A Spectral Splitting Solar Concentrator with Minimum Self-Shading for 4-Terminals and Bifacial Applications: Design and Numerical Evaluation of Power Conversion Efficiency

Efficient bifacial operation of solar modules is a hot topic in photovoltaics aiming at maximizing the optical power collection at the area of installation. A prerequisite for bifaciality is the effectiveness in collecting backscattered radiation. Self-shading effects are an obstacle to that, since they decrease the useful extension of illuminated surface that can re-radiate sunlight according to albedo. In this work we discuss the benefits of bifacial operation of a "solar tile" designed as an asymmetric 4-Terminals (4T) low concentrating and spectral splitting photovoltaic optics, featuring a wedged right-prism core with an apex angle of 30°. The geometry minimizes self-shading and the design is appealing also for Integrated applications in Buildings, Vehicles, Vessels, and also in Portable-PV, where functionality and aesthetics typically coexist and cost requirements may be somewhat relaxed. Ideally, we assume perfect optical coupling of all elements, anti-reflection treatment at the input surface, standard solar AM1.5G spectrum and uniaxial azimuthal tracking. An albedo coefficient of 0.8 is considered. Performances and Power Conversion Efficiency (PCE) values are numerically evaluated using commercial ray-tracing software, at different North-South elevation angle of the sun and different latitudes of installation, by considering a Si bifacial cell operating in the near-infrared range and a GaAs commercial reference cell operating over the visible spectrum. The numerical results show potential advantages and increased PCE of the 4T configuration with respect to standard ones. In the present case at a latitude of ~25° N, a global 39% increment in PCE is obtained with respect to the best-performing bifacial cell standard configuration. Since the electrical outputs of the 4T configuration heavily depend on the type of solar cell selected to operate in the visible, our results validate a positive trend and suggest a strategy for high PCE solar modules exploiting performant high-bandgap solar cells.