The renewable revolution is facing a major land use issue that threatens to seriously impede the growth trajectory of the clean energy sector. Mass-scale renewable energy infrastructure like wind and solar farms take up much more land area than traditional fossil fuel production plants, and the sector is increasingly competing for land with other major industries including agriculture. Going forward, the renewables sector will have to get creative about using land more efficiently and in a more collaborative manner with other major land users.
Late last year, global management consulting firm McKinsey & Company released an analytic report that included land shortages as one of three key challenges facing the renewable revolution, along with miles of bureaucratic red tape and woefully under-prepared power grids. Solar and wind farms need huge tracts of land to operate at scale, and there is often fierce competition for parcels of such scale, driving up prices for renewable energy developers. “Utility-scale solar and wind farms require at least ten times as much space per unit of power as coal- or natural gas–fired power plants, including the land used to produce and transport the fossil fuels,” McKinsey reports, adding that “wind turbines are often placed half a mile apart, while large solar farms span thousands of acres.”
One of the most promising solutions to this key issue is agricultural photovoltaics (AV), also called agrivoltaics, a practice in which crops and renewable energy production take place on the same land, working symbiotically. The plants benefit from the shade of solar panels, while the plants release water through transpiration, cooling the air around the panels and effectively increasing their efficiency.
AV is not a new concept, however. So why hasn’t it taken off since its development in the 1980s? While optimizing the system to meet the needs of both systems – solar energy production and agriculture – seems straightforward on paper, in reality it isn’t that simple. Both plants and solar panels need a lot of sun, and making sure that everything gets what it needs can get a little complicated. “A pressing question is how AV technology can maximize crop productivity and energy generation while minimizing plant water loss and irrigation needs,” Phys.org recently reported. “That's a lot to ask for on a piece of land.”
Scientists are busily looking into how to design efficient AV systems capable of striking this kind of a balance at scale. One potential solution, proposed by researchers from the University of California Davis, is to divide light into different wavelengths, directing different parts of light to different uses, such as red light for crops to photosynthesize, and blue light for solar panels. The study, which was published late last year in the scientific journal Earth’s Future, employed a mathematical framework to quantify how different kinds of plants use different wavelengths of light in their photosynthesis processes.
Modeled plant typologies included variables such as shade tolerance and leaf area, and findings indicate that the ideal candidate crops for AV are those that are shade tolerant and also have a large aboveground leaf area. The shade tolerance lends itself to life underneath a solar panel, whereas the large leaf area allows for greater solar uptake. Additionally, a larger overall plant size was correlated with greater respiration costs – another key component of the study, which was also concerned with efficient water use. Findings suggested that great candidates for AV include larger plants with lots of leaves such as arugula, kale, and tomatoes.
While AV has not been employed at scale yet, some AV pilot projects are already being implemented around the world. In Germany, farmers are growing hay in the furrows between rows of standing solar panels. In France, grapevines are growing in the shade of solar panels on vineyards, and in Japan tea leaves are benefitting from panel-produced shade. There are other related innovations in shared use systems as well, including sheep that share their pastures with solar panels in Canada and Australia, and apiaries that allow imperiled honeybees to share space on solar farms in the United States.
The potential benefits of advancing and scaling AV are enormous, and could positively change agriculture as well as the renewable energy industry. "We cannot feed 2 billion more people in 30 years by being just a little more water-efficient and continuing as we do," said corresponding author Majdi Abou Najm. "We need something transformative, not incremental. If we treat the sun as a resource, we can work with shade and generate electricity while producing crops underneath. Kilowatt hours become a secondary crop you can harvest."
By Haley Zaremba for Oilprice.com
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