting surfaces a component will blend with or comple-
ment the characteristic landscape. An effort of creativity, usually with small effect
on the total budget, can often result in a project acceptable to all parties con-
cerned: local communities, national and regional agencies, ecologists etc.
The penstock is usually the main cause of "nuisance". Its layout must be carefully
studied using every natural feature -rocks, ground, vegetation -to shroud it and if
there is no other solution, painting it so as to minimise contrast with the background.
If the penstock can be buried , this is usually the best solution . Expansion joints and
concrete anchor blocks can then be reduced or eliminated; the ground is returned to
its original state and the pipe does not form a barrier to the passage of wild life.
The powerhouse, with the intake, the penstock tailrace and transmission lines must
be skilfully inserted into the landscape. Any mitigation strategies should be incorporat-
ed in the project, usually without too much extra cost to facilitate permit approval.
The examination of two schemes carefully designed to shroud their components will
· convey to potential designers a handful of ideas that should help to convince the envi-
ronmental authorities that there is no place so environmentally sensitive as to prevent
the development of a energy conversion process, so harmless and acceptable. The
Cordinanes scheme in Picos de Europa (Spain) and the scheme on the river Neckar,
located in the historical centre of Heidelberg (Germany) are considered below.
Cordinanes scheme
A small reservoir such as the one existing in Cordinanes (Photo 7.1) has some posi-
tive aspects. The existence of an almost stable level of water, and the tourist attrac-
tions (swimming, fishing , canoeing, etc.) that it provides counter balance its negative
effects.
Figure 7.1 shows a schematic view of the Cordifianes scheme. The weir is a rela-
t ively airy concrete structure, but b e ing 14 m high it is the most obtrusive campo-
•
• • • • • • •
• • • • • • • • • • • • • •
• • • • • • • • • • • • • • • •
•
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208
Pboto 7.2
Pboto 7.3
Layman's Guidebook
nent in the scheme (Photo 7.2). It needs to be so high because the water must
reach the level of an old tunnel that, once rebuilt, makes part of the diversion canal.
That is precisely the reason why the water level in the reservoir cannot vary by more
than two metres and confers to the pond the character of a picturesque lake.
And while speaking of dams the Vilhelmina dam in Sweden, constructed of soil
materials with an impervious core, should be mentioned (Photo 7.3). The surface
of the crest and the downstream slope are protected against erosion by layers of
large stones and boulders, which are embedded in reinforced concrete up to half
Chapter 7. Environmental impact 209
Photo 7.4
figure 7.1
their height. The downstream slope has a normal inclination of 1 :3 except for a
part, 40 m wide, where the inclination is 1:10. This design makes it possible for
fish to pass the dam up the river. This dam has another environmental advantage
since even with a small discharge it has the appearance of a natural rapid.
An open canal built in reinforced concrete leads, from the integral intake (Photo 7.4)
leaves, with a section of 2 x 2 .5 m and a length of 1335 m, entirely buried and
covered by a layer of revegetated terrain. Photographs 7.5, 7.6 and 7.7 show a
stretch of the canal in its three construction phases: land excavation reinforced
concrete canal and finished canal with the recovered vegetal layer. The presence
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • •
210
Photo 7. 5
Photo 7.6
Layman's Guidebook
in the photographs of an electrical pylon -the transmission line between the
villages of Posada de Valdeon and Cordinanes -confirms that it is the same site,
because otherwise it could be impossible to identify the buried canal.
Photos 7.8 and 7.9 show how the entrance to the tunnel has been shrouded. In the
first one the tunnel being rebuilt can be seen; in the second the canal connecting
with the tunnel has been covered, as has the rest of the canal, and the entrance to
the tunnel made invisible. It is possible to enter the tunnel through the canal for
inspection, after it is dewatered. In fact the tunnel already existed but was unfin-
ished due to the lack of means to cross the colluvium terrain . It has now been rebuilt
Chapter 7. Environmental impact 211
Photo 7.7
Photo 7.8
with a wet section of 2 x 1.80 m and with a 1:1000 slope which conducts the water
down to forebay, a perfect match with the surrounding rocks , and provided with a
semicircular spillway. From the forebay a steel penstock, 1.40 m diameter and 650
m long, brings the water to the turbines. In its first 110 m the pipe has a slope close
. to 60°, in a 2.5 x 2m trench excavated in the rock. The trench was filled with coloured
concrete to match the surrounding rocks. A trench excavated in the soil, conceals
the other 540 m which were covered by a vegetal layer later on.
Few metres before arriving at the powerhouse the pipe bifurcates into two smaller
pipes that feed two Francis turbines of 5000 kW installed power each. The power-
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • •
• • • • •
• • •
• • • • • • • • •
212
Photo 7.9
Photo 7.10
Layman's Guidebook
house (Photographs 7.10) is similar to the houses dotting the mountain.lts limestone
walls, its roof made of old tiles arid its heavy wood windows don't show its industrial
purpose. In addition the powerhouse is buried for two thirds of its height improving its
appearance. To conceal the stone work of the tailrace a waterfall has been installed.
The substation is located in the powerhouse (Photo 7.11 ), in contrast with the
usual outer substation (see photo 6.11 ), and the power cables leave the power-
house over the penstock, under the tunnel and over the open canal. Close to the
village where there are several transmission lines the power cables come to the
surface, to be buried again when the line transverses the north slope, a habitat of
a very rare bird species-the "urogayo" .
Chapter 7. Environmental impact 213
Photo 7.11
Photo 7.12
The Neckar power plant (Photo 7 .12) is located in the historical centre of Heidel-
berg4 and was authorised under the condition that it would not interfere with the
view of the dam built in the past to make the river navigable. The powerhouse,
built upstream of the dam, is entirely buried and cannot be seen from the river
bank. Photo 7.13 shows better than a thousand words the conceptual design ,
where stand two Kaplan pit turbines , and each one with a capacity of 1535 kW.
The investment cost was of course very high -about 3760 ECU/installed kW.
• • • • •• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • •
• • • • • • • • • • • • • • • • • • • • • • • • •
•
214 Layman's Guidebook
Photo 7.13
7.3.3 Biological impacts
7.3.3.1 In the reservoir
7.3.3.2 In the streambed
7.3.3.2.1 Reserved flow
Reservoir projects are very unusual in small hydropower although there are some
schemes that store enough water to operate the turbine only during the periods
of maximum electrical demand. Such operation is referred to as "peaking" or
"peak-lopping". In integral low head schemes peaking can result in unsatisfactory
conditions for fish downstream because the flow decreases when the generation
is reduced. The lower flow can result in stranding newly deposited fish eggs in
spawning areas. The eggs 1 apparently can survive periods of dewatering greater
than those occurring in normal peaking operation but small fish can be stranded
particularly if the level fall is rapid .
A substantial proportion of small hydro plants is of the diversion type, where wa-
ter is diverted from a stream, or a lake, into a hydroelectric plant perhaps kilometres
from the diversion point to take advantage of the gain in head. The reduction in
flow in the streambed between the point of diversion and the tailrace downstream
of the powerhouse may affect spawning, incubation, rearing, and the passage of
anadromous fish and of living space for adult fish. Then in high-flow periods the
water spills over the weir and floods the streambed. It is precisely such frequent
changes from semi-dry to wet that can ruin aquatic life .
There is here a clear conflict of interest. The developer will maintain that the
generation of electricity with renewable resources is a very valuable contribution
to mankind, by replacing other conversion processes emitting greenhouse gases.
The environmentalists will say, on the contrary, that the water diversion in the
stream represents a violation of the public domain .
In many countries reserved flow is regulated by a national law that usually only
defines a minimum value, but still permits local communities to impose flow val-
ues unreasonably higher. The determination of reserved flow can be critical for
the development of a site because too large a residual flow can make an other-
wise good project economically unfeasible .
All the dominant methodologies for the determination of the reserved flow, in
force in Europe and U.S.A., can be classified in two groups:
Chapter 7. Environmental impact 215
• Hydrological methods based on an analysis of the historic time-series and sub-
sumed in easily applicable empirical formulae.
• Hydro-biologic methods based on scientific criteria, applicable only to a particu-
lar river, and taking into account both hydrologic and biologic parameters.
In the first group there are, worthy of mention -
• Those using a certain percentile (1 0%, 15%, etc.) of the "module" or long term
average flow.
• Those using the Matthey formula (based on the 0 347 and 0 330 representing the
flows equalled or exceeded respectively 347 and 330 days in a year). This
criterion inspires the Swiss and Austrian legislation and is applied with small
modifications in the regional governments of Asturias and Navarra in Spain.
• The Tenant method (1976) developed for the Montana, Wyoming and Nebraska
rivers in the U.S.A., proposing minimum flows corresponding to different per-
centiles of the module, variable with the season of the year.
In the second group there are -
• The method of the habitat analysis
• The method of the wetted perimeter (Randolph and White 1984)
• The incremental analysis
• The method of microhabitats by Bovee and Milhous 1978 and Stainaker 1980
• The method of Nehring, that together with the last two ones are considered as
the harbingers of the PHASBIM methodology
• The MDDDR and ORB based on the research work of Cacas, Dumont and
Souchon (CEMAGREF) in France. They have been largely demonstrated in
the French Alps
• The DGB method developed by HydroM 5 (Toulouse 1989)
• The APU method developed in Spain by Garcia de Jalon and others
The hydrologic methods are simple and user friendly, but are not supported by a
scientific criterion and are consequently arbitrary.
A large majority of the hydro-biologic methodologies are based in the knowledge
of the physical structure of the river. For the past two decades the state-of-the-art
model for the depiction of the riverine habitat has been the Physical Habitat Simu-
lation Model (PHABSIM), based on one-dimensional hydraulic modelling and re-
quiring an abundance of empirical calibration data and the collection of these
data along transects of the river. PHABSIM is expensive and often non-transfer-
able to other streams
For the time being the legislation on a large majority of the E.U. member states is
based in hydrologic methodologies, and defines the reserved flow as a percentage
of the "module". In France the Law 84-512 (Loi du Peche, 29-06-84) requires, in
watercourses with a long-term average flow under 80 m3/sec, 10% of the module.
Watercourses with a long-term annual average flow over 80 m3/sec require 5% of
the module (Art 232.6 du Code Rural). Those values are a minimum to be re-
spected by the local authorities which can require higher values. In Germany there
are the Lander authorities which are responsible for the definition of the reserved
flow. In Nordhein-Westfallen for instance it can vary from 0.2 to 0.5 of the module,
and in Rheinland-Piatz 1% of the module, but in the west of the country where most
of the rivers have salmon higher values are required (usually the discharge corre-
216 Layman's Guidebook
spending to a 30% excedance or 0 110 ). In Italy there is no national norm and there
are the regions, which specify the required values. In Regione Piedmont it must be
10% of the instantaneous discharge and the turbines should be stopped when the
river flow drop below 120 1/sec in the Anza river, 5 1/s in the Rosso, and 30 1/s in the
Ollochia (Bolletino Ufficiale della Regione Piedmont 20/5/1987). In Portugal the flow
value, based on the hydrologic and biologic characteristics of the river, is defined by
the INAG in the authorisation act. In Austria the norm is based on the 0 347 , the flow
that is equalled or exceeded 347 days a year. In Spain the Water Act (Ley de Aguas,
02-08-1988) requires a minimum equivalent to the average summer flow but not
less than 21/s per square kilometre of catchment area, but the required value varies
with the regional government. In Navarra it is 1 0% of the module for the rivers with
cyprinids but in the salmon rivers is equivalent to the 0 330 and in Asturias it follows a
rather complicated formula.
Once the reserved flow is defined, the hydraulic devices ensuring the achieve-
ment of this target must be implemented. In France, for instance, a recent inves-
tigation undertaken in the Southern Alps found that in 36 of the 43 schemes
investigated, the reserved flow was not respected (in half of the schemes due to
the poor quality of the implemented devices). Accordingly it is strongly recom-
mended to take care of this aspect.
It must be underlined that if any of the biologic methods for the definition of the
reserved flow value is implemented, there is a possibility for the developer to
decrease the level of the required reserved flow, by modifying the physical struc-
ture of the streambed. Actually growing trees on the riverbanks to provide shad-
owed areas, deposit gravel in the streambed to improve the substratum, rein-
force the riverside shrubs to fight erosion, etc.
Figure 7.2 (reproduced from a paper by Dr. Martin Mayo) illustrates the kind of
coverage and refuge against the flow and sunshine or to elude a danger, fur-
nished to vertebrates and invertebrates by both natural and artificial elements.
The existence of caves and submerged cornices provides a safe refuge against
the attacks of a predator. Also the riverine vegetation. which when close to the
water provides shadow coverage used by fish of any size to prevent overheating
or to provide concealment in face of terrestrial predators (it must be said that the
most dangerous terrestrial predator is the freshwater fisherman). All these ele-
ments contribute to the concept that in the APU method is known as refuge coef-
ficient. By increasing its importance the required value of the reserved flow may
be diminished. In that way a better protection of the aquatic fauna can be com-
bined with a higher energy production.
7.3.3.2.2 Fish passes (upstream fish)
Anadromous fish, which spawn in fresh water but spend most of their lives in the
ocean, and catadromous fish, which spawn in the ocean and reach adulthood in
fresh water requires passages at dams and weirs. A great variety of fishpass
designs2 are available, depending on the species offish involved. Otherwise fresh-
water fish seem to have restricted movements.
Upstream passage technologies are considered well developed and understood
for certain anadromous species including salmon. According to OTA 1995 (Office
7 Env1r Chapter · · act . onmental unp 217
• • • • • • • • • • • •
• • • • • •
218
Photo 7.14
Layman's Guidebook
-!}-----~-----~-----~------~-----· Section A-A
figure 7.3
ofTechnology Assessment in the U .S.A.) there is no single solution for designing
upstream fish passageways. Effective fish passage design for a specific site re-
quires good communication between engineers and biologists and thorough un-
derstanding of site characteristics . Upstream passage failure tends to result from
a lack of adequate attention to operation and maintenance of facilities .
The upstream passage can be.provided for through several means: fish ladders, lifts
(elevators or locks), pumps and transportation operations. Pumps are a very contro-
versial method . Transportation is used together with high dams, something rather
unusual in small hydropower Schemes. Site and species-specific criteria and eco-
nomics would determine which method is most appropriate .
Fish ladders (pool and weir, Denil, vertical slots, hybrid etc.) can be designed to
accommodate fish that are bottom swimmers, surface swimmers or orifice swim-
mers. But not all kinds of fish will use ladders . Fish elevators a nd locks are favoured
for fish that does not use ladders
Chapter 7. Environmental impact 219
Photo 7.15
The commonest fish pass is the weir and pool fish way, a series of pools with water
flowing from pool to pool over rectangular weirs. The pools then play a double role :
provide rest areas and dissipate the energy of the water descending through the
ladder. The size and height of the pools must be designed as a function of the fish to
be handled. The pools can be supported by:
• Baffles provided with slots, so that both fish and bedload, pass through them
• Baffles provided with bottom orifices large enough to allow fish to pass
• Baffles provided both with vertical slots and bottom orifices
transversal section
and baffle ....--r;-;"' .. -. I o I .. -o I
. .-r _,L
"· J .. -.. -
o I
l .•l
•• J
:·;~ r .:~
r•.' . . -. . ...
•• ••• •• •••• J .•• ••• •• .• ........
perspective
figure 7.4
...... . .
longitudinal section
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
220 Layman's Guidebook
Pools separated by baffles with bottom orifices only do not have practical interest
because are limited to bottom orifice fish swimmers. Salmon do not need them
because they can jump over the baffle itself, and shads, for instance, are not bottom
swimmers. The system of rectangular weirs (figure 7.3) is the oldest one, but pre-
sents the inconvenience that when the headwater fluctuates the fishway flow in-
creases or decreases, resulting in a fishway with too much or too little flow. More-
over this type of ladder will not pass bedload readily and must be designed with
bottom orifices for this purpose. Photo 7.14 shows one of these ladders with a rustic
construction designed for salmon checking on a river in Asturias (Spain).
Photo 7.15 illustrates a fishladder with vertical slots and bottom orifices that usually
yields very good results. The shape and disposition of the baffles are shown in
perspective in the figure 7 .4; the width of the pools, for lengths varying between 1.8
and 3.0 m, varies from 1.2 m to 2.4 m . The drop between pools is in the order of 25
-40 em. Shads require a drop not bigger than 25 em. TComputer programs 6 optimise
the width and length of pools, the drop between pools and the hydraulic load.
The vertical slotted fishway (figure 7.5) is very popular in the U.S.A. but not well
known in Europe 7 . Through the baffle's vertical slot passes both fishes and bedload.
A standard model has pools 2.5-m wide, 3.3 m long with a slot 30 em wide. Support-
ers of this type of ladder praise its hydraulic stability even with large flow variations .
...............
.......
.........
··... .... .~· .--~
····· ...
...............
....... '-..... ..
fi ure 7.5
····· ...
'······--.......... .
.......... , ..... .
Chapter 7. Environmental impact 221
Photo 7.16
The Denil fish pass (Photo 7.16) consists offairly steep, narrow chutes with vanes in
the bottom and sides as illustrated in figure 7.6. These vanes dissipate the energy
providing a low-velocity flow through which the fish can easily ascend. This charac-
teristic allows Denils to be used with slopes up to 1 :5. They also produce a turbulent
discharge that is more attractive to many fish species than the discharge from pool-
figure 7.6
• • • • • • • • • • • • • • • •
• • • • • • • • • • • •
222
ow
qual
-
1sation ""'
"'
Layman's Guidebook
max. water level
Io
min. water level
fi ure 7 7
type fishpasses, and are tolerant of varying water depths. The ladder must be pro-
vided with resting areas after approximately 2-m. gain of elevation.
attraction flow
arrival
The Borland lock (figure 7. 7) is a relatively cheap solution to
transfer fish from the tailrace to the forebay in a medium
dam. The fish climb a short fish ladder to the bottom cham-
ber. Then the entrance to the bottom chamber is closed and
the shaft rising from it to the top of the dam becomes filled
with the water flowing down from the forebay through the
top chamber. Once filled, the fish that are attracted by this
flow are close to the forebay level into which they can swim.
~ 8
~ '-:t;
'-;
~ ~
~
-~
~
1\,
~
/ punched
plate
'-./
fish ~water o
entrance
figure 7.8
In higher dams the best solution is to install a lift specifically
designed for this purpose. EDF in France has a wide experi-
ence with these lifts. The Golfech lift for instance when it was
commissioned in 1989 made it possible to pass twenty tonnes
of shad (about 66 000 individuals) that were blocked at the
base of the dam. Otherwise, the only possible solution is to
trap the fish at the base and transport them safely upstream.
These devices are discussed in reference 4 • All that is needed
is a small fishpass to bring the fish from the tailrace to the
trap. There, by mechanical means the fish are concentrated
in a trolley hopper, and loaded onto a truck. Eventually the
trolley hopper carries them directly over the dam's crest via a
cableway and they are discharged into the reservoir.
The most important element of a fish passage system, and the
utlet most difficult to design for maximum effectiveness, is the fish-
attraction facility. The fish-attraction facility brings fish into the
lower end of the fishpassage 3 and should be designed to take
advantage of the tendency of migrating fish to search for strong
currents but avoid them if they are too strong. The flow must
Chapter 7. Environmental impact
Photo 7.17
223
max. water level
Io
min. water level
fi ure 7 7
therefore be strong enough to attract fish away from spillways and tail-
races. The flow velocities at the entrance of the fish pass vary with the
type of fish being passed, but for salmon and trout, velocities from two
to three meters per· second are acceptable. A lack of good attraction
flow can result on delays in migration, as fish become confused, milling
around looking for the entrance. If necessary, water must be pumped
into the fishpass from the tailwater areas, but usually enough water
can be taken at the upstream intake or forebay to be directed down the
fishpass. Dealing with salmon the attraction flow should be maintained
between 1 m/s and 2 m/s, although if the water is too cold -less than
8°-or too hot -more than 22°-the speed must be decreased because
fish become lazy and do not jump. Water can be injected just at the
entrance of the fishway avoiding the need to transverse all its length
(figure 7.8)
The entrance to the fish passage should be located close to the weir
since salmon tend to look for the entrance by going around the
obstacle. In low-head integrated schemes the entrance should be
in the bank close to the powerhouse as illustrated schematically in
figure 7.9 and shown in photo 7.17.
The upstream outlet of the fish passage should not be located in an
area close to the spillway, where there is a danger of being sent
back to the base of the dam, nor in an area of dead circulating
waters where the fish can get trapped. Fishpassages must be pro-
tected from poachers, either closing it with wire mesh or covering it
with steel plates.
The use of fish pumps for fish passage at dams is controversial
and largely experimental. This technology is relied upon in aquae-
• • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • •
224 Layman's Guidebook
ulture for moving live fish. Several pumps are in the market and new ones are
being developed. Pumping of the fish can lead to injury and de-scaling as a
result of crowding in the bypass pipe.
7.3.3.2.3 Fishpasses (downstream fish)
In the past downstream migrating fish passed through the turbine. The fish-kill
associated with this method varies from a few percent to more than 40% de-
pending on the turbine design and more specifically on the peripheral speed of
the runner. In a Francis turbine increasing the peripheral runner speed from 12
m/sec to 30 m/sec increases the percentage mortality from 5% to 35%. Francis
turbines, due to their construction characteristics cause greater mortality than
Kaplan turbines. Bulb turbines reduce mortality to less than 5%8 .
Apparently head is not a decisive factor. A turbine working at a head of 12 meters
produces the same mortality as one working at a head of 120 m. The elevation of
the runner above tailwater is a very important factor, quite apart from the effect of
cavitation. The more efficient a turbine is, the less mortality it produces. A turbine
working at rated capacity consequently causes less mortality than one working at
partial load. Mechanical injuries by collision against solid bodies -guide vanes or
turbine blades-, exposure to subatmospheric pressures and shear effects produ-
ced at the intersections of high velocity flows in opposite directions are the main
causes of mortality.
Physical barrier screens are often the only approved technology to protect fish
from turbine intake channels, yet the screens are very expensive and difficult to
maintain. Factors to be considered in a diverting system include the approach
velocity to the screen (depending of the fish size the approach velocity should
fluctuate around 1.4 m/s ); adequate lateral flow to carry fish and debris past the
screen; and facilities for continuous or periodic cleaning of the screen to ensure
brush carriage
electric winch
j(
li:
pulleys
fish bypass
figure 7.10
Chapter 7. Environmental impact
trash rack
---~ stream flow ••mmllmmm11mm!lmmmm
jyV 11 1 scceens U
diversion flow
figure 7.11
225
uniform velocity distribution through them. But the success of any screening sys-
tem relies on means being provided to take fish from the screen to a safe haven.
The simplest solution is a static standard screen -made of 2mm-punched steel
sheet with 4-mm holes on 5.5-mm centres. Such a screen must be placed behind
the trash rack at the entrance to the penstock. Usually it is located at right angles
with the flow but, like this location is susceptible to clogging. It is better to incline
it to the flow, downsloping and ending in a trough so that fish slide in a small
quantity of water down the screen and into the trough, while most of the water
flow through the screen. There are also examples of upsloping and humpback
designs but the downslope is the most effective for self-cleaning. In some instal-
lations a brush, driven by a cable and pulley mechanism and powered by a re-
versible motor continuously clean the screen (figure 7.1 0). The screen can also
be manufactured of stainless steel wire or with synthetic monofilament. The screen
made with synthetic monofilament is too flexible to be cleaned by mechanical
brushes, but it can be cleaned by flow reversal.
In the classic intake, with its longitudinal axis perpendicular to the river axis. it is
recommended to align the screen with the riverbank, so the fish follow the flow
line without touching it (figure 7.11 ). If necessary the riverbanks will be gunited to
avoid eddy formations where the fish could get trapped and even be attacked by
predators. Although this configuration does not seem to be favourable from a
hydrodynamic viewpoint, the head loss generated by the change in direction of
the flow is irrelevant. If the screen cannot be located at the entrance a bypass,
such as the one illustrated by figure 7 .12, should be implemented to send back
the fish to the river.
For discharges over 3 m3/sec fixed screens, due to their large surface areas are
difficult to install. In those cases the use of vertical travelling screens or the rotary
horizontal drum screens may be recommended. The travelling screens are me-
chanically more complicated but need less space for their installation.
A typical example of a screen not needing a mechanical cleaning mechanism is
the Eicher screen (figure 7.13). This design9 uses an upsloping elliptical screen of
wedge wire, perforate plate or other screening material, within a penstock, and
operates under pressure, so that most fish and trash tend to move along near the
226
from intake
brush
ass-=-e=mtt:-:y-...
Plan
Section A-A
figure 7:12
Layman's Guidebook
+ fish return
to the river
penstock ...
top of the penstock, having little contact with the screen. A relatively high water
velocity moves both fish and trash through the penstock and out of a bypass
parallel to the central flow in a few seconds. Full-scale tests of the Eicher Fish
Screen performed in 1990 showed the design to be 99% effective in bypassing
penstock
-
shaft for
rotating screen
screen in working
position
screen in operating
position cleaning water
outlet
figure 7.13
to the turbine
Chapter 7. Environmental impact 227
salmon smolts without mortality 6 The Eicher screen does not require space in
the forebay area, and because it is installed inside the penstock, does not alter
the appearance of the installation.
Another screen type tolerating higher approaching velocities is the Modular Inclined
Screen (MIS) developed under the EPRI 10 sponsorship. It is a modular design easy
to adapt to any scheme, by adding the necessary number of modules. The MIS
module (figure 7.14) consists of an entrance with a trash rack, dewatering stop logs,
an inclined wedgewire screen set at a shallow angle of 10 to 20 degrees to the flow,
and a bypass for diverting fish to a transport pipe. The screen is mounted on a pivot
shaft so that it can be cleaned via rotation and backflushing. The module is com-
pletely closed and is designed to operate at water velocities ranging from 0.6 m/sec
to 3.3 m/sec. The module, depending on the screen angle selected, can screen a
maximum of 14 to 28 m3/sec of water. For bigger discharges it is possible to add
more modules. The results of hydraulic model tests demonstrated that the MIS en-
trance design created a uniform velocity distribution with approach flows skewed as
much as 45 degrees. The uniform velocity distribution of the MIS is expected to
trash rack
,..~ ' ~ ~ ............ :-
fish return
to the river
screen positioned
or cean1ng
flow
screen in
~ ~:: ~ ~ ~ war mg position -....... -......
~ ~'
figure 7.14
228 Layman's Guidebook
facilitate fish passage at higher velocities that can be achieved using any other
currently available type of screen. Passage survival was calculated as the portion of
fish that were diverted live and survived a 72 hours holding period. Passage sur-
vival generally exceeded 99% at velocities of 1.83 m/sec. This survival rate was
maintained up to 3.05 m/sec for several test groups including Coho salmon, Atlantic
salmon smolts and brown trout.
Recently an innovative self-cleaning static intake screen, that does not need power,
has been used for fish protection. The screen uses the Coanda 11 effect, a phe-
nomenon exhibited by a fluid, whereby the flow tends to follow the surface of a
solid object that is placed in its path. In addition, the V shaped section wire is
tilted on the support rods, (figure 7.15) producing offsets which cause a shearing
action along the screen surface. The water flows to the collection system of the
turbine through the screen slots, which are normally 1 mm wide. Ninety per cent
of the suspended solid particles, whose velocity has been increased on the
acceleration plate, pass over the screen thus providing excellent protection for
the turbine. Aquatic life is also prevented from entering the turbine through the
slots. In fact the smooth surface of the stainless steel screen provides an excel-
lent passageway to a fish bypass. The screen can handle up to 250 1/s per linear
meter of screen. A disadvantage of this type of screen is that it requires about 1 to
1.20 m. of head in order to pass the water over the ogee and down into the
E
0
N
, ,
,
figure 7. 15
Chapter 7. Environmental impact 229
Photo 7.18
collection system. This can be uneconomic in low head systems. Photograph
7.18 shows a Coanda screen supplied by DULAS Ltd 12 (e-mail dulas@gn ape org).
The photo is published by courtesy of this company.
Circular screens 8 make use of wedge-wire in short stubby pods (figure 7.16).
The pods can be placed under the streambed to collect water in a manner similar
to an infiltration gallery. The slot spacing between the wedge wires controls the
size of the fish that are kept out of the turbine. Several circular screens can be
disposed to feed water to the penstock, collecting relatively large volumes of
water with a reasonable head loss. Compressed air is used for cleaning.
Behavioural guidance systems and a variety of alternative technologies to di-
vert or attract downstream migrants have been recently object of studies by the
Electric Power Research Institute (EPRI). These technologies include strobe lights
for repelling fish, mercury lights for attracting fish, a sound generating device
known as "hammer" for repelling fish as well as quite a number of electrical guid-
ance systems. It has not yet been demonstrated that these responses can be
directed reliably. Behavioural guidance techniques are site-and species-specific
and it appears unlikely that behavioural methods will perform as well as fixed
screens over a wide range of hydraulic conditions13 •
As manifested by Mr. Turpenny of Fawley Aquatic Research Laboratories Ltd
U.K.14, "the disadvantage of behavioural screens over conventional mechanical
screens is that they do not exclude 100% of fish, whereas a mechanical screen of
sufficiently small aperture will do so. Typical efficiencies for behavioural barriers
range from 50% to 90%, depending upon type and environmental and plant con-
ditions. Most fish penetrating the barrier are likely to go on to pass through the
turbine, thereby putting them at risk of injury."
• • • • • • • • • • • • • • • • • • • ••
• • • • • • • • • • • •
230 Layman's Guidebook
flow watercourse
~tack
figure 7.16
Figure 7.17 illustrates the disposition of a system of underwater acoustic trans-
ducers which transmit their sound into a rising bubble curtain to create a wall of
sound to guide fish out of the turbine passage. This type is known as "BioAcoustic
Fish Fence" (BAFF) and has shown a 88-100% typical fish exclusion efficiency.
Trapping collection and trucking systems are similar to these employed with
upstream migrating fish. The fish must be collected in a trap to be transported in
tanks'5 . However the trapping and collecting operation with downstream migrat-
ing fish presents more difficulties than with upstream fish because there are not
high velocity flows to attract them. Downstream fish must be collected with fish-
ing nets fabricated with synthetic monophilament, or with travelling vertical screens
of the same material. The collected fish show symptoms of stress and superficial
injuries that make the system questionable. However these systems are the only
ones ensuring the exclusion of eggs and larvae, although seem to be proved that
both eggs and larvae pass through reaction turbines undamaged.
Chapter 7. Environmental impact 231
weir
fish ladder •--t--fish return bypass
~~3±1±~ sonic a d . n a,r bubbi
es barriers
water ---powerhouse
.,... intake
.....
figure 7.17
Bypass routes must be provided to allow fish to move from the area in front of a
physical barrier back to the river.
The screens located at the intake entrance do not need any return conduit because
fish are entrained by the water flow and return to the river usually over the spillway
which is of course less dangerous than the turbines, although it also can be damag-
ing. Surprisingly, high spillways are not necessarily more dangerous for fish than
low ones. Terminal velocity, as demonstrated by dropping salmon from helicopters
into a pound 1 •• is reached after about 30 meters of fall, and remains constant there-
after. Eicher mentions an experimental ski-jump spillway, which throws the fish out
in free fall to a pool 80 m below with a mortality rate reduced to virtually zero.
When the screen is located in the intake downstream of the entrance, a bypass
returning the fish to the river is needed. According to behavioural characteristics
migrating downstream fish cannot be expected to swim back upstream to find
the entrance, which must be located at the downstream end of the screen, as-
suming the screen is inclined in the direction of the flow. Fish are frequently reluc-
tant to move into small size entrances A minimum bypass entrance of 45 em is
recommended, especially when dealing with juvenile salmonids. It would be pref-
erable that the entrance width could be adjustable by the use of fabricated metal
inserts to reduce the size of the operating opening. The bypass entrance design
should provide for smooth flow acceleration into the bypass conduit with no sud-
den contractions, expansions or bends.
For returning fish from the bypass entrance to the river, fully close conduits or
open channels can be used. Fish do not like to enter in conduits with abrupt
contrast in lighting. Open channels are better suited for that role. Internal sur-
faces should be very smooth to avoid fish injury. High-density polyethylenes and
PVC are excellent materials for bypass conduits.
• • • • • • •
• • • • • •
•
• • • • • • • • • • • • • • • •
232
Photo 7.8
7.3.3.3 In the terrain
Layman's Guidebook
Abrupt changes in section should be avoided due to their associated turbulence
and pressure changes. In full flow conduits pressures below atmospheric should
be avoided because they can injure or even kill fish. Air entrainment in a full flow
conduit generates hydraulic turbulence and surging thus avoiding gas supersatu-
ration in the water that can be detrimental to fish. Conduit discharge velocities
should not be so high relative to the ambient velocities in the outfall as to create
shear forces that can injure fish. Velocities close to 0.8 m/sec are recommended .
Canals have always constituted an obstacle to the free passage of animals. To
avoid this, nowadays open canals are entirely buried, and even revegetated so
they do not represent any barrier. In any case in very sensitive areas, as in cer-
tain areas of Asturias, where the brown bear still lives, the environmental agen-
cies tend to take extreme measures and even to refuse water use authorisation .
7.3.4 Archaeological and cultural objects
In the construction phase the developer should take great care to avoid damage
to archaeologic or cultural objects of a certain value. This may be particularly
critical in schemes with reservoirs, where valuable objets or even historical monu-
ments can be submerged. In the Cordirianes scheme mentioned above, during
the excavation works to found the powerhouse, a middle age burial place was
found. With the aid of government experts the place was arranged as illustrated
in photo 7.19 .
Chapter 7. Environmental impact 233
Photo 7.20
7.4 Impacts from transmission lines
7 .4.1 Vi s ual impact
Above ground transmission lines and transmission line corridors will have a nega-
tive impact on the landscape. These impacts can be mitigated by adapting the
line to the landscape, or in extreme cases burying it.
The optimal technical and economic solution for a transmission line routing is that
which will often create the more negative aesthetic impacts. To achieve optimal
clearance from the ground the pylons are placed on the top of the hills, constitut-
ing a very dominating element of the landscape, A minimum of bends in the route
will reduce the number of angle and ordinary pylons and therefore reduce its
cost. Aesthetically neither a high frequency of bends, nor straight routes that are
made without consideration for the terrain and landscape factors are preferred .
In sensitive mountain areas where schemes are developed transmission lines
can dominate the landscape and therefore damage the beauty of the scenario. It
must be remarked that transmission lines exist even without the existence of
hydropower schemes. Villages even if they are high in the mountain require elec-
tricity to make life livable, and electricity, unless generated by photovoltaic sys-
tems, requires transmission lines. It is true that with a right siteing of the lines in
relation to larger landscape forms and a careful design of the pylons the impact
can be relatively mitigated. Other times, like in Cordiiianes, both stepping up
transformer substation and tra.nsmission lines are concealed from public view
and the situation entirely improved, but it is an expensive solution that only can
be offered if the scheme is profitable enough.
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
234
7 .4.2 Health impact
7 .4.3 Birds collisions
7.5 Conclusions
Layman's Guidebook
In addition to the visual intrusion some people may dislike walking under trans-
mission lines because of the perceived risks of health effects from electromag-
netic fields. Apart from the fact that this risk is only perceived in high voltage
transmission lines, and never is the case in a small hydropower scheme, after
several years of contradictory reports, the experts nowadays consider that living
in areas close to high voltage transmission lines does not increase the risk of
cancer, and more specifically of infant leukaemia. That is the conclusion of a
recent Cancer Institute report published in the prestigious medical review "The
New England Journal of Medicine". The report insists that it is time to stop wast-
ing resources on this type of study and focus research to discovering what are
the real biological causes of leukaemia.
Although birds are morphologically and aerodynamically adapted to fly, there are
limits in respect of their capability to avoid artificial obstacles. Areas where the
electric conductors are located close to the treetops seem to be high-risk wire
strike sites. Few collisions 26' seem to take place where it is a dense forest on one
or both sides of the line corridor. Wire strikes are especially frequent in areas
where the distance to the forest edge is about 50 m or more on one or both sides
of the line. However the only way to completely avoid bird collisions is under-
ground cabling. That is the solution adopted in Cordinanes to traverse the north
slope where the "urogayo", a rare bird specimen in danger of extinction, lives .
Electrocution takes place whenever a bird touches two phase conductor or a
conductor and an earth device simultaneously. This restricts the problem to power
lines carrying tensions below 130 kV (transmission lines in small hydropower
schemes are always 66 kV or lower). Similar to the collisions with the power
lines. electrocution has biological, topographical and technical factors, although
these are deeply interwoven and not easily separated. Humidity is also an im-
portant factor
A visit to Cordinanes will show to any bona fide person that a small scale hydro-
power scheme can be developed in a natural park without this being negatively
affected, and at the same time avoiding the emission on other part of the country
of thousands of tonnes of greenhouse gases and inducing acid rains.
Chapter 7. Environmental impact 235
Bibliography
1 European Commission-"Externalities of Energy-Volume 6 Wind and Hydro"
EUR 16525 EN
2 S. Palmer. "Small scale hydro power developments in Sweden and itd envi-
ronmental consequences". HIDROENERGIA 95 Proceedings. Milano
3 F. Monaco, N. Frosio, A. Bramati, "Design and realization aspects concerning
the recovery of an energy head inside a middle european town",
HIDROENERGIA 93, Munich
4 J. Gunther, H.P. Hagg, "Volltandig Oberflutetes Wasserkraftwerk Karlstor/
Heidelberg am Neckar", HIDROENERGIA 93, Munich
5 M. Mustin and others, "Les methodes de determination des debit reserves;
Analyse et proposition d'une methode pratique; Le debit de garantie biologique
(DGB)", Report pour le Comite EDF Hydroecologie.
