HomeMy WebLinkAboutToksook Wind Resource Assessment - Oct 2005 - REF Grant 2195385 Page 1 of 16
813 W. Northern Lights Blvd.
Anchorage, AK 99503
Phone: 907-269-3000
Fax: 907-269-3044
www.aidea.org/wind.htm
Wind Resource Assessment for
TOKSOOK BAY, ALASKA
Site # 0071
Date last modified: 10/4/2005
Compiled by: Mia Devine
Elevation: 65 ft Latitude:
(NAD27)
60 31 38.9 N
60 31.648 Tower Type: 30-meter NRG Tall Tower
Longitude:
(NAD27)
165 6 28.5 W
-165 6.475
Monitor Start:
Monitor End:
6/16/2004
08/31/2005
INTRODUCTION
On June 16, 2004, V3Energy and employees of the Alaska Village Electric Cooperative (AVEC) installed a 30-
meter meteorological tower in the village of Toksook Bay. The purpose of this monitoring effort was to evaluate the
feasibility of utilizing wind energy in the community. AVEC began installing three wind turbines in Toksook Bay in
August of 2005. This report summarizes the wind resource data collected before the wind turbines were installed
and the long-term energy production potential of the site.
SITE DESCRIPTION
Toksook Bay is located on Nelson Island in Kangirlvar Bay, approximately 115 miles northwest of Bethel. The met
tower and current wind farm site is located at the west end of town near the AVEC power plant. This location is at a
slightly higher elevation than the town site. Figure 1 shows the location of the met tower relative to the surrounding
terrain.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Figure 1. Topographic Map of Met Tower Site and Surrounding Area
Table 1 lists the types of sensors that were mounted on the met tower, the channel of the data logger that each
sensor was wired into, and where each sensor was mounted on the tower.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Table 1. Summary of Sensors Installed on the Met Tower
Ch # Sensor Type Height Offset Boom Orientation
1 #40 Anemometer 30 m NRG Standard 140 True
2 #40 Anemometer 20 m NRG Standard True North
7 #200P Wind Vane 30 m 140 True 320 True
9 #110S Temperature 5 m 0 -
Arial view of equipment on tower
N
NE
E
SE
S
SW
W
NW CH1
CH2
Tower
CH7
The photos below illustrate the terrain surrounding the met tower site.
View of met tower from power plant Facing NW towards met tower site
Facing SE from met tower site View of sensor layout Facing East
Facing West/NW Facing NE Facing west towards met tower site
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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DATA PROCESSING PROCEDURES AND DEFINITIONS
The following information summarizes the data processing procedures that were performed on the raw measured
data in order to create an annual dataset of typical wind speeds, which could then be used to calculate potential
power production from wind turbines. There are various methods and reasons for adjusting the raw data, so the
purpose of these notes is to document what was done in this situation. The raw data set is available on the Alaska
Energy Authority website (www.akenergyauthority.org) so one could perform their own data processing procedures.
Units Since most wind turbine manufacturer data is provided in metric units, those units are used here.
1 meter/second = 2.24 mph = 1.95 knots
1 meter = 3.28 feet
1 C = 5/9 (F 32)
Max/Min Test All of the 10-minute data values were evaluated to ensure that none of them fell outside of the
normal range for which the equipment is rated.
Tower Shadow The tower itself can affect readings from the anemometer at times when the anemometer is
located downwind of the tower. In this case, the 30-meter anemometer may record slightly lower values than the
free stream velocity when the wind is coming from the NW.
Icing Anomalies in the data can suggest when the sensors were not recording accurately due to icing events.
Since wind vanes tend to freeze before the anemometers, icing events are typically identified whenever the 10-
minute standard deviation of the wind vane is zero (the wind vane is not moving) and the temperature is at or below
freezing. Some additional time before and after the icing event are filtered out to account for the slow build up and
shedding of ice.
Filling Gaps Whenever measured met tower data is available, it is used. Two different methods are used to fill in
the remaining portion of the year. First, nearby airport data is used if available. A linear correlation equation is
defined between the airport and met tower site, which is used to adjust the hourly airport data recorded at the time
of the gap. If neither met tower nor airport data is available for a given timestep, the software program
Windographer (www.mistaya.ca) is used. Windographer uses statistical methods based on patterns in the data
surrounding the gap, and is good for filling short gaps in data.
