Agriculture and renewable energy have worked together for more than fifteen centuries, ever since ancient Persians began using windmills to pump water and grind grain. Today, in the Midwestern US, we see cornfields sharing acreage with megawatt-scale wind turbines that produce minimal shading effects on crops, significant power enhancements to the grid, and additional income for farmers. Researchers in Baden-Württemberg, a region in southern Germany, are looking for ways to increase sustainable energy production in an area where wind speeds are relatively slow, making solar the preferred electrical generating technology. But plants need sunlight just as much as photovoltaic panels do, so engineers are working on an elevated solar array that feeds both of society's energy needs: biological and technological.

Agrophotovoltaics: Edibles and Energy

In a pilot project known as Agrophotovoltaics - Resource-Efficient Land Use (APV-RESOLA), engineers at the Fraunhofer Institute for Solar Energy Systems designed and constructed a 194 kilowatt elevated solar array over a one-third hectare section of cropland. An adjacent section of the farm remains unaltered to serve as a control. In a three-year study, researchers from the University of Hohemhein are assessing crop quality and yield in both the experimental and control fields. Farmers hope to generate appreciable electricity while maintaining crop production levels at the 80% level.

On a field that grows wheat, potatoes, clover, and celery, solar panels are mounted five meters above the ground to allow clearance for farm equipment. The additional racking increases the price of the array, which, according to researchers, is on par with the cost (per watt) of a small residential rooftop array. That's obviously more than the levelized cost of a traditional PV farm, but the tradeoff increases the overall efficiency of the land by 60%.

Early results show that the PV array decreases crop yields by 5% to 20%, depending on the crop. Clover suffered the smallest impact at 5%, while wheat, potatoes, and celery lost nearly 20% of their production. Considering the fact that nearly 40% of the corn grown in the US is turned into ethanol fuel, that doesn't sound like a bad tradeoff.

Bifacial Photovoltaics

Bifacial PV panels allow the solar farm to directly catch the rays from above and harvest reflected light from below. In the winter, the snow-covered ground reflects so much light that the bifacial PV array can generate up to 25% more power than a single-sided solar array. (It also helps that PV panels are more efficient in cold weather.)

In its first year of operation, the solar array generated almost 250 MWh of electricity. About 40% of that energy was used to charge the electric farm equipment; the remainder powered the rest of the farm operation. The pilot study doesn't include on-site energy storage, so any time production exceeds demand, the surplus goes to the grid.

Here are a couple of videos that discuss the overall project and some of the construction details:

Crops and kilowatts are both essential to society. These engineers and scientists are showing that the two can work together for a sustainable - and palatable - future.

Images and videos courtesy of Fraunhofer ISE