A solar solution for the changing climate in the West?
- March 17, 2023
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March 17, 2023 – The summer of 2022 was tough for farmers in the American West: Hot, dry conditions caused snow to melt early, reservoirs to run dry and streams to become mere rivulets. For many, this meant less water for cultivation and lower yields. But Byron Kominek, a farm manager near Longmont, Colorado, was pleased with a bountiful harvest of peppers, tomatoes, squash and lettuce.
Protected from the high midday sun, plants under panels become little swamp coolers: when they open their pores for photosynthesis, water escapes from their leaves – creating a cooler microclimate. This reduction in heat increases the efficiency of the panels—even as the panels protect underlying plants from excessive solar radiation. Consequently, agrivoltaics can bring benefits to both farmers and power generators. Another potential benefit has emerged in recent years: plants grown under slabs need less water.
At one such site, Biosphere 2 near Oracle, Arizona, Barron-Gafford found that some plants under solar panels only need watering every few days, compared to every few hours for plants growing in direct sunlight. For example, Agrivoltaic cherry tomatoes were found to be 65% more water efficient than those grown outdoors, and total fruit production doubled. Researchers are now studying how different plate spacing affects the water needs of a range of crops in the hot, dry climate of the Sonoran Desert.
Barron-Gafford believes agrivoltaics could help western farmers who want to continue farming in the face of climate change. “We want to adapt our food system to survive periods of drought and warmer temperature swings, and that boils down to reducing our reliance on irrigation,” he says.
Against a backdrop of Sonoran Desert scrub, Nesrine Rouini tends to seedlings under a canopy of solar panels on a sunny but cold November morning on the grounds of Biosphere 2. The just 9 by 18 meters (30 by 59 feet) experimental site for agrivoltaics resembles a plant intensive care unit – stakes with barcodes identify each new shoot, and a network of cables and wires runs along each seedbed to a central data logger. This Gordian knot of wires and controls transmits hour-by-hour real-time data about a plant’s living environment—soil moisture, temperature, solar radiation, and a host of other variables—to the research group in Tucson. At the same time, cameras follow its growth from seedling through germination to flowering. A plant cannot even open a stoma without its actions being discovered, relayed and recorded.
Once a week, Rouini, an agrivoltaics researcher on Barron-Gafford’s team, visits the site and a control plot that isn’t under panels. With a portable gas exchange device, she measures the pulse of each plant and checks how well it copes with shade or the open sky. “We found out that plants in the control plot suffer from midday depression and do not engage in photosynthesis,” says Rouini. “While those under the panels continue.”
Irrigation on both plots begins at 7:00 am. At 9:00 a.m., the soil of the control plot already appears drier to the naked eye than the soil under the plates. “Without shade, the water evaporates much faster,” says Rouini.
Basic physics dictates that plants grown under panels require less water, but scientists still don’t know how each plant performs in each location and exactly how much water is saved. As a result, research groups in Arizona, Colorado and a network of nearly 30 sites across the country are attempting to fill this data gap.
Though scientists have studied the interaction between light and plants for decades, the novel shading system of solar panels hides many unknowns, says Jordan Macknick, senior energy-water-land analyst at the National Renewable Energy Laboratory and principal investigator of Innovative Solar Practices Integrated with Rural Economies and Ecosystems (InSPIRE) Network of agrivoltaic sites. “The holy grail would be if any farmer could pick a spot on a map of the United States and get information about what crops they could plant, what panels are best configured, and how much water they need,” he says.
Feasibility in focus
In Colorado, Liza McConnell, manager of Jack’s solar research farm at Sprout City Farms, observed that lettuces grown with half the amount of water applied on a control plot were only slightly smaller and significantly sweeter than their sun-exposed equivalents. Celery, typically a high water-using crop, also performed well with reduced irrigation, as did smaller peppers, but the larger Anaheim peppers under panels did not produce as much fruit as hoped. With the ongoing drought in the West and climate change taking its toll, people may have to adjust to not getting the exact variety of peppers they want year-round, says McConnell.
“In view of climate change, we have to put all options on the table,” she says. “Agrivoltaics isn’t the only solution, but it will be one of the things that will help keep our communities safe and resilient.”
Despite its many benefits, agrivoltaics may not be feasible for large single crop farms that grow corn and soybeans and rely on the use of heavy machinery. Farming under solar panels is a challenge even for farmers on their feet: McConnell likens it to farming on an obstacle course. On the other hand, the panels provide farmers with much-needed shade on hot days.
“We produce energy, we produce food, we conserve water, and we build soil health that further conserves water and nutrients,” says McConnell. “And then we also protect the necessary human labor and the quality of life of the farm workers.”
Warm-season yields of certain crops, particularly peppers and tomatoes, may also be lower in Colorado, McConnell says. But these fruits only ripen at certain temperatures; if it’s too hot, they won’t ripen at all. “So a lower yield is still better than no tomatoes in the face of climate change,” she says.
Macknick points out that the revenue farmers can generate from selling solar power will more than offset the reduction in farm produce, and that agrivoltaics could help farmers in the West and the Colorado River Basin become more financially resilient to droughts and the to be climate change.
Another potential benefit of agrivoltaics is that it could open up more land for agriculture, including indigenous lands where food security and access to energy have been issues. For example, in hot and arid desert areas, growing crops under panels can reduce the need for scarce water and increase the productivity and viability of agricultural efforts. “Can some of these places produce food now because we’ve removed that rough edge of the environment?” Macknick poses.
Agrivoltaics also offer the potential to harvest and store rain to use for irrigation. Gutters attached to the underside of solar panels can catch rain and channel it into small reservoirs. But challenges exist in execution. In Tucson, for example, water simply drains from water panels and is wasted. “It would be good to think about how to put gutters on panels to intentionally collect water and do it right,” says Barron-Gafford.
Large-scale agrivoltaic efforts will face many challenges, and they won’t be right for every farmer, Macknick says. But there is potential to improve yields of some crops while improving soil health, reducing water requirements and also generating electricity. “It will certainly play an increasing role in agriculture,” says Macknick. “I think we’re going to see more and more of that.”