Dynamic light environments, rather than shading ratios, determine rice yield and quality in agrivoltaic systems

Agrivoltaic (AV) systems offer a promising pathway to co-produce food and renewable electricity, yet rice paddies remain a challenging case because yield maintenance is strictly required in Japan. This study evaluated three AV panel architectures implemented at three commercial paddy sites in Japan over three consecutive growing seasons (2022–2024). High-frequency measurements of photosynthetic photon flux density (PPFD) at canopy level were used to quantify both seasonal cumulative light availability and short-term fluctuation characteristics. The relationships between PPFD dynamics and yield components were examined using factorial analysis and linear mixed-effects modeling, and a robust threshold analysis was conducted to identify the relative cumulative PPFD requirement for maintaining rice yield. Grain quality was assessed in 2024, and land-use efficiency and revenue robustness were evaluated using the Land Equivalent Ratio (LER) and sensitivity analyses incorporating both technical (meteorological and PV performance) and market uncertainties. Across sites, AV plots showed yield reductions relative to paired open-field controls (three-year means: 33.6% at Sakata, 20.6% at Higashine, and 31.6% at Yonezawa). Yield losses were consistently associated with reduced panicle number, while greater short-term PPFD variability was linked to larger yield penalties even under comparable cumulative PPFD. Maintaining ≥80% yield corresponded to a relative cumulative PPFD threshold of 76.5% (95% CI: 71.6–79.9%) of ambient conditions. Grain quality changes suggested potential market-grade risks; however, electricity revenue improved total revenue and buffered income under plausible rice price penalties and electricity price uncertainty during the FIT period. Overall, the results indicate that dynamic PPFD delivery—beyond the nominal shading ratio—provides decision-relevant insight for AV design and policy frameworks aiming to maintain rice productivity while securing economic resilience.