In many ways, greenhouses are not all that green.
Plants require only certain wavelengths of light to grow, which means the sunlight the plants don't use ends up lingering around inside greenhouses and driving up the temperature, which in turn means greenhouse keepers must expend time and energy keeping the temperature down at more ideal levels so the plants can thrive.
Viewed differently, though, this excess heat presents an opportunity for efficiency.
"Plants need the sunlight," says Wei You, an associate professor of chemistry at UNC-Chapel Hill. "But they don't need all of it."
Through a new project called Solar Powered Integrated Greenhouse, or SPRING, You and five other scientists from N.C. State and UNC-Chapel Hill intend to harness these underutilized wavelengths of light via semitransparent solar cells built into the roofs of greenhouses.
Traditional silicon solar panels offer no transparency and don't allow light through in a greenhouse setting. Polymer-based solar panels, though, are like plants, in that they only use certain wavelengths of light. Installing polymer solar panels in a greenhouse could have the win-win effect of simultaneously producing electricity and leaving enough light for flourishing plants.
If successful, the idea could change farming and greenhouse production in dramatic ways. Off-the-grid greenhouses could help alleviate farmers' financial burdens and allow greenhouse-aided crop production in new places.
"In countries like the U.S. and in Asia, where things are developed with infrastructure for a greenhouse, the impact may be less," You says. "But in terms of rural areas, the impact will be much more. You could go to [places in] Africa [that] might not have the grid infrastructure for a greenhouse."
After developing the transparent panels, SPRING intends to fine-tune the greenhouses for different climates and vegetables. Different plants require different light, and once the project is out of a demo stage, the focus will be on tailoring.
SPRING is supported by a four-year, $3 million grant from a new National Science Foundation program called Innovations at the Nexus of Food, Energy and Water Systems, which "looks at ways of sustaining food, energy, and water systems, taking into effect that one may affect the other two," says Carol Bessel, deputy division director for the NSF. The grant arrives in January.