6 Santos Coelho & Betamio de Almeida, "A computer assisted technique for
the hydraulic design of fish ladders in S.H.P." HIDROENERGIA 95, Munich
7 Osborne,J. New Concepts in Fish Ladder Design (Four Volumes), Bonneville
Power Administration, Project 82-14, Portland, Oregon, 1985
8 Department of Energy, Washington, USA. "Development of a More Fish-Tol-
erant Turbine Runner" (D.O.E.IID.10571)
9 George J.Eicher "Hydroelectric development: Fish and wild life considerations"
Hydro Review Winter 1984
10 Winchell, F. C. "A New Technology for Diverting Fish Past Turbines", Hydro-
Review December 1990
11 Dulas Ltd. Machynllet, Powys, Wales SY20 8SX. e-mail dulas@gn.apc.org .
"Static screening systems for small hydro" HIDROENERGIA97 Conference
Proceedings, page 190
12 James J.Strong. "Innovative static self-cleaning intake screen protects both
aquatic life and turbine equipment" HYDR0'88 Conference papers.
13 D.R. Lambert, A. Turpenny, J.R. Nedwell "The use of acoustic fish deflection
systems at hydro stations", Hydropower&Dams Issue One 1997
14 A. Turpenny, K. Hanson. "Fish passage through small hydro-turbines: Theorical,
Practical and Economic Perspectives". HIDROENERGIA 97, Conference Pro-
ceedings, page 451.
15 Civil Engineering Guidelines for Planning and Designing Hydroelectric Devel-
opments, Volume 4, American Society of Civil Engineers, New York
236 Layman's Guidebook
8 Economic Analysis
8.0 Introduction
An investment in a small hydropower scheme entails a certain number of payments,
extended over the project life, and procures some revenues also distributed over
the same period. The payments include a fixed component-the capital cost, insur-
ance, taxes other than the income taxes, etc-and a variable component -operation
and maintenance expenses-. At the end of the project, in general limited by the
authorisation period, the residual value will usually be positive, although some ad-
ministrative authorisations demand the abandonment of all the facilities which re-
vert to the State. The economic analysis compares the different possible alterna-
tives to allow the choice of the most advantageous or to abandon the project
From an economic viewpoint a hydropower plant differs from a conventional ther-
mal plant, because its investment cost per kW is much higher but the operating
costs are extremely low, since there is no need to pay for fuel.
The economic analysis can be made either by including the effect of the inflation or
omitting it Working in constant mpnetary value has the advantage of making the
analysis essentially independent of the inflation rate. Value judgements are easier
to make in this way because they refer to a nearby point in time which means they
are presented in a currency that has a purchasing power close to present experi-
ence. If there are reasons to believe that certain factors will evolve at a different rate
from inflation, these must be treated with the differential inflation rate. For instance,
if we assume that the electricity tariffs as a consequence of deregulation will grow
two points less than inflation, while the remaining factors stay constant in value, the
price of the electricity should decrease by 2% every year.
8.1 Basic considerations
The estimation of the investment cost constitutes the first step of an economic
evaluation. For a preliminary approach the estimation can be based on the cost
of similar schemes 12 • IDAE (lnstituto para Ia Diversificaci6n y Ahorro de Energfa,
Spain) in its recent publication "Minicentrales Hidroelectricas" 3 analyses the cost
of the different components of a scheme -weir, water intake, canal, penstock,
power-house, turbines and generators, transformers and transmission lines.
Fonkenelle also has published nomograms, but only for low-head schemes•.
The Departamento Nacional de Aguas e Energia Electrica (DNAEE) has written
a computer program, FLASH, that is probably the best program for small hydro
feasibility studies 5 . Under a contract with the European Commission (DG XVII),
the French consultant ISL is developing a computer program, running in Win-
dows 95 and NT, that includes an important database for the estimation of invest-
ment costs on small-hydro schemes.
D.R. Miller, ESHA Vice-President has produced a computer program, to estimate
the buy-back price necessary for guaranteeing an acceptable return on invest-
ment in small hydro, that includes an estimation of the investment cost The fol-
lowing table calculates the investment cost:
• • • • • • • •
• • • • • •
• • • • • • • • • • • • • • • • • • •
•
238
Plant capacity (kW)
250 >P> 200
500 >P> 250
1000 >P> 500
2000 >P> 1 000
5000 >P> 2000
10000>P> 5000
Layman's Guidebook
cost (ECU)
200 x 2250 + balance x 2250 x 0,548165
250 x 2050 + balance x 2050 x 0.824336
500 x 1870 + balance x 1870 x 0,817034
1000 x 1700 + balance x 1700 x 0.765111
2000 x 1500 + balance x 1500 x 0.777918
5000 x 1300 + balance x 1300 x 0,661133
The investment cost of a scheme with a capacity of 2650 kW will have an invest-
ment cost given by:
2000 x 1500 + 650 x 1500 x 0.777918 = 3758470 ECU or 1418 ECU/kW installed.
The above table doesn't take into account the head, and should be considered
useful only for medium and high head schemes.
In his communication to HIDROENERGIA'97 on the THERMIE programme, H. Pauwels
of the DG XVII (Energy Technology Department), showed the enclosed graph,
summarising data for schemes presented to the above programme, which correlates
the investment cost .in ECU/kW installed for different power ranges and heads .
IT Power LTD Stroom Lijn, lEE Kassel1997, presented also to HIDROENERGIA'97
a computer program, "Hydrosoft", which includes a set of curves correlating the
Chapter 8. Economic analysis 239
investment cost in ECU/kW and the installed capacity (between 100 kW and 10
MW) for low head schemes, with 2, 3, 4 and 5 m head. The curves are reproduced
here up to a maximum capacity to 2 MW. The computer program, of course, gives
· the cost directly against the installed capacity and head. A table with numerical data
is also provided and makes calculation less dependent on drawn curves.
However, as a cost estimate is essential for economic analysis, it is necessary as
a second step, to make a preliminary design including the principal components
of the scheme. Based on this design, budget prices for the materials can be
obtained from suppliers. Such prices cannot be considered as firm prices until
specifications and delivery dates have been provided. This will come later, during
the actual design and procurement process.
Do not forget that in a plant connected to the grid, the investment costs of the
connection line should be included, because according to various national regu-
lations this line, although it sometimes becomes the property of the grid owner, is
always built at the expense of the SHP developer. A plant close to the grid con-
nection point will be always cheaper than one installed far from it. The same
reasoning can be applied to telephone lines. In an unmanned plant the telephone
line to transmit telemetry and alarm signals is frequently used although occa-
sionally it might be cheaper to use the transmission line itself to establish a radio
link or use a digital cellular telephone provided there is good coverage.
r~,---~~ -"' -f"" 1\ l \
·;moo . -···t~< .
'3000 +---+_:.,+--+-:---!--if-+-+--+-+--1---l--ir---t--+--+-+--t-+-t---: l ,~~--+·"-f·-·""""""··r--+--!--1--f--+-..._,_-+L-.. --~i ~-L_ 12£A]
fd 2000 · .... a1.+-t-t-~-1-t-t-t-r4F~~t···=·~-~~~
o ~~~~~+n~~~~~~~n+~~-r~~~~~~~~~~~~~~~~~
0~~~-~-~-~~~~~~~~~~~~
C.i'*J«IM
·---~~-----~-------=·-· --·-------~'-· ·=--
• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
240 Layman's Guidebook
Total capacity capacity /Turbine 2m 3m 4m 5m
100 50 4023 3447 3097 2854
200 100 3344 2865 2574 2372
300 150 3004 2574 2313 2131
400 200 2786 2386 2145 1976
500 250 2628 2251 2023 1864
600 300 2506 2147 1929 1778
700 350 2407 2063 1853 1708
800 400 2326 1992 1790 1650
900 450 2256 1933 1737 1600
1000 500 2196 1881 1690 1558
2000 1000 1839 1575 1416 1304
3000 1500 1659 1422 1277 1177
4000 2000 1543 1322 1188 1095
5000 2500 1460 1251 1124 1036
6000 3000 1395 1195 1074 990
7000 3500 1342 1150 1033 952
8000 4000 1299 1113 1000 921
9000 4500 1261 1081 971 895
10000 5000 1229 1053 946 872
8.2 Financial mathematics
An investment project considers revenues and expenses that take places in very
different periods. In any economic analysis involving economic value there are
always two variables, money and time. A certain amount of money paid or re-
ceived at a point in time has a different value if it is paid or received at another
point in time. Money can be invested during a certain period of time with the
guarantee of a certain benefit. The term "present value" describes a monetary
amount now, i.e. at a point in time other than that at which it is paid or received.
For a discounting rater, the cost C, (or the benefit B;), disbursed or received in the
year i, is discounted to the year 0 by the equation:
(8.1)
The fraction within square brackets is known as the "present value factor" (PVF).
To find the comparable value of a given sum of money if it were received, or
disbursed, at a different time, the above formula may be used, or the correspond-
ing PVF as given in Table 8.1, may be multiplied by the given sum. For instance,
if the investor's opportunity earning potential is 8%, 1500 ECU to be received in 5
years from now would be equivalent to receiving now,
1 1.500 X----;;-
(1+0.1
1,020.9 ECU
Cash flows occurring at different times can be converted to a common basis,
Chapter 8. Economic analysis 241
Table 8.1
Values of PVF for various time periods n and opportunity cost r
single payment uniform series of payments
n 6% 8% 10% 12% 6% 8% 10% 12%
1 0.9434 0.9259 0.9091 0.8929 0.9434 0.9259 0.9091 0.8929
2 0.8900 0.8573 0.8264 0.7972 1.8334 1.7833 1.7355 1.6901
3 0.8396 0.7938 0.7513 0.7118 2.6730 2.5771 2.4869 2.4018
4 0.7921 0.7350 0.6830 0.6355 3.4651 3.3121 3.1699 3.0373
5 0.7473 0.6806 0.6209 0.5674 4.2124 3.9927 3.7908 3.6048
6 0.7050 0.6302 0.5645 0.5066 4.9173 4.6229 4.3553 4.1114
7 0.6651 0.5835 0.5132 0.4523 5.5824 5.2064 4.8684 4.5638
8 0.6274 0.5403 0.4665 0.4039 6.2098 5.7466 5.3349 4.9676
9 0.5919 0.5002 0.4241 0.3606 6.8017 6.2469 5.7590 5.3282
10 0.5584 0.4632 0.3855 0.3220 7.3601 6.7101 6.1446 5.6502
11 0.5268 0.4289 0.3505 0.2875 7.8869 7.1390 6.4951 5.9377
12 0.4970 0.3971 0.3186 0.2567 8.3838 7.5361 6.8137 6.1944
13 0.4688 0.3677 0.2897 0.2292 8.8527 7.9038 7.1034 6.4235
14 0.4423 0.3405 0.2633 0.2046 9.2950 8.2442 7.3667 6.6282
15 0.4173 0.3152 0.2394 0.1827 9.7122 8.5595 7.6061 6.8109
16 0.3936 0.2919 0.2176 0.1631 10.1059 8.8514 7.8237 6.9740
17 0.3714 0.2703 0.1978 0.1456 10.4773 9.1216 8.0216 7.1196
18 0.3503 0.2502 0.1799 0.1300 10.8276 9.3719 8.2014 7.2497
19 0.3305 0.2317 0.1635 0.1161 11.1581 9.6036 8.3649 7.3658
20 0.3118 0.2145 0.1486 0.1037 11.4699 9.8181 8.5136 7.4694
21 0.2942 0.1987 0.1351 0.0926 11.7641 10.0168 8.6487 7.5620
22 0.2775 0.1839 0.1228 0.0826 12.0416 10.2007 8.7715 7.6446
23 0.2618 0.1703 0.1117 0.0738 12.3034 10.3711 8.8832 7.7184
24 0.2470 0.1577 0.1015 0.0659 12.5504 10.5288 8.9847 7.7843
25 0.2330 0.1460 0.0923 0.0588 12.7834 10.6748 9.0770 7.8431
26 0.2198 0.1352 0.0839 0.0525 13.0032 10.8100 9.1609 7.8957
27 0.2074 0.1252 0.0763 0.0469 13.2105 10.9352 9.2372 7.9426
28 0.1956 0.1159 0.0693 0.0419 13.4062 11.0511 9.3066 7.9844
29 0.1846 0.1073 0.0630 0.0374 13.5907 11.1584 9.3696 8.0218
30 0.1741 0.0994 0.0573 0.0334 13.7648 11.2578 9.4269 8.0552
31 0.1643 0.0920 0.0521 0.0298 13.9291 11.3498 9.4790 8.0850
32 0.1550 0.0852 0.0474 0.0266 14.0840 11.4350 9.5264 8.1116
33 0.1462 0.0789 0.0431 0.0238 14.2302 11.5139 9.5694 8.1354
34 0.1379 0.0730 0.0391 0.0212 14.3681 11.5869 9.6086 8.1566
35 0.1301 0.0676 0.0356 0.0189 14.4982 11.6546 9.6442 8.1755
36 0.1227 0.0626 0.0323 0.0169 14.6210 11.7172 9.6765 8.1924
37 0.1158 0.0580 0.0294 0.0151 14.7368 11.7752 9.7059 8.2075
38 0.1092 0.0537 0.0267 0.0135 14.8460 11.8289 9.7327 8.2210
39 0.1031 0.0497 0.0243 0.0120 14.9491 11.8786 9.7570 8.2330
40 0.0972 0.0460 0.0221 0.0107 15.0463 11.9246 9.7791 8.2438
242 Layman's Guidebook
using the discount method, either using the formulae, available on an electronic
spreadsheet, or the Table 8.1. In this table the discount factors are calculated
from the discount formulas for various time periods and opportunity costs (ex-
pressed as rate of discount r). The time periods can be years, quarters, months
etc. and the periodic discount rate will be the corresponding to the period (if r is
the annual discount rate, r/4 will be the discount rate corresponding to a quarter
and 1/12r the corresponding rate for one month)
Although the PVF could be used to solve any present value problem that would
arise it is convenient to define a second term in order to speed the arithmetic
process: the present value of an annuity. An annuity is a series of equal amounts
of money over a certain period of time. The present value of an annuity over n
years, with an annual payment C, beginning at the end of the first year, will be the
result of multiplying C by a factor a", equal to the present value factors:
a = v1 + \'2 + v1 + ... +V11
II
Is easily demonstrated that
1-\'11 (1+r)"-1 1-(l+rrll
a = --= ----'-----'----
11 r r( 1 + r )" r
(8.2)
For instance, the present value of a series of 200 ECU payments over three
years, beginning at the end of the first year, will be given by the product of 200
ECU and the value a
11
in equation (8.2) or by the PWF in Table 8.2
1-(1+0.08(
a 1 = = 2.577; then 200 x a, = 515.42 ECU . 0.08 '
8.3 Methods of economic evaluation
When comparing the investments of different projects the easiest method is to
compare the ratio of the total investment to the power installed or the ratio of the
total investment to the annual energy produced for each project. Nevertheless
this criterion does not determine the profitability of the schemes because the
revenues are not taken into account, but constitutes a first evaluation criterion. In
the last few years, for example, to be eligible for a grant in the THERMIE pro-
gram, this ratio could not exceed 2 350 ECU/kW.
8.3.1 Static methods (which do not take the opportunity cost into
consideration)
8.3.1.1 Pay-back method
The payback method determines the number of years required for the invested
capital to be offset by resulting benefits. The required number of years is termed
the payback, recovery, or break-even period.
Chapter 8. Economic analysis 243
The measure is usually calculated on a before-tax basis and without discounting,
i.e., neglecting the opportunity cost of capital (the opportunity cost of capital is the
return which could be earned by using resources for the next available invest-
ment purpose rather tnan for the purpose at hand). Investment costs are usually
defined as first costs (civil works, electrical and hydro mechanical equipment)
and benefits are the resulting net yearly revenues expected from selling the
electricity produced, after deducting the operation and maintenance costs, at
constant value money. The pay-back ratio should not exceed 7 years if the small
hydro project is to be considered profitable.
However the payback does not allow the selection from different technical solu-
tions for the same installation or choosing among several projects which may be
developed by the same promoter. In fact it does not give consideration to cash
flows beyond the payback period, and thus does not measure the efficiency of
the investment over its entire life.
8.3.1.2 Return on investment method
The retum on investment (ROI) calculates average annual benefits, net of yearly costs,
such as depreciation, as a percentage of the original book value of the investment.
The calculation is as follows:
ROI = (Average annual net benefits/Original book value) x 100
8.3.2 Dynamic methods
These methods of financial analysis take into account total costs and benefits
over the life of the investment and the timing of cashflows
8.3.2.1 Net Present Value( NPV) method
The difference between revenues and expenses, both discounted at a fixed, pe-
riodic interest rate, is the net present value (NPV) of the investment.
The formula for calculating net present value, assuming that the cash flows occur at
equal time intervals and that the first cash flows occur at the end of the first period,
and subsequent cash flow occurs at the ends of subsequent periods, is as follows:
where
!=II R -(1 + 0 + M)
vAN = ' I I I i I + V,. L... ( ) (8.3)
1=t I+ r
I, = investment in period i
R, = revenues in period i
0, = operating costs in period i
M, = maintenance and repair costs in period i
V, = residual value of the investment over its lifetime, whenever the
lifetime of the equipment is greater than the assumed working life
of the plant (usually due to the expiration of the legal permits).
r = periodic discount rate( if the period is a quarter, the periodic rate
will be 1/4 of the annual rate)
n = number of lifetime periods (years, quarters, months)
244
8.3.2.2 Benefit-Cost ratio
Layman's Guidebook
The calculation is usually done for a period of thirty years, because due to the
discounting techniques used in this method, both revenues and expenses be-
come negligible after a larger number of years.
Different projects may be classified in order of decreasing NPV. Projects where
NPV is negative will be rejected, since that means their discounted benefits dur-
ing the lifetime of the project are insufficient to cover the initial costs. Among
projects with positive NPV, the best ones will be those with greater NPV.
The NPV results are quite sensitive to the discount rate, and failure to select the
appropriate rate may alter or even reverse the efficiency ranking of projects. Since
changing the discount rate can change the outcome of the evaluation, the rate
used should be considered carefully For a private promoter the discount rate will
be such that will allow him to choose between investing on a small hydro project
or keep his saving in the bank. This discount rate, depending on the inflation rate,
usually varies between 5% and 12%.
If the net revenues are constant in time (uniform series) their discounted value is
given by the equation (8.2).
The method does not distinguish between a project with high investment costs
promising a certain profit, from another that produces the same profit but needs a
lower investment, as both have the same NPV. Hence a project requiring one
million ECU in present value and promises one million one hundred thousand
ECU profit shows the same NPV as another one with a one hundred thousand
ECU investment and promises two hundred thousand ECU profit (both in present
value). Both projects will show a one hundred thousand ECU NPV, but the first
one requires an investment ten times higher than the second does.
The benefit-cost method compares the present value of the plant benefits and
investment on a ratio basis. Projects with a ratio of less than 1 are generally
discarded. Mathematically the Rblo is as follows:
" R I( 1
i o 1 +r) (8.4) I (I,+ lvf, ~0,)
o (l+r)
where the parameters have the same meaning as in equation (8.3). Projects with
a ratio lower than 1 are automatically rejected.
8.3.2.3 Internal Rate of Return method
The Internal Rate of Return (IRR) is the discount rater, at which the present value
of the periodic benefits (revenues less operating and maintenance costs) is equal
to the present value of the initial investment. In other words, the method calcu-
lates the rate of return an investment is expected to yield.
Chapter 8. Economic analysis 245
8.3.3 Examples
The criterion for selection between different alternatives is normally to choose the
investment with the highest rate of return.
A process of trial and error, whereby the net cash flow is computed for various
discount rates until its value is reduced to zero, usually calculates the rate of the
return. Electronic spreadsheets use a series of approximations to calculate the
internal rate of return.
Under certain circumstances there may be either no rate-of-return solution or
multiple solutions. An example of the type of investment that gives rise to multiple
solutions is one characterized by a net benefit stream, which is first negative,
then positive and finally negative again.
The following examples illustrate how to apply the above mentioned methods to
a hypothetical small hydropower scheme.
Example 8.1
Small hydropower scheme with the following characteristics
Installed capacity: 4 929 kW
Estimated annual output 15 750 MWh
First year annual revenue 1 005 320 ECU
It is assumed that the price of the electricity will increase every year one
point less than the inflation rate
The estimated cost of the project in ECU is as follows:
1. Feasibility study 6 100
2. Project design and management 151 975
3. Civil works 2 884 500
4. Electromechanical equipment 2 686 930
5. Installation 686 930
Total 6416435
Unforeseen expenses (3%) 192 493
Total investment 6 608 928 ECU
The investment cost per installed kW would be
6 608 928 I 4 929 = 1 341 ECUikW
Applying the D.R. Miller curves it will be 6,417,78414929 = 1,302 ECUikW
close to the above estimation
The investment cost per annual MWh produced
6 608 928 I 15 750 = 420 ECUIMWh
The operation and maintenance cost is estimated at 4% of the total investment
moght 6 608 928 x 0.04 = 264 357ECU
In the analysis it is assumed that the project will be developed in four years. The
first year will be devoted to the feasibility study and to application for the
authorisation. Hence at the end of first year both the entire feasibility study cost
and half the cost of project design and management will be charged. At the end
of second year the other half of the design and project management costs will be
charged. At the end of the third year 60% of the civil works will be finished and
246 Layman's Guidebook
50% of the electromechanical equipment paid for. At the end of the fourth year
the whole development is finished and paid. The scheme is commissioned at the
end of the fourth year and becomes operative at the beginning of the fifth (year
zero). The electricity revenues and the O&M costs are made effective at the end
of each year. The electricity prices increases by one point less than the inflation
rate. The water authorisation validity time has been fixed at 35 years, starting
from the beginning of year -2. The discount rate is assumed to be 8% and the
residual value nil. Table 8.2 shows the cash flows along the project lifetime.
Net Present Value (NPV)
Equation (8.3) can be written as follows:
;~<<> R -(0 + M )
NPV= I I . I i I
,=~ (l+r)
To compute the above equation it should be taken into account that R, varies every
year because of change in electricity price. Computing the equation manually or
using the NPV value from an electronic spreadsheet, the next value is obtained
NPV = 444,802 ECU
Internal Rate of Return (IRR)
The IRR is computed using an iterative calculation process, using different dis-
count rates to get the one that makes NPV = 0, or using the function IRR in an
electronic spreadsheet.
NPV using r=8% NPV:: 384 200
NPV using r=9% NPV = -1 770
Following the iteration and computing NPV with r=8.8% NPV = 0
Consequently IRR = 8.8%
Ratio Profit/cost
The net present value at year -4 of the electricity revenues is 7 685 029 ECU
The net present value at year -4 of the expenses (Investment, plus O&M costs) is
5 083 492 + 2 237 268 = 7 300 780
R b/c = 7 685 029/7 300 780 = 1.053
Varying the assumptions can be used to check the sensitivity of the parameters.
Tables 8.3 and 8.4 illustrate respectively the NPV and IRR, corresponding to
example 8.1, for several life times and several discount rates.
Table 8.3
NPV against discount rate and lifetime
r/years 6% 8% 10% 12%
25 986 410 (11 228) (691 318) (1 153 955)
30 1 415 131 234 281 (549 188) (1 070804)
35 1 702 685 384 270 (419 961) (1 028244)
Chapter 8. Economic analysis 247
Table 8.2
Investment cost [ECU] 6.608.928
Annual O&M expenses [ECU]
264.357
Disount rate[%] 8%
:<. . r. -' ,..,,...
·~ u~~·~J ~~
Year Investment Revenues O&M Cash Flow Cumulated
va::>rr nuw
-4 82.087 0 0 -82.087 -82.087
-3 75.988 0 0 -75.988 -158.075
-2 3.074.165 0 0 -3.074.165 -3.232.240
-1 3.376.688 0 0 -3.376.688 -6.608.928
0 0 1.005.320 264.357 740.963 -5.867.965
1 0 995.267 264.357 730.910 -5.137.055
2 0 985.314 264.357 720.957 -4.416.098
3 0 975.461 264.357 711.104 -3.704.994
4 0 965.706 264.357 701.349 -3.003.645
5 0 956.049 264.357 691.692 -2.311.953
6 0 946.489 264.357 682.132 -1.629.821
7 0 937.024 264.357 672.667 -957.154
8 0 927.654 264.357 663.297 -293.857
9 0 918.377 264.357 654.020 360.163
10 0 909.193 264.357 644.836 1.004.999
11 0 900.101 264.357 635.744 1.640.743
12 0 891.100 264.357 626.743 2.267.486
13 0 882.189 264.357 617.832 2.885.318
14 0 873.367 264.357 609.010 3.494.328
15 0 864.633 264.357 600.276 4.094.604
16 0 855.987 264.357 591.630 4.686.234
17 0 847.427 264.357 583.070 5.269.304
18 0 838.953 264.357 574.596 5.843.900
19 0 830.563 264.357 566.206 6.410.106
20 0 822.257 264.357 557.900 6.968.006
21 0 814.034 264.357 549.677 7.517.683
22 0 805.894 264.357 541.537 8.059.220
23 0 797.835 264.357 533.478 8.592.698
24 0 789.857 264.357 525.500 9.118.198
25 0 781.958 264.357 517.601 9.635.799
26 0 774.138 264.357 509.781 10.145.580
27 0 766.397 264.357 502.040 10.647.620
28 0 758.733 264.357 494.376 11.141.996
29 0 751.146 264.357 486.789 11.628.785
30 0 743.635 264.357 479.278 12.108.063
31 0 736.199 264.357 471.842 12.579.905
JL. v L.O.OJ L.V'"t.JJ '"tV'"t.'"tOV IJ.V'"t'"t.JUJ
248 Layman's Guidebook
Table 8.4
R b/c against discount rate and lifetime
r/years 6% 8% 10% 12%
25 1.13 1.00 0.89 0.80
30 1.17 1.03 0.92 0.82
35 1.20 1.05 0.93 0.83
The financial results are very dependent on the price paid for the electricity. Table
8.5 gives the values NPV and R b/c for tariffs 35% and 25% lower and 15% and
25% higher than the assumed in example 8.1.
NPV
R b/c
Table 8.5
NPV and R b/c for different electricity prices
(with r= 8% and lifetime= 35 years)
65%
(2 305 495)
0.684
75%
(1 536 988)
0.780
100% 115%
324 270 1 537 024
1.053 1.211
Example 8.2
125%
2 305 527
1.314
Show the annual cash flows if the investment is externally financed with
the following assumptions:
• 8% discount rate
• development time 4 years
• payments and expenses at the end of the year
• 70% of the investment financed by the bank with two years grace
• finance period 12 year
• bank interest rate 10%
• project lifetime 35 years
The disbursements are identical as in example 8, 1. The bank in the first two
years collects only the interest on the unpaid debt.
It must be remarked that the example refers to a hypothetical scheme, although
costs and revenues are reasonable in southern Europe. The objective is to illus-
trate a practical case to be followed and later on applied to another scheme with
different costs and revenues.
8.4 Financial analysis of some European schemes
In table 8. 7 several European schemes has been analysed. It must be remarked
that both investment costs and buy-back tariffs correspond to reality in the year
1991, and probably will not reflect the situation as it is nowadays. You can see
that ratios of investment per kW installed, or by annual MWh, produced differ
considerably from scheme to scheme. Actually civil works and electromechanical
Table 8.6
Investment cost (ECU) 6,608,928 Bank loan
O&M costs (ECU) 264.357 Loan term (years)
Discount rate(%) 8% Interest on loan
Lifetime (years) 35
Year Total Bank investor's Principal Principal Interest Revenues
lnvestmen loan investment repayment residual on loan
-4 (82,087)
-3 (75,988)
-2 (3,074,165) (2,151,916) 0 (2,151,916)
-1 (3,376.688) (2,363,682) ,013,006) 0 (4,515.597) (215,192)
0 0 (4,515 597) (451 ,560) 1.005,320
1 (135,023) (4,380,574) (451,560) 995,267
2 (296.835) (4,083, 739) (438,057) 985.214
3 (326.519) (3,757,220) (408,374) 975,160
4 (359, 171) (3,398,050) (375,722) 965,107
5 (395,088) (3.002,962) (339,805) 955,054
6 (434.596) (2.568.366) (300,296) 945,001
7 (478,056) (2,090,310) (256,837) 934,948
8 (525,862) (1 ,564,448) (209,031) 924,894
9 (578,448) (986,000) (156,445) 914,841
10 (636,293) (349,708) (98.600) 904,788
11 (349.708) 0 (34,971) 894,735
12 884,682
13 874,628
14 864,575
15 854,522
16 844,469
17 834.416
18 824,362
19 814,309
20 804,256
21 794.203
22 784,150
23 774,096
24 764,043
25 753.990
26 743,937
27 733.884
28 723,830
29 713,777
30 703,724
31 693,671
32 683,618
(4,515,597)
12
10.0%
O&M Investor
cash-flow
(82,087)
(75.988)
(922,250)
(1,013,006)
(264,357) 289,403
(264,357) 144,327
(264,357) (14,036)
(264,357) (24.089)
(264,357) (34, 143)
(264,357) (44, 196)
(264.357) (54,249)
(264,357) (64,302)
(264,357) (74,355)
(264,357) (84,409)
(264,357) (94,462)
(264.357) 245,699
(264,357) 620,324
(264.357) 610,271
(264,357) 600,218
(264,357) 590,165
(264,357) 580.112
(264,357) 570,058
(264,357) 560,005
(264,357) 549,952
(264,357) 539,899
(264.357) 529,846
(264,357) 519,792
(264,357) 509,739
(264,357) 499,686
(264,357) 489,633
(264,357) 479,580
(264,357) 469,526
(264,357) 459,473
(264,357) 449,420
(264,357) 439,367
(264,357) 429.314
(264.357) 419,260
accumulated
cash-flow
(82,087)
(158,075)
(1 ,080,325)
(2,093,331)
(1 ,803,928)
(1,659,601)
(1,673,637)
(1 ,697,726)
(1 ,731 ,869)
(1,776,064)
(1,830,313)
(1 ,894,615)
(1 ,968,971)
(2,053,379)
(2,147,841)
(1 ,902. 142)
(1 .281 ,817)
(671,546)
(71 ,328)
518,837
1,098,949
1,669,007
2,229.012
2,778,964
3,318,863
3,848,709
4,368,502
4,878,241
5,377,927
5,867,560
6,347,139
6,816 666
7,276,139
7,725.559
8,164,926
8,594,240
9,013,500
n
:::T'
-5 -(ll
""1
?0
m
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0
::I
0
3
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C>
::I
C>
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tv
_fo,.
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150
Country
Rated discharge
Gross head
Type of turbine
Installed capacity
Investment cost
Working hours
Annual production
Average price MWh
Annual revenues
O&M expenses
Gross profit
(O&M exp/investment)l
Layman's Guidebook
equipment costs varies from country to country. Environmental requirements -
affecting investment costs--differ not only from country to country but also region
to region. Buy-back electricity tariffs can be five times higher in one country than
in another.
The figures have been computed in a Quattro electronic spreadsheet for a dis-
count rate of 8% and a lifetime of 30 years. The enclosed table is a copy of the
spreadsheet results.
Table 8.7
Germany France Ireland Portugal Spain
m3/s 0.3 0.6 15 2 104
m 47 400 3.5 117 5
Francis Pelton Kaplan Francis Kaplan
kW 110 1.900 430 1.630 5.000
ECU 486.500 1.297.400 541.400 1.148.000 5.578.928
h 8.209 4.105 8.400 4.012 3.150
MWh 903 7.800 3.612 6.540 15.750
ECU 76,13 53,65 23,23 53,54 63,82
ECU 68.732 418.443 83.907 350.128 1.005.320
ECU 19,850 51,984 25,176 22,960 157.751
ECU 48,882 366,459 58,731 327,168 847.569
% 4,08% 4,01% 4,65% 2,00% 3,00%
Economic Analysis
Capital cost per kW installed ECU 4,424 683 1.259 704 1.132
Capital cost per MWh ECU 538.86 166.34 149.89 175.55 354,2
Simple payback period a nos 9.95 3.54 9.22 3.51 6,61
IRR % 9.36 14.25 10.25 28.31 13,17
Rb/c 1.10 2.52 1.15 2.83 1,40
NPV ECU 61,941 2,559,546 112,867 2,294,295 2.456.232
Chapter 8. Economic analysis
Bibliography
1. IDAE. Manual de Minicentrales Hidroeh§ctricas. Edici6n Especial CINCO DIAD. 1997
2. J. Fonkenelle. Comment selectioner une turbine pour basse chute. Proceedings HIDROENERGIA 91 ,
AGENCE FRANCAISE POUR LA MAITRISE DE L'ENERGIE.
251
3. DNAEE "APROVEITAMENTOS HIDRELETRICOS DE PEQUENO PORTE" Volumen V "Avalia9ao de Custos
e Benificios de Pequenas Centrais Hidreh§tricas" Modelo FLASH, Brasflia 1987
4. P. Fraenkel et al "Hydrosoft: A software tool for the evaluation of low-head hydropower esources".
HIDROENERGIA97 Conference Proceedings, page 380
252 Layman's Guidebook
9. Administrative procedures
9.0 Introduction
Exploitation of small-scale hydro power plants is the subject of government regu-
lations and administrative procedures, which, for the time being, vary from Mem-
ber State to Member State.
The regulations actually in force in most member states, include economic, tech-
nical and procedural issues. The economic issues mainly refer to who can gener-
ate electricity; the maximum installed power to be considered "small" and the
conditions for the sale of electricity, including purchasing prices and possible sub-
sidies. The technical issues mainly relate to specifications for connection to the
grid. The procedural issues concern water-use licensing, planning permission,
construction authorisation and commissioning of the plant.
The authorisation procedures, although somewhat arbitrary, have been until now,
well defined. Nowadays the approaching deregulation of the energy market is mak-
ing the situation more fluid, especially in the aspects related to buy-back prices
which it is impossible to describe accurately. Readers interested in the subject, as it
was in 1997 should read the 1994 EUR report "Small Hydropower General Frame-
work for Legislation and Authorisation Procedures in the European Union" presented
by ESHA under contract No.: 4.1030/E/93.07.
9.1 Economic issues
In most Member States, electricity generation and distribution has been up to
now, and in some countries still is, a monopoly of the state-owned utility or of the
well-established private utilities. Nevertheless electricity generation by indepen-
dent producers is also permitted although in some of them the electricity gener-
ated must be consumed at the generator's own facilities, any generation surplus
being delivered to the grid . In most member states, private generators can de-
liver to the grid all the generated electricity but they cannot sell it to third parties.
Prices for the electricity delivered to the grid vary from country to country, thus
making the investment worthwhile in some of them but not in others.
In France the Law 46-628 (8.4.1946) nationalised the electricity industry. Only
companies that generated less than 12 gigawatts in 1942 and 1943 were ex-
cluded from nationalisation. Nevertheless the amendment of 2.8.1949 (Loi
Armengoud) permitted any individual or corporation to generate electricity in plants
with a power capacity up to 8000 kVA. The decree 55-662 (20.5.1955) compels
EDF to buy electricity produced by private generators, and the decree 56-125
(28.11.1956) fixed the sale and purchase terms and tariffs to be applied; tariffs
that evolve in parallel with the E.D.F. tariffs. The private generator can choose
between several types of tariffs that take into account different kinds of hourly
and seasonal discrimination. Almost all independent producers choose the sim-
plified tariff, with two prices for the kWh: one for the winter season (Nov/March)
and another for the summer season (April/Oct), independently of the time of the
day the energy is delivered. The Federation of Independent Producers (EAF)
negotiated this tariff with EDF, valid for a period of ten years, and applicable to
independent producers with hydro plants up to a capacity of 4.500 kW
254 Layman's Guidebook
In Greece the generation transmission and distribution of electricity constitutes a
monopoly of the state utility Public Power Corporation (PPC) established by the
Law 1468/50. Nevertheless the Law 1559/1985 permits any individual or corpo-
rate body to generate electricity for their own use, in hydroelectric schemes up to
5000 kVA, after approval by PPC. The plant can be connected to the grid to
deliver surplus electricity, provided the generated power does not exceed twice
the consumption of the generator himself. For that, a contract between P.P.C. and
the autoproducer is needed, according to the Ministerial Decree 2769/1988. The
Ministerial Decree 2752/1988 established the prices at which P.P.C. purchases
electrical energy from the auto-producers
In Italy the Laws no.9/1991, 10/1991 and 308/1992 empower any person, corporate
body or local community to generate electricity with renewable resources, in plants
with a maximum apparent power of 3.000 kVA. ENEL, the state electrical utility, has
to buy the electricity generated by such independent producers and the Provedimento
CIP 15/1989, modified in August 1990 and finally revised in September 1992 (CIP 6/
92), determines the price to be paid for it. At the time of writting ( 1998) ENEL is being
privatised, and so the past tariffs may not be maintained.
In Portugal according to the Decree 189/88 of 27.05.1988, any person or corpo-
rate body, public or private, can generate electricity, provided it employs renew-
able resources, national fuels, urban or agricultural waste, complies with the tech-
nical and safety regulations in force and the apparent power of the scheme does
not surpass 10.000 kVA. Local communities can invest in the capital of the above
mentioned corporate bodies. Compulsory purchase benefits are granted to pri-
vate generators. The state utility, EDP, is required by law to buy the electricity
produced in the above mentioned circumstances. The situation here is similar to
that of Italy because EDP is aJso likely to be privatised
In Spain the Law 82/1980, Art.?, acknowledges the autoproducer, a person or
corporate body that produce electricity to meet a part or the whole of its own
needs. The RD 907/1982 develops the Article specifying that, to be considered
as auto-producers, they must employ renewable resources, urban or agricultural
wastes, or conventional fuel in heat and power schemes. It is understood that his
main activity is not the production and distribution of electricity. His installation
can be isolated or connected to the grid for an additional supply or to dispose of
surpluses. The Law also states that any person or corporate body can generate
electricity in small hydroelectric plants with a maximum apparent power of 10.000
kVA, either to meet its needs or to supply to the grid. Buy-back tariffs are now
( 1998) being discussed as a part of the new Electricity Act.
