Solar Energy, Crops, and Cattle Work Together

Solar energy, crops, and cattle work together at the University of Massachusetts Crop Research and Education Center. A research trial launched in 2010 suggests that generating solar energy can occur hand in hand with grazing livestock or growing vegetable crops.

“The purpose of our work has been to see if we could generate solar energy while keeping the land in agricultural production,” says University of Massachusetts (UM) agronomist Stephen Herbert. The research results show that agri-voltaics – or dual-use farming – can indeed work. The key is the design of the solar array.

Assessing Compatibility

The center is evaluating the crop and livestock compatibility of a solar array consisting of three panels vertically stacked and elevated by a unique racking design that supports the panels 4 to 7 feet off the ground; 2- to 5-foot spaces between panel clusters permit light to reach the crops and grass growing beneath the panels. Traditional configurations, such as arrays installed by large solar developers, are typically situated close to the ground in flatter, solid chains of arrays that block sunlight and, thus, take land out of ag production.

However, that’s not the case with the elevated 17-kilowatt solar installation at the UM research center. “Every spot beneath the panels gets about two thirds of the full amount of sunlight throughout the day,” Herbert says.

As a result, grass growing beneath the panels hardly misses a beat. Herbert’s initial, three-year evaluation focused on forage growth and the performance of cattle grazing within the solar array. “The area underneath the panels produced 90% to 95% of the yield of the pasture area not covered by solar panels,” he says. “On hot summer days, the cows would lie down in the shade underneath the panels.”

Herbert later implemented a three-year trial looking at the performance of vegetables grown in combination with the solar system. He planted kale, Swiss chard, broccoli, and bell peppers.

“The first year was very hot and dry. Although I irrigated well in the shaded research plot, as well as in the unshaded control plot, the plants growing underneath the panels yielded better than the control plants,” Herbert says.

One reason for the improved plant performance in the partially shaded area beneath the solar array could have resulted from a cooler temperature beneath the panels. “Tissue samples taken from plants growing beneath the panels were 15°F. cooler than those taken from plants growing in full sun,” he says.

During the next two years, growing conditions were cooler and wetter, resulting in more robust growth in plants grown in full sun. The partially shaded vegetables yielded 45% to 60% of the yield in the control plots.

Research results suggest that growing food and generating solar energy make good partners. “If farmers are planning on installing solar panels or are approached by a solar company hoping to develop their land into a solar farm, they should do it in such a way that they can keep agriculture going on the land,” he says. “They can continue to earn an income from farming in addition to the revenue earned from solar energy.”

Crop Limitations

Options for crop production beneath the panels, however, are limited to crops typically grown and harvested by hand or with small machinery. Shade-loving pollinator crops, bedding plants, nursery crops, and small-statured fruit trees or shrubs are options, in addition to vegetables and small- to medium-size livestock, such as most breeds of cattle and horses of nondraft breeds.

“There are a lot of different opportunities for dual-use farming,” says Jordan Macknick, an analyst with the National Renewable Energy Laboratory (NREL), which researches plant production on solar farms and funds partners across the country. “Conventional panel heights work particularly well with sheep grazing, and elevated panels work well with growing crops.”

Dual-Use Farming Gaining Ground

Besides Herbert’s work in Massachusetts, the NREL is funding dual-use research projects in Arizona, Oregon, and Colorado. Independent dual-use farming enterprises are gaining ground in Europe, he says.

Marketing dual-use crops for a premium may be possible in some marketplaces. “Besides earning an income through the sale of electricity, growers may be able to sell crops for a value-added price because they are grown in the shade of solar panels,” Macknick says. “We see some beekeepers, for instance, who are able to market their honey for a premium because it’s produced in conjunction with the generation of solar power.”

Investment costs of elevated solar arrays vary widely, ranging from $2 to $5 per watt. “The cost depends on the location, system configuration, and interconnection fees charged by local utilities,” Macknick says. “Farmers need to get a quote from a solar developer for installing a solar system in their region.”

The solar array at the center was installed by Hyperion Systems (hyperionsystemsllc.com) based in Massachusetts. Indeed, the company’s founder, David Marley, had a vision of creating solar systems that preserved the productive capacity of farmlands.

“His belief was food first and energy second,” says company owner James Marley of his deceased father. “His idea inspired the research project at the University of Massachusetts and the collaboration of a foundation and two public-sector agencies.”

Hyperion’s patented design for the solar-panel racking sets it at the forefront of the movement promoting the generation of solar power in conjunction with food production. “We install the systems without the use of concrete footings for the supports,” Marley says. “The concrete footings can typically take up a couple square feet around each support pole.”

The Hyperion supports are 4- to 8-inch steel posts anchored by steel flanges at the ends, which are driven into the ground to a depth of 8 feet. The system is rated to withstand winds of 120 mph.

Energy earnings from a solar system sized to meet the energy needs of a home or a farm typically occur through a net-metering arrangement with the local utility. The energy generated by the system is sent onto the grid, and the farmer withdraws electrical power from the grid at no cost, up to the amount generated by the on-farm system during a set period.

“Different states have different incentives in terms of what they’ll pay for electricity,” Macknick says.

Solar Incentives

USDA’s Rural Energy of America Program (energy.gov) offers grants for the installation of renewable energy systems. A federal tax credit can be claimed for installing a solar energy system.