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HomeMy WebLinkAboutSolar Wind Consultants Solar Site Survey Report Shungnak june 2009Solar Wind Consultants 915 30°Avenue Suite 229 Fairbanks,AK 99701 Solar Site Survey Report For the Alaska Village Electric Cooperative Shungnak,AK Report Date:30 June 2009 Prepared by Greg Egan Reviewed by Bruno Grunau P.E. Solar Site Survey Report For the Alaska Village Electric Cooperative Shungnak,AK Introduction: Alaska Village Electric Cooperative (AVEC)has requested a Solar Site Survey for their facility located in the village of Shungnak,Alaska.This report is intended to provide power production estimates for a proposed 50 kW photovoltaic (PV)system as well as solar array shading and layout considerations.It is based on information gathered during a visit to the proposed PV system site on May 29,2009. Using the Solar Pathfinder™(SP)site analysis tool,sunpath diagrams were generated from digital photos taken at the site.These images were then analyzed using Solar Pathfinder Assistant™Version 4.0 (SPA)software.SPA uses TMY3 data sets (see reference 1) derived from the 1991-2005 National Solar Radiation Data Base (NSRDB)update,which was developed by the National Renewable Energy Laboratory (NREL)and contains hourly solar radiation and meteorological data for 1,454 stations across the country'.In this case the nearest NREL-published data station is in Selawik,Alaska,a distance of 80 miles from Shungnak. References: 1."Users Manual for TMY3 Data Sets,”NREL/TP-581-43156 revised May 2008 retrieved 16 June 2009 from the National Renewable Energy Laboratory.Web Source:http://www.nrel.gov/docs/fy08osti/43156.pdf Site Survey: A site survey was conducted on the lot leased by AVEC just northwest of the Shungnak Power Plant facility.The lot consists of permafrost soils with scattered black spruce. Figure 1 depicts the south view of the lot,showing the SP and tripod in the foreground. 1 TMY3 data are Typical Meteorological Year (TMY)hourly values of solar radiation and meteorological elements derived from the 1961-1990 and 1991-2005 NSRDB. Digital photos,similar to those shown in Figures 2 and 3,were taken of the SP which were then uploaded to a computer and analyzed using SPA software. A sunpath diagram is a circular projection of the sky vault onto a flat diagram used to determine solar positions and shading effects of landscape features on a solar energy system.The sunpath diagrams have been edited within SAA to trace the landscape features which would cause shading on a PV array.Figures 2 and 3 are two sunpath diagrams generated from photos taken on site.Figure 2 shows the outline of spruce trees scattered on the property.In this image,the area between the yellow line and the edge of the SP lense is considered by the SPA software to be completely shaded and therefore it is presumed that no power will be produced when the sun is obstructed by the trees during certain parts of the year.Figure 3 shows the same photo of the sunpath diagram for this site assuming,however,that the trees that cause shading were removed from the site. The white line in Figure 3 describes the presumed shading effects. Trees and other obstructions can cause a substantial reduction in power output,even if only a small portion of the PV array is shaded.The software was run first using the image on the left and then the one on the right.The results showed an increase in power production of 15.5%using the image with most of the trees removed (Figure 3). Figure 2.Sunpath diagram with trees Figure 3.Sunpath diagram with trees cut Accumulation of snow during colder months can severely limit the power produced by solar electric panels.Fixing the array tilt at 90 degrees (plumb)will keep most of the snow from accumulating on the panels and adversely affecting output.However a 90-degree tilt is not the optimum angle for year-round power production.Having the panels mounted on adjustable racks will allow the tilt angle to be decreased and power generation increased during the late spring and summer. Estimating Power Production: The power production estimates in this report are based on a system employing two hundred eighty-eight PV modules rated at 175 watts each.The modules are made up of monocrystalline cells and are manufactured by Sharp Solar.The inverters used in this model!are manufactured by Fronius and produce 277 vac 3-phase power.' It is also assumed that (1)the tilt angle of the PV array would be adjusted twice annually, once in the late spring and again in early fall,and (2)that any trees or other obstructions to sunlight would be removed as needed to enhance system performance. Table 1 shows estimated power production for a 50.4 kW array assuming the array would be facing true south and that the array tilt angle would be at 52 degrees May through September and at 90 degrees the remainder of the year. Table 1.Estimated Power Production for 50.4 kW Array:Tilt Angle =90°/52° Actual Solar Rad w/Shading Actual AC Ideal AC Energy(KWhrim?)Energy (KWH)w/(KWH)w/o Azimuth=180.0 shading shading Tilt=90°for Azimuth=180.0 Azimuth=180.0 snow Tilt=90°for snow Tilt =90°for snow, Tilt =52°for Tilt=52°for Tilt=52°for Estimated Solar summer (May -summer (May -Summer (May -Cost Savings Month Sep)Sep)Sep)$0.46/KWH January 0.41 639.97 1,371.00 $294.39 February 1.12 1,457.00 1,709.00 $670.22 March 3.63 5,188.00 5,285.00 $2,386.48 April 4.06 5,144.42 5,152.00 $2,366.43 May 6.05 7,662.00 7,662.00 $3,524.52 June 6.72 8,186.81 8,194.00 $3,765.93 July 4.27 5,137.00 5,138.00 $2,363.02 August 3.83 4,830.93 4,850.00 $2,222.23 September 3.77 4,759.65 4,861.00 $2,189.44 October 2.18 2,929.45 3,505.00 $1,347.55 November 0.47 653.19 1,284.00 $300.47 December 0 0 268 $0.00 Totals 36.51 46,588.42 49,279.00 $21,430.67 Table 2 shows estimated power production for a 50.4 kW array assuming the array would be facing true south and that the array tilt angle would be at 34 degrees May through September and at 90 degrees the remainder of the year.Changing the summer tilt angle to 34 degrees shows approximately a 2.5%increase in power production compared to the 90/52 tilt scenario used in Table 1. 