HomeMy WebLinkAboutKaktovik Wind Diesel Feasibility Study Project Wind Resource Report - Aug 2010 - REF Grant 7040025Kaktovik Wind Resource Report
Report by: Douglas Vaught, P.E., V3 Energy LLC, Eagle River, Alaska
Date of Report: August 26, 2010
Kaktovik met tower; D. Vaught photo
Contents
Summary Information...............................................................................................................................2
Test Site Location......................................................................................................................................2
Photographs..................................................................................................................................................4
Data recovery................................................................................................................................................4
Wind Speed...................................................................................................................................................5
Time Series................................................................................................................................................6
Daily Wind Profile .....................................................................................................................................7
Probability Distribution Function..............................................................................................................8
Wind Shear and Roughness......................................................................................................................8
Extreme Winds............................................................................................................................................10
Temperature and Density...........................................................................................................................11
Kaktovik Wind Resource Report Page 2
Monthly temperature boxplot............................................................................................................11
Wind Speed Scatterplot..........................................................................................................................12
Wind direction ........................................................................................................................................13
Turbulence..................................................................................................................................................14
Airport AWOS Data.....................................................................................................................................16
Summary Information
With reference to two nearby Automated Weather Observing System (AWOS) sources (Barter Island
Airport and Barter Island DEW), the wind resource in Kaktovik is outstanding (Class 5 to 6), but
verification with the met tower was fraught with difficulty, namely a lost data card, significant data loss
due to icing, and loss of both 30 meter level anemometers in early January due to ice and wind damage
that were not replaced until early March. Given the anemometer problems, met tower data as collected
is not useful for calculating mean wind speed, but inserting synthesized data to the data set yields a
wind resource prediction in-line with the AWOS data sources. Other parameters, including turbulence,
wind shear, and directionality of winds, indicate a desirable wind resource for wind power development.
Met tower data synopsis
Data dates June 26, 2009 to July 19, 2010 (13 months)
Wind power class Presumed 5 (excellent)(from AWOS and synthesized data)
Power density mean, 30 m 479 W/m2 (synthesized data)
Wind speed mean, 30 m 6.49 m/s (synthesized data)
Max 10-min wind speed average 29.3 m/s
Maximum wind gust 35.2 m/s (Feb 2010)
Weibull distribution k = 1.82, c = 7.18 m/s (measured data)
Roughness class 0.68 (lawn grass)
IEC 61400-1, 3rd ed. classification Class III-c (lowest defined and most common)
Turbulence intensity, mean 0.076 (at 15 m/s)
Calm wind frequency 24% (<3.5 m/s)
Community profile
Current Population: 286 (2009 DCCED Certified Population)
Incorporation Type: 2nd Class City
Borough Located In: North Slope Borough
Taxes: Sales: None, Property: 18.5 mills (Borough), Special: None
Coastal Management District:North Slope Borough
Test Site Location
Met tower was located 650 meters (2100 ft) south of the village boundary near the village sewage
treatment plant. This site is not considered ideal for wind power development as a more likely site is
immediately west of the powerplant on the west-central edge of the village. But, the flat and
Kaktovik Wind Resource Report Page 3
featureless topography of Kaktovik ensures the met tower data is useable anywhere in the village
environs.
