HomeMy WebLinkAboutUnalakleet Wind Project Power System Model Report - May 2009 - REF Grant 2195401a DNV company
Power System Modeling for
Unalakleet Wind Energy Project
CS RP0022-A
May 27, 2009
Prepared for:
STG Inc
11820 South Gambell Street
Anchorage, AK 99515
DNV Global Energy Concepts Inc.
1809 7th Avenue, Suite 900
Seattle, Washington 98101
Phone: (206) 387-4200
Fax: (206) 387-4201
www.globalenergyconcepts.com
www.dnv.com
MANAGING RISK
Power System Modeling, Unalakleet, Alaska
Approvals
May 27, 2009
Prepared by Mia Devine Date
May 27, 2009
Reviewed thony L. R gets Date
Version Block
CSRP0022-A
Version
Release Date
Summary of Changes
A
May 27, 2009
Original
DNV Global Energy Concepts Inc. 1 May 27, 2009
Power System Modeling, Unalakleet, Alaska CSRP0022-A
Table of Contents
BACKGROUND...........................................................................................................................1
POWER SYSTEM DESCRIPTION........................................................................................... 1
DieselGenerators.................................................................................................................... 1
WindTurbines........................................................................................................................ 1
HeatRecovery System............................................................................................................ 2
BatteryBank........................................................................................................................... 2
SystemControl........................................................................................................................ 3
MODELING ASSUMPTIONS.................................................................................................... 4
MODELING RESULTS............................................................................................................... 6
DNV Global Energy Concepts Inc. ii May 27, 2009
Power System Modeling, Unalakleet, Alaska
List of Figures
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Figure 1. Proposed Wind Project Site, Unalakleet......................................................................... 2
Figure 2. Sensitivity Analysis of NPC on Battery Bank Installed Cost ......................................... 7
List of Tables
Table 2. Technical Assumptions for Unalakleet Power System ..................................................... 4
Table 2. Economic Assumptions for Unalakleet Power System .................................................... 5
Table3. Results Summary.............................................................................................................. 6
DNV Global Energy Concepts Inc. iii May 27, 2009
Power Svstem Modeling?, Unalakleet, Alaska
Background
CSRP0022-A
DNV Global Energy Concepts Inc. (DNV-GEC) has been retained by STG Inc to complete
modeling of a proposed wind -diesel power plant in the community of Unalakleet, Alaska. The
community has received funding from the Alaska Energy Authority (AEA) to install a number of
100 kW wind turbines to supplement the existing diesel power system. STG has been hired as
the construction contractor. STG, in coordination with the local utility, is considering the
installation of up to six wind turbines, and AEA has requested the consideration of an optional
battery bank as a replacement to one or two of the proposed units in a six -turbine system. The
purpose of the modeling described in this report is to compare the estimated fuel savings and life
cycle cost of the wind -diesel system options with and without battery storage. The methodology,
assumptions, and results of the analysis are described below.
DNV-GEC has previously completed a wind resource and energy assessment for the community
of Unalakleet, which is documented in the Unalakleet Rural Power System Upgrade Project
Conceptual Design Report (CDR) dated October 12, 2007. During the previous work DNV-GEC
visited the proposed wind project site and considered it acceptable for wind energy development.
The CDR is publicly available from the AEA. After completion of the CDR, STG contracted
DNV-GEC to complete a revised energy assessment based on additional wind resource data that
was collected and the potential installation of two 600 kW wind turbines. The methodology and
results are documented in a report titled Preliminary Energy Assessment for Unalakleet Wind
Energy Project dated October 6, 2008. Data from both reports are used in the current analysis
when appropriate.
Power System Description
The power system in Unalakleet is owned and operated by the Unalakleet Village Electric
Cooperative (UVEC)_ The sections below describe the major system components that are
currently installed or under consideration. According to the CDR, the average electric load in
Unalakleet is estimated to be 455 kW and the peak load is 831 kW.
Diesel Generators
The power plant is scheduled for upgrades with funding from the AEA Rural Power System
Upgrade program. The planned diesel power plant will consist of four Caterpillar 3456 model
diesel gensets rated at 475 kW each. The diesel generators can operate in parallel and the system
voltage is 480 V. The generators can operate at a minimum load of 100 kW and a maximum
sustained load of 425 M. According to AEA, at least one diesel generator will remain on-line at
all times in a wind -diesel hybrid system.
Wind Turbines
The wind power system currently under consideration will consist of either four or six 100 kW
wind turbines manufactured by Northern Power Systems. The wind turbines will be installed in a
single row on a hill located about 3 km north of the town of Unalakleet. The location of the
DNV Global Energy Concepts Inc. 1 May 27, 2004
Power System Modeling, Unalakleet, Alaska
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proposed project site and the turbine layout are shown in Figure 1. Also shown is the location of
the meteorological (met) tower where two years of wind resource data have been collected.
'.. i l —'
— 7'+'s 1250.
