Concept and design of “flat-plate” CPV module based on Ring-Array Concentrator

A high-concentration (400X-1100X) CPV module is investigated in view of developing a planar concentrator PV panel with the form factor approaching that of flat-plate solar panels. The module employs the Ring-Array Concentrator (RAC), a novel point-focus optical design based on the concept of a Reflective Lens^™ (RL). RLs, which can also be referenced to as refractionless lenses, combine the high collecting power of mirrors with the design flexibility and rear-focus operation of lenses. The receiver of the module has passive cooling and incorporates a III-V PV cell and a bypass diode. A number of individual square-aperture modules are arranged into a densely packed planar array to form a rigid concentrator PV panel. The optical layout and general design of the module are presented. The optical performance of the RAC-PV module was modeled using a dedicated software system for simulation, calculation and optimization of RAC (RACsolver^™). It is shown that a square-shaped focal spot corresponding to the most common shape of concentrator PV cells can be obtained while maintaining acceptable flux uniformity and avoiding secondary optics and associated losses. In order to maximize the acceptance angle, however, it is shown that certain low-loss focus improvers can be employed. We demonstrate that such focus improvers can be either reflective or refractive (with TIR) and they can also be low-profile, virtually lossless due to the minimum number of reflections and simultaneously serve as a cell encapsulant. We present and analyze the ray paths as well as flux maps in the receiver plane with and without focus improvers. The misalignment effects on the optical performance are also discussed. A prototype 3×2 mini-panel has been used to test the optical model. It is concluded that the current optical concept and proposed CPV module design allow for reducing the optical losses at the targeted high and uniform concentrations as well as c- - an result in a panel-like appearance of the product being developed.