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Home My WebLink AboutSaint Mary's - Pitka Point Wind Energy Project - Saint Mary's Area Wind Power Report - Jul 2010 - REF Grant 7040017 V3 Energy, LLC, Eagle River, Alaska 1 Saint Mary’s Area Wind Power Report Report written by: Douglas Vaught, P.E., V3 Energy, LLC Date of Report: July 20, 2010 Pitka’s Point met tower Saint Mary’s met tower Mountain Village met tower Aerial view of Village of Saint Mary’s Photos top and bottom right: Doug Vaught; photo bottom left: Dave Johnson Summary Information ...................................................................................................................................5 Project Recommendations ........................................................................................................................5 Pitka’s Point and Saint Mary’s Summary..................................................................................................6 Saint Mary’s and Mountain Village Summary ...........................................................................................7 Site Information............................................................................................................................................8 Meteorological Tower Data Synopses......................................................................................................8 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 2 Test Site Location Maps............................................................................................................................9 Intertie and Wind Farm Proposal................................................................................................................ 12 Village Load ............................................................................................................................................. 12 Turbine Output ....................................................................................................................................... 12 Turbines, Pitka’s Point Site ................................................................................................................. 13 Turbines, Saint Mary’s Site ................................................................................................................. 14 Turbines, Mountain Village Site .......................................................................................................... 14 Data Quality Control and Icing Loss ............................................................................................................ 15 Quality Control........................................................................................................................................ 15 Data Recovery Table, Pitka’s Point..................................................................................................... 15 Data Recovery Table, Saint Mary’s..................................................................................................... 16 Data Recovery Table, Mountain Village .............................................................................................. 16 Icing Loss ................................................................................................................................................. 17 Icing Data Loss Comparison Table, Pitka’s Point and Saint Mary’s..................................................... 17 Icing Data Loss Comparison Table, Saint Mary’s and Mountain Village ............................................. 18 Documentation of Icing Events ............................................................................................................... 18 Pitka’s Point Icing Event Photographs, 1/15/2009............................................................................. 19 Pitka’s Point Icing Event Data, 1/14 to16/2009.................................................................................. 19 Saint Mary’s Icing Event Photographs, 1/15/2009 ............................................................................. 20 Saint Mary’s Icing Event Data, 1/14 to16/2009 .................................................................................. 20 Pitka’s Point Icing Event Data, 12/30/2007 to 1/14/2008 .................................................................. 21 Pitka’s Point Met Tower .............................................................................................................................. 22 Met Tower Sensor Information, Pitka’s Point......................................................................................... 22 Measured Wind Speeds .......................................................................................................................... 22 Wind Speed Sensor Summary, Pitka’s Point (Oct 2007 to Feb 2009)................................................. 22 Seasonal Wind Profile, Pitka’s Point................................................................................................... 22 Daily Wind Profile, Pitka’s Point ......................................................................................................... 23 Wind Shear .............................................................................................................................................. 24 Wind Shear Profile, Pitka’s Point ........................................................................................................ 24 Wind Power Density ............................................................................................................................... 24 Temperature Scatterplots ....................................................................................................................... 25 Wind Speed vs. Temperature, Pitka’s Point, 38 m anem. .................................................................. 26 Wind Power Density vs. Temperature, Pitka’s Point, 38 m anem. ..................................................... 26 Extreme Wind Analysis ........................................................................................................................... 27 Probability Distribution Function ............................................................................................................ 27 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 3 PDF Curve, Pitka’s Point, 38 m ............................................................................................................ 28 CDF Curve, Pitka’s Point, 38 m ............................................................................................................ 28 Wind Roses.............................................................................................................................................. 29 Wind Frequency Rose......................................................................................................................... 29 Total Value (power density) Rose ....................................................................................................... 29 Turbulence Intensity............................................................................................................................... 29 IEC 3rd Edition Turbulence Intensity Graph, Pitka’s Point, 38 m Anemometer.................................. 30 Air Temperature and Density .................................................................................................................. 30 Annual Temperature Boxplot, Pitka’s Point........................................................................................ 