US Department of Energy photo.

Solar farms and wind farms have become familiar terms. Beyond metaphor, their connection with farms may not be obvious, but it’s important. When cropland is taken out of production to make room for renewable energy, it’s a bad tradeoff. Actually, as it turns out, renewable energy and agriculture work together very well.

In particular, leasing land for a wind farm has benefitted farmers. They can easily plant crops or graze cattle around the turbines. But what is the effect of the turbines on the crops?

Solar farms have a more uneasy relationship with agriculture. Solar panels sit lower to the ground, and they can’t have vegetation casting shadows on them. Fortunately, farmers have multiple ways of using land with panels on it.

Wind farms and agriculture

More and more farmers are leasing land to wind energy companies. They can continue to use the same land for growing crops. Essentially, then, they grow, say, soybeans and wind turbines on the same land.

The arrangements have some obvious financial benefits for farmers. Whatever money they get from the leases is more predictable than what they can get from their crops. It helps their planning and their cash flow.

But what effect, if any, do the turbines have on the crops? Researchers at Iowa State University decided to find out.

Wind blowing across a field affected crops before anyone ever thought of wind energy. Plants need water, but they use only a small portion of what their roots take in for metabolism and growth. More than 95% of it returns to the atmosphere through processes called transpiration and guttation.

As the crops transpire, air turbulence from the wind causes moisture to rise into the atmosphere. At the same time, it pulls down cooler and drier air. That is, moist, oxygenated air evaporates as carbon dioxide sinks. And the plants “inhale” the carbon dioxide.

At night, without the effect of the sun, the air becomes calmer and the crop cools. Dew forms on humid nights.

The effect of wind turbines on crops

Image by Michael Gaida. from Pixabay

Wind turbines block some of the air and slow its flow. Turbulence and surface temperature both increase. At night, turbulence from the turbines gives the air more nearly daytime conditions. It delays dew formation and may make it evaporate sooner. This shorter wet period creates less favorable conditions for mold and fungus. It also may allow farmers to start harvesting crops a little earlier in the morning.

Satellites can actually see these impacts from space. All the wind farms are slightly warmer than the surrounding areas. They show up on images in a different color.

What’s more, the top few feet of soil contain two or three times as much carbon dioxide as the air. As the turbines pump air downward, more carbon dioxide rises from the soil. That might seem like a bad thing, given all the concern about greenhouse gases. But the action of the turbines makes more of it available for the plants. It also causes the plants to move more, which allows sunlight to penetrate deeper into the crops’ canopy.

At night, however, the warmer air caused by the turbines becomes a slight disadvantage. Crops yield more carbon dioxide into the atmosphere than they would otherwise. Increasing nighttime temperatures have inhibited crop yields. Fortunately, comparing the daytime and nighttime effects of wind farms shows a net gain for agriculture as the daytime advantages outweigh the nighttime disadvantages.

The team is still investigating whether the wind farms foster cloud development or increase the rain in the surrounding areas. But clearly, whatever humans do on a large scale affects the environment somehow. In the case of wind farms on croplands, renewable energy and agriculture appears to have a favorable effect.

Solar farms and agriculture

Wikimedia Commons

Solar farms present different problems for renewable energy and agriculture than wind farms. For one thing, solar panels sit much lower to the ground. So solar farms can’t allow vegetation to cast shade on the panels.

Quite often, therefore, developers will either plant turfgrass or apply a gravel mulch intended to prevent anything from growing. They may apply herbicides to anything that sprouts up anyway.

Herbicides pollute nearby waterways. Planting and mowing grass have their own environmental impact. After all, this essentially useless crop requires water, and mowing it requires fuel that increases greenhouse gas emissions. And many solar farms used to be productive cropland. Taking cropland out of production to make solar energy doesn’t seem like a good tradeoff.

Compatibility of solar panels, crops, and farm animals

There’s another way. Some farmers have found a way to introduce vegetation in solar farms that has environmental and economic benefits.

Native plants, such as wildflowers or prairie grasses, attract bees and other pollinators. So planting them around solar panels enhances biodiversity and boosts crop yields in nearby fields. Solar farms also make a good place for beekeepers to operate.

Many of our food crops depend on pollinators. Taking out either crops or native vegetation in order to plant grass or install gravel on a solar farm drives pollinators away.

Besides attracting pollinators, wildflowers and prairie grasses require less maintenance than either crops or turf grass.

Perhaps you’ve noticed that wildflowers can grow so tall along the side of highways that road crews have to mow them. But a solar farm is enclosed behind fences. That makes them a good place to let cattle graze. The panels provide them some shade and protection from the wind.

Sheep in particular can reach where mowers can’t. Sometimes mowers are taller than the clearance under the bottom edge of the solar panels. Sometimes the panels are located on ground that’s too steep for mowers to operate safely.

Plenty of plants don’t grow tall enough to shade solar panels. Beans, broccoli, peppers, and various greens can grow under solar panels. Researchers at the University of Massachusetts are studying how such crops can help farmers grow food on the same ground they lease to solar farms. Farmers in Japan have started to grow mushrooms under solar panels.

Renewable energy certainly has environmental problems that offset some of its advantages, but interference with agriculture doesn’t have to be one of them.

See related posts: Solar vs trees: conflicting values in environmentalism / The looming problem of waste from renewable energy / Overbuilding solar capacity: how renewables can take over

Sources:

Can solar farms promote local food security, wildlife habitat? / Sarah Lozanova, Earth 911. December 17, 2020
Wind farms impact crops / Gene Takle, Agri-View. April 1, 2018