Spatial analysis of crop light model for optimizing fixed-tilt agrivoltaic system design across Japan

Agrivoltaic systems (AVS) co-locate crops and photovoltaic generation, requiring designs that balance electricity production with crop light needs. Prior national-scale assessments often assumed uniform designs and overlooked spatial irradiance variability, leaving the feasibility of balanced layouts uncertain in heterogeneous regions such as Japan. This study applies a transferable optimization framework to map the optimal module density of fixed-tilt, elevated AVSs across 376,871 1-km grid cells in Japan using MONSOLA-20 solar dataset and crop light requirements expressed as daily light integral. For each grid, we adopt the locally optimal tilt, vary the projected ground coverage ratio (pGCR) in 1-point increments under light constraints for shade-tolerant and shade-intolerant crops, and compute annual electricity yield and land equivalent ratio (LER). Results reveal substantial geographic variability: although the mean optimal pGCR is about 25%, local optima range from below 10% to above 40%, rather than clustering around the national mean. The analysis indicates that the prevailing Japanese AVS trend (pGCR ≥30%) often exceeds local climatic capacity, posing risks of crop yield loss in lower-resource regions. These spatially explicit benchmarks demonstrate that location-specific optimization, rather than uniform standards, is essential for sustainable AVS deployment in heterogeneous landscapes.