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HomeMy WebLinkAboutNaknek Service Area Wind Resource Report - Sep 2009 - REF Grant 7013005Report written by: Douglas Vaught, P.E., V3 Energy, LLC Date of Report: September 16, 2009 Photo © Doug Vaught V3 Energy, LLC, Eagle River, Alaska 1 Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 2 Summary Information The wind resource at proposed Cape Suwarof wind power site in Naknek shows very good potential for wind energy development as a high Class 4 (near Class 5) wind power class resource with excellent tur bulence behavior. Note that the measured wind power class is higher than predicted by the Alaska Wind Resource Map (see below) which forecast a Class 3 resource at the test site. Test Site Location Alaska Wind Resource Map Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 3 Meteorological Tower Data Synopsis Wind power class (High) Class 4 –Good Wind speed annual average (30 meters) 6.73 m/s Maximum ten minute average wind speed 28.2 m/s Maximum two second wind gust 37.1 m/s Wind power density (50 meters) 468 W/m 2 (projected) Wind power density (30 meters) 395 W/m 2 (measured) IEC 61400 1 3 rd edition classification Class III C Weibull distribution parameters k = 1.93, c = 7.59 m/s Surface roughness .0096 m (rough pasture) Power law exponent 0.128 (moderate wind shear) 1 hr autocorrelation coefficient 0.921 Diurnal pattern strength 0.060 Hour of peak wind speed 18 Frequency of calms (4 m/s threshold) 24% Mean turbulence intensity (30 meters) 0.104 (excellent) Data start date July 20, 2006 Data end date July 7, 2009 Tower Sensor Information Channel Sensor type Height Multiplier Offset Orientation 1 NRG #40 anemometer 30 m 0.765 0.35 ESE 2 NRG #40 anemometer 30 m 0.765 0.35 NNW 3 NRG #40 anemometer 20 m 0.765 0.35 ESE 7 NRG #200P wind vane (up to 9/18/07) 30 m 0.351 110 290° T 8 NRG #200P wind vane (after 10/18/07) 28 m 0.351 205 025° T 9 NRG #110S Temp C 2 m 0.136 86.383 N/A General Site Information Site number 3398 Site Description Site west of the city of Naknek at Cape Suwarof, on a sloping bluff above Naknek Bay Latitude/longitude N 58°43.709’W 157°03.496’,WGS 84 Site elevation 30 meters Datalogger type NRG Symphonie Tower type NRG 30 meter tall tower, 152 mm (6 in) diameter Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 4 Measured Wind Speeds The 30 meter anemometer annual wind speed averages (anemometer A and B) are 6.72 and 6.70 m/s. The 20 meter anemometer annual average wind speed is 6.35 m/s. The maximum recorded wind gust was 37.1 m/s recorded in January, 2009. 30 m A speed 30 m B speed 20 m speed Month Mean Max 10 min. Max gust Weibull k Weibull c Mean Max gust Mean Max gust (m/s) (m/s) (m/s) (m/s) (m/s) (m/s) (m/s) (m/s) Jan 7.28 28.2 36.7 1.93 8.22 7.24 37.1 6.73 35.5 Feb 7.53 22.4 28.7 2.18 8.48 7.47 29.1 7.08 28.3 Mar 7.71 23.2 27.1 2.00 8.71 7.71 27.5 7.35 26.0 Apr 7.19 21.3 27.5 1.89 8.09 7.07 27.9 6.85 27.1 May 6.08 26.6 33.6 1.93 6.86 6.14 34.4 5.91 33.6 Jun 5.58 20.5 27.5 2.11 6.30 5.54 28.3 5.36 27.5 Jul 5.98 17.4 22.1 1.99 6.74 5.87 22.9 5.66 21.4 Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 5 Aug 5.76 19.3 24.0 1.91 6.50 5.77 23.7 5.47 24.0 Sep 6.03 20.3 26.3 1.89 6.79 5.97 27.1 5.72 25.6 Oct 6.93 25.9 33.6 2.12 7.81 6.89 33.6 6.53 32.4 Nov 7.55 20.9 27.9 1.99 8.50 7.60 27.9 7.09 26.8 Dec 7.44 22.6 28.7 1.97 8.38 7.45 29.1 6.95 28.7 Annual 6.75 28.2 36.7 1.93 7.59 6.72 37.1 6.39 35.5 Note: max gust is a two second time average wind speed measurement Wind Speed Sensor Summary Variable Speed 30 m A Speed 30 m B Speed 20 m Measurement height (m) 30.0 30.0 20.0 Mean wind speed (m/s) 6.73 6.70 6.37 MMM wind speed (m/s) 6.75 6.72 6.39 Median wind speed (m/s) 6.2 6.1 5.8 Min wind speed (m/s) 0.4 0.4 0.4 Max wind speed (m/s) 28.2 28.5 27.0 Weibull k 1.93 1.96 1.93 Weibull c (m/s) 7.59 7.56 7.19 Mean power density (W/m²) 