Optical and thermal analysis of a beam-down linear Fresnel reflector integrated with a compound parabolic collector

Beam-down concentrating solar technology is a novel and promising technology consisting of two consecutive reflections, concentrating the available solar irradiation at ground level, where the receiver is located. Solar rays fall on the primary mirror field, which redirects them towards a secondary reflector, and finally, they are reflected and focused on the receiver. In this work, the integration of a beam-down linear Fresnel reflector and a compound parabolic collector is investigated. The novelty of this work lies in presenting the design of a new parabolic-segmental secondary reflector aiming to combine construction cost reduction and efficiency improvement compared to the parabolic design. Furthermore, the receiver is a complex of two compound parabolic concentrators. The optimization of the receiver's cavity was conducted using the Bezier polynomial parametrization method. The specific receiver is designed for the maximum utilization of solar irradiation and is intended for medium to high-temperature applications. Linear and flat reflectors comprise the primary mirror field. The maximum optical efficiency is equal to 34.83%. The system's geometrical concentration ratio is equal to 16.20, whereas the concentration ratio of each compound parabolic concentrator is 3.04. The thermal and exergy analyses were carried out for various operating scenarios, developing the system's performance curves, and the maximum thermal and exergy efficiencies were found to be equal to 33.70% and 16.93%, respectively. Furthermore, it is assumed to lead in potential construction cost reduction due to its simpler design and less manufacturing processes required, which is not claimed as an evidence of this study.