Researchers from the University of New South Wales (UNSW) in Australia have developed spectrally selective semi-transparent crystalline silicon (c-Si) solar modules for use in agrivoltaics.
“To allow sufficient light transmission to crops in protected cropping situations current state of the art (SOA) semi-transparent PV modules space out opaque c-Si solar cells leaving transparent glass area for sunlight to pass through,” corresponding author Ian L. Thomas told pv magazine. “However, plants only use a limited portion of the solar spectrum to drive photosynthesis called the photosynthetically active radiation (PAR). This matches a similar wavelength range to the one which humans use to see, approximately 400 – 700nm. Current SOA modules transmit a large portion of the solar spectrum that isn’t required by crops and could be used by the cells for electricity conversion, particularly wavelengths in the near infrared (NIR) which c-Si cells are really efficient in converting to electricity.”
“What we have invented is a way of embedding spectrally selective optics into the gaps between cells in a semi-transparent PV module,” he went on to say. “These embedded optics can redirect NIR light to the c-Si cells for electricity generation while still allowing a very high proportion of the PAR to be transmitted. What is particularly useful about our solution is that it intelligently combines existing large area dichroic technology used in the building industry with fabrication techniques currently used in PV module assembly.”
The module utilizes TOPCon solar cells and a distributed Bragg reflector (DBR) embedded in a dual-glass architecture with a flat-plate concentrator geometry to enable efficient spectral separation via total internal reflection. DBRs are highly efficient optical mirrors composed of alternating layers with differing refractive indices. By precisely engineering layer thicknesses, reflected light waves undergo constructive interference, achieving peak reflectivity of more than 99.9% across a targeted wavelength range.
The researchers evaluated two commercial DBR technologies in particular—silver-dielectric coatings and multilayer polymeric films—each offering different advantages in cost, efficiency, and optical performance. Multilayer polymeric films were found to provide higher near-infrared (NIR) reflection, negligible optical absorption, and sharper spectral selectivity, making them particularly attractive for the proposed module concept.
The module also relies on v-groove flat-plate concentrators, which use a series of angled reflective structures to redirect incoming sunlight toward a central region. In the proposed configuration, these angled surfaces direct NIR light into the glass substrate at angles that enable total internal reflection (TIR), effectively trapping the light within the module.
Using MATLAB software, the researchers developed a comprehensive optical model to evaluate annual module performance. Device performance was compared with both a conventional opaque photovoltaic module and a semi-transparent PV module with identical cell coverage. Performance was assessed in terms of optical efficiency, electrical conversion, and PAR transmission. The model assumes idealized operating conditions and simplifies several factors, including cell voltage variations, temperature effects, rear-side illumination, and crop-specific light response, focusing primarily on short-circuit current density.
Simulations conducted for three locations in Australia showed that, under direct irradiation, the proposed module achieved a 34% increase in electrical output compared with a conventional semi-transparent PV module while maintaining high PAR transmission. Performance was found to depend strongly on the solar incidence angle relative to the v-groove orientation, with stable behaviour along the grooves but reduced efficiency across them due to limitations in total internal reflection. The design also efficiently transmits PAR for crops while redirecting NIR light to the photovoltaic cells for electricity generation.
Results further showed that multilayer polymeric DBR films provide the best overall balance, significantly increasing electrical output while maintaining high PAR transmission. For a 50% cell coverage module, annual short-circuit current increases by around 23–27%, while a 38% coverage design achieves gains of 34–40%. Across all cases, more than 90% of PAR is preserved, while approximately 80% of NIR radiation is redirected for power generation.
“To date, we have constructed first stage prototypes around half the size of an A4 sheet of paper and confirmed their performance through testing, so there is still a way to go on the commercialisation path,” Thomas explained. “By filtering out approximately 80% of the NIR light our technology could reduce crop surface temperatures in semi-arid areas with high solar resource, and consequently reduce water consumption, though this depends a lot on the local conditions and crops involved.”
The module technology was described in “Spectrally selective c-Si agrivoltaic modules: Evaluating a new approach,” published in Applied Energy.
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