Site information
Site number 0224
Latitude/longitude N 70° 07.065’ W 143° 36.342’, WGS 84
Site elevation 2 meters
Datalogger type NRG Symphonie, 10 minute time step
Tower type NRG 34-meter tall tower, 152 mm diameter, erected to 30 m
Anchor type 1.5 m screw-in
Google Earth image
Tower Sensor Information
Channel Sensor type Height Multiplier Offset Orientation
1 NRG #40 anemometer 30 m (A) 0.760 0.43 181°T
2 NRG #40 anemometer 30 m (B)0.754 0.43 271°T
3 NRG #40 anemometer 20 m 0.758 0.38 272°T
7 NRG #200P wind vane 29 m 0.351 357 357° T
9 NRG #110S Temp C 3 m 0.136 -86.383 N
10 RH-5 relative humidity 2 m 0.098 0 S
12 Voltmeter 2 m 0.021 0 n/a
Kaktovik Wind Resource Report Page 4
Photographs
Missing 30 m anemometers, Feb 2010; D. Vaught photo Alternate wind site behind powerplant; D. Vaught photo
Data recovery
Data recovery to date in Kaktovik was poor, with only 62 to 71 percent data return from the
anemometers and wind vane with all of the missing data representing the winter months. This was due
to several problems. First was loss of a data card and hence all data from Oct. 2 to Nov. 13. Then,
beginning in early December, a number of apparent icing events rendered the anemometers and wind
vane inoperable for much of the month. In early January, the two 30 meter level (channels 1 and 2)
anemometers broke off the tower, apparently as a result of icing loads and high winds, and were not
replaced until March 3. Throughout winter and spring, frequent and severe icing events resulted in
significant data loss to the anemometers and wind vane. Note also much data loss from the relative
humidity sensor occurred as well. The RH sensor lost function due to loss of battery power with loss of
daylight (for recharge via the PV panels) and for unknown reasons, sensor function did not return with
return of sunlight in spring.
Data recovery summary table
Possible Valid Recovery
Label Units Height Records Records Rate (%)
Speed 30 A m/s 30 m 55,878 35,600 63.7
Speed 30 B m/s 30 m 55,878 34,822 62.3
Speed 20 m/s 20 m 55,878 39,748 71.1
Direction 29 ° 29 m 55,878 36,612 65.5
Temperature °C 55,878 48,823 87.4
RH-5 Humidity %RH %RH 55,878 14,196 25.4
iPack Voltmeter volts 55,878 49,800 89.1
Kaktovik Wind Resource Report Page 5
Anemometer data recovery
30 m A 30 m B 20 m
Year Month Possible Valid Recovery Valid Recovery Valid Recovery
Records Records Rate (%) Records Rate (%) Records Rate (%)
2009 Jun 720 720 100.0 720 100.0 720 100.0
2009 Jul 4,464 4,464 100.0 4,464 100.0 4,464 100.0
2009 Aug 4,464 4,464 100.0 4,464 100.0 4,464 100.0
2009 Sep 4,320 4,197 97.2 4,320 100.0 4,320 100.0
2009 Oct 4,464 228 5.1 228 5.1 228 5.1
2009 Nov 4,320 1,748 40.5 1,750 40.5 1,751 40.5
2009 Dec 4,464 1,033 23.1 750 16.8 750 16.8
2010 Jan 4,464 42 0.9 0 0.0 408 9.1
2010 Feb 4,032 0 0.0 0 0.0 3,971 98.5
2010 Mar 4,464 3,966 88.8 3,794 85.0 3,972 89.0
2010 Apr 4,320 3,602 83.4 3,213 74.4 3,483 80.6
2010 May 4,464 4,336 97.1 4,319 96.8 4,357 97.6
2010 Jun 4,320 4,202 97.3 4,202 97.3 4,262 98.7
2010 Jul 2,598 2,598 100.0 2,598 100.0 2,598 100.0
All data 55,878 35,600 63.7 34,822 62.3 39,748 71.1
Wind Speed
Wind data collected from the met tower, from the perspective of both mean wind speed and mean
power density, indicates an excellent wind resource when sufficiently manipulated. The extremely cold
arctic temperatures of Kaktovik contributed to the high wind power density. It is problematic, however,
analyzing wind data with significant concentrated data loss, such as occurred in Kaktovik with the
missing data card, broken 30 meter anemometers, and many icing events. To correct this problem,
synthetic data was inserted in the data gaps to create a more realistic wind speed data profile. To be
sure, long segments of synthetic data introduce uncertainty to the data set, but missing data does as
well. To overcome this uncertainty, improved data collection with heated sensors would be necessary.
But, considering the wind data collected and noting that two long-term airport AWOS data sources
confirm a robust wind resource in Kaktovik, continuing a wind study with heated sensors is not
absolutely necessary.
