Oregon State University study finds lambs thrive under solar panels

An experiment at Oregon State University has found that lambs can grow just as well under solar panels as they do in an open pasture, even when the pasture beneath the panels produces significantly less grass. Researchers at the university's research farm in Corvallis compared two groups of weaned Polypay lambs over two years. One group grazed in a conventional open field, while the other grazed beneath a working solar array.

The results challenged a simple assumption about solar panels on farmland: less grass does not always mean less livestock production.

The experiment was designed to make the comparison as fair as possible. The researchers used groups of lambs that were matched and weighed before being placed in two neighboring pastures. One pasture was fully exposed to the Oregon sky. The other was located beneath rows of solar panels.

Over the two-year study, the pasture beneath the solar panels produced 38% less forage than the open pasture. The areas receiving full shade directly below the panels produced the least amount of grass.

At first glance, that seemed like bad news for the lambs. With less forage available, it would be reasonable to expect the animals to gain less weight. But the scales told a different story.

In spring 2019, lambs grazing under the solar panels gained an average of 120 grams per day, compared with 119 grams per day for lambs in the open pasture. The following year, the solar-pasture lambs gained 89 grams per day, while the open-pasture group gained 92 grams.

The differences were small enough that researchers found the growth rates to be statistically similar. That meant the lambs under the panels were producing almost the same amount of growth despite having access to considerably less forage.

So how was that possible? The answer came from looking beyond the amount of grass and examining its nutritional value.

Plants growing in shade can develop differently from plants exposed to full sunlight. According to the study, the forage growing beneath the solar panels had higher nutritional quality, including greater protein and digestibility.

In simple terms, there was less grass, but the grass available to the lambs was more nutritious. The researchers found that the lower amount of forage in the solar pasture was offset by its improved quality, resulting in similar lamb production.

As the study showed, "the lower herbage mass in solar pastures was offset by higher forage quality, resulting in the same lamb production as the open field." For grazing animals, the amount of grass is only part of the equation. What matters is how much useful nutrition they can obtain from what they eat.

The panels provided another advantage, particularly during warmer weather. Lambs grazing in the open pasture had to spend more time dealing with direct sunlight and heat. The animals under the panels could use the shaded areas to escape the hottest parts of the day.

Researchers also observed that the solar-pasture lambs drank less water. During hot periods in late spring, the open-pasture lambs consumed nearly three-quarters of a liter more water per animal per day than those grazing beneath the panels.

The shade allowed the animals to rest and ruminate away from direct sunlight. That could matter because animals use energy to regulate their body temperature. When they experience less heat stress, more of their energy can potentially go toward growth.

The study also looked at the financial side of combining solar energy with livestock. Annual grazing returns were estimated at about $1,046 per hectare in the open pasture and $1,029 per hectare beneath the solar panels.

That difference was less than 2%. The researchers noted that these figures did not include the value of electricity generated by the solar panels. This is where the concept of agrivoltaics becomes important. Agrivoltaics involves using the same land for both agricultural production and solar power.

Instead of choosing between a field for farming and a field for renewable energy, the same piece of land can potentially support both.

The results were not completely straightforward. The areas in permanent, full shade beneath the solar panels produced less forage and were slower to establish. However, partially shaded areas between the panel rows sometimes performed better during the hotter parts of summer.

The reason was moisture. Solar panels can reduce the amount of direct sunlight reaching the ground, which can also slow the loss of water from the soil. During dry periods, that can help some shaded areas stay greener for longer.

This means the impact of solar panels on pasture can change depending on the season, weather and design of the solar array.

The Oregon State experiment offers an important lesson for the growing debate over solar panels on agricultural land. The pasture under the panels produced less total forage, but that did not translate into lower lamb growth.

The animals benefited from higher-quality forage and shade, while the land continued to generate electricity. The researchers' findings suggest that solar energy and livestock farming do not always have to compete for the same land.

There are still challenges, including panel placement, pasture management and the amount of shade created. But the lambs at the Oregon research farm showed that measuring only the amount of grass can miss a bigger part of the story.

The study's most surprising takeaway may be simple: less grass did not necessarily mean less food for the animals — because the grass they had was better, and the shade gave them another advantage.