Optical performance of quasi-stationary, low-concentration, and low-profile compound parabolic concentrators

Low-concentration and low-profile compound parabolic concentrators (CPCs) in the quasi-stationary state were designed and investigated for potential use in rooftop and building-integrated concentrating photovoltaic-thermal applications. All the designs were investigated with a geometric concentration ratio of two. The first design was the lowest-position-truncated CPC (LEMR), and the second was the highest-position-truncated CPC (HEMR). The performances of both concentrators were compared with a full CPC (without truncation). At the outlet aperture, the optical efficiency within the half acceptance angle for the LEMR and HEMR CPCs averaged nearly 97%, whereas for the full CPC, it was 95%. At the best concentration plane (BCP), the optical efficiency within the half acceptance angle was the highest for the LEMR CPC 95%. A distributive method was used to estimate accurately the nonuniformity in the solar flux at both the outlet and the BCP. The nonuniformity analysis revealed that the LEMR and HEMR designs exhibited a uniform distribution of solar flux at the BCP. The incident-angle modifiers for all three cases were investigated, and the annual accumulated solar energy was estimated for Xi'an, China. The material consumption of the LEMR CPC was approximately 48% that of the full CPC and 78% that of the HEMR CPC. The LEMR also exhibited the highest annual-energy efficiency per unit material consumption (η_m = 1.30). Finally, the results indicate that the LEMR CPC possesses higher solar flux uniformity and represents a better trade-off between energy collection and cost reduction, and thus, the novel design can be used as a quasi-stationary concentrator.