HomeMy WebLinkAboutCity of Napaskiak Wind Power and Heat Recovery Project Feasibility Study - Oct 2015 - REF Grant 7040016
Napaskiak Wind Power and Heat
Recovery
AEA Grant #740016
Marsh Creek, LLC
2000 E 88th Ave
Anchorage, AK 99507
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Table of Contents
I. Executive Summary ............................................................................................................................... 3
II. Wind Power and Feasibility Study Background .................................................................................... 3
III. Project Goals and Partners ............................................................................................................... 4
Project Contacts ........................................................................................................................................ 4
IV. Community of Napaskiak .................................................................................................................. 4
V. Napaskiak Inc. Skystream Wind Turbine ............................................................................................... 5
History ....................................................................................................................................................... 5
Performance ............................................................................................................................................. 5
Appendix A Wind Resource Assessment ...................................................................................................... 7
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I. Executive Summary
Analysis by Marsh Creek LLC confirms that the AWS Truepower wind resource map is correct in assigning
a Class 2 designation for Napaskiak. Due to a nearby stand of trees, there is a very high wind shear at
the site as well.
Despite the high cost of imported fuel, the known costs to install utility scale wind power equipment in
rural Alaska does not make economic sense in a Class 2 wind resource – especially with the wind shear
effect wear and tear on equipment that are likely at this site.
However, the success of the Skystream Wind Turbine installed at the Napaskiak Corporation Store
provides encouragement for the future of small wind in Napaskiak.
II. Wind Power and Feasibility Study Background
Marsh Creek staff traveled to Napaskiak in August of 2011 to scout sites for installing an anemometer
tower. Three sites were discussed. The final choice was a site behind the diesel plant and tank farm in a
“meadow”, which is a very swampy area. Not swampy enough to attract migratory birds, but too mucky
to work on when not frozen. We waited until December to install the anemometer tower.
USFWS Biologist Kimberly Klein affirmed that there are no birds of concern in the area. Although we
need to be careful not to site the project in a flight path for migratory birds or in a hunting area for owls,
hawks, or eagles overall USFWS does not have much concern with wind projects in this particular area.
According to all local contacts there is no reason to believe that SHPO will have a concern regarding
historical sites in this area.
A permit application to install the tower was sent to FAA and approved.
The City of Napaskiak collected data to assess their wind resource from December 2011 through April of
2014. Data was collected consistently except for when a card blew away while being changed out in a
blizzard losing everything from February 3 through March 5, 2012. The missing month and minor data
loss to icing events was synthesized with a Windographer software gap filling utility.
A joint meeting was held with the City Council and Tribal Council in April of 2014. Marsh Creek
personnel explained the wind resource would not support a utility scale wind project. The Council
members and utility staff understood, but also pressed that something needs to be done to alleviate the
high cost of energy in Napaskiak.
A Sky Stream is installed by the Corporation Store. Manager Phillip Nicholai showed us data sheets
showing a production of 2500 kWhs in 18 months. Performance has since improved as the tower was
leveled and production increased. The turbine is now routinely leveled and power production has
stayed high. The village is very interested in more small wind development to offset the high cost of
power.
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III. Project Goals and Partners
Marsh Creek set out to prove the wind resource in Napaskiak was worthy of a utility scale wind
development to help the village’s struggle with the high cost of imported fuel and diesel power.
Fuel prices dropped from $5.69 in January 2012 to $4.0595 in October 2014, but no one can predict
where the price will go next.
While utility scale wind is not economical to develop in this wind regime, small wind could serve a useful
purpose. While Marsh Creek did not spend a lot of time gathering information about the one Skystream
installed at the Napakiak Corporation Building and Store, we believe this information will be useful and
necessary for future efforts to install more small wind turbines on large community loads.
