In raising crops, a key factor is maximizing the solar energy that strikes the Earth, and it appears farmers are pretty good it. A new study from Oregon State University has found that cropland is the best place to install solar panels — not in those desert areas where large arrays have been installed.

The study, published recently in the journal Scientific Reports, found that if less than 1% of agricultural land was converted to solar panels, that would be sufficient to fulfill global electric demand. The study doesn’t support replacing ag land with solar panels; instead, it looks at the idea of co-developing the same area of land for both solar photovoltaic power and conventional agriculture, a practice called agrivoltaics.

Chad Higgins, associate professor in OSU’s College of Agricultural Sciences, says the results indicate there’s a “huge potential for solar and agriculture to work together to provide reliable energy. There’s an old adage that agriculture can overproduce anything. That’s what we found in electricity, too. It turns out 8,000 years ago, farmers found the best places to harvest solar energy on Earth.”

Avoiding deserts?

The study does have implications for siting solar arrays. Currently, large arrays are being built in desert areas on land that many see as useless for other purposes. “Solar panels are finicky,” Higgins says. “Their efficiency drops the hotter the panels get. That barren land is hotter. Their productivity is less than what it could be per acre.”

In the study, OSU researchers analyzed power production data collected by Tesla. The company has installed five large grid-tied, ground-mounted solar arrays on agricultural land owned by the university. The team looked at data collected every 15 minutes at the 35th Street Solar Array installed in 2013 on the west side of OSU’s Corvallis campus.

Researchers synchronized the Tesla information with data collected by microclimate research stations installed at the array. The stations recorded mean air temperature, relative humidity, wind speed, wind direction, soil moisture and incoming solar energy.

Using those results, Elnaz Hassanpour Adeh, a doctoral graduate from OSU’s water resources engineering program and a study co-author, developed a model for photovoltaic efficiency as a function of air temperature, wind speed and relative humidity.

Higgins explains that the results show cooler weather boosts efficiency. “If it’s hot, the efficiency gets worse. When it is dead calm, the efficiency is worse, but some wind makes it better. As the conditions became more humid, the panels did worse. Solar panels are just like people and the weather — they are happier when it’s cool and breezy and dry.”

A global view

To evaluate the model on a global basis, Adeh took global maps from satellite images and applied the model worldwide. The model spanned 17 classes of globally accepted groundcover, including classes such as croplands, mixed forests, urban and savanna. The classes were ranked from best to worst based on where solar panels would be most productive.

The model was also reevaluated to assess agrivoltaic potential to meet projected electric energy demand as determined by the World Bank.

Cropland showed the best results for producing power from solar arrays around the world. The researchers also published a study recently showing that solar panels increase agriculture production on dry, unirrigated farmland. Those results indicated that placing solar panels on pasture or ag fields could boost crop yields. Linking solar panels and farmland may be a win-win.

Co-authors on the recent study were Stephen Good, an assistant professor in OSU’s Department of Biological and Ecological Engineering; and Marc Calaf, an assistant professor of mechanical engineering at Utah State University.

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