Heavy rainfall that can damage crops is also increasing as a warmer atmosphere holds more moisture. “In times of extreme heat or extreme rainfall, protecting plants this way can actually benefit them,” said Madhu Khanna, an economist at the University of Illinois at Urbana-Champaign, who also won funding from the USDA’s new agricultural grant. . “So that’s another factor that we want to look at.”
Khanna will investigate what the ideal solar system might be for a particular crop, for example if it needs larger or smaller gaps between panels to let sunlight pass through. Height is also an issue: corn and wheat would need taller panels, while bushy soybeans would be fine with a more squat variety.
Thanks to these holes, crops grown under solar panels are not bathed in darkness. But in general, light is more diffuse, meaning it jumps off surfaces before hitting the plants. This replicates a natural forest environment where all plants, except the tallest trees, hang in the shade and soak up any sun rays breaking through.
Barron-Gafford has found that a forest-like shadow under solar panels elicits a physiological response from plants. To gather more light, their leaves grow larger than they would if planted in an open field. He has seen this happen in basil, which would increase the yield of the crop. Barron-Gafford has also found that the pepper Capsicum annuum, which grows in the shade of trees in nature, produces three times as much fruit in an agrivoltaic system. Tomato plants also grow more fruit. This is probably because the plants are less stressed by the constant bombardment of sunlight as they are not evolutionarily adapted.
But each crop will be different, so researchers will have to test each to see how they respond to shade. “For example, we probably would not recommend that any plants summer squash directly in the deepest shade, directly under a panel,” says Mark Uchanski, a horticultural researcher at Colorado State University who studies agrivoltaics and tested the exact scenario. “The better location for it may be further out towards the edges, where it is more likely to get a little more sun because we saw a yield drop in that case.”
Although setting up the panels involves some upfront costs, they can actually earn the farmers some money, as Kominek told Grist in this 2020 story before his panels were in place. They would produce energy to run the farm and the farmer could sell profits back to a utility company. And since some plants — like these salsa ingredients in Barron-Gafford’s experiments — will use less water, it can reduce irrigation costs. “If we can actually allow farmers to diversify their production and get more out of the same land, then it can benefit them,” Khanna says. “Having crops and solar panels is more beneficial to the environment than solar panels alone.”
This type of setup also cools the solar panels in two ways: Water that evaporates from the ground rises toward the panels, and plants release their own water. This is dandy for the efficiency of the panels because they actually work worse when they get too hot. They generate an electric current when the sun’s photons knock electrons out of atoms, but if they overheat, the electrons become overvoltage and do not generate as much electricity when they are released.