31 Saint Mary’s Met Tower.............................................................................................................................. 32 Met Tower Sensor Information, Saint Mary’s .................................................................................... 32 Measured Wind Speeds .......................................................................................................................... 32 Wind Speed Sensor Summary, Saint Mary’s (Aug 2008 to June 2010)............................................... 32 Monthly and Seasonal Wind Profiles, Saint Mary’s............................................................................ 33 Daily Wind Profile, Saint Mary’s ......................................................................................................... 33 Wind Shear.................................................................................................................................................. 34 Wind Shear Profile, Saint Mary’s........................................................................................................ 34 Wind Power Density ............................................................................................................................... 34 Scatterplot............................................................................................................................................... 35 Wind Speed vs. Temperature, Saint Mary’s, 38 m anem................................................................... 35 Extreme Wind Analysis ........................................................................................................................... 35 Probability Distribution Function ............................................................................................................ 36 Wind Roses.............................................................................................................................................. 36 Wind Frequency Rose......................................................................................................................... 37 Total Value (power density) Rose ....................................................................................................... 37 Turbulence Intensity ................................................................................................................................... 37 IEC 3rd Edition Turbulence Intensity Graph, Saint Mary’s, 38 m Anemometer.................................. 38 Air Temperature and Density .................................................................................................................. 38 Annual Temperature Boxplot, Saint Mary’s ....................................................................................... 39 Mountain Village Met Tower...................................................................................................................... 40 Met Tower Sensor Information, Mountain Village ............................................................................. 40 Measured Wind Speeds .......................................................................................................................... 40 Wind Speed Sensor Summary, Mountain Village (November 2009 to June 2010) ............................ 40 Monthly Wind Profile, Mountain Village ............................................................................................ 41 Daily Wind Profile ............................................................................................................................... 41 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 4 Wind Shear.................................................................................................................................................. 41 Wind Shear Profile, Mountain Village................................................................................................. 42 Wind Power Density ............................................................................................................................... 42 Scatterplot............................................................................................................................................... 42 Extreme Wind Analysis ........................................................................................................................... 43 Probability Distribution Function ............................................................................................................ 43 Wind Roses.............................................................................................................................................. 43 Wind Frequency Rose......................................................................................................................... 44 Total Value (power density) Rose ....................................................................................................... 44 Turbulence Intensity ................................................................................................................................... 44 IEC 3rd Edition Turbulence Intensity Graph, Mountain Village, 50 m B anemometer........................ 44 Air Temperature and Density .................................................................................................................. 45 Annual Temperature Boxplot, Mountain Village ................................................................................ 45 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 5 Summary Information Saint Mary’s, Alaska is the largest village on the lower Yukon River and a high priority wind power project site for Alaska Village Electric Cooperative (AVEC). In addition to the existing electrical intertie between Saint Mary’s and Pitka’s Point, current plans calls for continuation of an existing intertie west from the Saint Mary’s Airport to Mountain Village and possible future construction of an intertie east from Saint Mary’s to Pilot Station. Project Recommendations Wind data collected for more than one year at the Pitka’s Point met tower site, from October 2007 to February 2009, indicates a Class 6 (outstanding) wind resource. Wind data collected since October 2008 at the Saint Mary’s met tower site indicates a Class 4 (good) wind resource. In November, 2009, a met tower installed near Mountain Village has measured an excellent wind resource to date, possibly Class 5. The wind resource at the Pitka’s Point, Saint Mary’s and Mountain Village sites clearly are noteworthy for wind power development, but wintertime icing may present a challenge. Although analysis of met tower data cannot easily distinguish between icing events that are due to freezing rain and those due to rime icing, there is strong evidence that rime icing occurs, an example the collapse of the Pitka’s Point and Saint Mary’s met towers in February 2009. Interestingly though, there appears to have been fewer and less severe rime ice events at the Saint Mary’s met tower during winter 2009/2010 compared to winter 2008/2009. Additionally, the Mountain Village met tower data indicates relatively few icing events during winter 2009/2010. The original purpose of selecting three met tower sites in the Saint Mary’s area was to identify the opti- mum location for wind turbines based on proximity to power lines, geotechnical considerations, land ownership and access, physical space for a turbine layout, and wind resource considerations such as wind power class, turbine capacity factor, possible availability loss, extreme wind probability and turbu- lence. With these factors in mind, all three