HomeMy WebLinkAboutWind Diesel 201 Presentation RichStromberg 02-2013-WWind Diesel 201
Rich Stromberg
Alaska Energy Authority
Seward/AVTEC -Feb 2013
Highlights from WD 101
2
AEA Wind Program Values
http://www.akenergyauthority.org/programwind.html
•Involve the local community throughout all aspects of the project to increase local ownership.
•Be kind when judging our predecessors. They didn’t have the benefit of the hindsight we now possess.
•Make data -driven decisions.
•Admit when we’re wrong.
•Approach problems and projects holistically. Developed integrated solutions.
•There is great opportunity to increase cost savings and learning when we improve existing wind systems.
•Think and plan for the long term.
•Understand that wind energy isn’t always the best solution.
3
This will be on the test!
First Law of Thermodynamics: Energy can be
changed from one form to another, but it
cannot be created or destroyed.
An important facet of the Second Law of
Thermodynamics (which deals with entropy):
In the process of energy transfer, some energy
will dissipate as heat.
Everything we do with village
energy systems is based on
these two concepts.
4
Wind Classifications
•Class 1/Poor: Pursue options other than wind
•Class 2/Marginal: High costs of development in rural Alaska prevent an economical project.
•Class 3/Fair: A large project on the Railbelt may be cost effective. Remote village projects may have a payback longer than the 20-year life of wind turbines.
•Class 4/Good: A well-designed project will have a payback of 15-20 years.
•Class 5/Excellent: A well-designed project will have a payback of 12-15 years.
•Class 6/Outstanding: A well-designed project will have a payback of 10-12 years, but damaging high-wind events may be a concern.
•Class 7/Superb: Project developer may want to use a smaller rotor or find a sheltered site to protect turbines from periodic damaging winds.
5
A Typical Remote Alaska Village
Washeteria
Power house School
Wind turbines
Residences
Residences
Tank Farm
6
Wind-Diesel system challenges
•The design and integration of power systems is a
complex matter and although the models make it look
simple, it is never that easy.
•By their nature, renewable generation are stochastic
(uncontrolled) and vary with the resource.
•The amount of variation and thus the amount of
system control to handle the variation depends on the
–Renewable resource being used
–The load
–Power system design
7
Can your existing electrical distribution system
support wind technology?
Do you have newer diesel gensets with fast, electronic
injection controls or mechanical governors?
Are your gensets sized so that you can run at optimum fuel
efficiency both when the wind is blowing and when it’s calm?
Are your distribution lines, transformers and meters up to
code?
Are your phases balanced?
If you can’t answer “yes” to all of these questions, you could
save more money by fixing your existing power system.
8
Cooling System
Current diesel plants have many different types of cooling systems –some integrated, some not, but all provide primary heat to the power plant and sometimes other buildings as well.
In almost all cases the operation of the diesels provide more than enough heat for the plants needs, but in high penetration systems we would like to shut off the diesels
•Plant goes from heat surplus to heat deficit.
•To allow fast starting of the diesel engines, diesels in fast start mode must be kept warm
May require revamping of the cooling systems
•Implementation of electric boilers to allow use of wind energy
•Allow specific engine cooling systems to be separated
•Better energy management
•Different or conflicting pumping requirements.
•Heat efficiency of plant buildings may need to be considered
9
System Stability
Driven by maintaining system voltage, frequency and reactive power supply.
•Voltage: Currently uses an active controller on the diesel. Alternatives are synchronous condensers or a battery bank and solid state or rotary power converter.
•Frequency: A balance of power supply and demand, controlled by the throttle of the diesel. Can be solved through the use of dump loads or power converters.
•Power Factor: Balancing active and reactive power as needed by the inductive motors and electronics on the system . Capacitor banks, motors or advanced solid state power converters.