Anemometer data summary
Original data set Synthesized data set
Variable
Speed
30 A
Speed
30 B
Speed
20
Speed
30 A
Speed
30 B
Speed
20
Measurement height (m) 30 30 20 30 30 20
MMM wind speed (m/s)6.59 5.95 6.59 6.49 6.39 6.14
Max 10-min avg wind speed (m/s) 26.4 26.2 29.3 30.7 30.7 29.3
Max gust wind speed (m/s) 32.7 30.2 35.2
Kaktovik Wind Resource Report Page 6
Weibull k 1.82 1.82 1.68 1.63 1.63 1.62
Weibull c (m/s) 7.18 6.97 6.94 7.26 7.14 6.87
MMM power density (W/m²) 478 382 641 479 459 409
MMM energy content (kWh/m²/yr) 4,184 3,350 5,613 4,199 4,025 3,586
Energy pattern factor 2.16 2.15 2.49 2.55 2.57 2.58
Frequency of calms (%) 24.7 25.8 27.4 27.3 27.8 29.8
1-hr autocorrelation coefficient 0.952 0.950 0.958 0.957 0.956 0.957
Diurnal pattern strength 0.012 0.013 0.006 0.027 0.028 0.030
Hour of peak wind speed 23 21 1 4 5 4
Time Series
Time series calculations indicate high wind speed averages throughout the year, even during the
summer months. Because the 30 meter anemometers were inoperable (broken off the met tower) for
an extended period of time, the data summary graph below is presented with 20 meter anemometer
data which is more complete in original form.
20 m data summary
Original data Synthesized data
Mean
Max
10-min
Max
gust Mean
Std.
Dev.
Weibull
k Weibull c
Year Month (m/s) (m/s) (m/s) (m/s) (m/s) (m/s)
2009 Jun 5.73 11.7 14.0 5.73 2.20 2.87 6.45
2009 Jul 6.26 12.7 14.8 6.26 2.77 2.42 7.05
2009 Aug 5.78 14.7 18.6 5.78 2.63 2.33 6.51
2009 Sep 6.47 18.0 22.4 6.47 3.90 1.74 7.28
2009 Oct 2.68 7.4 8.3 6.14 3.65 1.72 6.88
2009 Nov 4.66 14.9 17.1 3.63 2.69 1.44 4.02
2009 Dec 8.07 24.8 29.5 7.68 5.11 1.57 8.58
2010 Jan 14.58 24.7 28.8 7.77 4.99 1.62 8.69
2010 Feb 7.29 29.3 35.2 7.23 5.33 1.41 7.96
2010 Mar 5.42 16.7 18.9 5.32 2.87 1.91 5.99
2010 Apr 4.80 17.1 20.1 4.54 2.82 1.71 5.11
2010 May 6.68 19.1 22.7 6.56 3.93 1.70 7.36
2010 Jun 6.85 19.5 23.5 6.79 4.13 1.72 7.64
2010 Jul 5.24 13.6 17.4 5.24 2.63 2.10 5.91
MMM annual 6.59 29.3 35.2 6.13 3.95 1.62 6.86
Kaktovik Wind Resource Report Page 7
Time series graph, synthesized data
Daily Wind Profile
The daily wind profile indicates a minor variation of wind speeds throughout the day, with lowest wind
speeds during the morning hours and highest wind speeds during late afternoon and early evening
hours. This perspective changes somewhat when considering monthly views of daily profiles as more
variation is observed.
Annual daily wind profile (synth. data)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
2
4
6
8
10 Seasonal Wind Speed Profile
Speed 30 A
Speed 30 B
Speed 20
0 6 12 18 24
0
1
2
3
4
5
6
7 Daily Wind Speed Profile
Hour of Day
Speed 30 A
Speed 30 B
Speed 20
Kaktovik Wind Resource Report Page 8
Monthly daily wind profiles (synth. data)
Probability Distribution Function
The probability distribution function (or histogram) of wind speed is a useful statistical tool to describe a
site with “normal” a wind range of wind speeds (normal is defined as the Raleigh distribution with a
Weibull k of 2.0). Given the data recovery problems in Kaktovik the probability distribution function
should be considered suspect in accuracy, both with original data and with synthesized data.