Long-term Estimates The year of data collected at the met tower site can be adjusted to account for inter-annual
fluctuations in the wind resource. To do this, a nearby weather station with a consistent historical record of wind
data and with a strong correlation to the met tower location is needed. If a suitable station is not available, there is
a higher level of uncertainty in the wind speed that is measured being representative of a typical year.
Turbulence Intensity Turbulence intensity is the most basic measure of the turbulence of the wind. Turbulence
intensity is calculated at each 10-minute timestep by dividing the standard deviation of the wind speed during that
timestep by the average wind speed over that timestep. It is calculated only when the mean wind speed is at least
4 m/s. Typically, a turbulence intensity of 0.10 or less is desired for minimal wear on wind turbine components.
Wind Shear Typically, wind speeds increase with height above ground level. This vertical variation in wind speed
is called wind shear and is influenced by surface roughness, surrounding terrain, and atmospheric stability. The
met tower is equipped with anemometers at different heights so that the wind shear exponent, , can be calculated
according to the power law formula:
2
1
2
1
v
v
H
H where H1 and H2 are the measurement heights and v1 and v2 are the measured wind speeds.
Wind shear is calculated only with wind speed data above 4 m/s. Values can range from 0.05 to 0.25, with a typical
value of 0.14.
Scaling to Hub Height If the wind turbine hub height is different from the height at which the wind resource is
measured, the wind resource can be adjusted using the power law formula described above and using the wind
shear data calculated at the site.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Air Density Adjustment The power that can be extracted from the wind is directly related to the density of the
air. Air density, , is a function of temperature and pressure and is calculated for each 10-minute timestep
according to the following equation (units for air density are kg/m3):
TR
P , where P is pressure (kPa), R is the gas constant for air (287.1 J/kgK), and T is temperature in Kelvin.
Since air pressure is not measured at the met tower site, the site elevation is used to calculate an annual average
air pressure value according to the following equation:
P = 1.225 (1.194 x 10-4) x elevation
Since wind turbine power curves are based on a standard air density of 1.225 kg/m3, the wind speeds measured at
the met tower site are adjusted to create standard wind speed values that can be compared to the standard power
curves. The adjustment is made according to the following formula:
3
1
tan
tan
dards
measured
measureddardsVV
Since the temperature sensor in Toksook Bay was not working, the wind speed measurements were not adjusted
for air density.
Wind Power Density Wind power density provides a more accurate representation of a sites wind energy
potential than the annual average wind speed because it includes how wind speeds are distributed around the
average as well as the local air density. The units of wind power density are watts per square meter and represent
the power produced per square meter of area that the blades sweep as they rotate around the rotor.
Wind Power Class A seven level classification system based on wind power density is used to simplify the
comparison of potential wind sites. Areas of Class 4 and higher are considered suitable for utility-scale wind power
development.
Weibull Distribution The Weibull distribution is commonly used to approximate the wind speed frequency
distribution in many areas when measured data is not available. In this case, the Weibull distribution is used to
compare with our measured data. The Weibull is defined as follows:
kk
c
v
c
v
c
kvP exp)(
1
Where P(v) is the probability of wind speed v occurring, c is the scale factor which is related to the average wind
speed, and k is the shape factor which describes the distribution of the wind speeds. Typical k values range from
1.5 to 3.0, with lower k values resulting in higher average wind power densities.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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DATA COLLECTION PROBLEMS
Originally, the offset for the temperature sensor was programmed into the data logger at a value of 0 instead of the
standard -123.501 so that the readings would match those of the data loggers internal temperature sensor. The
temperature readings seemed to be accurate until 9/9/2004, when the temperature reading began to drift up to a
value of over 150F on 9/12/2004. The signal conditioning module (SCM) for the temperature sensor was removed
and re-inserted at 16:30 on 2/22/2005, which seemed to correct the problem. For the data between 9/12/2004 and
2/22/2005, the standard offset of -123.501 was programmed into the data management software to adjust the
invalid readings from the logger. Temperature data between 9/9/2004 and 9/12/2004 was discarded. To ensure
that the revised temperature dataset is valid, the hourly average values were compared to those from the Mekoryuk
airport weather station, located about 40 miles to the West. The temperature data sets matched closely, with a
correlation coefficient of 0.94 (value of 1 is perfect).