Project Contacts
Entity Contact Position E-mail Phone
Native
Village of
Napaskiak
Stephen
Maxie
Tribal
Administrator
stephenmaxie@yahoo.com
737-7364
City of
Napaskiak
Fanny
Stevens
City Clerk cityofnapaskiak@live.com 737-7432
Marsh Creek
LLC
Maggie
McKay
Project
Coordinator
Maggie.mckay@marshcreekllc.com 343-0407
Marsh Creek
LLC
Connie
Fredenberg
Community
Liaison
Connie.fredenberg@marshcreekllc.com 444-6220
Alaska
Energy
Authority
Josh Craft Wind Program jcraft@aidea.org 771-3000
IV. Community of Napaskiak
Napaskiak has historically been occupied by Yup’ik Eskimos. First reported by the U.S. Coast & Geodetic
Survey in 1867, the 1880 U.S. Census reported a population of 196. By 1890 the population had
dropped to 97 and was as low as 67 in 1939. The City was incorporated in 1971. The official population
in 2014 was 451.
Located on the east bank of the Kuskokwim River along Napaskiak Slough and 7 miles southeast of
Bethel, Napaskiak is a traditional Yup’ik Eskimo village dependent upon fishing and subsistence
activities.
The weather is strongly influenced by storms and patterns in the Bering Sea and also by inland
continental weather. Average annual precipitation is 16 inches, with 50 inches of snowfall. Summer
temperatures range from 42 to 62 degrees F, and winter temperatures average -2 to 19 degrees F.
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V. Napaskiak Inc. Skystream Wind Turbine
History
The 3.7 kW Skystream Wind Turbine was purchased from Susitna Energy in 2011 and installed with
assistance from Kirk Garoutte. After initial issues with keeping the wind turbine level, there have been
no maintenance issues until just recently. In January the “brushes” wore out due to continued
performance in higher wind conditions than normal. Repairs are scheduled for the first week of March
2015. Down time will end up being less than one month.
Performance
Anecdotal information from Corporation Manager Phillip Nicholai is that the wind turbine has
outperformed its expectations. He reports a monthly savings of 30% of the building’s pre-wind kWh
usage. In February of 2014 he reports there was a 40% savings.
Jay Jaeger, a representative from Xeres, reported that the Skystream (formerly a Southwest Wind
turbine) is a robust machine with a reputation of little to no maintenance issues. When questioned
about the effects of wind shear, he offered that the Skystream is far shorter than the utility scale wind
turbines and is unaffected by the wind shear measured at the anemometer site.
Kirk Garoutte was expected to be in Napaskiak in March 2015 to replace the “bushings” in the wind
turbine. Other than leveling, this is the first maintenance issue in the 6 years it’s been up.
VI. Conclusion
Although utility scale wind is not economical at this time, Marsh Creek sees benefit in the following
efforts to diesel consumption in the village
Line Loss
As part of the wind study Marsh Creek looked at the utility’s annual reports and monthly ledgers for
2011 and 2012. A high level of line loss was noted at 21.48% in 2011, the last year reviewed by the RCA,
and in 2012 the kWhs generated made no sense. The RCA holds utilities to a 12% line loss standard. The
PCE rate is lowered for utilities exceeding the 12% level.
Marsh Creek noted that part of the problem was correctly documenting total kWh generated for
calendar year 2012. The meter at the plant rolled over and no one understood how to properly
document the change. Marsh Creek provided a correction to several previous month’s readings and
written directions for how to deal with a meter rollover to prevent future problems.
Another contributing factor was the Tribal Office metering. The meter didn’t register any usage, but
there was power in the building. Replacing the meter with another didn’t change anything. We
recommended an electrician investigate how the meter was wired. That has been done.
In a recent review of the 2014 annual report, the line loss was still unacceptably high at 17.62%.
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According to the utility clerk in a conversation August 2015, line loss now varies between 12-
16%. Although still high, it is more acceptable. We recommend the utility continue to investigate
causes for this line loss.
Small Wind Power in Napaskiak
The village corporation is building a new store. The old store will retain its Skystream wind turbine and
be rented out to “someone”.
The corporation was so pleased with the small Skystream that they plan to install a 10 kW Ventera on
the new store. Excess power will be put back into the grid at no cost to the utility.
The store is one of the largest customers for the utility. With the contribution of the Skystream, the
store still used 5-6,000 kWhs monthly. Loss of that revenue may be problematic for the utility, but I
don’t think there will be any issues with the diesel plant at that level.