2 Different models and/or brands of equipment may have significantly different operating efficiencies.Using different equipment could significantly affect system power production. Table 2.Estimated Power Production for 50.4 kW Array:Tilt Angle =90°/34° Actual Solar Rad wi Shading Actual AC Ideal AC (KWhrim?)Energy (KWH)-_Energy (KWH)Azimuth=180.0 wi shading wio shading Tilt=90°for Azimuth=180.0 =Azimuth=180.0 snow Tilt=90°for Tilt =90°for Estimated Tilt =34°for snow Tilt=34°snow,Tilt=34°Solar Cost summer (May-for summer for Summer Savings Month Sep)(May -Sep)(May -Sep)$0.46/KWH January 0.41 639.97 1,371.00 $294.39 February 1.12 1,457.00 1,709.00 $670.22 March 3.63 5,188.00 5,285.00 $2,386.48 April 4.06 5,144.42 5,152.00 $2,366.43 May 6.19 7,966.00 7,966.00 $3,664.36 June 7.02 8,651.81 8,658.00 $3,979.83 July 4.49 5,472.00 5,473.00 $2,517.12 August 3.84 4,869.95 4,911.00 $2,240.18 September 3.77 4,759.65 4,861.00 $2,189.44 October 2.18 2,929.45 3,505.00 $1,347.55 November 0.47 653.19 1,284.00 $300.47 December 0 0 268 $0.00 Totals 37.18 47,731.44 50,443.00 $21,956.46 Using the tilt optimization function of the software for the May through September timeframe,a tilt angle of 34 degrees was shown to produce the most power during this period;when the array is at a lesser angle and facing south,more of the solar insolation can reach the surface of the panels when the sun is in the northeast very early in the day, and from the northwest in the evening.However this model assumes that nothing would be placed on the land either northeast or northwest of the array that would obstruct solar access in the future. Other Considerations Affecting Production: Although the software and sunpath diagrams are very helpful in predicting how much power can be expected at a particular site,there are other issues that could affect power generation as well. For example there are a number of buildings and other obstructions visible in Figure 1 (and not evident in Figures 2 and 3)that could lower power output during the winter months. These obstructions are not indicated on the sunpath diagram therefore the actual power produced by the PV array could be slightly lower than what is indicated in Tables 1 and 2. The top of the SP when mounted on the tripod is about 3'above ground level.A solar array installed in the Arctic should be at least 3'above the ground to keep the modules above the snowpack.This means that all of the array would be higher than the level of the SP was when the sunpath photos were taken.If this system is installed in the yellow rectangular area shown in Figure 4,the top row of modules would be mounted about 16' above ground level. Because raising the solar array would have the same effect on power production as lowering the buildings and obstructions to the south,the probability of any shading from these obstructions would be minimal. Figure 4 shows the suggested location of the solar array.The array would require an area about 270'in length and 24'in depth.This layout for the array would keep all the modules on the same plane.The array could be split into 2 or more rows,however inter-row shading of modules can be significant,and can severely limit system power production. Figure 4.Overhead Photo of AVEC Facility in Shungnak,AK Showing Proposed Approximate Solar Array Location (Photo obtained from maps.google.com.) Conclusions: The site being considered by AVEC is only a few hundred feet from the Shungnak Power Plant.The relatively close proximity of the proposed PV array to the power plant allows for connection to the local grid without lengthy transmission lines which would add to project costs. Foundations for unheated structures on ice rich permanently frozen soils are usually constructed to ensure that the active layer is contained in a thaw-stable material such as gravel or that the load is supported by the frozen soil under the active layer.If a Triodetic foundation is used to support the array it would need to be installed on large quantities of non-frost susceptible soil such as gravel.Since gravel is not locally available,the shipping costs for this material would add substantially to overall project cost.The amount of gravel would be dependent upon the area of the foundation and the depth of the active layer of the soil that would have to be removed.Additionally,ballast material would need to be added to the foundation to keep the solar array from blowing over in the event of high winds in the area. An alternative installation option may be to drive piles into the permafrost at a depth substantial enough to resist jacking (and creep settlement)and install the array on the piles.