Study on the performance of a novel beam-down concentrating solar tower system

Development of the beam-down concentrating solar tower (BCST) is a particularly topic of active research due to its main advantages including higher optical concentration ratio and few heavy apparatus on tower top, as well as less heat loss for lower receiver position. A novel beam-down solar tower system has been introduced and theoretically analyzed in this paper. A demonstration prototype with a geometric concentration ratio of about 60 is installed at Sino-Italian Green Energy Laboratory in Shanghai Jiao Tong University. The novel BCST is mainly composed of three heliostats based on linear Fresnel reflectors, three beam-down concentrators with cylindrical mirrors. Correspondingly, the cylindrical mirrors are fabricated using the high-reflectivity aluminium materials pasted over the stainless steel substrate. A cavity receiver with a conical spiral tube is considered. In addition, optical analysis based on the ray-tracing method is performed. Detailed theoretical models for ray-tracing method are introduced and validated with ASAP. The objective of this paper is to report the optical performance of the novel BCST, evaluate the solar flux distribution on the absorber surface, effect of tracking errors, and effect of the conical concentrator equipped on the cavity receiver, thereby providing useful data for practical solar process heat application. According to solar flux distribution on the absorbed surface, a total optical efficiency of about 64.7% can be obtained at noon of autumn equinox.