sites – Pitka’s Point, Saint Mary’s and Mountain Village – present pros and cons for wind power development. Pitka’s Point clearly has the superior wind resource of the three sites, with approximately seven percen- tage points turbine capacity factor advantage over Saint Mary’s and an estimated four percentage points capacity factor advantage over Mountain Village. This equates to an extra 61 MWh/year of addi- tional power production vs. Saint Mary’s and 35 MWh/yr vs. Mountain Village (per 100 kW of wind tur- bine capacity). However, this assumes one hundred percent turbine availability. This is not possible even in with perfect operating conditions, but at the Pitka’s Point site, turbine availability likely will be negatively impacted by wintertime rime icing. Because rime ice has the potential to cause turbine avail- ability loss and given the known risk of rime icing at the Pitka’s Point site, active anti-icing and/or de- icing measures will likely be necessary to mitigate the risk of excessive turbine downtime during winter. This expense and effort, however, may well be worthwhile with increased power production at this high wind energy site. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 6 The Saint Mary’s site may be most advantageous from a project development perspective. It has more physical space for multi-turbine layout than the Pitka’s Point site, land use site control for wind turbine construction has already been secured, and it is nearer existing power lines than the Pitka’s Point site. Although it has the lowest wind resource of the three sites monitored, it still measures as a very res- pectable Class 4 wind resource and would yield approximately 30 percent turbine capacity factor. Rime icing, though less severe than at the Pitka’s Point site, still may be sufficiently problematic to warrant use of turbine anti-icing and de-icing features to maintain continuous wintertime turbine availability. Monitoring of the Mountain Village site has not yet reached the one year point, but to date it shows ex- cellent potential for wind power development. In a concurrent comparison with the Saint Mary’s met tower, Mountain Village experiences approximately three higher wind speed monthly averages. The site experienced very little icing during winter 2009/2010, turbulence intensity is extremely low, and the site has plenty of physical space for turbine layout. Disadvantages of the site, however, are its relative re- moteness from Mountain Village, lack of nearby power transmission infrastructure at present, and lack of winter maintenance of the road link between Saint Mary’s and Mountain Village. If the intertie is built, the infrastructure problem is solved as the power line will be near the site, but winter mainten- ance of the road, at least from the Mountain Village airport to the wind site, will be a new and necessary operational requirement. Considering the pros and cons of each site, which are discussed in this report, a possible wind power development approach might be to install turbines at all three sites. Advantages of this approach in- clude reducing the instantaneous power surge effects of gusting winds by displacing the turbine suffi- ciently that they will receive somewhat different winds at each site. This is especially true if turbines are located in both Pitka’s Point or Saint Mary’s and Mountain Village. Another advantage is that although turbines installed at Pitka’s Point would produce more energy than at the other sites, they likely will suf- fer more severe icing problems. This trade-off of power production versus icing would be less at the other two sites: Saint Mary’s and Mountain Village site turbines would generate less energy annually but probably also experience higher availability in winter. Because the energy production/icing loss trade-off is not at present well understood with respect to predicting a decrease in turbine availability, installing turbines at all three sites potentially optimizes energy recovery overall and at a minimum spreads the risk of lower than expected power recovery due to icing problems. Pitka’s Point and Saint Mary’s Summary In comparing the Pitka’s Point and Saint Mary’s met tower sites, the Pitka’s Point site appears to expe- rience slightly more frequent icing conditions than the Saint Mary’s site. On the other hand, the Pitka’s Point data clearly demonstrates a superior wind resource for wind power development. This can be seen in the table below. Comparing the standard anemometers mounted at 38 meters on both towers, one sees a 12.2 percent decrease in wind speed and a very significant 31.9 percent decrease in wind power density (WPD) from Pitka’s Point to Saint Mary’s. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 7 It is possible that given the complexity of terrain, high frequency of northeasterly winds, and location of the Saint Mary’s met tower north of and away from the bluff edge compared to the bluff proximity of the Pitka’s Point met tower, the wind resource at the Saint Mary’s met tower site might be better closer to the river. However, it seems unlikely that it would be sufficient to match the clearly superior wind resource measured at the Pitka’s Point met tower during the five month data overlap period. Pitka's 38 m speed mean St. M's 38 m speed mean Decrease of Wind Speed from Pitka’s Point to St. Mary's Pitka's 38 m WPD mean St. M's 38 m WPD mean Decrease of Wind Power Density from Pitka’s Point to Saint Mary's Year Month (m/s) (m/s) (m/s) (%) (W/m 2) (W/m 2) (W/m 2) (%) 2008 Sep 6.37 5.66 0.71 -11.1% 225.9 160.4 65.6 -29.0% 2008 Oct 6.75 5.98 0.76 -11.3% 411.8 285.2 126.6 -30.7% 2008 Nov 6.05 5.86 0.19 -3.1% 275.9 242.9 33.0 -11.9% 2008 Dec 9.43 8.05 1.38 -14.6% 875.7 520.6 355.1 -40.5% 2009 Jan 10.40 8.22 2.17 -20.9% 1299.8 684.3 615.5 -47.4% data average 7.80 6.76 1.04 -12.2% 617.8 378.7 239.1 -31.9% Saint Mary’s and Mountain Village Summary In comparing the Saint Mary’s and Mountain Village met tower sites, both sites during winter 2009/2010 appeared to experience similar icing loss. Also, both sites have experience similar wind speeds with a slight advantage recorded to date to Mountain Village as seen in the table below. Comparing the 40 meter anemometers, one sees a 2.9 percent decrease in wind speed and a 15.6 percent decrease in wind power density (WPD) from Mountain Village to Saint Mary’s. Mtn V. 40 m speed mean St. M's 40 m speed mean* Decrease of Wind Speed from Mtn Village to St Mary's Mtn V. 40 m WPD mean St. M's 40 m WPD mean Decrease of WPD from Mtn Village to Saint Mary'sYear Month (m/s) (m/s) (m/s) (%) (W/m 2) (W/m 2) (W/m 2) (%) 2009 Nov 7.32 7.31 0.01 -0.1% 524.3 410.5 113.8 -21.7% 2009 Dec 9.25 8.16 1.09 -11.7% 894.1 569.6 324.4 -36.3% 2010 Jan 8.56 9.08 -0.52 6.1% 600.6 720.7 -120.1 20.0% 2010 Feb 7.66 7.43 0.22 -2.9% 562.2 414.1 148.1 -26.3% 2010 Mar 8.02 7.92 0.10 -1.2% 478.9 470.7 8.2 -1.7% 2010 Apr 7.07 6.94 0.13 -1.8% 445.4 402.2 43.1 -9.7% 2010 May 5.93 5.60 0.33 -5.6% 220.4 195.9 24.5 -11.1% 2010 Jun 7.31 7.02 0.29 -3.9% 380.4 322.8 57.6 -15.1% data average 7.64 7.43 0.21 -2.7% 513.3 438.3 75.0 -14.6% *data adjusted to 40 m from 38 m anemometer Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 8 Site Information Pitka’s Point Saint Mary’s Mountain Village Site number 0066 0026 0068 Site Description Near a construction bor- row pit near the bluff overlooking Pitka’s Point and the Yukon River On a plateau near the Airport Road about 1.5 km northeast of the Pitka’s Point met tower On a plateau near the Yukon River approx- imately 5 km east of the Mountain Village airport Latitude/longitude N 62° 02.252’ W 163° 14.82’ (WGS 84) N 62° 02.951’ W 163° 13.54’ (WGS 