As solar energy projects continue to grow across the United States, researchers are gaining a better understanding of how these installations influence stormwater management.
Although solar panels are often compared to impervious surfaces like rooftops or paved parking lots, new findings from Penn State indicate they interact with rainfall in a much different way.
Researchers Femeena Pandara Valappil and Lauren McPhillips found that solar farms do not simply block water from entering the ground. Instead, the panels redirect rainfall, creating varying moisture levels across a site.
Water flowing off the edges of the panels increases soil moisture along the driplines, while the areas directly beneath the panels remain drier because they receive less rainfall. Meanwhile, the vegetated spaces between panel rows absorb water, encourage infiltration, and help reduce surface runoff.
Field research conducted at two solar farms in Pennsylvannia showed clear differences in soil moisture. Areas beneath the panels consistently contained less moisture than nearby reference sites, while the driplines were noticeably wetter.
The team also observed lower rates of evapotranspiration beneath the panels, demonstrating that solar farms create distinct hydrologic conditions rather than behaving as uniformly impervious landscapes.
Additional findings from the Photovoltaic Stormwater Management Research and Testing (PV-SMaRT) project reinforce the importance of site design. Researchers concluded that maintaining healthy vegetation, preserving quality soils, and tailoring designs to local conditions are essential for limiting erosion and improving water infiltration. Stormwater performance also varies depending on rainfall intensity, slope, soil characteristics, and vegetation cover.
The researchers note that properly designed solar farms typically generate little runoff during smaller storms, though larger rainfall events may require additional stormwater management measures.
Tools such as Penn State's Virtual Solar Array and advanced hydrologic models are helping engineers and land managers design solar projects that support renewable energy while protecting water resources, improving soil health, and promoting sustainable land management.
Photo Credit: panels-istock-shansekala

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