Can agriculture and solar farms coexist? It depends

LONGMONT, Colo. — On a bright October morning, education specialist Allison Jackson leads a small tour group down a wide grassy lane. Rows of solar panels stretch out on either side, their blue-black crystalline faces gleaming in the sun. Between them grows a bounty of leafy green vegetables: dinosaur kale, celery, Swiss chard and more.

This is Jack’s Solar Garden, a 1.2-megawatt agrivoltaics research site in Longmont, Colorado, where farmers and scientists are studying how different crops fare when grown in the partial shade of solar panels. ​“Agrivoltaics” is a portmanteau of ​“agriculture” and ​“photovoltaics,” or solar energy technology, and it’s a burgeoning field in the U.S.

Two farmers — Liza McConnell and Meg Caley — join the group, tugging a cart of hefty, just-harvested celery. They are both with Denver-based Sprout City Farms, a partner organization at Jack’s that for the past two years has farmed two acres of land here, collaborating on research with teams at the National Renewable Energy Laboratory (NREL) and the University of Arizona. (McConnell is research farm manager and Caley is Sprout City’s co-founder and executive director.)

It might seem counterproductive to plant crops where, for at least part of the day, they’ll be shaded, but according to McConnell, some types of vegetables have thrived in this setting. She enthusiastically tells the group about the lettuce heads that she helped harvest this summer: They were ​“much bigger and more delicious,” she says, than the lettuce that they grew in full sun.

“It was dramatic how much better the lettuce tasted being in some shade,” Jackson chimes in. ​“It was super crunchy and sweet,” whereas the lettuce that wasn’t sheltered by solar panels was bitter, nearly inedible. ​“It was almost limp.”

It’s not just the lettuce that has excelled under the panels.

“The size of the chard leaves — they’re like the size of your torso. I kept wanting to compare one to my four-year-old,” Caley says. The chard and kale plants at Jack’s Solar Garden were ​“three to five times as big here as they were at our other farms.”

Sprout City works on multiple farm sites and sells produce at farmers markets and through a community-supported agriculture program. ​“The CSA members and farmstand customers were totally wowed,” she adds. ​“In fact, this year, we decided not to grow these greens at our other farms. We grew all of our greens up here [at Jack’s] because we knew they were the happiest here.”

While agrivoltaics is still a niche field, it has room to grow. Solar panels are projected to cover up to 11 million acres, or about half a percent of land area in the contiguous U.S. by 2050 based on the Department of Energy’s 2021 projections, Jordan Macknick, lead agrivoltaics analyst at NREL in Golden, Colorado, told Canary Media. And ​“agricultural land is frequently targeted by solar developers,” because it’s already flat and is usually close to roads and transmission lines.

Agrivoltaics can also be a financial boon for farmers, Macknick said. Farmers can opt either to own the solar panels (though it will take a decade or two for the investment to pay dividends), or lease their land to solar developers.

By leasing their land, farmers can make something like $1,000 per acre per year, he added. Generally, ​“having solar panels on your land will bring in a lot more money per acre than the crops that are grown.”

But first, researchers need to figure out under what conditions agrivoltaics works best. ​“We really want to crack the nut of growing specialty crops and vegetables for the local community under solar panels,” Caley says. ​“Then we can share [best practices] out really widely and…open the door to entrepreneurs, so the sector can take off.”

Solar panels keepin’ it cool 

The panels of a solar array can help crops grow by creating a microclimate that, like a blanket of clouds, buffers against weather extremes.

“The soil can stay a little bit cooler in super hot temperatures,” said Brittany Staie, graduate research intern at NREL and former farm manager for Sprout City Farms at Jack’s Solar Garden. Researchers in Arizona have measured up to a 4.5˚F air temperature drop in the area shaded by panels during the summer. That ​“can keep the soil moist longer,” she said.

Staie is part of an NREL team researching how crops fare both underneath and outside of an existing solar array on a half-acre plot on NREL’s campus. They’re tracking tomatoes, poblano peppers, carrots and more.

The tomatoes seem to be doing approximately as well whether grown in shade or full sun. A taste test confirmed that their Berkeley tie-dye variety was bursting with flavor.

But basil has shown a clear preference, according to the researchers. Grown in full sun, the herb got stressed, flowered and stopped producing sweet leaves much earlier than the plants between the panels.

The more moderate temperatures under the panels don’t just result in better-tasting vegetables. They also extend the growing season. At Jack’s, the kale grew into December, six weeks after the irrigation had been shut off. ​“It was like, ​‘This kale will never die,’” NREL’s Macknick said. And that tasty lettuce Caley and McConnell raved about? It was growing well into the summer.

