Science and Technology
Installing solar panels in a pasture can help cool dairy cows on hot days, indicates a study conducted in the United States. In the summer of 2019, researchers from the University of Minnesota monitored cows grazing in the shade of a photovoltaic system on a dairy farm in Morris, Minnesota, to measure the effects of shade on the animals. The conclusion was that solar panels reduced signs of heat stress, although without increasing milk production.
The experiment, published in 2021 and presented as a starting point, lasted only one summer and involved 24 crossbred cows, half with access to shade and half in full sun. According to the authors, the animals sought the shade of the panels on only 28 of the 175 pasture days, too short a time to reveal long-term effects. Even so, during the hottest hours, the shaded cows breathed more slowly and maintained a lower body temperature.
The research arose from a gap, as no previous work had installed a solar system on the ground to shade dairy cows and measure the effects. The study was conducted at the University of Minnesota’s dairy farm in Morris, which milks about 275 cows twice a day and represents a medium-sized property in the state. The motivation was to test agrivoltaics, the idea of using the same land to generate clean energy and produce food, reducing dependence on fossil fuels.
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In the summer of 2018, a 30-kilowatt photovoltaic system was installed, with solar panels positioned between 2.4 and 3 meters high, tilted at 35 degrees and facing south, at an approximate cost of US$ 90,000, about R$ 490,000. Between June and September 2019, 24 crossbred cows were divided between a shaded group and another in full sun. Each animal wore a CowManager ear sensor and a SmaXtec device in the stomach, which measured internal temperature, activity, and water intake, while maximum temperatures ranged from 27 to 34 degrees Celsius. The results were published in the Journal of Dairy Science in 2021, by a team led by Professor Brad Heins.
Where the sun was strong, the shade from the solar panels made a measurable difference. In the afternoon, shaded cows breathed more slowly, about 66 times per minute, compared to 78 for those exposed, a clear sign of less heat stress. The internal body temperature confirmed the situation, with cows in full sun recording values up to about half a degree Celsius higher between mid-afternoon and dawn.
For the researchers, even a small temperature difference is relevant from the animal’s perspective. Professor Brad Heins summarized that, for the cow, this variation “is quite a lot,” and raised the hypothesis that cooler bodies could, in the future, sustain higher milk production. During the hottest hours, between milkings, cows with access to shade remained more comfortable.
Despite the relief from heat stress, the solar panels did not increase milk production, contrary to expectations. The study found no differences between the two groups in production, fat and protein content, weight, body condition, water intake, injuries, gait, or number of flies. In practical terms, the shade improved comfort but did not translate into more milk in the bucket.
The authors’ own explanation is simple, as the cows used the shade on only 28 of the 175 pasture days in the summer. This exposure was too short to measure long-term effects, and the team suggests that if the animals had stayed in the shade the entire summer, changes in production might appear. Therefore, the work is treated as preliminary, a starting point, and not as proof that panels increase milk production.
The shading also brought an unwanted effect, as the cows ended up with dirtier bellies and hooves. This happened because they used the shaded area to rest and lie down, and they defecated and urinated right there, leaving the soil dirty under the panels. The ground under the panels was cooler and more humid, and the animals tended to concentrate in a smaller space.
The researchers also noted that the shaded cows had fewer periods of high activity, as they spent the hottest hours standing under the solar panels. There is, therefore, a possible embedded cost, as it is plausible that the animals traded grazing time for refuge in the shade. The balance between comfort and feeding behavior appears as a point to observe in larger studies.
First of all, the agrivoltaic system was still an energy plant, not just a roof for the cattle. Throughout 2019, the 30-kilowatt solar panels generated about 35,535 kWh, equivalent to approximately 35.5 MWh, a volume that, according to the study’s environmental benefit calculations, would avoid about 37 tons of CO2, the same as planting around 2,066 trees. These numbers are estimates from the study itself, and in 2020 a larger plant, of 240 kilowatts, was added to the pasture.
The study was explicitly a starting point, and the team has already announced a new project in 2021. The idea is to design solar structures that serve as shade in the summer and as a barrier against wind and snow in the winter, as well as to test tracking panels on low-value agricultural land. In subsequent tests, researchers found that good quality forage grows under the panels, but in fully shaded areas, pasture production dropped significantly, reinforcing the need to balance shade and cultivation.
The University of Minnesota study suggests that solar panels can be an acceptable way to alleviate the heat for grazing dairy cows while generating clean energy. The thermal comfort gains coexist with clear limits, such as the lack of increase in milk production in this short experiment and the dirt accumulated under the panels. More than a ready solution, agrivoltaics applied to livestock appears as a promising path that still needs larger and longer studies.
And you, would you plant solar panels on your property to generate energy and provide shade for the cattle, or do you think the land yields more without the panels? Share your opinion, respecting different views on the subject
I cover construction, mining, Brazilian mines, oil, and major railway and civil engineering projects. I also write daily about interesting facts and insights from the Brazilian market.
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