Researchers at the in Sweden have provided an extensive review of all wavelength-selective PV systems for applications in agrivoltaics.
“Traditional opaque silicon panels often create excessive shading that limits light availability for most shade-intolerant crops. Yet, plants do not need the full spectrum of sunlight for growth but only the region where they are photosynthetically active. In some cases, a full spectrum may even hinder their development,” the research's lead author, Silvia Ma Lu, told pv magazine. “This opens the door for wavelength-selective solar photovoltaic (WSPV) technologies. WSPV systems are designed to transmit light at the wavelengths most beneficial for photosynthesis, while reflecting or absorbing less essential wavelengths to generate electricity.”
Wavelength selectivity in agrivoltaics can be achieved through several approaches, including tuning photoactive layers, using semi-transparent colored coatings, incorporating mirrors and lenses, or designing spectrally selective luminophores. “Evidence suggests that these methods can effectively share sunlight between energy generation and crop production, though full-scale evaluations of crop and energy impacts remain limited,” Ma Lu added. “We offer a set of recommended performance metrics tailored to WSPV technologies in agricultural applications, along with guidelines for standardized experimental procedures and reporting to advance consistent and reliable research practices in the field.”
In the study “Wavelength-selective solar photovoltaic systems to enhance spectral sharing of sunlight in agrivoltaics,” published in Joule, the research team explained that plants selectively absorb blue and red light, with favorable spectral bands being 430–480 nm and 630–680 nm, respectively. As in agrivoltaics crop production is a top priority, the WSPV system should be designed to transmit or redirect the corresponding solar spectral band to the crop, with the remaining spectrum being utilized for power generation.
The paper provides a comprehensive review of solutions aimed at achieving wavelength-selectivity in agrivoltaics, presenting a classification of WSPV technologies and discussing their current status, challenges, and future directions for effective implementation in agrivoltaic systems.
The classification of the WSPV systems was based on where or how the spectral selectivity occurs. “In thin-film WSPV, the active layer, or, in the case of ultrathin nano-absorbers, the rear contact is responsible for absorbing the non-desired wavelengths for the plants,” the group specified. “Spatially segmented PV with selective-colored layer WSPV achieves spectral selection by adding a colored layer to conventional c-Si or thin-film PV modules. Spectral selection in CPVs is accomplished using dichroic mirrors or lenses. LSCs rely on luminescent materials (organic dye or quantum dot) that absorb the undesired wavelengths and re-emit them to the embedded PV cells, thus not relying on straightforward reflection or refraction.”
The group also suggested creating standards for reporting on the performance of WSPV technologies.
“Beyond reviewing current WSPV technologies, our work aims to inspire future development by outlining efficiency limits for various solar cell types under spectral sharing conditions, specifically when shared with crop production,” Ma Lu stated.
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