Wind Shear and Roughness
A wind shear power law exponent of 0.097 indicates very low wind shear at the site; hence turbine
construction at a low hub height is possibly a desirable option, although note again that data recovery
problems impact the accuracy of this calculation. Related to wind shear, a calculated surface roughness
0 5 10 15 20 25 30
0
1
2
3
4
5
6
7 Probability Distibution Function, All Sectors
Speed 20 (m/s)
Kaktovik Wind Resource Report Page 9
of 0.0059 meters (indicating the height above ground level where wind velocity would be zero) indicates
very smooth terrain (roughness description: lawn grass) surrounding the met tower, especially toward
the primary wind direction of northeast, location of a large lagoon (with a frozen surface most of the
year).
Vertical wind shear profile (synth. data), wind speed > 4 m/s
Wind shear by direction sector table (synth. data), wind speed > 4 m/s
Direction Sector
Time
Steps
Mean Wind Speed (m/s)Best-Fit
Power Law
Exp
Surface
Roughness (m)Speed 30 B Speed 20
348.75° - 11.25° 557 7.53 7.11 0.142 0.0212
11.25° - 33.75° 1,324 6.38 6.03 0.141 0.0199
33.75° - 56.25° 8,212 7.91 7.71 0.063 0.0000
56.25° - 78.75° 7,959 9.02 8.91 0.030 0.0000
78.75° - 101.25° 1,619 8.33 7.94 0.116 0.0045
101.25° - 123.75° 1,065 9.11 8.70 0.114 0.0038
123.75° - 146.25° 849 8.43 8.03 0.122 0.0065
146.25° - 168.75° 492 9.02 8.60 0.118 0.0051
168.75° - 191.25° 543 7.77 7.32 0.149 0.0298
191.25° - 213.75° 857 7.05 6.61 0.159 0.0456
213.75° - 236.25° 3,310 8.64 8.13 0.149 0.0296
236.25° - 258.75° 4,683 9.06 8.58 0.133 0.0134
258.75° - 281.25° 2,287 8.27 7.88 0.119 0.0055
281.25° - 303.75° 1,584 8.37 7.97 0.120 0.0057
303.75° - 326.25° 634 8.22 7.86 0.112 0.0031
326.25° - 348.75° 517 7.38 7.08 0.103 0.0015
0 2 4 6 8 10
0
20
40
60
80
100 Vertical Wind Shear Profile, All Sectors, 4 - 100 m/s
Mean Wind Speed (m/s)
Measured data
Power law fit (alpha = 0.0965)
Log law fit (z0 = 0.000773 m)
Kaktovik Wind Resource Report Page 10
Extreme Winds
Although thirteen months of data is minimal for calculation of extreme wind probability, use of a
modified Gumbel distribution analysis, based on monthly maximum winds vice annual maximum winds,
yields reasonably good results. Caution should be exercised though in that one month of data – October
2009 – had to be removed due to the lost data card and data recovery in general was problematic in
Kaktovik. That said, extreme wind analysis indicates a desirable situation in Kaktovik: moderately high
mean wind speed combined with relatively low (probable) extreme wind speeds. This may be explained
by particular climactic aspects of Kaktovik which because of its extreme northerly latitude, is not
exposed to Gulf of Alaska storm winds which tend to significantly increase the long-term probability of
damaging winds.
Industry standard reference of extreme wind is the 50 year, 10-minute average probable wind speed,
referred to as Vref. For Wainwright, this calculates to 35.4 m/s, below the threshold of International
Electrotechnical Commission (IEC) 61400-1, 3rd edition criteria (of 37.5 m/s) for a Class III site. Note that
Class III extreme wind classification is the lowest defined and all wind turbines are designed for this wind
regime.
Extreme wind sped probability table
Period (years)
Vref Gust IEC 61400-1, 3rd ed.
