HomeMy WebLinkAboutEmmonak-Alakanuk Wind Design and Construction Project Wind Power Report - Jun 2010 - REF Grant 2195468 V3 Energy, LLC 1
Emmonak, Alaska Wind Power Report
Report by: Douglas Vaught, P.E., V3 Energy, LLC, Eagle River, Alaska
Date of Report: June 29, 2010
Photos: Doug Vaught
Summary Information ...................................................................................................................................2
Met Tower Data Synopsis .....................................................................................................................2
Test Site Location ..................................................................................................................................3
Data Quality Control.....................................................................................................................................3
Data coverage .......................................................................................................................................4
Wind Speed Data Summary ..........................................................................................................................4
Long-term Wind Reference ...........................................................................................................................5
Wind Turbine Performance ..........................................................................................................................6
NW100/21 B, 37 m hub height.............................................................................................................7
Aeronautica 29-225, 40 m hub height..................................................................................................7
Aeronautica 29-225, 50 m hub height..................................................................................................7
Turbine Time Series ..............................................................................................................................7
Wind Farm .....................................................................................................................................................8
Village Load...........................................................................................................................................8
Wind Farm Performance, Emmonak-Alakanuk Intertied .....................................................................9
Met Tower Data ............................................................................................................................................9
Tower Sensor Information.................................................................................................................. 10
Anemometer Data ...................................................................................................................................... 10
Tower Shading Analysis ...................................................................................................................... 10
Anemometer Monthly Time Series ..................................................................................................... 11
Extreme Winds.................................................................................................................................... 11
Wind Shear .......................................................................................................................................... 12
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Probability Distribution Function................................................................................................................ 12
Wind Roses.................................................................................................................................................. 13
Wind Frequency Rose......................................................................................................................... 13
Total value (power density) rose ........................................................................................................ 13
Air Temperature and Density...................................................................................................................... 13
Speed vs. Temperature Scatterplot.................................................................................................... 14
Turbulence.................................................................................................................................................. 14
Turbulence vs. wind speed ................................................................................................................. 15
Turbulence vs. wind direction............................................................................................................. 15
Summary Information
Alaska Village Electric Cooperative (AVEC) is planning a wind power project in the village of Emmonak
that will include approximately 500 kW of installed wind turbine capacity, an electrical intertie to the
nearby village of Alakanuk, and a control system to integrate the turbines to the existing power system.
In anticipation of this project, a met tower was installed in Emmonak in July, 2007 and continues to col-
lect data. In addition to wind data collection, other information such as electric load and diesel power-
plant performance data is collected by AVEC for Emmonak and Alakanuk. This data was analyzed with
software tools to evaluate the wind resource itself and to predict the performance of wind turbines and
their operation as a wind-diesel hybrid system once connected to the village’s existing power system.
The Emmonak met tower site is located on the tundra in a clearing of willow trees just west of the vil-
lage boundary. This site was selected based on the intended location for wind power development in
2007, but later plans call for turbines to be placed in an open clearing in the north-central portion of the
village. Given the uniform terrain characteristics of Emmonak, the met tower site is considered reason-
ably representative of the new turbine site, although aspects of the data indicate an undesirable influ-
ence of the brush surrounding the met tower. If wind turbines are installed at or near the met tower
location, plans call for the brush to be cleared sufficiently to mitigate this problem.
For AVEC’s planned wind power project, it is anticipated that 500 kW of installed capacity wind power,
using five NW100/21 B model turbines, will generate 1,057 MWh/yr at a 23.4 percent capacity factor
(this assumes 100 percent turbine availability). HOMER software modeling predicts that this will save
approximately 69,500 gallons of powerplant diesel fuel usage per year.
