Solar farms are an increasingly popular way for landowners to power their communities. With an array of ground-mounted solar panels absorbing the energy from the sun, solar farmers are paid to send any unused electricity to the power grid for distribution.
As solar farms pop up across the U.S., researchers at the University of Georgia are working to improve the biodiversity on solar sites as part of a larger, multidisciplinary research program designed to support both sustainable energy and ecosystem health.
Funded by the U.S. Department of Energy’s Solar Energy Technology Office, the Photovoltaic Stormwater Management Research and Testing (PV-SMaRT) project is using five existing solar sites in Georgia, New York, Colorado, Oregon and Minnesota to study stormwater infiltration and runoff at solar farms.
A solar farm of more than 3,800 panels now sits on a seven-acre research site in Plains, Georgia, where former President Jimmy Carter’s family used to grow peanuts and soybeans.
President Carter was an early advocate for clean energy development across the U.S., from the West Wing of the White House to pockets of rural America, like his hometown of Plains, Georgia. The Plains solar site now feeds into Georgia Power’s grid, providing power to about half of the town’s residents, according to a case study from Fresh Energy.
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When solar farms are installed, it removes ecologically important habitat, particularly for pollinators, said Bodie Pennisi, UGA professor of horticulture and a researcher on the project.
To study how to increase biodiversity on solar farms, UGA Cooperative Extension specialists and researchers in the College of Agricultural and Environmental Sciences are testing wildflower mixes planted among the panels to measure habitat establishment and success over several seasons.
They will also assess the impact of the grass and wildflower mixes on pollinator populations in an effort to restore pollinator habitat, a well-known priority for former First Lady Rosalynn Carter, who helped create the Rosalynn Carter Butterfly Trail.
Jason Schmidt, associate professor of entomology, said that choosing what plants to grow on the solar farm involved determining whether they would grow in south Georgia, attract pollinators and natural enemies of common pests (beneficial insects), and easily start from seed. The researchers were also sure to select annuals and perennials that would bloom throughout the season.
The species chosen for the project were specifically selected for the potential to do well in hot, dry conditions at the farm, which is not irrigated.
“We also looked for varieties that would bloom under the panels so they were not in direct competition with the primary goal of the site, which is solar energy,” Schmidt said. “We wanted full-season bloom, so we chose species that would bloom at certain periods and then combined all of those bloom periods so we would always have something blooming across the season.”
The UGA team chose three different seed mixes for the flat, sandy clay site including a grass mix with crabgrass, annual ryegrass, and panicum; a low-diversity pollinator mix containing seven species including Indian blanketflower, common sensitive plant, butterfly milkweed, southern elephant’s foot, fringed bluestar, rayless sunflower and southern beardtongue; and a high-diversity pollinator mix of 18 species including Indian blanketflower, partridge pea, black-eyed Susan, yarrow, lanceleaf coreopsis, southern elephant’s foot, mistflower and 11 others.
While they are still monitoring the wildflower plots on the solar site at the Carter farm to determine the full impact of the pollinator-friendly seed mixes, Pennisi and Schmidt said only about 35% percent of the species planted established well on the site. Using existing research from other parts of the country, the researchers knew that many of the plant species — including those in the daisy family such as asters and blanketflower — were attractive to pollinators, primarily bees.
Josh Grant, a doctoral student in entomology working on the project, is monitoring insect populations using sweep nets and summarizing findings into functional groups including pollinators, natural enemies, herbivores and decomposers. During the 2021 season, herbivores and decomposers constituted more than 65% of the total arthropods caught, while pollinators comprised the least populous group of insects in each plot.
“Our maintenance mowing height of 12 inches most likely hindered bloom production, and hence lowered pollinator counts,” Grant reported. Researchers expect the number of blooms — and therefore the number of pollinator insects observed — to increase this year as the perennial plants in the study reach their mature size.
Unfortunately, the researchers also have encountered extreme weed pressure from native and exotic weeds.
“Even if the native plant species are grown in ideal conditions from transplants, a lot of attention has to be given to weeding. What we will learn is what to plant and when to plant it in these novel agrivoltaic environments,” Schmidt said.
“One of the really eye-opening lessons for me and for everyone involved is watching the plants over the years and how they have germinated and behaved — and how much labor, materials and chemicals are required to maintain the site in an acceptable appearance,” Pennisi said.
“Weed pressure is unrelenting,” Schmidt added. “That’s really the challenge anywhere, because the (weed) seed bank is very rich in the soil, and every time you turn the soil, it moves seeds toward the surface. This is a problem that occurs over and over, but if you mow often enough you hope to reduce the seed bank so you are not going to have newly formed seed. But it takes years and years to know whether you’ve exhausted the seed bank meaningfully.”
UGA soil scientists will monitor the site to explore the relationship over time to soil moisture, temperature and whether soil microflora is enriched by the plantings.
The research in CAES is linked to work at four other solar sites in Minnesota, New York, Colorado and Oregon, expanding scope of the work into the national conversation on the environmental impact of solar sites.
The project has been renewed for three years through recent funding to the National Renewable Energy Laboratory (NREL), leaders of the overall project.
