Solar Farms Can Grow Biofuels—Just Add Agave

Sujith Ravi, an environmental science postdoc at Stanford, has discovered an ingenious way to optimize the energy efficiency of solar farms—by planting biofuel crops underneath the photovoltaic cells. This “colocation” of two renewable energy sources in one place is outlined in greater detail in the most recent issue of Environmental Science & Technology.

“This study is based on a life cycle analysis of colocation,” Ravi told me. “So far, this idea of colocation seems to have potential. Field experiments are needed to explore the full potential.”

Solar farms are typically built in sun-soaked deserts, both to maximize the amount of radiation collected and to prevent interference with agricultural enterprises. Very few biofuel crops could thrive in this harsh environment, but the wonder plant agave is a happy exception.

Most people are already familiar with agave's ethanol-producing powers because, well, tequila. But in addition to providing us with the world's most treacherous liquor, the plant is a bioenergy powerhouse. As a biofuel, agave outperforms corn, soybeans, sorghum, and wheat by a huge margin. On top of that, it would be perfectly comfortable to chill underneath desert solar panels where other crops would fry.

But there's more! Desert-based solar panels get jammed with dust, and need to be cleaned with water in order to maintain maximum efficiency. Water is also spread on the ground underneath the cells to prevent more dust kicking up and clogging the equipment.

If agave was planted underneath the panels, it could absorb runoff water from cleanings, solidify the ground with its roots, and block dust from kicking up with its foliage. Not only would this increase the energy output of a photovoltaic farm, it would decrease the amount of water needed to service the equipment, as well as the overall damage.

“It could be a win-win situation,” Ravi said in a statement. “Water is already limited in many areas and could be a major constraint in the future. This approach could allow us to produce energy and agriculture with the same water.”

Photovoltaic farms aren't the only solar power plants with the potential to produce crops underneath their machinery. Though it may be decades before we get space-based solar power, the SPS-ALPHA concept proposed by John Mankins also allows for crops to be grown under large microwave receivers, similar to the garden underneath the Arecibo Observatory.

Along those lines, Ravi is hoping to extend the concept beyond the desert environment. “We are looking forward to studies in different locations and exploring ideal plants suitable for colocation in different systems,” he told me.

“For example, in collaboration with research institutes in India, we are working on a similar colocation analysis in north western India using Aloe Vera (another high value desert plant). I think this colocation approach will be applicable to other areas as well, in particular in areas where land or water is scarce. Based on the field experiments, we can work on design modifications for future solar installations and select appropriate (location specific plants) suitable for colocation.”

As the renewable energy industry evolves, we're likely to see increased colocation of multiple fuel sources—both to amplify yields and to conserve land and resources. As the planet's thermostat marches ever upwards and our non-renewable resources dwindle, advances like these cannot come soon enough.