Agrivoltaics — using land to grow food and host solar panels at the same time — seems like such a good idea, you may wonder why it is not used more often. It can increase yields and generate extra income for farmers. However, not all plants thrive while sharing space with solar panels. Potatoes, wheat, cucumbers, and lettuce do not do well, for instance, but tomatoes often thrive,.
A research paper published by the National Renewable Energy Laboratory in August surveyed agrivoltaic research all across America. It noted that, on average, tomato yields doubled compared to non-agrivoltaic sites. The NREL found there are 5 characteristics that determine whether agrovoltaics are feasible in any given situation.
Climate, Soil, and Environmental Conditions: The ambient conditions and factors of the specific location that are beyond the control of the solar owners, solar operators, agrivoltaic practitioners, and researchers.
Configurations, Solar Technologies, and Designs: The choice of solar technology, the site layout, and other infrastructure that can affect light availability and solar generation.
Crop Selection and Cultivation Methods, Seed and Vegetation Designs, and Management Approaches: The methods, vegetation, and agricultural approaches used for agrivoltaic activities and research.
Compatibility and Flexibility: The compatibility of the solar technology design and configuration with the competing needs of the solar owners, solar operators, agricultural practitioners, and researchers.
Collaboration and Partnerships: Understandings and agreements made across stakeholders and sectors to support agrivoltaic installations.
Agrivoltaics, Extreme Heat, And Drought
Tomatoes are a billion dollar industry in America. California grows the most tomatoes, with Florida in second place. But California is experiencing severe drought and heat as the climate change impacts its agricultural industry. Those factors have led to a shortage of so-called processing tomatoes, which are typically used to make sauces and ketchup.
Drought and extreme heat in California’s Central Valley in recent years has meant shortages of tomatoes, particularly processing tomatoes, and those conditions are only expected to get worse with climate change. Shade provided by solar panels can help conserve water, create humidity, and lower temperatures that can become too much even for heat-loving tomatoes, Canary Media reports.
When it is too hot, tomatoes will abort the development of fruit from flowers since the plant senses that the fruit won’t flourish. Solar panels cool the air down enough to avoid this process, research has shown. And most importantly in a place like California, where the vast majority of the nation’s tomatoes are grown, solar panels can mean significantly less irrigation is needed.
At the University of Arizona’s Biosphere 2, cherry tomatoes doubled their yield when grown under solar panels, as noted in a 2019 study published in Nature Sustainability. “They got plenty of light, plenty of water, and the temperature stress was brought down just below that threshold so they could fruit through the summer and get an extra month of production, and more production per plant,” said Greg Barron-Gafford, lead author of the paper and professor at the University of Arizona.
The Arizona study found that not only do solar panels cool the air during the day, but they also warm the air at night — a benefit for tomatoes and other crops in desert climates like Central California and Arizona where temperatures can plummet after the sun sets.
The tomato plants provided benefits to the solar panels as well. They become less efficient at generating energy when they are especially hot. The plants growing beneath panels create a cooling effect on the panels thanks to their transpiration.
Practical Considerations For Agrivoltaics
Tomatoes often grow to about five feet high, so they can fit under solar panels that are elevated to six feet — taller than most commercial arrays, but standard for agrivoltaics. Tomatoes are often harvested by hand, and the research in Arizona noted that agrivoltaics could benefit farm workers. Preliminary research showed that skin temperature could be as much as 18º F lower working under the shade of panels.
While processing tomatoes are grown in vast fields, many whole tomatoes sold in stores are grown in greenhouses. Researchers said that growing tomatoes under solar panels could mimic the conditions of a greenhouse in some climates, and energy from solar panels could also power on-site greenhouses.
Whether agrivoltaics are adopted by the tomato industry depends in large part on meeting the needs of both solar developers and farmers. Elevating solar panels higher to accommodate tomatoes underneath means extra costs, and machinery used to pick and plant tomatoes on many large farms might not work in concert with solar panels.
Research At Oregon State
Researchers at Oregon State University examined tomato cultivation with agrivoltaics in a cooler climate for a 2021 study. They found mixed results that bolstered the idea that tomatoes are ideal agrivoltaic candidates in hot climates where most commercial production is done, but not a fit for small farmers in cooler climates. The researchers placed some tomatoes under solar panels, others in between solar arrays, and a control group in an open field. Other research suggests mounting solar panels vertically can increase the output of a solar array.
The soil and air temperatures were significantly lower in the plots below the panels compared to the between-row plots and the control field. The soil temperature under the panels was a full 5º C lower than the between-rows and the control. The sunnier control plot yielded the most fruit but it also used significantly more water than the other plots, even in a relatively cool climate — an effect that might be amplified in a hotter place.
The researchers concluded that agrivoltaics offered the opportunity to “trade a reduction in yields for reductions in water use.” The study notes that using water more efficiently may not matter in a place with lots of rain like western Oregon or Florida but “could be critical in areas which are currently water-stressed and expect to become more water-stressed in coming years.”
Agrivoltaics may benefit farmers who cultivate certain crops in certain locations. The importance of scientific research is to determine when and where solar panels and agriculture can benefit each other. Farmers are highly sensitive to productivity and profitability. Particularly in places that are experiencing drought conditions and rising temperatures during the growing season, adopting agrivoltaics may provide the edge some farmers need to survive in a world where climate change is putting stress on traditional farming practices.
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