The City is considering putting a wind turbine on their washeteria. Marsh Creek recommends that they
use it to heat water, rather than connect to provide electric.
Ways to Increase the Power Cost Equalization subsidy rate for the Community
Marsh Creek recommended that all the Community Facilities should be on PCE. Several City-owned
facilities were in the unbilled section while the utility had plenty of spare kWhs for their community
facility quota. A blank application was provided to the clerk.
Marsh Creek advised the City to pay all Community Facility Bills (even if it seems silly to write yourself a
check – do it). PCE credit will not be given for a facility that isn’t current with its payments.
If any City or Tribal staff also provides services to the electric utility, bill the utility for their time. It can
be on a % basis, rather than hourly, to make it easier.
This way you get your money back for paying the electric bills AND you increase the allowable non-fuel
expenses for the utility on the annual report to the RCA. Increased expenses on the annual report
equals a higher PCE rate for the community.
If the utility doesn’t collect enough revenue to pay for all expenses, subsidize the operation by buying
fuel – NOT by paying for non-fuel expenses such as personnel, parts, repairs, etc. The RCA tracks down
the source of all non-fuel expenses and disallows expenses paid for by any entity outside of the utility.
The RCA does not track down the source of fuel payments, though, so you get credit for all fuel costs
even if it is subsidized.
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Appendix A Wind Resource Assessment
Napaskiak, Alaska Wind Resource
Assessment Report
Napaskiakmet tower, photo by Connie Fredenberg
May 7, 2013
Douglas Vaught, P.E.
V3 Energy, LLC
Eagle River, Alaska
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Summary
The wind resource measured at the Napaskiak met tower site is fair with mean annual wind speed of
5.66 m/s and wind power density of 208 W/m2 at 34 meters above ground level. This confirms the AWS
Truepower wind resource map which predicts Class 2 winds at Napaskiak. Although the wind resource
in Napaskiak is modest compared to communities on the Bering Sea coast, development of renewable
power in the village may be viable with turbines specifically suited to lower wind environments. Also of
consideration is the high cost of fuel in Napaskiak and the environment risk of transporting and storing
fossil fuel. Wind power provides a long-term renewable energy alternative for Napaskiak that has the
potential to buffer residents from unpredictable variations of the petroleum market. These and other
issues will be explored in a follow-up feasibility study.
Met tower data synopsis
Data dates 12/04/2011 to 04/02/2013 (16 months)
Wind power density mean, 34 m 208 W/m
2
Wind speed mean, 34 m 5.66 m/s (12.6 mph)
Max. 10-min wind speed 28.6 m/s
Maximum 2-sec. wind gust 37.1 m/s (83.0 mph), December 2011
Weibull distribution parameters k = 2.16, c = 6.43 m/s
Wind shear power law exponent 0.303 (high)
Roughness class 3.79 (description: forest)
IEC 61400-1, 3rd ed. classification Class III-A (at 34 meters)
Turbulence intensity, mean (at 34 m) 0.133 (at 15 m/s)
Calm wind frequency (at 34 m) 28% (< 4 m/s) (16 mo. measurement period)
Test Site Location
A 34 meter NRG Systems, Inc. tubular-type meteorological (met) tower was installed in Napaskiak in an
open area of corporation land located
south of the village and east of the airport
runway. Napaskiak is located on the east
bank of the Kuskokwim River along the
Napaskiak Slough, about seven miles
southeast of Bethel. It is a traditional
Yup’ik Eskimo village, population of 434
people (2012 Alaska Dept. of Labor
estimate), largely dependent on fishing
and subsistence activities (Alaska DCED
website). Napaskiak is strongly influenced by storms and patterns in the Bering Sea and also by inland
continental weather. Average annual precipitation is 16 inches, with 50 inches of snowfall.
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AWS Truepower wind power class overlay; Google Earth image
Site information
Site number 1101
Latitude/longitude N 60° 42.157’ W 161° 45.649’
Time offset -9 hours from GMT (Yukon/Alaska time zone)
Site elevation 1 meter (3 ft.)
