An asymmetric low concentrator and spectral splitting approach to bifacial four-terminal photovoltaic modules

We introduce the conceptual design of the optical core for a spectral-splitting and light-guiding four-terminal (4T) photovoltaic (PV) module, with appealing features for bifacial operation. We analyze the applicability of the solution and its performance using a commercial ray-tracing software for direct and diffused solar irradiance at standard AM1.5G spectrum. The core is a right-angle transparent wedged (RAW) prism. Complementary, two dichroic mirrors are optically coupled to the rear and bottom faces of the wedge to perform the spectral-splitting (SS) function. Low-gain concentration in the visible (VIS) band is provided by combining dichroic reflections with achromatic total internal reflection (TIR) at the topmost air-dielectric interface for light guiding. The module can support 4T heterojunction connection, implemented with wide-bandgap (WG) solar cells for the VIS and silicon-based solar cells for the near infrared (NIR). At a geometrical concentration gain CG-VIS approximate to 4 and wide optical acceptance angle theta(A) approximate to 48 degrees, also VIS diffused light is effectively collected and a spectrally integrated optical efficiency eta(o,diff) = 62%, (eta(o(diff,NIR)) =45%, eta(o(diff,VIS)) = 17%) is estimated. Under direct illumination eta(o,dir) > 80% is obtained over the whole angular acceptance with a maximum optical efficiency eta(o,dir-MAX) approximate to 88.7% at theta(i) = 37 degrees. Low-concentrating RAW-SS can work stationary and trackless. The tilt angle for the orientation beta$$ \beta $$ is set according to the latitude at the installation site, and in the northern hemisphere, it is more north-oriented with respect to standard panels. The collection of albedo irradiance from the ground is favored, since the scaling coefficient for self-shading of the module at sun elevation phi$$ \phi $$ is lower than for standard flat panels of equivalent input area and normally oriented. The decrease in self-shading is therefore an asset for bifacial operation and specifically effective at lower latitudes where solar irradiance is stronger. The possible applications range from sub-watt indoor PV and Internet-of-Things power suppliers to utility-scale plants and building-integrated solutions.

Automated summary

We introduce the conceptual design of an optical core for a four-terminal photovoltaic module that can split and guide light, making it suitable for bifacial operation. The performance of the module was analyzed using a ray-tracing software, showing that it can effectively collect both direct and diffused solar irradiance. With a low-concentration design, the module achieves high optical efficiency and can be used in various applications.