Three-dimensional v-trough solar concentrator with diffuser for uniform cell illumination

Abstract

V-trough concentrators are usually implemented in low-concentration ratios photovoltaics for its low-cost and ease of manufacturing. The three-dimensional (3-D) configuration using four mirrors offers higher effective concentration ratios than the conventional two-dimensional v-trough concentrators. However, the skew rays hitting the photovoltaic cell in the 3-D case leads to an increase in the intensity non-uniformity and the formation of hot spots. One method to smooth incident rays on a receiver aperture is to add a diffuser in the light path such that the light incident on a diffuser is scattered in all directions following Lambertian distribution. In this work, we present a compound concentrator based on 3-D v-trough embedding a transmission diffuser to improve the illumination uniformity and reduce the hot spots. A concentrator with input and output apertures of 7.5 cm and 5 cm, respectively, and a length of 4.8 cm is proposed. Using ray tracing, the optimal position of diffuser inside the concentrator was located at a distance of 4 cm from the input aperture. The tilting angle effect on the effective concentration and the illumination non-uniformity were analyzed. The illumination nonuniformity is decreased by 33 %, while the effective concentration ratio is decreased by 17 %. The structure was realized using low-cost commercial flat mirror segments and tracing paper diffuser and was used for solar collection in a normal incidence case. The illumination profile of the cell was recorded before and after installing the diffuser showing an improvement of 41 % in non-uniformity and reduction in the effective concentration by 22 % only.