In the UK the Electricity Act 1989 denationalised the electricity industry, and en-
abled the Secretary of State for Energy, by Orders, to regulate competition within
the privatised industry, and between it and genuine independents. At the time of
writing the situation is fluid and contradictory statements emerge quite frequently
from the Department of Energy. Section 32 of the Act sets out to protect the
public interest through continuity of supply by requiring that the public electricity
suppliers (the distributors) contract for some capacity of non-fossil fuelled gen-
eration, of which some may be nuclear and some renewable (the non-fossil fuel
obligation or NFFO). Section 33 enables the Secretary of State to levy money on
sales of fossil-fuelled electricity (the NFFO or ), of which some may be nuclear
Chapter 9. Administrative procedures 255
and some renewable. Section 33 enables the Secretary of State to levy a tax on
sales of fossil-fuelled electricity and to distribute the proceedsto cover the added
cost of the non-fossil supplies over their cost had they been fossil-fuelled. To
implement all that, a Non-Fossil Purchasing Agency (NFPA) has been set up.
The NFFO does not apply in Scotland, which already has 50% of non-fossil gen-
er< ;n (nuclear and hydro). However a Scottish Renewables Order, or SRO, is
issued at (until1988) about 2 years intervals which operates similarly to the NFFO
in England and Wales, though the contracted prices are 10-15% lower. As the
major part of the small hydropower potential of the UK lies in Scotland, this price
differential detracts from its full development.
The price situation is becoming particularly critical at a time when much progress
has been achieved towards completion of the Internal Energy Market. Opening the
markets for electricity will bring market forces into play in sectors which until recently
were for the most part dominated by monopolies. This will provide a challenging new
environment for renewable energies, providing more opportunities but also posing
the challenge of a very cost-competitive environment. Suitable accompanying mea-
sures are needed in order to foster the development of renewables
According to the «White Paper for a Community Strategy and Action Plan on
RENEWABLE SOURCES OF ENERGY», COM (97) 599 final (26/11/97): "A com-
prehensive strategy for renewables has become essential for a number of rea-
sons. First and foremost, without a coherent and transparent strategy and an
ambitious overall objective for renewables penetration, these sources of energy
will not make major inroads into the Community energy balance. Technological
progress by itself can not break down several nontechnical barriers, which ham-
per the penetration of renewable energy technologies in the energy markets. At
present, prices for most classical fuels are relatively stable at historically low
levels and thus in themselves militate against recourse to renewables. This situ-
ation clearly calls for policy measures to redress the balance in support of the
fundamental environmental and security responsibilities referred to above. With-
out a clear and comprehensive strategy accompanied by legislative measures,
their development will be retarded."
The above statement calls for a new Directive dealing with the relations between
producers and the Distribution utilities. A greater use of structural funds to sup-
port renewables as suggested by the European Parliament would help to de-
velop this market.
"The Member States have a key role to play in taking the responsibility to promote
Renewables, through national action plans, to introduce the measures necessary
to promote a significant increase in renewables penetration, and to implement this
strategy and Action Plan in order to achieve the national and European objectives.
It is the case that certain countries-e.g. Portugal and Spain-had already made a
legislative effort to cope with the situation, and others are sure to follow, either by
themselves or under pressure of the Commission. The White Paper states that
legislative action will be taken at EU level when measures at national level are
insufficient or inappropriate and when harmonisation is required across the EU.
256 Layman's Guidebook
9.3 How to support renewable energy under deregulation*
9.5.1 Set asides
We are moving away from a monopoly on generation toward a competitive mar-
ket in which customers will have the opportunity to choose among power suppli-
ers. We are moving away from complex regulatory schemes toward greater reli-
ance upon market mechanisms. But as we restructure the electric industry, it will
be the essential role of Governments to establish new «market rules» that will
guide competition. One essential element of the new market rules is to ensure
that those rules drive the restructured market toward cleaner resources that are
compatible with the public interest. Fossil fuels are causing enormous damage to
the environment, including smog, acid rain, global climate change, and mercury
poisoning in lakes. Climate scientists overwhelmingly agree that greenhouse gases
are causing the climate to change and believe that serious damage to the earth's
environment will result, with enormous consequences for humanity. Renewable
energy technologies provide critical environmental benefits; and use indigenous
resources that reduce our dependence upon imported fuels.
Governmental options to support renewables fall into four categories. The first cat-
egory involves a requirement that a certain percentage of generation be renewable,
through set asides, portfolio standards, or simple mandates. The second approach
focus on setting limits to emissions of fossil fuel generators. The third category
contains a variety of approaches, such as green marketing and education. The
fourth approach is to set a price (from 80% to 90%) of the average electricity price
(total invoices divided by number of kWh invoiced), to be paid by the distributors to
the independent producers generating electricity with renewable resources.
Some of the above approaches would require financial aid from the State. How to
get the money for that purpose? Clean air is a benefit shared by all, therefore all
customers should share the cost. Under most proposed industry structures, the
"wires company" would continue to be a regulated monopoly. Since all buyers
and sellers would have to use the "wires company", this is the only place that no
electricity company can short-circuit. This fund could also finance RD&D, as well
as renewable generation projects that are above market prices.
A set-aside is a requirement that a portion of new generation capacity be from
renewable sources. Currently five USA states and the United Kingdom have set-
asides for clean energy, commonly in the form of a requirement on regulated
utilities. There have been a number of ways proposed to continue mandated
investment in renewables in a competitive market
*Note of the author: Most of the comments under this section have been obtained
through the Electric Library in Internet and in a good part have been inspired on a
paper by B. Paulos and C. Dyson "Policy Options For the Support of Renewable
Energy In a Restructured Electricity Industry"
Chapter 9. Administrative procedures 257
9.2.1.1 NFFO (Non Fossil Fuel Obligation)
The UK Government provides support principally through the Non Fossil Fuel
Obligation (known as the NFFO) in England and Wales, the Scottish Renewables
Obligation (SRO) in Scotland and the Northern Ireland NFFO. The NFFO re-
quires Recs. to purchase specified amounts of electricity from renewable sources.
Projects proposed must represent new capacity and must operate on renewable
energy. The NFFO is structured to include a number of technology bands to en-
able a variety of technologies to contribute to the obligation. The current bands
are landfill gas, hydro, wind, municipal and industrial waste, energy crops, com-
bined heat and power schemes and agricultural and forestry waste.
Support for NFFO and SRO is funded through the Fossil Fuel Levy on electricity
sales. This levy, following the flotation of British Energy in July 1996, was re-
duced to 3. 7% for the period November 1996 to 31 March 1997 and to 2.2% from
1 April1997. In Scotland, the fossil fuel levy to cover renewables obligations rose
from 0.5% to 0.7% from 1 April 1997. Financed through this Fossil Fuel Levy,
renewable electricity producers get the difference between the NFFO contract
price and the electricity pool price
To date, there have been four NFFO orders. The first NFF0-1 order was made in
September 1990 for 75 contracts and 152 MW capacity. NFF0-2 was made in Oc-
tober 1991 for 122 contracts and 472 MW capacity. NFF0-3 was made in Decem-
ber 1994 for 141 contracts and 627 MW capacity and NFF0-4 was made in Febru-
ary 1997 for 195 contracts and 843 MW capacity. Proposals for a fifth NFFO order
will be made in late 1998. Scottish Office expects to make an announcement in
respect of proposals for a third Scottish Renewables Order, SR0-3, shortly.
9.2.1.2 Renewable Portfolio Standard (RPS)
In USA, the most popular way to continue mandated investment in renewables in
a competitive market is the "Renewable Portfolio Standard (RPS)", as proposed
by the American Wind Energy Association (AWEA) and adopted by the California
PUC. The portfolio standard requires retail sellers (or distribution companies) to
buy a set amount of renewably generated electricity from wholesale power sup-
pliers. Current proposals set the percentage at the present level of renewable
energy production; roughly 21 percent in California.
The requirements would be tradable so those power suppliers who chose not to
invest in renewable generators themselves could buy credits from those who did.
If a retail seller had sales of 1 ,000,000-kilowatt hours in one year, they would be
required to have generated or purchased 210,000 kilowatt hours using renew-
able resources to meet the Renewable Portfolio Standard. If they did not meet
this requirement, they could purchase credits from a California local distribution
utility or other retail seller that had more than 21% of their sales from renewable
resources. Credit transactions would not actually result in kilowatt-hours deliv-
ered to the retail seller needing the credits. Credit trades would result in a mon-
etary exchange for the right to use the credits.
In this pure form, the portfolio standard would promote only the lowest cost
renewables. There is currently pending in the California legislature a bill that would
require power suppliers to purchase a minimum amount of electricity from biomass
258 Layman's Guidebook
generators. In fact to support technologies that are less competitive, awards could
be given to separate bands, like biomass, wind, solar and waste-to-energy, as in the
UK's Non Fossil Fuel Obligation.
9.2.2 Emission Taxes, Caps and Credits
9.2.3 Green pricing.
Emissions taxes, caps, and credits are all policies, which can promote renewable
energy use. Renewable energy sources produce few or no emissions of sulphur
dioxide (802), carbon dioxide (C02), oxides of nitrogen, and other air pollutants.
Policies, which increase the cost of such emissions, internalise the social costs of
pollution, making renewable energy sources more competitive. Under a restruc-
tured utility industry, emission-based policies can be a market approach to pro-
moting renewables.
Of this group of emission policies, taxes have been used the least. Emission
taxes can be assessed a number of ways. If reasonable estimates of the costs of
the emissions to society are available, as they are for S02, then this is the most
equitable method. However, for many emissions, such as C02, reliable cost es-
timates are not available. In these cases it may be necessary to base the taxes
on the costs of pollution control or some arbitrary amount. The design is intended
to make the tax changes revenue neutral, shifting $1.5 billion in state taxes from
"goods" like income and property, to a tax on "bads."
Emission credits are permits that allow an electric generator to release an air
pollutant. These credits can be traded with other polluters, providing an incentive
for companies to reduce emissions below mandated levels. Currently a national
market for tradable permits is only available for 802 emissions. However, the
EPA is considering expanding credit trading to N02 and mercury emissions.
A positive feature of emission taxes and credits is their efficiency in allocating
pollution costs. Electricity generators pay directly for the pollution they produce.
Low or no emission renewable energy sources are thus able to compete on a
more even playing field. Emission taxes also generate revenues that could be
used to support renewable generation or renewable research and development
In USA, the recent introduction of commodity markets for emission credits should
give utilities more options for managing the uncertainty of future credit prices The
biggest problem with energy and emission taxes is that they are politically un-
popular.
Green pricing is an evolving utility service that responds to utility customers' pref-
erences for electricity derived from renewable energy sources such as solar, wind,
or biomass. Under green pricing, utilities offer customers a voluntary program or
service to support electricity generated from renewable energy systems. Cus-
tomers are asked to pay a rate premium, which is meant to cover the costs that
the utility incurs above those paid today for electricity from conventional fuels.
Surveys indicate that in USA and in Denmark many consumers are willing to pay
a premium for green power. A 1995 survey conducted by seven USA utilities
Chapter 9. Administrative procedures 259
9.2.4 Imposed tariffs
9.2.5. Miscellaneous
found that 45 percent of respondents were willing to pay a surcharge of up to 4
percent for green power; 29 percent were willing to pay up to 9 percent; 18 per-
cent were willing to pay up to 19 percent; and 1 0 percent were willing to pay up to
a 29 percent surcharge
Knowledge of and experience with green-pricing programs is only just develop-
ing. These programs tend to fall into one of three categories: (1) a renewable
energy contribution fund, which offers customers an opportunity to contribute to a
fund to be used in the future to pay for as-yet-unspecified renewable electricity
projects; (2) tailored renewable energy projects, in which customers pay a pre-
mium price for power generated from a specific renewable electric project; and
(3) a renewable electric grid service, for which the utility may bundle power from
a number of renewable projects with other power sources for sale to customers.
Germany, and Spain support special tariffs for a certain number of technology
bands. In Spain the buyback tariffs for those bands, varies from 80% to 90% of
the average national electricity price and are paid by the distribution utilities. The
Minister of Industry and Energy fix the bonus to be paid for the electricity gener-
ated with the technologies comprised in the different bands. The situation in Ger-
many was very similar after the law issued in December 1996.
ESHA Vice President, David R. Miller, made a very interested proposal: the modu-
lated tariff. Actually in the cost price or renewable electricity, the influence of the
capital cost is decisive. According to the different studies -see chapter 8 -the
investment cost per kWh generated decreases with the size of the plant. Figure
9.1 shows the trend in capital cost per kW installed. Consequently, to get a cer-
tain return on investment, the price to be paid for the electricity should be higher
in smaller plants that in larger plants. In order to make things D. Miller proposes
modulate the tariff in function of the amount of electricity delivered to the net.
Calculations indicate that High Head Installations with a 45% output requiring a
10% Real rate of Return over 10 years need price modules as follows:
151 Million Kwh
2nd Million
3rd Million
41h Million
51h & 61h
7-10 Million
at 10.58 Ecu cents yielding
8.89
6.27
5.56
5.44
5.30
10.58 Ecu cents
9.74
8.58
7.83
7.03
6.34
Let us suppose that '90% of the average selling price' or 'city gate plus the tax' is
equivalent to ca. 6.5 Ecu cents, we may then propose that this should be the
base price for all Small Hydro Producers. But producers may opt to avail of a
modulated tariff as follows:
260
0 2000
Capital cost per kilowatt installed
4000 6000
Kilowatts installed
Figure 9.1
1st Million Kwh at
2rct Million
3'd Million
4'h Million
5'h and 6'h Million
7-10 Million
8000
10.58
8.89
6.20
5.52
5.46
5.26
yields
Layman's Guidebook
10000 12000
10.58 Ecu cents kWh
9.73
8.55
7.80
7.02
6.32
9.3 Technical aspects
In all Member States the independent producer must meet a minimum of techni-
cal requirements to be connected to the grid, so that end users will not be af-
fected by the service's quality.
In Belgium the technical specifications for the connection to the grid of indepen-
dent power plants of less than 1 MW installed power are set out in the note
C.G.E.E. 2735 of 10.2.1987.
In France the technical requirements for connection to the grid are regulated by
EDF bylaws. The connection point will be fixed by E.D.F and in case of disagree-
ment, by the DIGEC. The line between the powerhouse and the grid has to be
built at the expense of the independent producer. The same happens in Italy,
where ENEL states the technical conditions and the connection fees.
In Greece technical conditions for the connection of private generators to the grid
are listed in the Ministerial Decree 2769/1988.
Chapter 9. Administrative procedures 261
In Portugal the connection point will be chosen by agreement between the par-
ties. In case of disagreement the Directorate General of Energy (DGE) will arbi-
trate the conflict within 30 days. The line between the powerhouse and the grid
has to be built at the expense of the producer but then becomes part of the grid.
The maximum nominal apparent total power of the plant will be 100 kVA, if it is
connected to a low voltage line or 10.000 kVA if it is connected to a medium or
high voltage line. Asynchronous generators when connected to a medium or high
voltage line may not exceed 5000 kVA. The apparent power of the plant may not
exceed the minimum short-circuit power at the connection point.
The technical requirements for the connection to the grid are specified in a docu-
ment published by the Ministry of Industry and Energy "Guia Tecnico das
lnstalac;6es de produao independente de energia electrica" (December 1989)
In Spain the OM 5.9.1985 stipulates the technical requirements for the connec-
tion to the grid of small hydroelectric plants. The distributor to which the private
generator will be connected must indicate the connection point, the connection
voltage, and the maximum and minimum short-circuit power. The connection point
should be chosen to minimise the investment on the connection line. In case of
disagreement the Directorate General of Energy (DGE) or the corresponding re-
gional authority will arbitrate. Asynchronous generators can be connected to a
low voltage line, whenever its maximum nominal apparent power does not ex-
ceed neither 100 kVA or 50% of the power of the transformer feeding the line. For
plants connected to medium or high tension lines, the maximum total nominal
apparent power of the generators should not exceed 5.000 kVA if they are asyn-
chronous, or 10.000 kVA if they are synchronous. In both cases the apparent
power cannot exceed 50% of the power of the transformer feeding the line.
In the United Kingdom the Electricity Council Regulation G59 specifies require-
ments for paralleling independent generators with the national distribution sys-
tem. The main aim is safety, for both parties. Recent developments have enabled
manufacturers to meet the requirements at an economic cost, certainly for gen-
erators who can supply the distribution system at 15 kW and above, both at single
and three phase, 240/415 volts, 50 Hz.
In Scotland the new electricity Companies are in the course of producing their
own requirements for grid connections but in the current economic climate there
is no incentive to produce and publish these in the near future.
9.4 Procedural issues
The administrative procedures needed to develop a small hydropower site are
complex and, in general, very lengthy. These procedures concern water-use li-
censing, planning permission, construction requirements and commissioning and
operation of the plant.
Table 9.1, reproduced from a presentation by George Babalis to HIDROENERGIA
97, identifies the administrative procedures, still in force, in the E.U Member States,
for authorisation to use water.
262 Layman's Guidebook
Table 9.1
Country Authority granting rights for water use Validity time of the author
Austria < 200 kW local governments ual30 years
> 200 kW country qovernments "ble more 160-90 vearsl
Belgium < 1 MW the provinces undetermined
> 1 MW same + Ministry of Energy 33 a 99 afios
• Denmark Ministry of Enemv undetermined
France < 4,5 MW Prefecture
> 4,5 MW State in practice up to 40 years
Germany Landers 30 years
Greece Ministry of Energy 10 years, renewable
Ireland Not needed. Riparian rights in force perpetual
Italy < 3MW regional authorities
> 3MW Ministry of Industry 30 vear
Luxemburg Ministries of Agriculture,Public Works,
Environm.& Employment+ local authorities undetermined
Netherlands National & Local Water Boards at minimum 20 years
Portugal
Spain
Sweden
U.K.
DRARN (Regional Authority for Environ-35 years renewable
ment & Natural Resources)
Basin authority except in some rivers in
Catalunya and Galicia 25 years + 15 of grace
Water Court perpetual (30 years)
Environmental Agency England & Wales 15 years
In Scotland not required if P<1MW; Scotland undetrmined
if P>1 MW Secretary of State
At present, a developer who decides to invest in the construction of a small hy-
dropower scheme should be prepared for a three years hurdle-race with a high
probability of getting a "no" at the end or no answer at all. If the European Com-
mission wishes to achieve its ALTENER objectives, concrete actions aimed at
removing the existing barriers to the development of SHP -relationships between
utilities and independent producers, administrative procedures and financial con-
straints-should be undertaken.
In order to attain the ambitious ALTENER objectives in electricity generation
through renewables, new schemes must be developed. These never will be pos-
sible unless an appropriate framework is set up. To eliminate the procedural bar-
riers, administrations must give authorisation within a reasonable period (18
Chapter 9. Administrative procedures 263
months), and by introducing the principle that the authorisation is granted, when
no answer is given within the fixed period or, based on objective criteria it is
denied ..
9.5 Environmental constraints
In chapter 7 environmental burdens and impacts have been identified, and some
mitigating measures have been advanced. It has been made clear that small hydro-
power, by not emitting noxious gases -greenhouse or acid rain gases-has great
advantages from a global viewpoint. Notwithstanding that, the developer should imple-
ment the necessary mitigation measures so that the local environment is minimally
affected. Small hydropower uses, but does not consume water, nor does it pollute it.
It has been demonstrated, see chapter?, that provided the scheme is profitable
enough it may be possible to substantially increase the investment to implement
mitigating measures so that development is possible even in the most sensitive
natural park. The French position barring the possibility of developing small hy-
dropower schemes on a certain number of rivers, without previous dialogue, is
unjustified.
From all the environmental aspect the most crucial and controversial one is the
determination of the reserved flow. For the developer the fact of producing elec-
tricity without damaging the global atmosphere merits every kind of support with-
out heavy curtailments in the generation capacity; for the environmental agen-
cies a low reserved flow is equivalent to an attack to a public good which is the
aquatic fauna. Only a dialogue between the parties based on the methodologies
mentioned in chapter 7 can open the way to a mutual understanding.
264 Layman's Guidebook
GLOSSARY
Alternating current (AC): electric current that reverses its polarity periodically (in contrast to direct current).
Anadromous fish:
Average Daily Flow:
Baseflow:
BFI baseflow index:
Butterfly Valve:
Capacitor:
Catchment Area:
Cavitation:
Compensation flow:
Demand (Electric):
Demand Charge
Direct Current (DC):
Draft tube:
Energy:
Evapotranspiration:
FDC:
Fish Ladder:
In Europe the standard cycle frequency is 50 Hz, inN. and S. America 60Hz.
fish (e.g. salmon) which ascend rivers from the sea at certain seasons to spawn.
the average daily quantity of water passing a specified gauging station.
that part of the discharge of a river contributed by groundwater flowing slowly
through the soil and emerging into the river through the banks and bed.
the proportion of run-off that baseflow contributes.
a disc type water control valve, wholly enclosed in a circular pipe, that may be
opened and closed by an external lever. Often operated by a hydraulic system.
a dielectric device which momentarily absorbs and stores electric energy.
the whole of the land and water surface area contributing to the discharge at a
particular point on a watercourse.
a hydraulic phenomenon whereby liquid gasifies at low pressure and the vapour
bubbles form and collapse virtually instantaneously causing hydraulic shock to
the containing structure. This can lead to severe physical damage in some cases.
the minimum flow legally required to be released to the watercourse below an
intake, dam or weir, to ensure adequate flow downstream for environmental,
abstraction or fisheries purposes.
the instantaneous requirement for power on an electric system (kW or MW).
that portion of the charge for electric supply based upon the customer's demand
characteristics.
electricity that flows continuously in one direction sd contrasted with alternating
current.
a tube full of water extending from below the turbine to below the minimum
water tailrace level.
work, measured in Newton metres or Joules. The electrical energy term generally
used is kilowatt-hours (kWh) and represents power (kilowatts) operating for
some period of time (hours) 1 kWh = 3.6x10 3 Joules.
the combined effect of evaporation and transpiration.
flow duration curve:: a graph of discharges against v. the percentage oftime (of
the period of record) during which particular magnitudes of discharge were
equalled or exceeded.
a structure consisting e.g. of a series of overflow weirs which are arranged in
steps that rise about 30 em in 3 50 4 m horizontally, and serve as a means for
allowing migrant fish to travel upstream past a dam or weir.
Output:
(In) Parallel:
Overspeed:
P.E.:
Peak Load:
Peaking Plant:
Penstock:
Percolation:
Power:
Power factor:
Rating curve:
Reynolds Number:
Rip-rap:
Runoff:
Run-of-river scheme:
SOIL:
Stage( of a river):
Supercritical flow:
Synchronous speed:
Tailrace:
267
the amount of power (or energy, depending on definition) delivered by a piece
of equipment, station or system.
the term used to signify that a generating unit is working in connection with the
mains supply, and hence operating synchronously at the same frequency.
the speed of the runner when, under design conditions, all external loads are
removed
polyethylene
the electric load at the time of maximum demand.
a powerplant which generates principally during the maximum demand periods
of an electrical supply network.
a pipe (usually of steel, concrete or cast iron and occasionally plastic) that
conveys water under pressure from the forebay to the turbine.
the movement of water downwards through the soil particles to the phreatic
surface (surface of saturation within the soil; also called the groundwater level).
the capacity to perform work. Measured in joules/sec or watts (1 MW = 1 j/s).
Electrical power is measured in kW.
the ratio of the amount of power, measured in kilowatts (kW) to the apparent
power measured in kilovolt-amperes (kVA).
the correlation between stage and discharge.
a dimesionless parameter used in pipe friction calculations (interalia), and derived
from pipe diameter, liquid velocity and kinematic viscosity.
stone, broken rock or concrete block revetment materials placed randomly in
layers as protection from erosion.
the rainfall which actually does enter the stream as either surface or subsurface
flow.
plants where water is used at a rate no greater than that with which it "runs"
down the river.
a parameter of permeability
the elevation of water surface
rapid flow who is unaffected by conditions downstream
the rotational speed of the generator such that the frequency of the alternating
current is precisely the same as that of the system being supplied.
the discharge channel from a turbine before joining the main river channel.
1
INTRODUCTION
1.1 The Place of Micro Hydro
Micro hydro, defined as a plant between 10 kW and 200 kW, is perhaps the most mature
of the modem small-scale decentralised energy supply technologies used in developing
. countries. There are thought to be tens of thousands of plants in the 'micro' range
operating successfully in China 2 , and significant numbers are operated in wide ranging
countries such as Nepal, Sri Lanka, Pakistan, Vietnam and Peru. This experience shows
that in certain circumstances micro hydro can be profitable in financial terms, while at
others, unprofitable plants can exhibit such strong positive impacts on the lives of poor
people and the environment that they may well justify subsidies.
The evidence from this extensive experience shows such wide variation in terms of cost,
profitability and impact, that it has often been difficult for investors and rural people to
determine whether, and under what circumstances, this technology is viable and best
meets their needs.
Whilst supplying improved energy services to people for the first time is difficult,
supplying such services profitably to very poor people who live far away from roads
and the electricity grid poses a particularly difficult challenge. This report shows that
micro hydro compares well with other energy supply technologies in these difficult
markets. Despite this micro hydro appears to have been relatively neglected by donors,
the private sector and governments in the allocation of resources and attention. In the
past, rural electrification by means of grid extension was the option favoured by donors.
More recently the fashion has switched towards photovoltaics, probably because of its
higher foreign content, and the higher added value returned to the metropolitan
· countries.
The relative neglect of micro hydro has also been in part due to the fact that the
circumstances under which it is financially profitable have not been systematically
established, at least not in ways that investors find credible. In addition, while it is
known that the growth and sustainability of the micro hydro sub-sector depends on
certain types of infrastructure and institutional investments, it was often not clear which
elements of this 'enabling environment' were essential, nor how they were best
financed .
.,
-In 1979 the total generating capacity of all small plants was 6300 MW. with 40.000 stations built in the period from
1975 to 1979 having an average size of 85 kW. Ian Juang. draft document on micro power in China. to be submitted
for an MSc dissertation. Oxford University. October 1999.
2 Best Practices for Sustainable Development of Micro Hydro Power
This study attempts to rectify these omissions by analysing and then synthesising the
experience of micro hydro over many years, across a broad range of developing
countries. Primary evidence was obtained from Peru, Nepal, Sri Lanka, Zimbabwe and
Mozambique. On the basis of this evidence an attempt has been made to establish 'Best
Practice' in tem1s of the implementation and operation of sustainable installations.
National teams, usually consisting of an independent consultant and a staff member of
The Intermediate Technology Development Group, carried out the work using a
common methodology developed at the start of the work. National reports were written
separately and were subject to review at national workshops involving the key actors in
the sector.
The microanalysis sought to examine a sample of specific installations. The sample was
drawn from comprehensive databases of micro hydro plants in each of the five
countries. It was selected using a typology which combined end-uses (productive uses,
electricity for lighting, combined end-uses, etc.) with types of ownership (community-
led projects, projects implemented by central bodies such as the utilities, and projects
initiated by private entrepreneurs).
Table 1-1: Summary Table Showing the Sample of Projects Studied In Detail
Community-led Top Down-Private Total
projects led projects Entrepreneur
( utilities )
Shaft power only Zimbabwe ( 1 ) Mozambique (2) 3
Electricity for Sri Lanka (2) Peru (2) 4
domestic end uses and Kandaloya Pedro Ruiz
services Pathavita Pucara
Lighting and Zimbabwe ( I) Nepal ( 3) 9
productive uses of Nepal ( I) Sri Lanka ( 1)
electricity Peru (2)
Sri Lanka ( I)
TOTAL 8 2 6 16
*The numbers in brackets show the number of schemes per country.
Although Zimbabwe and Mozambique have relatively few micro hydro plants
operating, it was decided to include them in the sample to illustrate some of the special
issues that are faced by countries trying to start programmes. The implication of this
experience for other countries is brought together in Section 4.1
1.2 The Differing Objectives of Micro Hydro Development
One of the most important findings to emerge from the study of this experience is that
micro hydro plants can achieve a wide range of quite different objectives. Much
confusion and misunderstanding arises when all micro hydro plants are treated as a
homogenous category. Analytically it is therefore important to judge the viability of
each micro hydro investment in tem1s of a specific objective. Similarly in the
formulation of government or donor policy, it is important not to expect micro hydro to
achieve many, often conflicting, objectives. For instance, it is not possible to provide
Introduction 3
electricity to very poor people in remote locations through micro hydro and make a
return on capital similar to that achieved in London capital markets.
1.3 Technology Demonstration, Social Infrastructure, or Small Enterprise?
The field of micro hydro is 'evolving', particularly in relation to the motivation of
project developers. Recently the majority of initial installations in each country might
be said to be the result of a 'technology push'. That is, plants were installed to test their
technical viability and their acceptability. This experience has established the technical
reliability of the micro hydro systems, reduced their cost, and has resulted in substantial
technical improvement. Micro hydro is now a mature technology that has been greatly
improved by electronic load controllers, low cost turbine designs, the use of electric
motors as generators 3 , and the use of plastics in pipe work and penstocks.
The next group of projects is characterised by investments in micro hydro that were
seen as part of the 'social infrastructure' more akin to the provision of health services,
roads or schools. Due to their social objectives, these experiences have often generated
little information on the capital and operating costs or cash flow returns of the
investment, particularly of a form and quality that would be regarded as reliable by
potential investors in conventional financial institutions. Indeed many of the promoters
of this type of project justify their work solely in terms of contributions to social justice,
the quality of life of marginalized people, and to the environment. In Sri Lanka, for
instance, many micro hydro plants have been installed primarily to "improve the quality
of life by providing electric light 4 ". ln Peru the key question for many project
developers was "how long will the plant last", rather than "how high is its rate of
return", or "how quickly the capital will be paid back"5 .
More recently support programmes have returned to what might be called an older
vision what might be considered an earlier approach where micro hydro is seen
primarily in tern1s of securing livelihoods and for the development of small profit-
making businesses. This can be seen in part as an admission that, like the previous
attempts at rural electrification through grid extension, the sustainability of grant-based
programmes is limited. Methods must be established to attract private capital if these
programmes are to have anything but a marginal impact. Nepal has shown that small,
almost subsistence businesses can survive using micro hydro power to mill grain. Over
900 micro hydro plants had been installed in Nepal by 1996, and over 80% of these
were for grinding grain. ln recent years there has been quite a rapid take-up ofthe small
(I kW) 'peltric' sets for generating small amounts of electricity. Introduced in the early
1990's, there were said to be over 250 operating in the first five years 6 .
These very different starting points, along with the performance indicators used to
evaluate projects, have important implications for what is regarded as a success. Micro
hydro as 'social infrastructure' uses the approaches and indicators appropriate to
schemes for the supply of drinking water, health clinics and schools. Micro hydro as
'physical infrastructure' uses the approaches applied to electric power generation more
generally, and to such investments as the provision of roads and irrigation systems.
'Sec for instance \ligcl Smith. Motors as Gencralm:v
Publications. London. ISBN I X5339 ::!1\6 .~
~Sri Lanka Report. Section 3.4.
5 Peru Report. Section 1.1.
1
' See Nepal Report.
Jficro Hvdro Power. 1994, Intermediate Technology
4 Best Practices for Sustainable Development of Micro Hydro Power
Even more recently micro hydro has been seen in terms of small and medium enterprise
development, and the role that such enterprises can play in 'securing livelihoods'.
There is little to be gained from arguing that one approach is superior to another, as in
all probability each strand has a role to play. But failure to distinguish these very
different motivations has lead to confusion and ineffective policy advice. Each
approach is associated with very different mindsets of the people involved, and the
differing objectives will result in quite different management 7 , allocation of resources,
approaches and even site selection.
1.4 Hard Choices Have To Be Made in the Allocation of Scarce Resources
Investments that are primarily intended to increase the adoption of micro hydro are
likely to need to be financially viable and will therefore be located where there are
concentrations of effective demand, or there are so-called 'anchor customers' who can
pay for the bulk of the power supplied. This might include sales to the grid where
possible and profitable. Programmes that are intended primarily to increase the ·access'
of specific groups of people to improved energy supplies are likely to be located where
poor live. This will frequently be in more remote areas that will not be reached by the
central grid for some time, if ever, where all other options will also be expensive but
where micro hydro is the least cost 8 .
Examples of the strategy to increase sales, regardless of their income or need. can be
found in a number of renewable energy programmes, particularly in photovoltaics.
Here it is argued that increased sales will reduce the cost of production, and more
importantly, enable the overhead costs of providing technical support and supplying
'retail' credit to be spread over a larger number of unit sales. The danger is that some of
the soft money that is intended for social investment is used to subsidise the costs of
these supply options for those who can already afford to pay for it.
A key dimension of the trade-off is that the benefits and burdens of the choices made
fall on different social groups. The people who can pay the full cost of energy supply
often reside in different parts of the country from those \vith the greatest need. This
means that if concepts of fairness are introduced to government policy or, more
generally, into the allocation of resources, micro hydro is likely to have an important
role in spreading access to electricity, even if the users cannot pay the full cost. The
review of programmes in Nepal and Sri Lanka both suggest that they have both been
explicitly motivated by ideas of social justice and fairness. Certainly rural people in
many countries can be expected to ask why they should not they be entitled to the levels
of subsidy provided to urban dwellers.
Micro hydro developers and the financial institutions that they work with have to make
choices between these two extremes of profitability and social impact. There is likely to
be a middle ground where social impacts can be achieved profitably, but its size is not
yet known. What is clear. is that many rural people will remain without electricity
unless there is some sort of redistribution of income from urban to rural areas.
Sec Peru Report. Section 'i.
' Sec Peru Report. "there is no guarantee that electrification cxdtbivcly under the private ~ector would increase the
electrification rate. although it would increase energy consumption ... due to the relatively high consumption of a
minority".
Introduction 5
There is a parallel here with arguments between the advocates of micro hydro and
Ministries of Energy and their conventional utilities. Proponents of micro hydro are
often disappointed that utilities will not take them seriously. Certainly micro hydro
often faces unfair competition from a highly subsidised grid, and from subsidised fossil
fuels. But, there is a genuine trade-off between maximising the access of people to
'efficient and affordable energy', and doing so in those places where micro hydro (and
other renewable energy) is the least cost. The scarce resource is not energy, but the
capital to make energy accessible .. lf the objective is to provide electricity to as many
people as possible rather than to distribute electricity evenly across the country, the
most effective way of doing it may well be through extensions of the grid, or more
likely 'intensification' of the use to which the grid is put. Similarly where utilities have
very severe limits on capital, the 'opportunity cost' of capital at the margin rises to very
high levels, explaining perhaps why they then opt for diesel generators rather than hydro
with its higher initial capital cosL
1.5 The Main Forms Of Support-Extending the Concept Of
'Intermediation'
The case studies show that a wide range of actions have to be brought together to ensure
the success of micro hydro investments. These actions take place a various levels: at the
micro level of particular investment in a hydro plant at a particular location; at the
macro level of policy formulation; and in the design and implementation of programmes
of financial and other support mechanisms.
In undertaking the case studies, it was found that the idea of 'intermediation' offered a
convenient way to group the many hundreds of tasks that were identified as necessary.
This provided considerable analytical insight about how policies might be developed to
ensure that these tasks were indeed performed and integrated into the costings. The
approach extends the idea of 'financial intermediation' and considers three additional
forms of intermediation, namely technical intermediation, social intermediation and
organisational intermediation.
Financial Intermediation involves putting in place all the elements of a financial
package to build and operate a micro hydro plant. A process sometimes referred to as
'financial engineering'. It covers:
• the transaction costs of assembling the equity and securing loans;
• obtaining subsidies;
• the assessment and assurance of the financial viability of schemes;
• assessment and assurance of the financial credibility of borrower;
• the management of guarantees;
• the establishment of collateral ('financial conditioning'); and
• the management of loan repayment and dividends to equity holders.
Financial Intermediation can also be used to cover whole schemes rather than just
investment in an individual plant. ln this way projects can be 'bundled' together to
make them attractive to finance agencies, to establish the supply of finance on a
'wholesale' basis from aid agencies, governments, and development banks, and to
create the mechanisms to convert it into a supply of retail finance (equity finance, and
loan finance at the project level).
6 Best Practices for Sustainable Development of Micro Hydro Power
Technical Intermediation involves the 'upstream' work of improving the technical
options by undertaking R and D and importing the technology and know-how, 'down'
through the development of the capacities to supply the necessary goods and services.
These goods and services include: site selection; system design; technology selection
and acquisition; construction and installation of civil, electro-mechanical and electrical
components; operation; maintenance; Trouble Shooting; overhaul; and refurbishment.
Organisational Intermediation involves not only the initiation and implementation of
the programmes, but also the lobbying for the policy change-required to construct an
'environment' of regulation and support in which micro hydro technology and the
various players can thrive. This involves putting in place the necessary infrastructure,
and getting the incentives right to encourage owners, contractors, and financiers.
The case studies show that this organisational intermediation is also usefully
distinguished from the Social Intermediation. Social intermediation involves the
identification of owners and beneficiaries of projects and the 'community development'
necessary to enable a group of people to acquire the capabilities to take on and run each
individual investment project.
1.6 The Importance of the Technology
While the rest of this is report focuses mainly on the 'software' of finance, management
and social development, it would not be right to end this introduction without stressing
the importance of the hardware and engineering skills in the success of micro hydro
development. The experiences reviewed here repeatedly confront the need to get the
technology right, and develop the technical skills necessary to build, install, operate and
maintain the equipment and the associated civil works.
A study on the functional status of the state of existing micro hydro plants in Nepal9
emphasises the point. Despite much work on manuals, standards, training, and
correcting faulty engineering and associated errors, the physical assets remain a
substantial cause of failure. A study on the functional status of the state of existing
micro hydro plants in Nepal 1 0 emphasises the point that despite much work on manuals,
standards and training, faulty engineering and associated errors, the physical assets
remain a substantial cause of failure. Some 30% of the installations were not operating,
due in part to:
• Poor site selection, inadequate/inaccurate surveys, wrong s1ze, poor
installation, faulty equipment;
• Plants affected by f1oods and land slides;
• Poor estimation of hydrology, in part due to surveys being conducted in the
ramy season;
• Uneconomic canal length, bad canal design;
• Neglect of civil works;
• Inability of owners to replace generators after breakdown; and
9 Earth Consult (P.) Ltd. 'A Report o/ Ram/om Sample to Determine Actual Staflls u/ Primte Micro H<·dro Pom:T
Plams in :\epa!'. ICIMOD-ITDG Nepal. May !99S.