84) N 62° 05.513’ W 163° 35.38’ (WGS 84) Site elevation 177 meters 139 meters 85 meters Datalogger & modem type NRG Symphonie, Iridium iPack NRG Symphonie, Iridium iPack NRG SymphoniePlus, Iridium iPack Tower type NRG 40-meter SHD tall tower, 202 mm (8 in.) NRG 40-meter SHD tall tower, 202 mm (8 in.) NRG 50-meter XHD tall tower, 254 mm (10 in.) Meteorological Tower Data Synopses Pitka’s Point Saint Mary’s Mountain Village Data start date October 26, 2007 August 15, 2008 November 5, 2009 Data end date February 13, 2009 June 30, 2010 (in progress) June 30, 2010 (in progress) Wind power class Class 6 –Outstanding Class 4 – Good Class 5 – Excellent (note: 7.7 mo. data) Wind speed annual average (38 meters) 7.72 m/s 6.84 m/s 7.68 m/s (40 m anem., to date) Maximum wind gust 36.3 m/s (Jan. 2008)30.6 m/s (Jan. 2009)32.7 m/s (Nov. 2009) Maximum ten minute aver- age wind speed 29.5 m/s 24.0 m/s 25.6 m/s Wind power density at 50 meters 662 W/m2 (extrapo- lated) 382 W/m2 (extrapo- lated) 581 W/m2 (measured, to date) Wind power density (38 me- ters) 572 W/m2 (measured)360 W/m2 (measured) 518 W/m2 (measured, to date, 40 meters) IEC 61400-1 3rd edition ex- treme wind class Class III (may be Class II) Class III Insufficient data at present to calculate Weibull distribution parame- ters k = 1.95, c = 8.70 m/s k = 2.16, c = 7.49 m/s k = 2.27, c = 8.95 m/s (to date) Surface roughness 0.106 m (few trees)0.095 m (few trees)0.137 m (few trees) Power law exponent 0.178 (moderate wind shear) 0.183 (moderate wind shear) 0.175 (moderate wind shear) Frequency of calms (>4 m/s)20% 20% (to date)13% (to date) Mean TI, at 15 m/s 0.076 (IEC cat. C)0.105 (IEC cat. C)0.068 (IEC cat. C) Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 9 Test Site Location Maps Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 10 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 11 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 12 Intertie and Wind Farm Proposal AVEC has proposed construction of an intertie to electrically connect Saint Mary’s and Pitka’s Point (these two village are already intertied with a three phase connection) to the village of Mountain Village, located thirty kilometers (19 miles) west of Saint Mary’s on the Yukon River. Concurrent with an intertie project, AVEC proposes to install wind turbines to augment the diesel generators and to offset the use of fossil fuel for power generation. Village Load A combined Saint Mary’s and Mountain Village hourly load profile was synthesized using the Alaska vil- lage load calculator Excel spreadsheet developed by Alaska Energy Authority several years ago. The re- sults were adjusted slightly to match actual village average and peak loads of Saint Mary’s and Mountain Village (separately) documented by AVEC in their 2009 annual power generation report. The result is a virtual Saint Mary’s -Mountain Village community with a 669 kW average load, 1,226 kW peak load and average daily power usage of 16.0 MWh/day. HOMER software was used to create a combined Saint Mary’s -Mountain Village simulation model. Seasonal, daily and DMap profiles of the Saint Mary’s- Mountain Village virtual load are shown below. Turbine Output It is perhaps counterintuitive that wind power density and wind class do not correlate linearly with tur- bine power output. This is due to a number of factors, including theoretical limitations of a lift- producing aerodynamic device (the turbine rotor blades) and practical limitations of generator weight and rated output. For these reasons and others, a wind turbine in a lower power class wind regime may Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 13 still produce sufficient energy to warrant installation of turbines while a turbine in a higher power class wind regime may not generate as much energy as one might expect. A simplistic consideration of possible turbine output at the Pitka’s Point, Saint Mary’s and Mountain Vil- lage wind sites is to model power output of a particular turbine with mean of monthly means data col- lected to date and extrapolating to the turbine hub height if necessary. Note that the analyses are based on raw data with no synthetic data inserted in place of icing data removed for data quality control or data missing for other reasons. Turbine performance was analyzed with the HOMER software using the Northern Power Northwind 100 B model (100 kW, 21 meter rotor diameter, stall control, synchronous generator), the Aeronautica 29- 225 (225 kW, 29 meter rotor diameter, stall control, asynchronous generator) and the Vestas V27 (225 kW, 27 meter rotor diameter, pitch control, asynchronous generator). These turbines were selected for analysis for several reasons, including present wide use in Alaska village wind power applications, ready availability, and appropriate rated capacity for the intertied village electrical load. Note that the met tower in Mountain Village was installed in November 2009 and hence less than one year of data has been collected. The Mountain Village airport is not equipped with an Automated Weather Observing System (AWOS) to provide reference wind data, so an average ratio of collected monthly Mountain Village data compared to equivalent Saint Mary’s data was calculated and applied to Saint Mary’s data of the missing months to create probable monthly average wind speeds in Mountain Village (for the missing months). The HOMER software can use monthly data with other parameters such as the Weibull k (shape value) and autocorrelation factor to generate a synthetic full year wind da- ta set. Turbines, Pitka’s Point Site Saint Mary's to Mountain Village intertied, Pitka's Point site Turbine No. Hub ht. Penetration CF Wind prod. Displ. fuel Excess elec. Excess elec. Storage needed? (m) (%) (%) MWh/yr (gal) MWh/yr (%) NW100/21 4 37 22.9 37.1 1,340 88,413 6 0.1 possibly 6 37 34.3 37.1 2,010 126,984 94 1.6 yes 8 37 45.7 37.1 2,680 157,169 308 5.0 yes Aero 29-225 2 40 24.5 36.4 1,434 93,757 18 0.3 possibly 3 40 36.7 36.4 2,151 132,249 154 2.6 yes 4 40 49.0 36.4 2,868 160,159 478 7.5 yes Vestas V-27 2 40 25.1 37.3 1,472 95,979 23 0.4 possibly 3 40 37.7 37.3 2,208 134,656 178 2.9 yes 4 40 50.2 37.3 2,944 160,979 527 8.3 yes Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 14 Turbines, Saint Mary’s Site Turbines, Mountain Village Site Notes: 1. Wind resource based on specific site met tower data, assume turbines at that location 2. HOMER modeling assumes 100% turbine availability 3. Displaced fuel estimate is for electrical generation only 4. Excess electricity to dump, preferably heat recovery for thermal load 5. SLC and/or energy storage might be necessary to avoid curtailment control of turbines 6. Availability loss due to icing not considered; turbines at this site may require active de-icing capa- bility to maintain wintertime availability 7. Penetration refers to average annual load supplied by wind turbines 8. Wind data is not adjusted against long-term average 9. Mountain Village met tower data incomplete; St Mary's data used as substitute for missing months Saint Mary's to Mountain Village intertied, Saint Mary's site Turbine No. Hub ht. Penetration CF Wind prod. Displ. fuel Excess elec. Excess elec. Storage needed? (m) (%) (%) MWh/yr (gal) MWh/yr (%) NW100/21 4 37 18.6 30.2 1,091 72,143 1 0.0 possibly 6 37 28.0 30.2 1,634 105,212 45 0.7 possibly 8 37 37.3 30.2 2,183 133,519 165 2.7 yes Aero 29-225 2 40 19.5 28.9 1,140 75,053 6 0.1 possibly 3 40 29.2 28.9 1,711 108,122 77 1.3 yes 4 40 38.9 28.9 2,281 134,048 260 4.2 yes Vestas V-27 2 40 20.0 29.7 1,172 76,852 9 0.1 possibly 3 40 30.0 29.7 1,757 110,291 90 1.5 yes 4 40 40.0 29.7 2,343 135,899 294 4.8 yes Saint Mary's to Mountain Village