Tests Show Yield Boost Under Solar Arrays

Tests Show Yield Boost Under Solar Arrays While some fear that large solar arrays will negatively impact food production, the University of Arizona suggests the opposite can be true. For the past 12 years, Greg Barron-Gafford has been combining agriculture and photovoltaics (solar panel-generated energy) in a concept called agrivoltaics. He’s been testing the concept in Arizona, at a Colorado farm called Jack’s Solar Garden (Vol. 47, No. 3), and in Kenya and Mexico. Among his findings was that plants as an understory reduced the heat island that naturally forms around solar panels and reduces their efficiency. He also found that the same heat island allowed plants that normally would not have survived to survive through the winter and increased yield. “We started trying to understand how solar arrays can increase yield,” says Barron-Gifford. “We developed a device to measure photosynthesis and measure how much photosynthesis is taking place on an hourly basis.” The researcher reports that plants in full sun, especially in dryland, kick photosynthesis in full gear early in the morning. However, unless irrigated, they experience a midday depression. That wasn’t the case for the plants under the array. “Plants under a solar array get less sun early in the day, but don’t go through the depression midday, which is a net win,” says Barron-Gifford. The research examined basil harvested for its leaves, as well as tomatoes and dry beans. One unexpected finding was that plants in semi-shade tend to grow taller and produce larger leaves as they reach for the sun. The team evaluated the impact on yield. “While all three would’ve produced more yield in full sun, it would’ve required irrigation,” says Barron-Gifford. “Water stress was reduced in the plants under the solar arrays. We saw statistically significantly more photosynthesis and yield in the tomatoes and beans, and the basil leaned that way.” The research team examined a variety of agrivoltaic systems, including elevated and row-based systems. They also looked at growing food crops, cover crops for grazing, and succulents such as prickly pear and agave. Carrots were successfully planted several months ahead of the normal planting time. “In all cases, we saw increased production in agrivoltaic settings,” says Barron-Gifford. “While the plants weren’t necessarily cooler, the soil was. As a result, the effect of every irrigation or rain event lasted longer — 10 days instead of 2.” In drought-prone areas or areas where irrigation water is scarce, farming under solar arrays may become a high-value practice. Contact: FARM SHOW Followup, School of Geography, Development & Environment; Biosphere 2, University of Arizona, Tucson, Ariz. 85721 (ph 520-548-0388; gregbg@arizona.edu; www.salsav.org).

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