In a world with a growing population that needs to produce significantly more renewable energy as well as significantly more food, you’d think that solar farms and more traditional agricultural farms would be competing for often-scarce space. However, there is increasing evidence that combining the two by growing crops underneath solar panels is not only feasible but also produces better results for both power generation and crop production.

Agrivoltaic farming is the name given to growing crops, providing grazing for livestock production or maintaining pollinator habitats underneath solar panels, and several studies have shown that some crops actually thrive in such an environment. The solar panels can provide shade to protect the plants from the hot sun, reducing plant stress and cutting evaporation from the soil. The plants in turn give off water vapor that rises and helps to cool the photovoltaic panels from below, which can increase panel efficiency.

The panels are mounted typically up to 4 metres above the ground to allow farm machinery to pass underneath; alternatively, they can be mounted lower but on pivots to enable them to be moved into a vertical position for access to the crops. In other installations, farmers graze their sheep on the grasses growing beneath the panels, which eliminates the need to cut the grass to prevent it from encroaching in the panels. That in turn cuts the emissions associated with mowing and offers protection for ground-nesting birds and other wildlife.

Some agrivoltaic system designs use a tracking system to optimise the position of the panels to improve agricultural production by increasing shade, or to boost electricity production through light maximisation. Insolight in Switzerland is developing translucent solar modules with an integrated tracking system that allows the modules to remain static. The module uses lenses to concentrate light on to solar cells and a dynamic light transmission system to adjust the amount of transmitted light. A company named Artigianfer has developed a photovoltaic greenhouse whose solar panels are installed on movable shutters and can follow the course of the sun along an east-west axis.

Can wildflower planting boost pollinator numbers?

Researchers from Cornell University in the US are looking at the benefits of pollinator-friendly plantings on solar farms. One goal is to see whether wildflower plantings on solar sites can increase pollinator populations; another is to see whether such plantings encourage pollinators to visit crop flowers. Other Cornell research is looking at how sheep grazing may influence pollinator habitat and sequestration of soil carbon, what the long-term impacts of solar energy infrastructure might be on soil quality, and what crops, in what regions, are best suited for agrivoltaic systems.

Greg Barron-Gafford, an earth system scientist at University of Arizona, has been running experiments to determine which crops might benefit most. He’s grown cilantro, peppers and tomatoes and found that they grow just as well, if not better, under solar panels than in the open; and they also only use half the water. He found that the leaves of basil plants grow bigger under panels than they would if planted in an open field, to absorb more light. He also found that the pepper Capsicum annuum produces three times as much fruit in agrivoltaic conditions and that tomato plants also produce more fruit. (“Growing Crops Under Solar Panels? Now There’s a Bright Idea”

In the meantime, agrivoltaic installations are already returning impressive results. Jack’s Solar Garden in Boulder County, Colorado, has solar panels covering four of its 24 acres and a wide variety of crops is being grown underneath: carrots, kale, tomatoes, garlic, beets, radishes, lettuce and others. The panels in turn have been generating enough electricity to power 300 homes.

Selective light transmission for greenhouse roofs

Greenhouse-based farming reportedly produces 10 times more food than growing in an open field, but it can require 10 times as much power. One of the latest innovations is a polymer film that selectively transmits the blue and red wavelengths that are needed for photosynthesis, while all other wavelengths are reflected and concentrated on solar cells for power generation. What impact could this have for greenhouse growers?

Researchers in the UK and Italy have found that orange-tinted solar panels allow orange and red light to pass through, while absorbing blue and green light to generate electricity. The team claims that its approach can produce crops that offer superior nutrition. According to the journal Advanced Energy Materials, the researchers grew basil and spinach in greenhouses in northern Italy using semi-transparent, orange-tinted solar panels in place of the traditional glass roofs. The yield of both crops was lower than for plants grown in normal greenhouses, but the agrivoltaic system was more profitable.

The combined value of the spinach and electricity produced was 35% higher than in a standard set-up, while the basil and electricity combination was worth 2.5% more. Basil sells for five times more than spinach, so the study showed that the greatest rewards for agrivoltaic greenhouses lie with lower-value crops. The researchers found that the basil produced larger leaves and the spinach longer stems, and both basil and spinach plants grown under the solar panels contained more protein than those grown in standard greenhouses.

A study by Brendan O’Connor and a team at North Carolina State University, reported in the journal Joule, looked at how much energy could be produced by installing solar cells on greenhouses, using similar filtering technology. They found that there are greater opportunities in hot and moderate climates. But because the cost of heating greenhouses is so high in colder climates, offsetting those energy costs is critical. If the solar cells can be designed to minimise losses in plant yield, there should be benefits across different climate zones, the study concluded.

Solar energy continues to excite the global market and, between agrivoltaics and floating solar solutions, one of the main challenges – finding available space for solar farm installations – should soon be a thing of the past.