intertied, Mountain Village site Turbine No. Hub ht. Penetration CF Wind prod. Displ. fuel Excess elec. Excess elec. Storage needed? (m) (%) (%) MWh/yr (gal) MWh/yr (%) NW100/21 4 37 20.7 33.6 1,213 80,079 3 0.0 possibly 6 37 31.1 33.6 1,819 116,032 64 1.1 possibly 8 37 41.4 33.6 2,426 145,794 225 3.7 yes Aero 29-225 2 40 21.9 32.5 1,280 83,968 10 0.2 possibly 3 40 32.8 32.5 1,921 119,921 108 1.8 yes 4 40 43.7 32.5 2,561 147,011 346 4.2 yes Vestas V-27 2 40 22.4 33.4 1,315 85,952 15 0.3 possibly 3 40 33.7 33.4 1,972 122,169 127 2.1 yes 4 40 44.9 33.4 2,630 148,757 390 6.2 yes Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 15 Data Quality Control and Icing Loss Data was filtered to remove presumed icing events that yield false zero wind speed data and non-variant wind direction data. Data that met the following criteria were filtered: wind speed < 1 m/s (or non- variant direction), standard deviation = 0, temperature < 3 °C and high relative humidity if that data is available. Note that for all three met towers, icing data is removed from the data set and hence not counted in summary data calculations such as average wind speed, wind power density, etc. Synthetic data to fill the removed data was not employed. It was thought that at Pitka’s Point, installation of a heated anemometer and wind vane would result in better data recovery than from the standard non-heated sensors, but that did not prove entirely true. As one can see below in the Data Recovery Table, Pitka’s Point, data recovery for the heated (IceFree) anemometer is no better than the other anemometers, although data recovery from the heated wind vane is somewhat better than from the standard vane. It is not clear why data recovery from the heated sensors was so poor. One possible explanation is excessive voltage drop from the power line tie-in to the sensors on the met tower. Quality Control Data Recovery Table, Pitka’s Point anemometers vanes 38 m 28 m IceFree 29 m 21 m 38 m 29 m IceFree Year Month Recovery Recovery Recovery Recovery Recovery Recovery Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) 2007 Oct 87.9 77.9 87.9 87.9 80.4 27.0 2007 Nov 52.2 100.0 55.2 54.7 43.6 100.0 2007 Dec 73.3 76.5 83.4 83.4 74.4 75.9 2008 Jan 24.4 24.4 31.9 37.9 54.1 69.6 2008 Feb 75.6 76.6 78.7 76.2 65.1 86.4 2008 Mar 89.5 80.7 90.5 94.1 77.3 88.5 2008 Apr 37.8 78.4 55.3 41.1 65.9 75.8 2008 May 97.7 100.0 96.4 96.3 96.1 97.9 2008 Jun 100.0 100.0 100.0 100.0 100.0 100.0 2008 Jul 100.0 100.0 100.0 100.0 100.0 100.0 2008 Aug 100.0 100.0 100.0 100.0 100.0 100.0 2008 Sep 100.0 100.0 100.0 100.0 96.6 100.0 2008 Oct 96.3 92.3 98.8 96.9 92.4 98.8 2008 Nov 62.3 27.6 59.9 56.7 54.3 81.5 2008 Dec 62.2 33.8 64.6 61.0 44.4 70.9 2009 Jan 52.6 39.6 53.7 56.2 42.3 51.5 All data 75.7 75.5 78.5 77.6 74.2 82.7 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 16 Data Recovery Table, Saint Mary’s anemometers vanes 38 m 29 m 18 m 38 m 29 m Year Month Recovery Recovery Recovery Recovery Recovery Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) 2008 Aug 100.0 100.0 100.0 100.0 100.0 2008 Sep 100.0 100.0 100.0 96.4 96.3 2008 Oct 100.0 100.0 94.6 95.9 96.1 2008 Nov 61.6 65.0 65.1 55.2 58.9 2008 Dec 86.7 83.7 82.7 70.6 73.6 2009 Jan 52.1 53.3 51.7 47.3 47.3 2009 Feb 37.8 56.3 39.1 40.0 40.0 2009 Mar 0.0 0.0 0.0 0.0 0.0 2009 Apr 46.2 0.0 47.2 45.2 45.2 2009 May 97.7 0.0 97.7 96.4 96.4 2009 Jun 100.0 0.0 100.0 100.0 100.0 2009 Jul 100.0 0.0 100.0 100.0 100.0 2009 Aug 100.0 0.0 100.0 100.0 100.0 2009 Sep 99.7 0.0 99.0 100.0 100.0 2009 Oct 92.4 0.0 92.4 90.4 90.4 2009 Nov 95.8 74.4 93.6 93.3 93.3 2009 Dec 93.4 93.7 93.2 87.1 87.1 2010 Jan 98.3 98.3 98.3 95.3 96.4 2010 Feb 79.5 78.3 78.1 93.5 94.4 2010 Mar 100.0 100.0 84.5 100.0 100.0 2010 Apr 96.9 99.8 99.8 94.0 94.0 2010 May 100.0 100.0 100.0 95.9 95.9 2010 Jun 100.0 100.0 100.0 100.0 100.0 All data 84.1 55.6 83.2 82.2 82.6 Data Recovery Table, Mountain Village anemometers 50 m A 50 m B 41 m 40 m 32 m 31 m Year Month Recovery Recovery Recovery Recovery Recovery Recovery Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) 2009 Nov 97.8 97.8 97.8 97.8 94.2 97.8 2009 Dec 91.6 91.6 91.6 91.6 91.6 91.6 2010 Jan 87.8 87.3 89.0 95.7 90.6 92.4 2010 Feb 85.5 83.3 77.5 86.7 86.9 85.6 2010 Mar 78.7 78.5 90.9 87.8 85.3 86.3 2010 Apr 100.0 100.0 100.0 100.0 100.0 100.0 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 17 2010 May 100.0 100.0 99.2 99.2 100.0 100.0 2010 Jun 100.0 100.0 100.0 100.0 100.0 100.0 all data 92.6 92.2 93.3 94.8 93.6 94.2 Icing Loss In comparing Pitka’s Point to Saint Mary’s, one can see in the Icing Loss Comparison Table, Pitka’s Point and Saint Mary’s, which is focused only on the complete common data months of September 2008 to January 2009, that data recovery is six to ten percent better at the Saint Mary’s met tower. This indi- cates fewer icing events and/or less severe icing than at the Pitka’s Point met tower. Note again, how- ever, that Pitka’s Point recorded significantly higher wind speeds during this comparison period, indicat- ing a tradeoff between stronger winds and an increased icing risk. In the following table of icing loss comparison between Saint Mary’s and Mountain Village, one can see comparable icing data loss during winter 2009/2010, but this data loss was very minimal and stands in sharp contrast to the previous winter when the Saint Mary’s met tower experienced considerable icing loss, culminating in loss of the met tower in February 2009 due to icing. Because there is no simultaneous data from all three met towers addressed in this study, it is not possi- ble to directly compare wind resource and icing of all three sites. But, one can conclude that rime icing does occur, the Pitka’s Point site appears to experience worse icing than the Saint Mary’s and Mountain Village sites, but the number and severity of icing events apparently differ considerably from one winter to the next. The Saint Mary’s and Mountain Village met towers will remain in place at least through winter 2010/2011, so an excellent opportunity exists to determine if the coming winter more resembles winter 2008/2009 or winter 2009/2010. Icing Data Loss Comparison Table, Pitka’s Point and Saint Mary’s anemometers vanes Pitka's Pt St Mary's Pitka's Pt St Mary's Pitka's Pt St Mary's Pitka's Pt St Mary's 38 m 38 m 29 m 29 m 21 m 18 m 38 m 38 m Year Month Recovery Recovery Recovery Recovery Recovery Recovery Recovery Recovery Rate (%) Rate (%) Rate (%) Rate (%)Rate (%)Rate (%) Rate (%) Rate (%) 2008 Sep 100.0 100.0 100.0 100.0 100.0 100.0 96.6 96.4 2008 Oct 96.3 100.0 98.8 100.0 96.9 94.6 92.4 95.9 2008 Nov 62.3 61.6 59.9 65.0 56.7 65.1 54.3 55.2 2008 Dec 62.2 86.7 64.6 83.7 61.0 82.7 44.4 70.6 2009 Jan 52.6 52.1 53.7 53.3 56.2 51.7 42.3 47.3 data average 74.7 80.1 75.4 80.4 74.2 78.8 66.0 73.1 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 18 Icing Data Loss Comparison Table, Saint Mary’s and Mountain Village Saint Mary's Mountain Village anemometers anemometers 38 m 29 m 18 m 50 m A 41 m 32 m Year Month Recovery Recovery Recovery Recovery Recovery Recovery Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) Rate (%) 2009 Nov 95.8 74.4 93.6 97.8 97.8 94.2 2009 Dec 93.4 93.7 93.2 91.6 91.6 91.6 2010 Jan 98.3 98.3 98.3 87.8 89.0 90.6 2010 Feb 79.5 78.3 78.1 85.5 77.5 86.9 2010 Mar 100.0 100.0 84.5 78.7 90.9 85.3 2010 Apr 96.9 99.8 99.8 100.0 100.0 100.0 2010 May 100.0 100.0 100.0 100.0 99.2 100.0 2010 Jun 100.0 100.0 100.0 100.0 100.0 100.0 95.5 93.1 93.4 92.7 93.3 93.6 Documentation of Icing Events Rime icing is more problematic for wind turbine operations than freezing rain (clear ice) given its tenaci- ty and longevity in certain climatic conditions. For this reasons, wind