Met Tower Data Synopsis
Data dates September 25, 2007 to April 14, 2010 (31 months;
9 months missing)
IEC 61400-1, 3rd ed. classification III-b (measured);likely III-c
Power density mean, 30 m 181 W/m2 (not AWOS adjusted)
Wind speed mean, 30 m 5.72 m/s (AWOS data adjusted)
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Maximum 10-min wind speed average 19.5 m/s (not AWOS adjusted)
Maximum wind gust 29.1 m/s (March 2009)
Weibull distribution parameters k = 2.13, c = 5.90 m/s (to date)
Roughness class 3.60 (forest)
Power law exponent () 0.297 (high wind shear possibly affected by brush;
lower value, more typical of tundra, likely)
Frequency of calms (4 m/s threshold) 35%
Mean turbulence intensity 0.135 (IEC3 turbulence category B; possible brush
effect, likely IEC3 turbulence category C)
Test Site Location
Google Earth Image of Emmonak
Data Quality Control
Data was filtered to remove obvious icing events. Typically, anemometer icing is identified by non-
variant data readings at the sensor offset value for anemometers and a “frozen” heading for wind vanes,
a standard deviation of zero, and temperature near or below freezing. The data collected to date in
Emmonak indicates a number of icing events typical of freezing rain at a low elevation site. These pe-
riods of data loss are shown in the graph below as thin while lines in the colored data fields and are not
significant. More substantially, note that nine months of data are missing – from December 11, 2007 to
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April 5, 2008 and again from September 12, 2009 to February 22, 2010. The first data loss period oc-
curred when a data card failed and data was unrecoverable. The second data loss period is unexplained
at present but may indicate a problem with the datalogger. Also note that the met tower was installed
in Emmonak on July 20, 2007. The data card containing data logged from July 20 to September 25, 2007
was lost in the mail.
Label Ch Units Height
Possible
Records
Valid
Records
Recovery
Rate (%)
Speed 30 m A 1 m/s 30 m 134,124 89,797 67.0
Speed 30 m B 2 m/s 30 m 134,124 88,937 66.3
Speed 20 m 3 m/s 20 m 134,124 88,940 66.3
Direction 30 m 7 ° 30 m 134,124 89,554 66.8
Temperature 9 °C 2 m 134,124 93,792 69.9
Data coverage
Wind Speed Data Summary
The primary data of interest from the met tower is from the 30 meter anemometer. This data set is
used for the wind turbine power generation calculations in this report. An annual summary (mean of
monthly means) from the 30 meter A anemometer is presented below.
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Month Mean Max
Std.
Dev.
(m/s) (m/s) (m/s)
Jan 4.69 16.4 2.68
Feb 6.07 19.2 3.49
Mar 6.48 18.7 2.87
Apr 5.56 15.1 2.46
May 4.89 11.1 1.86
Jun 4.73 13.8 2.07
Jul 5.05 15.5 2.13
Aug 4.58 11.8 1.76
Sep 4.72 13.3 2.05
Oct 4.79 18.7 2.59
Nov 5.13 19.4 3.14
Dec 6.77 19.2 3.06
Annual 5.29 19.4 2.58
Long-term Wind Reference
The nearby Emmonak Airport has an Automated Weather Observing System (AWOS) that has collected
data for many years. To gain a perspective of wind conditions during the met tower test period, AWOS
data from 1985 to present were analyzed. Although some older data (pre-1997) is missing or otherwise
appears somewhat inconsistent (especially 1993 and 1995), in general one observes that 2007 through
2009 were relatively low wind years compared to a long-term average (represented by the line titled
Linear (Wind Speed)in the graph below), representing about 92.5% of the mean wind speed measured
from 1985 through 2009 and 92.4% if considering just 1997 through 2009. Note that the long term
trend of wind speed appears to be decreasing slightly. This may not necessarily be true with a longer
term perspective of wind speeds, but for this study only a twenty-five year period was examined.
To normalize the met tower data to long-term, a simple approach was employed of dividing the meas-
ured mean wind speeds by 0.925, which yielded a mean annual wind speed at 30 meters of 5.72 m/s.
