Clean energy journalism for a cooler tomorrow

Mixing solar power and agriculture: A blueberry farm does a test run

A farmer in Maine has teamed up with a solar developer and university researchers to find out how his berries fare when partially shaded by solar panels.
By Kari Lydersen

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Two workers in safety gear look at blueberry crops underneath solar panels
Members of the University of Maine team at the solar-blueberry research site (University of Maine Extension)

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.”

An agrivoltaics project in Massachusetts with cranberries has shown better results, she said, perhaps because the panels are higher off the ground and spaced more widely apart. But more steel to elevate panels and fewer panels in a given area make a solar array less lucrative.

This array was put in with a certain energy output goal,” Calderwood said. So if one increases the cost of the array and there’s less energy you’re getting out of it, that makes it not as worthwhile.”

She noted that soil moisture has increased under the panels in Maine, which is desirable since the area’s quickly draining soil and seasonal droughts can be tough on berries.

The soil moisture is definitely a benefit, but it cannot alone make up for the fact that it’s so shaded,” she said. She thinks it likely makes more sense for blueberry farmers to convert their less productive land entirely to solar and forgo solar on the land where blueberries naturally thrive most.

When farmers are considering this, they really want to think about whether they want the land to be energy first or farming first — either one or the other,” she said. The overlap is not quite there yet.”

Variation by location

The National Renewable Energy Laboratory is studying agrivoltaics with crops including kale and chard in Massachusetts, a variety of potato species in Oregon’s Willamette Valley, and beans and peppers in Arizona. NREL’s best-known agrivoltaics project, Jack’s Solar Garden in Colorado, generates power for more than 300 homes and trains young farmers in growing vegetables under solar panels. NREL is partnering with the U.S. Department of Energy to study dual-use agrivoltaics and related projects like beekeeping and pollinator habitats co-located with solar, through the InSPIRE project.

In Arizona, partial shade from the panels has been incredibly beneficial, especially for tomatoes and peppers,” said NREL analyst Jordan Macknick. We saw doubling of yield of tomatoes using 30% less water, and we saw tripling of yield for beans and peppers using half as much water. In these hot, arid environments, that partial shade from the solar panels can really have a beneficial effect on crop yields as well as reducing water demands.”

But the results seen at the Maine blueberry farm fit with what NREL has observed in the Northeast.

In a place like Massachusetts that’s much cooler and wetter, you see much more mixed results,” Macknick said. Some crops see a reduction in yield — you might see a 30% reduction for broccoli because it’s a crop that wants more sun than it might be receiving.”

Farmers may be able to tolerate production declines because of the extra income they get from solar.

This always has to make economic sense,” both for the farmer and solar developer, Macknick said. Currently the amount of revenue that a landowner could get from having solar panels over an acre of land could be an order of magnitude more than they’d have from just growing crops.”

Hopes for the future

Robertson-Dubois said interest in agrivoltaics in the U.S. is dramatically shifting over the past few years. The U.S. as a whole is a decade or two behind Europe and Japan, where agrivoltaics have been a part of their photovoltaics for decades now.”

BlueWave was recently purchased by Axium Infrastructure, a major firm with renewable holdings across North America and headquarters in Canada and New York. So in the future, BlueWave will be able not only to develop but also to own projects, said Robertson-Dubois, who is eager for the ability to have that long-term relationship with the farmer and landowner, making sure we’re doing a great job protecting soils, and also being more involved in the operations and maintenance and management of a project.”

He said BlueWave is exploring new projects co-locating solar with different types of agriculture.

We’re looking at everything from orchard crops like apples to potatoes to grazing systems to hay to forage,” he said. I’m working on one early-stage hybrid system that can have corn in the array. This farmer does corn and hay and rotates between fields over time. We’re giving up a little [cultivation space] on the field for solar potential, but we can fit that combine through and potentially manure sprayers. It’s challenging to come up with these designs, but I’m confident over the next five to 10 years we’ll see solar rollout on types of agricultural crops that nobody would have imagined a few years ago.”

Sweetland, like Calderwood, has observed that since the solar construction, the blueberries are not growing as tall or producing as many stems as they normally would have. Nonetheless, he is hopeful that dual-use agrivoltaics could work.

My expectation is that we will get a good growth of new stems next year, and the following year when they bloom, hopefully, we’ll be back on course,” said Sweetland, who has worked in local blueberry fields since he was eight years old. We do need energy; we also need to feed ourselves. If we can make it work that we’re getting a dual purpose out of the land, then we should benefit. I kind of look at it as my whole life has been changing all the time — that’s part of our goal in life…to roll with the changes.”

Kari Lydersen is an author and journalist based in Chicago.