~'1 Earth Consult (P.) Ltd. :4 Report o(Random Sample to Determine Aclual Sraws o!Primte Micro Hrdro Po11·er
?lams 111 :Vcpal'. ICIMOD-ITDG NepaL May 1998.
• • • •• • • • • • • • • •
•
• • • • • • • • • • • • • • • • • • • •
• Wrong estimation of raw materials,
oversized plants, over-estimation of
ignorance of competition with diesel 11 •
Turbine Manufacturing in Sri Lanka
Introduction 7
of demand, of end-use possibilities,
tariff collection, inappropriate rates,
Furthermore, there are still a
number of unresolved technical
issues. In particular there is a
trade-off between the quality
(and therefore the costs) of the
civil works and the resulting
costs of operation and
maintenance. Low cost civil
works tend to be swept away by
the monsoon rains and have to
be substantially repaired each
year. It is not yet clear where
the optimum balance lies
between these two types of
cost 12 •
11 See also Wolfgang Mostert, 'Scaling-up Mi cro Hydro , Lessons from Nepal, and a few Notes on Solar Home
Systems', Village Power 98 Conference, NREL/ World Bank, Washington October 6-8, 1998.
12 Wolfgang Mostert, personal communication .
2
THE COST OF MICRO HYDRO AND ITS FINANCIAL
PROFITABILITY
2.1 The Cost Per Kilowatt Installed
In the examples examined in the five countries, the capital cost 13 of micro hydro plants, limited
to shaft power, ranged from US$714 (Nepal, Zimbabwe) to US$1,233 (Mozambique). The
average cost is US$965 per installed kW which is in line with the figures quoted in some
studies. The installed costs for electricity generation schemes are much higher. The installed
cost per kW ranged from US$1,136 (Pucara, Peru) to US$5,630 (Pedro Ruiz, Peru) with an
average installed cost of US$3,085. The data for the complete sample and detailed summary of
the financial analyses of the 16 sample projects is provided in the annex to this report.
An important observation is that the cost per installed kilowatt is higher than the figures usually
cited in the literature. This is partly due to the difficulty analysts have in establishing full costs
on a genuinely comparative basis. A significant part of micro hydro costs can be met with
difficult to value labour provided by the local community as 'sweat equity'. Meaningful dollar
values for local costs are difficult to establish when they are inflating and rapidly depreciating
relative to hard currencies. In addition, there is little consistency in the definition of boundaries
of the systems being compared, for instance, how much of the distribution cost, or house
wiring, is included, how much of the cost of the civil works contribute to water management
and irrigation, and so forth.
In this study very great care was taken to produce estimates of the actual costs on a rigorously
comparable basis. It is for example of paramount importance to distinguish between schemes
limited to mechanical power only and schemes which include electricity generation.
As with any de-centralised energy supply system, the comparison of actual costs at the 'micro'
level of individual plants can also be misleading. Successful programmes require investments
in the systems necessary for training, repair, and marketing. The critical issue is that these
tasks exhibit substantial economies of scale in that the cost per micro hydro plant installed falls
as the number of plants increases. Comparisons based on average costs will therefore be
strongly influenced by the number of plants built.
Estimates of these ·macro' costs associated with developing and supporting a programme -
sometimes referred to as "system overhead costs"14 are also difficult to establish, particularly as
many of the costs associated with Research and Development and the training of engineering
workshops are 'sunk costs' which took place over many years.
i\11 monetary values in USSJ 9911 unless specified.
10 These activities were first identified as "system overhead costs" in the late 191\(J's. see A Barnett .. The Di{/i1sion o!Energ1·
Technologies in the Rural A reus of' De1·eloping Coumries: A Smthesis of Recenl ExpcTiencc. World Development, Pergamon
Press. Vol. 18,1\o. 4. Aprill9QO, pp.539-553.
9
10 Best Practices for Sustainable Development of Micro Hydro Power
Table 2-1: Summary of Financial Returns on Sample Micro Hydro Plants After
Financing
Cost per kW including transmission (US$1998)
Year of Capacity Cost per ~~I o;., IRR% End~ uses
Installation kW installed kW ( main end use cited first)
Sri Lanka cur con* cur con
Katepola 1994 35 $2.181 14.7 8 No retum Electricity for domestic end
uses and services
Kanda! Oya 1997 10 $3.115 15 9.3 10 6.9 Electricity for domestic end
uses and services
Pathavita 2 1997 10 $2.203 32 16.3 6 3.1 Electricity for domestic end
uses and services
Seetha Eliya 1983 60 $3.761 24 12.4 24 12.-+ Tea factory. Electricity for
domestic end uses
Nepal cur eon cur con
Barpak 1992 50 $2345 33 27 22.8 17 Mechanical power (milling
etc); Electricity for domestic
end uses
Gorkhc !984-6 25 $714 42 32 17.4 4 Mechanical power (milling
(Rupatar) etc); Electricity for domestic
end uses
Ghandruk 1985-8 50 $2.446 I 0.48 l No retum Electricity for domestic end
uses; Mechanical power
(milling etc):
Gaura 1987 25 $2.277 13.2 3 7.39 NA Mechanical power (milling
etc): Electricity for domestic
end uses
Peru cur con cur con
Atahualpa 1992 35 $2.358 NA 17.5 14.5 Electricity for domestic end
uses and services:
Mechanical power
i Yumahual 1998 II S3J71 NA 17.6 14.6 Electricity for incubating
plant
Pedro Ruiz 1980 200 $5,630 NA No Retum Electricity for domestic end
uses and services
Pucara 1986 2x200 $1.136 NA 7 3 Electricity for domestic end
uses and services
Zimbabwe cur con cur con
Nyafaru 1995 20 $3,307 Grant H NA Electricity for domestic end
uses and services
Svinurai 1993 13 S715 Grant 48 20 Mechanical power only
(grain milling)
Mozambique cur con cur con
Elias 1996 15 $1,200 NA insufficient Mechanical power only
accurate (grain milling)
data
Chi tofu 1995 15 $U33 insufficient Mechanical power only
accurate (grain milling) data
• • • • • • • • • • • • • • • •
• •
• • • • • • • • • • • • • • •
The Cost of Micro Hydro and its Financial Profitability 11
• All currencies in $1998 unless specified.
• *Calculations carried out in constant dollars 1998 .
• In current local currencies apart from Peru and Mozambique which are in current US$ .
• N/ A applies where the project was funded entirely or to a large extent from non-reimbursable external
sources, the IRR on capital invested is extremely high .
• The results regarding the internal rate of return (IRR) and the return on capital invested refer to
calculations after financing, when loans were taken up.
• IRR for Mozambique were not calculated due insufficient accurate data .
• For schemes where the producer is also the only consumer (ex. Yumahual in Peru, Seethe Eliya in Sri
Lanka) the analysis assumes that the production is sold at the opportunity cost of electricity generated by a
credible alternative, either the grid or diesel.
2.2 Wide Variation in Costs
The variations in capital costs have a number of explanations. While common-sense su~gests
that micro hydro is likely to experience some economies of scale in the size of each plant 1 , this
cannot be concluded from this particular sample . The main explanation appears to lie in the
two types of project, namely: schemes designed to provide mechanical power for productive
activities such as agro-processing; and schemes for which the bulk of the production is to
supply electricity for domestic end-uses and services. The investment cost for mechanical
power is relatively low .(US$714 to US$1,233), as there are no transmission lines, connections,
or generator. The lowest cost per kilowatt installed were found in Gorkhe, originally built to
supply mechanical power, Svinurai, Chifotu and Elias which supply mechanical power only.
Figure 2-1 Installed Cost per kW (US$1998)
6000 US$ perkW
5000
4000 •
3000 • Meehan power
• Electricity
2000 •
1000 • 0
Electricity generation schemes, as expected have a higher installed cost per kW. there are also
some differences between countries and even within the same country which might be
explained by the following parameters:
15 Economies of scale arising from the size of each individual plant should not be confused with economies of scale associated
with the size of the programmes supporting micro hydro expansion discussed in Section 2.1.
12 Best Practices for Sustainable Development of Micro Hydro Power
• Site characteristics;
• Transport to site (in Nepal transport is said to constitute 25% of total costs 16 );
• The labour content, and the wide variation between the cost of labour in the countries
studied;
• Standards 1 7 ;
• Sizing (municipal plants in Peru were often over sized); and
• Transmission and distribution costs.
A major conclusion can be drawn from this: Costs are highly site spec(jic, are controllable with
good management, proper sizing and appropriate standard'i.
Two other issues emerge from this analysis of costs. ln addition to the costs identified here for
supplying energy, all systems also require substantial investment in end-use technologies to
make the supplied energy useful.
Furthermore, a major advantage of micro hydro is that it can be built locally at considerably
less cost than it can be imported 18 , and the costs of local manufacture can be reduced still
further by developing local engineering capabilities and advisory services. For instance in Sri
Lanka imported turbine generating sets up to l 00 kW cost approximately Rs.50,000 to
Rs.l50,000 (US$700-US$2,000) per kW, while the local manufacturers are now capable of
delivering them at Rs.l 0,000 to Rs.l5,000 (US$140-US$200) per kW, with marginally reduced
turbine efficiencies 19 .
2.3 How Do the Costs of Hydro Compare with Other Options?
The picture seems quite favourable to micro hydro. When bringing improved energy services
to poor people is the priority, the focus moves to the type of energy services they require and
their locations. If minimum lighting is the only energy end-use required in remote locations,
photovoltaics may be the main altemative, being cheaper than dry cell batteries, and capable of
producing a better light than kerosene. Where falling water is available, micro hydro compares
well with photovoltaics. In Peru the cost of 50-Watt systems (modules, regulator, battery, 3
lamps, other components and installation) is said to be $1 ,020 20 . Jn South Africa it is currently
suggested that the unsubsidised delivered cost of Solar Home systems is approximately
US$625 for a 50 Watt system (including battery, controller, wiring and 4 lights), giving a
US$10/month break even cost using money at 14% real 21 . This is equivalent to about $12,500
per kW and would therefore appear to be much more expensive than the cost of the most
expensive electricity from micro hydro.
Fossil fuels (particularly kerosene) will remain the main altemative to biomass fuel for poor
people, as it can be purchased in the tiny quantities and for the small sums of money that are
most consistent with poor people's cash availability22 . Micro hydro, like many other
16 World Bank. Rural Energy and Development. page 51.
I" Tampoe notes that early schemes spent about Rs. 2.000-3.000 on household wiring per household but this increased toRs.
4.000-g.ooo in later schemes in 1996/7 where the CEB standards were applied (Tampoe. M .. 1998. unpublished report to
!TOG ppl40).
"However. very inexpensive (but possibly unreliable) micro hydro equipment is sometimes available from China and other
countries that are keen to obtain foreign exchange at almost any price.
19 Sri Lanka Report Section 5.3.
211 Peru Report.
21 Personal observation. 1999.
22 It is perhaps important to note. in passing. the favourable environmental consequences of using kerosene. Professor Kirk
Smith and others have shown that a switch from biomass to kerosene and LPG as a cooking fuel would result in a considerable
The Cost of Micro Hydro and its Financial Profitability 13
decentralised renewable energy options, are characterised by high initial capital costs (certainly
higher than diesel systems) which are otiset to some extent by relative low recurrent costs.
This means that 'entry costs' are likely to be beyond the reach of poor people, even if the
lifetime costs of these options is lowest23 .
Diesel is the real bench-mark against which micro hydro has to be judged. One of the
outstanding features of micro hydro is that under the right conditions it can provide the power
(both electric and shaft power) to secure livelihoods through the use of electric motors and
other equipment for production. Here the picture is mixed. A comparison with diesel generator
sets carried out in Peru shows that micro hydro was the least cost option at the sample sites. It
is even more beneficial if the impact on the environment over the lifetime of the project is
included. However, the results depend on the cost of transporting the fuel and the cost of
capital. A study conducted in Nepal by New Era revealed that five out of the 25 micro hydro
plants were not economically viable because diesel generating sets were operating in the
vicinity.
In Sri Lanka the cost of diesel generation is estimated to be about US$1,000 per kilowatt
installed 24 . However, the lack of trained technicians to provide regular maintenance is currently
a major obstacle to their further penetration into the rural environment. Even so, some several
thousands electric generators of less than 75 kVA were imported into Sri Lanka in 1996 at a
cost of over $1 0 million.
In practice the crucial factor is likely to be the availability and cost of transporting the fuel, and
the extent to which the price of diesel (and the system on which it is transported) is subsidised.
2.4 Micro Hydro can be Financially Profitable
The profitability of the sample projects was measured using both an intemal rate of retum
(IRR) and a retum on capital invested 25 . The consulting firm, London Economics (LE), was
contracted to design a simple spreadsheet model to generate and test the profitability of the
schemes and to assess the quality of the resulting data.
Two types of I RR were calculated:
• In the first calculation all the income is taken into consideration (grants, subsidies
etc.). This is the real retum of the investment made by the owner. But with this
method, schemes that were able to attract a high level of subsidy or grant will have a
very high retum. When a loan is taken up, the repayment is made according to the
agreement with the financial intermediary, usually a bank.
• In the second case, it has been·assumed that grants and subsidies are covered by soft
loans. This indicator shows what the IRR would be in the case where subsidies and
grants are in effect replaced by soft financing facilities.
The two indicators are important because they reflect prevailing and future situations.
reduction in green house gases (GHG) per person meal. This is due to the considerably greater efficiency with which liquid
and gas fuels can be converted into heat for cooking. Burning wood fuel in a normal cooking fire or traditional stove is not
"green house gas nemral" because of the products of incomplete combustion (Kirk Smith. et al 1998. Report for the US EPA
Green House Gases fi'om Smull Scale Comhustion De1·ices in Dn·eloping Counlries Phase IIA Household Stoves in India
(October 12)).
23 See Fig 3.1 and Table 4.1 , World Bank. 1996, Rural Energy and Development.
::~FeasibilitY ofDendro Power Based Electricitv Generation In Sri Lanka, Forum. Sri Lanka. 1998.
:;:; See anne~. •
14 Best Practices for Sustainable Development of Micro Hydro Power
All IRR were calculated after financing. When a scheme was almost entirely financed by
grants and subsidies, it has been assumed that the scheme was financed by a soft loan, at rates
which vary between the countries in which the plant is located. The IRR were calculated in
current and constant US dollars. Assumptions were made about what the inflation rate would
be for the lifetime of those schemes that were implemented only recently .
· Experience across the study countries shows a wide range of financial profitabilio/6 and some
interesting common features. The microanalysis reveals that there are plants that can be run
profitably without subsidy. These are the projects with a constant price rate of return of more
than 8%. These plants are Seetha Eliya (12.4%), Barpak (17%), Atahualpa (20.5%) Yumahual
(14%) and Svinurai (20%), plus possibly the two mechanical plants in Mozambique 27 • All
these tend to be the plant installed initially or solely to produce mechanical powe-r for a
profitable end-use such as milling.
Where plants are used exclusively for electric lighting, operating costs can usually be covered
by electricity sales, but the capital costs will have to be subsidised by grants.
The analyses in current prices inevitably have higher IRR than those in constant prices. This is
because tariff setting is often very poor and therefore the price of electricity is not being
adjusted to keep pace with the rate of inflation. An important conclusion of the review is,
therefore, that the financial return of many of the projects could have been improved
considerably if the tariffs had been adjusted merely to keep level with inflation. This is
particularly the case in Seetha Eliya in Sri Lanka and Svinurai in Zimbabwe (see Table 2.1).
Figure 2-2: IRR Without Subsidy
IRR without subsidy
%
60~-----------------------~
50+-------------------------------------------:
40+-------------------------------------------~
30+---------------------------• 20+-~~~------------~~~----~---••
10+---~.r-------~----~~--~ • 0 -t,----"""'T"-----r--...;;....-----1
• IRR current
e IRR constant
At a more fundamental level, variation in financial performance of the projects reviewed was
due to variation in load factor. High load factors were achieved in schemes supplying
mechanical power or electricity to motors rather than those installed primarily for lighting.
Lighting for 4-5 hours a day can theoretically give maximum plant factors in the order of 0.15
to 0.20. This is indeed the typical plant factor for many micro hydro plants examined. In
Nepal 90 % of the schemes are supplying mechanical power. These schemes have a better
profitability and can be financially sustainable in remote locations.
26 As a result of some gaps in the data and assumptions made, the internal rates should be seen a broad indicators and trends,
rather than precise returns actually achieved in each plant. (See annex for details.)
27 Due to insufficient accurate data, we did not include the IRR for the two Mozambican schemes investigated.
• • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • •
The Cost of Micro Hydro and its Financial Profitability 15
The micro hydro industry appears, therefore, to be faced with a particularly difficult paradox.
Most of the financially viable installations provide mechanical power to productive enterprises,
but the main demand from consumers in a number of countries appears to be for electric
lighting.
Micro hydro is therefore most likely to be profitable or at least financially self-sustaining,
where there is:
• a high load factor (the actual consumption as a proportion of total possible generation),
• a financially sustainable end-use,
• costs are contained by good design and management, and
• effective management of the installations, including the setting and collection of tariffs
that keep pace with inflation.
2.5 Cash Generating End-Uses.
It is a truism to say that MHP is likely to be more financially viable if the electricity generated
can be used to supply power to a profitable cash generating enterprise. The use of a single mill
for a few hours per day can clearly raise plant load factors substantially. Furthermore the
choice of end-uses can have a profound effect on extending the benefits of micro hydro to
households that cannot be connected directly to the system, either for reasons of cost or
location. Such end-uses range from street lighting, access to public television, battery charging
centres, to mills and other forms of agro processing. However, the studies show that such
enterprises are otl:en difficult to develop. Combining new micro hydro installations with new
income generating enterprises that have a daytime use for hydro electricity in remote locations
is difficult, not least because local markets are small and isolated.
In discussions of this review in Sri Lanka, for instance, both practitioners and policy makers
were united in expressing their extreme scepticism about the creation of such enterprises. They
argued that:
• Attempts to create electricity using enterprises in the past have tended to increase
social tensions within the village and within the management of the Electricity
Consumer Societies that own the hydro plant. It is seen as offensive that the public
asset of water is being used to increase the power and wealth of an individual.
• Community-owned enterprises, such as rice mills, have often been too large in relation
to the local small and isolated market, too costly in relation to the capital available in
the village and too difficult to manage in relation to the managerial capacities in the
village. It is to assume away the problems of underdevelopment to assume that such
enterprises will start up spontaneously after the arrival of electricity.
• The support for small and micro enterprises that is offered in Sri Lanka is said to be
limited and could not be assumed to be available to people or groups setting up
businesses to use micro hydro plants.
16 Best Practices for Sustainable Development of Micro Hydro Power
Mechanical energy for grain milling from a micro hydro plant
Similar problems have been experienced about community-owned enterprises in Nepal,
particularly where villages contain a wide range of castes 28 . However there have been notable
exceptions, particularly in Nepal and Peru were particular entrepreneurs have not only invested
in micro hydro, but they have sold power to their neighbours and started up a number of
businesses29 .
2.6 Links To The Grid
Sales to the grid represent a special case of cash generating end-uses. Sales, when power is in
excess, could provide a better load and the potential for reliable cash flow . The opportunities
for selling to the grid are likely to be more feasible at the 'mini', however, than the 'micro'
hydro scale.
In one case in Sri Lanka the high returns to one of the plants (Seetha Eliya) was a consequence
of the high value imputed to the electricity from the micro hydro plant. The plant provided
electricity to the Tea Estate where otherwise only expensive and unreliable power from the grid
would be available. In the case of Peru (Yumahual), the high return is due to the opportunity
cost from of electricity generated by a diesel generator. The cost per kWh from genset is
usually quoted at around 18 US cents per kWh. Of course with such a cost it is likely that the
investor would have opted for other options.
28 Wolfgang Mostert, Scaling-up Micro Hydro , Lessons from Nepal and a few Notes on Solar Home Systems, Village Power 98
Conference NREL/World Bank, Washington October 6-8, 1998
29 See for instance Private Micro Hydro Power and Associated Investments in Nepal: The Barpak Village Case and Broader
Issues, Bir Bahadur Ghale, Barpak Entrepreneur, Ganesh Ram Shrestha, Executive Director, Centre for Rural T echnology and
Russell J. D e Lucia, Ph.D., President De Lucia and Associates, Inc., Small-Scale Natural Resources and Related Infrastructure
Development, June 1999, Natural Resources Forum, Special Issue.
• • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • •
The Cost of Micro Hydro and its Financial Profitability 17
In Sri Lanka the Ceylon Electricity Board (CEB) introduced the small Power Purchase
Agreements (PP As) in 1996, and specified the prices they would pay for energy from grid
connected small power producers with generation capacities of up to l 0 MW. These prices are
set by the CEB on the basis of their avoided costs. Consequently the prices vary according to
the time of the year and the availability of water in large hydro reservoirs. These prices do not
reflect the environmental costs and benefits from small hydro development. The profitability
of this option clearly depends on the regulatory framework and the price that the utility is
prepared to pay.
In 1999 the prices offered for the dry season were 4.6 US cents per kWh and in the wet season
3. 9 US cents per kWh30 . This would appear to be in line with the average cost of production of
a properly run micro hydro plant and with a significant load factor.
Proximity to the grid nonetheless poses its own problems. For many rural people the presence
of grid electricity puts the purpose of a hydro plant into doubt. In Sri Lanka it is feared that
where an Electricity Consumer Society (ECS) is near enough to the grid to make the necessary
connections the ECS members will abandon the MH power and buy directly from the grid at a
price that currently is below the cost of production. Similarly in Nepal a study carried out in
1998 found that 3 8% of the 60 micro hydro plants reviewed were located within 10 km of the
grid (particularly in the Central Development Region) and this had an adverse effect on their
business 3 1•
Uncertainty about when the grid will arrive in a village, often as a result of politicians making
false promises prior to elections, considerably increases the risk of investing in a micro hydro
plant. Such risks could be reduced by government or the utility developing a clear plan for grid
extension, and making it publicly available. Similarly where the private sector is involved in
extending central grids near to existing micro hydro plants, it will be important to have a
regulatory framework that requires the grid to buy power from the hydro plant at a reasonable
price, or buy the plant at its depreciated value.
In Sri Lanka it is estimated that in general micro hydro will not be financially viable if the
national grid is available within 4 km to 5 km. The cost of grid extension is currently estimated
at US$7 ,200 per km of primary distribution lines.
2.7 Making the 'Profitable' Social is Easier than Making the 'Social' Profitable!
A clear lesson that emerges from the review at this stage is that projects that start out primarily
with social objectives find it very difficult to add on profitable end-uses. Micro hydro
investments envisaged at the outset as primarily supplying power to a business venture can
more easily add on the provision of a social service such as lighting, or power for schools or
health clinics.
'
0 Source: Government press notices. Daily News. Sri Lanka. various dates.
31 Earth Consult (P) Ltd. in 1998.
3.1
3
MEETING NEEDS AND THE CIRCUMSTANCES OF
AFFORD ABILITY
Price and Demand
The cases show that micro hydro can be profitable, but they also show that when it is profitable
it is not necessarily also affordable. A recent report from the World Bank confirms the view
held by many people involved in the practical implementation of rural energy schemes when it
says that:
"It is illusmy to expect that increasing access to electricityfor a sign(ficant part of
the population traditionanv excluded .fi'om grid based electricity can be financed
1 b h 0 ,, ) on J' y t e przvate sector ·-.
The case studies support this view. Tariffs that are considered high in relation to local
conditions can have a marked effect in choking off demand. In Peru, State owned micro hydro
plants charge $1 0/month, and private companies charge $9/month. It was found that "although
the service is reliable, it is evident that the high rates (three times higher than those paid by
companies run by communities or municipalities) restrict the service coverage". At these rates
only 50% of households can afford power compared to 70% of households buying from
municipal plants charging lower rates 33 .
A Dutch funded scheme appears to have had a similar experience. The government of the
Netherlands has been particularly innovative and an early supporter of decentralised energy
options. But its assistance to micro hydro development in Peru does not appear to have been
successful. In an effort to push the schemes to a more financially sustainable orientation the
scheme had very few takers prepared to borrow at rates of interest which were similar to the
nom1al (high) commercial rates 34 .
These experiences lead the Peruvian report to conclude that if the private sector were to take
over all rural electrification, they would tend to select the more profitable markets and expand
only slowly towards users with lower income using less energy. In their experience private
forms of ownership tend to be more sustainable in both financial and administrative tenns, but
tend to neglect service coverage. Similarly, municipal schemes tend to be less financially
sustainable, but when they work properly they tend to have a wider coverage. 35
32 Best Practice Manual: Promoting Decentra/ised E/ectri/icationlm·estment. ESMAP World Bank. 1999. Page I 0. (Sec this
page also for characteristics of Smart Subsidy.)
33 See Pem Report. Section 5.
34 Tarnawiecki. Donald: Win· is Dutch Aid lneffi'ctive in Pem:) In Renewable America No.2, September 1997. PUC. Lima.
·1' Peru Report.
19
20 Best Practices for Sustainable Development of Micro Hydro Power
3.2 The Benefits and Burdens of Remoteness
Even if micro hydro were affordable to poor people with easy access to equipment, advice and
credit, it is certainly likely to be more expensive and more difficult for people in isolated rural
communities. This is particularly so for families that earn less than US$500 a year in areas
where municipal resources are scant. They do not have sufficient information and contacts to
identify credit sources, credit tern1s, existing technical alternatives, etc. These are the typical
and recurrent failures of both markets and policies that affect activities in remote rural areas. In
this context, development activities with such populations result in high transaction costs for
both financial institutions and for the suppliers of equipment and technical assistance, making
them unattractive to customers. Consequently, this section of the population is effectively
'excluded' from the marker3 6 .
At the same time this remoteness adds to the costs of all energy supply options, albeit not in the
same way. Remoteness increases the comparative advantage of micro hydro relative to other
options that require transportation of fuels, or frequent visits from urban-based technicians or
revenue collectors.
3.3 The Case for Subsidy
If the price of the energy supplied oy micro hydro is too expensive for poor people who need it,
then the issue of subsidies and/or grants cannot be avoided. The political acceptability of
subsidies has undergone wild fluctuations in recent years. All governments provide subsidies,
but it is clear that some have done more harm than good. The essential question that has
emerged from the ideological posturing of recent years is less about the rights and wrongs of
subsidies in principle, but rather whether a particular form of subsidy actually achieves its
intended purpose.
The arguments for using money that is supplied at less than full commercial rates of interest are
overwhelming if large numbers of people are to be given access to improved energy services.
This 'soft money' will be required to enable people with insufficient purchasing power to gain
access to electricity, and to other more convenient fonns of energy.
In the most general tern1s, the reasons why agencies of the state, whether national or
multinational, should provide soft money are well known:
• to capture the existence of many positive 'externalities' not reflected in market prices,
such as the benetits of health, education, welfare, and environment;
• to redistribute income from richer to poorer parts of the community for reasons of
equity and or human rights:
• to kick start an 'infant' industry by enabling the volume of production to be increased
and skills developed to the extent that unit costs of production fall to levels where the
target consumers can afford to buy them on a sustainable basis in the future;
• to remove or reduce the barriers associated with inefficient operation of the market.
Usually including the unequal distribution of information between buyers and sellers,
monopoly elements among both buyers and sellers, and hostile features of the
'enabling' environment, such as the unintended consequences of taxes, subsidies to
competing options, lack of appropriate regulation, inadequate financial and physical
infrastructure, etc.; and
"' Peru. country report
Meeting Needs and the Circumstances of Affordability 21
• to assist users in overcoming the high initial costs of purchases that are 'least cost'
when considered over the their operational lifetime.
While subsidies to 'pump prime' markets are quite different from those intended to lower the
cost of 'social infrastructure', perhaps the most persuasive argument for subsidising micro
hydro is made in terms of 'levelling the playing field' with other competing options and
concern about 'fairness'. This arguments suggests that:
• micro hydro should receive subsidies that are equivalent to those received by
competing options such as the grid or PV;
• micro hydro needs to be compensated as it is unfairly discriminated against in-so-far
as it does not get the same tax breaks and other concessions as other technologies;
• micro hydro needs to be compensated because the full cost of other options· is not
included in the price. For example, the environmental costs of using fossil fuels such
as petrol, or biomass fuels such as woodfueL
There is also weight in the argument that people in remote locations 'deserve' electricity as
much as poor people in other parts of the country. Furthermore, subsidies to micro hydro may
well be justified because they are the least cost way of achieving other development objectives,
such as motive power to secure livelihoods, lighting for health and education, refrigeration for
the storage of food or medicines.
3.4 Limitations of Financial Analyses
The aforementioned arguments suggest that in the analysis of competing options, such as on the
basis of 'least cost', conclusions are likely to be misleading if the analysis is restricted to
market prices alone. Clearly if the arguments listed here are accepted, market prices for goods
and services are unlikely to fully reflect their value to poor people or to the nation. Finding the
'true value' of electricity becomes particularly complex if it is to take into account the so-called
'externalities' mentioned earlier. When externalities are considered, gains are made by, for
example, calculating the value of other sources of energy not used (kerosene, dry batteries), and
the improvements made to the quality of life of those people switching to electricity from other
sources of energy. More fundamentally, prices cannot reflect value if the existing distribution
of income is judged to be unacceptable, as this restricts the consumers' communicating their
'willingness to pay' to meet their basic needs, by their 'ability to pay' for them.
Most international financial institutions such as the World Bank accept the validity of these
arguments and make the necessary adjustments by using some form of 'economic' or real
resource cost analysis in combination with financial analyses based on market prices:n.
However, it is market prices that consumers have to pay to gain access to micro hydro power,
and therefore it is important that the regulatory framework brings market prices closer to
'economic' values, and that subsidies compensate for the remaining 'distortions'.
3.5 Filling the Gap Between Full Cost Finance and Free Grants
Before considering subsidies in more detail, it is important to stress two points that have
emerged in the current debate. Firstly, the ability of governments, aid agencies or charities to
provide subsidies is severely limited in relation to the numbers of people who do not have
access to modern forms of energy. Secondly, there is probably more energy-related purchasing
The World Bank's own approach is set out in L Squire and H.G van der Tak "The Eco11omic Anah·sis of" Proiecls" !975
John Hopkins Press.
22 Best Practices for Sustainable Development of Micro Hydro Power
power in poor communities than was previously thought. There is now substantial evidence 38
that people currently excluded from most 'modern forms of energy' do already spend
considerable amounts of money to meet their energy requirements, on charcoal, dry cell and
lead acid batteries, candles and kerosene, and in some locations, on fuel wood.
This variability in the ability of even poor people to pay for energy services suggests that from
a policy perspective it will be important to distinguish at least three types of financial
sustainability. In this way subsidies are used to maximise access and are not wasted on people
who already have the ability to pay. This approach forms the basis of recent changes in the
Peruvian government's policies for rural electrification. In this case the National
Electrification Plan established three types of electricity expansion projects, depending on the
economic characteristics of the target market:
Class I Projects: Profitable Projects. These projects are intended to make a profit, and
under the provisions established in the Electricity Concessions Law, any entrepreneur who
identifies a profitable energy project is given the opportunity and the necessary guarantees to
implement it.
Class 11 Projects: Non-profitable but sustainable projects. If these projects are
adequately managed they are capable of covering their operating and maintenance costs, even if
they do not make a profit. In this case, the State tries to implement joint financing programmes
in order to obtam the so-called 'investment commitments' from the private sector. Such
projects include those built with State funds but which are subsequently transferred to private
or other companies for their operational phase.
Class III Projects: Non-profitable and non-sustainable projects. These are projects
aimed at expanding the electrical frontier, for which all that is required is to select
technological alternatives that produce the least operating and maintenance costs 39 .
The experience in Sri Lanka reflects a similar situation where micro hydro schemes that are
designed for industrial activities on the Tea Estates can be highly profitable (i.e. Class 1)
because of the size of the costs avoided by not using grid electricity. Schemes that supply
electricity for rural communities are unlikely to be financially viable without soft money. But
even in this sub-market, relatively small one-off grants can result in schemes that can be
financially sustainable in this more limited sense (i.e. Class Ilfw.
3.6 Smarter Subsidies
If the case can be made for subsidies, experience suggests that the use of soft money can both
help the expansion of the micro hydro sector and harm it. As always the 'devil is in the detail'
and in the specifics of each context. Hence the phrase 'smart subsidies' 41 has been coined to
put some distance between current forn1s of subsidy and the earlier fonns that were shown to
stultify innovation, destroy markets, and support the already rich. Examples of this were the
subsidies for grid-based electricity, kerosene and diesel.
1x For instance from studies in India. Uganda and Zimbabwe undertaken by the UNDPIWorld Bank's ESMA P programme .
. N Pent. Section 4.2. However under the current schemes in Peru there is a market segment who are not being sen ed by the
systems run by private concession holders. and which are also not included in the medium-term plans of the small systems or
facilities run by the StatiC. This is the segment that is currently met by ~GO.
Sri Lanka, Section 4.
"1 See Dr Subodh Mathur. Presentation to the World Bank/NREL Village Power 9K Conference. Washington DC October
199K and Best Practice Manual: Promoting Dccentraliscd Electrifieation Investment, ESMAP World Bank. 1999 Page l 0.
Meeting Needs and the Circumstances of Affordability 23
The key lesson from past experience appears to be to avoid app~ving un-ending subsidies to the
recurrent costs of micro hydro operation. or more 5pecijically do not direct(v subsidise the
price charged to the energy end-user.
'Smart subsidies' should be designed in such a way as to re-enforce the commercial orientation
of micro hydro schemes to reduce costs and improve service. In most cases this will mean
focussing on reducing the cost of the initial investment, thereby increasing the numbers of
people who have access to electricity, rather than continuously subsidising the recurrent cost of
operation42 .
More generally subsidies that are based on rules and are transparent to all parties and well
known before investments have taken place are less likely to result in waste and corruption.
It is also important to consider a wide range of ways in which the costs of the whole micro
hydro development can be reduced, and not just be a subsidy to the providers of finance.
Providing subsidised assistance for the training of turbine manufacturers, or independent on-
site feasibility studies appears to be particularly effective in reducing costs to the user, and in
reducing the risks to the investor.
A particular problem with current subsidies provided by bilateral donors is that they have a
tendency to 'pollute the well' that is, they use their subsidies to. spoil the market for others.
This can occur if aid subsidies are a~ailable to a particular technology thereby making it very
difficult for other technologies to compete. This again happens where subsidies are tied to a
particular supplier, usually nationals of the donor country, thereby giving them an unfair
advantage. Donor subsidies are currently even being awarded to huge multinational
corporations in a number of areas of renewable energy and in particular countries, which makes
it particularly ditlicult for smaller local suppliers to compete.
3.7 The Poverty Impact of Micro Hydro
It was not the intention of this study to measure the poverty impact of micro hydro. However
David Fulford, Paul Mosley and others have recently attempted this very difficult task in a
parallel study commissioned by the UK's Department for International Development. As these
authors point out, it is conceptually and empirically difficult to attribute measurable poverty
impacts to relatively small investments, such as micro hydro. This is because in such cases
there are many other circumstances, such as climatic variation and macro economic change that
affect the measurable poverty status of remote communities over any particular time period.
However, these researchers used a 'second best' approach, consisting of tracking, by partial
equilibrium methods, the effects of micro hydro on the incomes of the poor through changes in
entrepreneurs' incomes, labour incomes, consumer real incomes and backward and forward
linkages. Following this approach the researchers found:
"in relation to the number o{ schemes in existence the povertJ' reduction
peF.formance of micro hydro is impressive. particular~v in Nepal and
Ethiopia .... micro hydro is indeed a relative~v efficient method (~fpovert_l' reduction,
in terms of costs per person moved across the poverty line. The poverty gap
measure suggests that micro hydro is also able to reach a number of the extremely
12 Lifeline tariffs may well be an exception to this. but may be justified where the subsidy is essentially paid by a '"cross
subsidy" from richer consumers, so preserving the idea that the whole enterprise covers its operating costs.
24 Best Practices for Sustainable Development of\llicro Hydro Power
poor .... through the channel of wage employment in micro hvdro schemes
themselves and linkage activities derived from those schemes. In addition, we
believe that the estimates of poverty reduction from micro hydro .. !:>)'Stematically
understate pover(v impact, as they exclude a range of voy difficult to measure but
important effects such as time savings Jj'om no longer having to carry kerosene or
other fuel, improved education .fl-om the availability of electric light and improved
health and agricultural production ji·om drinking and irrigation ·water made
available out o{channels originally developedfor micro hydro schemes."
"On the prelimina~:v data presented here, therefore, there would seem to be
evidence enabling a poverty reduction case to be made for the promotion of micro
hydro. in particular through the policy instruments spec(fied. Whether that indeed
turns out to be the case depends on whether the estimates presented here can be
validated by a broader range of data, both from the countries considered here and
elselvhere". 43 .
3.8 Gender and Micro Hydro
The five country reports provide little or no gender disaggregated information. However one of
the authors had carried out a path-breaking piece of research on the gender related impact of
micro hydro in Sri Lanka in the mid 1990's. This covered a sample of 5 plants, selected to
represent different income levels and end-uses. Unfortunately only one of the sampled plants
was also covered in the more recent survey (Pathavita)44 . A random sample of some 86
connected and unconnected households were investigated (within which a sub-sample of 45
households was selected where both male and female members of the household were
interviewed).
