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 siteto 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.
Liza McConnell demonstrates the necessary quad strength to get under panels in the morning when they’re tilted toward the horizon. (Alison F. Takemura)
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.