10
Old Wind Penetration Classes
11
y = 0.5589x -0.0261
R² = 0.7956
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
0.0%10.0%20.0%30.0%40.0%50.0%60.0%70.0%80.0%90.0%100.0%% Excess ElectricityAvg. Wind Penetration
Excess Electricity vs. Wind Penetration Level -Alaska Village Systems
% Excess Electricity
Linear (% Excess Electricity)
Net electricity has greater economic benefit because it
offsets 35% efficient diesel gensets with 100% efficient wind
power (~65% benefit). Excess electricity has less economic
benefit because it offsets 85% efficient heating oil boilers
with 95% efficient electric boilers (~10% benefit).
* Graph assumes diesel gensets can run at min 15% loading.
Actual UNK Data
12
New Wind Penetration Classes
Penetration
Class Operating Characteristics Instantaneous
Penetration
Average
Penetration
Diesel runs full time
Wind power reduces net load on diesel
All wind energy goes to primary load
No supervisory control system
Diesel runs full time
At high wind power levels, secondary loads are
dispatched to insure sufficient diesel loading or
wind generation is curtailed.
Requires relatively simple control system
Diesel runs full-time
At medium to high wind power levels, secondary
loads are dispatched to insure sufficient diesel
loading.
More complex secondary load control system is
needed to ensure that heat loads do not become
saturated during extended windy periods.
Diesels may be shut down during high wind
availability
Auxiliary components are required to regulate
voltage and frequency
Requires sophisticated control system
Medium 120%-300%20%-50%
High 300%-900%50%-150%
Very Low <60%<8%
Low 60% - 120%8%-20%
Exact
numbers are
not
sacrosanct.
13
Batteries in Medium Penetration W/D Systems
•Batteries can play a role
in medium penetration
systems
•Used for short periods of
load/supply time shifting
•Not intended for diesel-
off operation
•An option to be weighed
against/with more
secondary loads,
synchronous condensers
14
Monitoring and Remote Access
• Remote access allows
oversight of system
performance
• Enables real time system
interrogation and
troubleshooting even when
off site
• With expert analysis
system reduces
maintenance and down time
• Small incremental cost
15
Financial Impacts of PCE on W-D
Village name:Anuqamute
Total kWh produced:3,202,657
kWh sold:3,065,046
Station service:137,611 4.49%
PCE eligible residential kWh:747,592 24.39%
PCE eligible community facilities kWh:514,346 16.78%
Non PCE and commercial kWh:1,803,108 58.83%
Diesel kWh:2,202,657 68.78%
Wind kWh:1,000,000 31.22%
Non fuel expenses:$777,960
Fuel expenses $622,165
Calculated res/comm rate - before PCE $0.4568 Without wind energy
Calculated PCE reduction $0.2973 Without wind energy
Calculated residential rate after PCE $0.1595 Without wind energy
Fuel expense with wind energy $436,460
Drop in fuel cost per kWh with wind $0.0606
Calculated res/comm rate with wind $0.3962 With wind energy
Drop in Calculated residential rate $0.0606
Calculated PCE reduction with wind $0.2397 With wind energy
Drop in PCE discount with wind $0.0576
Calculated residential post PCE rate $0.1565 With wind energy
Actual change to residential rate after PCE----->$0.0030
Actual change to commercial rate with wind energy $0.0606
* Actual rates will be higher when residential customers exceed the 500kWh per month PCE limit.16
NOW FOR THE WIND-DIESEL 201
PRESENTATION
You’re caught up on Wind-Diesel 101
17
Wake Losses
•The space behind a wind turbine that is marked by decreased wind power capacity due to the fact that the turbine itself used the energy in turning the blades. The wind behind the turbine, in its wake, is less effective at generating energy for a certain distance in the downwind direction due to turbulence created by the upwind machine. Thus, when siting a wind farm, it is important to space turbines as to minimize the impact each has on the others’ power production capacity, taking into account additional costs for laying of electrical cable and other infrastructure required when machines are spaced further apart.
(http://www.windustry.org/resources/wake-losses)
18
Horns Rev offshore wind farm -
Denmark
•Horns Rev 1 owned by Vattenfall . Photographer Christian Steiness
19
Wake effect –Sandia Labs
20
Graphical representation
of wind turbine wakes
•http://www.nvidia.com
http://www.eps.ee.kth.se/windpower/images/wak
esim.jpg
http://www.windpowerengineering.com/constructi
on/simulation/seeing-the-unseeable-in-a-rotor-
wake/
21
Wake and the Park Effect
•Ideally, we would space turbines as far apart as possible in the prevailing
wind direction. But land use and the cost of connecting wind turbines to
the electrical grid would indicate spacing them closer together.