Datalogger type NRG Symphonie, 10 minute averaging time step
Tower type Tubular tall tower, 6-inch diameter, 34 meter height
Tower sensor information
Channel Sensor type SN Height Multiplier Offset Orientation
1 NRG #40C anemometer 87878 34.1 m 0.757 0.38 338 T
2 NRG #40C anemometer 87863 34.1 m 0.757 0.37 158 T
3 NRG #40C anemometer 88311 18.2 m 0.758 0.34 338 T
7 NRG #200P wind vane 34 m 0.351 047 047 T
9 NRG #110S Temp C 4 m 0.136 -86.383 Not avail.
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Google Earth image, Napaskiak
Topographic map
Data Quality Control
Data was filtered to remove presumed icing events that yield false zero wind speed data and non-variant
wind direction data. Data that met criteria listed below were automatically filtered. In addition, data
was manually filtered for obvious icing that the automatic filter didn’t catch, and invalid or low quality
data for situations such as logger initialization and other situations.
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Anemometer icing – data filtered if temperature < 1°C, speed SD = 0, and speed changes < 0.25
m/s for minimum 2 hours
Vane icing – data filtered if temperature < 1°C and vane SD = 0 for minimum of 2 hours
Tower shading of 34 meter A and B paired anemometers – refer to graphic below
Note that all data was lost for the period February 3 to March 5, 2012 due to a misplaced data card.
Missing data, due to the lost data card and from icing loss, was synthesized with a Windographer
software gap filling utility. This smooths the data somewhat and results in a more realistic and likely
representation of actual wind speed during the time periods of missing data.
Sensor data recoverytable
Data Column
Possible
Records
Valid
Records
Recovery
Rate (%)
Unflagged
data Icing Invalid
Tower
shading
Speed 34 m A 69,894 56,415 80.7% 56,415 3,534 13 6,375
Speed 34 m B 69,894 59,627 85.3% 59,627 2,726 8 3,112
Speed 20 m 69,894 63,173 90.4% 63,173 2,273 14 0
Direction 34 m 69,894 60,064 85.9% 60,064 5,329 67 0
Temperature 69,894 65,449 93.6% 65,449 0 11 0
Sensor data recovery rate by month
Sensors
Year Month 34 m A 34 m B 20 m Vane Temp
2011 Dec 63.1 56.4 64.7 88.0 100.0
2012 Jan 73.6 97.3 99.3 97.1 100.0
2012 Feb 8.0 8.9 8.9 8.9 8.9
2012 Mar 73.9 81.2 84.7 44.9 85.9
2012 Apr 89.9 95.1 100.0 100.0 100.0
2012 May 85.6 97.7 100.0 99.5 100.0
2012 Jun 89.3 96.7 100.0 100.0 100.0
2012 Jul 93.7 92.5 100.0 100.0 100.0
2012 Aug 98.2 91.7 100.0 100.0 99.8
2012 Sep 88.1 90.7 100.0 100.0 100.0
2012 Oct 82.4 92.4 100.0 97.1 100.0
2012 Nov 82.0 89.5 89.3 89.2 100.0
2012 Dec 90.4 95.7 100.0 92.1 100.0
2013 Jan 93.0 89.7 96.6 69.7 100.0
2013 Feb 86.8 94.9 99.7 93.7 100.0
2013 Mar 87.9 88.4 96.7 91.6 100.0
2013 Apr 97.5 95.5 100.0 100.0 100.0
All data 81.4 85.5 90.6 86.6 93.8
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Tower shading filter plot
Icing Data Loss, December 2011
Wind Speed
Anemometer data obtained from the met tower, from the perspectives of both mean wind speed and
mean wind power density, indicate a relatively fair wind resource. Note that cold temperatures
contributed to a higher wind power density than standard conditions would yield for the measured
mean wind speeds.
