Point Focus Solar Spectral Splitting System for CPV Applications

Abstract

Solar spectral splitting technologies have been investigated over the years as alternatives to improve the efficiencies obtained from photovoltaic devices by splitting the incident solar light into its respective wavelengths, and aligning a series of photovoltaic cells arranged next to each other as opposed to being physically stacked on top of each other as is the case with multijunction cells. Limitations previously posed by multijunction cells like current matching and lattice matching are circumvented through this approach, allowing for a broader and potentially cheaper pool of candidate cells to be used for energy conversion. In this study, we design and gauge the performance of a single optical element capable of splitting the light and concentrating it simultaneously unto a bed of photovoltaics, each illuminated by the part of the spectrum that corresponds best to its relevant properties such as the bandgap and the external quantum efficiency. The prismatic structure constituting the device relies on the device’s transmission in the visible region and its dispersion. Presented in this study is the mathematical framework used in designing the structure for a specific merit function; in particular, the study focuses on minimizing optical losses at the interfaces of the structure with the ambient air. Variables like the index of refraction of the material used, the angle of incidence on the surface, the exit angle of the light out of the structure factor into the optical center’s design. Compared to alternative splitting technologies like dichroic mirrors, the model splits the incident polychromatic light into a continuous band of wavelengths as opposed to discrete wavelengths that can be adapted on to different sets of single junction cells. The device is an improvement to our published 1-axis linear concentrator reported earlier in the year for its point-focus output yielding in even higher concentration and potentially lowers costs.