This changes the Emmonak wind classification from Class 2 to Class 3, without consideration of air densi-
ty effects on either data set.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
30 m A (m/s) 4.69 6.07 6.48 5.56 4.89 4.73 5.05 4.58 4.72 4.79 5.13 6.77 5.29
30 m A, AWOS
corrected ’85
to ’09 (m/s)
5.07 6.57 7.00 6.01 5.29 5.12 5.46 4.95 5.10 5.18 5.55 7.32 5.72
0.00
2.00
4.00
6.00
8.00
JanFebMarAprMayJunJulAugSepOctNovDecMean wind speed, m/s30 meter wind speed
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Wind Turbine Performance
It is perhaps counterintuitive that wind power density and wind class do not correlate linearly with tur-
bine power output. This is due to a number of factors, including theoretical limitations of a lift-
producing aerodynamic device (the turbine rotor) and practical limitations of generator weight and
rated output. For these reasons and others, a wind turbine in a low power class wind regime may still
produce sufficient energy to warrant installation of turbines.
A simplistic consideration of possible turbine output in Emmonak is to model power output of a particu-
lar turbine with mean of monthly means data collected to date and extrapolating to the turbine hub
height. Taking the analysis slightly further, turbine performance estimates was normalized to the long-
term average wind as measured by the airport AWOS. Note the this analysis is based on raw data with
no synthetic data inserted in place of icing data removed for data quality control or data missing for
other reasons.
Turbine performance was analyzed with the HOMER software using the Northern Power Northwind 100
B model (21 meter rotor diameter) and the Aeronautica 29-225 (225 kW, 29 meter rotor diameter). At
present the NW100 is AVEC’s preferred turbine choice for Emmonak and the Aeronautica 29-225 is an
alternate choice. Extrapolating to the 37, 40, and 50 meter hub heights with a power law exponent ()
of 0.14 instead of the met tower derived of 0.297 (note that this is a more conservative approach as
extrapolated wind speeds above 30 meters are less with an of 0.14 than an of 0.297; see detailed
explanation on page 12 for more information), anticipated turbine performance for 100 percent and 90
percent turbine availabilities is shown in the tables below.
0
1
2
3
4
5
6
7
1985198719891991199319951997199920012003200520072009Mean wind speed, m/sEMK Airport AWOS Wind Data, 1985 -2009
Wind speed
Linear (Wind speed)
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NW100/21 B, 37 m hub height
100% turbine avail. 90% turbine avail.
30 m
mean
(m/s)
37 m hub
(m/s)
NW100/21
(MWh/yr)
NW100/21
CF (%)
NW100/21
(MWh/yr)
NW100/21
CF (%)
Met tower 5.29 5.45 177.2 19.6 159.5 17.6
AWOS data
adjusted 5.72 5.89 211.7 23.5 190.5 21.2
Aeronautica 29-225, 40 m hub height
100% turbine avail. 90% turbine avail.
30 m
mean
(m/s)
40 m hub
(m/s)
29-225
(MWh/yr)
29-225 CF
(%)
29-225
(MWh/yr)
29-225 CF
(%)
Met tower 5.29 5.51 349.3 17.7 314.4 15.9
AWOS data
adjusted 5.72 5.95 428.0 21.7 385.2 19.5
Aeronautica 29-225, 50 m hub height
100% turbine avail. 90% turbine avail.
30 m
mean
(m/s)
50 m hub
(m/s)
29-225
(MWh/yr)
29-225 CF
(%)
29-225
(MWh/yr)
29-225 CF
(%)
Met tower 5.29 5.68 384.6 19.5 346.1 17.6
AWOS data
adjusted 5.72 6.14 467.3 23.7 420.6 21.3
Turbine Time Series
The graphs below illustrate NW100 and Aeronautica 29-225 turbine outputs for a typical winter day
(November 29, 2007) and a typical summer day (July 29, 2008). Note that wind speed was high enough
that both turbines would have reached rated power output mid-afternoon on November 29.
