Selective light transmission in agrivoltaics: Modeling light spectra and photosynthetic rate

While most agrivoltaic systems use opaque silicon photovoltaics, their excessive shading has shifted interest toward semi-transparent wavelength-selective photovoltaic (WSPV) technologies. These technologies aim to transmit light beneficial for crops’ growth while converting unused wavelengths into electricity. This study presents two modeling approaches: one for simulating light transmission through WSPV systems and the other for estimating leaf photosynthetic rates from the wavelengths received at the crop level. Both models incorporate the composition of the light spectrum, an aspect often overlooked in earlier models where broadband light values were sufficient. However, in WSPV systems, consideration of the spectral light distribution is key. The models were validated using experimental data from semi-transparent magenta-colored cadmium telluride (CdTe) WSPV systems, demonstrating satisfactory accuracy (R2 > 0.89). Additionally, the study evaluates two metrics, the yield photon flux (YPF) and effective photosynthetically active radiation (EPAR), to assess the photosynthetic efficiency of WSPV technologies in terms of light quality. A global crop suitability assessment, based on light requirements (light quantity) for different plants, highlights the potential of various WSPV technologies in agrivoltaics and aims to guide their future implementation. For instance, semi-transparent magenta CdTe PV and red-transmittance-dominated organic PV (OPV) modules, with average PAR light transmittance around 20%, appear to provide effective shading in most regions. These systems can support medium-light plants (daily light integral [DLI] >6 mol m−2 day−1) even in higher latitudes during sunnier months. Conversely, blue-dominated OPV and a neutral-colored semi-transparent crystalline silicon PV provide higher transmittance (around 50%), making them suitable for plants with very high light demands (DLI >16 mol m−2 day−1), but the quality of the light transmitted is less efficient or unaltered in terms of photosynthetic performance with respect to sunlight.