Major utility-scale ground solar panel installations, called ‘solar farms,’ are rapidly growing. There is potential for impacts on natural hydrologic processes, including runoff generation and erosion. Literature review shows there is still limited research in this area, and that best management practices to address these impacts are variable and not well understood. We have been conducting field research on two solar farms in central Pennsylvania that are representative of the complex terrain in our region (e.g., high or variable slopes). Soil moisture monitoring indicates redistribution of water relative to panels, with elevated soil moisture at the dripline, and drier conditions under the panel. Despite reduced solar radiation under the panels, there is still good vegetation coverage, which is important for managing runoff and erosion. Soil moisture data also indicate periods of saturation and likely runoff generation near panel driplines, but very limited occurrence of saturation in the interspace between panel rows, indicating infiltration of runoff. Data from the infiltration basin and trench document the ability to adequately retain and infiltrate runoff. This indicates that well-vegetated open space between panel rows plays a critical role in managing runoff. In certain landscapes, structural stormwater management may be necessary on solar farms, in order to prevent net adverse impacts on runoff. Continued development of these practices will ensure that solar farms are developed in the most sustainable way possible, with maximum benefit.
