Concentration performance of solar collector integrated compound parabolic concentrator and flat microchannel tube with tracking system

Abstract

The compound parabolic concentrator is a non-imaging concentrator that can concentrate solar radiation without tracking system. However, as the concentration ratio increases, the maximum half acceptance angle and the effective working hours decrease. To increase the effective working hours at high concentration ratio, a tracking solar collector is proposed that integrates the compound parabolic concentrator and flat microchannel tube. This new solar collector can track solar radiation by rotating the two reflective surfaces around their respective starting lines. A two-dimensional model is developed for the irradiation concentration of the tracking compound parabolic concentrator. For the geometry of the compound parabolic concentrator and solar irradiant angle, the optimal rotation angles of the reflective surfaces are determined to minimize the irradiation loss. The effects of the rotation angle of the two reflective surfaces on the concentration performance are simulated. The simulation results show that in the tracking mode, the averaged heat flux on the surface of the absorber can reach 7.61 kW m−2 when the concentration ratio and truncation ratio are 8 and 0.5, respectively. Even when the incident angle of solar irradiation is 30°, the averaged heat flux is still 5.12 kW m−2. Compared with other kinds of reflector, the concentration performance of the compound parabolic concentrator is merely influenced by the tracking error. The positive and negative tracking errors lead to different declining rates of normalized optical efficiency and the influence of positive tracking error is more acceptable.