On 5/22/05 the data logger failed and was replaced on 6/9/05. This resulted in a gap in the entire dataset.
LONG-TERM REFERENCE STATION
Wind data from the Mekoryuk Airport weather station (shown in Figure 2), located about 40 miles west of the met
tower site, serves as a long-term reference for the wind resource in the area. This data is measured at a height of
10 meters above ground level and at an elevation of 15 meters.
Figure 2. ASOS Equipment in Mekoryuk
Over 20 years of wind speed measurements are summarized in Table 2 and Figure 3. The average wind speed
over the 20-year period is 6.4 m/s. The cause of the unusually high wind speeds in 1985-1987 is unknown.
Excluding those years, the annual wind speed rarely deviates more than 10% above or below the average.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Table 2. Average Wind Speeds at 10-meter Height at Mekoryuk Airport
Year JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC AVG
% of 20-Yr
Average
1984 7.0 6.1 5.5 5.4 3.4 3.3 4.5 5.8 4.0 6.2 4.8 7.2 5.3 82%
1985 6.4 6.7 6.9 8.3 9.2 7.1 7.1 7.8 9.9 12.3 11.5 8.7 8.5 132%
1986 9.6 9.0 8.7 7.5 7.4 8.6 6.3 7.2 6.4 7.6 9.8 9.8 8.1 127%
1987 9.8 9.6 7.5 8.9 7.6 7.4 7.3 7.3 9.9 9.5 9.8 9.4 8.7 135%
1988 8.6 7.5 6.1 6.5 4.8 4.0 3.1 3.5 4.3 4.4 5.3 5.7 5.3 83%
1989 5.7 7.0 6.0 6.8 6.4 4.7 3.8 4.2 6.1 6.9 7.2 6.2 5.9 92%
1990 6.3 5.9 5.3 5.7 6.3 5.0 4.3 6.1 6.6 5.6 6.3 7.4 5.9 91%
1991 6.4 6.0 6.3 3.5 4.2 5.6 5.4 3.9 5.4 7.4 5.3 6.4 5.5 85%
1992 4.1 5.1 3.5 5.2 5.7 4.7 3.9 6.1 6.7 7.4 6.6 6.6 5.5 85%
1993 9.2 7.8 5.9 5.3 5.9 5.3 4.6 5.0 7.1 6.4 7.3 6.7 6.4 99%
1994 6.3 7.0 7.3 5.6 4.3 5.1 5.1 7.4 6.2 6.8 9.1 8.3 6.6 102%
1995 6.7 7.0 5.4 6.4 4.6 5.3 4.3 5.3 6.0 7.2 5.5 6.8 5.9 91%
1996 7.2 9.2 6.4 6.8 5.6 6.2 5.0 6.7 7.2 6.7 8.3 6.2 6.8 106%
1997 6.8 7.8 5.6 4.3 6.3 4.3 4.5 5.9 5.9 6.5 7.7 6.5 6.0 93%
1998 6.9 5.2 7.4 8.3 6.7 5.0 3.7 6.8 6.3 6.5 7.3 7.4 6.5 100%
1999 7.1 7.8 6.1 7.7 4.7 4.7 3.8 5.6 6.0 6.5 8.2 6.6 6.2 97%
2000 7.6 8.8 6.9 5.5 4.5 4.3 4.5 6.7 6.2 5.9 8.4 8.7 6.5 101%
2001 7.6 9.4 7.5 6.9 5.5 5.1 5.5 6.0 5.9 7.1 7.7 6.7 6.7 105%
2002 8.6 7.6 6.9 7.6 6.6 4.7 5.0 5.5 6.4 6.4 6.3 6.1 6.5 101%
2003 5.8 5.9 7.6 6.8 4.9 5.3 5.5 4.9 5.4 7.8 7.3 6.5 6.1 95%
2004 6.8 7.6 6.7 6.3 6.0 4.8 4.3 5.1 5.9 7.4 7.7 8.4 6.4 100%
AVG 7.2 7.3 6.5 6.4 5.7 5.3 4.8 5.8 6.4 7.1 7.5 7.3 6.4 100% g p
0
1
2
3
4
5
6
7
8
9
10
0
5
10
15
20
Figure 3. Annual Average Wind Speeds at 10-m Height at Mekoryuk Airport Weather Station
Hourly wind speed measurements from the Mekoryuk Airport weather station that are concurrent with recordings
from the Toksook Bay met tower site were purchased from the National Climatic Data Center. Data between these
sites was compared and a correlation coefficient of 0.73 was calculated (a value of 1 is perfect). A bulk regression
equation of the year of concurrent data was used to calculate a long-term wind speed dataset at the met tower site
based on the long-term 2001-2005 data from the Mekoryuk airport site.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
Page 8 of 16
WIND DATA RESULTS FOR MET TOWER SITE
Table 3 summarizes the amount of data that was successfully retrieved from the 30-meter level anemometer at the
met tower site. The month with the lowest data recovery rate is May, due to data logger failure. There is also
significant data loss due to icing of the sensors in the winter months.