(m/s) (m/s) Class Vref, m/s
2 25.1 30.1 I 50.0
10 30.3 36.2 II 42.5
15 31.6 37.8 III 37.5
30 33.7 40.4 S designer-
specified5035.4 42.3
100 37.5 44.9
average gust factor:1.20
Extreme wind speed probability graph
24.0
29.0
34.0
39.0
44.0
49.0
0 10 20 30 40 50 60 70 80 90 100
Period, years
Vref
Gust
Kaktovik Wind Resource Report Page 11
Temperature and Density
Kaktovik experiences cool summers and very cold winters. The result is high air density. Calculated air
density exceeds standard air density for a sea level elevation (1.225 Kg/m3) by over eight percent. This is
advantageous in wind power operations as wind turbines produce more power at low temperatures
(high air density) than at standard temperature and density.
Temperature and density table
Temperature Air Density
Mean Min Max Mean Min Max
Month (°C) (°C) (°C) (kg/m³) (kg/m³) (kg/m³)
Jan -25.8 -38.6 -11.4 1.427 1.348 1.504
Feb -22.7 -40.1 -12.6 1.410 1.354 1.513
Mar -24.2 -35.7 -11.7 1.412 1.224 1.485
Apr -10.3 -29.7 1.5 1.343 1.284 1.449
May -4.0 -21.4 8.0 1.294 1.224 1.401
Jun 2.4 -1.1 10.0 1.280 1.246 1.296
Jul 6.7 1.0 17.4 1.261 1.214 1.287
Aug 5.7 -0.4 14.7 1.265 1.225 1.293
Sep 1.9 -9.5 16.3 1.283 1.219 1.338
Oct -4.0 -6.1 -2.4 1.229 1.224 1.321
Nov -21.1 -30.0 -15.8 1.325 1.224 1.451
Dec -17.9 -31.9 -1.7 1.383 1.299 1.462
Annual -9.4 -40.1 17.4 1.325 1.214 1.513
Monthly temperature boxplot
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
-50
-40
-30
-20
-10
0
10
20 Monthly Statistics for Temperature
max
daily high
mean
daily low
min
Kaktovik Wind Resource Report Page 12
Air density DMap
Wind Speed Scatterplot
The wind speed versus temperature scatterplot below indicates that a substantial percentage of wind in
Kaktovik coincides with very cold temperatures, as one would expect give the location on the Arctic
Ocean coast. Temperatures have fallen below -40°C, the minimum operating temperature of arctic-
capable wind turbines presently operating in Alaska, but only a few times during the measurement
period.
Wind speed versus temperature scatterplot (synth. data)
Kaktovik Wind Resource Report Page 13
Wind direction
Wind frequency rose data indicates highly directional winds from the northeast and southwest. Power
density rose data (representing the power in the wind) indicates power winds are very strongly
directional, from 060°T and directly opposite, from 240°T. Calm frequency (percent of time that winds at
30 meter level are less than 3.5 m/s) was 27 percent during the met tower test period, but this statistic
may be suspect due to the large amount of data loss.
Wind frequency rose Mean value rose
Total energy rose Scatterplot rose
Kaktovik Wind Resource Report Page 14
Wind density roses by month
Turbulence
Turbulence intensity at the Kaktovik test site is well within acceptable standards with an IEC 61400-1, 3rd
edition (2005) classification of turbulence category C, which is the lowest defined. Mean turbulence
intensity at 15 m/s is 0.076 (at 20 meters).
Turbulence intensity, all wind sectors
0 5 10 15 20 25 30 35
0.0
0.1
0.2
0.3
0.4
0.5
0.6 Turbulence Intensity at 20 m, All Sectors
Wind Speed (m/s)
Representative TI
IEC Category A
IEC Category B
IEC Category C
Kaktovik Wind Resource Report Page 15
Turbulence intensity, NE to ENE wind sector
Turbulence intensity by direction
Turbulence table (20 m anemometer)
Bin Bin Endpoints
Records
in Bin
Mean
TI
Std.
