Resource heterogeneity induced by ground-mounted photovoltaics uniquely alters plant and ecosystem processes in a semi-arid grassland.

To meet decarbonization goals, a transition from fossil fuel infrastructure to renewable energy systems for electricity production is urgently needed. Although ground-mounted photovoltaic (PV) energy production offer a viable solution for reducing carbon emissions, PVs require ~20 times more land area than existing energy infrastructure. Sprawling PV infrastructure can cause land use tension in grassland ecosystems, particularly those in the semi-arid western United States. This is because these ecosystems occur where solar radiation is high and topographic relief is low. Most of these grasslands are non-irrigated and typically water limited, raising questions about how the redistribution of precipitation and sunlight by PV panels might affect plant productivity, physiological capacity, and ultimately ecosystem structure and health.

Here, in a 1.5 ha, 1.3 MW agrivoltaic (AV, combination of agriculture and photovoltaics) research site, we recorded high resolution soil moisture and light measurements throughout the growing season to determine how patterns of resource redistribution between and beneath single axis (East-West) tracking PV panels affected physiological processes and patterns of plant growth. We took diurnal measurements of stomatal conductance (gs) and water potential (ψL) for leaves of a C3 perennial grass (Bromus inermis) located between rows of PVs, directly beneath rows of PVs, and at panel edges that receive morning or afternoon light, respectively. Biomass was collected at end of season to determine if differences between plots were related to patterns of physiological response and resource availability.

We found that leaves receiving primarily morning sunlight had drastically different diurnal patterns of gs and ψL than those receiving only afternoon sunlight, and that these patterns were not simply mirror images of each other. We also found that light saturation of photosynthesis was consistent across all sites in the PV array, indicating that sunlight did not strongly alter physiological capabilities of this grass, even when growing directly beneath PV panels. We further discuss how this heterogeneity in environmental drivers and physiological responses may impact ecosystem resilience to shifting seasonality of rainfall, drought, and warming.