•As a rule of thumb, turbines in wind parks are usually spaced somewhere
between 5 and 9 rotor diameters apart in the prevailing wind direction,
and between 3 and 5 diameters apart in the direction perpendicular to the
prevailing winds.
•Typical park losses are ~ 5%.
22
Seasonal changes in wind resources
•One year of quality wind data is the minimum
required to assess the local wind resource.
•Multiple years give a better representation of
variation and the potential resource.
•Secondary load systems can be better
designed with multiple years of data.
•Move forward with a project design, but leave
the met tower up to improve project
confidence.
23
AWS Truepower Wind Speed Anomaly Map: Q2 2012
24
AWS Truepower Wind Speed Anomaly Map: Q2 2012
A strong pressure gradient
between a persistent low
over Alaska and a high over
the Canadian Archipelago
resulted in anomalously
strong winds (+10% or
more) over Western Canada,
while winds were
below-average (-10% or less)
in Alaska and Nunavut.
25
AWS Truepower Wind Speed Anomaly Map: Q3 2012
26
AWS Truepower Wind Speed Anomaly Map: Q3 2012
In September, a very strong
pressure gradient developed
between a ridge in the west
and a trough in the Bering
Sea, bringing high winds and
numerous strong storms to
the southern coast of
Alaska. Wind speeds in
southern Alaska and the
Yukon were more than 35%
above-average for the
month as a result.
27
AWS Truepower Wind Speed Anomaly Map: Q4 2011 –Q3 2012
28
AWS Truepower Wind Speed Anomaly Map: Q4 2010 –Q3 2011
29
Turbulence
•Turbulence induces additional mechanical and vibration loads on wind
turbines.
•IEC61400-1 edition 2 defines the characteristic turbulence intensity as the
mean plus standard deviation of random ten-min measurements. Load
cases are defined by the characteristic turbulence intensity at 15 m/s, called
I15. A=0.18, B=0.16, no C classification.
•IEC61400-1 edition 3 defines the representative turbulence intensity as the
mean + 1.28 times standard deviation of random ten-min measurements.
(The calculation has changed so it is important to understand which formula
is used.)Load cases are defined by the reference turbulence intensity Iref
which is equal to the mean turbulence intensity at 15 m/s.
30
IEC Wind Turbine Class
•It is critical to know what the expected maximum wind speeds are at your
turbine site.
•Some turbines are designed for surviving high winds while others are
designed to capture the most energy in calmer regimes.
•Ensure that your turbine can survive the environment while producing the
most energy possible.
31
Wind shear and roughness
•In general, the more pronounced the roughness of the earth's surface, the more the wind will be slowed down.
•In the wind industry, people usually refer to roughness classes or roughness lengths, when they evaluate wind conditions in a landscape. A high roughness class of 3 to 4 refers to landscapes with many trees and buildings, while a sea surface is in roughness class 0.
•Concrete runways in airports are in roughness class 0.5.
32
Wind shear and roughness
•Roughness and wind shear are directly correlated.
•This graph shows how wind speeds vary in roughness class 2 (agricultural land with some houses and sheltering hedgerows with some 500 m intervals), if we assume that the wind is blowing at 10 m/s at a height of 100 meters .
33
Wind shear formula
•The wind speed at a certain height above ground level is:
v = v ref ln(z/z0 )/ln(z ref /z0 )
•v = wind speed at height z above ground level.
•v ref = reference speed, i.e. a wind speed we already know at height z ref . ln(...) is the natural logarithm function.
•z = height above ground level for the desired velocity, v.
•z0 = roughness length in the current wind direction.
•z ref = reference height, i.e. the height where we know the exact wind speed v ref .
