Solar Panels Give Edge to Tomatoes Grown Underneath

By Wayne Hicks

Experiments lead to a greater understanding, deeper insights, and sometimes they even bear fruit. That was certainly the case last summer at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), where researchers nurtured a dozen tomato plants.

Tucked into a corner on the second floor of the Field Test Laboratory Building, the plants were housed in two custom greenhouses. Six were exposed to the full solar spectrum, serving as a control to the six plants grown under less light. The reduced sunlight reaching the other plants was filtered through purplish panels so that only the spectrum most beneficial to the tomatoes would reach them.

The experiment was meant to prove the effectiveness of what is called a BioMatch, which enables the exact spectrum of light that best suits the physiological needs of the plant to pass through organic semiconducting materials found in solar cells. Now in the second year of the multi-disciplinary project known as “No Photon Left Behind,” the researchers determined limiting the spectrum made the tomatoes grow faster and bigger than those under direct sunlight.

“When light comes into contact with a plant, there are a lot of things that can happen. Different physiological pathways are triggered based on the type and amount of light. Those physiological pathways often determine productivity of the plant,” said Bryon Larson, an NREL chemist with expertise in organic photovoltaics (OPV) and principal investigator on the project. “We are studying what happens to plants when sunlight is filtered into only the spectrum and dose the plant needs, which is the plant light requirement, and we can produce that through the concept of BioMatched spectral harvesting, while using the light plants don’t need to make electricity with transparent OPV modules.”

Earlier Efforts Focused on Algae

Researchers grew the tomatoes adjacent to a lab space devoted to algae. In fact, the initial experiments on this project involved algae. They covered bottles containing the single-cell organism with a BioMatched photovoltaic filter intended to stimulate optimal growth. Rather than the months it takes to grow tomatoes, the work on algae proved fruitful over a single weekend.

Lieve Laurens, a plant biologist who heads NREL’s algae research, serves as the co-PI on the project. “We demonstrated that the cells grew faster, yielding more biomass, even though a large part of the spectrum was removed and the algae received fewer photons overall,” she said. “We found that photosynthetic algae had a much higher rate of converting photons to electrons to biomass, so it was great. So naturally we asked the question if the same effects would translate to plants and crops, where you could get the same yield with only the light spectrum the crop needs, without needing to bounce back the light it doesn’t need as wasted photons.”

Those findings showed the science was sound, provided preliminary data, and gave the researchers confidence to make their pitch for funding from the Laboratory Directed Research and Development program. A dedicated greenhouse would have been ideal, but the scientists had to make do with the available space.