Solar farming: How does agrivoltaic use affect crop yields?

Climate solutions that rely on agrivoltaics—the practice of integrating solar panels into farm fields and ranches—can offer benefits because they boost clean energy production while sharing space with cows and crop rows. What’s been less clear is how yields might be affected in a world of growing demand, but a new paper that reviews 54 such operations, all over the planet, offers insight on the ways that agrivoltaics might best be used.

The researchers from Bern University of Applied Sciences and Agroscope, the Swiss center for agriculture, looked at solar panels on land used for everything from potato farming in Germany to raspberries in Italy, apple orchards in France, and sheep raised in the United States.

Vegetable farming accounted for about two-thirds of the studies, which came primarily from Europe (44%), Asia (37%) and North America (15%). Lettuce was the most frequently studied product, with mixed results on how plants performed when they were no longer grown in full sun due to the solar panels. On balance, the changes in yield and chemical composition weren’t especially promising.

Potatoes, on the other hand, did well when agrivoltaics became part of the land use plan, at least according to a two-year study near Lake Constance in southwest Germany. “The yields obtained under the panels were above the national average in both years,” said the authors, whose work is published in the journal Renewable and Sustainable Energy Reviews.

Other crops that performed well included sweet peppers, and broccoli and cabbage. Garlic, spinach, and sun-loving basil saw decreases in their yields. Tomatoes grown under solar panels showed a mix of responses, with results of one study showing increased production despite a 45% decrease in light and others noting lower yields or changes in tomato color.

The tomatoes illustrate how light exposure is just one factor in cultivation, though. The paper authors note that other variables, such as the tomato varietals or lower levels of heat stress, might offset the impact of light alone. There also appears to be some level of tomato adaptation to the production system itself.

While most of the studies were about vegetables, concerns about food insecurity often center on maize, rice, grains, and other staple crops that feed the world. There was some promising news with maize grown at the Jeollanamdo Agricultural Research and Extension Services facility in South Korea: yields actually increased when shaded up to the level of 21.3% but decreased at greater levels.

The results were consistent with maize yields grown at the CHO Institute of Technology in Japan. The Japanese researchers say the improved yields were due to carefully balancing light saturation in the plants, along with reduced soil water evaporation—another resource benefit of agrivoltaic farming. Rice, however, saw significant drops when shaded by solar panels.

Berries and fruits require more study, the authors note. Rooftop strawberries benefited from the shade in one Chinese study, while 75% shading of grapes grown under solar panels in northern Italy led to drops, primarily due to fewer grapes in the clusters.

“Livestock and some crops, such as potatoes, seem to be adaptable to large areas,” the authors conclude. “In addition, crops that require a lot of sunlight, such as tomato and maize, could still be grown under solar panels.”

There may be an even better solution: Agroscope has been working with Insolight (a Swiss agrivoltaic company with 13 installations across Europe) to develop clear solar panels that adjust to how much sun a plant needs. Last year, the first results of a pilot project (above, with partner Romande Energie) showed promise when using the panels with strawberries and raspberries.