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

Abstract

AbstractWe 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 ≈ 4 and wide optical acceptance angle θA ≈ 48°, also VIS diffused light is effectively collected and a spectrally integrated optical efficiency ηo,diff = 62%, (ηo(diff,NIR) =45%, ηo(diff,VIS) = 17%) is estimated. Under direct illumination ηo,dir > 80% is obtained over the whole angular acceptance with a maximum optical efficiency ηo,dir‐MAX ≈ 88.7% at θi = 37°. Low‐concentrating RAW‐SS can work stationary and trackless. The tilt angle for the orientation 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 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.