power in the Saint Mary’s area should be developed with consideration to the possible need for anti-icing and de-icing measures. These measures may include redundant control sensors, heated rotor blades, and/or leading edge blade heaters. This may be a particular concern at the Pitka’s Point wind site. Although ideally one would fac- tor availability loss due to icing into turbine performance Following is documentation of rime icing conditions encountered in the met tower data and observed by AVEC personnel. Note also that rime icing during a winter storm led to collapse of the Pitka’s Point and Saint Mary’s met towers in February 2009. An icing event leading to data recovery loss from the sensors is indicated in the January 15, 2009 photo- graphs below, which clearly indicate the presence of icing conditions. This icing event is also shown in the data graphs of January 15 below. Note that temperature is below freezing, relative humidity is high, wind speed standard deviation equals zero, and the wind speeds are stopped at their offset values of 0.4 m/s. Note that both met towers collapsed on February 13, 2009 from ice loading, providing graphic evi- dence of the problematic icing environment at the sites. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 19 Pitka’s Point Icing Event Photographs, 1/15/2009 Brian Fouts photos Pitka’s Point Icing Event Data, 1/14 to16/2009 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 20 Saint Mary’s Icing Event Photographs, 1/15/2009 Brian Fouts photos Saint Mary’s Icing Event Data, 1/14 to16/2009 Note: Saint Mary’s temperature sensor malfunctioned, repaired midday Jan. 15 Note, however, that the January 15, 2009 icing event was relatively minor in that the ice layer accumu- lated on the met towers was relatively thin and the anemometers were frozen and out of service for only forty hours or so. Other icing events, although not documented with photographs, have been more significant. For instance, from December 30, 2007 to January 14, 2008, an icing event occurred at the Pitka’s Point met tower sufficient to render all four anemometers, including the heated IceFree anemo- Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 21 meter, inoperative. The humidity sensor was not installed on the met tower at that time, so relative humidity data cannot be reviewed, but clearly this had been an icing event. Pitka’s Point Icing Event Data, 12/30/2007 to 1/14/2008 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 22 Pitka’s Point Met Tower Met Tower Sensor Information, Pitka’s Point Channel Sensor type Height Multiplier Offset Orientation 1 NRG #40C anemometer 38 m 0.765 0.35 NNE 2 NRG IceFree III anemo- meter 28 m 0.572 1.0 WNW 3 NRG #40C anemometer 29 m 0.765 0.35 NNE 4 NRG #40C anemometer 21 m 0.765 0.35 NNE 7 NRG #200P wind vane 38 m 0.351 260 080° T 8 NRG IceFree III wind vane 29 m 0.351 350 350° T 9 iPack Voltmeter 0.021 0 10 NRG #110S Temp C 2 m 0.136 -86.383 N/A 12 RH-5 relative humidity 2 m 0.097 0 Measured Wind Speeds Measured wind speeds at the Pitka’s Point met tower are quite high, with an annual average exceeding 7.7 m/s at the top of the tower. Wind Speed Sensor Summary, Pitka’s Point (Oct 2007 to Feb 2009) Variable Speed 38 m Speed 29 m Speed 28 m IceFree Speed 21 m Height above ground (m) 38 29 28 21 Mean wind speed (m/s) 7.72 7.21 7.24 6.88 MMM wind speed (m/s) 7.81 7.27 7.36 6.94 Max 10-min avg wind speed (m/s) 29.5 29.2 28.2 28.4 Max gust wind speed (m/s) 35.9 36.3 35.1 36.3 Weibull k 1.96 1.88 2.07 1.91 Weibull c (m/s) 8.70 8.12 8.16 7.74 Mean power density (W/m²) 579 491 450 420 MMM power density (W/m²) 587 493 474 419 Mean energy content (kWh/m²/yr) 5,069 4,299 3,941 3,676 MMM energy content (kWh/m²/yr) 5,145 4,320 4,156 3,672 Energy pattern factor 1.95 2.02 1.84 2.00 Frequency of calms (%) 20.1 22.7 19.6 24.3 Data recovery rate (%) 75.2 78.1 75.1 77.2 1-hr autocorrelation coefficient 0.946 0.947 0.944 0.946 Diurnal pattern strength 0.046 0.045 0.050 0.044 Hour of peak wind speed 24 23 23 22 Seasonal Wind Profile, Pitka’s Point Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 23 Daily Wind Profile, Pitka’s Point The daily wind profile indicates that the lowest wind speeds of the day occur midday from about 10 a.m. to 2 p.m. and the highest wind speeds of the day occur during the evening hours of 8 p.m. to midnight. The daily variation of wind speed is remarkably minimal on an annual basis but more pronounced on a monthly basis (second graph). Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 24 Wind Shear At the Pitka’s Point met tower, the power law exponent was calculated at 0.175 with wind speeds fil- tered to include only those greater than 4 m/s, the cut-in speed for most turbines. This indicates mod- erate wind shear at the Pitka’s Point met tower site. Considering the high wind class of the site, a lower turbine hub height is likely a preferred option. Wind Shear Profile, Pitka’s Point Wind Power Density Another view of wind shear is wind power density by height above ground level. Wind power density is defined as the power per unit area of the wind with units of Watts per square meter. It is calculated by multiplying ½ times the air density times the wind speed cubed for each time step. The equation is P/A 3. 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 analy- Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 25 sis 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 in- creases substantially with turbine hub height at the Pitka’s Point site. Note that the measured power densities in the figure below differ from those reported in the data summary table of this report. The figure below uses all collected data (October 2007 to February 2009) while in the summary table these data are presented as annual averages. Temperature Scatterplots An observation of some interest is to compare by scatterplot 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 the entire temperature range of the Pitka’s Point site, even as low as (near) -30° C. A turbine selected for the Pitka’s Point site should be capable of operation down to at least -30° C but a -40° C temperature rating is preferable as an arctic standard. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 26 Wind Speed vs. Temperature, Pitka’s Point, 38 m anem. Wind Power Density vs. Temperature, Pitka’s Point, 38 m anem. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 27 Extreme Wind Analysis modified Gumbel distribution, the probability of winds exceeded a certain value within a defined period of time is predicted. Another way to consider the analysis though is by the concept of return pe- riod. 