Table 3. Data Recovery Rates for Met Tower Data
Table 4 and Table 5 summarize the wind resource data measured at the met tower site as well as the estimated
long-term data for this site. Figure 4 and Figure 5 show this same data graphically. As shown, the highest wind
month is November and the lowest wind month is July. Also, the diurnal variation is more pronounced during the
summer months than the winter months, with winds typically lowest in the morning and increasing in the afternoon.
Table 4. Measured Wind Speeds at 30-m Height at Met Tower Location, June 2004 - Aug 2005 (m/s)
Hour Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
0 8.1 8.2 7.8 7.3 6.2 6.1 5.1 6.4 5.3 8.5 10.0 8.8 7.3
1 7.8 8.6 7.7 7.0 6.1 5.7 4.8 6.3 5.5 8.4 9.7 8.6 7.2
2 7.8 8.9 8.0 6.7 6.5 5.3 4.7 6.2 5.6 8.2 9.3 8.6 7.2
3 8.0 9.1 8.0 6.6 6.5 5.3 4.5 6.1 5.4 8.0 9.4 8.4 7.1
4 8.2 9.2 7.8 6.8 6.7 5.2 4.4 6.1 5.6 7.9 9.3 8.4 7.1
5 8.0 8.8 8.1 6.7 6.6 5.1 4.3 6.2 5.4 7.8 9.1 8.6 7.1
6 7.9 8.7 8.2 6.4 6.0 5.4 4.4 6.1 5.3 8.0 8.8 9.0 7.0
7 7.9 9.0 7.7 6.4 5.5 5.2 4.4 6.1 5.2 8.4 8.6 9.0 6.9
8 7.7 9.5 8.0 6.4 5.4 5.4 4.7 6.4 5.2 8.1 8.8 9.3 7.1
9 7.7 9.0 7.6 6.7 5.7 5.9 4.9 6.9 5.4 8.3 9.2 9.2 7.2
10 7.6 8.8 6.8 6.7 6.4 6.1 5.2 7.1 6.1 7.9 9.2 9.1 7.2
11 7.6 9.0 7.2 7.1 6.0 6.4 5.3 7.3 6.2 8.1 9.3 8.8 7.4
12 7.2 9.0 7.2 7.1 5.6 6.7 5.6 7.4 6.8 8.2 9.4 8.9 7.4
13 6.9 8.1 7.7 7.2 5.6 6.9 5.8 7.4 6.7 8.6 9.1 8.8 7.4
14 7.0 7.8 7.5 7.3 6.0 7.1 5.9 7.7 6.6 8.5 8.9 8.2 7.4
15 7.5 7.5 7.5 6.9 6.4 7.3 6.1 7.6 6.6 8.8 8.8 8.4 7.4
16 7.7 7.6 7.7 7.4 6.6 7.7 6.0 7.5 6.8 8.8 8.7 8.6 7.6
17 7.8 7.6 7.5 7.6 6.8 7.5 6.0 7.5 6.5 9.0 8.6 8.9 7.6
18 9.1 7.6 7.9 7.1 7.0 7.5 6.3 7.4 6.0 8.9 9.3 9.1 7.8
19 8.6 7.7 7.8 6.9 7.3 7.4 6.5 7.1 5.7 8.7 10.0 9.4 7.8
20 8.8 8.0 7.8 7.3 6.8 7.4 6.1 6.8 5.7 8.6 9.7 9.6 7.7
21 8.2 7.9 8.0 6.8 6.1 7.2 5.5 6.7 5.5 8.7 9.9 9.7 7.5
22 8.6 7.9 7.7 7.2 6.4 7.3 5.3 6.6 5.5 8.7 9.5 9.4 7.5
23 9.1 7.4 7.8 7.6 6.0 6.9 5.1 6.6 5.2 8.6 9.7 9.2 7.4
Avg 8.0 8.4 7.7 7.0 6.3 6.4 5.3 6.8 5.8 8.4 9.3 8.9 7.3
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Table 5. Estimated Long-term Wind Speeds at 30-m Height at Met Tower Location (m/s)
Hour Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
0 6.5 6.6 8.9 7.4 4.3 2.6 3.9 4.3 5.6 8.5 8.6 7.1 6.2
