Grassland productivity responds unexpectedly to dynamic light and soil water environments induced by photovoltaic arrays

Abstract

Agrivoltaic (AV) systems are designed to coproduce photovoltaic (PV) energy on lands simultaneously supporting agriculture (food/forage production). PV infrastructure in agroecosystems alters resources critical for plant growth, and water‐limited agroecosystems such as grasslands are likely to be particularly sensitive to the unique spatial and temporal patterns of incident sunlight and soil water inherent within AV systems. However, the impact of resource alteration on forage production, the primary ecosystem service from managed grasslands, is poorly resolved. Here, we evaluated seasonal patterns of soil moisture (SM) and diurnal variation in incident sunlight (photosynthetic photon flux density [PPFD]) in a single‐axis‐tracking AV system established in a formerly managed semiarid C3 grassland in Colorado. Our goals were to (1) quantify dynamic patterns of PPFD and SM within a 1.2 MW PV array in a perennial grassland, and (2) determine how aboveground net primary production (ANPP) and photosynthetic parameters responded to the resource patterns created by the PV array. We hypothesized that spatial variability in ANPP would be strongly related to SM patterns, typical of most grasslands. We measured significant reductions in ANPP directly beneath PV panels, where SM and PPFD were both low. However, in locations with significantly increased SM from the shedding and redistribution of precipitation by PV panels, ANPP was not increased. Instead, ANPP was greatest in locations where plants were shaded in the afternoon but received high levels of PPFD in the morning hours, when air temperatures and vapor pressure deficits were relatively low. Thus, contrary to expectations, we found relatively weak relationships between SM and ANPP despite significant spatial variability in both. Further, there was little evidence that light‐saturated photosynthesis (Asat) and quantum yield of CO2 assimilation (ϕCO2) differed for plants growing directly beneath (lowest PPFD) versus between (highest PPFD) PV panels. Overall, the AV system established in this semiarid managed grassland did not alter patterns of ANPP in ways predictable from past studies of controls of ANPP in open grasslands. However, our results suggest that the diurnal timing of low versus high periods of PPFD incident on plants is an important determinant of productivity patterns in grasslands.

Agrivoltaic system design tools for managing trade-offs between energy production, crop productivity and water consumption

“…At cooler, wetter Aurora, CO the model predicts no beneficial shading effects. Intriguingly, recent results from a nearby site showed that grasses growing beneath a photovoltaic array exhibited higher growth in regions receiving morning sun and afternoon shade despite having lower average soil moisture content than regions with morning shade and afternoon sun (Sturchio et al 2023). These experimental results suggest that (1) plants may acclimatize to agrivoltaic shading or (2) that the benefits of afternoon agrivoltaic shading may be more pronounced when crops experience water restriction.…”

Photovoltaic + Photosynthetic Coexistence: Towards a Sensible Accelerated Mass Integration of PV Onto a Perturbed Planet

“…Nevertheless, on sites with very short stature (or an absence of) autochthonous vegetation and animals, typical of dry, sunny rangelands of the world, LoCoAgri-PV and LoCoEco-PV might indeed be quite appropriate options, as the shade from a high concentration of PV may be beneficial to the vegetation and animals. On several sites in temperate and arid regions, researchers have noted improved vegetation health and yield improvements on low-cost agri-and eco-PV arrays without increases in spacing from mainstream LoCoPV (Sturchio et al, 2022). This point is again examined in Section 4.2.…”

From Fields to Photovoltaics: Effects of Agrisolar Co-Location on Food, Energy, Water, and Economic Security

“…The total displaced water use was 8 times the O&M use for those arrays, thus installing solar PV in water scarce regions has significant potential to reduce water use, which bolsters findings from previous studies [63][64][65][66][67][68] . This analysis does not incorporate the additional hydrologic effects of modifying surface energy and water budgets, including reducing evapotranspiration and the potential for increased groundwater recharge 22,[69][70][71][72][73][74] .…”