Deviation
of TI
Represen
tative TI Peak TI
Midpoint Lower Upper
(m/s) (m/s) (m/s)
1 0.5 1.5 1,676 0.363 0.155 0.561 1.111
2 1.5 2.5 3,458 0.174 0.084 0.282 1.250
3 2.5 3.5 4,851 0.115 0.049 0.178 0.515
4 3.5 4.5 4,924 0.090 0.037 0.137 0.400
5 4.5 5.5 4,654 0.076 0.031 0.116 0.378
6 5.5 6.5 3,863 0.073 0.027 0.108 0.309
0 5 10 15 20 25 30
0.0
0.1
0.2
0.3
0.4
0.5
0.6 Turbulence Intensity at 20 m, 45° - 75°
Wind Speed (m/s)
Representative TI
IEC Category A
IEC Category B
IEC Category C
Kaktovik Wind Resource Report Page 16
7 6.5 7.5 3,671 0.074 0.024 0.105 0.269
8 7.5 8.5 2,936 0.073 0.021 0.101 0.320
9 8.5 9.5 2,328 0.073 0.019 0.098 0.326
10 9.5 10.5 1,826 0.074 0.017 0.096 0.231
11 10.5 11.5 1,579 0.074 0.016 0.094 0.159
12 11.5 12.5 1,134 0.074 0.015 0.094 0.183
13 12.5 13.5 587 0.076 0.016 0.097 0.154
14 13.5 14.5 499 0.077 0.015 0.096 0.152
15 14.5 15.5 404 0.076 0.014 0.095 0.166
16 15.5 16.5 261 0.080 0.013 0.097 0.123
17 16.5 17.5 189 0.080 0.014 0.098 0.145
18 17.5 18.5 95 0.080 0.017 0.102 0.183
19 18.5 19.5 46 0.075 0.011 0.088 0.104
20 19.5 20.5 15 0.076 0.009 0.088 0.097
21 20.5 21.5 40 0.074 0.008 0.084 0.086
22 21.5 22.5 74 0.072 0.010 0.084 0.096
23 22.5 23.5 73 0.074 0.010 0.087 0.100
24 23.5 24.5 34 0.068 0.007 0.078 0.085
25 24.5 25.5 28 0.062 0.007 0.071 0.080
26 25.5 26.5 33 0.060 0.007 0.068 0.073
27 26.5 27.5 29 0.063 0.008 0.072 0.089
28 27.5 28.5 13 0.064 0.006 0.072 0.076
29 28.5 29.5 4 0.067 0.006 0.074 0.072
30 29.5 30.5 0
Airport AWOS Data
In 2005, Alaska Energy Authority (AEA) personnel analyzed the wind resource at all Automated Weather
Observing Station (AWOS) and Automated Surface Observing System (ASOS) sites in Alaska. At most
stations, AWOS/ASOS data has been collected for twenty-five or more years. Barter Island DEW Station
(ICAO station identifier: PABA) data has been collected by an AWOS since 1973. AWOS data summarized
below is through 2004.
The AEA report documents data from AWOS sensor, which is 8 meters above ground level. To compare
this data to the met tower lower sensor height of 20, the AWOS data was adjusted using an exponent
extrapolation function with a power law exponent value of 0.097, the measured shear value at the met
tower site. Comparing to the met tower 20 meter anemometer (both the collected data set and the
synthesized data set), one can see that average wind speeds recorded by the met tower are
approximately that predicted by the Barter Island DEW Station AWOS data. By itself, the AWOS data
indicates a Class 6 wind resource, hence confirming the wind resource measured at the met tower site,
data recovery problems aside.
Kaktovik Wind Resource Report Page 17
DEW Station/met tower data comparison
Barter Island DEW Met Tower, 20m anem.
AWOS, 8
m sensor
Data adj.
to 20 m
Collected
data
Synthesized
data
(m/s) (m/s) (m/s) (m/s)
Jan 6.8 7.43 14.58 7.77
Feb 5.9 6.45 7.29 7.23
Mar 5.7 6.23 5.42 5.32
Apr 5.2 5.68 4.80 4.54
May 6.0 6.56 6.68 6.56
Jun 5.2 5.68 6.69 6.64
Jul 5.3 5.79 5.88 5.88
Aug 5.2 5.68 5.78 5.78
Sep 5.8 6.34 6.47 6.47
Oct 7.0 7.65 2.68 6.14
Nov 6.9 7.54 4.66 3.63
Dec 6.2 6.78 8.07 7.68
Annual 5.9 6.48 6.59 6.14