392 383 336 MMM power density (W/m²) 395 386 338 Mean energy content (kWh/m²/yr) 3,434 3,355 2,940 MMM energy content (kWh/m²/yr) 3,460 3,382 2,960 Energy pattern factor 2.0 2.0 2.0 Frequency of calms (%) 24.5 24.3 27.9 1 hr autocorrelation coefficient 0.921 0.92 0.922 Diurnal pattern strength 0.060 0.060 0.063 Hour of peak wind speed 18 18 17 MMM = mean of monthly means Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 6 Monthly Time Series of Wind Speed Seasonal Wind Profile Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 7 Daily Wind Profile The daily wind profile indicates that the lowest wind speeds of the day occur in the morning hours of 4 to 7 a.m. and the highest wind speeds of the day occur during the afternoon and evening hours of 3 to 6 p.m. The daily variation of wind speed is minimal on an annual basis but more pronounced on a monthly basis. Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 8 Wind Shear The power law exponent was calculated at 0.128 with wind speeds filtered to include only those greater than 4 m/s, the cut in speed for most turbines, indicating moderately low wind shear at the Cape Suwa rof met tower site. The practical application of this data is that a higher turbine tower height may be desirable as there will be a worthwhile marginal gain in wind speed and hence power recovery with ad ditional height. A tower height/power recovery/construction cost tradeoff study is advisable. Wind Power Density Another view of wind shear is wind power density by height above ground level. Wind power densi ty is defined as the power per unit area of the wind with units of Watts per square meter. It is cal culated by multiplying ½ times the air density times the wind speed cubed for each time step. The Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 9 equation is P/A = ½**U3. The time step values are averaged to produce an overall wind power density. The wind power density at 50 meters elevation is a wind industry standard method of comparing and evaluating sites. If the anemometer measurement heights are at other than 50 meters, the wind analysis software uses the power law exponent derived from the two (or more) measurement heights to extrapolate up or down. As can be seen in the figure below, power density and hence potential turbine power production increases substantially with turbine hub height at Naknek’s Cape Suwarof, as is true at most sites. Note that the measured power densities in the figure below differ from those reported in the data summary table on page 2 of this report. The figure below uses all collected data (July 2006 through July 2009) while in the summary table these data are presented as annual averages. An observation of some interest is to compare by scatter plot the power density and, separately, the mean wind speed to temperature. As one can see below, the power producing winds (winds greater than 4 m/s, the typical wind turbine cut in speed) are present through all temperature ranges, even as low as 30° C. For this reason, it will be important that a turbine for Naknek is capable of cold climate operation, with a minimum operating temperature at least 30° C. Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 10 Scatterplots Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 11 Extreme Wind Analysis Using a Gumbel distribution, one can predict the probability of winds exceeded a certain value within a defined period of time. Another way to consider the analysis though is by the concept of return period. In other words, in a defined period of time, typically 50 years, one can determine the maximum wind speed likely to occur. This is important when selecting a wind turbine as manufacturers classify their turbines by IEC standards of Class (see IEC 61400 1, edition 3). At the Naknek test site, using data col lected to date, the maximum predicted 50 year