Throwing shade is solar energy’s new superpower

Published : 06 Oct 2022 10:12 PM

In rural America, the shoulder-high corn is increasingly competing with a new cash crop: solar power. Acres of solar panels shine brightly in fields along interstates and rural byways, signaling a change in how America’s farming country generates income. The need for a happy marriage between these old and new industries has inspired a burst of innovation and a new word to describe the combination: Agrivoltaics.

The Inflation Reduction Act includes billions of dollars in renewable energy funds that will accelerate the adoption of solar and other renewables. Some of the new solar panels will land on rooftops, but most will be concentrated in large utility-scale arrays that the US Department of Energy claims could eventually cover an area roughly equivalent in size to Massachusetts, Rhode Island and Connecticut.

Solar panels work best in light winds, moderate temperatures and low humidity. Rooftops share some of these characteristics. But nothing maximizes that combination of traits quite so well as cropland. For solar developers keen to get the most from their investments, that makes farm country irresistible.

For farmers, the attraction is mutual. Depending on the location, solar can be one of the most profitable uses of land. Texas farmers can receive as much as $500 an acre, annually, from solar leases, and California’s Central Valley farmers occasionally see as much as $1,000 an acre. That’s easy money compared to the complicated and often uncertain business of farming.

But the potential scale of these new projects has rattled some agricultural communities, where opposition is growing and threatening the effort to decarbonize the US power supply.

Critics are focusing on the drawbacks of converting farmland to solar generation. Panels are typically placed 18 to 36 inches off the ground, blocking access to the soil. Some dislike the aesthetics and fear that vast solar arrays will change the rural character of their communities. 

Right or wrong, rising opposition to solar in rural America is putting climate progress at risk, said James McCall, a researcher at the Energy Department’s National Renewable Energy Laboratory, in a call from Denver. “We need to find a solution that’s a middle ground,” he said.

Brad Heins, professor of animal science at the University of Minnesota, is working on just such a compromise. He’s a leading researcher in agrivoltaics, a growing set of technologies and methods designed to exploit synergies between energy production and agriculture. “We harvest the sun twice,” Heins explains as he unlocks a gate to a large cattle pasture in west-central Minnesota, near the border of North and South Dakota.

The sun’s energy feeds grazing fodder and crops side-by-side with solar panels. “For farmers, it’s a two-income stream,” Heins said. That might mean planting crops that thrive in the shade cast by the panels. Or, in Heins case, it can mean cooling cows in the panels’ shade rather than resorting to expensive fans in a barn.

Heins and his colleagues are at the cutting edge of this new field, but they aren’t alone. There are hundreds of agrivoltaics projects underway in the US. Some work better than others, and some may wind up not working at all. But the best will lead to a greener and more profitable rural America that embraces renewable energy as an asset.

The idea that shade cast by solar panels might boost farm productivity dates to the early 1980s. Japan, a country long obsessed with its limited land and energy reserves, was among the first to explore the concept. Its first known agrivoltaic facility was established in 2004, and by 2019 there were 1,992 agrivoltaic farms in the country.

For example, the high-grade green tea plant that’s ground into matcha is traditionally grown under shading nets for several weeks. 

Deploying those nets is not only a labor intensive process, but it can damage delicate and valuable plant shoots. Agrivoltaics offers an alternative. 

Farmers carefully position solar panels to provide the shade, thereby doing away with the need for netting and the expensive labor to deploy it. Farmers who invest in the system save money on production costs, while making money from renewable energy and a premium crop that they can market as sustainable.

None of these Japanese systems are designed to cover Midwestern corn fields or Texas livestock operations that sprawl for thousands of acres. Most Japanese farms are less than 3 acres and support the cultivation of high-value, hand-harvested crops that enjoy premium markets in Japan. Their agrivoltaics projects are adapted to that model.

Starting small, though, is a chance to prove the concept. In the US, some of the most successful agrivoltaics pilots also focus on hand-harvested crops. In Arizona, researchers recently found that tomato production doubled beneath solar arrays, and was 65% more efficient in the use of water. They also found that jalapeños were 167% more water efficient, even though production remained the same. That’s an important, money-saving finding for agriculture in arid regions, especially as the climate warms.

