Mixing solar power and agriculture: A blueberry farm…

This story was first published by the Energy News Network.

Maine’s wild blueberries are a unique crop that can’t be planted from seed, explains lifelong blueberry farmer Paul Sweetland. They must be gently cultivated where the low-lying bushes grow naturally, and the small, sweet berries are sold in the local area because they’re too delicate to easily transport far. 

But blueberry land and other unoccupied parcels of rural Maine are increasingly being eyed for housing development, and Sweetland feels the wild blueberry sector is under pressure, especially when blueberry market prices drop.

He hopes that a new ​“crop” growing in tandem with berries could help boost the local industry and preserve farmland. That would be solar panels that have been installed across 11 acres of the land where Sweetland farms blueberries in Rockport, Maine. 

The University of Maine is studying this example of dual-use agrivoltaics. The solar installation was developed by the Boston-based solar developer BlueWave, and it is owned by the company Navisun, which makes lease payments to the landowner. Sweetland tends, harvests and sells the blueberries, and shares profits with the landowner.

Across the country, farmers regularly lease their land for utility-scale or community solar installations, but typically crops are not grown on that same land. With dual-use agrivoltaics, crops are grown under or between the rows of solar panels, with the aim of generating renewable energy without removing farmland from production. 

Farmers or landowners can collect incentives for solar energy, and some states including Virginia, New York, New Jersey and Massachusetts have or are considering incentives specifically for agrivoltaics. Agrivoltaics work best with crops that don’t grow too high, that are picked by hand, and that benefit from the shade the panels provide. 

From sheep to blueberries

BlueWave Director of Sustainable Solar Development Jesse Robertson-Dubois grew up on a homestead with a vegetable garden and livestock, and launched a career as a commercial farmer and conservationist.

But soon, ​“the intersection of land use and solar piqued my interest,” he said. ​“Upon looking into the ongoing national dialogue and community conversations more, I came to understand that solar can coexist symbiotically with farmland.”

He first worked with sheep grazing under solar panels, a practice that makes more territory for grazing available while alleviating the need to mow the grass around a solar array.

While sheep are small enough to graze easily under conventional solar panels, grazing cattle or growing many crops necessitates higher panels. And higher panels may not be financially viable without specific incentives, Robertson-Dubois noted. The Maine blueberry project was unable to tap any particular incentives, but since blueberries are low-growing perennial shrubs, a fairly typical 4.2-megawatt array was feasible.

“We were able to do it by just sharpening our pencils and making it fit,” Robertson-Dubois said. ​“We wanted to really protect that crop. We realized because of the way they’re harvested, we didn’t need a lot of clearance for equipment, but we really needed to protect the soils and protect the plants during the construction phase.”

Mixed results so far

Construction of the Rockport panels was done in three different sectors as part of the University of Maine study. One was standard construction; another was labeled ​“mindful,” with fewer trips made by machinery staying on certain paths; and the most protective ​“careful” sector had mats placed over the plants and as few driving trips as possible.

“Our goal is to understand the impact of construction — how will blueberries react to being driven over?” said Lily Calderwood, a University of Maine assistant professor of horticulture and wild-blueberry expert. ​“Anecdotally, the careful treatment definitely recovered faster in terms of blueberry cover. But they all recovered quite well.”

While the plants survived the trauma of the array’s construction, Calderwood said it appears the blueberry plants shaded by the panels won’t produce much fruit. The researchers won’t know for sure for several years, since wild blueberries grow on a long cycle.

The university received grant funding to continue the study for three more years from the Northeast Sustainable Agriculture Research Education program, which is supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture. The research team will compare the blueberry yield among the plants fully shaded by panels, plants partially shaded by panels and plants with full sun. The panels are 8 feet tall in rows spaced 8 feet apart, Calderwood said, which she considers relatively ​“tight” spacing.

“We know already that the plants have adapted to this new environment. We call that ​‘genetic plasticity’ or ​‘phenotypic plasticity’ — the plant can adapt to shade,” she said. ​“In shade, they have larger leaves that are darker green. We see that happening here. But that doesn’t necessarily mean there is more fruit. We haven’t seen that at all. It’s leaning toward not really producing much fruit below the panels.”