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Anemometer data summary (filtered data)
Variable Speed 34 m A Speed 34 m B Speed 20 m
Measurement height (m) 34.1 34.1 18.2
Mean wind speed (m/s) 5.71 5.65 4.65
MoMM wind speed (m/s) 5.66 5.62 4.64
Median wind speed (m/s) 5.50 5.40 4.40
Max 10-min avg wind speed (m/s) 28.4 28.6 22.8
Max gust wind speed (m/s) 36.7 37.1 34.1
Weibull k 2.16 2.11 2.06
Weibull c (m/s) 6.43 6.35 5.24
Mean power density (W/m²) 207 213 120
MoMM power density (W/m²) 201 208 118
Mean energy content (kWh/m²/yr) 1,811 1,862 1,055
MoMM energy content (kWh/m²/yr) 1,764 1,820 1,037
Energy pattern factor 1.773 1.791 1.832
Frequency of calms (%) (< 4 m/s) 29.2 30.5 44.6
MoMM = mean of monthly means
Anemometer data summary (with filtered and gap-filled data)
Variable Speed 34 m A Speed 34 m B Speed 20 m
Mean wind speed (m/s) 5.65 5.60 4.61
MoMM wind speed (m/s) 5.63 5.60 4.61
Weibull k 2.13 2.09 2.05
Weibull c (m/s) 6.37 6.30 5.19
Mean power density (W/m²) 204 209 119
MoMM power density (W/m²) 200 206 117
Mean energy content (kWh/m²/yr) 1,784 1,832 1,038
MoMM energy content (kWh/m²/yr) 1,752 1,803 1,023
MoMM = mean of monthly means
Time Series
Time series calculations indicate higher wind speeds during the winter months compared to the summer
months. This correlates well with Napaskiak’s load profile where there is high demand for electricity
and heat during winter months and lower energy demand during summer. The daily wind profile
(annual basis) indicates relatively even wind speeds throughout the day with slightly higher wind speeds
during night hours.
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34 m A anemometer data summary
Mean Max Gust
Std.
Dev.
Weibull
k
Weibull
c
Year Month (m/s) (m/s) (m/s) (m/s) (-) (m/s)
2011 Dec 8.03 28.4 36.7 3.30 1.52 8.37
2012 Jan 6.05 13.4 19.3 2.90 2.19 6.81
2012 Feb 5.30 15.5 21.9 2.84 1.94 5.97
2012 Mar 4.38 13.5 17.8 2.46 1.82 4.92
2012 Apr 4.50 17.2 21.6 2.34 1.99 5.06
2012 May 4.88 10.6 14.4 1.82 2.90 5.47
2012 Jun 4.57 11.8 15.5 1.72 2.84 5.13
2012 Jul 5.25 15.9 21.9 2.44 2.26 5.92
2012 Aug 5.91 16.1 22.4 3.18 1.94 6.66
2012 Sep 5.30 14.3 19.7 2.49 2.24 5.97
2012 Oct 6.85 16.5 24.6 2.99 2.40 7.70
2012 Nov 7.04 14.2 20.4 2.47 3.12 7.88
2012 Dec 5.92 14.7 20.0 2.65 2.33 6.65
2013 Jan 6.49 15.5 19.7 2.52 2.79 7.29
2013 Feb 5.35 14.3 18.6 2.49 2.24 6.02
2013 Mar 5.72 16.3 20.4 2.70 2.20 6.43
2013 Apr 2.41 6.0 6.4 1.46 1.61 2.67
All Data 5.63 28.4 36.7 2.76 2.13 6.37
Monthly time series, mean wind speeds (gap-filled)
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Daily wind profile (annual)
Probability Distribution Function
The probability distribution function (PDF), or histogram, of the Napaskiak met tower site wind speed
indicates a shape curve dominated by moderate wind speeds and is reflective of a “normal” shape
curve, known as the Rayleigh distribution (Weibull k = 2.0), which is defined as the standard wind
distribution for wind power analysis. As seen below in the wind speed distribution of the 34 meter A
anemometer, the most frequently occurring wind speeds are between 3 and 7 m/s with very few wind
events exceeding 18 m/s (note that the cutout speed of most wind turbines is 25 m/s; see following
wind speed statistical table).