The benefits of agrivoltaics didn’t just accrue to the farmers. The Arizona studies found that solar panels with a garden growing beneath them stayed cooler and produced more energy. That kind of synergy is leading solar developers to look more carefully at working with farmers and encouraging further investments in rural solar.

The question now: Can techniques that have shown their greatest promise in small-scale demonstration projects and hand-harvested farms be scaled up enough to work for crops like corn, livestock and the communities that thrive on them?

“Twelve years ago, when I started here, I never imagined I’d be doing renewable energy,” Heins tells me as he stands beneath a solar panel array at the West Central Research and Outreach Center in Morris, Minnesota. He grew up on a dairy farm, and after receiving his PhD from the University of Minnesota, his research focused primarily on organic dairy production. “But the thing is, farming is very energy intensive,” he said. 

In 2013, the research center began looking at ways to reduce its energy footprint. So, in addition to seeking efficiency gains, it also began installing renewable energy systems, including solar arrays.

Agrivoltaics was part of the mix from the beginning. The center has some traditional installations just a few inches off the ground. But it’s also gone to additional expense to elevate panels several feet into the air. As we stand beneath an array shared with the University of Minnesota-Morris, Heins points to the cows grazing on the other side of the pasture. 

“Cows don’t do great in 80, 90-degree heat,” he said. Among other problems, heat stress in cows raises body temperatures and lowers milk production. One common solution is to place the cows in a barn with fans. But that requires electricity.

Heins and his colleagues tried a different approach: they raised the panels at least six feet, high enough to accommodate cows in search of shade. The cows didn’t hesitate to use it, and over the course of a study the cows stayed cooler and breathed more slowly. In other words: they were less stressed. 

“That’s a big issue with dairy cows,” explains Heins. Stressed dairy cows are less productive and, ultimately, less profitable. Heins tells me he’s received calls from livestock farmers outside of Minnesota keen to know whether their solar arrays can be made compatible with their herds.

It’s not just about the cows in Morris. During a morning tour, Heins and Esther Jordan, co-Director of the research center’s horticulture department, showed me a range of plants and crops that they’re trying to grow beneath solar arrays in this pasture and others. There’s good reasons to be hopeful about this work. A recent Yale study of Minnesota agrivoltaics projects found that incorporating pollinator-friendly plants not only improved the efficiency of the solar panels above them, but potentially spread benefits to surrounding farms that depend upon pollinators. It’s the kind of outcome, along with the direct economic benefits via improved crops, that could help to overcome opposition to solar arrays in US farm country.

For now, the conversation is in early stages. Agrivoltaics, at least on a large scale, remains a subject of research more than a method of doing business. Furthermore, the effort of lifting solar panels six to eight feet off the ground — rather than 18 inches — poses a considerable cost burden, especially when the price of steel is so high. More difficult yet, even eight feet isn’t high enough for many modern farming machines to operate under. 

The large-scale farming operations that define so much of US agriculture — and which depend on large planting and harvesting equipment— will not, for now, be a candidate for these new techniques.

But these are short-term issues. McCall, from the Department of Energy’s renewables lab, tells me that interest in agrivoltaics is high and growing. He said he’s hearing from landowners, state and local regulators, universities — ”people who want to see these sites. There’s lots of interest in setting up demonstration facilities in local communities.”

That’s good news for rural communities seeking ways to diversify their economies, for farmers keen to add on another income stream, and for anyone determined to see the US decarbonize its power grids. 

Agrivoltaics won’t solve every economic problem in farm country. But it’s an important tool that farmers and solar developers are just beginning to understand and use.

In coming years, agrivoltaics will bind them in an effort to build more sustainable farming and energy systems. That’s reason for long-term optimism down on the farm, and across rural America.

 Adam Minter is a Bloomberg Opinion Columnist.

Source: Bloomberg