Solar farm naysayers often throw out two major criticisms of power utility-scale projects, depending on where they are located: Solar farms intended for relatively flat, well-draining land can take up much-needed and valuable agricultural spaces. Meanwhile, any solar farms installed across more complex terrain or steeper slopes may exacerbate issues like excessive stormwater runoff and erosion. According to researchers at Pennsylvania State University, however, dealing with the latter concern is relatively simple—like dual-use solar and agricultural farms, it all comes down to design.
A yearlong, first-of-its-kind study published in the Journal of Hydrology indicates that including a combination of healthy vegetation and well-draining soil mixtures can easily manage most solar farm storm runoff, even in regions with more difficult and hilly landscapes prone to erosion.
[Related: This new floating solar farm follows the sun like a flower.]
“We were especially interested in stormwater movement in solar farms on complex terrain and steep slopes,” Lauren McPhillips, a PSU assistant professor in civil and environmental engineering and study co-author, said in an accompanying statement. “There’s a lot of concern that solar is eating up prime agricultural land with well-draining soils that are pretty flat. From those sites, you have minimal runoff concerns. We are interested in facilitating making use of more challenging marginal lands for solar farms.”
McPhillips and her colleagues spent 12 months monitoring soil moisture patterns, vegetation health, and solar radiation levels at two solar farms in central Pennsylvania, both of which are built on the kinds of sizable slopes that are common across the Northeast US. In terms of stormwater redistribution, the soil moisture underneath driplines (the area directly beneath a panel’s lower edge) averaged 19-percent higher than nearby land. Moisture levels under the panels themselves, in contrast, measured 25-percent lower than neighboring soil on average. And although more severe storms could cause the solar panels to increase local runoff, open interspaces between panel rows along with tools like infiltration basins and trenches more-than-adequately compensated for the water.
While the paneling did lower evapotranspiration (the transportation of water from land into the atmosphere) somewhere between 37-and-67-percent in the summer, there was minimal differences during the winter months. Even taking this into consideration, the team saw negligible effects on overall vegetation health. The university’s announcement describes “almost complete ground coverage” under each panel, which is vital for preventing runoff and reducing erosion.
“While our observations document clear alteration in natural hydrologic patterns, they also demonstrate that adequately sized vegetated spaces between solar panel rows, and in some cases, structural stormwater management, can manage these changes,” McPhillips said on July 18.
“These types of insights, along with investigation of how land management on solar farms can affect other ecosystem services, can allow us to facilitate this critical transition to renewable energy with minimal ecosystem impact,” she added.
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