1 6.4 6.7 8.7 7.3 4.0 2.9 4.0 4.3 5.3 8.4 8.4 7.1 6.1
2 6.4 6.9 8.5 6.9 3.6 2.7 4.0 4.1 5.4 8.5 8.4 7.2 6.1
3 6.4 7.3 8.5 6.8 3.9 2.7 3.6 3.8 5.2 8.6 8.0 7.7 6.0
4 7.3 7.2 8.6 7.1 4.1 2.6 3.8 4.0 5.2 8.5 8.1 8.0 6.2
5 7.4 7.3 8.8 7.0 3.9 2.4 3.8 3.7 5.2 8.8 8.3 8.0 6.2
6 7.3 7.5 8.6 7.1 4.0 2.7 3.7 3.7 5.2 8.7 9.2 8.2 6.3
7 7.6 7.5 8.6 7.5 4.2 3.3 3.8 3.9 5.5 9.0 8.2 8.4 6.5
8 7.4 7.3 8.7 7.6 4.6 4.3 4.4 4.0 5.6 8.9 8.2 8.1 6.6
9 7.3 7.1 8.3 7.3 5.3 5.0 5.0 4.7 5.8 8.7 8.2 7.9 6.7
10 7.6 7.5 8.1 7.9 5.7 5.6 5.5 5.4 6.3 8.9 8.5 8.3 7.1
11 7.1 7.6 8.3 8.3 6.4 6.2 6.2 5.7 6.5 9.1 8.3 8.3 7.3
12 6.9 7.8 7.9 8.6 6.9 6.5 6.2 6.1 6.7 9.5 8.6 8.0 7.5
13 6.4 7.5 8.1 8.5 7.3 7.1 6.3 6.5 6.8 9.7 9.0 8.2 7.6
14 6.8 7.7 8.2 8.8 7.2 7.2 6.7 6.8 7.1 9.5 8.7 8.0 7.7
15 6.5 7.9 8.2 8.9 7.0 7.5 6.7 7.0 7.2 9.5 8.8 8.2 7.8
16 6.7 7.7 8.8 8.6 7.1 7.3 6.7 6.7 6.9 9.7 8.9 8.3 7.8
17 6.9 8.2 8.8 8.5 7.2 6.8 6.5 6.8 6.9 9.6 8.8 8.3 7.8
18 6.9 7.6 9.0 8.3 7.0 6.4 6.3 6.7 6.7 9.0 8.7 8.0 7.6
19 6.5 7.0 8.8 7.5 6.7 5.9 6.0 6.0 6.5 9.2 8.7 8.2 7.2
20 6.4 7.4 8.9 7.6 6.3 5.4 5.5 5.6 5.9 9.1 8.7 8.1 7.1
21 6.4 6.9 8.3 7.5 5.5 4.6 5.0 5.0 5.8 9.0 8.7 7.6 6.7
22 6.1 7.3 8.6 7.4 4.8 3.4 4.4 4.7 5.9 8.7 8.8 7.3 6.5
23 6.2 6.7 9.0 7.2 4.4 2.9 4.0 4.5 6.2 8.2 8.9 7.7 6.3
Avg 6.8 7.3 8.5 7.7 5.5 4.8 5.1 5.2 6.1 9.0 8.6 7.9 6.9
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10 11 12
Month
Measured Met Tower Data
Longterm Estimate
Month m/s mph m/s mph
Jan 8.0 17.8 6.8 15.2
Feb 8.4 18.7 7.3 16.4
Mar 7.7 17.3 8.5 19.1
Apr 7.0 15.6 7.7 17.3
May 6.3 14.0 5.5 12.2
Jun 6.4 14.4 4.8 10.6
Jul 5.3 11.9 5.1 11.4
Aug 6.8 15.2 5.2 11.6
Sep 5.8 13.0 6.1 13.5
Oct 8.4 18.8 9.0 20.1
Nov 9.3 20.7 8.6 19.2
Dec 8.9 19.9 7.9 17.7
Avg 7.3 16.4 6.9 15.4
Long-term EstimateJune 04 - Aug 05
Figure 4. Monthly Average Wind Speeds at Met Tower Site (30m Height)
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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0
1
2
3
4
5
6
7
8
9
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour of Day
6/2004 - 9/2005 Longterm Estimate
0
1
2
3
4
5
6
7
8
9
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour of Day
Longterm Estimate - July Longterm Estimate - January
Figure 5. Hourly Average Wind Speeds at Met Tower Site (30m Height)
