WEST LAFAYETTE, Ind. – A team of eight researchers from Purdue University and Aarhus University in Denmark have demonstrated how to optimize yield in corn fields with solar power arrays that cast dynamic shadows across growing crops throughout the day.

With constantly moving panels, every corn row received different light intensities throughout the day, but none sat under steady shadow, according to the researchers.

“We developed a model to calculate what fraction of light is falling on each row,” said Rakesh Agrawal, Purdue University professor of chemical engineering and co-author of a July 26 article published in Cell Reports Sustainability.

According to the Solar Energy Industries Association, solar power arrays keep crops cool, creating shade beneath their panels that can protect plants from extreme heat, leading to better crop yields and helping to maintain food production levels.

Matthew O’Neal, Iowa State University professor of plant pathology, entomology and microbiology, and Ajay Nair, Iowa State University professor of horticulture, are currently working on a project with vegetable production under solar power arrays panels at the university’s Alliant Energy Solar Farm.

O’Neal said, “The Purdue group is using a single-axis tracking system such that the panels follow the sun to maintain maximum exposure. This means that some of the shadows that the panels produce move across the ground such that no one spot on the ground is in permanent shadow. The shadows move across the rows of the corn as the sun moves across the sky.”

He said permanent shadows are produced with a fixed-tilt panel system in which the panels do not move; fixed tilt panels do not produce as much electricity as a single-axis tracking system.

He said the single-axis tracking solar systems have solar power arrays (or photovoltaics) panels that are mounted on a long post that rotates: “This rotation is produced by a motor that rotates the post. This motor turns on and off, based on the position of the sun that is tracked by sensors.”

The Purdue team tested an agrivoltaics system (the dual use of land for solar energy production and agriculture) that towers high above the crops to permit combine harvester operations.

The panels in the Purdue experiment stood 20 feet high, but the modeling already had shown panels 10 feet high would produce similar results with much lower construction costs: “We are showing the world that, for corn, such a thing can be done, and it works very well,” Agrawal said.

Margaret Gitau, Purdue University professor of agricultural and biological engineering and co-author said, “Some areas could experience wetter, cooler conditions, while in other areas, conditions might be no different than in areas without solar panels. Shading provided by the panels can be important in conserving moisture in areas that experience water and temperature stress during particularly dry periods.”

She added most U.S. agrivoltaics work focuses on specialty crops such as Brussels sprouts, raspberries, cabbages and peppers, but those crops occupy a small land percentage when compared to row crops.

O’Neal said, “My initial thoughts on the Purdue solar power array and the team’s research is that this is yet another example of how a renewable source of energy can be coupled with agriculture. Their results, especially the model portion, suggest that photovoltaic (solar power arrays) panels can be mounted above plants, and a crop can be sustainably produced underneath them.”

For the Iowa State project, O’Neal and Nair are growing broccoli, squash, peppers, raspberries and strawberries within a replicated experiment. O’Neal said wine grapes, honey berry and asparagus are being grown on a smaller scale as more of a demonstration.

He said the vegetation treatments are not agricultural, but reflect what a solar developer could do in the absence of any agricultural activity: A grass and clover mix and a pollinator mix that include 30 species of perennial flowering species. He added these are both replicated on the same scale as the broccoli, squash, peppers, raspberries and strawberries currently being used in the project.

He said there are some big differences between the Purdue project and the Iowa State project.

“The approach we are exploring is to model an interaction between a landowner (in this case, Iowa State University), a utility company (Alliant Energy), and farmers (which may not be the landowner, but in this case, it’s the faculty and students at Iowa State University),” he said.

O’Neal said he, Nair and Alliant Energy settled on two heights, resulting in four distinct areas of panels in two general configurations: a single axis tracking configuration similar to that of the Purdue group, but at a much lower height; and a fixed tilt configuration that does not track the sun.

“We elected to explore horticultural crops as those can be grown profitably on smaller acreages, and thrive in the microclimate (the climate of a very small or restricted area) that occurs under solar panels, and often require insect pollination,” he said.

“This last point was important as we are also exploring if native bees can be conserved, and if honeybees can be kept sustainably at a solar farm,” he said. “Since many fruit and vegetable crops require bee pollination, we can explore two forms of agriculture that benefit from each other.

“As the Purdue group noted at the end of their article, a detailed, holistic approach is required to determine the short- and long-range costs and benefits,” he added.