“The fact that we were getting big, beautiful heads of lettuce in late July is a little insane,” Macknick added. 

Longer growing seasons mean an easier schedule for farmers, Staie said: ​“You can plant fewer successions.”

This is only the first year of data at the NREL site — the researchers expect to see variability in how the agrivoltaic crops fare over time. ​“Mother Nature can behave very differently from year to year,” Staie said, so the more data, the better.

“Farmers want as much data as possible because they want to reduce risk,” she said. ​“If they know definitively, in Colorado, pepper plants [or other crops] do better underneath the panels, they’ll be more willing to try it out.”

Farmers might also pursue agrivoltaics for its benefits to worker safety, said James McCall, energy and environment analyst at NREL. At a study site in Tucson, Arizona, preliminary results show that working in the panels’ shade can keep skin temperatures up to 18˚F cooler.

But agrivoltaic setups do come at a premium, he added: Raising the height of solar panels to cultivate crops underneath requires more steel and can cost 5 to 20 percent more. ​“But if you’re keeping your workers and plants healthy, I think that you could make the business case for that.”

For the arid, sun-soaked Western U.S., agrivoltaics looks promising, Macknick said. ​“There’s more than enough sunlight for plants to photosynthesize what they need.” And the panels help retain water by reducing evaporation, which means lower water bills for farmers and less of a drain on a scarce resource.

But the advantage of solar panels varies widely with geography, climate and soil conditions, hence the need for further study, according to an August NREL report. For example, an agrivoltaics site in Amherst, Massachusetts where farmers are growing crops including peppers, broccoli and beans is showing that seasonal variability can tip the balance on crop productivity.

“When it’s kind of a cold, wet year, they’re actually seeing really bad yield [from crops] underneath the solar array,” McCall said. ​“But when it’s a really dry and hot year, they’re seeing a much better yield.”

Agrivoltaics growing pains

Even at Jack’s Solar Garden in typically warm, dry Colorado, some crops have struggled under the panels. In one case, the unexpected culprit was too much water coming from the panels themselves.

At night, the panels lie flat, collecting condensation. In the morning, they reset to face the rising sun in the east. ​“And there’s this waterfall of dew” that sloughs off, said Caley of Sprout City Farms. When they were planning their crop beds, the team had thought the free water from the panels might be a good thing.

But the receiving cucumber and squash plants didn’t like to have ​“all that water on their leaves,” Caley said. The winter squash crop failed because fungus grew — not a typical concern farming in the parched West, Caley noted wryly. Excess moisture ​“was something that we didn’t expect to be such a factor” in farming with solar panels.

Another challenge has been physically maneuvering around the panels, according to Caley. ​“It’s like farming in an obstacle course,” she said.

The panels at Jack’s were even mounted at greater heights than at a typical commercial solar site to help accommodate farmers. At the panels’ midpoints, they’re 6 and 8 feet off the ground as opposed to a typical 4 feet.

But working among them is still a ​“rigamarole,” Caley said. The solar panels at Jack’s tilt throughout the day, tracking the sun from east to west. In the morning — ​“when you’re most stiff,” McConnell said — the panels are at a steep angle, forcing the farmers to duck underneath them in order to access some of the crops.

“You’re constantly worrying about hitting your head,” Caley said.

The farmers have also learned lessons from the site’s design. Jack’s Solar Garden maximizes solar energy production with long, unbroken lines of panels that constrain the farmers’ access.

“We can’t take the cart into the middle of the field,” McConnell said. Instead, they have to park it at the edges and spend more time going back and forth to load the cart with crops when they’re harvesting, for example.

“There’s a lot of wasted time. And time is money,” Caley said.

On small farms growing a variety of different vegetables, ​“labor is the biggest cost,” said McConnell. About 90 percent of Sprout City Farms’ budget is for staff, and farms in general work on extremely tight margins, she noted. ​“So efficiency in labor is really important. Having to double back for anything…is problematic.”

A site layout with paths cutting across the panel rows would be more farmer-friendly, according to McConnell.

She and Caley have been advising interested farmers to also consider whether they want to space the panel rows further apart, which could better accommodate irrigation lines or large machinery, such as tractors.

“If you were going to develop your own [agrivoltaic] site, those things need to be designed in from the beginning,” she said.

More agrivoltaics insights will be featured at a Dec. 7 research webinar hosted by the Colorado Agrivoltaic Learning Center.

Meanwhile, Sprout City Farms will keep farming and researching at Jack’s Solar Garden, where the panels deliver benefits that salad lovers can taste.

Next year, ​“we’re going to corner the market on lettuce in July,” Caley laughed.