A common method of displaying a year of wind data is a wind frequency distribution, which shows the percent of
the year that each wind speed occurs. Figure 6 shows the measured wind frequency distribution as well as the
best matched Weibull distribution (c = 7.88, k= 1.62).
0
2
4
6
8
10
12
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Wind Speed (m/s)
Measured Weibull
Bin m/s
Measured
Hours Bin m/s
Measured
Hours
0 430 15 143
1 589 16 109
2 644 17 83
3 700 18 64
4 789 19 34
5 794 20 23
6 749 21 15
7 709 22 9
8 683 23 3
9 585 24 2
10 500 25 2
11 376 26 1
12 303 27 1
13 237 28 0
14 184 29 0
Total: 8,760 Figure 6. Wind Speed Frequency Distribution of Measured Met Tower Data
The cut-in wind speed of many wind turbines is 4 m/s and the cut-out wind speed is around 25 m/s. The frequency
distribution shows that a large percentage of the wind in Toksook is within this operational zone.
Table 6 shows the annual wind rose at the Toksook Bay met tower site versus the Mekoryuk Airport. The
correlation coefficient of the directional data between the Mekoryuk and Toksook Bay sites is 0.72. Table 7 shows
the monthly wind roses for the year of data measured at the Toksook Bay met tower.
Table 6. Annual Wind Rose for Met Tower Site and Airport Site
Legend Annual Wind Rose for Toksook Bay Annual Wind Rose for Mekoryuk Airport
Percent of Total Wind Energy
Percent of Total Time
NRG Systems SDR Version 5.03
N
EW
S
Wind Frequency Distribution Rose (% of Time)
0
2
4
6
8N
NE
E
SE
S
SW
W
NW
Average Distribution
January
July
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Table 7. Monthly Wind Roses for Toksook Bay Met Tower Site
July 2004 Aug 2004 Sept 2004
N
EW
S
N
EW
S
N
EW
S
Oct 2004 Nov 2004 Dec 2004
N
EW
S
N
EW
S
N
EW
S
Jan 2005 Feb 2005 Mar 2005
N
EW
S
N
EW
S
N
EW
S
Apr 2005 May 2005 June 2005
N
EW
S
N
EW
S
N
EW
S
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
Page 12 of 16
Table 8 summarizes the monthly turbulence intensity and wind shear at the met tower site. A turbulence intensity
of less than 0.10 is considered low and unlikely to contribute to excessive wear of wind turbines. Wind shear was
calculated between the 30-meter anemometer and the 20-meter anemometer. Both turbulence intensity and wind
shear were only calculated for wind speeds greater than 4 m/s.
