Solar energy transitions on agricultural land: soil health impacts from site construction and on-site sheep grazing

Introduction Utility-scale solar energy infrastructure in the U.S. has rapidly expanded through the first decades of the 21st Century. In many regions, much of this development has taken place on agricultural land, in some cases billed as a means of preserving agricultural land for the future by removing the panels after retirement and returning the land to food production. While this may indeed be true, relatively little is known of the ecological effects of utility-scale solar development and land use, particularly those that pertain to future or concurrent agricultural uses. Methods We present the results of a two-year soil health assessment at three recent utility-scale solar facilities in Southern Pennsylvania. One of these sites uses sheep grazing to manage on-site vegetation, allowing us to also assess potential differences between agrivoltaics vs conventional site management during the early years of operation. We conducted a suite of soil health assessments (both in situ and in a lab) including labile carbon, respiration, wet aggregate stability, surface compaction, and earthworm abundance along transects at each site annually for two years. Identical assessments were also conducted along transects on adjacent land that remains in agriculture at each site for comparison. Results We found that site construction has a clear, if modest, impact on soil health, particularly the labile carbon pool and water stabile soil aggregates (both decline), and earthworms, which are more abundant with solar facilities. Soil physical properties show signs of recovery in year 2, while assessed carbon fractions remain depressed throughout the study, with no significant differences found between agrivoltaics and conventional site management as assessed in our study. Discussion Our results do not indicate that utility-scale solar is significantly detrimental to soil heath, yet it seems clear that site construction does degrade some aspects of soil health. Our results also expand our understanding of the ecological dimensions of solar grazing. While we did not find any increased degradation resulting from sheep grazing, neither did we detect any improvements to soil health as have been documented by other studies in temperate ecosystems. Our study indicates that site construction and management practices should continue to be refined to ensure future and concurrent agricultural land use is not only possible, but profitable.