Having a solar installation on rural land is something that can benefit both humans and animals. We have already told on other occasions how the agrivoltaics can have positive effects on animals, such as in birds and insectseither even in sheep. A team from the University of Minnesota has discovered that it also provides benefits to a much larger and much more heat-sensitive animal: the dairy cow. And they have answered the question of what would happen if we let cows graze under the shade of a solar panel system.
What is the study about? According to the authors of the work themselvespublished in the proceedings of the AgriVoltaics2021 conference, there was no previous research that analyzed the use of a ground-mounted solar system to shade dairy cows and measure how it affects them. So without further ado, they got to it.
Everyone wins. Livestock farming is heavily dependent on fossil fuels, with the economic and environmental cost that this entails. The idea of agrivoltaics is to kill two birds with one stone, using the same land to generate clean electricity and, at the same time, to produce food. In the case of a dairy farm, the panels could shade cows during heat waves, as heat stress directly affects their well-being and production. On a farm in Morris, Minnesota (where the study was done), about 275 cows are milked twice a day, figures that represent the average for the State.
How have done. In the summer of 2018, they installed a 30-kilowatt ground-mounted solar system in a pasture, with the panels placed 8 to 10 feet high so the cows couldn’t reach them. The animal study was carried out from June to September 2019 with 24 cross-breed cows, divided into two groups: half with access to the shade of the plates and the other half grazing without any shade.
To measure everything without relying only on the human eye, each animal wore a CowManager ear sensor (which recorded whether it ruminated, ate or was active) and a SmaXtec bolus housed in the stomach reticulum, which measured internal body temperature, activity and how many times they drank. Added to this were daily visual observations of hygiene, lameness and injuries, as well as fly counts. Maximum temperatures during the study ranged from 27 to 34°C.
What didn’t change. On many key indicators, there were no differences between the two groups. Not in the number of flies, nor in the production of milk, fat or protein, nor in body weight, physical condition, how many times they drank, injuries or the way they walked. So the shade did not trigger milk production as one would expect.
The reasons for the absence of these changes, according to the authorsis that the cows were only in the shade 28 of the 175 days they grazed during the summer. That is, the experiment was too brief in actual exposure to determine long-term effects. They themselves point out that, if it had been under the plates all summer, perhaps changes in the milk would have been observed.
What did change. Where the sun really shines, the plates made a difference. During the afternoon, the shaded cows breathed more slowly (about 66 breaths per minute compared to 78 for the unshaded cows), a clear sign of less heat stress. And the internal body temperature also confirmed it, because between one in the afternoon and midnight, the cows without shade registered temperatures up to half a degree higher. During the middle hours, between milkings, the cows in the shade stayed cooler.
Bad. The shady cows ended up with dirtier bellies and legs. The reason is that the cows used the shaded area to rest and lie down, and since they also defecated and urinated right under the panels, the floor became dirty. Added to this was that the ground under the plates was cooler and more humid, and the cows tended to crowd into less space.
It was also observed that the cows with shade had fewer peaks of high activity, because they spent the hottest hours quiet under the panels.
ANDenergy. It should not be forgotten that the system was still, above all, a solar plant. During 2019, those 30 kilowatts generated 35,535 MWh of energy. According to the environmental benefit calculations that collect the studythat is equivalent to saving 37,238 kg of CO₂ emissions, the same as planting about 2,066 trees, according to what they say.
Conclusions. The team says it is possible that the cows sacrificed pasture time in exchange for shelter in the shade. Even so, they conclude that agrivoltaics can be a more than acceptable method to combat the heat in grass-fed dairy cows, while generating energy and reducing the carbon footprint of the farm. Additionally, they say, incorporating agrivoltaics into a pasture dairy system could improve cow health, reduce heat stress and increase land use efficiency.
And now what. The study was explicitly a starting point. The team itself announced a new project that same year with the idea of designing solar structures that serve as both shade in summer and windbreaks or screens against snow in winter, in addition to testing solar tracking systems and arrays on marginal lands.
To do this, they built a “portable solar shade station” towed by an electric tractor. In that study they concluded that good quality forage grows under the panels and that they improve the well-being of livestock by providing shade in summer and protection from the wind in winter. Of course, they also said that in total shade, grass production plummeted, so the key was to balance shade and cultivation.
Cover image | Twin Cities PBS
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