�a
�x
Figure 1. Proposed Wind Project Site, Unalakleet
Heat Recovery System
A heat recovery system is in place to provide waste heat from the diesel generators to the school
and other community buildings. An electric boiler will be installed to utilize excess electricity from
the wind turbines. According to UVEC, the heat provided by the diesel generators and/or wind
turbines will be charged to the customer at the current diesel fuel rates. According to AEA, the
thermal load at the community buildings ranges from about 500 kW in the winter months to 50 kW
in the summer months. In absence of heat recovery from the diesel generators, the thermal demand
would result in approximately 85,000 gallons of heating fuel consumption per year.
Battery Bank
In a hybrid power system, the primary advantage of energy storage equipment is to allow a diesel
generator to shut down when the wind turbines supply more power than is needed by the load.
During short-term lulls in wind power generation, the energy storage device supplies any needed
power. If the lulls are prolonged and the storage becomes discharged, a diesel generator is started
and takes over supplying the load, For this type of system to operate with minimal power loss to
the community, the energy storage system must be appropriately sized to cover the electric load
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Power System Modeling, Unalakleet, Alaska CSRPOO22-A
long enough for a diesel generator to come online if the wind turbines were to fault and suddenly
drop off-line.
For the proposed hybrid power system in Unalakleet, since one diesel generator will be in
operation at all times, the primary purpose of a battery storage system would be to prevent a
second diesel generator from turning on. In sizing the battery bank, DNV-GEC considered the
situation where the community demand is high (at 725 kW), the first diesel generator is operating
at full capacity (475 kW), and the wind turbines are supplying the remainder of the community
demand (250 kW). If the entire wind farm suddenly drops off-line, the battery bank would need
to supply 250 kW for a period of time that would allow a second diesel generator to warm up and
come online (about 10 minutes). Therefore, the battery bank would need to provide at least 40
kWh of usable capacity. Specification of the battery type and configuration is beyond the scope
of this report; however, the ability of a battery bank to provide 250 kW of spinning reserve is
included in modeling of the system control as described below.
System Control
It is DNV-GEC's understanding that the proposed wind -diesel system will be operated as a
"medium -penetration" system where at least one diesel generator will remain in operation at all
times, regardless of the output of the wind turbines. Enough operating reserve will be in place,
either in the form of online diesel generators or battery capacity, to serve the electric load in the
event that 100% of the wind output drops to zero at any given time.
For system options without battery storage, DNV-GEC used an operating reserve value equal to
10% of the electric demand plus 100% of the wind power output. In this situation, enough diesel
generator capacity must be online at any given time to be able to cover a 100% drop in wind
power output and a 10% increase in the electric load.
For the system options where a battery bank is installed, the operating reserve that the diesel
generators would need to provide is reduced in the model to 10% of the electric demand and
40% of the wind power output in a four -turbine system or 50% of the wind power output in a
five -turbine system. The battery bank will provide the extra operating reserve.
DNV Global Energy Concepts Inc. 3 May 27, 2009
Power System Modeling, Unalakleel, Alaska
Modeling Assumptions
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DNV-GEC used the software program HOMER, developed by the National Renewable Energy
Laboratory, to model the hybrid power options under consideration. The HOMER modeling
software compares the hourly output of the wind turbines with the hourly electric load of the
community and dispatches the appropriate diesel generator to make up any difference in power
needs. The operating reserve, minimum loading of the diesel engines, and the diesel -fuel
efficiency curves are also taken into consideration to calculate the fuel consumption of the
system. Inputs into the model include the local wind resource, the wind turbine power curve, the
community's hourly electric load, diesel dispatch strategy, and diesel generator fuel curves. The
HOMER model does not consider short-term power fluctuations caused by system dynamics or
component transients.
Table 1 and Table 2 summarize the technical and economic assumptions used in the analysis.
Table 1. Technical Assumptions for Unalakleet Power System
Description
Value
Source
Community electric consumption
4,000 MWh/yr
[1]
Annual average electric load
455 kW
[1 ]
Annual peak electric load
831 kW
[1 ]
Community heating load
2582 MWh/yr
(85,000 gal/yr)
AEA
Diesel generator make and model
Caterpillar 3456
AEA
Number of diesel generators
4
AEA
Diesel generator rated capacity
475 kW
AEA
Diesel generator lifetime
60,000 hours
AEA
Diesel generator heat recovery rate
25%
AEA, DNV-GEC
Diesel generator minimum load
100 kW
AEA
Wind turbine make and model
Northern Power
Systems NW100-B
STG
Number of wind turbines
4 or 6
STG
Wind turbine rated capacity
100 kW
Northern Power Systems
Wind turbine hub height
36.7 m
Northern Power Systems
Battery bank usable capacity
50 kWh, 250 kW
AEA
Battery bank lifetime
10 years
DNV-GEC
AC/DC converter rated capacity
250 kW, 480 V
AEA
Annual average hub height wind speed
6.5 m/s
[2], DNV-GEC estimate
based on updated data
Annual average air density
1.28 kg/m3
[2]
[1] Unalakleet Rural Power System Upgrade Project Conceptual Design Report dated October 12, 2007.
