Why Solar & Farming Is A Match Made In Heaven

A plot of land can do a number of things. It can grow trees and crops. It can support a home, an office tower, or a factory. It can be a parking lot. But it can’t do all those things at the same time. Choices have to be made. It’s no use to erect the world’s tallest apartment building if there is not enough food for the people who will live there. It is no use to put solar panels everywhere if they don’t leave space available for crops or dwellings.

Multi-tasking is a word that has crept into our vocabularies lately. Computers can have a bunch of tabs open at the same time and still be able to do online chats. As the world becomes more densely populated, land will need to multi-task as well. Here are some examples of how that can work.

Solar Makes Land More Productive

In Wisconsin, one million acres of farmland are used to grow corn which is then converted into ethanol. In a report published last week by Paul Mathewson and Nicholas Bosch of Clean Wisconsin, the researchers make some startling observations. Here is the introduction to their findings.

Wisconsin already uses over 1,000,000 acres of agricultural land for energy production in the form of corn used to produce ethanol. Ethanol is a much less efficient form of energy production compared to solar photovoltaics (PV).\ Using Energy Return on Investment (EROI) as a metric, solar PV is around 8 EROI, while corn derived ethanol is approximately 1.2 EROI. Using this metric, 88% of the energy generated by solar PV goes to society, while 12% is offset by production requirements.

In contrast, 20% of the energy generated by corn ethanol goes to society, while 80% is offset by production requirements. Assuming average EROI, net energy production per acre is 100 to 125 times greater [emphasis added] for solar PV than for corn-based ethanol. To meet Wisconsin’s carbon-free goals, 240,000 to 285,000 acres will be needed for solar PV with today’s technology. This amounts to 1.7 to 2.0% of agricultural land in the state and less than 1/3 of the land currently being used to grow corn for ethanol.

Clean Wisconsin says those 1 million acres of Wisconsin farmland that grow corn for ethanol could produce 100 times as much energy if planted with solar farms instead. “There is a concern that we’re going to take too much farmland out of production to put on solar panels,” Mathewson says in a press release accompanying the new study. “But we’re already using a lot of land to primarily harvest energy in the form of corn made into ethanol. This analysis demonstrates how, with solar, we can harvest more energy using far less land.”

Show Us The Money!

Raising corn is close to a religion in America’s heartland. The money farmers earn from corn production is often the difference between making a living and bankruptcy. So why would they want to change a system that has been paying the bills for generations? Income stability is one reason. Farming can be tough because a farmer never knows from one year to the next how much money a farm will earn.

A 2021 national survey from Purdue University claimed than half the offers farmers received to lease their land for solar generation were for $750 an acre or more, Amy Barrilleaux of Clean Wisconsin tells the Wisconsin Examiner. “Corn fluctuates year to year and profits to farmers is complicated by government payments, but our understanding is that net corn profits are typically less than $600 per acre, putting a good corn year on the lower end of solar leases.”

“To build a healthier future for our kids in rural and urban communities alike, we urgently need more solar projects in Wisconsin,” says Chelsea Chandler, director of Clean Wisconsin’s climate, energy and air program. “This study demonstrates that we could use a fraction of the land currently used to grow corn for ethanol and instead build solar farms that create abundant clean, homegrown energy.”

The upshot of all this is that growing corn to make ethanol may be good for farm incomes — mostly because of government subsidies — but it is a lousy deal for the country because it is so wasteful and inefficient. In the world to come, efficiency will have a much higher priority for human society. In transportation, the typical vehicle powered by an internal combustion engine has converts only about a quarter of the energy in a gallon of gasoline or diesel into forward progress. In a typical electric vehicle, at least 80% of the energy stored in a battery is converted into motion. Just as electric vehicles do more with less, so too should our agricultural industry.

Red Light, Blue Light

Image credit: Andre Daccache/UC Davis

We think of sunlight as a single thing, but it is a combination of several wavelengths, including those the human eye cannot see. Researchers at the University of California Davis are conducting experiments with light at both ends of the visible spectrum. Their research shows that blue light is best for solar panels, while red light is best for growing crops.  “Why does [agriculture] have to be a zero-sum game if we can optimize the land for both?” asks Majdi Abou Najm, an associate professor at UC Davis, who is a co-author of a recent report.

Photons have different properties, he explains. Blue ones have higher energy than their red counterparts, resulting in light with shorter wavelength and higher frequency. While that gives blue light the jolt needed to generate power, the extra pulsing also results in higher temperatures. “From a plant perspective, red photons are the efficient ones,” says Abou Najm. “They don’t make the plant feel hot.”

Through computer modeling, the researchers found that applying red light waves to plants increases photosynthesis and carbon assimilation while lowering transpiration. In other words, “crops can get the same amount of CO2 using less water,” he says. One of the main goals of the study, says Abou Najim, is “to motivate the industry to create a new generation of solar panels.”

There’s a drawback, however. Crops growing beneath solar panels are partially shaded, which can lower yields — not something a farmer wants to hear. Last summer, the researchers planted processing tomatoes — a common Sacramento Valley crop — on small, equal-sized plots. One was covered with a red filter, another with a blue one, while the third was left uncovered as a control.

After approximately four months, including a record heatwave in early September, the two filtered plots each yielded about a third less than the uncovered one. Yet when sorted for quality — ripe, unripe or “bad” — the control plot accounted for twice the amount of rotten tomatoes. “So the filters helped in reducing heat stress,” and “cut wastage by more than half.” Add in the value of the electricity generated and the net gain would more than compensate for the diminished harvest. By co-locating crops and solar generation, “100 percent becomes a very low number when you can get 120 or 140 percent yields,” Najm tells Modern Farmer.

He sees the canopied approach as a way for farmers to build climate resilience. Filtering the sun helps the soil retain moisture and shield farm workers from harsh rays while lower transpiration means less water is needed for crops. By generating their own power, farmers could offset rising energy costs and nudge the industry towards embracing electric equipment and vehicles as well, he adds.

“By 2050, we’ll have [an additional] two billion people on this planet, and we’ll need 60 percent more food, 40 percent more water and 50 percent more energy” than is currently produced, says Abou Najm. Research needs to occur on a transformative level in order to meet those ballooning needs. By maximizing the solar spectrum, “we’re optimizing an endlessly sustainable resource. If a technology kicks in that can develop these panels, then the sky is the limit on how optimized we can be.”

The Takeaway

There is a popular myth in the farming community that solar and agriculture don’t mix. That may be a common attitude but that doesn’t mean it is accurate. People used to believe that asbestos was a miracle substance and that airplanes could never fly across the oceans without stopping to refuel. As Mark Twain once observed, “What you don’t know won’t hurt you near as much as what you do know that ain’t true.”

As humanity struggles to control global heating while providing food for all the people on Earth, a convergence between solar and agriculture will need to take place. These two research studies show how that could happen.