Modeling reflection loss from an evacuated tube inside a compound parabolic concentrator with a cylindrical receiver.

Linear compound parabolic concentrators with cylindrical receivers are often combined with evacuated tubes along their focal length to suppress convective heat loss for use as thermal collectors. When investigating the optical efficiency of such collectors it is important to consider the reflection loss introduced by the evacuated tube particularly at large angles of incidence of light onto the CPC aperture. In this paper reflection losses are determined using ray-tracing as a function of the angle of incidence in both the longitudinal and transversal planes of a CPC. The reflection losses are found to be approximately constant except close to the maximum acceptance angle.