[2] Preliminary Energy Assessment for Unalakleet Wind Energy Project dated October 6, 2008.
DNV Global Energy Concepts Inc. 4 May 27, 2009
Power System Modeling, Unalakleet, Alaska CSRP0022-A
Table 2. Economic Assumptions for Unalakleet Power System
Description
Value
Source
Price of diesel fuel
$4.75/gal
AEA
Diesel generator operation and maintenance cost
$3.501hr
AEA
Diesel generator replacement cost
$200,000
AEA
Price of community heating fuel
$4.75/gal
STG, UVEC
Installed cost of wind turbines and associated balance
of plant
$9,000/kw
AEA, STG
Annual wind turbine operation and maintenance cost
$5,000/turbine
AEA
Installed cost of battery bank and AC/DC converter
$175,000
AEA, DNV-GEC
Battery disposal and replacement cost
$175,000
AEA, DNV-GEC
Battery bank operation and maintenance cost
$400/year
DNV-GEC
Annual real interest rate
3%
AEA
Project economic lifetime
25 years
AEA
DNV Global Energy Concepts Inc. 11 May 27, 2009
Power System Modeling, Unalakleef, Alaska
Modeling Results
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Table 3 presents the results of the analysis. Five possible system configurations were evaluated
(diesel -only system, diesel system with four wind turbines, diesel system with four wind turbines
and battery bank, diesel system with five wind turbines and battery bank, and diesel system with
six wind turbines). The primary metrics for comparing the different power system options are the
net present cost (NPC) and the total fuel savings in the community. The results are based on the
modeling assumptions described above; any changes to the assumptions will have an impact on
the results.
Table 3. Results Summary
Net
Annual
Annual
Total
Gross Annual
Present
Diesel Fuel
Heating Fuel
Community
Wind Generated
System
Cost
Savings
Savings
Fuel Savings
Electricity
Configuration
(millions)
(gal)
(gal)
(gal)
(MWh)
Diesel -only with heat
$26.4
0
40,000
40,000
0
recovery
Diesel + 4 wind
$26.0
60,000
33,000
93,000
1,010
turbines
Diesel + 4 wind
$26.1
62,000
32,000
94,000
1,010
turbines + batteries
Diesel + 5 wind
$26 1
74,000
32,000
106,000
1,262
turbines + batteries
Diesel + 6 wind
$26.3
76,000
37,000
113,000
1,515
turbines
Note: The results are based on the gross energy production from the wind turbines. System energy losses,
which were estimated to be 21 % in the Preliminary Energy Assessment for Unalakleet Wind Energy Project
dated October 6, 2008, would reduce the estimated gross annual wind generated electricity and resulting diesel
fuel savings.
A sensitivity analysis was completed to evaluate the uncertainty in the installed cost of a battery
storage system. Figure 2 illustrates the NPC of the evaluated systems based on a battery bank
installed cost that ranges from $140,000 to $350,000.
DNV Global Energy Concepts hic, 6 May 27, 2009
Power System Modeling, Unalakleet, Alaska
$27.0
$26.8
O
'a $26.6
H $26.4
c
$26.2
E $26.0
o $25.8
U
$25.6
m
y $25.4
Diesel Only
Diesel + 6 WTGs
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Diesel + 5 turbines + battery
Diesel + 4 turbines + battery
—Diesel + 4 turbines
EL $25.2
z $25.0 -
$140 $175 $210 $245 $260 $315 $350
Installed Cost of Battery Bank (thousands of dollars)
Figure 2. Sensitivity Analysis of NPC on Battery Bank Installed Cost
Overall conclusions of the system modeling are summarized below.
• The NPC of the hybrid power system options evaluated is approximately the same as the
NPC of the diesel -only power system. The difference in NPC is up to 1,5%, which is
within the margin of error of the modeling assumptions.
• The NPC of a four -turbine system with batteries versus a four -turbine system without
batteries is essentially the same. The increased fuel savings that the batteries provide is
offset by the lifecycle cost of the battery bank.
• The system with six wind turbines and no batteries results in the largest amount of overall
fuel savings of the systems evaluated.
• Other potential benefits of reduced fuel consumption in the community (such as reduced
risk of fuel spills, reduced exposure to fuel price volatility, reduced size and O&M cost of
tank farm) are not included in the economic analysis.
• For all hybrid systems evaluated, the heating fuel consumption at the school and other
community buildings increases compared to the diesel -only system with heat recovery.
The reduced load on the diesels results in less heat available to community buildings. The
system with six wind turbines comes close to making up for the reduced heat from the
diesels by providing heat from excess electricity.
• System energy losses and fuel price escalation rates were not included in this analysis and
are likely to have an impact on the actual economic performance of a wind -diesel system,
• The NPC of all the hybrid power systems evaluated are very close (within the margin of
error of the modeling assumptions). The power system option that is ultimately selected
for the community may depend more on non -economic factors, such as the level of
community acceptance or desire for wind power, the comfort level and experience of the
utility operators with the various system components, and the utility operator's level of
acceptable system complexity.
DNV Global Energy Concepts Inc. 7 May 27, 2009