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HomeMy WebLinkAboutSolar Wind Consultants Solar Site Survey Report for Noatak july 2009Solar Wind Consultants 915 30"Avenue Suite 229 Fairbanks,AK 99701 Solar Site Survey Report For the Alaska Village Electric Cooperative Noatak,AK Report Date:22 July 2009 Prepared by Greg Egan Reviewed by Bruno Grunau P.E. Solar Site Survey Report For the Alaska Village Electric Cooperative Noatak,AK Introduction: Alaska Village Electric Cooperative (AVEC)has requested a Solar Site Survey for their facility located in the village of Noatak,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 26,2009. 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 So/ar 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 104 miles from Noatak. 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/fyO8osti/43156.pdf 2."Wattsun Solar Tracker Spacing,”Solar Shading Design Tool retrieved 01 July 2009 from www.wattsun.com/reference. Web Source:http://www.wattsun.com/spreadsheet/Wattsun_Tracker_Spacing.xls Site Survey 1: A site survey was conducted on land located between the existing AVEC Power Plant and the Noatak River.The site consists of a gravel 4-wheeler trail that runs for a few hundred feet along the west side of the river.Figure 1 depicts a northern view of the north end of the trail,showing the existing AVEC tank farm and power plant facilities on the west side. 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 the one shown in Figure 2,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 diagram has been edited within the SPA software to trace the landscape features which would cause shading on a PV array.Figure 2 shows a photo of the SP and a sunpath diagram generated from the same photo,side by side.The outline of part of the Noatak power plant and tank farm can be seen in both images. As indicated in the sunpath diagram there is significant shading due to the fuel tanks and willows located higher on the riverbank to the west.These obstructions can cause a substantial reduction in power output even if only a small portion of the PV array is shaded. Figure 2:Digital photo of SP (left)next to a sunpath diagram (right)generated with SPA software 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 increasedduringthelatespringandsummer. Analysis of digital photos of the 5S?with the SPA software indicate an azimuth angle of 153 degrees to be optimum for power production.However,this does not take into consideration the site available for the PV array is narrow and runs on a north-south (N-S) axis. To accommodate a 50.4 kW PV array on this site,16 pole mounted sub-arrays could be installed in a row along the riverfront with approximately 20'separating each sub-array from the next.Unfortunately this configuration would result in most of the sub-arrays being shaded part of the day due to the arrays being lined up on a N-S axis (see Figure 3). The southernmost array would not be shaded by any PV modules in the system,however all remaining arrays would be shaded part of each day by the pole mounted arrays located to the south, Figure 3.Possible location of pole mounted PV arrays along the river These shading concerns were verified using an inter-row shading calculator developed by Array Technologies,Inc.of Albuquerque,NM (see reference 2).Unfortunately,even on the summer solstice,the bottom row of modules on most of the sub-arrays would be shaded.This partial shading would severely limit the PV systems ability to generate electric power throughout the year. An alternative array configuration for the riverbank site would be to install the modules facing east along the river.The modules could be mounted side by side in a long row on adjustable ground or top of pole mounts.As is indicated by the sunpath diagram in Figure 2,the landscape to the east of the power plant is virtually flat all the way to the horizon.Though not an optimal design solution,it would eliminate the problem of inter-row moduleshading. Figure 4.Possible location for ground mounted PV arrays facing east along the Noatak. Site Survey 2: A second site survey was conducted on property west of the village and adjacent to the newly constructed school.The lot consists of permafrost soils with occasional scrub spruce trees among the tussocks.Figure 5 shows a panoramic view to the southwest of the proposed site.The SP instrument can be seen in the foreground.The west end of the school can be seen on the left. Figure 5.View 'ooking southwest from a potential solar site nearschool ) For reference,the photo (Figure 5)was taken from near the center of the cross hatched 100'x 100'square lot in Figure 6.The building on the left side of the photo is the existing school.The current site shows the area to be relatively free of significant shading issues however;the proposed new power plant and tank farm would significantly change the landscape.Without knowing the height of the tanks and power plant facilities or their exact location it is difficult to predict how they would affect a 50 kW array to the northeast.A proposed future addition to the school (outlined in blue -see figure 6)may create shading on the PV array. AVEC Tank Farm and Dispensing Facility Potential Solar Cells Figure 6.Proposed location of new AVEC facilities and potential solar array site An alternative solution to the potential solar site shown in Figure 6 would be to have the PV array installed to the south of the proposed power plant facilities,as suggested in Figure 7.The 50.4 kW PV array is represented by one yellow rectangle to the south of the power plant and one yellow rectangle located on top of the plant.The reason for placement of a second section of solar modules above the power plant buildings is the lack of available space on the property to install all the modules in one long south-facing row. If the remainder of the modules were mounted above