PDF of 34 m A anemometer (all data)
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Weibull k shape curve table
Weibull values table, 34m A anemometer
Weibull Weibull Mean Proportion Power R
k c Above Density Squared
Algorithm (-) (m/s) (m/s) 5.706 m/s (W/m2) (-)
Maximum likelihood 2.157 6.431 5.695 0.462 201 0.9938
Least squares 2.122 6.473 5.733 0.465 208 0.9922
WAsP 2.124 6.408 5.675 0.458 202 0.9923
Actual data 5.706 0.458 202
Occurrence by wind speed bin (34 m A anemometer)
Bin Endpoints
(m/s) Occurrences Cumulat.
Bin Endpoints
(m/s) Occurrences Cumulat.
Lower Upper No. Percent Percent Lower Upper No. Percent Percent
0 1 1,480 2.43% 2.43% 15 16 85 0.14% 99.89%
1 2 3,145 5.17% 7.60% 16 17 19 0.03% 99.92%
2 3 5,447 8.95% 16.55% 17 18 9 0.01% 99.93%
3 4 7,381 12.13% 28.68% 18 19 6 0.01% 99.94%
4 5 9,059 14.89% 43.57% 19 20 5 0.01% 99.95%
5 6 8,549 14.05% 57.62% 20 21 8 0.01% 99.97%
6 7 7,910 13.00% 70.62% 21 22 6 0.01% 99.98%
7 8 6,273 10.31% 80.93% 22 23 3 0.00% 99.98%
8 9 4,261 7.00% 87.93% 23 24 1 0.00% 99.98%
9 10 2,968 4.88% 92.81% 24 25 3 0.00% 99.99%
10 11 2,010 3.30% 96.11% 25 26 0 0.00% 99.99%
11 12 1,141 1.88% 97.99% 26 27 2 0.00% 99.99%
12 13 592 0.97% 98.96% 27 28 5 0.01% 100.00%
13 14 297 0.49% 99.45% 28 29 1 0.00% 100.00%
14 15 183 0.30% 99.75% 29 30 0 0.00% 100.00%
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Wind Shear and Roughness
Wind shear at the Napaskiak met tower site was calculated with the 34 m A and 20 m anemometers,
both of which are oriented toward 338° T. The calculated power law exponent of 0.303 indicates a very
high wind shear at the site. Calculated surface roughness at the site is 0.86 m (the height above ground
where wind speed would be zero) for a roughness class of 3.79 (description: forest). Although the area
surrounding the met tower is not covered by very tall trees, they are high and dense enough to result in
significant roughness and wind shear. Given the high power law exponent, extrapolation of wind speed
above 34 meters should be done with caution and the shear likely decreases with elevation above
ground level.
Vertical wind shear profile
Comparative wind shear profiles
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Wind shear by direction sector table
Mean Wind Speed (m/s)
Direction
Sector
Time
Steps
Speed 34
m A
Speed 20
m
Best-fit
Power Law
Exponent
Surface
Roughness
(m)
345° - 015° 11,466 6.02 5.14 0.252 0.465
015° - 045° 7,766 6.05 5.03 0.295 0.833
045° - 075° 5,788 5.99 4.96 0.300 0.877
075° - 105° 2,575 5.18 4.01 0.406 2.097
105° - 135° 2,072 4.94 3.80 0.419 2.261
135° - 165° 4,727 7.03 5.28 0.456 2.743
165° - 195° 5,399 6.15 4.95 0.347 1.378
195° - 225° 3,116 5.05 4.14 0.316 1.045
225° - 255° 2,286 4.46 3.77 0.268 0.590
255° - 285° 4,044 4.60 4.03 0.212 0.220
285° - 315° 5,813 5.21 4.53 0.224 0.287
315° - 345° 1,628 5.07 4.30 0.263 0.550
Wind shear by direction sector graph
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Extreme Winds
A modified Gumbel distribution analysis, based on monthly maximum winds vice annual maximum
winds, was used to predict extreme winds at the Napaskiak met tower site. Sixteen months of data
though are minimal at best and hence results should be viewed with considerable caution.