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 International Electrotechnical Commission (IEC) standards of Class (per IEC 61400-1, edition 3). At the Pitka’s Point met tower site, maximum predicted 50 year wind speed (ten minute av- erage) at 38 meters is 36.2 m/s and the maximum predicted 50 year wind gust (two second) at 38 me- ters elevation is 44.0 m/s. This (just barely) qualifies the site as IEC Class III, the lowest and most com- mon extreme wind designation class. RETURN PERIOD SPEED Average Gust Factor:1.22 IEC 50-year extreme wind Pitka's Point RETURN YR 10 min average, m/s 2 sec gust, m/s Class Vref (10 min), (m/s) 38 meter 2 26.8 32.6 I 50.0 10 31.5 38.3 II 42.5 15 32.7 39.8 III 37.5 30 34.7 42.2 S mfr specified 50 36.2 44.0 100 38.3 46.5 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 24.0 26.0 28.0 30.0 32.0 34.0 36.0 38.0 40.0 2 10 15 30 50 10010 min Extreme Wind Speed, m/sReturn Period, years Extreme Wind Speed vs. Return Period Max. 10 min Avg Wind Speed, m/s Power (Max. 10 min Avg Wind Speed, m/s) Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 28 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 38 meter level, Weibull parameters are k = 1.95 and c = 8.67 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 (Raleigh) 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 22 percent of the winds at 38 meters are less than 4 m/s, the standard cut-in speed of most turbines and almost 100 percent of the winds are less than 25 m/s, the standard high wind cut-out speed for most turbines (speeds refer to 10-min averages). PDF Curve, Pitka’s Point, 38 m CDF Curve, Pitka’s Point, 38 m Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 29 Wind Roses Pitka’s Point winds are bi-directional with the wind frequency rose indicating a nearly equal component of north and east-northeast winds, with slightly more frequent ENE winds. For power producing winds, one can then see that ENE winds dominate. Note that a wind threshold of 4 m/s was selected for the definition of calm winds. This wind speed represents the cut-in wind speed of most wind turbines. By this definition, Pitka’s Point experiences twenty percent annual calm conditions (see wind frequency rose below). Wind Frequency Rose Total Value (power density) Rose Turbulence Intensity The turbulence intensity (TI) is acceptable with a mean turbulence intensity of 0.076 and a repre- sentative turbulence intensity of 0.105 at 15 m/s wind speed, indicating quite smooth air for wind turbine operations. This equates to an International Electrotechnical Commission (IEC) 3rd Edition (2005) turbulence category C, which is the lowest defined category. These data are shown in the turbulence intensity graph below. As seen, representative TI (90th percentile of the turbulence in- tensity values, assuming a normal distribution) at 15 m/s is well under IEC Category C criteria at the Pitka’s Point met tower site. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 30 IEC 3rd Edition Turbulence Intensity Graph, Pitka’s Point, 38 m Anemometer Air Temperature and Density Over the reporting period, the Pitka’s Point met tower had an average temperature of -2.8° C. The min- imum recorded temperature during the measurement period was –28.8° C and the maximum tempera- ture was 27.7° C, indicating a wide variability of an ambient temperature operating environment impor- tant to wind turbine operations. Consequent to the cool temperatures, the average air density of 1.285 kg/m 3 is nearly seven percent higher than the standard air density of 1.204 kg/m 3 (13.8° C and 99.2 kPa standard temperature and pressure at 177 m elevation), indicating that the Pitka’s Point met tower site has denser air than the standard air density used to calculate turbine power curves (note that all turbine power curves are cal- culated at a sea level standard of 15.0° C and 101.3 kPa pressure). Temperature Air Density Month Mean Min Max Mean Min Max (°C) (°C) (°C) (kg/m³) (kg/m³) (kg/m³) Jan -15.1 -29.0 3.9 1.321 1.204 1.416 Feb -18.0 -28.8 0.2 1.355 1.264 1.414 Mar -11.7 -25.7 3.8 1.323 1.248 1.397 Apr -7.0 -21.3 6.8 1.299 1.235 1.372 May 4.1 -10.1 18.6 1.247 1.185 1.314 Jun 9.5 -1.4 21.2 1.223 1.174 1.272 Jul 10.3 3.3 27.7 1.220 1.149 1.250 Aug 10.7 0.6 21.6 1.218 1.173 1.263 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 31 Sep 7.3 -1.1 18.1 1.233 1.187 1.270 Oct -5.2 -15.0 2.9 1.287 1.204 1.339 Nov -8.7 -25.9 7.0 1.308 1.234 1.398 Dec -10.1 -26.8 7.2 1.305 1.204 1.403 Annual -2.8 -28.8 27.7 1.285 1.149 1.416 Annual Temperature Boxplot, Pitka’s Point Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 32 Saint Mary’s Met Tower Met Tower Sensor Information, Saint Mary’s Channel Sensor type Height Multiplier Offset Orientation 1 NRG #40C anemometer 38 m 0.765 0.35 N 2 NRG #40C anemometer 28.5 m 0.765 0.35 N 3 NRG #40C anemometer 18 m 0.765 0.35 N 7 NRG #200P wind vane 38 m 0.351 265 085° T 8 NRG #200P wind vane 29 m 0.351 285 105° T 9 iPack Voltmeter 0.021 0 11 NRG #110S Temp C 2 m 0.136 -86.383 N/A 12 RH-5 relative humidity 2 m 0.098 0 Measured Wind Speeds Measured wind speeds at the Saint Mary’s met tower are moderately high, with an annual average ex- ceeding of 6.8 m/s at the top of the tower. Wind Speed Sensor Summary, Saint Mary’s (Aug 2008 to June 2010) Variable Speed 38 m Speed 29 m Speed 18 m Measurement height (m) 38 28.5 18 Mean wind speed (m/s) 6.80 6.56 5.99 MMM wind speed (m/s) 6.83 6.37 6.02 Max 10-min avg wind speed (m/s) 24.0 23.8 22.3 Max gust wind speed (m/s) 29.8 29.8 30.6 Weibull k 2.21 2.16 2.15 Weibull c (m/s) 7.66 7.40 6.76 Mean power density (W/m²) 353 327 248 MMM power density (W/m²) 359 299 251 Mean energy content (kWh/m²/yr) 3,092 2,867 2,169 MMM energy content (kWh/m²/yr) 3,142 2,621 2,199 Energy pattern factor 1.742 1.776 1.791 Frequency of calms (%) 20.4 22.0 26.9 Data recovery rate (%) 84.1 55.6 83.2 1-hr autocorrelation coefficient 0.917 0.918 0.913 Diurnal pattern strength 0.040 0.034 0.051 Hour of peak wind speed 21 20 18 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 33 Monthly and Seasonal Wind Profiles, Saint Mary’s Daily Wind Profile, Saint Mary’s Similarly as measured by the Pitka’s Point met tower, daily wind profile at the Saint Mary’s met tower is rather flat but higher wind speeds do occur in the afternoon and early evening as one would expect. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 34 Wind Shear At the Saint Mary’s met tower, the power law exponent was calculated at 0.175 with wind speeds fil- tered to include only those greater than 4 m/s, the cut-in speed for most turbines, indicating moderate wind shear at the Pitka’s Point met tower site. Wind Shear Profile, Saint Mary’s Wind Power Density Power density and hence potential turbine power production increases substantially with turbine hub height at the Saint Mary’s site. Note that the measured power densities in the figure below differ from those reported in the data summary table of this report. The figure below uses all collected data (August 2008 to June 2010) while in the summary table these data are presented as annual averages. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 35 Scatterplot At the Saint Mary’s site, power producing winds (greater than 4 m/s) are present through the entire temperature range of the site, even as low as (near) -30° C. A turbine selected for the Saint Mary’s site should be capable of operation down to at least -30° C but a -40° C temperature rating is preferable as an arctic standard. Wind Speed vs. Temperature, Saint Mary’s, 38 m anem. Extreme Wind Analysis At the Saint Mary’s met tower site, maximum predicted 50 year wind speed (ten minute average) at 38 meters is 33.1 m/s and the maximum predicted 50 year wind gust (two second) at 38 meters elevation is 40.6 m/s. This qualifies the site as IEC Class III, the lowest and most common extreme wind designation class. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 36 Probability Distribution Function At the 38 meter level at the Saint Mary’s site, Weibull parameters are k = 2.21 and c = 7.66 m/s (“k” is the shape factor and “c” is the scale factor) for the data period. This shape factor is indicative of a near normal (Raleigh) wind distribution for wind power sites. Wind Roses Saint Mary’s winds are bi-directional with the wind frequency rose indicating a nearly equal component of north and east-northeast winds, with an edge towards more frequent ENE winds. Power density winds are also bi-directional north and ENE without the domination of ENE winds observed at the Pitka’s Point site. This lesser extent of powerful ENE winds may be a reflection of the wind class difference be- Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 37 tween Pitka’s Point and Saint Mary’s. Note also that the Saint Mary’s site experiences 20 percent calm wind conditions (winds less than 4 m/s). Wind Frequency Rose Total Value (power density) Rose Turbulence Intensity The turbulence intensity (TI) is acceptable with a mean turbulence intensity of 0.101 and a repre- sentative turbulence intensity of 0.132 at 15 m/s wind speed, indicating smooth air for wind turbine operations. This equates to an International Electrotechnical Commission (IEC) 3rd Edition (2005) turbulence category C, which is the lowest defined category. These data are shown in the turbu- lence intensity graph below. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 38 IEC 3rd Edition Turbulence Intensity Graph, Saint Mary’s, 38 m Anemometer Air Temperature and Density Over the reporting period, the Saint Mary’s met tower recorded an average temperature of -1.8° C. The minimum recorded temperature during the measurement period was –30.9° C and the maximum tem- perature was 25.5° C, indicating a wide variability of an ambient temperature operating environment important to wind turbine operations. Consequent to the cool temperatures, the average air density of 1.271 kg/m 3 is five percent higher than the standard air density of 1.209 kg/m3 (14.1° C and 99.6 kPa standard temperature and pressure at 139 m elevation), indicating that the Saint Mary’s met tower site has denser air than the standard air density used to calculate turbine power curves (note that all turbine power curves are calculated at a sea level standard of 15.0° C and 101.3 kPa pressure). Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 39 Annual Temperature Boxplot, Saint Mary’s Month Mean Min Max Mean Min Max (°C) (°C) (°C) (kg/m³) (kg/m³) (kg/m³) Jan -14.0 -26.7 4.0 1.309 1.209 1.409 Feb -12.5 -30.9 3.2 1.329 1.209 1.433 Mar -15.6 -29.0 2.5 1.279 1.209 1.422 Apr -3.7 -17.5 9.7 1.268 1.209 1.358 May 4.3 -6.3 18.8 1.252 1.189 1.301 Jun 12.0 2.7 23.7 1.217 1.170 1.259 Jul 13.2 6.0 25.5 1.213 1.162 1.244 Aug 10.6 -1.0 20.9 1.224 1.181 1.276 Sep 7.1 -2.6 18.2 1.239 1.192 1.283 Oct -2.5 -15.9 12.4 1.283 1.216 1.350 Nov -11.9 -27.0 1.1 1.327 1.209 1.410 Dec -9.5 -28.6 4.3 1.317 1.209 1.420 Annual -1.8 -30.9 25.5 1.271 1.162 1.433 Temperature Air Density Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 40 Mountain Village Met Tower Met Tower Sensor Information, Mountain Village Channel Sensor type and design. Height Multiplier Offset Orientation 1 NRG #40C, 50 m A 50.3 m 0.760 0.36 000° T 2 NRG #40C, 50 m B 50.5 m 0.757 0.41 135° T 3 NRG #40C, 40 m 40.8 m 0.761 0.33 000° T 13 NRG #40C, 41 m 41.1 m 0.758 0.33 135° T 14 NRG #40C, 31 m 31.8 m 0.758 0.34 000° T 15 NRG #40C, 32 m 32.0 m 0.761 0.33 135° T 7 NRG #200P wind vane 46.1 m 0.351 270 090° T 8 NRG #200P wind vane 40.1 m 0.351 270 090° T 9 NRG #110S Temp C 2 m 0.136 -86.383 000° T 10 RH-5 relative humidity 2 m 0.098 0 12 iPack Voltmeter 0.021 0 Measured Wind Speeds Measured wind speeds at the Mountain Village met tower are reasonably high to date, with an average of 8.0 m/s at the top of the tower (50 meters). Note however that most of summer data has yet to be collected so annual average wind speed is likely to be less than 8.0 m/s. Wind Speed Sensor Summary, Mountain Village (November 2009 to June 2010) Variable Speed 50 m B Speed 50 m A Speed 41 m Speed 40 m Speed 32 m Speed 31 m Measurement height (m) 50.5 50.3 41.1 40.8 32 31.8 Mean wind speed (m/s) 8.017 7.896 7.667 7.624 7.364 7.323 Max 10-min avg wind speed (m/s) 25.1 24.9 24.8 25.6 24.8 24.9 Max gust wind speed (m/s) 30.8 31.1 Weibull k 2.231 2.245 2.21 2.221 2.213 2.228 Weibull c (m/s) 9.036 8.899 8.644 8.596 8.302 8.259 Mean power density (W/m²) 586 558 518 509 459 450 Mean energy content (kWh/m²/yr) 5,135 4,884 4,541 4,458 4,021 3,946 Energy pattern factor 1.722 1.714 1.74 1.739 1.74 1.737 Frequency of calms (%) 14.39 14.76 15.77 16.08 17.26 17.37 Data recovery rate (%) 92.21 92.56 93.27 94.83 93.56 94.16 1-hr autocorrelation coefficient 0.927 0.925 0.924 0.925 0.921 0.922 Diurnal pattern strength 0.045 0.041 0.036 0.032 0.035 0.033 Hour of peak wind speed 20 20 19 19 19 19 Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 41 Monthly Wind Profile, Mountain Village Daily Wind Profile Similarly as measured at the Pitka’s Point and Saint Mary’s met towers, daily wind profile to date at the Mountain Village met tower is rather flat but higher wind speeds do occur in the afternoon and early evening as one would expect. Wind Shear At the Mountain Village met tower, the power law exponent is calculated date at 0.169 with wind speeds filtered to include only those greater than 4 m/s, the cut-in speed for most turbines, indicating moderate wind shear at the Mountain Village met tower site. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 42 Wind Shear Profile, Mountain Village Wind Power Density Power density as a function of height at the Mountain Village met tower site will be presented when additional data has been collected. Scatterplot At the Mountain Village site, power producing winds (greater than 4 m/s) are present through the entire temperature range of the site, even as low as (near) -30° C. A turbine selected for the Saint Mary’s site should be capable of operation down to at least -30° C but a -40° C temperature rating is preferable as an arctic standard. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 43 Extreme Wind Analysis At present, insufficient data exists to calculate extreme wind probabilities for the Mountain Village met tower test site. Probability Distribution Function At the 50 meter level at the Mountain Village site to date, Weibull parameters are k = 2.25 and c = 8.90 m/s (“k” is the shape factor and “c” is the scale factor) for the data period. This shape factor is indicative of a near normal (Raleigh) wind distribution for wind power sites, although one weighted toward higher wind speeds. The shape factor will likely decrease toward 2.0 as additional summer data is included. Wind Roses To date, Mountain Village winds are dominated by north, northeast and east winds. Power density winds are more bi-directional with NNE and east winds. Note also that to date the Mountain Village site experiences 13 percent calm wind conditions (winds less than 4 m/s). This percentage will almost cer- tainly increase with inclusion of additional summer data. Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 44 Wind Frequency Rose Total Value (power density) Rose Turbulence Intensity The Mountain Village site turbulence intensity (TI) is acceptable with a mean turbulence intensity of 0.068 and a representative turbulence intensity of 0.095 at 15 m/s wind speed, indicating very smooth air for wind turbine operations. This equates to an International Electrotechnical Commis- sion (IEC) 3rd Edition (2005) turbulence category C, which is the lowest defined category. These data are shown in the turbulence intensity graph below. IEC 3rd Edition Turbulence Intensity Graph, Mountain Village, 50 m B anemometer Saint Mary’s, Alaska Wind Power Report V3 Energy, LLC, Eagle River, Alaska 45 Air Temperature and Density Over the reporting period, the Mountain Village met tower recorded an average temperature of -7.3° C. The minimum recorded temperature during the measurement period was –33.3° C and the maximum temperature was 24.3° C, indicating a wide variability of an ambient temperature operating environ- ment important to wind turbine operations. Note, however, that the data period does not include most of the summer months, so average annual temperature will be higher, and likely equivalent to that rec- orded at the Pitka’s Point and Saint Mary’s met towers. Annual Temperature Boxplot, Mountain Village