Have your solar electricity and eat tomatoes, too?

A California university demonstrates using translucent dye-treated glazing for PV powered greenhouses that can also provide photosynthetic light for plant growing.

November 27, 2017 Mark Burger

Any color you want, as long as it’s magenta.

University of California

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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