Solar power in the desert has problems: big land use requirements, and the need for scarce water to clean the panels and suppress dust. In an unrelated story, biofuels production has problems: life cycle greenhouse gas emission issues, and land use questions again. How about solving both sets of problems at once? Stanford researchers have modeled the co-location of solar panels with agave plants used to make ethanol, and found it to be a winning combination.
The idea of “agrivoltaics”, or combined solar power and agricultural production, has been floating around for a while now. It’s an idea that springs at least partially from the modern distaste for “monoculture”, or the growing of a single crop over huge swaths of land. The reasoning: Instead of “growing” only solar power on a plot of land, why not use the space between and underneath the photovoltaic panels to also grow crops? There are some projects in France that have tried this, and a post-Fukushima Renewable Energy Village in Japan also features crops underneath PV. There are also experiments at the University of Massachusetts, and some small-scale “solar farm” installations in Wisconsin.
It seemed unlikely, however, that the idea of studding the land around the solar plants that have started cropping up across the arid deserts of the American southwest would take root. But the Stanford folks, led by post-doctoral researcher Sujith Ravi, realized that the water required for a solar plant could actually make the desert more hospitable to agriculture as well. To test the idea, they chose agave plants, biofuel sources that are already quite hardy and require little water to survive.
They found that by combining a PV plant with agave production, a given area could yield more energy for the same amount of water than either PV or agave alone. The study, published in the journal Environmental Science Technology, showed a “high-yield” scenario where only 0.42 liters of water would be needed to produce one mega-joule of energy.
“It could be a win-win situation,” Ravi said in a press release. “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.” This marriage of agave and solar panels is especially compelling for two reasons. First, because agave plants require roughly the same amount of water needed to keep solar panels clean and to suppress dust, it’s possible to use the water dripping off a newly cleaned solar panel to nourish the plant. And a 2011 study found that the plants, also used to make tequila, perform just as well or better than corn, sugarcane, and switchgrass in terms of lifecycle greenhouse gas emissions and other parameters.
Aside from planting crops beneath existing solar panels, there are other ways to think about combining PV with plants. In a report on the topic, the National Renewable Energy Laboratory encouraged farmers to consider locating solar panels in the unused corners of their center-pivot farm plots. In Colorado alone, those currently underused spots could generate enough power to meet all of the state’s electricity needs. Clearly, farming and solar power should become much better friends in the future.