The changing landscape of energy generation in Virginia: How construction of utility-scale solar sites impacts soil physical and hydraulic properties

Abstract

Utility-scale solar development is crucial for meeting renewable energy demand in many states in the United States, including Virginia. However, construction and operation of these large-scale facilities can substantially alter the ground surface, which subsequently has potential to impact soil hydraulic and physical properties. The extent of alteration to soil properties has not extensively been studied using field-based measurements. This study attempts to fill that gap by comparing field measurements of infiltration, permeability, soil texture, bulk density, and ponding between a stabilized utility-scale solar site and seven reference sites that represent common land uses in the area, such as forest, cropland, grassy areas, and pine plantation. Permeability was measured at the soil surface using single ring infiltrometers and in the subsurface using borehole permeameters; saturated hydraulic conductivity (Ksat) from both measurement types. The solar site had significantly lower Ksat at both the surface and subsurface compared to the reference profiles (p < 0.05). Measurements were collected from three different typical settings in utility-scale solar sites. No significant differences in Ksat values were detected between under-panel sections, alleyways between panels, and in the perimeter surrounding the panels within the solar site. Soil textures were significantly different between the solar site and reference sites near the surface (5-10 cm) and at 50-55 cm depth (p < 0.001), but bulk density was only significantly different at 80-85 cm (p < 0.001). Ponding is a crucial part of runoff generation as overland flow but is understudied in field settings, particularly utility-scale solar sites. We measured ponding in three developed solar and three reference catchments using modified crest-stage gauges (i.e., ponding gauges) and water level loggers. Ponding depths were significantly higher in the solar catchments than in reference catchments managed for timber. Variability in ponding depth was significantly different between the reference catchments but not the developed ones, indicating that ponding was more even within the solar site. Water level loggers showed that each catchment had a unique ponding threshold (between 11 and 30 mm of depth) that needed to be surpassed for runoff to occur. Reduced permeability, altered soil textures, and higher ponding depths point to substantial alterations of the soil as a result of solar developments. These changes could translate to increased runoff from solar sites. It is therefore imperative to accurately account for these types of changes in soil hydraulic and physical properties when designing and managing utility-scale solar sites, especially as this energy source continues to grow globally.