wind speed (ten minute average) at 30 meters is 31.4 m/s while the maximum predicted 50 year wind gust (two second average) at 30 meters is 41.8 m/s. This qualifies the site as IEC (International Electrotechnical Commission) Class III, the lowest and most common extreme wind designation. Note below for reference the graph of the return period for 10 minute average wind speed. Probability Distribution Function The probability distribution function provides a visual indication of measured wind speeds in one meter per second “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. At the 30 meter level, Weibull parameters are k = 1.93 and c = 7.59 m/s (“k”is the shape factor and “c”is the scale factor) for the data period. This shape factor is indicative of a normal wind distribution for wind power sites. The PDF information is shown visually in another manner in the second graph, the Cumulative Distribu tion Function. In this view, one can see that about 25 percent of winds (at 30 meters) are less than 4 m/s, the standard cut in speed of most turbines and essentially 100 percent of the winds are less than 25 m/s, the standard high wind cut out speed for most turbines. Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 12 Wind Roses Naknek winds are multi directional with the wind frequency rose indicating frequent north, northeast, southeast and southwest winds. This observation is reinforced with reference to the mean value and total value power density roses below. Power producing winds are chiefly north northeast and south east with secondary power winds from the east and west. The practical application of this information is that a site should be selected with adequate freedom from ground interference to the north northeast and southeast directions and if more than one turbine is installed, the turbines should be adequately spaced apart to prevent downwind shadowing and turbulence problems between the turbines. Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 13 Note also 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, Naknek experienced approx imately 25 percent calm conditions during the measurement period (see wind frequency roses below). Wind Frequency Rose, Ch. 7 Vane Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 14 Wind Frequency Rose, Ch. 8 Vane Mean Value Rose, Ch. 7 Vane Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 15 Mean Value Rose, Ch. 8 Vane Total Value (power density) Rose, Ch. 7 Vane Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 16 Total Value (power density) Rose, Ch. 8 Vane Turbulence Intensity The turbulence intensity is acceptable with a mean turbulence intensity of 0.104 and a representa tive turbulence intensity of 0.130 at 15 m/s wind speed, indicating quite smooth air for wind turbine operations. This equates to an International Electrotechnical Commission (IEC) 3 rd Edition (2005) turbulence category C, which is the lowest defined category. Turbulence Table Turbulence Intensity (TI) Table, 30 m A speed, 7/20/06 to 7/07/09 Bin Bin Endpoints Records Standard Midpoint Lower Upper In Mean Deviation Representative Peak (m/s) (m/s) (m/s) Bin TI of TI TI TI 1 0.5 1.5 3,877 0.430 0.165 0.641 1.444 2 1.5 2.5 7,857 0.208 0.098 0.333 1.000 3 2.5 3.5 13,039 0.142 0.060 0.218 0.697 4 3.5 4.5 16,514 0.116 0.046 0.175 0.667 5 4.5 5.5 18,032 0.104 0.038 0.153 0.574 6 5.5 6.5 16,859 0.098 0.034 0.142 0.419 7 6.5 7.5 15,038 0.096 0.031 0.135 0.370 8 7.5 8.5 12,479 0.095 0.028 0.131 0.383 Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 17 9 8.5 9.5 10,039 0.096 0.026 0.130 0.348 10 9.5 10.5 7,991 0.097 0.025 0.128 0.284 11 10.5 11.5 6,377 0.099 0.023 0.129 0.292 12 11.5 12.5 4,669 0.100 0.022 0.129 0.269 13 12.5 13.5 3,553 0.102 0.022 0.130 0.267 14 13.5 14.5 2,573 0.102 0.021 0.128 0.209 15 14.5 15.5 1,816 0.104 0.021 0.130 0.203 16 15.5 16.5 1,233 0.105 0.020 0.131 