by Tamara Scully
One of the many land uses to which farmland is increasing converted is solar energy. Solar farms are cropping up on farmland across the nation, replacing agricultural land with commercial scale solar panels. But losing food production to produce renewable energy isn’t very palatable.
Instead of removing land from ag production to produce energy, dual-use solar allows land to be utilized to generate power and produce food – a practice known as agrivoltaics. Co-locating photovoltaic panels and commercial farming has the potential to provide farmers with a new revenue stream and can keep agricultural lands in food production. If solar arrays on working farms can provide a return on investment that allows farmers to continue growing crops, renewable energy and farming can coexist.
Greg Barron-Gafford of the University of Arizona addressed agrivoltaics in a recent webinar. While the primary goal of photovoltaics is to capture the energy of the sun, dual-use agrivoltaics leaves “some sun for the crop production underneath,” he said.
Ecosystem benefits with properly sited agrivoltaic arrays can help adapt crop production to climate change. Increasing temperatures, combined with periods of drought, can mean that crops grown in the shade of solar panels may have an advantage. Solar panel arrays can actually benefit crop growth in some regions, providing much needed shade from increasingly intense sunlight, allowing them to optimize photosynthesis.
Photosynthesis occurs on a curvilinear basis, increasing slowly as light intensity increases. However, increases slow down as that intensity becomes greater, until any increase in intensity has no real effect on photosynthesis. Decreasing available light by 75% does not mean decreasing photosynthesis by that same amount.
Solar arrays can shade crops, but it’s possible to do so without having a detrimental impact on net photosynthesis. In direct sun, plants only maximize photosynthesis for a few hours, decreasing photosynthetic activity when it’s too hot or dry. Providing periods of shade also enhances carbon capture, as prolonged hours of photosynthesis equates to more capture of carbon than does photosynthesis from plants for only a few peak hours each day, Barron-Gafford explained.
By keeping temperatures cooler, solar panels can protect plants from wilting in the heat. In return, plants can cool solar panels (via transpiration), increasing panel efficiency. Shade from solar panels also keeps soil moisture levels higher than in unshaded ground, reducing irrigation needs and costs.
Trials showed that certain crops, such as tomatoes, actually increase fruit production when grown in the shade of solar panels. Leaves of plants grown with some shade from solar panels can be of larger size than those grown in full sun. Leaves with increased surface area help plants optimize the capture of sunlight. Lettuce and basil grown under solar panels were also shown to have larger leaf size than those grown in open fields.
“Some crops really love it. Some crops don’t like it. Some crops don’t really mind,” Barron-Gafford said. “We can get enormously greater production. There’s not a one-size-fit-all solution.”
Solar arrays will change the microclimate. The cooler growing conditions under the panels can also allow the opportunity for season extension. Cool weather crops can be planted sooner in the summer for an early harvest. Panels also provide protection from frost and can block hail from damaging crops.
Elevating panels farther off the ground, to heights of six, eight or 10 feet, can allow for production of a variety of crops or for livestock grazing. Farmers can design arrays to allow for equipment clearances as fits their operation. Shade produced by panels can protect farmworkers or livestock from the sun, lessening heat stress and increasing production.
Solar on Working Farms
Byron Kominek is farm manager at Jack’s Solar Garden in Boulder, CO, and was also a featured webinar speaker. His family farms 24 acres and installed a 1.2 MW solar array on four acres in 2020, planting one acre of crops under the array in summer 2021. Research on carbon sequestration, pasture grass and wildflower growth and water conservation is occurring on other sections of the array. Energy from the array powers 300 homes.
The solar panels at Jack’s Solar Garden rotate, built on a single axis, raised either six or eight feet off of the ground. As the sun travels across the sky, the panels move east to west to maximize sunlight capture. Crops are grown in three beds under each row of solar panels. The microclimate will vary from row to row depending on the bed’s position underneath the panel. Each bed gets sun at different times of the day as the panels turn. They’ve grown 30 different crops in the solar field thus far.
Kominek coordinates each bed’s tilling with the turning of the solar panels, rather than turning off the array. Wires for the array are buried three feet deep, so he wasn’t worried about tilling any infrastructure out of the ground.
Elevating the panels from the standard four feet to eight feet meant four more feet of steel in the ground, as well as four feet additional out of the ground, increasing the cost of the array by about 5% over a standard height installation. In cold-weather regions, snowfall amounts dictate how high panels are installed off the ground.
Equipment used for installations can be the same no matter the height, Barron-Gafford said. Elevating at 10 feet is a canopy-style situation, which is the system used at the University of Arizona. Six- and eight-feet panels arrayed in the field in rows, such as at Jack’s Solar Garden, are being researched to determine optimal heights for crop production.
At Jack’s Solar Garden, the array was meant for maximum production of electricity, so the panel density is high. Tractors, planters and other equipment can operate under the array as long as the wheels don’t run into the panels. Solar arrays can be designed to accommodate specific spacing requirements. Solar developers will want to maximize electricity production. But if the farmer is the owner, electricity production may not be the goal, and less density may be preferred.
“The solar array can be designed for the purposes of agriculture as best as you like. But then you are also going to be giving up the potential production for electricity, so we did not increase the width of our rows. The only thing that we changed was the height of our panels,” Kominek said.
In cooler climates, such as the Northeast, much of the land available for solar is the remaining farmland, and renewable energy has to go somewhere, Barron-Gafford said. The dilemma is how to keep that land in agriculture and utilize it for solar, providing farmers with additional revenue and communities with local food and a source of renewable energy. Energy production, farm revenue, water conservation and food production are melded together in dual-use solar installation, so land can remain in ag production while generating renewable energy.
“How much solar can I bring into this farm and not have negative impacts? Energy production is going to end up in the area around the cities, where the farms already are,” Barron-Gafford said. “This land use change is definitely on the horizon.”