34
Roughness Class and
Length
Rough-ness Class Roughness Length m Energy Index (per
cent)Landscape Type
0 0.0002 100 Water surface
0.5 0.0024 73 Completely open terrain with a smooth surface, e.g.concrete runways in
airports, mowed grass, etc.
1 0.03 52 Open agricultural area without fences and hedgerows and very scattered
buildings. Only softly rounded hills
1.5 0.055 45 Agricultural land with some houses and 8 metre tall sheltering hedgerows
with a distance of approx. 1250 metres
2 0.1 39 Agricultural land with some houses and 8 metre tall sheltering hedgerows
with a distance of approx. 500 metres
2.5 0.2 31 Agricultural land with many houses, shrubs and plants, or 8 metre tall
sheltering hedgerows with a distance of approx. 250 metres
3 0.4 24 Villages, small towns, agricultural land with many or tall sheltering
hedgerows, forests and very rough and uneven terrain
3.5 0.8 18 Larger cities with tall buildings
4 1.6 13 Very large cities with tall buildings and skycrapers
For example, assume we know
that the wind is blowing at 7.7
m/s at 20 m height. We wish to
know the wind speed at 60 m
height. If the roughness length is
0.1 m, then
v ref = 7.7
z = 60
z0 = 0.1
z ref = 20
Therefore:
v = 7.7 ln(60/0.1) / ln(20/0.1) =
9.2966 m/s
35
Wind shear –Power law
•The power law exponent is α. For fairly flat terrain, it is common to use the one-
seventh power law, where α = 1/7.
•1/7 power law for height adjustments
for a known wind speed V1 at height H1, you can calculate V2 at height H2:
V2=V1*(h2/h1)(1/7)
•For example: 9.008=7.7*(60/20)(1/7)
Terrain Description Power law exponent, α
Smooth, hard ground, lake or ocean 0.10
Short grass on untilled ground 0.14
Level country with foot-high grass, occasional tree 0.16
Tall row crops, hedges, a few trees 0.20
Many trees and occasional buildings 0.22 –0.24
Wooded country –small towns and suburbs 0.28 –0.30
Urban areas with tall buildings 0.4
36
So, with wind shear you can predict the
wind speed at higher elevations…sort of.
•Estimating performance for a turbine with a
40-meter hub height off of 20m and 30m
anemometers has lower risk than estimating
the performance of a turbine with a hub
height of 70 or 80 meters.
•Wind shear formulas estimate annual
averages –not diurnal patterns.
37
Delta Wind Farm Diurnal Pattern
38
West TX A&M Diurnal Pattern
39
Drivers of winds at different heights
•Lower level winds are driven by solar heating of the Earth’s surface, so winds increase throughout the day and subside at night.
•Higher-level winds are dominated by stably stratified flows that sink down at night into the rotor swept area, but get pushed higher during the day as solar-induced turbulence picks up.
•Knowing the true diurnal pattern at your hub height is critical when designing secondary load systems on moderate and high penetration wind-diesel systems.
40
30m data extrapolated to 75m
41
75m data
42
30m data extrapolated to 75m
43
75m data
44
30m data extrapolated to 75m
45
75m data
46
30m data extrapolated to 75m
47
75m data
Big change in secondary load considerations
48
Wind Shade
•The higher you are above the top of the upwind
obstacle, the less wind shade. The wind shade,
however, may extend to up to five 10 times the
height of the obstacle at a certain distance.
•If the obstacle is taller than half the hub height,
the results are more uncertain, because the
detailed geometry of the obstacle, (e.g. differing
slopes of the roof on buildings, different species
of bushes/trees) will affect the result.
49
Emmonak Wind Turbine Site
50
Wind Shade Calculator
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
51
Wind Shade Calculator
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
52
Cape Stebbins
53
Wind Shade Calculator
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
54
Wind Shade Calculator
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
•
55
Wind Shade Calculator –37m Turbine
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
•
Don’t forget
to consider
rotor
diameter.