Table 8. Monthly Turbulence Intensity and Wind Shear at Met Tower Site June 2004 to Aug 2005
Turbulence Intensity
0.12
0.130.15
0.15
0.11
0.08
0.08
0.080.09
0.09
0.080.09
0.10
0.12
0.12
0.12
0.120.12
Wind Shear0.11
0.150.20
0.20
0.14
0.09
0.12
0.140.31
0.26
0.190.12
0.12
0.16
0.13
0.13
-0.03-0.02
Figure 7. Turbulence Intensity and Wind Shear by Direction, June 2004 - Aug 2005
The air temperature can affect wind power production in two primary ways: 1) colder temperatures lead to higher air
densities and therefore more power production, and 2) some wind turbines shut down in very cold situations
(usually around 25 C). The monthly average temperatures measured at the met tower are shown in Figure 8.
The temperature never dropped below -25 C and was below -20 C for about 150 hours of the year.
-6.8
-7.7 -9.3
6.9
2.9
-3.2
-7.1
12.612.011.3
-7.2
2.6
-15.0
-10.0
-5.0
0.0
5.0
10.0
15.0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 8. Monthly Average Temperatures at Toksook Bay Met Tower Site
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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POTENTIAL POWER PRODUCTION FROM WIND TURBINES IN TOKSOOK BAY
Table 9 lists a number of parameters used to characterize the power production potential of a particular site.
Table 9. Summary of Power Production Potential of Met Tower Site
Average Wind Power Density (30m) 518 W/m2
Wind Power Class 6
Rating Outstanding
Various wind turbines, listed in Table 12, were used to calculate energy production at the met tower site based on
the long-term wind resource data set. Results are shown in Table 10. Although different wind turbines are offered
with different tower heights, to be consistent it is assumed that any wind turbine rated at 100 kW or less would be
mounted on a 30-meter tall tower, while anything larger would be mounted on a 50-meter tower. The wind
resource was adjusted to these heights based on the measured wind shear at the site.
Table 10. Gross Annual Energy Production from Different Wind Turbines at Met Tower Site
Month Proven
2.5kW
Proven
6kW
Bergey 10
kW FL30 Entegrity FL100 NW100 FL250 V27 V47
Jan 716 1,814 1,959 9,065 14,937 29,251 23,807 67,748 61,260 204,550
Feb 714 1,827 2,005 9,131 14,852 29,233 23,918 65,900 60,080 202,436
Mar 990 2,474 2,663 12,350 21,377 41,206 33,671 93,442 85,219 278,858
Apr 835 2,138 2,329 10,618 17,875 34,643 28,582 75,591 69,936 235,723
May 471 1,249 1,329 6,228 9,063 18,244 14,859 40,806 37,271 133,511
Jun 351 933 975 4,514 6,424 13,190 10,746 30,535 27,874 97,501
Jul 369 975 980 4,700 6,303 13,144 10,535 29,339 26,376 94,347
Aug 426 1,115 1,172 5,489 8,104 16,360 13,266 38,609 35,150 122,059
Sep 527 1,396 1,490 6,943 10,308 20,652 16,885 49,813 45,611 159,515
Oct 1,020 2,554 2,666 12,770 22,139 42,236 34,503 98,340 89,047 292,766
Nov 925 2,297 2,337 11,431 19,973 37,927 30,840 88,086 79,760 260,861
Dec 846 2,124 2,169 10,710 17,916 34,377 27,813 79,753 72,035 241,488
Annual 8,190 20,895 22,072 103,948 169,271 330,464 269,426 757,962 689,619 2,323,615
Annual
kWh/m^2 853 878 573 782 956 950 949 1,108 1,204 1,339
Table 10 also lists the annual energy production per square meter of swept area (kWh/m2). This allows one to
directly compare the efficiency of one wind turbine against another, as shown in Figure 9.