the power plant any affects of shading caused by the row of modules to the south would be minimal.This configuration may lower installation costs by reducing the amount of foundation materials needed to support the building-mounted array. Since solar modules have an expected service life of 30 years or more,strategically locating solar arrays in places where they will not be shaded by existing structures or future construction projects (for the next 30 years)would be a prudent use of resources. Suggested Solar Farm and Site Dispensing Facility Figure 7.Suggested PV Array Location Digital photos were taken of the SP at the potential solar site.The images were then uploaded to a computer and analyzed using SPA software.Figure 8 shows the sunpath diagram generated for this site.The grey area visible in the top left portion of the diagram represents shading from the existing school building. Figure 8.Sunpath diagram for the potential solar site noted in Figure 6 Power Production Estimate: 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 used in these production estimates consist 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.” The production module assumes 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 located at the riverfront site facing east (as described by Figure 4)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 Production for 50.4 kW Array Riverfront Site:Tilt Angle =90°/52° Average Solar Actual AC Actual AC Red w/Shading Energy (KWH)Energy (KWH) (KWhr/m'2)wi shading wio shading Azimuth=100°Azimuth=100°Azimuth=100°Estimated FuelTilt=90°for snow'Tilt=90°for snow ='Tilt=90°for snow Savings Tilt=52°for Tilt=52°for Tilt=52°for (Gallons) summer (May -summer (May -summer (May -(based on 13.5 Month Sep)Sep)Sep)kWh /Gallon) January 0.14 170.00 221.00 12.59 February 0.44 472.18 477.00 34.98 March 1.86 2,518.51 2,551.00 186.56 April 2.89 3,722.95 3,826.00 275.77 May 4.85 6,323.01 6,389.00 468.37 June 5.51 6,866.14 6,960.00 508.60 July 3.59 4,468.64 4,632.00 331.01 August 3.00 3,849.57 4,066.00 285.15 September 2.70 3,403.87 3,445.00 252.14 October 0.93 1,115.55 1,119.00 82.63 November 0.19 228.08 243.00 16.89 December 0.01 5.42 7.00 0.40 Totals 33,143.92 33,936.00 2455.11 Table 2 shows estimated power production for a 50.4 kW array that would be located at the site near the school,as described by Figure 6.The production model assumes the array would be located facing due south and that the array tilt angle would be at 52 degrees May through September and at 90 degrees the remainder of the year. 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 Production for 50.4 kW Array West of School:Tilt Angle =90°/52° Average Solar Actual AC Actual AC Rad wi Shading Energy (KWH)w/=Energy (KWH)(KWhr/m*'2)shading wio shading Azimuth=100°Azimuth=100°Azimuth=100°Estimated Fuel Tilt=90°for Tilt=90°for snow Tilt=90°for snow Savings snow Tilt=52°Tilt=52°for Tilt=52°for (Gallons) for summer summer (May -summer (May -(based on 13.5 Month (May -Sep)Sep)Sep)kWh /Gallon) January.0.41 639.97 1,371.00 82.86 February 1.12 1,457.00 1,709.00 107.93 March 3.63 5,188.00 5,285.00 382.36 April 4.06 5,144.42 5,152.00 381.63 May 6.05 7,662.00 7,662.00 567.56 June 6.72 8,186.81 8,194.00 606.96 July .4.27 5,137.00 5,138.00 380.57 August 3.83 4,830.93 4,850.00 359.02 September 3.77 4,759.65 4,861.00 389.94 October 2.18 2,929.45 3,505.00 216.86 November 0.47 653.19 1,284.00 77.73 December 0 0 268 19.85 Totals 46,588.42 49,279.00 3573.26 The power production estimate takes into account the effects of shading by the existing school structure to the west,as shown in Figure 8.If,however,the proposed power plant building structures were placed to the south of the array,the effects of shading compromise the array's ability to perform as estimated in Table 2.Since these effects are unknown,they have not been considered in the power production estimate. Other Considerations Affecting Production: Future construction across the road to the south of the proposed power plant could adversely affect future power production at the suggested site of the array.As noted above,since solar modules have an expected service life of 30 years or more,locating solar arrays in areas where they will not be shaded by existing structures or future construction projects (for the next 30 years)is a most effective strategy. Conclusions: The riverfront site is the less desirable of the locations surveyed,most notably,due to the effects of significant shading from the western sun.A south-facing array at this location would suffer from the effects of shading from the arrays to the south as well as the tanks to the west.As estimated in Table 1,an east-facing array at this location would produce approximately 34,000 KWH/year. The future power plant location,as described by Figures 6 and 7,would be the most desirable of the locations surveyed due to the lack of existing solar obstructions.The site survey was conducted at the position described in Figure 6 and the estimated power production was found to be approximately 46,600 KWH/year. As described by Figure 7,the recommended strategy to increase annual power production (to a maximum of 49,000 KWH/year,as described in Table 2)would be to place one array on an adjustable rack to the south of the proposed power plant and another array on the power plant structure in such a manner that the array to the south does not shade the array on the power plant structure.Should this approach be taken to increase power production,due diligence must be practiced to ensure that future construction,materials storage and the like,do not shade the arrays for the anticipated usable life of the PV array (at least 30 years). The relatively close proximity of any of the proposed PV array sites to the power plant would allow 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 would 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.