Nevertheless, with data available the predicted Vref (maximum ten-minute average wind speed) in a 50
year return period (in other words, predicted to occur once every 50 years) is 34.2 m/s. This result
classifies the site as Class III by International Electrotechnical Commission 61400-1, 3
rd edition (IEC3)
criteria. IEC extreme wind probability classification is one criteria – with turbulence the other – that
describes a site with respect to suitability for particular wind turbine models. Note that the IEC3 Class III
extreme wind classification indicates moderate winds and that turbines installed at this location can be
IEC3 Class III rated. It would be highly beneficial, however, to obtain more met tower data before
making a final determination of IEC extreme wind classification.
Site extreme wind probability table, 34 m data
Vref Gust IEC 61400-1, 3rd ed.
Period (years) (m/s) (m/s) Class Vref, m/s
3 23.6 32.0 I 50.0
10 29.0 39.2 II 42.5
20 30.3 41.0 III 37.5
30 32.6 44.1 S designer-
specified5034.2 46.3
100 36.5 49.4
average gust factor:1.35
Extreme wind graph, by annual method
20.0
25.0
30.0
35.0
40.0
45.0
50.0
55.0
3 10 20 30 50 100
Period, years
Napaskiak Extreme Wind Probability
Vref (m/s)
Gust (m/s)
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Temperature, Density, and Relative Humidity
The Napaskiak met tower site experiences cool summers and cold winters with resulting higher than
standard air density. Calculated mean-of-monthly-mean (or annual) air density during the met tower
test period exceeds the 1.225 kg/m
3 standard air density for a sea level elevation by 5.8 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 (°C) Temperature (°F) Air Density
Mean Min Max Mean Min Max Mean Min Max
Month (°C) (°C) (°C) (°F) (°F) (°F) (kg/m³) (kg/m³) (kg/m³)
Jan -17.2 -38.6 4.3 1.0 -37.5 39.7 1.382 1.272 1.504
Feb -15.0 -38.0 1.4 5.0 -36.4 34.5 1.302 1.225 1.501
Mar -11.3 -35.4 6.2 11.6 -31.7 43.2 1.341 1.225 1.484
Apr -2.0 -26.7 10.9 28.3 -16.1 51.6 1.302 1.242 1.432
May 5.1 -12.0 18.0 41.2 10.4 64.4 1.269 1.212 1.351
Jun 11.4 0.5 23.9 52.5 32.9 75.0 1.240 1.188 1.290
Jul 12.0 6.3 23.6 53.6 43.3 74.5 1.238 1.189 1.263
Aug 12.3 4.8 25.6 54.2 40.6 78.1 1.236 1.181 1.270
Sep 7.0 -1.8 14.6 44.5 28.8 58.3 1.260 1.226 1.300
Oct 0.9 -8.2 12.6 33.7 17.2 54.7 1.288 1.235 1.332
Nov -9.9 -19.5 5.9 14.3 -3.1 42.6 1.341 1.265 1.391
Dec -12.3 -37.1 4.0 9.8 -34.8 39.2 1.355 1.273 1.495
Annual -1.5 -38.6 25.6 29.3 -37.5 78.1 1.296 1.181 1.504
Napaskiak temperature boxplot graph
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Wind Speed Scatterplot
The wind speed versus temperature scatterplot below indicates cold temperatures at the Napaskiak met
tower site with a preponderance of below freezing temperatures. During the met tower test period,
temperatures were often below -20° C (-4° F), the minimum operating temperature for most standard-
environment wind turbines. Note that arctic-capable (operational rating to -40°C) wind turbines would
be required at Napaskiak, but that extreme cold temperatures, although not infrequent, are associated
with generally calm wind conditions.
Wind speed/temperature
Wind Direction
Wind frequency rose data indicates that winds at the Napaskiak met tower site are primarily bi-
directional, with northerly and southerly winds predominating. The mean value rose indicates that east-
southerly winds are of higher intensity than northerly winds, but with more frequent northerly winds,
the energy winds are mostly balanced between northerly and southerly.
Calm frequency (the percent of time that winds at the 34 meter level are less than 4 m/s, a typical cut-in
speed of larger wind turbines) was 28 percent during the 16 month test period.
