Performance evaluation of a nonimaging solar concentrator in terms of optical and thermal characteristics

A nontracking, nonimaging solar concentrator with a low-heat-loss configuration was proposed, and its optical and thermal performance was investigated. The reflector has a compound parabolic and involute shape so that the absorber is heated as uniformly as possible. To eliminate heat loss by conduction and convection, the mirror and absorber are enclosed in an evacuated glass tube. The concentrator presented here was simulated for the location of Sendai, Japan, and its acceptance angle was estimated as 23.44°. A ray-tracing model was developed to evaluate its optical and thermal performance. The average optical efficiency was evaluated by a 2-D ray-tracing model, and a value of 72.7% was obtained. A thermal analysis of the absorber was conducted to evaluate the temperature uniformity. The results indicate that the temperature distribution of the absorber can be considered uniform. The thermal efficiency of the proposed solar concentrator was calculated as a function of the incidence angle and absorber temperature. With a concentration ratio of 2.51, the concentrator, even at an absorber temperature of 373 K, operates with an average efficiency of 47.8%, although the absorber was assumed to have a gray surface. The concentrator's thermal efficiency was compared with that of other solar collectors, and found to be higher than that of conventional solar collectors.