While participation in village activities was generally found to be higher for males than
females, the sample showed a wide variation between the villages in the extent of female
participation in the hydro schemes. As might be expected, those households that are connected
to the hydro system participated considerably more than those that were not. Generally males
dominated the planning and initiation of the projects. In some Electricity Consumer
Societies women were ·'not regarded as decision makers" while in others they were
encouraged. ECS meetings were frequently held on weekday evenings, which were
particularly difficult for women to attend. Technical issues were frequently regarded as "male".
The benefits were largely at the household level (lighting, TV and battery charging) for
connected households, but unconnected households benefited by access to TV and the
possibility of hiring lights for special occasions. Women tended to see the benefit of electricity
largely in terms of reducing their workload, health, reduced expenditures. Whereas the men
saw benefits in terms of leisure, quality of life and the education of children. In connected
households the benefits of lighting ("a public good") were equally distributed between males
and females, but in unconnected households, the males were able to obtain more benefit as the
women were often excluded. Most Perhaps the most important finding was that the impact
upon uncmmected households was greatly affected by the choice of end-uses. For example, it
4·' Micro hnlro generution as ins/rumen/ ojpo1·ertr reduction: Asian achiel'e/1/enl and A/dean pole/Ilia/, by David Fulford,
Alistair Gill and Paul Mosley, Reports to DFID. Reading University.
·l·l Kiran Dhanapala. I 995. Report on !he Gender Rela!ed lmpacl o( Micro lfrdm Tcchnolog\· a1 the I "ill age Lend, Imcrmediate
Technology. Study Report Number 2. 59 pages.
Meeting Needs and the Circumstances of Affordability 25
is suggested that the addition of a chilli mill would probably produce more benefits to the
excluded group than say the addition of a battery charging station.
The survey showed that typically less than 50% of the households benefited from micro hydro,
re-enforcing village level power structures or increasing friction within the village. This
evidence has implications for poverty alleviation policy. Earlier we saw the impact the chosen
end-use had upon the type and distribution of benefits between households and between men
and women. Together these observations underline the importance of including both women
and non-connected households in the decision-making process if poverty impact is to be
maximised.
In Nepal, an assessment of the impact of Gandruk hydro plant suggested that the advent of
television had a significant 'cultural impact'. Women could see that they, "don't have to remain
as second class citizens"45 .
~'Social Impacts o( Electrification: Micro Hnlro in Gandruk, .'Iiepa/. by Joshua Thumim. MSc Thesis. 1999. Imperial College
London. In this case only one quarter of the households were electrified. with the richer households consuming more power
than the poorer ones. Thirty households were interviewed (of which some 30~o of the interviews were with women). The data
are not disaggrcgated by gender.
4
INTERMEDIATION IN PRACTICE: EXPANDING THE
USE OF MICRO HYDRO
4.1 Many Dimensions
A variety of approaches have been used to diffuse micro hydro. The chosen strategies vary
according to local circumstances and how long the programmes have been going. In the early
days the approach typically involved a small group of enthusiasts (usually engineers in NGO)
who raised awareness of the possibilities by building and demonstrating plants, while more
mature programmes involved strong interactions with the main agencies of government and
development assistance. Broadly speaking each strategy involves a combination of the
following five elements:
Project
Promoters:
Financing
Mechanisms
Plant Owners
I Managers
Technical
Support
Mechanisms
Main End-
uses
• Government owned utilities
• Non-Governmental Organisations
• Equipment manufacturers
• Individual entrepreneurs
• Multilateral or bilateral aid agencies
• Formal development bank loans and grants
• Grants from charities
• Equity from private (local) savings and
contributions in kind
• Utilities
• Municipal authorities
• Existing formal businesses such as Tea Estates
• Individual (village based) entrepreneurs
• Village or community groups
• Change agents (Village Catalysts, barefoot
engineers)
• Engineering workshops
• Existing consulting engineers
• NGO
• Domestic lighting I radios
• Social services (to schools, health centres, street
lights)
• Productive end-uses, usually using motive _Qower
27
'
28 Best Practices for Sustainable Development of Micro Hydro Power
4.2 The Main Diffusion Strategies
The uncertainty surrounding the best method of expanding micro hydro was due to a number of
factors: the situation was changing rapidly; the current strategies were not necessarily fully
documented 46 ; and due to the number of different actors involved, each with a different
strategy, some of which were implicit rather than explicit.
In most cases it would appear that the govemments in the countries examined do not have
policies specifically for the development of micro hydro. Although some had policies to
encourage rural electrification, these were usually through grid extension. Where there were
policies to support a particular technology. such as solar photovoltaics, these tended to be
driven by extemal donors.
The main elements of the current expansion strategy can be characterised as follows.
Summary of Strategies to Expand the Use of Micro Hydro Plants in Selected Countries
Peru An NGO led strategy based on a revolving fund financed by the Inter-American
Development Bank.
Sri Lanka
Nepal
• The Government's Executive Projects Directorate (DEP) created a
strategy for isolated areas (1997-2000) but m practice this focuses
largely on mini hydro power plants (60) and diesel generators (72).
• There is no explicit strategy for the smaller. micro hydro power.
• The regulatory framework is aimed at promoting private investment in
generating and distributing electricity but the Govemment's clear
preference is to support grid based electrification.
A long standing programme in many phases:
• Initiated in 1979 by the Altemative Energy Unit of the state O\vned
utility.
• Followed by an NGO-led strategy based initially on the refurbishment
and demonstration of MHP in the Teas Estates and subsequently on
workshop training programmes and the creation of village-based
Electricity Supply Committees (#check name)
• A Technical Assistance Committee (subsequently Energy Forum)
provided co-ordination and direction between government, NGO and
private companies.
• The current phase based on World Bank funding of more commercially
orientated approaches through the Energy Services Delivery Project
operated by the Development Finance Corporation of Ceylon.
A long standing programme based on:
• The provision of subsidies to micro hydro through the Agricultural
Development Bank ofNepal (ADB/N).
• Credit support through the ABD/N.
• NGOs drove the sector, and combined building-up the capability of the
local turbine manufacturers with the development of a number of
Intennediation in Practice 29
technical improvements (the electronic load controller and the use of
electric motors as turbines).
• A significant part of the sector (turbines for milling grain) is financially
self-sustaining, and receives no subsidised support.
• The current phase of the strategy involved the creation of The Alternative
Energy Promotion Centre (AEPC) in 1996 as an autonomous body under
the Development Committee Act, and is overseen by the Ministry of
Science and Technology (MST). The mandate of AEPC is to promote
renewal energy technologies to meet the needs in rural areas of Nepal.
DANIDA is assisting those elements of the programme that promote
micro hydro development and PV.
Zimbabwe An NGO led strategy, currently at the early stage of awareness raising and the
construction of demonstration plants.
• An important element of the strategy is the Energy Forum of Zimbabwe
(EFORZ), originally the Hydro Forum. The forum draws its
membership from interested individuals, NGOs, government
departments, universities, tertiary education institutions, research
institutions and the private sector. EFORZ works closely with
government on policy and planning of micro hydro development.
Mo2m11bique An NGO-led strategy, currently at the early stage of awareness raising and
constructing demonstration plants.
• The development of new and renewable sources of energy is a result of
isolated initiatives and no institution has staff oriented solely to these
activities. The Government 1s investigating alternative methods of
supplying household and small industrial concerns with energy.
• A local NGO, KMS, funded by FOS-Belgium, is working with ITDG to
rehabilitate a number of schemes to raise awareness and demonstrate the
technology.
4.3 The Key Agents Behind The 'Strategy'
The case studies showed that even the most modest hydro development programme is likely to
involve many stakeholders: government (national and local); utilities; project owners and
operators: aid agencies; financial institutions; equipment manufacturers, assemblers and
suppliers; providers of Technical Assistance; contractors plant owners; community developers
('animators'); communities; and the beneficiaries.
Agents of the state have played a particularly significant, if intermittent, role in encouraging
micro hydro. In Nepal, the Agricultural Development Bank appears to have been the lead
institution, drawing on the services of NGOs. In Sri Lanka, the utilities (the Ceylon Electricity
Board) similarly expressed an early interest in micro hydro and then drew on the services of an
NGO and local consultant engineers.
The international financial institutions, both multilateral and bilateral, now appear to be taking
an interest in micro hydro. In the 1960's and 1970's these aid agencies invested heavily in
rural electrification, but this was almost entirely through grid extensions. This experience, and
particularly the sense that rural electrification was a bottomless pit of financially unsustainable
projects, meant that they remained reluctant to fund more recent, decentralised systems.
30 Best Practices for Sustainable Development of Micro Hydro Power
Installation of hydro system in Sri Lanka
However, they have begun to
re-consider decentralised
energy options, prompted no
doubt by their new interest in
. renewable sources of energy47
and by the enthusiasm of
manufacturers of
photovoltaics in industrialised
countries.
In Sri Lanka the World Bank
included micro hydro in its
Energy Services Delivery
loan, which was initially
envisaged to cover only solar
PV. In Nepal substantial
funding is now coming from
Danida aimed at increasing
the scale of the effort devoted to micro hydro (and PV), and to put the schemes on a more
financially secure basis.
4.4 The Issue of Ownership and the Main 'Clients' of the Strategies
The cases show that there is a wide variation in the types of actors that own and operate MHP
and that this determines both what support they require, and also the objectives that they are
attempting to achieve, and even the cost at which they do it.
In Peru the municipal authorities have played a particularly important role in owning and
operating micro hydro installations. This is partly because they are the entity that has access to
government funds and can raise local resources through taxation. The municipalities are
usually district or provincial capitals with a population that usually exceeds 500 people ( 1 00
families). The electricity services managed by them tends to have a greater coverage (higher
electrification coefficient) than those operated by 'peasant communities' or private operators,
because the Mayors tend to justify themselves by providing services to as many families as
possible.
However, this political factor also has negative consequences, as there is a change over of
Micro Hydro operating staff at each change of mayor (re-elected every four years).
Furthermore, access to central government funds means mayors are under no pressure to charge
cost-covering rates for the service and generally politicians are reluctant to raise tariffs . All but
one of the municipal plants reviewed had a negative financial balance and high rates of
outstanding payments (23%) even though rates are relatively low, equivalent to $3.2 per month
peruser.
In Sri Lanka in village hydro schemes, the ownership, management, financial control and load
regulation are carried out by the Electricity Consumer Society (ECS). These are societies
47 Interestingly the enthusiasm for "new renewables" has taken place at time during which lending for conventional scale hydro
electricity has declined rapidly. This probably means that there has been a net fall in donors' contribution to energy supplies
from renewable sources. See, for instance, World Bank Operations E valuation Department Report No. 17359, Feb. 1998, on
Renewable Energy, pages 57 and 58 .
•• • • • • • • • • • • • • • •
• • • • • • • • • • • •
Intermediation in Practice 31
formed by the villagers that consume the power delivered by the village hydro plants (see Box).
However, under the more 'commercial orientation' of the World Bank programme, the ECS
were not eligible for loans and have to be converted into limited liability Electricity Consumer
Companies (ECC). An unfortunate consequence of this is, apparently, that the consumers feel
less like 'owners'. There is less motivation to stay with the village hydro scheme or to pay back
the loan, as responsibility lies with the ECC48 .
Where utilities are the owners or substantial contributors to micro hydro, there is a tendency for
the technical standards to be higher, thus raising the cost of supply substantially 49 (see Section
4.13).
Private owners have also played an important ownership role. For instance, Tea Estates have
been particularly important in Sri Lanka, as many of the initial micro hydro plants were located
there and their refurbishment enabled the technology to be demonstrated, and experience to be
gained. However, private companies have had difficulty in getting the necessary approvals to
use publicly owned resources such as river water or the river bank (which in Sri Lanka at least
is usually owned by the state), or the necessary 'way leave' to allow conductors to cross a
public road. Individual owners may face similar constraints, but they have also been important
players and have successfully developed and owned micro hydro businesses (see footnote 29).
The case studies also contain many different forms of ownership and different styles (and
quality) of management. This is particularly taken up in the Peru report (Section 5). Generally
the reports do not support the view that there is a relationship between the quality of
management and type of ownership. Small owner operators tend to have weak management
(e.g. in Mozambique), while politically dominated management experienced in Municipal
plants and co-operatives are likely not to raise tariffs with inflation.
Experience around the world suggests that it is possible to have efficient 'business-like'
management, whether the plant is owned by individuals, state-owned utilities, or community
groups. The lesson from big utilities is to ensure that the regulatory authority is able to produce
the incentives necessary for effective management. In the smaller decentralised systems, such
as micro hydro mini grids, this also probably means setting up (corporate) structures that
minimise political interference, and provide clear delegated authority to a management to
achieve clearly stated objectives (related to profitability, coverage and the quality of service).
4.5 Intermediation and the Critical Importance of 'Project Developers'
But perhaps the most important 'agent' in the implementation of strategies for micro hydro has
been the 'project developer'. 'Project developers' are the people or agencies that: identify the
sites; help organise the community into an organisation (such as the Electricity Consumer
Societies in Sri Lanka); act for the community or plant owner to arrange the finance; obtain the
equipment; supervise design and installation; train the operators; and press for change in the
regulatory environment, etc.
~'The ECC at Pathawita is facing a severe threat to its existence with the national grid penetrating into its area. The loss of
existing consumers and the difficulty of attracting new customers may result in difficulties paying back the 8-year loan under
the ESD program.
~" Tampoe notes that early schemes spent about Rs. 2.000-3.000 on household wiring per household but this increased to Rs.
4,000-8.000 in later schemes in 1996/7 where the CEB standards were applied (Tampoe. M .. 1998. unpublished report to
JTDG ppl40).
32 Bcsl Practices for Sustainable Development of Micro Hydro Power
NGOs have been major suppliers of 'project development services' as they saw the provision of
these services as a necessary step in demonstrating the technology, or as their contribution to
helping a specific group of marginalized people gain access to improved energy supplies.
However, there are also important cases where individual entrepreneurs have acted as their own
project developers 50 .
Almost regardless of the financing mechanisms or the strategies of governments and aid
agencies, the critical factor in the development of micro hydro programmes has been the
existence of the aforementioned individuals or agencies. They have had the skill to put the
various elements of a micro hydro project together and the tenacity to see it through to
operation. This suggests another key conclusion: the rate at which the micro hydro sector can
be expanded will be dependent on the rate at which such project development capabilities can
be developed, expanded and paid for.
4.6 Transaction Costs and the Cost of Intermediation
While the case studies showed the importance of the various types of intermediation, they also
showed that there was very little knowledge about how much each of them cost. For instance,
the long process of technology development and capacity building took place over many years
and involved substantial investments by the companies involved, institutions such as the
ADB/N, numerous aid agencies and international NGOs. No estimate has been made of the
amount involved, but if micro hydro is to be successful in other countries similar investments
will have to be made.
Similarly the costs of 'animating' the commumtles to own and operate micro hydro
installations is difficult to establish, but again the investment is likely to be considerable and
the process likely to last many years, with each community.
A key conclusion therefore is that finding the funds to cover the costs of intermediation is
likely to be a key factor in the successful introduction and scaling up of micro hydro
programmes. As with other decentralised energy options, private financial institutions cannot
or will not cover the cost associated with many of the transactions necessary to get these energy
options installed. Indeed many financial institutions will probably have considerable difficulty
even in covering the relatively high transaction costs of 'retailing' their capital resources to the
people who want power from micro hydro plant.
This situation is well illustrated by the case in Sri Lanka. When the World Bank funded the
Energy Services Delivery (ESD) project, the supervision and certification of loans became a
major cost element. Many of these tasks were originally carried out 'for free' by Intermediate
Technology for both village people and financial institutions. With ESD they either had to be
supplied at very much greater cost by local consulting engineers or did not take place at alL
This meant that the draw down of the loan funds was very low until additional funds were
made available through a grant from the Global Environmental Facility (GEF). After this point,
it was possible to undertake the tasks associated with loan monitoring, and the establishing of
title to land for the purposes of providing collateral for the loans.
Similarly in Peru relatively few people initially applied for support from the lOB funded
revolving Credit Fund. The 'marketing' programme that was then initiated required a
considerable effort of visits to the target areas. Luckily it was possible to cover the costs of this
with non-reimbursable funds provided by the IDB. In addition it would appear that for every
5" A particularly interesting example is that ofBir Bahadur Ghale. from Barpak in Nepal. referred to in footnote 29.
Intermediation in Practice 33
$100 spent on a micro hydro plant in Peru (from grant or loan) an additional $15 is currently
spent on the system over head costs (for a $36,000 plant these costs would be $5,400).
But private entrepreneurs who develop their own projects also incur huge intermediation costs.
The most fully documented case is in Nepal where a private individual took about two years to
develop a basic micro hydro scheme. During the period, according to his own account, he
made 'forty-one trips to Kathmandu to meet with suppliers, government officials, bankers and
others including ITDG in order to build his scheme' 5 .
Such activities are systematically omitted from the estimation of costs in the comparison of
options for decentralised energy supply (see the earlier discussion in Section l ). The result is
that no account is taken of the size of a programme that is necessary to capture the economies
of scale associated with the provision of the necessary elements of 'intermediation' (see
footnote 15 ).
In the case studies reported here an attempt was made to identify all the activities associated
with the installation and operation of the individual plant (and quantify the associated costs),
and all of the various actors who performed them (manufacturers, contractors, plant owners,
customers and other beneficiaries, government, banks, utilities, and the vanous
'intem1ediators' ).
4. 7 The Size of the Micro Hydro Market and the Sustainability of Current
Support Mechanisms
The relatively high cost of intermediation frequently means that the tasks of project
development will often fall to NGOs. Certainly it is NGOs that can most easily access the soft
money that these projects will need if poor people are to benefit from them. But it will also
often only be not-for-profit agencies. such as NGOs. that can cope with the high transaction
costs involved. The costs of these 'intermediation· activities are frequently absorbed in the
general programme costs of NGOs and cannot be separately identified. Indeed none of the
NGOs investigated could tell the researchers how much they had spent on this type of general
support activity over the many years that they had been involved. This means that NGOs will
not be in a position to scale up their operations, not only because such activities are dependent
on the size of the grants they receive. but also because installing hydro plant is rarely the sole
purpose of these NGOs.
This raises the critical questions of whether NGO dominated programmes are in fact
sustainable in the longer term, and whether such programmes can be scaled-up without
adequate funding for more mainstream and commercial project development mechanisms. The
current reliance on NGOs is often too ad hoc and the programmes too small to capture the
economies of scale, in these 'system overheads' costs. This is likely to prove a difficult barrier
to overcome when the programmes are to be scaled-up and these costs dealt with on a more
commercial basis.
In principle these project development functions could be spun off into separate entities, either
single purpose NGOs or consultif!~ firms. But it is precisely these entities that have proven to
be so difficult to fund in the past'". It is not yet clear whether there will be enough work for
'1 See reference in footnote 29
'c In one of the most innovative programmes to create business plans for the renewable energy businesses in Africa (FINESSE)
the main constraint appears to be the lack of institutions who can operate as project developers working between the people
34 Best Practices for Sustainable Development of Micro Hydro Power
such businesses to be run on a financially self-sustaining basis. There is great uncertainty about
the size of the micro hydro market, particularly as the demand will be affected greatly by the
level of soft money available and how the money is used.
Many of the estimates of the potential for micro hydro are based on overly simplistic views
about micro hydro potential, based solely on approximations of appropriate sites with falling
water. For instance, in Sri Lanka conservative estimates of the technical potential of MH are
about 80-90 MW. But these estimates do not include the costs of harnessing this potential. As
with other energy resources, such as PV or natural gas, there is rarely a shortage energy, but
rather a shortage of the skills and capital to make use of it.
In Peru market development is said to be limited. This is in part due to the lack of information
on consumers that fall between 'real' markets (profitable and in charge of private concession
holders) and consumers whose only chance of gaining access to electricity (in the medium
tern1) is a state subsidy. In at least one case, the government over estimated the demand and
offered a concession. However, when the grid extension projects were implemented, it was
found that the demand was much 10\ver than anticipated and in some cases non-existent. The
State ended up covering the deficit.
In the case of Sri Lanka an attempt has been made to develop the capacity to perform some
project development tasks as self-sustaining businesses in the form of 'Village Catalysts'.
These people do appear to provide an important function in stimulating demand and providing
some technical input to the projects. However, the new sources of finance (such as the World
Bank financed ESD project) appear to require 'certification' of project designs and the quality
of construction from people more formally qualified than the village catalyst. Either aid
agencies and foreign NGOs will have to adapt their requirements of the people who arrange
loan and subsidy finance or Village Catalysts will have to have their skills enhanced still
further. The issue is one of balance between the cost of high quality intermediation and the
reduction in risk that results from using more skilled people.
In Nepal equipment suppliers themselves perform some of the project development tasks. But
here there would appear to be at least the potential for a conflict of interest and lack of
independence in the advice given to the purchaser53 .
The scale and manner in which these 'intern1ediation services' will be perforn1ed will therefore
depend on the form and scale of the money necessary to pay for them.
4.8 Specific Examples of Intermediation
The case studies shO\v a number of interesting examples of the extent of intermediation.
4.8.1 Tecltnological Intermediation
A great deal of the current success of micro hydro results from the early attempts to build
technological capability with existing metal workshops in NepaL The first oil crisis in 1973
<>timulated the Nepalese govemment to look for alternative energy sources. A number of
companies that had experience in building the traditional water wheel, graduated to adding
with a need and the people with the finance.
Wolfgang Mostert. personal communication.
Intennediation in Practice 35
electricity generation onto improved water turbines 54 . By 1979 ADB/N had established their
Appropriate Technology Units (ATU) to promote micro hydro and other technologies.
Intermediate Technology Development Group (ITDG) became involved at this stage and
worked with a number of the existing engineering companies to develop the technology. The
capabilities of the manufactures was further enhances through a series of training programme
starting in 1987 financed by ADB/N and ITDG. This experience was then transferred, and
adapted, to other parts of the developing world 55 .
4.8.2 Socia/ Intermediation and Participative Approaches to the Management of
Technical Changtl 6
A major theme in the development of micro hydro technology has been the huge effort put in to
'Participative Approaches' to create, nurture and capacitate communities to build, own and
operate micro hydro plant. These efforts trace their origins to the more general use of
participatory development methodologies in the implementation of technology based projects.
In Sri Lanka this process evolved into the development of Electricity Consumer Societies
(ECS).
Box 4-l: ELECTRICITY CONSUMER SOCIETIES
The village hydro schemes of Sri Lanka are usually managed by an Electricity Consumer Society
(ECS) or its legal and more recent equivalent, the Electricity Consumer Company (ECC), established
for each project. These innovative mechanisms facilitate the participatory ownership and
management of micro hydro schemes within village communities. Assistance in setting up the ECS
was generally provided by an outside agency (a Non-Government Organisation, such as ITDG). A
Society (ECS) was created in each village before it was able to request technical assistance to
undertake a scheme. The ECS involves all potential beneficiaries of the scheme and becomes the
operational and implementation conduit tor the project. As the scheme moves into the operational
phase it takes on a more managerial and regulatory role, although the structure and composition of the
organisation remained the same.
The ECS became a pivotal institution within the village community. The office bearers would be
selected at an annual general meeting, and sometimes include women. They would manage such
issues as financial control, tariff setting. load regulation, agreeing electricity end-uses, taking action
following breakdowns, and settling disputes arising from electricity usage within the community.
With the advent of bank finance for micro hydro the ECS had to be formalised into Electricity
Consumer Companies in order to become a legal body, with a status of a small company. Any loan
repayment thereby became the sole responsibility of the ECC.
54 Prominent among these were Balaju Yantra Shala (BYS) established in 1960 with the assistance of Swiss Development
Corporation (SDC); Butwal Technical Institute (BTl) established with the assistance of United Mission to Nepal ICMN),
National Srmcture ( 1963) Thapa Engineering Works at Butwal ( 1972); and The Engineering Company at Kathmandu ( 1973 ).
In 1975 Butwal Engineering Works (BEWt a sister conccm of BTl, designed and tested the first Pelton turbines. Nepal Yantra
Shala (KYS) also started turbine manufacture in 1975. BEW fabricated the first Cross flow turbine in 1976. BYS fabricated the
first turbine for generating 6 kW in 19n. In the same year Thapa Engineering Works built their first crossflov,· turbine,
Kathmandu metal Industries (KMI), and National Structure and Engineering developed and installed the first Multi Purpose
Power Cnit ('v1PPU) to improve the traditional ghatta (water wheel).
" See for instance "Micro H1·dro Design Manuaf' by Adam Harvey. Andy Brown, Priyantha Hettiarachi and Allen Invcrsin,
IT Publications. London. 1993 228 pp, ISBN I 85339 I 03 4.
These issues arc dealt with at greater length in "Panicipmh·e Planning Guidelines j(n· O!f~grid Electriciz1·" October 1999
(this material is available from IT Consultants ww~; .itchltd.com). It provides evidence of a need for technical and managerial
capacity being built at the project level at an early stage of project planning. Furthermore. unlike in other sectors. participation
in micro hydro appears to need people with technical knowledge such as the "Village Catalysts" of Sri Lanka.
36 Best Practices for Sustainable Development or Micro Hydro Power
Similar village committees build and operate many of the hydro schemes examined in Nepal.
They are responsible for the loans, set taritTs, and appoint the staff who operate the plant. In
Peru rural people also had to organise themselves into 'pre-electrification committees' or other
ad-hoc organisations in order to gain formal access to credit. This represents a major
contribution that the IDB/ITDG revolving credit scheme made to building institutions with civil
society in rural areas.
Community participation not only facilitates involvement in the design and operation of hydro
plant, but it also enables costs to be reduced in three ways:
• it allows people to contribute their labour (or other communally owned asset such as
land 57 ) to the scheme. If people are under employed the opportunity cost ofthis labour
can be close to zero, and its use need not involve the transfer of cash. This is often
described as 'sweat equity' in that by contributing its labour the community gains a
share in the ownership of the scheme;
• involvement of the whole community enables the richer elements (richer households,
small mills and shop owners) to carry the bulk of the costs and thereby make a service
available to the poorer people in the community. This can be done either through
actual cross subsidy to the selling price (through a 'lifeline taritr) or by allowing them
into the scheme at the marginal cost of including extra consumers rather than the
average cost;
• increasing the number of people involved in a scheme can reduce the cost to everyone
when micro hydro schemes exhibit economies of scale.
However, while involvement of the community is certainly a necessary condition for the
success of some types of schemes, and can lower costs, the process itself is costly and time
consuming. These costs are associated with understanding the needs of different users (for
instance including both men and women), developing community motivation and 'ownership',
and in training. Such processes may take a number of years and can add significantly to the
costs of the NGO or other agency involved in project development 5 ~. If a single entrepreneur
or a municipality is able to raise all the capital, it may well be that they can avoid the cost of
community development and still have a successful micro hydro scheme.
4.8.3 Village Catalysts
In Sri Lanka another major element of the participative elements of village hydro programmes
was the training of 'Village Catalysts' (sometimes known as 'barefoot' technologists). Ten
catalysts have been trained. These were usually village level electricians or electrical repair
technicians whose skills \vere upgraded by ITDG and their services re-orientated toward
operational and maintenance support to village hydro schemes. They met the need to have
'trouble-shooting' capacity located near to the sites. Some catalysts are also capable of
designing and manufacturing Pelton turbines up to 5 kW or so in capacity. In some areas there
is sufficient demand to enable these catalysts to grow into entrepreneurs working
independently. But despite their business-like approach they still perform services free of
charge or at low cost to certain communities due to a sense of personal loyalty. Catalysts also
promote hydro in other villages and are often the first point of contact for potential
beneficiaries and respond to inquiries and demands of Provincial Councils. However, as
'o Th~.: contribution of land is said to be crucial to the success of schemes in Sri Lanka where the state owns river banks. and
would be unlikely to grant permission for individuals to usc this land for their mvn profit.
It has also been suggested that where community assets are used to build a hydro plant. such as the publicly ·shared assets·
of the river bank or river water. there may be an insistence that I 00% of the households are connected. This may affect costs.
profitability and timing of the project. Diesel generating sets arc said not to suffer from this ··1om;, connection rate syndrome'"
(Wolfgang Moster!. personal communication).
Intermediation in Practice 37
suggested in Section 4.5, these catalysts cannot perform all the roles of project developer, as
they are not yet perceived as sufficiently credible to financial institutions.
4.8.4 Marketing and the 'Creation' of Demand
The need to stimulate the demand for micro hydro through 'marketing' and publicising the
existence of the necessary funding opportunities is a particularly important element of social
intermediation in the examples cited in the Peru case study. This activity was an essential
element in the success of the programme as relatively few people initially applied for support
from the IDB funded, revolving Credit Fund. Even though interest rates and payment
conditions seemed attractive when started, virtually no effective loans were made when the
scheme was first set up. It was therefore necessary to adjust the strategy. Programmes that
included visits of a team of promoters to the target towns to explain the details of the proposed
funding scheme were established, including the participation in local and regional events, use
of the radio and visits of students and others. Over a period of two years ( 1996 and 1997),
nearly 40 visits were made, many of them to areas that involve many hours of travel from the
nearest small town on a bridle path, the only means of access.
4.8.5 Lobbying
In most countries, technical competence in micro hydro has had to be complemented with the
capacity to lobby for micro hydro development and the conditions that would at least give this
technical option a fair hearing in the allocation of resources and in the formulation of policy.
The most formal and successful of this advocacy function is probably the formation in 1990/1
of a Technical Assistance Committee (T AC) Sri Lanka which united a diverse set of
individuals and organisations interested in micro hydro. Participants included representative of
all sectors but, mainly NGO and the private sector. Staff from the utility were also active
members. Its initial strategy was to incorporate micro hydro into the government's Rural
Development plan but later facilitated greater co-ordination among all the actors working on
micro hydro initiatives. More recently the T AC evolved into an 'Energy Forum' that lobbies
for all decentralised and renewable energy options. Similar Forums have proved effective in
Nepal and Zimbabwe and Peru.
4.9 Financial Intermediation and the Main Funding Mechanisms 59
Micro hydro investments are costly and capital intensive. Therefore, access to appropriate
forms of medium I long-term financing is critical. This means financial intermediation services
in rural markets -the supply of debt and other financing to both suppliers of electricity (micro
hydro owners) and to electricity users.
There are two broad channels for the flow of financing and related support to investor/owners
and the ultimate energy end-users:
• the first channel is one of direct access by investors to finance the purchase to the
technology and know-how and provide the necessary working capital;
• the second channel is indirect and supplies support through intermediaries who deliver
technical and financial intermediation services to the investor or end-use consumer.
A number of business models employ versions of the indirect channel. For example, rather
than a direct sale, an equipment supplier might provide an owner with a micro hydro turbine
under a lease, or lease towards purchase ('hire purchase') arrangement. But the more common
59 In addition to evidence provided by the country reports. this section draws heavily on a paper specially commissioned from
Dr Russell de Lucia.
38 Best Practices for Sustainable Development or Micro Hydro Power
of indirect approaches is in the form of a 'utility' or 'energy service company' (ESCO). In the
most straight-forward of these, the owner not only sells electricity to the end-user but provides
finance at least for the customer connection and perhaps end-use equipment (lights, TV etc).
The investor/owner role is maintained for a long period or indefinitely.
The old-fashioned (but still existent) micro hydro grain mills are a form of ESCOs. the
customer pays only for the energy-service (e.g. grain milled) and perhaps even pays in kind (a
small fraction of the milled grain). In modem variants the customer pays only for energy (e.g.
kWh), or energy-service (lighting or water being pumped).
Box 4-2 presents an indicative menu of the broad types of financing, structures and their
sources. This draws on the body of experience on options that have been successfully used in
OECD countries in supporting market penetration of small energy investments. Increasingly
these options are now being used in a growing number of developing countries. While this
menu is generally representative of the direct project financing approach, in many instances it is
also indicative of the indirect financing approach.
Box 4-2: Indicative Menu of Financing Options (Types and Sources)
Equity Financing with financial resource mobilisation from:
• internal funds from the project sponsor I active investors I users;
• other active investors, such as venture capital funds. or investments by merchant banks:
• supplier (e.g. of equipment) as investor (part or all of equipment costs);
• passh·e investors through 'private placement' of equity financial-security instruments (e.g.
shares certificate):
• passive investors through public (security-agency-regulated) placement/offering; and
• special categories of above where the investor has additional (non-financial) objectives. such
as targeting environmental/green project or entity investments.
Primary and Secondarv (mezzanine*) Debt Financinu with financial resource mobilisation from:
• commercial and/or development bank and other Financial Institution providing working
capital and tenn loans (limited recourse or balance sheet);
• complementary and/or alternative (often mezzanine) debt from 'active/directly involved'
equity sources (categories l.(a-c) above):
• export credit agency (ECA) source when equipment is imported;
• investment grade term-debt instnunent (e.g. bonds) placed through limited offering to sources
for which fiduciary and/or other constraints limit pontolio positions largely to such investment
grade instnnnents;
• as in (d) but from a broader range of sources through a registered offering;
• 'junk' (non-investment grade) bonds (the more general case) placed to similar sources as in (d)
and (e) but pa11icipation of sources for (d) constrained as noted; and
• analogy of l.(t) tor debt, sometimes as complementing equity position.
Other Financing/Financial Support-with financial resource mobilisation and/or support from:
• grants/contingent grants, cost shares sometimes tor specific costs (e.g. pre-investment studies)
or cost components from public agencies at federal, state or local level;
• depreciation and/or tax credits from federal, state or local authorities, which, in effect. lower
the cost of debt and/or equity financing;
• lease fmancing from equipment suppliers, or through arrangements with Financial Institutions; and
• myriad guarantees. credit enhancements and/or other support usually from Development
Finance Institutions' suppmi by federal, state or local governments; to facilitate one or another
of financing options above. or the creation of subcategory of one of these options such as 'tax-
free' development. pollution control or other special bonds.
Intermediation in Practice 39
Source: modified from tables in previous de Lucia and Associates, Inc. reports and papers.
Mezzanine finance is defined as "unsecured. higher yielding loans that are subordinate to banks and secured
loans but rank above equity" (Enearta, 1998).
The most critical question in financial intermediation is who is responsible for transaction
decisions and who bears what risks. If support from an International Financial Institution (IFI) is
to work, experience suggests two very clear lessons. First, given the nature of transaction costs,
this support can only be cost-effective if the Institution 'off-loads' most if not all transactional
responsibilities to intermediaries. The smaller the scale of the investment transaction, the more
necessary is this 'off-loading'. However the IFI must retain the responsibility of the appraisal and
evaluation of the intermediaries, at least those at the highest level.
Secondly, the intermediaries must be responsible for the appraisal of the transaction (the
investment and the credit worthiness of the borrower or end-user), the management of financial
and associated risks, and of course, be responsible for ensuring transaction re-flows (the
repayments).
A recent review of IFI operations in support of micro hydro and other small energy investments
suggests three useful but sometimes overlapping representative categories of financial
intermediaries 60 :
'Classical' Intermediation via Bank or Non-Bank Financial Institutions. Nepal's
Agricultural Development Bank of Nepal is perhaps the most well known example for
financing micro hydro. ADB/N is a government owned bank which serves as an
intermediary tor the government's micro hydro (and other) programs; it has also been an
intermediary for various International Financial Institutions. More recently the Sri Lanka
Development Finance Corporation of Ceylon (DFCC) acts as one of the intermediaries
for the funds provided by the World Bank under its Energy Services Delivery loan.
Intermediation via Other Non-Bank Specialised Financial Institutions. Again citing an
example with micro hydro experience, perhaps most well known of such institutions is
IREDA -The Indian Renewable Energy Development Agency Ltd. IREDA was created
in 1987 as a public limited company owned by the Central Government to promote
renewable energy and to serve as a 'chmmel' for Government and International Financial
Institution external funds. IREDA has supported a number of micro/mini/small hydro
projects.
Intermediation via Non-Financial InsTitutions. This is an envelope category including
such entities as utilities, ESCOs, special purpose investment entities (e.g. development
authorities, infrastructure funds) and others, including NGOs. An example of this is the
revolving fund operated by ITDG Peru using funds sourced from the Inter American
Development Bank.
The World Bank and other international development finance institutions are increasingly using a
class of intermediaries which are financing funds or facilities whose management is the
responsibility of a local bank or non-bank Financial Institution (or consortium). Such
International Financial Institution operations, referred here as Fund or Facility Operations. are
usually designed to provide a mechanism for the International Financial Institution to support
of these categories is discussed. along with examples in the aforementioned report (De Lucia and Associates. Inc. July
1998) which is available from the World Bank.
40 Best Practices for Sustainable Den: opmcnt of Micro Hydro Power
private sector involvement in energy and other infrastructure development and to facilitate greater
flow to these investments from the capital markets.
In Nepal where there is a new World Bank, 'Power Development Fund', it will be important to
find a way of handling the transaction costs so that it will be giving extended support to viable
micro hydro investments. Even when such operations exist and 'in principle' are open to
supporting small-scale hydro, transaction costs lead the fund managers to avoid such investments.
Many NGOs have some experience in financial intermediation, for example operating savings and
lending societies. While these loans are generally much smaller (and shorter term) than is required
for investment in micro hydro, they may bring important knowledge of the financial strengths and
weakness of certain individuals and groups (the NGOs' existing clients) who are potential
bonowers for micro hydro schemes. Such NGOs might well 'graduate' to greater financial
intermediation responsibilities, ur amalgamate with larger financial intermediaries.
4.10 Current Financing Models for Micro Hydro
The case studies show that in practice many micro hydro plants are financed in the same way as
houses arc in developing countries. The funds come from a variety of sources, the investment
is started before all the financing is in place, and construction takes place piecemeal when the
necessary resources come available. often over a very long period. Schemes were generally
implemented using grants or multilateral soft loans obtained by the project developer (usually
an NGO). The exception in the schemes under review was in Nepal, where the ADB/N played
a central role in financial inte1mediation.
This means that financial intermediation (or financial engineering) has crucial inputs that can
be very costly. It also means that most of the existing financial mechanism targeted at micro
hydro frequently do not provide sufficient funding. and certainly not ffom a single source.
