Solar panels on farmland

Sheep graze underneath a solar array at Oregon State University in Corvallis, where researchers discovered grass growing more lush later in the season than elsewhere in the pasture. Such dual use projects are subject to special provisions under new Oregon rules for solar developments.

Researchers at Oregon State University may have accidentally stumbled upon a new use for solar panels on farms and ranches.

Not only can solar power lower energy bills and increase efficiency, but the shade afforded by photovoltaic panels might also boost agricultural production on non-irrigated farmland, retaining more moisture for crops and livestock forage.

The question now is whether solar panels can be situated to reap the benefits without hindering farm practices, such as spraying fertilizer, tilling fields, grazing or operating machinery during harvest.

Chad Higgins, associate professor in the Department of Biological and Ecological Engineering at OSU, said the study began serendipitously in 2015 after he noticed more lush, green grass growing underneath solar panels installed several years earlier by the university on a six-acre sheep pasture near campus in Corvallis.

“(The solar array) wasn’t designed as an experiment when it was put in,” Higgins said. “But we did notice that some changes were occurring underneath the solar panels with the pasture grass, in particular in the late autumn. We wanted to understand that.”

Higgins and his team divided the pasture into several test plots, and installed microclimate tools to measure the differences in air temperature, humidity, wind and soil moisture beneath the panels, versus areas exposed to direct sunlight. None of the grass received irrigation water.

Between May and August, data showed plots that were shaded by the solar panels maintained higher soil moisture and grew nearly double the amount of grass, especially toward the end of the season. That is because grass uses water more slowly and efficiently when it has less light to grow, Higgins explained.

“It’s like a tortoise and hare race,” Higgins said. “The plants that experience the full brunt of the sun use their water resources as quickly as possible. They grow to the extent they can, and then they die. On the other hand, the plants in the shade take sips of water because they are less stressed, and they keep chugging along.”

Higgins said the shaded plants were three times more efficient with water than the rest of the pasture. The findings were published Nov. 1 in the scientific journal PLOS One.

Higgins said he wants to expand the project moving forward to include more high-value crops, such as berries and vegetables. His next challenge is coming up with a design for installing solar panels on farms and ranches that would not burden traditional agricultural practices, or take farmable land out of production.

One possible solution, he said, is lifting panels up off the ground by installing them on posts, and tilting them at an angle that would allow farm equipment — such as tractors, sprayers and combines — to pass without damaging the machinery.

“There are classical engineering things that need to be done still,” Higgins said. “I see those as the practical challenges to make it viable as an agricultural practice.”

Higgins, who founded the Nexus of Energy, Water and Agriculture Laboratory at OSU, said this research could change the way farmers and ranchers think about managing light for agronomic benefit.

“Opening ourselves up to managing light in the same way we think about managing water or nutrients or soil gives us a heck of a lot of flexibility in what we do,” he said.

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