Growing food and generating power in communities is often treated as an either-or option, especially if enclosures like greenhouses are used. Opaque PV modules create shade issues. Even with the use of transparent back sheets and a lower cell coverage ratio, a separate module and mounting system creates additional costs on a greenhouse, and may not admit the right spectrum of light that plants need to effectively grow. The same problem of useful light for plants exist with present building integrated PV systems.
A demonstration of solar powered greenhouses by the University of California, Santa Cruz (UCSC) addresses these challenges by using plastic-constructed greenhouses, including the photovoltaic cell containing panels, with only a small percentage of surface areas covered with PV cells and the rest treated with a translucent material that will transmit the photovoltaic spectrum to the cells, while allowing a pass thru of sufficient photosynthesis wavelength for effective plant growth.
The technology is called Wavelength-Selective Photovoltaic System (WSPV) by USCS, as described in their findings published in the American Geophysical Union’s journal Earth’s Future. The glazing system has a 12% silicon PV cell coverage with the remaining 88% treated with a luminescent solar concentrator (LSC) that has an 4% effective system factor. The theoretical efficiency is estimated to be 9.4%, and a 7% efficiency considered commercially feasible. Cost factors are significant in that a square meter bof WSPV can cost as low as $45/square meter, divided by $30 for PV cells, $10 for the LSC and $5 for the remaining materials. This would compare to $300/ m2 for smaller scale 90% cell coverage PV systems. Further cost reductions may be realized by using thin film PV instead of silicon. The visual result of WSPV is a striking magenta color.
The USCS study reported little or no difference in plant growth compared to a control greenhouse, and possible collateral benefits like reduced water usage. WSPV applications are scalable from backyard or community greenhouses up to multi-acre commercial farms. Commercialization of WSPV systems can lead to a multiplying factor in sustainably growing food and generating electricity.
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