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Wind Farm
AVEC has proposed construction of an intertie to electrically connect Emmonak to the village of Alaka-
nuk, located approximately twelve kilometers southwest of Emmonak on the Alakanuk Pass of the Yu-
kon River. HOMER software was used to create a combined Emmonak-Alakanuk village simulation
model.
Village Load
A combined Emmonak and Alakanuk hourly load profile was synthesized using the Alaska village load
calculator Excel spreadsheet developed by Alaska Energy Authority several years ago. The results were
adjusted slightly to match actual village average and peak loads of Emmonak and Alakanuk (separately)
documented by AVEC in their annual power generation report. The result is a virtual Emmonak-
Alakanuk village with a 555 kW average load, 883 kW peak load and average daily power usage of 13.3
MWh/day. Seasonal, daily and DMap profiles of the Emmonak-Alakanuk virtual load are shown below.
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Wind Farm Performance, Emmonak-Alakanuk Intertied
Met Tower Data
Presented below is information regarding the met tower installed in 2007 in Emmonak and pertinent
technical information regarding data results.
Site number 0007
Site Description Tundra clearing among willow brush northwest of Emmonak
Latitude/longitude N 62° 46.964’, W 164° 33.447’, WGS 84
Site elevation 3 meters
Datalogger/modem type NRG Symphonie/no modem
Tower type NRG 30-meter tall tower, 102 mm (4 inch) diameter
Anchor type Buried plate
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Turbine No. Hub ht. Penetration CF Wind prod. Fuel displ. Excess elec. Excess elec. SLC needed?
(m) (%) (%) MWh/yr (gal) MWh/yr (%)
NW100/21 5 37 21.7 23.4 1,057 69,470 8 0.2 possibly
6 37 26.1 23.4 1,268 81,972 33 0.7 possibly
7 37 30.4 23.4 1,480 93,249 78 1.6 possibly
8 37 34.8 23.4 1,691 103,106 145 2.9 possibly
Aero 29-225 3 40 26.4 21.7 1,282 80,979 63 1.3 possibly
4 40 35.1 21.7 1,709 99,388 224 4.4 possibly
3 50 28.8 23.7 1,400 87,866 79 1.6 possibly
4 50 38.4 23.7 1,866 107,047 270 5.3 possibly
Notes:
1. Wind resource based on Emmonak met tower adjusted against long-term AWOS data
2. HOMER modeling assumes 100% turbine availability
3. Displaced fuel estimate is for electrical generation only
4. Excess electricity to thermal dump load, either water boiler or air heating
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Tower Sensor Information
Channel Sensor type Height Multiplier Offset Orientation
1 NRG #40C anemometer 30 m (A) 0.765 0.35 North
2 NRG #40C anemometer 30 m (B)0.765 0.35 East
3 NRG #40C anemometer 20 m 0.765 0.35 North
7 NRG #200P wind vane 30 m 0.351 080 West
9 NRG #110S Temp C 2 m 0.136 -86.383
Anemometer Data
Met tower anemometer data is presented below, although note that the met tower test period of late
2007 to 2009 apparently was dominated by lower than long-term average winds (see earlier discussion).
Variable
Speed 30 m
A
Speed 30
m B
Speed 20
m
Measurement height (m) 30.0 30.0 20.0
Annual mean wind speed (m/s) 5.29 5.24 4.74
Max wind speed (m/s) (10-min) 19.4 19.5 18.0
Max wind speed (m/s) (gust) 28.3 29.1 26.8
Weibull k 2.13 2.05 2.08
Weibull c (m/s) 5.91 5.83 5.28
Annual mean power density (W/m²) 181 180 134
Mean energy content (kWh/m²/yr) 1,584 1,578 1,172
Energy pattern factor 1.83 1.89 1.89
Frequency of calms (%) 34.3 35.2 43.6
1-hr autocorrelation coefficient 0.923 0.922 0.922
Diurnal pattern strength 0.067 0.074 0.109
Hour of peak wind speed 18 18 17
Tower Shading Analysis
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Anemometer Monthly Time Series
Extreme Winds
Emmonak classifies as IEC 61400-1, 3rd edition Class III, the most common category of extreme wind
classification and that for which most wind turbines are designed.
