Two new research papers shed light on the growing practice of grazing sheep in fields with solar arrays. One demonstrates that, in the right numbers, sheep grazing increases populations of beneficial insects like bees and lady beetles compared to mowing around solar panels. The other research describes a decision-making support tool to help farmers profitably grow their solar grazing herds.

A team from the College of Agriculture and Life Sciences (CALS) found that when two sheep per hectare graze around solar arrays, the abundance of wild bees, honey bees and lady beetles jumped by 38%, compared to a control plot that was mowed. The increase was driven primarily by an 83% increase in honey bees alone, according to the team’s findings in “Low solar-grazing densities support beneficial insects in agrivoltaic systems,” published Oct. 7 in Environmental Research Letters.

“Sheep grazing and beneficial insect habitat are two prominent conversation topics around solar development right now,” said Leana Zoller, the paper’s first author and a postdoctoral associate in natural resources in the Cornell CALS Ashley School of Global Development and the Environment. “But what’s been missing is research that treats them as parts of the same system. When we talk about sustainable solar development, integrating these discussions into a single framework is really helpful to farmers and community decision makers.”

For three years, Zoller and a team of entomologists, ecologists and animal and plant scientists tested various stocking rates – how many sheep per hectare are allowed to graze a certain plot of land – using Cornell’s teaching sheep grazing at the university-owned Cascadilla Community Solar Farm in Dryden, New York. At four sheep per hectare, they found beneficial insect abundance was similar to the mowed control site, while vegetation management effectiveness was greater than at two sheep per hectare. At eight sheep per hectare, vegetation management was maximized and sheep flock health remained high, but honey bee abundance dropped by 45%.

“We zeroed in on stocking rates because that’s a concrete number that sheep farmers understand and work with every day, and we want this research to be useful,” said Steve Grodsky, paper senior author and assistant professor of natural resources in the Ashley School. “With solar grazing, people, energy, agricultural animals, plants and insects are all part of this ecosystem. We’re trying to understand the connections between those pieces so that when solar developers, municipalities looking at solar development, or farmers are faced with a decision, they can have scientific information about potential trade-offs and synergies.”

Grodsky is also assistant unit leader of the U.S. Geological Survey New York Cooperative Fish and Wildlife Research Unit. Additional co-authors are sheep farmer and solar grazing consultant Nikola Kochendoerfer, Ph.D. ’20; Antonio DiTommaso, professor in the School of Integrative Plant Science; John Losey, professor of entomology; Scott McArt, Ph.D. ’12, associate professor of entomology; Paige Muñiz, formerly a technician in McArt’s lab; and Todd Ugine, Ph.D. ’04, research associate in Losey’s lab, all in CALS. Sarah Carson, director of Cornell’s Campus Sustainability Office, was key in coordinating site access between researchers and the solar company that manages the Cascadilla solar farm.

Another Cornell research team, from the Cornell SC Johnson College of Business, has developed a tool that helps farmers whose sheep graze in solar arrays to make better decisions about their operation. The team described the tool in “Flock Management for Solar Grazing,” which published Sept. 28 in Manufacturing & Service Operations Management.

After a chance encounter with Caleb Scott, Ithaca-based sheep farmer and founder of United Agrivoltaics, Vincent Slaugh, assistant professor at the Cornell Peter and Stephanie Nolan School of Hotel Administration and first author of the paper, began thinking through the economics and logistics of solar grazing. He recruited Linwei Xin, associate professor of operations research and information engineering, and Shane Henderson, Charles W. Lake, Jr. Professor in Productivity, both in the Cornell Duffield College of Engineering, to work on the topic.

Together, they developed a spreadsheet-based model that helps sheep farmers to optimize procurement and sales decisions, based on factors like target flock size, costs, anticipated revenues, and expected vegetation in particular solar sites; if a farmer doesn’t have enough sheep to keep the grass down, they’ll have to cut it some other way. It also helps solar developers understand growers’ needs and develop contracts that are more profitable and sustainable for all parties long-term. United Agrivoltaics has already incorporated the tool into its onboarding process.

Slaugh sees opportunity for U.S. shepherds to grow their operations – especially with solar contracts offering a steady source of income and animal feed. Current domestic sheep production for meat and wool doesn’t come close to meeting domestic demand; about half of all lamb and mutton consumed in the U.S. is imported, primarily from New Zealand and Australia.

“If we grow the sheep industry, will the American diet eventually include more lamb? Could that be a side effect of the solar energy revolution? I think the answer is very likely yes,” Slaugh said. “And then when that happens, we’d expect processors and supporting industries to come back, for banks to be willing to give more loans, and for supply chains to follow. All of that grows the economy, and rural economies in particular.”

Kochendoerfer, who grazes 700 ewes on solar installations in New York and Vermont, said that economy is already growing. 

“I work with a lot of farms that are now scaling up because of solar,” Kochendoerfer said. “There is a new wave of sheep farmers who are capitalizing on this access to good land. With solar grazing, you get paid to graze as opposed to having to pay to graze. That leads to sustainable, meaningful economic income that these farmers can use to expand, build a barn, buy equipment or hire someone. It’s enabling a lot of folks to build sound, viable agricultural businesses.”

Funding for these research projects came from the Cornell Atkinson Center for Sustainability, the National Institute for Food and Agriculture and the National Science Foundation.