0
20
40
60
80
100
120
140
160
180
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Proven 2.5kW
Proven 6kW
Bergey 10 kW
FL30
Entegrity
FL100
NW100
FL250
V27
V47
Figure 9. Comparison of Power Production per Square Meter of Swept Area from Various Wind Turbines
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Table 11 summarizes the gross capacity factor of the wind turbines per month. Gross capacity factor is the amount
of energy produced based on the given wind resource divided by the maximum amount of energy that could be
produced if the wind turbine were to operate at rated power during that entire period. The gross capacity factor
could be further reduced by up to 10% to account for transformer/line losses, turbine downtime, soiling of the
blades, icing of the blades, yaw losses, and extreme weather conditions.
Table 11. Gross Capacity Factor of Different Wind Turbines at Met Tower Site
Month Proven
2.5kW
Proven
6kW
Bergey 10
kW FL30 Entegrity FL100 NW100 FL250 V27 V47
Jan 39% 41% 26% 41% 30% 39% 32% 36% 37% 42%
Feb 42% 45% 30% 45% 33% 44% 36% 39% 40% 46%
Mar 53% 55% 36% 55% 44% 55% 45% 50% 51% 57%
Apr 46% 49% 32% 49% 38% 48% 40% 42% 43% 50%
May 25% 28% 18% 28% 18% 25% 20% 22% 22% 27%
Jun 20% 22% 14% 21% 14% 18% 15% 17% 17% 21%
Jul 20% 22% 13% 21% 13% 18% 14% 16% 16% 19%
Aug 23% 25% 16% 25% 17% 22% 18% 21% 21% 25%
Sep 29% 32% 21% 32% 22% 29% 23% 28% 28% 34%
Oct 55% 57% 36% 57% 45% 57% 46% 53% 53% 60%
Nov 51% 53% 32% 53% 42% 53% 43% 49% 49% 55%
Dec 45% 48% 29% 48% 36% 46% 37% 43% 43% 49%
Annual 37% 40% 25% 40% 29% 38% 31% 35% 35% 40%
CONCLUSION
This report provides a summary of wind resource data collected from June 2004 through August 2005 in Toksook
Bay, Alaska. The data was compared to long-term trends in the area. Based on correlations with the Mekoryuk
weather station, estimates were made to create a long-term dataset for the Toksook Bay met tower site. This
information was used to make predictions as to the potential energy production from wind turbines at the site.
It is estimated that the long-term annual average wind speed at the site is 6.9 m/s at a height of 30 meters above
ground level. Taking the local air density into account, the average wind power density for the site is 518 w/m2.
This information means that Toksook Bay has a Class 6 wind resource, which is outstanding for wind power
development.
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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Table 12. Specifications of Wind Turbines Used in Power Production Analysis
Proven
2.5 kW
http://www.provenenergy.com
Tower Height: 30 meters
Swept Area: 9.6 m2
Turbine Weight: 190 kg
Proven
6 kW
http://www.provenenergy.com
Tower Height: 30 meters
Swept Area: 23.8 m2
Turbine Weight: 500 kg
Bergey
10 kW
www.bergey.com
Tower Height: 30 meters
Swept Area: 38.5 m2
Weight: not available
Fuhrlander FL30
30 kW
www.lorax-energy.com
Tower Height: 30 meters
Swept Area: 133 m2
Weight (nacelle & rotor):
410 kg
Entegrity
66 kW
www.entegritywind.com
Tower Height: 30 meters
Swept Area: 177 m2
Weight (drivetrain & rotor):
2,420 kg
Fuhrlander FL100
100 kW
www.lorax-energy.com
Tower Height: 30 meters
Swept Area: 348 m2
Weight (nacelle & rotor):
2,380 kg
Northern Power NW100/19
100 kW
www.northernpower.com
Tower Height: 30 meters
Swept Area: 284 m2
Weight (nacelle & rotor):
7,086 kg
Fuhrlander FL250
250 kW
www.lorax-energy.com
Tower Height: 50 meters
Swept Area: 684 m2
Weight (nacelle & rotor):
4,050 kg
Vestas V27
225 kW
(refurbished, various suppliers)
Tower Height: 50 meters
Swept Area: 573 m2
Weight: not available
Vestas V47
660 kW
www.vestas.com
Tower Height: 50 meters
Swept Area: 1,735 m2
Weight: not available
Alaska Energy Authority TOKSOOK BAY, AK Wind Resource Assessment
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