In Peru, the ITDG/IDB revolving fund was created by the contribution from lOB with a capital
of US$400,000, plus $120,000 for technical assistance. The repayment terms to the
intem1ediary. ITDG. are set at a very low cost with repayments being made in local Pemvian
cun·ency . The funds for technical assistance are a grant and are not reimbursable. The scheme
was designed for loans ranging from US$1 0,000 to $50,000 for each micro hydro power plant.
The repayment was to be over (up to) five years, with an annual interest rate of 8% in U.S.
cuncncy (at this time the commercial current rate of interest in US dollars is at least 12 % per
year).
However, the demand for credit from the revolving fund only became effective when additional
funds were made available from other sources (regional government, poverty relief projects
FONCODES 61 ) and the rural consumers themselves. In Peru it was found that regional and
sub-regional governments are more willing than the central government to support essentially
dccentraliscd schemes of this nature.
An interesting feature of the revolving funds is that ITDG hired an independent Credit
Operator. This is a local entity (in the city of Cajamarca) that was contracted by ITDG to carry
out independent assessments of the credit worthiness of the potential borrowers, to draw up and
file the relevant credit agreement, disburse the loan and recover it. In this way, the project
<d Compensation Fund for Development
Intermediation in Practice 41
developer, ITDG, was able to concentrate on the promotion, technical assistance and general
supervision of the projects.
By the beginning of 1999 15 loans, totalling US$465,718, had been granted from the revolving
loan. A total investment of$ 1, 730,000 had been made for the installation of 15 micro hydro
power plants in small towns in Cajamarca, Apurimac, Amazonas and Lambayeque.
Repayment has been at a high level.
The following tables summarises this scheme:
Table 4-1: Sources of Finance from Micro Hydro Development in Peru
Source Amount o;o
ITDG/IDB Credit $465,718 27
Regional and Sub-regional $418,044 24
Govemment
FONCODES $328,475 19
Direct contribution of $242,730 14
municipalities and small
businesses
Local contribution (population) $47,330 3
Others(*) $226.852 13
TOTAL $1,729,149 100
*Including technical assistance and promotion funds provided by IDB (up to
US$ I 20 thousand} and other donors.
Table 4-2: Types of Finance from Micro Hydro Development in Peru
Financial Component Use of Funds %of total
costs
Loans Civil works and electro-mechanical 27% equipment
Contribution by Pre-investment and other complementary 14% municipalities and small expenses
businesses
Grants Technical assistance and promotion (13%) 56% Civil works and distribution lines (43%)
Contribution by local Manpower, materials 3% people
TOTAL 100%
When a municipality is the owner of the micro hydro funds are sourced from both central
govemment (transferred to municipalities), and from the local population through taxes.
Indeed municipalities raise commercial loans against the guarantee of a 'retention', that if they
do not service the debt, the payments will be deducted directly by central government from
national tax revenues payable to the municipality.
42 Best Practices for Sustainable Development of Micro Hydro Power
In Sri Lanka, until the recent advent of the World Bank financed ESD project, funding for each
project had come from a wide range of sources such as foreign donors, the government's
poverty alleviation programs, local government bodies and charities such as the Rotary Club.
Contributions in kind (sweat equity), mainly for the civil works, were a significant element in
resource mobilisation. · The cases showed that this source could be significant: at the
Katepoloya scheme in Sri Lanka this was as high as 44%62 of all costs, including labour . More
generally in Sri Lanka beneficiaries provided some 30 of the total project cost, when sweat
equity is properly costed.
The World Bank is now the major contributor to village hydro finance in Sri Lanka by means
of its Energy Services Delivery (ESD) project. The ESD provides a credit line to Participating
Credit Institutions (PCls) for medium and long-term credit for many renewable energy and
demand side management projects. This includes village micro hydro and the rehabilitation of
Tea Estate mini hydro sites. Finance for electricity end-uses at the community level is not
specifically included, though it is implicitly recognised as a part of the project cost. However,
existing micro credit institutions in rural areas (such as Sarvodaya and Sanasa) can provide
both business development support services and micro-finance to new businesses based on
electricity.
The Development Finance Corporation of Ceylon (DFCC) is the main operator of the World
Bank programme and manages the loans to the Participating Credit Institutions. These loans
are usually based on Average Weighted Deposit Rates (AWDR) in the commercial banking
sector and PCI are free to on-lend at market rates. PCls are free to adopt their own eligibility
criteria with no specifications on debt to equity ratios as often the case with previous other
World Bank loans. Nominal market interest rates usually vary but range between 15%-22% in
current prices in local currency (inflation is cun·ently about 7%). Rates are dependent on bank
policies and individual project situations. The loan period is a maximum of 10 years including
a maximum two-year grace period.
Borrowers repay ESD loans to the PCls, and the PCls make repayments in stages to the DFCC
which in turn repays the money to the Government of Sri Lanka (GOSL) five years after
initially drawing down the funds. The Government then repays the loan to the World Bank
after a time lag.
The ESD provides grant funds for capacity building through training and through technical and
generic market support for renewable energy services, by supporting educational promotion
campaigns for off-grid energy technologies. This activity is subcontracted out to the Sri Lanka
Business Development Centre (SLBDC).
Collateral in the Sri Lankan ESD programme is provided by the project's capital equipment and
land leasehold rights. In such projects, land is often state or Crown land leased on a long-term
basis and then mortgaged. In the event of defaulting, the site and land can be transferred and
sold as a going concern.
As in the case of the Peruvian programme, ESD has required additional grant funds to get their
programmes off the ground. These have been provided mainly through co-financing from the
Global Environment Facility (GEF). These grant initiatives came into effect one year into
project implementation following representation from banks, equipment dealers, and
62 This figure seems quite high. However in schemes where a great deal of civil work is necessary. in kind contribution from
bcneficiari.:s might be significant.
Intermediation in Practice 43
consultants. In effect hard commercial funds from the private sector are 'leveraged' with softer
public funds in order to cover the 'system overhead costs'.
The grant elements associated with ESD now includes:
• Grant co-financefor loan applicants. These are $400 for each kilowatt up to $20,000
for micro hydro plant (compared to $100 per 30 Watt Solar Home Systems SHS);
• Grants for Project Preparation. These cover 95% of costs up to $9,000 for Micro
Hydro (90% up to $6,500 for SHS);
• A campaign to promote o.trgrid electricity;
• Grants to the PCUfor Pro_ject Supervision. Currently these are $1 ,200 for each micro
hydro project ($50/SHS up to $600/sub project);
• Grantsfor pro_ject supervision. These grants enable consultants to verify the design of
micro hydro projects and site specifications before loan disbursements.
• Consumer education and protection facility. This currently applies only to solar home
systems and is a facility to investigate consumer complaints about dealers and to seek
appropriate solutions.
It also appears that additional grant support is required for technical assistance to micro hydro
development through ESD schemes and is currently being arranged through additional soft
funds.
The ESD project started at the end of 1997 and has been in operation almost two years. To date
it has approved around 13 grid connected and 7 off-grid micro hydro schemes.
In Nepal the Government requires commercial banks to invest 7 percent of their total deposits
in the priority sectors. However the Government has to rely on the Agricultural Development
Bank of Nepal (ADB/N) to administer its subsidy scheme for micro hydro. Formal financial
institutions have been reluctant to provide rural credit. Commercial Banks (such as the Nepal
Bank Limited and Rashtriya Banijya Bank) have a strong network of field offices and are able
to provide credit in rural areas. The new joint venture banks have so far failed, however, to
provide such services due to their inexperience in this sector. They mobilise funds through
contractual arrangements with ADB/N.
Subsidies are provided for rural electrification programme through ADB/N. The terms of the
subsidy have changed over the years. but currently they are available for systems up to 1 00 k W
for water turbine and Peltric sets. The subsidy is available for the electrical components and
varies from 75 percent for remote areas and 50 percent for other hill areas 63 . In etiect this
means that the subsidy is approximately 20-25% of the total investment cost. The micro hydro
subsidy covers generators, load controllers, ballast heaters, earthing set, lighting arrestor. circuit
breakers, drive system and transmission components including transmission cables, poles,
insulators, stay wires and transfom1ers. The subsidy on Peltric set is limited to capacities up to
5 kW. The limiting size of the penstock pipe for Peltric set is set at 100 m in length and 150
mm internal diameter High Density Polyethylene pipe. US $ 67/kW is provided for
transmission poles in remote areas, US$75/kW is provided for other hilly areas. The subsidy
for poles cannot exceed the cost of the turbine in the case of Peltric set. No subsidy is given
specifically for household wiring, but a loan is provided to each household up to US $ 20.
"·' Information supplied by Dcvendra Prasad Adhhiari. Agricultural Development Bank.
44 Best Practices for Sustainable Development of Micro Hydro Power
Over the past 1:2 years ADBN has changed its interest rate for micro hydro development. As a
result of price escalation, the higher cost of borrowing and the higher cost of lending, the rate
has grown in stages from II percent to 19 percent. The current ADB/N's interest rates are high
and appear to discourage borrowers.
Normally in :Nepal some :20% of the total project cost must be found by the prospective ·owner'
usually in the form of local labour. However in the case of Barpak, the local contribution (for
the civil works) represented only 7% of the total costs.
Table 4-3: Summary of Current Financing Terms for Micro Hydro
Primary Funds Financing Models
Actors
Peru ITDG Inter American Revolving Fund
Development Bank, Plus grants for project
Local Govemment. development.
Sri Lanka Utility Multiple sources ·Ad Hoc' multi donor,
Energy Forum local grants, banks.
ITDG World Bank ESD loans
World Bank at 16%
(recently) Grants.
Nepal ADB/N loans and AB DIN and government Loans and Government
Govemment Subsidy subsidy.
Rural Energy
UNDP tunds, plus Development
Programme ADB/N loans, and
contributions from
District and Village
Development
RADC Committees
Govemment funds
Zimbabwe ITDG ITDG Grants only
Mozambique ITDG and KSM* ITDG Grants only, private
contribution
' . *KSM (Kwasa1 Sunuka1) IS a Mozambican NGO.
4.11 Collateral and Guarantees
Securing loans by means of collateral has frequently posed problems in micro hydro
development, particularly in community-owned schemes. As with many project loans, the
project's capital equipment and land leasehold rights are used as collateral. But in the case of
micro hydro in Sri Lanka, land is often state or Crown land that is leased on a long-tem1 lease
and then mortgaged. In the event of defaulting, the site and land can be transferred to another
and sold as a going concem. However, in practice it often takes time and considerable effort to
establish title to the land, and particularly when the loan is to be raised by a limited liability
company rather than the whole community.
Furthermore, the lack of technical expertise within financial institutions means that they are
often unable to effectively monitor the construction and operation of the schemes that act as the
Intermediation in Practice 45
collateral for the loans. This has also handicapped the financing mechanisms of the m1cro
hydro sector in Sri Lanka.
In Peru the risks of loans has been reduced in a number of innovative ways. In one case (the
'Atahualpa' Farming Co-operative) the loan was guaranteed by 'hypothecating' rights to the
income stream from the future sales of milk.
In the case of municipalities the loans are guaranteed by means of an 'intercept', whereby if the
municipality defaults on the loan, the loan repayment is deducted at source from future
transfers of resources from the central government to the municipality.
4.12 "Organisational Intermediation' and the 'Enabling Environment'
The success of micro hydro is clearly context specific. This specificity refers not only to the
location of a particular site (is there enough water and a sufficiently 'concentrated' demand) at
the micro level of analysis, but also at the specifics of the institutional arrangements at the
macro level. The development of micro hydro has required one or more organisations to
develop the national energy context the 'enabling environment' -in ways that support (or are
at least not hostile to) micro hydro development.
The characteristics of a favourable 'enabling environment' are relatively easy to list, but often
requires huge effort to put in place. They are likely to include:
• A legal framework for contracts and effective means of their enforcement;
• A 'level playing field' in relation to the aid, taxes, subsidies and regulations that are
provided to the main alternatives to hydro (grid electricity, fossil fuels, PV, etc.);
• A transparent policy framework (provided by the government or utility) for the
development of energy options in general and the expansion of the electricity grid in
particular (to reduce the risk of arbitrary or politically motivate expansion of the grid
or other subsidised alternatives, such as PV);
• Capital supply systems (capital markets) able to supply adequate financial resources
(grants, soft and hard loans, equity);
• Reasonable arrangements for collateral;
• Government support to training, R and D, and 'public goods' such as infonnation
about the resource base;
• Systems for the competitive supply of technical and business support that is suited to
small scale enterprise in rural areas;
• Adequate access to competitively priced micro hydro technology and related
knowledge;
• Sufficient competitive suppliers with the technical capacity to select, design, instalL
test, operate, and maintain the plant, equipment and civil works required by m1cro
hydro;
• Systems for defining and enforcing appropriate technical standards; and
• Transparent and fair mechanisms for the sale of micro hydro electricity to the grid.
The following sections describe some of the features of the 'enabling' or indeed 'disabling'
environment that is confronting the expansion of micro hydro in practice. Yluch of the pre-
existing policy environment was not designed specifica1ly for micro hydro, and whilst it may
have not been actively discriminated against, a large amount of complaints stem from the fact
that governments forget about it as a viable option Ylany of the negative effects are likely to
be unplanned. For instance governments subsidise grid electricity explicitly and implicitly for
46 Best Practices for Sustainable Development of Micro Hydro Power
a variety of reasons, but are unwilling or unable to extend the same concessions to micro hydro.
Diesel engines are imported free of duty but not the technology associated with micro hydro,
and so on.
But those that seek to 'regulate' the development of the micro hydro sector need to keep in
mind that many of the regulations governing rural development merely provide another
mechanism by which those in power can exploit the weak by demanding bribes and other kinds
of 'rent seeking behaviour'.
4.13 The Regulatory Framework
The ad hoc nature of the regulatory framework governing micro hydro is illustrated by the case
of Sri Lanka. The regulatory framework is unclear and is characterised by a multiplicity of
institutions at various levels. The required approvals are illustrated in the following table:
Table 4-5: Approval Required for Micro Hydro Installations in Sri Lanka
Environmental approval or Licence Institution
Letter of Support on general project viability & willingness Ceylon Electricity Board
to purchase electricity (for Grid connected sites) to (CEB)
facilitate other agency approvals
Use of water resources, road development, construction of Divisional Secretary I
buildings & canals Irrigation Engineer etc. or,
Pradeshi Sabha
Letter on site observations & recommendations on Pradeshi Sabha or
environmental impacts based on Environmental Impact Divisional Secretariat to The
Assessment Questionnaire for Micro Hydro ( 1997) Central Environmental
Authority (CEA)
Electricity Licence to generate & sell electricity Chief Electrical Inspector,
Ministry of Irrigation & Power
Investment & Tax concession for large infrastructure Board of Investments
projects
Title or lease or pennission on land use Land owner or Divisional
Secretary
In Sri Lanka, the Electricity Utility (CEB) limits its regulatory role to determining the standards
for connecting private power generation to the national grid. Otherwise there is very limited
regulation in relation to off grid micro hydro. That regulation that does impinge on micro
hydro relates to use of natural resources such as lands, water and forestry resources. Land use
is dependent on property rights where the use of public lands requires local government (at the
level of the Pradeshi Sabha). The same approval is required with use of waterways.
Regulation of waterways feeding irrigation channels come under the purview of a separate
entity, the Irrigation Department.
When transmission lines within a village cross public land they do so without any pern1ission
or approvals being sought and with no forn1alities encountered. If a micro hydro site requires
significant use of public land however, either by a private developer or rural community,
government lease procedures may apply and approvals obtained from both the Minister of
Lands and the President. Private land is frequently used for the construction of micro hydro
Intermediation in Practice 47
powerhouse buildings with little regulation except for verbal agreements with the landowner
who is almost always a beneficiary in the project.
In Sri Lanka, non-state actors have often stepped in to fill gaps left within the state structure.
Developments in micro hydro tend to 'fall out' of the plans and procedures of the formal
electricity generation and distribution systems. While there are specific standards for
construction and installation of all electricity installations in Sri Lanka, they are not strictly
enforced in the village hydro sector, and were not specifica11y designed for the village energy
use. Construction and safety standards depend entirely on the people involved with the project
and the requirements of the institutions that provide the funds. In order to tackle this problem
the World Bank financed Energy Services Delivery (ESD) programme has commissioned a
study to establish appropriate standards in vi1lage-hydro electricity distribution systems 64 .
It is likely that environmental regulation will become an important feature of the regulations
governing micro hydro in Sri Lanka. The Central Environmental Authority (CEA) the main
body overseeing environmental policy and regulatory processes developed an Environmental
Impact Assessment Questionnaire for Micro Hydro in 1997. This has many shortcomings, not
least that it does not distinguish between different scales of micro hydro plant, adding a
considerable burden to very small systems 65 . Implementation is variable, as local government
capacity on environmental issues and regulations is generally weak and unclear. Some
Provincial Councils do have Environmental Officers but they are often marginalized in the
institutional process and have little authority.
The situation regarding private power producers in Sri Lanka is still evolving. Private Power
Producers can only legally sell power to the Ceylon Electricity Board. However there can be
exceptions if specific approval is given, although this permission is rare. Electricity Consumer
Societies (in villages) avoid this problem by selling power only to their members (and
technically they pay a 'membership fee' rather than a 'fee for electricity').
In Peru the regulatory environment also appears to by-pass micro hydro. What exists is a
regulatory framework, largely related to the allocation of concessions aimed at promoting
private investment in generating and distributing electricity. The legislation essential1y leaves it
to 'market forces' to select the technologies to be used to generate power and distribute
electricity to areas not covered by the electricity grid. In practice, however, the incentive
structure demonstrates a clear preference to support grid based electrification.
As far as the public sector is concerned, the institutional framework for rural electrification
consists of The Ministry of Energy and Mines. Through its Executive Projects Directorate
(DEP) it is responsible for expanding the electrical frontier throughout the country. A number
of other government institutions are involved, but their role is limited to financing schemes in
rural areas. With the restructuring of the power sector since 1990, several municipalities will
be handing over the electricity services to concession companies, given the legal, financial and
economic guarantees that make it attractive.
64 These specifications are based on relevant national and international standards. They specify separate standards for systems
under 5 kW, between 5 to 15 kW and. systems between 15k W to 50kW (Village Hydro Distribution System Specifications for
the ESD Project. March 1999 Draft version. Intermediate Technology Sri Lanka). These specifications have been in use since
June !999.
"'Currently even sites 2-3 kW in capacity have to go through the process of filling in these environmental clearance fonns and
getting the necessary approvals from the CEA and Provincial Councils.
48 Best Practices for Sustainable Development of Micro Hydro Power
Experience with Peru's revolving fund shows that the criteria generally used in larger
construction works in urban areas cannot be applied to micro hydro installations in rural areas.
Technical standards and the costs of equipment, and machinery must be modified for small
projects of this nature to ensure that they are appropriate to their rural surroundings.
In Nepal the Ministry of Water Resources (MOWR) is directly responsible for electricity and
supervises the Nepal Electricity (NEA) and Electricity Development Centre (EDC). EDC was
established in 1993 under MOWR to promote private sector participation and license both NEA
and private power producers on behalf of MOWR. The EDC grants licenses for independent
generation and sale to NEA and assists Independent Power Producers through a range of
activities including site identification for small and medium scale projects. EDC supports the
Electricity Tariff Commission (ETC) which was set up in 1993 as an independent body to
regulate electricity tariffs and ultimately to arrange for the power sales between NEA and
private power producers.
The Ministry of Science and Technology (MST) has a mandate to promote national science and
technology and oversees the Alternative Energy Promotion Centre (AEPC). The mandate of
AEPC is to promote renewal energy technologies to meet the needs in rural areas of Nepal, but
as a technology based organisation it does not become involved in creating appropriate
frameworks for rural tariffs or the organisational frameworks necessary for the creation of
decentralised power companies.
The Nepal Electricity Authority (NEA) is a semi-autonomous institution responsible for the
generation and supply of energy. However neither NEA nor any other government authority
appears to be responsible for isolated grids. NEA has been able to cover 15 percent of the total
population through expansions from the national grid. The service provided by NEA is largely
been limited to urban and semi-urban areas. Micro hydro development is governed by two acts
passed in 1992: the Water Resources Act; and the Hydropower Development Policy Act.
Licenses are not required for running water mills, as they are considered a cottage industry. The
Electricity Act of 1993 opened up investment opportunities in the electricity sector from
nationaL foreign or joint venture companies and made provision for concessional loans to
generate and distribute electricity. The policy has also waived the license fee for surveys,
generation, transmission and distribution and stipulated that the Nepal Electricity Authority
(NEA) will provide compensation to existing private owners and operators of micro hydro
plant if the grid is extended to their customer area.
A particular void in appropriate institutional arrangements concerns the standardisation of the
turbine-related components and quality assurance of the technical performance of the turbines.
The Nepal Bureau of Standard could take a lead role in this.
4.14 The Special Case of Mozambique and Zimbabwe as New Entrants Into The
Micro Hydro Sector
Zimbabwe and Mozambique were included in the case studies to illustrate programmes at the
earliest stages of development. In both countries the first micro hydro power plants were
installed in the 1930s. However, interest in this technology faded with the coming of grid
electricity and the hope that this would be extended to the remotest users. Both economies
have suffered civil war and although Mozambique seemed to be faring better than Zimbabwe in
terms of recent economic growth (at least before the devastating floods in 2000), every sector
of each economy has to compete for the available but inadequate resources. There is therefore
Intermediation in Practice 49
pressure to use the available resources (such as renewable energy resources) more efficiently
and to direct them towards sustainable options in trying to achieve economic growth.
In Zimbabwe the energy sector is going through important change. New policies and strategies
are being formulated to address needs, meet national objectives, regional and intemational
obligations. There is also a renewed interest in decentralised (often renewable) energy
resources. Most investment in the energy sector goes to the standard energy options of liquid
fuels, coal and grid electricity, but this investment serves only between 1 0%)-20% of the
population while the remainder, mainly in the rural areas, do not have access to modem forms
of energy.
In both countries the utilities see the expansion of decentralised and small scale energy options
as against their commercial objectives. There has been more activity and interest in small scale
renewables in Zimbabwe than in Mozambique. In Zimbabwe a range of stakeholders including
foreign donors have begun to develop the renewable energy sub-sector, spurred by such
processes as the World Solar Summit Process, and the attentions of the Global Environment
Fund.
Zimbabwe has accumulated some experience on renewable energy technologies among them:
wind; solar PV; solar water heaters; solar dryers; micro hydro; biogas; and, other biomass
technologies. However, in Mozambique very few elements of the 'enabling environment' are
yet in place at the national level for decentralised energy supply to thrive. The govemmenfs
ability to formulate energy policy is professionally weak, and there is a clear need to
systematically review policies relating to energy pricing in general and electricity tariffs in
particular. Policies for supporting and financing small scale renewables also need to become
more consistent. Local financing mechanisms are totally absent, and most of the initiatives in
the small renewables sub-sector have relied on extemal donor funding.
In both countries the strategy has been to demonstrate what micro hydro technology can do,
using this experience both to gain familiarity with the technologies and to lobby govemment,
and other agencies, about the role of decentralised (largely renewable) energy technologies.
In Zimbabwe a few plants providing milling services and electricity to remote rural areas have
demonstrated the potential of this technology. Some of the locations have had electricity more
than thirty years ahead of grid electrification, and at a significantly lower cost than competing
options such as diesel engine generator sets or PVs.
Two micro hydro plants were examined in detail in each country. In Zimbabwe they were
located at Nyafaru and Svinurai, and are both community-owned and benefiting from local
subsidies. In Mozambique the two plants selected were at Elias and Chitofu. In contrast these
are both privately owned schemes and were grant financed.
A conventional financial analysis shows schemes intended to produce mechanical power might
be financially profitable whereas there is no return for Nyafaru which main purpose is
electricity generation for domestic end uses. This is mainly due to the high capital costs of the
installation, low tariffs and low plant utilisation, usually at less than 50% capacity. In all the
schemes, social objectives dominate the setting of tariffs, and no allowance was made for
depreciation in tariffs. Such schemes cannot be used to model loan finance unless their
utilisation can be increased and the tariffs raised.
50 Best Practices for Sustainable Development of Micro Hydro Power
In the Zimbabwe cases each type of consumer pays a different tariff, with households paying
less than more commercial enterprises. Steps are being taken at both Svinurai and Nyafaru
schemes to improve the utilisation of the plant and then increase the tariffs. At Svinurai a
generator awaits commissioning, due to extend power to commercial units at the farm. At
Nyafaru there is a proposal to move down from around 5 Amp miniature circuit breaker (MCB)
to 3.5 Amp MCB, in order to increase the number of users but maintain the same tariff at least
in the short term.
In both cases the communities and entrepreneurs do not look at the hydro plants as stand-alone
business units, but as part of bigger enterprises. All four plants show cross subsidies at the
local level. However the movement and cost of finance, labour and materials at the local level
are not easy to track. This could be best tackled by building up the capacity to account for such
movements and costs at the local level. Local capacity to account for costs and income should
complement the capacity to operate and manage management such small enterprises. In the
case of Svinurai this is already happening through the efforts of various stakeholders assisting
in building up the management capacity of the co-operative.
5
BEST PRACTICES: THE LESSONS LEARNED
5.1 The Critical Factors
• Micro hydro programmes and projects need clear objectives. Is the project or
programme:
o An investment in social infrastructure (that will be considered in the same way
as a training scheme, a safe water supply, school, a health programme?);
o A programme to sell as many micro hydro schemes as possible (regardless on
the users' needs); and
o To create small profit making enterprises that are financially self-sustaining.
• Financially self-sustaining projects have cash generating (usually day time) end-uses to
produce cash flow and increase the use of the plant (load factor). Lighting-only systems
will have the greatest difficulty in achieving financial sustainability.
• Subsidies are likely to be necessary if micro hydro schemes are to substantially improve
the access of poor people to electricity.
• The cost of micro hydro plants is dependent on location and standards although
effective management can contain this.
• The form of ownership of micro hydro plant is probably less important to success than
creating an effective business-like style of management.
• Selecting and acquiring micro hydro technology that is appropriate to the location and
task remains a necessary condition for success (wrongly sized plant and inappropriate
standards remain a constant threat).
5.2 Best Practice and Profitable End-uses
• It is easier to make a profitable micro hydro plant socially beneficial than to make a
socially beneficial plant profitable
• Profitable end-uses are difficult to develop because of the limited size of the local
market and the general difficulty of small and micro enterprise development in remote
locations.
• Financial institutions willing to finance micro hydro should consider funding associated
end-use investments in order to build profitable load.
• It may well be that micro hydro should be promoted for its role in securing livelihoods,
or developing small enterprises, rather than as an 'energy programme'.
• The choice of end-use can affect those who benefit from micro hydro and will therefore
effect the poverty and gender impacts, even if not all the community has direct access to
the energy.
51
52 Best Practices for Sustainable Development of Micro Hydro Power
5.3 Best practice and Tariff Setting
• The financial performance of all micro hydro plant could be improved if the average
tariff was kept in line with local inflation.
• Life line tariffs under which the richer consumers cross subsidise households that
cannot pay will spread the poverty reducing benefits of micro hydro -as long as the
total revenue is adequate.
• While there is clear evidence that demand is sensitive to the tariff charged (many
potential users would be excluded by full cost covering tariffs in many locations). there
is also evidence that the ability of some people to pay is higher than originally thought.
5.4 Best Practice for Governments
• Governments need to assign clear responsibilities for micro hydro development and the
development of the necessary 'enabling environment'. Best Practice suggests that this
would ideally be part of assigning more general responsibilities for the provision of de-
centralised energy services to rural (or marginalized).
• Governments need to treat all energy supply options equally ('offer the full menu of
options') and to favour what best meets the needs of the consumer in different locations.
• Governments need to ensure fair competition between competing supply options and
provide equal access to aid and other concessional funds, subsidies, tax breaks and
support.
• Plans for the expansion of the electricity grid should be rule based, and in the public
domain to reduce the uncertainty about when the grid will reach a particular location.
Clear rules should be published regarding the actions the grid supplier must make to
compensate micro hydro owners when the grid arrives (either to buy out the plant at
written down costs or to buy the hydro electricity produced).
• While government finance tends to favour large scale energy inves~ments (in say power
or fossil fuels), micro hydro has the opportunity of utilising local capital (even the
creation of capital through direct labour to build civil works) and it is part of the new
trend towards 'distributed' power with much reduced costs of transmission.
5.5 Best Practice for Regulation
• Regulation should aim to produce a structure of incentives that result in the needs of
consumers being met most cost-effectively. It should be technologically neutraL and at
costs that are in keeping with the scale of the investment and the ability of the various
parties to pay.
• Regulation should be transparent, stable and free from arbitrary political interference so
as to foster competition between suppliers of technology, services and finance.
• Regulation should set standards that are appropriate to the project cost and the ability of
the various actors to pay.
• Quality and safety standards should be enforced to prevent the users being exploited by
shoddy equipment and installations.
• Regulations should be designed so that they do not merely increase the opportunities for
"rent seeking behaviour" of officials.
• Regulations should be set so that: independent power producers can supply power to the
grid at 'realistic' prices; and connection standards are appropriate for the power to be
sold. Rules should be transparent and stable.
Best Practices: The Lessons Leamt 53
5.6 Best Practice in Financing
• Best practice suggests that the expansion of micro hydro will continue to need both 'soft
funds' and funds at commercial rates, particularly if micro hydro is to meet the needs of
people with low money incomes.
• Funding will be needed to cover capital costs, technical assistance and
social/organisational 'intermediation'.
• Micro hydro development will need to leverage funds from many sources including
those for small enterprise development, livelihood development, technical assistance
social infrastructure, as well as the more usual energy and environment sources.
• Micro hydro will need to widen the menu of financing options for acquiring both debt
and equity, including leasing, novel forms of debt guarantee, and novel forms of
collateral (e.g. in Peru the hypothecation of the cash flow from energy end-use, and
municipal loans guaranteed by 'intercept' on revenues from Central government).
• Loan conditions should be simplified, and collateral conditions modified to suit local
conditions for asset (land, equipment) ownership.
• Some financial institutions are likely to require training to understand the special needs
and risks of micro hydro, or to build on analogous experience in other forms of rural
investment.
5.7 Best Practice for Smarter Subsidies
• Subsidies should be designed to achieve clearly stated objectives and should develop
rather than destroy markets.
• A particular problem with current subsidies provided by bilateral donors is that they
have a tendency to 'pollute the well' that is, they use their subsidies to spoil the
market for others.
• Smart subsidies should:
o follow pre-established rules that are clear, and transparent to all parties;
o focus on increasing access by lowering the initial costs (technical advice, capital
investment) rather than lowering the operating costs;
o Provide strong cost minimisation incentives such as retaining the commercial
orientation to reduce costs;
o remain technologically neutral;
o cover all aspects of the project including end-use investments, particularly to
encourage pro-poor end-uses; and
o use 'cross subsidies' within the project to pay for life line tariffs and other 'pro-
poor' recurrent cost subsidies (e.g. enable transfer from richer sections of the
community. and commercial users to marginal connections).
5.8 Best Practice for Donors
• Build programmes on a thorough understanding of what has already been tried before in
the country and elsewhere.
• Adopt funding strategies that enhance (rather than duplicate or destroy) local
capabilities including organisations, regulatory frameworks, and technical capacities.
• Maintain the 'full menu' of options, so as to give micro hydro the same chances for
funding as other decentralised energy supply options.
• Ensure funds build markets rather than destroy them -apply the principles of 'smarter
subsidies'
54 Best Practices for Sustainable Development of Micro Hydro Power
• Ensure funds are available for both micro hydro and associated end-uses. Give
particular attention to the encouragement of pro-poor end-uses (and the views of women
as major players in traditional energy systems).
• Ensure funds are available for all aspects of project development.
• Use soft funds to leverage access to large flows of more conventional loan and equity
finance.
• Be transparent to make others aware of what you are doing and try to harmonise
activities with other donors, partners, equipment suppliers, contractors, and government
programmes.
5.9 Best Practice for Project Developers
• Project developers who have the skill and tenacity to put all the elements of a micro
hydro plant together are crucial to the success of programmes, and are likely to be the
main constraint to programme expansion, particularly if their costs cam10t be covered
by grants
• Successful micro hydro programmes will need to be sufficiently large to produce
sufficient work for the project developers and to achieve economies of scale in the
supply of such services -such as where there are a number of plant in the same area
allowing for costs of site visits to be shared by a number of installations.
• Financial institutions and regulatory agencies need to strike a balance between their
need for project developers they regard as credible (speaking English with formal
qualifications in engineering and accountancy) and their cost. Best practice probably
requires lower cost project developers with specific practical experience with micro
hydro and the communities that use them.
• The costs of 'intermediation' in project development should be recorded, and attempts
made to cover them directly with grant funding.
• Efforts should be made to estimate the realistic size of the market for micro hydro,
taking into account, costs, alternatives, and the likely availability of finance, so as to
detem1ine whether the process of project development can be put on a more sustainable
financial basis (including grants). Additionally the scale of project development
capabilities should be increased sufficiently so as to reduce unit costs by capturing the
economies of scale.
• Technical assistance services should be separated from credit functions to ensure that
sound judgements are made about the financial viability of each project (with or without
subsidies) and credit worthiness of project owners.
• Consideration should be given to productive end-uses from the outset, and treat micro
hydro investment as a small enterprise (regardless of actual ownership structure).
• Endeavour to create a business like management structure, even if co-operative or other
forms ofjoint ownership are used.
• Attempt to institute rules for tariff setting and for inflation adjustments that are
technical and routine rather than arbitrary and politicised (e.g. link the price of
electricity to some other freely traded commodity -such as a staple crop, kerosene, or
candles).
• Successful programmes include activities that stimulate demand for hydro and the
financial and other support activities that are available.
• Successful programmes include activities that lobby for changes in the 'enabling
environment' created by government, financial institutions and donors. These are
Best Practices: The Lessons Learnt 55
probably most effective when operating as an 'Energy Forum' combining the interests
of all people interested in rural, 'alternative', or decentralised energy options.
• Project development would benefit from technical catalysts who can work in close
proximity to villagers at relatively low cost.
5.10 Best Practice for Capacity Building
• There would appear to be no short cuts in developing local capacities. The process
takes a long time and is costly, but without such capacities micro hydro programmes
cannot succeed.
• Local capacities to build micro hydro plants locally appear to substantially reduce costs
• Local capacities to manage, operate and maintain micro hydro plants are a necessary
condition for success and resources will need to be devoted to building this capacity.
5.11 Best Practice for Management of Micro Hydro Plant
• Regardless of ownership structure, it would appear that the successful management of
micro hydro plants requires a 'corporate structure' that minimises political interference
(e.g. from municipal authorities or powerful community members) by providing clear
delegated authority to a management to achieve clearly stated objectives related to
profitability, coverage, and the quality of the service to be provided.
ANNEX
SUMMARY OF THE CASE STUDIES
1. SRI LANKA
1.1 The Sample
There are approximately 130 MHP plants 66 currently in operation in Sri Lanka. Most
are less than 100 kW in capacity. The sample of projects were drawn from a total of
about 70 67 village micro hydro plants and 13 estate MHP sites. There is estimated to be
60 estate MHP plants in operation. This number has been obtained from various
information sources6 l:i as there are no database records for this category of MHP.
Although MH development dates back to the tea plantations in the pre-independence
British colonial era, the availability of data is extremely limited. The recent resurgence
of interest in MH in the 1980's has generated a great deal of experience of improved
technology, but systematic data remains scarce.
Study criteria led to purposive selection of sites for in-depth review and assessment.
The selected sites and the criteria are given in the table below:
Table A-1: Selected Sites and Criteria, Sri Lanka
Site Name District Date Ownership Capacity Source of Finance End-use
Pathavita 2 Malara 1997 Community IOkW Loan +Comm. Ironing
centre
Kandaloya Kegalle 1998 Community IOkW Loan + Grant / Fridge &
Comm. ice-making
Katepola Ratnapura 1995 ECS* 24kW Grant+ Comm. Rice mill
Seetha Matara 1985 Private 60kW Private + Bank -'-Tea factory
Elin Grant +lighting
' * Electnclly Consumer Soctety
Four micro hydro sites representing different financing arrangements and end-uses were
selected to carry out the sample analysis on financial viability of such projects. Three of
the sites have been established only during the last two to three years while the other has
been in operation for 14 years. At the first three sites energy sales to individual
households are not metered; each household pays a fixed monthly fee with the
understanding that the restriction on power use is adhered to.
"'' Details of these sites arc available through Intermediate Technology Development Group's (ITDG) Sri Lanka
database on MH (referred to as ITSL ). These are listed briefly in the annex.
67 This number is derived from !TOG's Sri Lanka database. January 1999. Figures change periodically as more MH
sites enter the pipeline or are implemented and incorporated accordingly into the database. Sec ann.:x l for excerpts
from this database.
'''For more details see Country Report for Sri Lanka, December 1999.
57
58 Best Practices for Sustainable Development of Micro Hydro Power
Figure A-1: Map showing the locations of the case study sites in Sri Lanka
J~~~:~r~;;;~~:;t1, ..
·--... ,,, ·-_::r:-:-:;:~~3.\.
.-.-. ~--
f;ig}k WtWP ; .. -~ ~
;{
.,, ......... ~'>
;Mannar
40
.::~
4fJ :Blhni .,
t:it
8¥Jtlfj~J
:·~
Kalpitiya~ .. ··
. ·.· :.Trincomalee
.Anuradha;:n.iia :\j
Guir
~Jf
'j'f.tJt'tr'1t1f
• ······· Puttalam
. ·~ Matale.
Negombo.
Site 1 : Katepola
Site 2: Kandal Oya
.BaduUa ·;
I
Site 3: Pathawita
Site 4: Seetha Eliya
1.2 Case Study Details
1.2.1 Site 1: Katepola
Katepola, a community-based village hydro project, is predominately financed by
grants, with equity contributions made by villagers in the form of labour and finance.
No commercial loans have been used.