56
Wind Shade Calculator –50m Turbine
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
57
Wind Shade Calculator –75m Turbine
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
58
Cape Stebbins Preferred Turbine Site
59
Wind Shade Calculator –50m Turbine
http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm
60
Voltage Rise in Distributed Generation
(DG) Systems
“Connections of distributed generation (DG) in distribution networks
are increasing. These connections of distributed generation cause
voltage rise in the distribution network.” -
http://seit.unsw.adfa.edu.au/staff/sites/hrp/papers/mhp11a-c.pdf Analysis of Voltage Rise Effect on Distribution
Network with Distributed Generation M. A. Mahmud, M. J. Hossain, H. R. Pota
“Since the modern distribution systems are designed to accept bulk power from the
transmission network and to distribute it to customers, the flow of both real and reactive
power is always from the higher to lower voltage levels. However, with significant
penetration of distributed generation, the power flows may become reversed and the
distribution network is no longer a passive circuit supplying loads but an active system with
power flows and voltages determined by the generation as well as load.”
“Connections of distributed generation in distribution systems are susceptible to voltage
rise. Moreover, the impact of losing a single or a few distributed generation following a
remote fault may not be significant issue, but the connection or disconnection of a large
penetration of distributed generation may become problematic which may lead to sudden
appearance of hidden loads and affect the voltage profile of low voltage distribution
network.”
61
DG Voltage Rise Example
Analysis of Voltage Rise Effect on Distribution Network with Distributed Generation M. A. Mahmud, M. J. Hossain, H.
R. Pota
In this case, 240 KW generator 15km away from the primary distribution system is replaced by a 1 MW generator. This increased amount of generation reverses the power flow through the line, from the generator towards the DS.
The voltage profile of DS with 1 MW of distributed generation is shown in Fig. 7. From Fig. 7, it is seen that the voltage in some parts of the system rises above the permitted +6% voltage limit.
62
DG Voltage Rise Factors
Analysis of Voltage Rise Effect on Distribution Network with Distributed Generation M. A. Mahmud, M. J. Hossain, H.
R. Pota
The level of DG generation that can be connected to
the distribution system depends on the following
factors:
•voltage at the primary DS
•voltage level of the receiving end
•size of the conductors as well distance from the
primary DS
•load demand on the system
•other generation on the system
63
DG Voltage Rise Mitigation
Analysis of Voltage Rise Effect on Distribution Network with Distributed Generation M. A. Mahmud, M. J. Hossain, H.
R. Pota
The voltage rise on DS can be mitigated through
the following approaches:
•Resistance reduction (increase conductor size
or energize to higher voltage)
•Reactive power compensation (switched
capacitor or DVAR)
•Coordinated voltage control
•Generation curtailment
64
DG Voltage Rise –Other Reading
“A Case Study of a Voltage Rise Problem Due to a Large Amount of Distributed
Generation on a Weak Distribution Network” –Sami Repo, et al.
http://labplan.ufsc.br/congressos/PowerTech/papers/51.pdf
“The integration of relatively large capacity of wind power into a weak distribution network
may cause a voltage rise problem during low demand periods.”
“A review on voltage control methods for active distribution networks” –
Tengku Hashim, et al http://pe.org.pl/articles/2012/6/71.pdf
“The conventional distribution networks are designed based on the assumption of
unidirectional power flow. With the increasing connection of DG, the network has become
more dynamic with bidirectional power flow and it known as active distribution networks
(ADN).”
“With the increasing number of DG penetration, the issue of voltage level in distribution
systems has become important. Increasing the number of connected generators will result in
voltage rise above its permissible level.”
65
DG Voltage Rise –Other Reading
“Integration of Distributed Generation in Low Voltage Networks: Power
Quality and Economics” –Konstantinos Angelopoulos
http://www.esru.strath.ac.uk/Documents/MSc_2004/angelopoulos.pdf
“It is possible to estimate the effect of a generator by using the standard voltage drop equations
with reverse power flow. The voltage drop along a feeder due to a load is approximately equal to:
Vdrop = IRR+IXX
Where:
Vdrop = voltage drop along the feeder
R = line resistance, ohms
X = line reactance, ohms
IR = line current due to real power flow, amps (negative for a generator injecting power)
IX = line current due to reactive power flow, amps (negative for a capacitor)
66
DG Voltage Rise Analysis on Alaska WD
Systems
•Power flow analysis can be costly and take
time, but is needed in come cases.
