Photosynthetically active radiation complexities in agrivoltaic policy mandates: Insights from controlled environment yields under semitransparent photovoltaics

Agrivoltaics, which integrate photovoltaic (PV) energy generation with crop production, can enhance land use efficiency but reduces photosynthetically active radiation (PAR) essential for plant growth. While some studies report increased yields, the relationship between PV transparency, PAR, and crop productivity remains complex and underexplored—especially for shade-tolerant crops like lettuce. This study addresses this gap by experimentally evaluating romaine lettuce yield under cadmium telluride PV modules (offering uniform partial transparency) with seven transparency levels (10–80 %) in a controlled environment simulating outdoor summer conditions. PAR levels ranged from 43 to 419 micromol/m 2 -s (43–131 micromol/m 2 -s underneath the modules), using artificial light and natural light. Fresh weight data were collected for each treatment and compared to an unshaded control. In parallel, a review of agrivoltaic regulatory frameworks across Europe was conducted to contextualize results. Lettuce yields ranged up to 102 % relative to control conditions. Statistical analysis confirmed significant differences among treatments. Strong correlations were observed between PAR and fresh weight, and between PV transparency and yield, supporting the hypothesis that optimal PAR and transparency conditions can be identified. These relationships were expressed using mathematical trendlines for future modeling use. The findings suggest that minimum-yield-based agrivoltaics regulations offer a more effective policy framework than fixed-area limitations. Due to the inherent variability in crop yields, Germany's flexible approach of setting minimum yield requirements aligns best for maximizing agrivoltaic benefits while minimizing detriments. Establishing dynamic mandates with periodic review cycles will allow future agrivoltaic policies to remain adaptable to technological progress and regional agricultural variability.