Village Overview
Katepola is a village with a population of 350 families situated in Ayagama secretarial
division in the Ratnapura District. Inhabitants of Katepola are generally in the low-
income category, earning their living from rubber, cinnamon and paddy cultivation, or
by employment at the Dumbara Estate. The neighbouring· village of Katepola,
Umangedara, is home to the first village hydro scheme established by ITDG Sri Lanka.
Project Overview
The Katepola village hydro plant using the flow of Thundola stream, has a capacity of
25 kW. It consists of a stand-alone synchronous generator with an Electronic Load
Controller (ELC), supplying power to 1 06 houses and a rice-mill.
• • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • •
Annex: Summary of Case Studies 59
A significant part of the project cost was born by the ECS, whilst important
contributions in the areas of technical assistance and financial co-ordination were made
by ITDG.
Table A-2: Katepoloya Scheme Profile (US$1998)
I Capacity of MHP:
Start date:
125kW
1994
Total Capital cost: US$54,529
of which Electromechanical: US$21,664 (39.7 %)
Civil: US$23,874 ( 43.8 %)
Other* (incl transp/distrib) US$8,991 (16.5 %)
Grant: US$34,654
Connection charge per HH: US$64 in 1995 then US$174 from 1997
HH allocation in Watts: 200W
Hours of HH usage per day: 5 hours
Cost per installed k W: US$2, 181
Other costs: mainly transport and distribution for electricity generation schemes.
The management, financial control and load regulation is carried out by the Electricity
Consumer Society (ECS) established at the conceptual stages of the project. This is a
society formed by the villagers consuming the electrical power delivered by the village
hydro plant. The office bearers, selected at an annual general meeting are responsible
for the management, which includes taking necessary action for breakdowns and any
other disputes arising from electricity usage within the community.
This village hydro scheme provides electricity to 106 houses; each supplied with 200
Watts of power at a monthly charge of US$1.43 (Rs 100 in 1999) per household. The
scheme also powers a rice mill, which is supported through grant funding from ITDG
and operated solely during the daytime. The mill is supplied with electricity free of
charge while the income from rice milling is credited to the ECS after paying the
operator.
1.2.2 Site 2: Kandal Oya
This is a community-based project, predominately financed through the Energy Services
Delivery (ESD) scheme, with equity contributions made by villagers in the form of
labour and finance. There is a great diversity of small-scale end-uses at this site.
Village Overview
Kanda! Oya is a remote rural village located approximately 23 km away from
Yatiyantota, in Y atiyantota divisional secretariat of Ratnapura District. The community
is largely agricultural, with a reasonable household income. There is a high demand for
electricity for lighting and other household requirements.
Project Overview
The project consists of a 10 kW stand-alone induction generator with an induction
generator controller (IGC) and presently serves about 88 households. This village
hydro scheme has been financed through the World Bank's ESD project. The scheme is
owned by a limited liability company formed by the membership of Electricity
· 60 Best Practices for Sustainable Development of Micro Hydro Power
Consumer Society, consisting of connected households. This is a legal entity set up to
facilitate the management and to support long-term financing and repayment.
Table A-3: Kanda) Oya Scheme Profile (US$1998)
I capacity of MHP: II 0 kW
Start date: 1997
Total Capital cost: US$31,148
of which Electromechanical: US$6,152 (19.8%)
Civil US$9,822 (31.5%)
Other (inclu trans/dist): US$15, 174 (48.7 %)
Loan interest: 0.16%
Loan amount: US$8274
Grant component of the loan: US$4468
Repayment period: 5 years
HH allocation in Watts: 100W
Hours of HH usage per day: 5 hours
Tariff per HH/month: US$3.85
Costper installed kW: US$3,115
1.2.3 Site 3: Pathawita 2
This is a community-based project, funded through the ESD project, with equity
contributions from villagers in the form of labour and money.
Village Overview
Pathawita is a remote village situated in the Matara District of the Southern Province,
about 200 km from Colombo. The village, separated into two major sections by a
mountain, consists of around 200 houses spread over a large area of land. This
dispersal of housing has created major barriers in supplying electricity to the whole
village economically, and with an acceptable voltage profile. The closest access to the
village is through Kotapola and off Beralapanathara in Kotapola Divisional secretariat.
Project Overview
The site identified for the establishment of a hydro plant had a continuous potential of
10 kW. With the financial assistance of the Rotary Club of Colombo-West, an
induction generator (capacity 5.5 kW) and an induction generator controller made in
China were imported and installed. At the initial stage, the project could supply power
to only 66 houses.
Table A-4: Pathawiata Scheme Profile (US$1998)
Capacity of M HP: 10kW
Start date: March 1997
Total costs: US$22,031
of which Electromechanical: 12,811 (58.1 %)
Civil work: 5,926 (26.1%)
Other (inc.trans/dist) 3,294 (15 %)
Loan interest: 16%
Loan amount: US$8,274
Grant Component of the Loan: US$2,797
Annex: Summary of Case Studies 61
Repayment period: 8 years
HH allocation in Watts: 100W
Hours of HH usage per day: 5
Tariff /HH/month: US$2
I Cost per mstalled kW: I US$2,203
A second stage of the project was initiated in a bid to harness the total hydro potential.
Commissioned in November 1997, a new turbine generator with a capacity of 10 kW
was installed in the place of the previous turbine and generator. This new scheme
supplies power to 103 houses in the village.
The second stage of the project was funded through the World Bank's ESD programme.
ITDG co-ordinated the finances and any technical contributions required, arranging
technical services through the consultancy firm Consultancy and Professional Services
(CAPS).
The loan was granted to a company formed by the village electricity consumers' society
(ECS). Along with the loan of US$8,274 (Rs. 500,000 in 1997), the company received
a grant of US$2,797 (Rs. 169,000 in 1997).
The company charges US$2 (Rs. 140) per month per household, allocating 100 Watts
per household. The operator of the powerhouse receives US$14.3 (Rs. l ,000) monthly.
Presently the company is facing a severe threat to its existence with the national grid
penetrating into the areas supplied by the hydro scheme. The immediate problem of
losing its consumer base and in attracting new customers may result in difficulties
paying back the 8 year loan under the ESD program.
1.2.4 Site 4: Seetha Eliya.
Village Overview
This is a private project, with equity and commercial loan financing. Energy is used to
supply the operating requirements of a tea factory. Seetha Eliya micro hydro plant is
situated in Kandilpana, Deniyaya in the Matara District. This is one of the few plants
initiated, constructed and managed by the estate sector in the country. The plant has a
capacity of 60 kW, which falls in a range clearly above the average capacity of village
hydro plants of Sri Lanka.
Table A-5: Seetha Eliya Scheme Profile (US$1998)
Capacity of MHP: 60kW
Start date: 1985
Total costs: US$225,665
Loan interest: 26%
Loan amount: US$98,544
Grant Component of the Loan: 0
Repayment period: 10 years
End-use: Electricity supply for a tea factory
Cost per installed kW: US$3,761
62 Best Practices for Sustainable Development of Micro Hydro Power
Project Overview
This plant was constructed by Seetha Eliya Tea Factory with the main intention of
supplying power to the operations of the factory, including lighting. The total cost has
been borne by a loan and an equity investment by the tea factory.
The plant was initiated with the aim of using streams in the land of the Seetha Eliya Tea
Estate, thus relieving the burden of costly electricity bills. Construction of the plant
started in 1983 and the plant was commissioned in 1985. Initially an induction
generator was used; later generation was transferred to a synchronous generator. Unlike
other micro hydro schemes, there was no grant component associated with the loan.
Project financing was done through a commercial loan at an interest of 26%. The
management, financial control and load regulation is carried out by the factory itself.
There is no separate management body for the plant and no separate income stream,
apart from the avoided cost of grid electricity.
A major difficulty faced in the process of construction was getting the required approval
from local authorities. Most of the land within the tea estate has been used for the
project apart from around 0.5 hectares of land, donated by the owner of the estate to
outsiders in return for using their land for the pipelines.
/.3 Financial and Economic Analysis
The key results and findings are presented in Table tf 9 . Two sets of scenario were
considered.
Table A-6: Internal Rates of Return and Return on Capital Invested (IRRci)
After Financing (%)
Katepola Kandaloya Pathewita 2 Seetha Eliya
cur const cur const cur const cur const
IRRci 14.7 8 15 9.3 32 16.3 24 12.4
IIRR Negative 10 6.9 6 3.1 I 24 12.4
The community-based projects with financing from the ESD programme (Kandaloya
and Pathewita) have an IRR in constant dollars of around 7% and 3%, while the scheme
with total grant funding (Katepola) has a very low or negative IRR. The privately-
owned project (Seethe Eliya) has a very high IRR, 24% and 12.4% respectively in
current and constant dollars.
The return on capital invested (IRRci) in ESD project-based schemes is around 9% and
16% in constant dollars. The present bank interest rates for cash deposits, and interest
rates for treasury bills vary between 7% to 12% depending on the type of deposit.
Considering these rates and the IRRci, it is apparent that projects financed under the
conditions similar to those of the ESD project can be justified not only on social
grounds, as in the case of all village hydro schemes, but also on financial grounds. It
can be seen that IRRs of projects are below the interest rates paid for the loans (I 6% ).
If there is no grant component associated with the project, the community will find it
difficult to pay off the Joan solely with the income they receive from the sale of
''"Detailed methodology and calculations arc available from the country reports.
Annex: Summary of Case Studies 63
electricity. Unlike the ESD project-based schemes, the charging rate at Site is not
satisfactory for it to remain financially viable.
Clearly the investment in Seetha Eliya can easily be justified by private sector financing
owing to its high IRR, while Seetha Eliya itself avoids the high cost of grid-supplied
electricity.
In the sensitivity analysis we considered several cases, in particular the impact on the
variations of the capital costs and the financing conditions on the IRR and the IRRci.
Among the series of cases analysed, the most important was the sensitivity of IRR and
lRRci to the capital costs and tariffs. This implies that the profitability and
sustainability of the schemes will depend a great deal on the ability to build low cost
schemes with high plant factors, and deliver services based on realistic tariffs, i.e. a
dynamic policy of tariffs, while taking into consideration the ability of the beneficiaries
to pay.
1.4 Conclusions from Sri Lanka
• Village hydro 70 projects are primarily meant for off-grid rural electrification in
remote locations and they tend to show poor financial viability on their own.
• With a grant component similar to that of the ESD project, these schemes could
be financially viable, but the electricity tariffs need to be kept at a reasonable
level as in the case of Kandaloya site.
• Within the community-owned village hydro (VH), small-scale individual end-
use activities such as battery charging and ice-making are more sustainable
than large community-owned end-use activities such as rice milling.
• Private, productive end-use activities such as electricity use in a tea factory
make MH schemes very attractive in terms of their financial viability.
• Extension of the national grid into areas where village hydro schemes have
already been established jeopardises cost recuperation, contributing to poor
sustainability of these projects due to their customer base being affected.
• It is worthwhile exploring the possibility of grid connection of such micro
hydro projects as an end-use where excess energy can be sold.
'o The concept of village hydro was introduced by ITSL and refers not only to the implementation of the scheme. but
also to the involvemem of the local population from the decision-making process until the management.
64 Best Practices for Sustainable Development of Micro Hydro Power
2. NEPAL
2.1 The Sample and Assumptions .
The study areas include three MHPs located in the hilly regions of Nepal in the Western
Development Region in the districts of Gorkhe, Kaski and Baglung where about 134
MHP plants of more than 10 kW capacity (about 37%) are located. One MHP has been
considered from lllam District of Eastern Development Region where there were 35
MHP (about 10%) above 10 kW capacity. Attention was given to the selection of plants
with electrification as well as processing facilities where power has been generated
using cross flow and Pelton turbines.
Figure A-2: Map showing the locations of the case study sites in Nepal
• Dhangadhf
IN 0 I A
Site 1: Barpak Site 2: Gor khe
0 50 100 km
o ~; 100n~
CHINA
'· .• B!rganJ
'-.
" ···: ..... ..-'"": .Janakpur
·-,.,.--
Site 3: Ghandrak -Site 4: Gaura
The general characteristics of the selected plants are as presented in the table below.
Table A-7: Selected Sites and Criteria, Nepal
Region Scheme Owner Capacity Turbine End-uses
(kW)
Western Barpak Community 50 Pelton Milling Lighting
Western Gorkhe Private 25 Pelton Milling Lighting
Western Ghandruk Private 50 Pelton Milling Lighting
Eastern Gaura Private 25 Cross flow Milling Lighting
Other
Other
Other
Other
• • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • •
Annex: Summary of Case Studies 65
2.2 Case Study Details
2.2.1 Site l: Barpak Micro Hydro Power Project
Village and Project Overview
This plant is located in Chhara Village, ward No.5 of Barpak Village District
Committee (VDC) in the Gorkhe District situated in Western Development Region ..
The site is situated in the northern part of Gorkhe District and is not accessible by the
road. The plant is located 3.2 km from the settlement area. The source, Ghatte Khola,
is located 375 m from the powerhouse. The annual income of the users is estimated at
US$36-72.
Works started in September 1990 and were completed in June 1992. There were no
major problems apart than difficulties in the transportation of construction materials and
plant to the site. The plant has been able to provide services to 538 households, covering
3,362 people.
The consumers and other local residents were involved in civil construction works. The
consumers contributed labour while other local residents were paid on a daily basis
according to their skill. The borrower had to bear the cost toward the civil construction.
Table A-8: Barpak Scheme Profile (US$1998)
Capacity of MHP: Design capacity: 50 kW
Effective capacity: 30 kW 71
Start date: 1992
Total Capital cost ($1990): US$64.757
of which Electromechanical: USS57,356 (88.6 %)
Civil works: US$4.344 (6.7 %)
Other ( inc. trans/dist) US$3,057 (4.7 %)
Loan interest: 17%
Loan amount: USS35,913
Subsidy: US$15,812
Household end-uses: On average 3 bulbs of 25 Watts per household.
Morning 05.00h-06.00h, evening 17.30h-
22.00h.
Productive end-uses: Ropeway, sawmill, grain milling.
Tariff for domestic use in 1999: 38 US cents per month for 25 W bulb (fixed
tariff)
Productive end-uses (sawmill, etc.): 6 US to 7 US cents per kWh (metered)
Cost per installed kW: I US$1,295
The use of power for commercial application seemed encouraging. A ropewa/2 of 2.3
km in length was established to operate cable cars, linking Barpak with Rangrung
village. It was designed by Himal Hydro General Construction Co, Nepal, with a total
load capacity of 300 kg. Two cable cars are attached with 150 kg payload each. A total
of 30 k W is required to operate the system. The carrying time from Rangrung to
Barpak is 15 minutes. The total system was completed at the cost of US$1 00,000,
Effccllve capacity in 1998. source ITDG.
•: This scheme was badly damaged. The topography and the design seem to be the main causes.
66 Best Practices for Sustainable Development of \<licro Hydro Power
funded jointly by British Embassy, ITDG and Northern Gorkha Development Group
(NGDG). Local people contributed about 9 percent of the total cost in kind.
Table A-9: Source of Financing Ropeway between Barpak and Rangrung
lsN I source of Funding I Amount in US~ %1
1 British Embassy 65,714.29 65.71
2 ITDG 14,285.71 14.29
3 NGDG ll .428.57 11.43
4 People Contribution 8571.43 8.57
Total 100,000.00 100.00
The ropeway is completely managed by the community. lt has a nine-member
management committee fully responsible for operating and managing the system. The
management charges US$0.07 per kg for goods transported.
The owner established an agro-processing mill, at a cost of about US$971, which was
supplied by Katamandu Metal Industries (KMI). The mill has one rice huller and one
grinder, consuming 4 kW of power for each unit. The respective processing costs are 1
US cent per kg and 0.9 US cents per kg. The huller has capacity to process 50-75 kg
per hour while the grinder can process 34-41 kg per hour. A total of 20,000-25,000 kg
of paddy is hulled annually at present. The grinder is able to process 60,000-80,000 kg
of wheat, maize and millet annually.
Other Micro Hydro Plants
A traditional water wheel is still working at Baluwa village, located at Bhalswara, about
4 km from Barpak village. It is mainly operated for agro-processing and the rates are
some 14 percent higher than those fixed by the owner of Barpak. However, the rate for
grinding is about 13 percent lower than the rate fixed by Barpak's owner. In addition
there is one peltric set of 1 k W capacity installed around 6 krn outside of the Barpak
village. The power is used for lighting the owner's own house only. The national grid
is located roughly 1.5 days walking distance away.
Financial Results
The results show that without subsidy the IRR after financing, expressed in current
values, is 22.8%, which is a good return. However, the results expressed in constant
dollars show a lower return of 17%. This latter rate is still in-line with the interest rate
charged by ADBN. The main explanation is that the increment of prices in current
tenns is not correlated with inflation.
2.2.2 Site 2:Gorkhe Micro Hydro Project
Village Overview
This plant is located at Rupatar village of Illam District in Eastern Development Region.
The plant is situated at a walking distance 73 of about 2 hours from the nearest roadhead
whereas the source, Jogmai Khola, is located at about 500 m from the powerhouse.
The annual income of the middle-class consumers is estimated at US$429-714. The
average income of the lower class family is estimated at US$171-286. The plant is
''All distances c\prcss~d in hours are walking distance.
Annex: Summary ofCase Studies 67
currently providing electricity services to 12 households with a population of about 80.
The owner intends to expand the services to include an additional 55 households with a
population of 450.
Project Overview
The Gorkhe water turbine mill was completed in 1984. The plant has a 25 kW capacity
and was the first plant installed in the lllam District. The cross flow turbine was
designed, manufactured, supplied, and installed by Development Consultancy Services
(DCS), who carried out the technical survey. ADBN sub-branch office at Nayabazar
conducted the financial feasibility analysis. The owner supervised and supported the
costs of all the civil works.
The electrification component was added in 1986, with battery charging and a drier
installed in 1988. Domestically, electricity is used for lighting, radio, televisions and
tromng. The bulbs are easily available for US$0.43-1.00 in local markets. The
consumers are also using low wattage electric cookers known in Nepal as 'Bijuli
Dekchi'.
Table A-10: Gorkhe Scheme Profile (US$1998)
I Capacity of MHP: I 25 kW
Start date: Milling-1984
Electrification, Battery Charging and Cardamom
Drying -1986
Total Capital cost: US$16,374
of which Electromechanical: US$10,311 (63 %)
Civil: US$3,479 (21.2 %)
Other US$2,584 (15.8 %)
Loan: US$8,269
I ~ubstdy: US$5,469
epayment peno : years .d 10
HH consumption: 2-5 bulbs, 1 h/moming and 4.5 h/evening.
Productive end-uses: Battery charger, cardamom drier.
Tariff domestic end-use: 3 I cents per month for 40 Watts (fixed tariff)
I Cost per mstalled k W: I $655
Other facilities for income generating activities were installed in the next phases. The
owner installed a processing mill and agro-processing units at the cost of US$1 ,332 and
US$1,645 respectively. The facilities comprise of a huller, grinder and oil expeller. He
borrowed US$893 from ADBN as a working capital in 1986. The processing charges in
1999 were: hulling, 0.6 US cents per kg; grinding, 1.25 cents/kg; and expelling, 1.56
cents/kg. These rates are higher, in nominal terms, than those fixed some years ago.
The owner expanded his activity further in 1988, installing a cardamom drier supplied
by DCS as a pilot project. The drier was supplied at a cost of US$1 ,343, of which DCS
paid 50 percent as part of their promotion. The owner has contributed the balance -
US$672, as his equity. The cardamom processing unit works seasonally for about four
months between August and November. The owner dries the cardamom harvested on
his farm, producing around 125 kg of dried cardamom annually from 400 kg of green
cardamom. The final dried cardamom is of a fine quality and fetches a good price in the
68 Best Practices for Sustainable Development of Micro Hydro Power
market compared with cardamom dried in the traditional way.
The owner used his own resources to establish the battery charger. There is a constant
load of 2 kW from the battery charger throughout the day. The load increases during
daytime mainly due to the operation of a processing mill. The load characteristics of the
plant are presented below. The rate for battery charging varies as per its capacity and is
set at 63, 31 and 19 US cents for 12, 8 and 6 volt batteries respectively.
Figure A-3: Load Characteristics of Gorkhe Micro Hydro Plant
Load Management
10.00
~
.::£.
c 5.00 ·-"0
<':l
0
-l
Time
The owner fixes tariffs for domestic end-uses and income generating activities. The
consumers have no complaint about the present tariff levels. An increment was made
on initial processing charges fixed during the year 1985-1990 for hulling, grinding and
expelling by I 00. 300 and 50 percent respectively. This rate remained unchanged for
the years 1991-199 5. The processing charges were again revised in 1996 and fixed at
33 and 100 percent above the 1991 rates for hulling and grinding, whilst the rate for oil
expelling was reduced to 33 percent of the 1991 fixed rate.
Financial Ana(psis
Gorkhe has the lowest cost per installed k W. This is certainly due to the fact that it is
principally aimed at providing mechanical power and as such the capital cost per
installed kW is relatively low. The return on the capital invested is 32% in constant
dollars. lf the scheme was not subsidised, the internal rate of return is above 17% in
current dollars, but just 4°/t> in constant dollars because of the disconnection between the
rate of inflation and tariffs.
Other Existing Micro Hydro Plants
A traditional water wheel is located about 4 km walking distance from the plant and is
mainly used for agro-processing. The charge for processing is 1.4 US cents per kg, 0. 7
cents/kg and 2.15 cents/kg for hulling, grinding and oil expelling respectivel/4 . The
charge for hulling is 150 percent higher than that fixed by Barpak's owner, the rate for
oil expelling is maintained at the same level and the rate for gtinding has been
maintained at around 38 percent less. There is also a MHP plant of 64 kW, Gorkhe
Sana Jal Vidyut located at about I hour walking distance. The plant was established by
the Small Hydro Power Development Project, funded by the Nepalese Government.
c~ Usually charges are per 40 kg.
Annex: Summary of Case Studies 69
The plant is currently under utilised due to limited end-uses and NEA district office
approached the owner to take over the plant. It requires highly skilled operators to
operate the plant and there is no plan at present to expand its services. The national grid
is located at about 1 hour walking distance and there is no programme to expand their
line to that area.
2.2.3 Site 3:Ghandruk Micro Hydro Project
Village Overview
The plant is located in Ghandruk village, in Kaski District, Western Development
Region. It is about 6 hours walking distance from the nearest roadhead. The distance
from the nearest trail road to the site is about 100 m. The plant is located at about 200
m from the settlement area, whereas the source, Chane stream, is located at 2.3 km from
the powerhouse.
The average annual income of consumers involved in business is estimated as
US$2,000-US$7,000. The average annual income of the middle class and lower class
family is estimated as US$430-US$700 and US$170-US$210 respectively. Agricultural
production and tourism are the main occupations of the community. The village is en-
route to Annapurna base camp and is considered as one of most beautiful Nepalese
villages.
Project Overview
The agro-processing mill was completed in 1985 and the electrification component was
added in 1988. During the implementation phase there were no major problems apart
from the transportation of construction materials and plant machinery to the site. A
pelton turbine and generator were imported from Stamford, UK. The system was
designed, installed and supervised by DCS.
The plant experienced serious technical problems after it came on stream: low output
was observed and the turbine shaft was broken after installation. The penstock pipe was
damaged during the test run of the plant as a result of its poor quality and poor
workmanship. DCS reinstalled the penstock pipe free of charge. Because of this
incident the supplier installed a separate 16 kV A diesel generator in July 1991 which
supplled power nightly until the MHP plant started operating again.
Table A-11: Ghandruk Scheme Profile (US$1998)
Canacitv of MHP: 50kW
Total Capital cost US$112,597
of which Electromechanical: US$89,910 (79.9 %)
Civil: US$19,308 (17.1 %)
Other US$3,379 (3 %)
Start date: Mill-1985 Electrification-1988.
Loan interest: 17%
Loan: US$14 481
Subsidv: US$73 499
Hours of usage oer dav: Processina mill 6 hours oer dav.
Tariff for domestic end-use: 0.8 cents /W/month
Hotel and lodges: 1.2 cents /W /month
Productive (sawmill): 1.2 cents /W /month
Cost oer installed kW: US$2 252
· 70 Best Practices for Sustainable Development of Micro Hydro Power
The power plant supplies electricity to 241 households covering a total population of
1900 people. The plant also supplies power to 22 hotels/lodges and 6 restaurants.
Heating appliances are used by all the hotels and lodges. The plant is managed and
operated by the community with the support from Annapurna Conservation Area
Project (ACAP), a Non-Governmental Organisation (NGO). The community provided
both cash and voluntary work estimated at US$8,132. Daily wages were paid to the
non-beneficiaries. The borrower and ACAP contributed the remaining amount required
for the establishment of plant.
Most of the energy consumption takes place during the morning as a result of the water
heaters and refrigerators used at hotels and lodges. The load improved after the
operation of processing and saw mill units. Now the load is relatively uniform during
whole day and evening. Load management becomes difficult during the dry season and
with the increase of domestic consumption. The load characteristic of Ghandruk MHP
plant is shown below.
Figure A-4: Load Characteristics of Ghandruk Micro Hydro Plant
Load Management (Ghandruk)
60.00
::;
..:.< 40.00 c:
-,;:) 20.00 0::
~
Time
There are no connection or fixed charges, but a reconnection charge of US$1.43 applies
if the consumer's consumption exceeds the power allocated 75 • For the processing unit,
power supply is available from 1 Oam to 4pm.
Financial Analysis
Ghandruk is the least profitable scheme in financial terms. Even with the subsidy, the
return for the investor is just over 10% in current values and l% in constant dollars.
The relatively high initial capital cose6 and the tariffs policy are key factors, explaining
this low profitability.
Other 1\tlicro Hydro Plants
A traditional water wheel, mainly used for agro-processing, is located two hours
walking distance from the plant. The processing charges are US cents 0.4 per kg for
hulling and US cents 1.1 per kg for grinding.
A micro hydro plant has recently been installed at ward no 9 of Ghandruk with a total
installed capacity of 6 k \V. It is located at a walking distance of about 3 hours from the
existing MHP plant. The plant is managed and operated by the community and the
~~ Households are fitted \\'ith lo\v cosl circuit breakers. Pov,.:cr is automatically cut off \Vhen consun1crs usc more
than the wattage allocated. Allocated supply usually falls between 40 W-I 00 W.
7
". The capital cost per k\V of Ghandruk is the highest oft he four schemes of the Nepalese sample.
Annex: Summary of Case Studies 71
users' committee fixes the tariff. The tariff is US$0.57 per month for 40 Watt. This is
at least 100 percent higher than the tariff of the existing MHP plant in Ghandruk. A
newly constructed hotel has installed a diesel generator due to the lack of available
power from the existing MH plant.
The charge for hulling is 150 percent higher than the rate at Ghandruk MHP. The rate
for oil expelling is maintained at the same level whereas the rate for grinding is about 38
percent lower than the rate fixed by the owner of Ghandruk MHP. The national grid is
located about I hours walking distance away.
2.2.4 Site 4: Gaura Rice Mill (Harichaur Micro Hydro Project)
Village Overview
The plant is located in Harichaur village in Baglung District in Western Development
Region. It is 8 hours walking distance from the nearest roadhead and 30 minutes
walking distance from the nearest trail road. The plant is located at the bank of Daram
Khola, which is about 700 m from the village. Harichaur was previously the district
headquarter, later shifted to Baglung. It is situated en-route to Dhorpatan, one of the
promising areas for tourists and trekkers. There is a holy place called Utar Ganga,
which is located at a walking distance of about 3-days from the settlement. There is a
police station, a hospital, boarding school and short-wave communication transmitting
station. The main occupation of the community is agricultural production.
The annual average income of the consumers is estimated as US$170-US$290. The
plant supplies electricity to 236 households including 11 offices and institutions
covering 1575 people. Most of the power is used for household lighting, television and
radios and to run the agro-processing plant.
The daily time saving of 1-2 hours has been used by the community to set up a kitchen
garden and operate a Non Formal Education (NFE) programme. It is estimated that
about 70 percent of the community (an increase of about 45 percent) have become
literate and the enrolment of girl students has increased every year. The study hours of
the students has also increased, by 1-1.5 hours daily.
Project Overview
The initial system was designed, installed and supervised by DCS who manufactured
and supplied the cross flow turbine. Nepal Machine and Steel Structure (NMSS) also
designed and installed a new turbine in 1997 which enhanced the output by an
additional 2 kW.
Table A-12: Gaura Scheme Profile (US$1998)
lc apac1ty o fMHP 125 kW
Start date: 1987
Total capital cost: US$54,000
of which Electromechanical: US$35,785 (66.3%)
Civil: US$15,330 (28.4 %)
Other costs ( incl. transp/dist.) US$2,885 (5.3 %)
Loan interest: 17% average interest rate
Loan: USS26,394
72 Best Practices for Sustainable Development of Micro Hydro Power
Subsidy: US$8,053
Repayment period: 12 years including 3 years grace period.
Household and institutional end-uses: On average 3 bulbs of 25 Watt for lighting
05.30 h-06.30 h in the morning and from
17.30 h-22 h in evening.
Productive end-uses: Agro-processing (huller, grinder expeller).
Tariffs domestic lighting: US cents 34 /25W /month
Cost per installed kW: US$2,160
The processing mill was established at a cost of US$2,080. The owner carried out all
the civil construction. Local skilled and unskilled labour was used in the construction
works.
The loan repayment schedule for the plant was arranged for 12 years, which also
included a grace period of 3 years. The borrower had to repay the loan for working
capital within 12 months and there was no provision for a grace period for such a loan.
The consumers and other non-beneficiaries were involved in civil construction works.
The consumers provided voluntary labour \Vhereas non-beneficiaries were paid as per
the prevailing rate depending upon their skill.
The morning and night-time loads are mainly from household lighting. A battery-
charging service has been provided which was developed by DCS in 1997. The battery
lighting system has been installed in the hospital to provide light for the maternity ward
in case of an emergency.
The load characteristics of the plant are shown in the chart below.
Figure A-5: Load Characteristics of Gaura Micro Hydro Plant
Load Management
30.00
3
...'<: 20.00 ::::
"" 10.00 "' 0
...J
Time
The processing charge for rice hulling was fixed at 0.57 US cents per kg of paddy from
1984 -1986. The rate was increased from 1987 to I. 7 cents/kg. The grinding charge
was 0.68 cents/kg, which was increased to 2.9 cents/kg in 1987. The oilseed was
expelled at 3.8 cents/kg and was increased to 8.4 cents/kg in 1987 77 . However none of
these rates were changed after 1987 which signifies a sharp decrease in constant values.
Usually charges are per IOkg.
Annex: Summary of Case Studies 73
Financial Analysis
The internal rate of return on the capital invested is over 13% in current values but just
3% in constant values. If we assume that the plant was not subsidised, the internal rate
of return would be 7.39% in current values, with no return in constant values. This is
predominately the result of the stabilised processing tariffs which were kept unchanged
from 1987 onwards.
Other Micro Hydro Plants
Harichour has numerous MHPs in its vtcmtty. An improved water wheel was
established in 1980 and is located at Hatiya village; about 45 minutes walk from the
MHP. It has the same rates as the plant investigated. Also, a MHP plant of 7 kW
capacity was installed a decade ago under the loan assistance from ADBN and with
subsidies from the Nepalese Government. The national grid line is about 1-days
walking distance from Harichour. A community-managed micro hydro of 50 kW
capacity has recently being installed at a working distance of about 45 minutes. The
plant was established with the grant assistance of US$29,851 from the Canadian Co-
operation Office (CCO). The balance fund was arranged through a subsidy from the
Government ofNepal, a loan from ADBN and equity from the community.
74 Best Practices for Sustainable Development of Micro Hydro Power
3.· PERU
3.1 The Sample
This economic and financial analysis is based on four small-scale hydroelectric · plants.
The first case concerns Atahualpa farming co-operative. The power generated by this ·
MHP is used for income-generating activities, as well as for domestic and institutional
purposes. A small entrepreneur owns the second plant and the power generated is used
entirely for an incubating plant. The third case consists of a public electricity service in
the district capital of Pedro Ruiz. The MHP is managed by the municipality and
provides electricity to the town of Pedro Ruiz. The fourth case is a public service in the
Pucara District, managed by an electricity distribution company.
Table A-13: Selected Micro Hydro Schemes in Peru
·1 Atahual a lvumahual I Pedro Ruiz I Pucara
Owned b Coinmunit Private Owner Communit Private Owner
Ca 35 10 185 2 x200
Figure A-6: Map showing the locations of the case study sites in Peru
·Su.urn
PtJc.tfit
Dctat3n
Huanuoo
UMA
Callao~
() 2QO 400 1011
Q 200 400 mi
Site 1: Atahualpa
Site 2: Yumahual
Site 4: Pucara
. Pueno
•Huan~ • MSii<:IOM(fO
·:>:.
'· .et.tsto
\
·\,.
AMcJ Jjpe,.
UetarA;,fl... ·.II 0
Ta
Site 3: Pedro Ruiz
• • • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • •
Annex: Summary of Case Studies 75
3.2 Case Study Details
3.2.1 Site 1: Atahualpa Farming Co-operative
Village Overview
The project's objective was to provide the co-operative with a permanent and reliable
source of energy to improve the development of a previously implemented and
flourishing agro-industrial activity. Before putting the MHP plant into operation, the
co-opemtive had facilities for transforming farm products and had other machinery.
These were fed by a low powered diesel generator with limited output and high
production costs. The farming co-operative of Atahualpa-Jerusalen Workers has about
58 members at present, of which 48 are active members and the other 10 are retired.
Project Overview
The 35 kW MHP was set up as part of a demonstration project that ITDG promoted in
Cajamarca. The power generated by the MHP is used for productive activities, and for
domestic and institutional purposes.
Table A-14: Atahualpa Scheme Profile (US$1998)
Department, Province and District: Cajamarca
Settlement: Porc6n
Owner: Atahualpa-Jerusalen Fam1 Workers' Co-operative
Plant capacity: 35 kW
Start date: March 1992
Total project cost: US$82,541
of which Electromechanical: US$31,116 (37.7%)
Civil work: US$ 19,009 (23 %)
Other costs US$32,416 (39.3 %)
Number of domestic users: 28 families. no charges, assumed part of the
benefits of the Co-operative.
Use of energy: Carpentry workshops and milk processing plants.
Domestic and institutional purposes (lighting,
cooking, TV and radio): battery charging, and
other services.
Cost per installed kW in US$2,358
The only workshops that produce earnings using the electricity generated in the MHP
are the carpentry workshop and the milking and dairy unit. Both are seasonal activities
and the annual consumption was estimated taking into consideration this impmiant
parameter. In fact, the bulk of the consumption is currently absorbed by domestic end-
uses.
The co-operative has a registry of users in which they record the number of fluorescent
tubes and light bulbs. On average 3 fluorescent tubes and one light bulb per home are
used, as well as electric appliances for both domestic and institutional purposes. The
annual consumption7x was estimated at 56,337 kWh/year according to the following
breakdown.
" Unfortunately the electricity meter instalkd in the MHP was not working properly and these figures had to be
estimated.
76 Best Practices ror Sustainable Development of Micro Hydro Power
Table A-15: Energy Consumption for Productive and Domestic End-Uses (kWh),
Atahualpa
Domestic and institutional end-uses 47 347
Carpentry workshop 6 909
Milk and dairy 2 081
Total 56 337
Financial Analysis
The MHP was financed with contributions from the Peru-Canada Countervalue Fund
(67%), ITDG (12%) and the Atahualpa Co-operative, which provided US$12,000 for
machinery as well as manpower and local materials for civil works. ITDG assumed the
commitment to supervise the works from start to finish and to train the operating and
maintenance staff. The finance structure was as follows (overleaf):
Table A-16: Financing breakdown for Atahualpa Micro Hydro Plant (US$)
Own I<~GCPC'" ITDG
Total Contribution Contribution
1. Institutional l, I jtJ,OVV 0 I ,260,400 476,200
expenses
2. Investments 4.188,400 I ,488,400 2,700,000 0
3. Installations 500,000 0 500,000 0
4. Transport 472,000 0 171,000 301,000
6,897Mal TOTAL I ,488400 4,631,400 777,200
Source: Power and Producl!ve Development of the Capmarca R1ver Basm. MHP of Huacatas and
Atahua lpa. J unc 1990. Average exchange rate = 0.21 Soles per dollar (according to C uanto S.A.
Institute).
The selling price of the electricity was derived from the opportunity cost of the
electricity produced by a diesel generator, estimated at 18 US cents per kWh in 1998.
The calculations were based on the average price of the fuel in the area, obtained from
local distributors and gave a life expectancy of 7 years for the diesel generator. We
have assumed that the selling price increases according to the inflation rate.
Under these assumptions, the internal rate of return is 17.5% in current dollars and
14.5% in constant dollars. Our calculations show that the project could be financially
viable. However. this remains linked to the management of the scheme and policy
regarding the payment of the electricity. Domestic users, who are not charged for this
service. absorb the bulk of the power produced. It is obvious that a system of tariffs in
line with the purchasing power of poor end-users will lead to a much lower IRR.
The initial investment in Atahualpa's MHP had a high grant component as ITDG was
promoting it as a demonstration project. Standards of living have improved as a result
of the domestic supply of electricity for lighting, entertainment and even for cooking ( 1
kW to 2 kW electric cookers). Despite this, little value is placed on the energy
c,, FGCPC: Fondo General Contravalor Pt::ru Canada.
Annex: Summary of Case Studies 77
produced by the MHP, due to the lack of control, limited internal regulations and above
all, the non-existence of a charge for its use.
By making more electricity available, the project has also had a considerable impact on
institution building. This is evident in the mechanisation of inventory and cost controls,
lighting of public areas such as roads, and stronger income-generating industries.
Religious activities have also been boosted by a radio station and lighting for the
church. It is worth pointing out that religion plays a prominent role in community life
and religious activities have been made more comfortable since spot lights,
loudspeakers, videos and electric organs were installed.