Return Extreme Wind Speed (m/s)
Period
(yr) 10-min means Gusts
20 25.5 36.3
25 26.2 37.4
50 28.3 40.5
100 30.3 43.5
IEC 50-year extreme
wind
Class Vref (10 min, m/s)
I 50.0
II 42.5
III 37.5
S mfr specified
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Wind Shear
The power law exponent was calculated at 0.297 for all wind directions, indicating higher than expected
wind shear at the Emmonak test site. Note however that the measured high wind shear is very likely
influenced by the brush surrounding the test site. If turbines are installed in more open terrain and at
hub heights exceeding 30 meters, it is likely that shear values will be less than calculated. To extrapolate
data to levels higher than 30 meters, a power law exponent () value of 0.14, typical of open tundra ter-
rain, was used throughout this report.
Probability Distribution Function
The probability distribution function (PDF) provides a visual indication of measured wind speeds in one
meter per second or smaller “bins”. Note that most wind turbines do not begin to generate power until
the wind speed at hub height reaches 4 m/s, known as the “cut-in” wind speed. The black line in the
graph is a best fit Weibull distribution. The Weibull shape factor (k) value of 2.13 is near the “normal”
shape curve k value of 2.0, also known as the Raleigh distribution.
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Wind Roses
Winds at the Emmonak met tower test site are primarily northerly to northeasterly and to a lesser ex-
tent easterly to southeasterly winds. Importantly though, southeasterly winds are higher strength,
hence the power density rose indicates an approximately equal share of northerly, northeasterly and
southeasterly power-producing winds at the met tower site.
Note that a wind threshold of 4 m/s was selected for the definition of calm winds. This wind speed
represents the cut-in wind speed of most wind turbines. By this definition, the Emmonak site expe-
rienced 35 percent calm conditions during the measurement period (see wind frequency rose below).
This percentage was not adjusted based on adjustment to the AWOS long-term average; if it were to be,
calm condition percentage likely would be lower.
Wind Frequency Rose Total value (power density) rose
Air Temperature and Density
During the measurement period, Emmonak experienced an average temperature of -1.9° C. The mini-
mum recorded temperature during the measurement period was –38.6° C (February) and the maximum
temperature was 27.9° C (July).
Consequent to Emmonak’s cool temperatures, the average air density of 1.272 kg/m3 is approximately
four percent higher than the standard air density of 1.225 kg/m
3 (15.0° C and 101.2 kPa standard tem-
perature and pressure) at 3 m elevation, indicating that Emmonak has denser air than the standard air
density used to calculate turbine power curves.
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Speed vs. Temperature Scatterplot
A scatterplot of 30m A anemometer wind speed versus temperature indicates that the higher wind
ranges where wind turbine power production becomes substantial generally occur at temperatures
warmer than -30° C. Although a wind turbine installed in Emmonak should be rated to -40° C, little
power production will occur during periods of severe cold.
Turbulence
Air turbulence at the Emmonak test site during the measurement period is somewhat high, exceeding
International Electrotechnical Commission (IEC) Category C criteria and classifying as IEC 3rd Edition tur-
bulence category B at the 30 meter level and as IEC turbulence category A at the 20 meter level. Turbu-
lent air is highly unusual in open tundra environments and in this case is likely due to effects of the
brush and vegetation surrounding the met tower. This assumption can be noted in the turbulence rose
(turbulence vs. wind direction) graph which shows higher turbulence with southerly winds – the direc-
tion where heavy brush exists at the met tower site. It is presumed that wind turbines at hub heights
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exceeding 30 meters at the test location, or if located elsewhere in Emmonak less dominated by brush,
will experience less turbulence, likely within category C criteria.
Turbulence vs. wind speed
Turbulence vs. wind direction