•UVIG DG toolkit is a quick method to
determine if more detailed PF analysis is
needed. http://www.uwig.org/distwind/default.htm
•A simple voltage drop/rise calculation can be
done in two minutes.
67
Voltage Rise –Kotzebue Example
68
Single phase VD = (2 * L * R * I) / 1000 ft
Distance in miles 4
Equivalent feet 21,120
Resistance in Ohms/1,000 feet from chart at right 0.1265 2/0 Quail
Load in amps is based on total power and line voltage
Max power (Watts) from all wind turbines 1,100,000
Voltage rating of transmission line 12470
Single phase amps from wind turbine 88.21
Convert to 3-phase (Div by sqrt of 3) gives load in amps from turbine 50.93
Using above bold formula, voltage drop/rise is ------>272.14
Percentage of voltage drop/rise 2.18%
3-phase VD = SPVD * (1.732/2) Drop between any 2 phases
3-phase voltage drop/rise is------------------------------>235.68
Percentage of voltage drop/rise 1.89%
Voltage Rise –Kotzebue Example
<3% is desired
Before adding two
EWT 900kW turbines.
69
Voltage Rise –Kotzebue Example
Single phase VD = (2 * L * R * I) / 1000 ft
Distance in miles 4
Equivalent feet 21,120
Resistance in Ohms/1,000 feet from chart at right 0.1265 2/0 Quail
Load in amps is based on total power and line voltage
Max power (Watts) from all wind turbines 2,900,000
Voltage rating of transmission line 12470
Single phase amps from wind turbine 232.56
Convert to 3-phase (Div by sqrt of 3) gives load in amps from turbine 134.27
Using above bold formula, voltage drop/rise is ------>717.46
Percentage of voltage drop/rise 5.75%
3-phase VD = SPVD * (1.732/2) Drop between any 2 phases
3-phase voltage drop/rise is------------------------------>621.34
Percentage of voltage drop/rise 4.98%
0.622596
<3% is desired
Voltage can rise as wind power
increases on distributed generation
microgrids.
After adding two EWT
900kW turbines.
70
Voltage Rise at KEA After 2013
Energize to 25kV
Goal
achieved
Single phase VD = (2 * L * R * I) / 1000 ft
Distance in miles 4
Equivalent feet 21,120
Resistance in Ohms/1,000 feet from chart at right 0.1265 2/0 Quail
Load in amps is based on total power and line voltage
Max power (Watts) from all wind turbines 2,900,000
Voltage rating of transmission line 25000
Single phase amps from wind turbine 116.00
Convert to 3-phase (Div by sqrt of 3) gives load in amps from turbine 66.97
Using above bold formula, voltage drop/rise is ------>357.87
Percentage of voltage drop/rise 1.43%
3-phase VD = SPVD * (1.732/2) Drop between any 2 phases
3-phase voltage drop/rise is------------------------------>309.92
Percentage of voltage drop/rise 1.24%
0.622596
71
Induction Generators vs. Inverter Systems
•An induction (asynchronous) generator must have its magnetic field maintained through the same mechanism as an induction motor. It must exchange energy with a capacitor or with a synchronous generator that can be adjusted to “act as a capacitor.” In order to function as a generator, an induction generator requires an external source of reactive volt-amperes (VARs). This is typically supplied by the diesel gensets. Power factor drops as the WTG produces more energy.
•Inverter-based WTG controllers create a wall from the microgrid where VARs are produced by the inverter using power from the wind turbine once it has spun-up. The microgrid only sees clean power.
72
Generator Sizing and Spinning Reserve
Engine Make/Model
Serial #Min Load %Rated Capacity (kW)
(kVA)
Average Load
on Genset
Average Load on
Genset w/ Wind
Det diesel 60 363
Cummins KTA 19G4 499
MTU 12V2000 700
Heat Recovery Loop: None currently, but possibility for water treatament plant and the school.
