A Hybrid Ray-Tracing Optical Model for Compound Parabolic Concentrators

Abstract

Compound parabolic concentrator (CPC), as a hybrid of the stationary and the tracking collectors, can collect both direct beam and diffuse radiation. CPCs are favorable choices for medium-temperature applications for their high thermal efficiency and their cost-effectiveness. Optical models are important tools to predict the solar concentrating capability of the CPC. Despite the numerous, optical models developed in the literature and used for parametric studies of the optical characteristics of CPCs, the angular optical properties of the glass envelope, reflector, and receiver are rarely included. Moreover, most existing optical modeling studies of CPCs did not consider or present the loss associated with the refraction in the glass envelope. This study aims to fill these gaps by developing a comprehensive CPC optical model with the capability of profile generation, hybrid ray-tracing (HRT), surface property simulation, and sky model. The HRT can achieve high accuracy using significantly fewer computation resources compared with Monte Carlo ray-tracing (MCRT) and was validated against tracepro. The new optical model incorporates angular and spectrum dependence of optical properties for refraction and reflection using multilayer thin-film theory. Finally, the proposed HRT model was used to analyze the error associated with neglecting geometric design parameters and angular dependency of optical properties in optical simulation. The results suggest that the gaps between the receiver, glass envelope, and the reflector, the refraction of the glass and angular dependence of transmittance, and absorptance should be included in simulation to avoid considerable errors.