The following article by The National Renewable Energy Laboratory – summary by Kari Lydersen via Energy News Network – demonstrates mixed and sometimes puzzling results, indicating researchers need more time and resources to figure out how to maximise agrivoltaics’ potential. This is part one of a two-part article.
A recent analysis reveals the daunting number of variables that need to be considered when attempting to pair agricultural production and solar generation.
Federal researchers know that solar panels and crops can coexist and provide mutual benefits in certain scenarios. A recent study by the National Renewable Energy Laboratory (NREL) confirms this but also shows that such co-location can lead to crop or financial losses, including from complications like mold-causing dew accumulation and soil damage from construction equipment.
Advocates who see the concept as a potential solution to land-use constraints are now pushing for more funding and collaboration with farmers to test and document outcomes in as many different settings as possible. The hope is that they can prove benefits in enough scenarios to help the solution scale beyond the handful of small farms that have currently implemented it.
“We know we can grow food under solar projects,” said the NREL paper’s lead author, Jordan Macknick. “What remains to be seen is if we can scale up agrivoltaics in a way that meaningfully improves local food production and farmers’ bottom lines while also aligning with the realities of solar development costs, timelines and practices.”
Moisture and soil
NREL defines agrivoltaics as the “sharing of sunlight between the two energy conversion systems: photovoltaics and photosynthesis,” and notes that “the solar and agricultural activities [must] have an influence on each other.”
Agrivoltaics includes planting pollinator habitats in and around solar panels, and allowing animals to graze around the panels. But the sector with the most variables to study is arguably the growing of crops under and between solar panels.
In 2015, the US Department of Energy began researching agrivoltaics through the InSPIRE (Innovative Solar Practices Integrated with Rural Economies and Ecosystems) program. The August NREL paper compiles results from InSPIRE sites with universities and other partners in states including Arizona, Georgia, New York, Minnesota, Colorado, Idaho, Oregon, California, Pennsylvania, Massachusetts and Washington DC.
The analysis confirmed that agrivoltaics can help in water-stressed areas, since the shade from panels reduces evaporation due to sun and wind, and water from precipitation or even water used to clean panels can be collected and funneled to crops. Electricity generated can also be used on-site to power pumps for irrigation. At a “dry farming” test site in Oregon’s Willamette Valley, researchers are exploring whether agrivoltaics minimise a condition in tomatoes known as blossom end rot, which is exacerbated by drought.
Increased moisture retention from solar panels can also create complications, however. Rodents and insects may be attracted by humidity and moisture, the study notes; rodents can hurt crops and also chew through electrical wires. At Jack’s Solar Garden in Colorado, fungus grew where runoff from dew on the panels collected. Researchers noted that problems could be averted by moving beds away from the drip, or otherwise managing dew collection.
Greg Barron-Gafford, a geography professor and director of food, water and energy research at the University of Arizona’s Biosphere 2, noted that despite some of the challenges, increased moisture under panels is generally a boon for plants.
“If a plant is in a more humid environment, it is less stressed about conserving water, and it can do more photosynthesis,” he said. That means more growth of leafy greens like kale and lettuce, and more resources drawn from the leaves for fruiting plants like peppers.
Construction of agrivoltaics — with heavy equipment — can compact soil, making it harder for it to hold water and nutrients. InSPIRE research in Colorado showed soil at agrivoltaic sites still compacted a decade after construction. But using certain types of equipment and construction processes can reduce the impact on soil. University of Maine researchers are studying whether lower-impact “careful” or “mindful” construction practices can improve agrivoltaic blueberry yields.
Understanding the local soil variation and quality can help minimise harm. Investigating previous uses of the land, including herbicide and pesticide use and types of crops grown, also helps in designing successful agrivoltaic projects.
Mixed results
Performance of certain crops can be counterintuitive, underscoring the need for evidence-based research, the NREL study notes. For example in Colorado, “sun-loving” grass performed better than “shade-loving” grass in the shade of solar panels, surprisingly. Additionally, some crops must be rotated after several seasons because of their effect on soil, so an agrivoltaic array must be planned for multiple seasons.
The study aggregates the effect of agrivoltaics on crop yields at different sites. Tomatoes saw up to double yield with agrivoltaics, while wheat, cucumbers, potatoes and lettuce showed significant negative impacts and corn and grapes showed minimal impact.
In areas that don’t have extreme sun or heat, reduced yields can be due to reducing the amount of sunlight that plants get under panels. These realities must be considered, but there are also ways to moderate the sun-blocking influence, researchers say.
Tracking solar panels that move with the sun only shade plants for part of the day. Moreover, Barron-Gafford noted advancing technology includes solar panels that could allow the wavelengths of light that plants need most to pass through, while blocking and generating energy from light rays that are less helpful to plants.
Pollinator habitats planted beneath solar panels are perhaps the most widely used type of agrivoltaics currently, with some states including Illinois and Minnesota offering incentives for pollinator habitat solar projects. Research is progressing on this front as well, with more research needed to evaluate the effectiveness of pollinator habitat and to what extent it is maintained over multiple years.