National Academies Press: OpenBook

Guidebook for Energy Facilities Compatibility with Airports and Airspace (2014)

Chapter: Appendix D - Solar Module Reflectivity Testing Data

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Suggested Citation:"Appendix D - Solar Module Reflectivity Testing Data." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Appendix D - Solar Module Reflectivity Testing Data." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Suggested Citation:"Appendix D - Solar Module Reflectivity Testing Data." National Academies of Sciences, Engineering, and Medicine. 2014. Guidebook for Energy Facilities Compatibility with Airports and Airspace. Washington, DC: The National Academies Press. doi: 10.17226/22399.
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Page 81

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D-1 Solar Module Reflectivity Testing Data In research for preparation of this Guidebook, testing was performed to measure solar reflectivity of different PV mod- ules to determine the potential impact of glare. PV modules and samples from different manufacturers were obtained, and the solar reflectance (total and specular) was measured on 24 different samples using a Surface Optics Corporation 410 Solar Reflectometer (see Figure D-1). The incidence angle of the light source in the 410 Solar was 20 degrees. Results show relatively similar reflectance values and behavior for all the samples.1 The total solar reflectivity generally ranged from 6 to 12 percent, while the specular solar reflectivity ranged from approximately 1 to 4 percent. Interestingly, the deep- textured glass sample did not show any measurable specular reflectance, which indicates a significant amount of scatter- ing of the reflected light relative to smooth or lightly textured surfaces. Smooth surfaces, such as mirrors and smooth glass, produce more specular reflections with greater intensity and tighter beams (i.e., larger retinal irradiances and smaller sub- tended angles), while solar receivers, textured glass, and anti- reflective coatings produce more diffuse reflections with lower solar intensities but greater subtended angles (see Figure D-2). However, it is important to note that these values are for an incidence angle of 20 degrees. At higher incidence angles, the reflectivity can increase significantly. Also as part of the testing, the reflectivity of selected PV samples as a function of incidence angle was measured using an illuminance meter and lasers (see Figure D-3). Reflectiv- ity measurements at incidence angles of 20, 40, 60, 70, and 80 degrees for different types of PV modules were made (e.g., glass texture, anti-reflective coating, etc.). Figure D-4 shows that nearly all of the results follow a consistent trend— the near-normal reflectivity is approximately 1 to 4 percent, remains stable (and even decreases slightly) until 60 degrees, and then increases significantly beyond 60 degrees. Only the deep-textured glass sample yielded reflectances that remained below 5 percent above an incidence angle of 70 degrees. For several samples, we also measured the reflectivity when aim- ing the laser over different parts of the module—the cell, the metal tabs, the backsheet, and the frame. We found that the area-weighted average of the reflectance was not significantly affected by the non-cell areas, so only the reflectivities mea- sured over the cells were reported in Figure D-4. A p p e n d i x d 1 The area-weighted solar reflectance was not significantly affected by reflectance values measured over the non-cell areas (i.e., backsheet, frame, metal tabs).

D-2 Note: Total and specular values, recorded using 410 Solar reflectometer with 20° incidence angle and 6° specular acceptance angle. 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Re fle c vi ty Total Solar Reflecvity Specular Solar Reflecvity Figure D-1. Measured solar reflectance values from different PV modules and samples. Figure D-2. PV glass samples resulting in different solar glare intensity and size. Left: Smooth float glass; Middle: Glass with anti-reflective coating; Right: Deeply textured glass. Source: Canadian Solar, Inc.

D-3 Note: Measured as a function of incidence angle, using laser pointers and an irradiance meter. Figure D-3. Measuring reflectivity. Notes: 1. Measured as a function of incidence angle. 2. Nomenclature for labeling: “AR_glass-texturing_cell-type_backsheet-color_frame-color_power-rating” a. b. c. d. e. f. AR: Anti-reflective coating was present Glass-texturing: smooth (none), light, or deep Cell-type: monocyrstalline or polycrystalline Backsheet-color: white or black Frame-color: silver or black Power-rating: power rating (in Watts) Figure D-4. Reflectance of different PV modules.

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TRB’s Airport Cooperative Research Program (ACRP) Report 108: Guidebook for Energy Facilities Compatibility with Airports and Airspace describes processes to plan, develop, and construct energy production and transmission technologies at and around airports. The guidebook emphasizes aviation safety practices in order to help ensure a safe and efficient national air system while still helping to meet U.S. domestic energy production needs.

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