Two for One: Growing Food and Solar Energy Together
As more projects are plugging into off-site solar, dual-use installations are gaining favor to minimize adverse impact.
Solar developers and farmers have something in common. They both need sunlight to grow their ‘crops’ and often the best place to do that is a flat, sunny field. For the most part, though, the two industries interact only when a farmer is leasing or selling land to a developer.
But that is starting to change.
In recent years, dozens of farmers and solar developers have figured out ways to work together. And researchers are studying the benefits and tradeoffs of ‘growing’ food and solar energy in the same location. In addition, some developers are integrating plant species that attract pollinators in a solar array.
These efforts come in the wake of growing opposition to solar projects that take fertile land out of production.
One of the first to do field research on farming-friendly solar (also known as “dual use” or “co-location”) is Stephen Herbert, Ph.D., a professor of agriculture at the University of Massachusetts, Amherst.
About seven years ago he received a call from a builder seeking advice: “I got a farmer who wants to make hay under solar panels,” he recalled the builder saying. Herbert’s response? “I think it is a crazy idea!”
Herbert was concerned farmers might drive their tractors into the solar arrays, damaging the panels, farm machinery, or even worse—themselves. But the idea sparked a different approach. “What we could do, though,” Herbert suggested, “is graze cattle under solar panels.”
No one had researched anything like this before.
For four years starting in 2011, Herbert pastured Angus beef cattle under rows of solar panels. His study found the grass and clover were 90% to 95% as productive growing under the panels as in an open field.
Herbert says it was really good for the animals. “The cattle liked it. They could rub up against the poles. They could lie down in the shade.”
With a grant last year from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), Herbert shifted his research to investigate growing hand-harvested crops under solar panels, including kale, Swiss chard, and peppers.
He has learned that the panels need to be much higher than normal—about 7.5 feet from the ground at the lowest point—so cows and farm workers can move comfortably underneath.
Pushback against solar on farmland
Herbert’s research coincides with a growing controversy over using productive farmland to produce solar energy. Jordan Macknick, an energy and environmental analyst with NREL, said, “There has been a major pushback from rural communities, agricultural communities, but also urban communities that don’t want to see land, that could be farmed, taken forever out of production.”
Macknick says traditional solar development takes its cues from residential construction, which clears the land, creating a clean slate.
“Laying gravel down so you have a flat, known surface rather than working with the natural contours of the land. That certainly has an impact on soil quality, on erosion, on stormwater management,” said Macknick. “That certainly doesn’t bode well for returning land back to agriculture after a 25-year project life. “
Macknick says co-location works well for grazing sheep and cows, and for small farm operations on about one to two acres.
“This would not really make sense if you are in the middle of a corn field in Iowa with a giant combine that is kicking up a lot of dust and going down the field,” said Macknick. “This is really for smaller-scale sites that are focused on hand-harvested and hand-managed crops.” That limits where co-location makes sense.
There are also challenges for solar developers, such as leaving extra space between the panels to allow light penetration for crops. “You would not be able to fit as many solar panels per acre of land that you are using, which would mean a slight reduction in the energy output on a per acre basis,” said Macknick. In addition, raising the solar panels higher off the ground costs more, because more steel is needed for the posts.
A pocket full of posies—and panels
Some solar developers are finding ways to improve habitat around solar arrays without adding costs. SoCore Energy, a solar developer in Chicago, says it is saving money in the long run, by planting flowering pollinator plant species, such as Black-eyed Susans and Yarrow, next to solar panels.
Growing pollinator species has several advantages over planting turf grass, according to Gavin Meinschein, SoCore’s lead civil engineer.
Although the upfront costs for establishing a mix of native pollinator species are “six times more expensive than doing a standard grass mix or a turf mix,” said Meinschein, “over the 25 years of the project, from the numbers we have run… you can save up to 40%.” He says the method works best for developers who own a project for the long term so they can recoup the initial investment.
Once the pollinator species are established, solar companies need to mow only once a year, rather than four or five times for turf grass. And the long roots of the native pollinator plants (several feet long, compared to several inches for grass) reduce stormwater runoff and may also reduce frost heaves that can disturb solar arrays.
According to researchers with NREL, communities often support fields of solar panels with native flowers—and nearby farms have higher crop yields because of the pollinators, attracted by the flowers.
Voluntary standards, which allow solar developers to be certified for having a pollinator-friendly site, exist or are being developed in at least three states: Maryland, Minnesota, and Vermont.
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