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Wind frequency rose Mean value rose
Wind energy rose Scatterplot rose of wind power density
Turbulence
The turbulence intensity (TI) calculated from the 34 m A anemometer at the Napaskiak met tower site is
relatively high with a mean turbulence intensity of 0.133 and a representative turbulence intensity of
0.161 at 15 m/s wind speed, indicating fairly rough air for wind turbine operations. This equates to an
International Electrotechnical Commission (IEC) 61400-1, 3
rd Edition (2005) turbulence category B, which
is the middle defined category.
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Note however that data from the 34 m B anemometer indicates IEC 61400-1 Category A turbulence,
which is the highest defined category. Data from the 20 m anemometer is more turbulent yet, at IEC
61400-1 Category S, or special conditions. The fairly high turbulence at the Napaskiak met tower is due
to the surrounding trees and brush with resultant high roughness. Smoother air would be found at
higher elevation above ground level as the effect of surface roughness diminishes with height.
Turbulence synopsis
34 m A anem. 34 m B anem. Legend
Sector
Mean TI
at 15
m/s
Repres.
TI at 15
m/s
IEC3
Category
Mean TI
at 15
m/s
Repres.
TI at 15
m/s
IEC3
Category
IEC3
Categ.
Mean TI at
15 m/s
all 0.133 0.161 B 0.140 0.164 A S >0.16
315° to 045° 0.147 0.165 A 0.147 0.166 A A 0.14-0.16
045° to 135° 0.138 0.181 B 0.138 0.165 B B 0.12-0.14
135° to 225° 0.130 0.155 B 0.137 0.162 B C 0-0.12
225° to 315° - - - - - -
Turbulence rose, 34m A anemometer
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Turbulence rose, 20m anemometer
Turbulence intensity, 34 m A, all direction sectors
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Turbulence intensity, 34 m B, all direction sectors
Turbulence intensity, 20 m, all direction sectors
Napaskiak, Alaska Wind Resource Assessment Report P a g e | 20
Turbulence table, 34 m A data, all sectors
Bin Bin Endpoints Records Standard
RepresentativeMidpoint Lower Upper In Mean Deviation Peak
(m/s) (m/s) (m/s) Bin TI of TI TI TI
1 0.5 1.5 1,937 0.382 0.149 0.573 1.111
2 1.5 2.5 3,801 0.208 0.097 0.333 0.867
3 2.5 3.5 6,014 0.153 0.066 0.238 0.759
4 3.5 4.5 7,551 0.132 0.051 0.197 0.718
5 4.5 5.5 8,438 0.126 0.044 0.182 0.609
6 5.5 6.5 7,775 0.130 0.036 0.176 0.435
7 6.5 7.5 6,641 0.134 0.032 0.175 0.319
8 7.5 8.5 5,042 0.138 0.030 0.177 0.363
9 8.5 9.5 3,298 0.144 0.028 0.180 0.261
10 9.5 10.5 2,375 0.147 0.027 0.182 0.238
11 10.5 11.5 1,486 0.147 0.028 0.183 0.243
12 11.5 12.5 762 0.145 0.027 0.180 0.237
13 12.5 13.5 431 0.143 0.030 0.181 0.232
14 13.5 14.5 224 0.137 0.024 0.168 0.201
15 14.5 15.5 114 0.133 0.022 0.161 0.190
16 15.5 16.5 45 0.131 0.021 0.158 0.182
17 16.5 17.5 11 0.115 0.020 0.140 0.167
18 17.5 18.5 5 0.108 0.010 0.121 0.120
19 18.5 19.5 6 0.119 0.019 0.143 0.150
20 19.5 20.5 8 0.134 0.016 0.154 0.160
21 20.5 21.5 6 0.126 0.014 0.144 0.146
22 21.5 22.5 3 0.132 0.011 0.146 0.144
23 22.5 23.5 1 0.131 0.000 0.131 0.131
24 23.5 24.5 2 0.137 0.015 0.156 0.148
25 24.5 25.5 2 0.133 0.017 0.155 0.145
26 25.5 26.5 1 0.131 0.000 0.131 0.131
27 26.5 27.5 1 0.128 0.000 0.128 0.128
28 27.5 28.5 6 0.126 0.010 0.139 0.137
29 28.5 29.5 0