46%38%
33%27%
Application/Grant #
Diesel Gensets
Noorvik Wind Farm
Comments: Manual switchgear in Noorvik would need to be upgraded and possibly new feeders.
64%52%30%
30%
30%
73
Generator Sizing and Spinning Reserve
•Being able to step up or down to the appropriate
size diesel genset as wind production moves up
and down can minimize fuel efficiency hit.
•Larger diesel genset may still be needed for VARs
support or spinning reserve.
•Sufficient spinning reserve (diesel, battery, etc.)
must be maintained to handle sudden drops in
wind output. 50% may be needed.
•Diesel generators will see a greater number of
starts/stops –some efficiency loss.
74
What if the wind doesn’t drop off
suddenly, but keeps getting stronger?
75
What if the wind doesn’t drop off
suddenly, but keeps getting stronger?
76
What if the wind doesn’t drop off
suddenly, but keeps getting stronger?
•If all turbines are set to trip off at exactly 25 m/s, Unalakleet could lose 600kW of power generation in a few seconds.
•What diesels are online and how quickly can they make up for the 600kW?
•Staggering wind turbine cut-out speeds can minimize the power loss steps to 100 or 200kW.
•Single wind turbines make this harder to accomplish unless they have variable pitch blades plus controls that allow for reducing energy output as the turbine gets close to the cutout speed.
•Smart systems control logic will bring additional spinning reserve online when wind turbines get close to cut-out speed.
77
12-month Unalakleet met tower study
showed no incidents of hitting cut-out
speed
However, UVEC has seen instances where wind turbines
cut out at 25 m/s and the diesel gensets trip offline.
78
An opposite problem
•A small community with small load in a class 7 wind regime.
•Average load is 29kW. Average wind penetration is 81%.
•One 65kW wind turbine installed –stall -regulated, basic controller.
•Turning on the wind turbine at 15-25m/s first causes an rush of current into the wind turbine’s induction generator. Then, the turbine pushes 65kW of power back onto the local grid.
•If diesel genset and secondary loads can’t respond fast enough, high voltage or frequency will trip off the diesel genset and village loses power.
Solutions:
A single smaller turbine.
Multiple smaller turbines with automated switchgear that turns on one turbine at a time.
Develop a smart wind turbine controller that starts the turbine with a long ramp rate to max power.
79
Other wind turbine features to
consider
•Soft start
•Dynamic braking
•Variable-pitch blades
•Tilt-up towers vs. monopole towers vs. lattice
towers
80
Secondary load considerations
81
Secondary load considerations
82
Secondary load considerations
83
Secondary load considerations
•Is there a heat recovery loop on the existing
diesel system?
•How much energy (mmBTUs) currently goes
into the HR loop and at what rate throughout
the year?
•How much energy is pulled off the HR loop by
value loads and non-value loads? At what rate
throughout the year?
84
Secondary load considerations
•Does the “dead zone” where wind picks up and diesels throttle back reduce the energy in the HR loop below the value load demand? If this happens fairly often, consider placing an electric boiler on the HR loop before any other secondary load options.
•If the energy loss in the HR loop rarely or never drops below the value load demand, an electric boiler on the HR loop buys you no economic benefit for your excess electricity.You should consider value electric heat loads elsewhere in the community (school, village office, water treatment, washeteria, wastewater system, residential).
•Don’t overlook the opportunity for dispatchable electricloads like pumping water.
85
Secondary load considerations
•At what rate do your thermal loads “consume”
heat (mmBTUs)?
•Will your wind turbines produce excess energy at
a rate faster than can be absorbed by your
secondary thermal loads?
•If so, you will either need to curtail wind turbines
and lose economic benefit, send excess power to
an open air dump load (no value) or add electric
boilers/heaters to value loads elsewhere in your
community.
86
Conclusion
•Much of the needed design activity on Alaska
wind-diesel systems deals with integrating wind
power with the existing power plant, distribution
system and community heat loads.
•Detailed understanding of how your wind
turbines will interact with your existing or
planned power generation and distribution is key
to a successful project that will last decades.
87