0.226 17 16.5 17.5 792 0.106 0.019 0.131 0.237 18 17.5 18.5 485 0.105 0.018 0.127 0.171 19 18.5 19.5 277 0.106 0.020 0.132 0.205 20 19.5 20.5 196 0.105 0.019 0.129 0.159 21 20.5 21.5 103 0.105 0.017 0.127 0.168 22 21.5 22.5 55 0.106 0.024 0.138 0.193 23 22.5 23.5 35 0.111 0.019 0.136 0.147 24 23.5 24.5 34 0.113 0.015 0.132 0.148 25 24.5 25.5 25 0.112 0.011 0.126 0.135 26 25.5 26.5 19 0.114 0.014 0.132 0.141 27 26.5 27.5 9 0.124 0.016 0.144 0.151 28 27.5 28.5 3 0.107 0.005 0.113 0.113 29 28.5 29.5 30 meter Turbulence Intensity Rose Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 18 IEC 3 rd Edition Turbulence Category Graph Air Temperature and Density During the study period, the Cape Suwarof test site recorded an average temperature of 2.2° C. The minimum recorded tempera ture during the measurement period was 32.8° C and the maxi mum temperature was 29.0° C, indicating a wide variability of an ambient temperature operating environment important to wind turbine operations. Consequent to Naknek’s cool temperatures, the average air density of 1.274 kg/m 3 is over four percent higher than the standard air density of 1.222 kg/m 3 (14.8° C and 100.9 kPa standard temperature and pressure at 30 m elevation), indicating that Naknek has denser air than the standard air density used to calculate turbine power curves (note that all turbine power curves are calculate at a sea level standard of 15° C and 101.3 kPa pressure). Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 19 Temperature Air Density Month Mean Min Max Mean Min Max (°C) (°C) (°C) (kg/m³) (kg/m³) (kg/m³) Jan 10.4 32.8 11.4 1.330 1.221 1.463 Feb 8.3 29.1 8.8 1.318 1.221 1.441 Mar 7.4 22.5 8.0 1.296 1.221 1.403 Apr 1.7 14.2 15.9 1.280 1.217 1.358 May 7.7 2.9 21.7 1.252 1.193 1.301 Jun 11.1 2.3 29.0 1.236 1.164 1.277 Jul 13.3 6.6 24.9 1.227 1.180 1.257 Aug 13.9 4.8 23.4 1.225 1.186 1.265 Sep 11.1 1.7 20.4 1.235 1.198 1.279 Oct 2.9 16.6 15.0 1.264 1.220 1.371 Nov 4.3 23.4 10.6 1.309 1.239 1.408 Dec 6.1 25.5 9.7 1.318 1.243 1.420 Annual 2.2 32.8 29.0 1.274 1.164 1.463 Data Quality Control Data was filtered to remove presumed icing events that yield false zero wind speed data. Data that met the following criteria were filtered: wind speed < 1 m/s, wind speed standard deviation = 0, and tem perature < 3 °C. Other obvious icing event data not meeting these criteria were filtered manually. Note that the met tower collapsed on September 18, 2007 due to a guy wire anchor that failed. Fortu nately, the tower fell straight over and sustained only minor damage. On October 18, 2007, the met tower was reinstalled at the same location with new sensors. The new wind vane was connected to Channel 8 because of anomaly with Channel 7 after the tower collapse. Possible Valid Recovery Label Units Height Records Records Rate (%) Speed 30 m A m/s 30 m 155,952 145,266 93.2 Speed 30 m A SD m/s 155,952 145,266 93.2 Speed 30 m A Max m/s 155,952 147,367 94.5 Speed 30 m A Min m/s 155,952 147,367 94.5 Speed 30 m B m/s 30 m 155,952 145,189 93.1 Speed 30 m B SD m/s 155,952 145,189 93.1 Speed 30 m B Max m/s 155,952 147,367 94.5 Speed 30 m B Min m/s 155,952 147,367 94.5 Speed 20 m m/s 20 m 155,952 145,680 93.4 Speed 20 m SD m/s 155,952 145,680 93.4 Speed 20 m Max m/s 155,952 147,367 94.5 Naknek, Alaska (Cape Suwarof) Wind Resource Report V3 Energy, LLC, Eagle River, Alaska 20 Speed 20 m Min m/s 155,952 147,367 94.5 Direction 30 m ° 30 m 155,952 62,963 40.4 Direction 30 m SD ° 155,952 62,963 40.4 Direction 30 m Max ° 155,952 63,940 41.0 Direction 30 m Min ° 155,952 63,940 41.0 Direction 28 m ° 28 m 155,952 85,003 54.5 Direction 28 m SD ° 155,952 81,767 52.4 Direction 28 m Max ° 155,952 85,279 54.7 Direction 28 m Min ° 155,952 92,419 59.3 Temperature °C 155,952 143,756 92.2 Temperature SD °C 155,952 143,772 92.2 Temperature Max °C 155,952 143,301 91.9 Temperature Min °C 155,952 143,748 92.2