Solar panels and farming can work together to put more food on the table and more money in the pockets of farmers.
Symbiosis — 1. an interaction between two different organisms living in close physical association, typically to the advantage of both. 2. a mutually beneficial relationship between different people or groups. By those definitions, researchers at Cornell University led by graduate student Henry Williams have identified a symbiotic relationship between solar panels and agriculture. Their findings were published February 15 in the journal Applied Energy in a paper entitled “The potential for agrivoltaics to enhance solar farm cooling.”
In the study, the researchers developed a numerical model to investigate the micro-climate of a solar farm. That model measured the influence of evapo-transpiration, panel height, and ground albedo on the crops and the solar panels. The findings were used to compare an agrivoltaic system to a traditional solar panel system. The results indicate crops can provide up to a 10 °C cooling benefit to the solar panels in an agrivoltaic system.
In the abstract to the study, the researchers say:
“Human society is at a critical point where rapid adoption of renewable energy alternatives is necessary to mitigate climate change effects while meeting global energy demands. At the same time, agricultural production must increase significantly by mid-century to feed an anticipated 10 billion people worldwide. These impending food-energy needs create land use competition between crops and energy production, particularly with solar photovoltaics. Co-locating agriculture and solar PV is one attractive solution, but its widespread adoption is hindered by the perception that co-located sites will see major tradeoffs between food and energy production.
“Here we investigate the potential for agrivoltaic design features to influence the solar farm micro-climate and surface temperature of solar PV modules. We develop a CFD-based microclimate model, evaluated against extensive experimental data, to investigate the effects of panel height, ground albedo, and evapotranspiration in a solar PV site.
“We show that an agrivoltaic solar farm mounted at 4 meters with soybeans underneath exhibits solar module temperature reductions of up to 10 °C compared to a solar farm mounted at 0.5 m over bare soil. These results indicate that ground conditions and panel height play important roles in solar farm cooling, and that agrivoltaic systems can potentially help to resolve the global food-energy crisis by improving solar PV conversion efficiency while enabling agricultural production on the same land.”
Decoding The Science
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Photo by Werner Slocum, NREL
In a blog post by Cornell about the research, Williams says, “We now have, for the first time, a physics based tool to estimate the costs and benefits of co-locating solar panels and commercial agriculture from the perspective of increased power conversion efficiency and solar panel longevity.”
“There is potential for agrivoltaic systems — where agriculture and solar panels coexist — to provide increased passive cooling through taller panel heights, more reflective ground cover and higher evapo-transpiration rates compared to traditional solar farms,” added senior author Max Zhang, a professor in the Sibley School of Mechanical and Aerospace Engineering at Cornell, “We can generate renewable electricity and conserve farmland through agrivoltaic systems.”
In New York, for example, about 40% of utility-scale solar farm capacity has been developed on agricultural lands, while about 84% of land deemed suitable for utility-scale solar development is agricultural, according to a previous research study from Zhang’s group.
By using a computational fluid dynamics based micro-climate model and solar panel temperature data, the group evaluated solar panel height, the light reflectivity of the ground and rates of evapo-transpiration (the process where water vapor rises from the plants and soil). They found that agrivoltaic systems can potentially help resolve future global food/energy problems.
The engineers showed that solar panels mounted over vegetation reveal surface temperature drops compared to those arrays built over bare ground. Solar panels were mounted 4 meters above a soybean crop and the solar modules showed temperature reductions by up to 10 degrees Celsius, compared with solar panels mounted a half-meter above bare soil.
The cooling effect due to enhanced evapo-transpiration and surface albedo from vegetation and soil is more significant than that induced by greater panel height and the passive cooling adds to solar panel efficiency, compared with exposed soil or gravel, according to the paper. Better yet, the temperature drops lead to an improved solar panel lifespans and improved, long term economic potential.
“As you decrease the solar panel operating temperature, you can increase efficiency and improve the longevity of your solar modules,” said Williams, “We’re showing dual benefits. On one hand, you have food production for farmers, and on the other hand, we’ve shown improved longevity and improved conversion efficiency for solar developers.”
Understanding this mutually beneficial concept comes at a critical time for agricultural production, as global food demands are expected to increase by 50% by 2050, to feed an anticipated 10 billion people, according to the World Resources Institute. At the same time, it is imperative to accelerate the deployment of renewable energy to mitigate the impact of climate change. In hot climates like the western United States, agrivoltaic farms would be ideal.
“Up to this point, most of the benefits from agrivoltaic systems have revolved around hot and arid climate zones,” said Zhang, who is also a director of the Cornell Atkinson Center for a Sustainable Future, “This paper is taking a step toward evaluating the viability of agrivoltaics in climates representative of the Northeastern U.S. in relaxing the land-use competition the world faces.”
The Takeaway
Farmers tend to be quite risk averse. Their institutional memory stretches back in time over centuries and there is a strong preference for doing things the way they have always been done. But changes are coming to farms all across America as tractors powered by batteries and guided by autonomous driving systems begin to appear. There are groups who are pushing back against putting solar panels on farm land because they believe doing so will lead to hunger and famine.
Clearly, not all farms should be converted to agrivoltaics. Not every crop thrives in the presence of solar panels, but a surprising number of them do. Tomatoes, for instance, can benefit from the partial shade and cooler temperatures the solar panels provide and farmers can benefit from the extra income that solar panels make possible.
A symbiotic relationship is one in which two or more actors — in this case farmers and crops — do better when they work together. Today we call that a win-win situation. If it helps farmers increase their yields and earn more money, that’s a win for society as well.
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Source: Clean Technica