3.2.2 Site 2: Micro Hydro for Productive End-Use: Yumahual Scheme
Business Overview
All the production of Yumahual scheme is devoted to supply power to a privately-
owned broiler chicken farm. The micro hydro scheme and the chicken farm belong to
the same person. The initiative to incubate fertilised eggs was promoted as an across-
the-board business strategy aimed at reducing costs by incorporating activities and/or
processes, thus severing the dependence on suppliers of broiler chicks. Only one person
in the MHP is involved in supplying energy to the incubating plant. The same person is
also responsible for maintenance, for the entire process of incubation and hatching of
baby chicks, as well as for selling soft drinks.
Pro}ect Overview
The MHP has the capacity for 11 kW, of which 8.77 kW are used for incubation and the
remaining 2.33 kW would be for future operations. The initial investment in the MHP
in Yunahual was US$37,082, which was financed partly with a loan from a financial
entity (82.2%) and partly with a donation from ITDG ( 1 0.3%). The investor contributed
the remaining 7.6%.
Table A-17: Yumahual Scheme Profile (US$1998)
I Department and Province: I Cajamarca
District and Settlement: Magdalena, Yumahual
Start date: October 1 998
Plant capacity: 11 kW (for 4 months a year the capacity of the
MHP is 4 kW due to the shortage of water)
Owner: Mr. Andres Leoncio Sangay Terrones
Total project cost: US$37,082
of which Electromechanical: US$14,062 (37.9 %)
Civil works: US$13,640 (36.8 %)
Other ( inc. trans/dist) US$9,380 (25.3 %)
Loan: US$30,000 in 1997
Interest and repayment period: On average 6.5% per year: 5 years.
Use of energy: Operation of an incubating plant.
Cost per kW installed: 3,371 US$
78 Best Practices for Sustainable Development of Micro Hydro Power
In practice the effective capacity is 4 kW during low water stages in the Yumahual
watercourse (four months a year). The following will be the maximum annual
production capacity of the MHP:
3 months x 30 days x 24 hours x 4 kW = II ,520 kWh
8 months x 30 days x 24 hours x 11 kW = 63,360 kWh
This means that the MHP will have a maximum annual production capacity of 74,880
kWh a year. This limited capacity requires an adequate management of the annual load.
It is worth noting that there were maintenance problems as rocks shifted due to rainfall,
causing the MHP to stop operating on four occasions when it was necessary to resort to
a small generator that was used for more than 26 hours in 1999, consuming 12 V2 gallons
of petrol.
The MHP supplies electricity for the incubation and hatching compartments, lighting
inside and outside the incubating plant as well as for charging a battery that supplies
power to a short wave radio receiver/transmitter used for communication with the farm.
Table A-18: Energy Distribution in the Incubating Plant, Yumahual
Load Power (kW) Daily working Energy (kWh)
hours
Incubator (I of 3 units) 4,5 24 108,0
Hatcher 4,0 24 96,0
Battery charger 0.3 12 3,6
Lighting 0,4 6 2,4
I Total 210 I
Source: Interview with the power plant operator.
A correcting factor of 0.8 was considered, because the incubator does not consume 4.5
kW continuously as it has a power capacity of 1.5 kW that works perfectly. The total
annual consumption is therefore:
210 kWh/day x 30 days x 12 months x 0.8 = 60,480 kWh/year.
Our analysis is based on this figure.
Comments
The same methodology and assumption as Athahualpa were used for Yumahual. The
selling price of the electricity was derived from the opportunity cost of the diesel
generator, which was estimated at 17 US cents per kWh in 1998 The calculations were
based on the average price of the fuel in the area, obtained from local distributors and a
life expectancy of 7 years for the diesel generators. We have assumed that the selling
price increases according to the inflation rate.
Under these assumptions, the internal rate of return in cun·ent dollars is 17.6% and
14.6% in constant dollars. This shows that the project could be financially viable. For
the entrepreneur the choice of micro hydro for electricity generation seems a better
option since the cost per kWh is cheaper than the cost of a diesel generator. However, if
Annex: Summary of Case Studies 79
we assume that there are no incentives, such as soft loans, the up-front capital could be a
major constraint in the replication of similar micro hydro projects.
The promotion of small-scale companies in Cajamarca requires a change in behaviour
patterns, as, by tradition, this area primarily produces consumer goods (mainly farn1
products). In this respect, the Yumahual MHP has two potential roles, the first to
generate income, and the second, in demonstrating alternative end-uses for MH power.
3.2.3 Site 3: Public Electricity Service in Pedro Ruiz
Village Overview
Pedro Ruiz town is strategically situated at the junction of two main highways. The first
of these connects the higher jungle with the northern coast (Chiclayo, Piura, etc.), and
the second links the coast and the highlands (Chachapoyas, Celendin, etc.).
Consequently, Pedro Ruiz is a resting point for travellers to these areas.
Project Overview
Electricity generating comes from two watercourses -Ingenio and Asnac. The plant
design capacity is 200 kW and the effective capacity is 140 kW leading to some
shortage of electricity supply in the growing town of Pedro Ruiz. In 1980, MHP
activities began under the responsibility of Electronorte (a state-owned regional
distribution company). Ten years later, the district municipality of Jaz<'m took over the
running of the MHP.
The staff here have not been adequately trained to carry out their jobs. One operator has
been there since the previous administration and he took it upon himself to teach the
other operator despite the fact he was not well trained. No consideration was given to
using skilled staff for corrective plant maintenance, instead people with no MHP
training were hired, for example, electricians used to solve the mechanical problems.
The plant is consequently rapidly deteriorating.
Table A-19: Pedro Ruiz Scheme Profile (US$1998)
Department, Province and District: Amazonas, Bongara, Jazan
Town: Pedro Ruiz
Owner: District Municipality of Jazan
Start date: 1985
Plant capacity: Design capacity 200 kW; Effective capacity
140 kW
Total project cost: US$1,126,075
of which Civil works: US$28,477 (2.5 %)
Electromechanical: US$806,162 (71.6%)
Other costs (inc.trans/dist) USS291 ,436 (25.9%)
722 users.
Number of users and load • Monday to Fridays: 10:00 a.m. to 5:00
management: a.m. (total: 95 hours)
• Saturdays: 2:00p.m. to 5:00a.m .
(15 hours)
• Sundays: from 8:00 a.m. to 5:00 a.m.
(total: 21 hours)
Cost per installed kW US$5,630
. 80 Best Practices for Sustainable Development of Micro Hydro Power
In order to save energy, the use of fluorescent lights was established, both for domestic
purposes and for public lighting. The peak hour is 6:00 p.m., which causes difficulties
for certain commercial activities, such as photocopiers.
Financial Analysis
The calculations are based on a historical interpolation from 1996 data -assuming
energy demand from 1980 to 1996 grew at 3.10% and connections grew at the rate of
population growth (i.e. the 1996 figure for sales is extrapolated backwards). The
economic-financial analysis of Pedro Ruiz shows that there is no return in constant
dollars when the plant was financed by relatively soft loans. This is mainly due to the
high initial capital costs 80 and relatively low tariffs.
The following entities participated in the construction and implementation ofthe MHP:
I Project Funding· I Central Government
Civil Works: The firm Opil
Electrical-mechanical Electronorte
Equipment and Networks:
Manpower: Population of Pedro Ruiz and
neighbouring communities.
The total investment was slightly over US$0.5 million in 1979.
Table A-20: Structure of the Investment, Pedro Ruiz (US$Current)
Total US$
1. Land in which the p_ower house is situated 55,728
2. Civil works L268,40 I
3. Electro-mechanical equipment 35,906,336
4. Grids and electrical facilities 12,924,882
Total (US$) 50,153,3461
Source: lnitiallm emory of the Electricity Area at 17th October 1990 adjusted to December 1979.
There are three main categories of income: connections for new subscribers; sales of
energy; and other income, such as reconnections or payments for arrears. New
subscribers were taken into account for the calculation of the MHP' s income from the
sale of electricity and other income. Meters were considered part of the capital
contribution as the municipality considers them as fixed assets. On average, 92% of the
income is obtained from selling the service and fi·om subscriptions.
The rate structure has hardly changed since 1996. Payment dates vary between the first
ten days of each month, after which default interest is charged. The rates were
'" Out of the 16 schemes investigated. Pedro Ruiz has the highest cost per installed kW.
Annex: Summary ofCase Studies 81
established during the previous municipal government by agreement with the counciL
The population's interest in keeping the service as cheap as possible prevailed.
The registration fee for new users is US$49.00 (since 1997) and they have to buy their
own meter and accessories. The average rate per kWh charged is US$0.032. In case of
no payment the following sanctions are contemplated:
• Simple re-connection: US$1.12
• Re-connection due to overdue payment: US$1.87
• Unauthorised handling ofmeter: US$3.74
• Extending the service to another home: US$5.61
• Repetition of (a) and (b): service suspended for 8, 15 and 30 days, respectively.
The default interest rate is equivalent to 4% of the monthly bill per day; the electricity is
cut off after 60 days. According to the administrator, no sanctions are being applied at
present due to a change in the municipal administration, indicating that consumers have
become used to paying their bills on time.
As regards the theft of posts and cables, the administration addresses the culprits
directly and demands the respective payment; if payment is refused then a complaint is
filed at the police station. There is no fine for offences of this nature.
Table A-21: Income From the Sale of Electricity, Pedro Ruiz (US$Current)
1996 1997 1998
Income from the sale of energy (US$) 2,134,152 2307629 2,518,682
Average annual consumption 661,680 682197 703,351
Average Price of Energy (US$) 32 34 36
Other income (US$) of which 725,690 632,120 659,6071
Reconnections 60,220 15,341 13,932
Payment arrears 174,510 215,511 182,792
Various changes 319,115 408,268 462,883
Others l7L845 --
Total income
Source: District Municipality of Jazan, Electricity Area
Cost Analysis
The total costs are summarised in the following table. Under our assumptions the cost
per kWh comes to US$0.14.
Comments:
The initiative of the authorities of Pedro Ruiz and the population in general to take over
the MHP marked a significant change in the quality of the services. It must be stressed.
however, that municipal elections and consequent changes of authorities do not
influence the electricity service. The funds are managed adequately despite the technical
and economic limitations. In this respect the current administration has been successful.
Nevertheless, the management model is far from being worth replicating, considering its
earning potential and the size of its user-base.
82 Best Practices for Sustainable Development of Micro Hydro Power
It is also worth mentioning that the entire economy was going through a serious crisis in
1990 that affected the management and supply of electricity services. The new legal
and institutional framework governing the electricity sector promotes private investment
as we11 as quality. As a result of this state initiative, several municipalities will be
handing over the electricity services to concession companies, given the legal, financial
and economic guarantees that make it attractive to meet the electricity requirements of
users in remote areas.
3.2.4 Site 4: Public Electricity Service in Pucara District
Town Overview
The town of Pucara is a nexus for cities like Chiclayo, Trujillo and Lima, as all farm
traders and transport are required to drive through it. Like the town of Pedro Ruiz,
farming is the main activity, and the main crops are coffee, cocoa, rice and fruit. The
main access to Pucara is the "Marginal de Ia Selva" highway, a fully paved road
(Chilcayo-Pucara) that connects the town with the main towns on the coast and in the
jungle (Jaen, Bagua, and Chachapoyas). Pucara is home to major institutions: the
district municipality, the medical post, the national pol iee force, and Electronorte,
among others.
Project's Overview
The MHP supplies electricity to 972 users in the towns of Pucara and Pomahuaca,
consuming an average of 98.4 kWh/month per family, with an estimated power capacity
of 53.3%. given the peak hour demand of 120 kW. Business activities have increased
since this plant started operating, as fatm products can now be traded without
restriction. Furthermore, service activities have developed, such as small restaurants,
shops, photocopying services, welding, carpentry and sewing workshops, etc.
Table A-22: Pucara Scheme Profile (US$1998)
lo t p epartmen, rovmce an 1stnc : a1amarca, t I c · J , p a en, ucara
Town: Pucara
Owner: 1986 --1991, Electroperu
1991 -1998, Electronorte
1998 onwards, Gloria Group
Start date: 1986
Number of users: 972 current users, of which 810 have a
meter.
Plant capacity: 2 x 200 kW, Effective capacity 200 kW.
Total project cost: US$454.460
Cost per kW installed : US$1,136
Water for generating electricity is obtained from El Chaupe watercourse. The MHP has
a plant capacity of 400 kW with two power generating units of 200 kW each. The
maximum demand is 284 kW. The plant's effective capacity is currently equivalent to
that of one generator as the speed regulator of the second unit is damaged and there is a
shortage of water during the low-water stage. Consequently, there is an auxiliary
thermal generator with an effective potential of 150 kW. The demand during 18 hours a
day does not exceed 150 kW, which is equivalent to the power generated by one
hydroelectric generator, providing that water is available.
Annex: Summary of Case Studies 83
The MHP came on stream in 1986 under the responsibility of Electroperu.
Subsequently, in 1991, the management was transferred to the regional company
Electronorte. This firm was transferred to the private sector in 1998 and the Gloria
group became the plant's new owners. The Electronorte Office in Jaen (a unit of
Cajamarca), which depends on the main office in Chiclayo, is responsible for the
system.
The MHP in Pucara was financed with the participation of the Agency for International
Development (AID) and Electroperu. The latter was responsible for implementing the
project. As far as the finance structure is concerned, only the Physical Inventory of the
works was accessible, showing the network expansion structure but not civil works or
electrical-mechanical equipment. Nevertheless, according to the information obtained
from Ministry of Energy and Mines publications. the cost of the MHP was equivalent to
US$454.460.
Source of Income
The registration fee for new users is US$50.00. The Jaen office establishes this fee and
the finance method. By December 1998, 972 authorised users were registered.
Income from new users' subscriptions, sale of energy and other income were taken into
account to calculate the MHP's income.
Table A-23: Estimated Income, Pucara (US$Current)
1996 1997 1998
Annual Average Energy (kWh) 1,306,800 1,337,428 1,368,774
Income from the sale of energy 79,458 83,721 59,763
(US$)
Average price of energy (US$) 6 6 4
Other income (US$) of which 725,690 632,120 659,607
Payment arrears and interest 165.600 267,800 235,600
Reconnection 146,600 76,600 55,400
Replacement and maintenance 189,500 172,300 I ] 56,400
charges
Source: Interview with the power plant s operator.
The total running costs estimated for 1998 were US$59,351. More than half of this
amount was spent on paying the operating and maintenance staff (54%), whilst security
service costs were equivalent to 46% of the total cost. Hence the decision to reduce the
number of staff.
Financial Analysis
The calculations show that the internal rate of return before financing is just 8% when
calculations are expressed in nominal values. This is beyond the discount rate of 18%
usually used for projects implemented in Peru. ln constant tern1s and after financing,
there is no return.
84 Best Practices for Sustainable Development of Micro Hydro Power
Comments
Taking into consideration the government's plans to expand the networks, it is very
likely that the Pucara MHP plant will be connected to the general Electronorte network
in the medium term. This would certainly improve the project's profit margin as the
diesel generator would be no longer needed, and staff expenses would be cut down as
the electricity supply in Pucara and Pomahuaca would be re-organised and sold through
the grids.
The electricity service in Pucara has become more profitable as the management has
improved. This improvement in management is in part due to the restructuring of the
distribution company that took place before it was privatised.
As in the previous case, the donation is critical in the project's earning capacity,
suggesting that even for services of the size of those provided in Pucara, a soft loan
financing scheme is required. Pucara is probably within the limits of the type of
projects that need strong financial backing in order to operate under the current
circumstances in this country. Larger projects would have to be self-sufficient, even if
the management acquired higher skills in order to reduce energy production costs and
losses, improve distribution and increase income and collections.
3.3 Key Conclusions Peru
In all these cases part of the investment was covered by a grant provided by private
organisations or the state. It was difficult to obtain examples of plants where costs were
fully covered by the owner. Even in the case of the private owners, part of the total
investment (studies, technical assistance among others) was provided in the form of a
grant.
At first sight, the financial situation of the projects analysed is not very encouraging.
Future prospects may be better however: the economy is fairly stable (the possibility of
traumatic changes seems remote); the government is promoting clear regulations for the
electricity business; and government policies are placing priority on the struggle against
poverty, showing a preference for overall projects in which energy is a component. It is
therefore expected that experiences like those of Atahualpa or Yumahual (less than 100
kW) will be disseminated and that under the current regulatory framework, appropriate
management alternatives will be proposed for projects like Pucara and Pedro Ruiz
(more than 100 kW).
The following are the key lessons to be considered for the future:
• The sustainability of micro hydro plants requires not only adequate technical
training in operation and maintenance but also business and managerial
training from the design stages of the project.
• The lack of credit for micro hydro is a constraint, but its availability does not
guarantee project sustainability. Good project design and careful risk analysis
of productive activities are a must.
• The best prospects for economic and financial sustainability exist for projects
that use the energy produced for a diversified portfolio of productive activities,
and not just for domestic lighting.
Annex: Summary of Case Studies 85
• Financial and economical sustainability of a plant will be adversely affected
where there are high costs associated with plant installation (due for instance to
over-design, wrong selection of equipment.
• Although no conflicts over the use of water were observed in these cases, it is
necessary to establish a water utilisation system for low water stages, which
does not limit the power generating capacity.
86 Best Practices for Sustainable Development of Micro Hydro Power
4. ZIMBABWE AND MOZAMBIQUE
4.1 Case Study Details
4.1.1 Site 1: Nyafaru Micro Hydro Co-operative: Domestic and Services End-
Uses
Village Overview
Nyafaru Co-operative Farm covers 600 hectares of land. It is run by a committee of
seven chosen from the membership at the farm. The committee is accountable to a
board of trustees. For purposes of management the farm is divided into units including:
the clinic; fisheries; schools crop production and retail. Sub-committees run each of
these units.
Until the current hydro project was commissioned, people on the farm depended on
paraffin and candles for lighting. A wind generator installed at Nyafaru more than
fifteen years ago was never commissioned because it was wrongly designed for the site
conditions. The use of solar PV at the clinic and a wind electricity generator at the shop
were discontinued with the advent of hydro electricity because the micro hydro plant is
more reliable. A diesel engine generator
that had been operating on the farm was
·also disconnected because of high
operational costs.
Project Overview
The Nyafaru plant was commissioned in
1995. A Nepalese expert in designing and
manufacturing cross flow turbines was
hired to help with local construction of a
cross flow machine. Four local technicians
were simultaneously involved in building-
up the turbine and in training with a
Nepalese expert. ITDG planned the course
and provided overall guidance. The
training covered all components of the
project, including installation,
commissioning, operation and
maintenance. A small-scale workshop at
Cold Comfort Trust (CCFT) in Harare and
the University of Zimbabwe 's mechanical
engineering workshop provided facilities
and materials.
,.-~~····
Nyafaru, Zimbabwe, inside the power
The plant generates about 20 kW reliably, house
m
"'
-0
which is used by a shop, a clini c, one primary and one secondary school, and farm staff
houses . The scheme is run by the Nyafaru Hydro Committee (NHC), composed of
representatives from the various units using the electricity, the chairperson of the co-
operative, and three co -opted teachers. The hydro committee is responsible for setting-
• • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • •
Annex: Summary of Case Studies 87
up and implementing electricity tariffs. A fixed monthly charge is levied on each user.
The tariff levied per user depends on the upper limit of the load for that consumer. A
miniature circuit breaker (MCB) installed at each user sets this upper limit. The tariffs
are set at socially attractive levels supported by a generous subsidy from the school.
When the hydro plant incurred a debt of about US$532 in 1998 (Z$ 11 ,400), the school
provided an interest free loan.
The domestic load consists of about twenty households, mostly teachers, nursing staff
and the co-operative chairman. Other farm workers have not yet been connected mainly
because they have not been able to afford the installation charge. Of the connected
households about 80% already have radios and televisions powered by the plant.
Benefits have been spread to the community beyond the farm through electrification of
the clinic, schools and shop. Over 200 school children on the boarding facility have
moved away from using paraffin lights and candles, to electricity. A weaving shop used
mainly by women has been electrified. This has enabled the women to engage in their
weaving activities well into the evenings. The improved service at the clinic benefits
mainly women and children who are in the majority within the farm and the surrounding
rural community. Women's presence in the committee is a sign of their participation in
the running of the plant. The provision of electricity for refrigeration has played a vital
role in increasing sales to a larger number of customers, some coming from distant
places like Magadzire, Tsatse and Gairezi.
There is a marked difference between the load pattern at planning stage and after
commissioning. During the planning phase an analysis of demand showed a peak of
17.5 kW and an average of 6 kW. However, the demand forecast included a mill and a
trout farm, which have not been connected.
Table A-24: Nyafaru Scheme Profile (US$1998)
I Capacity of MHP: 120 kW
Start Date: 1995
Total Capital Cost: US$66,156
of which Electromechanical: US$21,382 (32.3 %)
Civil: US$14,980 (22.6 %)
US$29,794 (45 %)
Connection charge per HH: US$73
End-Uses: Domestic, services.
Tariff hh/month: US$2.65 (Z$30) per SA connected
initially, now US$7.1 (Z$80) per SA
connected ( 1999).
Cost per installed kW: US$3,307
Financial and Economic Analysis
The Nyafaru scheme was financed through grants from external organisations and
contributions by the Nyafaru community. The grants were negotiated by ITDG in close
liaison with the community. The main funders for the design and construction of this
scheme included: the European Commission: Cadburys; the UK Overseas Development
Agency (ODA): and German Agro Action (GAA). These funds covered technical
inputs from ITDG, local contractors, local and external consultants, local labour and all
materials including electricity transmission and distribution lines. The grants were also
88 Best Practices for Sustainable Development of Micro Hydro Power
extended to connecting the shop, clinic and a few blocks at the schooL Each of the
connected user/group paid for their connection. These users consisted of the remaining
school blocks, teachers' and nurses' houses.
The investment cost of the scheme was about US$3 307 per kW 81 • However, this was a
prototype project with high external costs and the design was rather conservative.
A tariff based on meeting operation, maintenance and depreciation costs has been
recommended, but the hydro committee is not yet implementing it. Indications are that
unless tied with some income generating activities the communities are unable to meet
the tariff When the project came on stream only the shop, the clinic and the school
were connected. By the end of 1996 about nine households had been connected. The
fixed monthly charge of US$2.5 (Z$30) for each SA connected in 1996, had risen to
US$7.1 (Z$80) in 1999. In other words, a consumer with a 15A supply paid US$21 per
month. This type of tariff structure has encouraged the consumer to fully utilise the
installed capacity whilst stimulating the connection of new consumers.
From the records available the plant has experienced down time of about 50 days per
year. The annual electricity consumption is estimated at about 57 000 kWh. However,
meter readings of power over a nine-month period from November 1997 seem to
suggest that the load factor is around 43%.
In trying to build up a picture of the cash flow situation for the plant the following points
were noted:
• The cost of getting the power from the nearest distribution pole to the user
constitutes the connection costs and this is borne by the user.
• Average connection costs have been used in the analysis.
• lt is assumed that the Civil Engineering Index on plant can be used to predict
inflation on the power plant.
• It is assumed that investment costs for the plant was incurred over one year
only.
• Inflation on labour is assumed to be about 30% per annum. This is confirmed
by an analysis of the payments to the operator.
• The US$532 (ZS 11 ,400) borrowed from the school to pay for otherwise
avoidable damage to the equipment was in the first quarter of 1998. It is
assumed that in future preventive maintenance will be practised to avoid such
disasters.
• It is assumed the tariff increases by ISc;-·o each year. ZESA is increasing its
tariffs at 15% per quarter.
J',;yafaru scheme was almost entirely funded by grants. The IRR is extremely high if the
grants are considered as an income. We have therefore assumed that the capital is
borrowed from a renewable energy fund such as the UNDG-GEF Solar fund. This fund
levies an annual interest rate of 15%. We have considered a repayment period of five
years. A period of twenty-five years has been selected as the minimum life of the plant.
Under these assumptions the internal rate of return is 8% in current tern1s and there is no
return in constant dollars. This is largely due to the rather low load factor and the high
initial capital cost, and the tariffs increase which is below the rate of inflation.
"S Fernando. S Khcnnas and K Rai.ITDG Zimbabwe Micro Hydro Project Evaluation. 1997.
Annex: Summary of Case Studies 89
4.1.2 Site 2: Svinurai Micro Hydro Mill
Village Overview
This was originally a commercial farm called Tabanchu. It is located at Cashel, about
80 km south of Mutare. In the early 1980s, government bought it for resettlement
purposes. This scheme is run by a Micro Hydro Committee, which is composed of
elected people from the general membership of the co-operative. The committee is also
responsible for setting and implementing electricity tariffs after consulting the general
membership. Membership of the co-operative has fluctuated over the years, but
averages about 23 people. A committee of seven runs the farm.
Milling is one of the minor activities at the farm. Although it does not stand out as a
major activity, the mill has provided the co-operative with a more consistent source of
income than the other activities. Apart from the co-operative members, the 280
households in the surrounding community benefit from the milling service. The main
beneficiaries are women and children who would otherwise walk up to 8 km to the
nearest mill, which is powered by a diesel engine. Apart from unreliability of the
diesel-powered mills users would have to pay up to 50% more per bucket milled.
Project Overview
In 1993 rehabilitation work started with the assistance of ITDG. The mill is operated by
an worker who checks the whole system about three times a week on average. The
operator is a member of the co-operative and is employed full-time. Virtually all repairs
are now done at the fam1. During peak times the mill operates on three eight hour
shifts, seven days a week. A single eight hour shift is the normal mode of operation.
Routine maintenance is carried-out by the committee. This involves greasing and
replacing bearings, replacing belts and cleaning the intake, channel and forebay.
All members of the co-operative benefit from the milling service and therefore they
would like to enjoy a low tariff. However, they also get a monthly allowance as part of
their income from the farm activities. Co-operative members are charged 1.5 US cents
less per bucket milled than non-members. This forces them to charge reasonable tariffs
as they both try to maximise their income and avoid getting overcharged themselves.
The operator gets the same monthly allowance and milling tariffs as other members of
the co-operative.
Table A-25: Svinurai Scheme Profile (US$1998)
Capacity ofMHP: 13kW
Start Date: 1993
Total Capital Cost: US$9,296
of which Electromechanical: US$662
Civil: US$8,634
Cost per installed kW: US$715
90 Best Practices for Sustainable Development of Micro Hydro Power
Figure A-7: Map showing the locations of the case study sites in Zimbabwe
() 100
ZAM BIA
~-··
L.~>.Jk{;S
K:lnba • c h!irl hoy1 .
Binga .. Hwal"ige
• Bulawa)'O'
BOTSWANA
Site 1: Nyafaru Co-operative Farm
Site 2: Svinurai Mill
Financial and Economic Analysis
MOZ .
The rehabilitation works were funded through grants. The estimated cost for restoring
milling and electricity at the Svinurai scheme was US$9,296 including the co-
operative's contribution. The grants were negotiated by ITDG in close liaison with the
community. The Svinurai community contributed all the labour for the rehabilitation of
the civil works, penstock and powerhouse, including the installation of a new mill.
African Devel.opment Foundation (ADF) funded the irrigation component including
management support and training. Funds for the first and second stage rehabilitation
were secured from the States of Gu.emsey. For the electrification component funds
were secured from a grant raised through an individual's cycling trip around Zimbabwe.
Calculations were based on a twenty-five year life expectancy. The tariff for a hydro
milling service is set per bucket of milled grain. No rigorous analysis has been done on
the tariff but the revenue generated has been shown to meet the operation, maintenance
and management costs. An analysis of the co-operative 's books shows that the mill is
not regarded as a stand-alone enterprise. There is evidence that costs incurred on other
farm activities are financed from the mill income while records show that operation,
maintenance and repairs of the hydro mill are only financed from the mill income.
Milling tariffs are set from a social standpoint and are generally below those of
competing diesel fuelled mills. Income from the mill has not been consistent over the
• • • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • •
Annex: Summary of Case Studies 91
years and this can be attributed to various factors, chief of which is the lack of target-
oriented management.
The financial analysis shows that if tariffs are constant in current terms over the life
time of the project there is a very good return, 48% in current currency and 20% in
constant dollars. We have assumed that the capital is borrowed from a renewable energy
fund such as the UNDG-GEF Solar fund. This demonstrates once more the issue of
services pncmg.
4.1.3 Site 3: Elias Mill-A Private Micro Hydro Scheme (Mozambique)
Village Overview
This mill is in the Manica District of Mozambique, within 16km of Manica town. The
main focus of the Elias plant is hydro milling. There has been no extension of the
enterprise to other end-uses. Electricity generation from this plant is possible but as the
houses are scattered, the number of beneficiaries may be very limited. The owner could
however, install a pico-hydro plant for use at the mill and homestead. Such a generator
would provide electricity for lighting, communication and small-scale enterprises.
Elias mill is an old scheme using an old pelton turbine to drive a rudimentary mill. The
powerhouse is a simple timber off-cut structure thatched with grass. The Portuguese
first installed this equipment around the 1930s at a different site. Mr Elias later
acquired the equipment from them and installed it at his homestead. The capacity of
this scheme is about 15 k W.
Project Overview
This scheme was identified by a Mozambican non-governmental organisation, K wazai
Simukai (KSM), who invited ITDG to provide them with the technical skills for the
mill's rehabilitation. Up until 1999 the owner did most of the work on repairs following
advice from ITDG. KSM is close to the site and, as such, does most of the follow-up.
In addition KSM's in-house staff received intensive training on feasibility studies of
micro hydro schemes from ITDG and turbine manufacturing from Water Energy and
Development Services (WEDS) -a small Zimbabwean consultancy Company. The
main funder of KSM has been exploring the possibility of Elias receiving credit
assistance for components that have to be bought and involve large amounts of money
relative to the monthly income from the mill. These include cement, the penstock,
turbine and mill. The owner has already accepted the working arrangement, and
manufacture of the turbine is already at an advanced stage. This is being done by local
technicians with technical support from WEDS of Zimbabwe.
The owner runs this scheme with assistance from his family. In fact it is run as a family
business and no payments are made to any associated family labour contributions. In
some rare situations external labour is hired, for example when major repairs on the
civil works are necessary. This labour is paid from family income without regard to
whether the money was generated from the mill or not. Family members interviewed
indicated that they were very comfortable with this situation. Their motivation seems to
be driven by a strong household head committed to the well being of the family. This
mill serves about 300 households mainly from Ndirire village R2 •
"Funding Proposal for Three Micro Hydro Schemes in Mozambique. ITDG. 1996.
92 Best Practices for Sustainable Development of Micro Hydro Power
The mill operates an average eight hours per day six days a week. In emergencies it
opens briefly on the seventh day. Routine maintenance is done especially on greasing
and replacing bearings, belts and cleaning the intake, channel and forebay.
Table A-26: Elias Mill Scheme Profile (US$Current)
Capacity of MHP: 15 kW
Start Date: 1996
Total Capital Cost: US$18,000
Grant: US$10,000
Hours of usage per day: 8 hours
Cost per installed kW: US$1,200
Financial and Economic Analysis
In 1996 the estimated cost of rehabilitating the power plant was US$16,000 (£1 0,000),
excluding training, monitoring, evaluation, administrative overheads and contributions
by the ownerli 3 . Part of the funding for ITDG' s technical input on the first stage of
rehabilitation was provided by Andersen Consulting, UK. A grant secured by KSM
from FOS-Belgium financed designs of the turbine and a training course leading to the
production of a prototype. The total amount on this grant was estimated at US$8,000.
The income and expenditure of this mill was monitored over a month. This data was
used to extrapolate to 25 years guided by some basic assumptions on external factors
and on the performance of the mill ~4 . Our ca1culations show an internal rate of return of
9% assuming that the capital is borrowed at an annual interest rate of 15% over the
repayment period. It is assumed that the turbine currently being fabricated will be
installed in 1999 and the mill will be replaced the same year. lt is also assumed that the
civil works will be rehabilitated in 2000.
4.1.4 Site 4: Chitofu Mill (Mozambique)
Village Overview
The Chitofu hydro mill is in the Manica District of Mozambique, within 18km of
Manica town. The owner runs this scheme with assistance from his family. The mill
has served a community of over I 00 households with an average of six members for
over sixty years. These come from two villages. namely Maridza and Nyaronga, where
the alternative mill is powered by a diesel engine and charges up to 50% more than the
Chitofu mill. Poorer people get the service on credit ad sometimes on barter. The
owner sets tariffs for the Chitofu mill, driven by both social and business objectives. It
is evident that the deployment of resources on operation and maintenance has been kept
at a level just high enough for minor repairs.
Project Overview
This is an old scheme using an old pelton turbine to drive a mill. The powerhouse is a
simple brick structure with corrugated iron roofing. The scheme has a capacity of about
15 kW. The owner used his own resources to develop the plant but has been getting
assistance form lTDG and KSM to rehabilitate ie~s
'·'These costs were estimated at USS2.000 according to intl?rviev>'s with the owner and ITDG records.
'4 A Project for Rehabilitation of Two Micro Hydro Plants in Mozambique. G Go neal\ cs. 1998.
'' Mini ProJect Proposal. Nyaronga --Chitofu. ITDG. 1995.
Annex: Summary of Case Studies 93
Like the Chitofu mill this scheme was identified by KSM who invited ITDG to provide
technical skills and financial assistance for its rehabilitation. The memorandum of
understanding signed in 1995 also governed the co-operation between KSM and ITDG
on this project. The owner has done most of the work on repairs following advice form
ITDG. The first task done was the replacement of the old-worn out bearings with new
ones. At the same time some repairs were done to the old mill and penstock. A second
stage involved repairs to the channel, forebay tank penstock, powerhouse and
replacement of the old mill with a new one. The owner provided labour for all the
rehabilitation work. KSM continues to provide most of the follow-up because of its
proximity to the project site.
As in the case of the Elias mill, the local authority under which the scheme falls had not
been involved in the planning or implementation of the rehabilitation work. The mill
operates an average eight hours per day, six days per week, but in emergencies it opens
briefly on the seventh day. Routine maintenance is done especially on greasing and
replacing bearings, replacing belts and cleaning the intake, channel and forebay.
The main focus of the Chitofu plant is hydro milling. There has been no extension of
the enterprise to other end-uses. Current efforts are to improve this service but there is
potential to use the same plant to generate electricity. This would be a very attractive
option considering that within 600 m of the plant there is a school, clustered houses and
a business centre. Small-scale industries could also surface provided other conditions
such as finance and training are attractive.
Table A-27: Chitofu Mill Scheme Profile (US$1996)
Capacity ofMHP: 15 kW
Start Date: 1995
Total Capital Cost: US$18,500
End-use: Grain milling
Hours of household usage per day 8
I Cost per installed kW 1 uss !.233
Financial Analysis
A combination of grants and owner finance has been used to rehabilitate the scheme.
Estimates for rehabilitation of this mill were done at the same time as for Elias, and a
figure of US$16,000 (£ 10,000) was reached. This excludes training, monitoring,
evaluation, administrative overheads and contributions by the owner 86 · The core funding
for this project was a grant secured by ITDG from Andersen Consulting and the DFlD
of the United Kingdom. These funds covered materials for repair to the powerhouse,
the turbine housing and replacement of bearings, repairs to the old mill and its eventual
replacement and the technical inputs by lTDG. Chitofu contributed labour dming the
repairs. The owner also provided labour for repairs to the intake works, canal, forebay
tank and penstock.
No systematic monitoring of income and expenditure has been done on this scheme.
Historical data has been generated through interviews with the members of the family
responsible for milling. Our calculations show an internal rate of return of 9%,
'1' Estimated at USS2,500 from interviews with owner and ITDG 's records.
94 Best Practices for Sustainable Development of Micro Hydro Power
assummg that the capital is borrowed at an annual interest rate of 15 % over the
repayment period .
Figure A-8: Map showing the locations of the case study sites in Mozambique
SOUTH
AFRICA /
TANl.'ANlA "
Pemba~
Cidade de Nacat a'i-
Nampula•
\"\ )OU elima ne
3 &4 ,J,/
//' ]tBeira
lnh amban~,
Mtxt$mbique
01ta nnei
truitan
Om an
Site 3: Elias Mill
Site 4: Chitofu Mill
-:;:"
4.2 Summary of Findings of Micro Level Analysis
Significant effort has been made by NGOs working with various stakeholders to
demonstrate that micro hydro can supply much needed energy to remote rural
commumties. The four cases selected for Zimbabwe and Mozambique are a clear
demonstration of the technical viability of hydro as an alternative en ergy source and
can, therefore, be replicated with relative ease. Management of such schemes appears
to be within the grasp of the ordinary rural farmers. Moreover, their capabilities can be
extended with additional training, and personnel should only need to be brought in in
• • • • • • • • • • • • • • • • • • • • • • • • •
• • • • • • • • • • • • • • • •
Annex: Summary of Case Studies 95
exceptional cases where system failures are experienced. The only apparent constraints
concern financial management, particularly regarding the approach taken on tariff
setting. All four schemes need to improve on the utilisation of the available power.
This can in tum improve on the returns from the investment.
A point of concern, however, is the cost involved in micro hydro technology. The cost
is prohibitive particularly for rural productive operations, which often have low output
due to the demand conditions that prevail in the rural areas. The technology lends itself
well to variations in scale thus allowing different size systems to be installed to suit
particular needs or particular resource potentials.
In both Zimbabwe and Mozambique lack of energy planning at the local and regional
levels can be attributed in part to lack of awareness on energy options available at that
level. This highlights the fact that energy provision has not yet been recognised as an
integral part of the development process that needs to be planned for. The tendency is
to regard the national grid as the only energy source of electricity. This is only supplied
by utilities, and at the local level electrical power has tended to be synonymous with the
utilities.
The process of getting information from the rural communities on local resources and
development needs could also be improved to allow for better planning that would,
hopefully, incorporate energy issues. Embarking on community empowerment
exercises that would give communities an insight into their role in the development of
their ward or district could further facilitate this.
The environmental impacts of the four micro hydro schemes selected for this study can
be classified as minor according to Zimbabwe's guidelines on environmental impact
assessment.
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