Calculation of the field optical efficiency of a solar tower photothermal mirror with double shade shielding and a multi-base collector efficiency model

Abstract

Optical efficiency is a crucial evaluation parameter for assessing the strengths and weaknesses of tower heliostat fields. Previous studies have indicated that optical efficiency is determined by factors such as shadow blocking rate, cosine efficiency, collector truncation efficiency, atmospheric transmission, and specular reflectance. This paper enhances the modeling of shadow blocking rate and collector truncation efficiency by abstracting real-world scenarios into mathematical problems involving trigonometric functions, coordinate systems, and normal vectors. For the shadow blocking rate, we establish a double shadow blocking model that considers both the inter-heliostat shadows and shadows between the absorption tower and heliostats. Regarding collector truncation efficiency, we develop a multi-base collector efficiency model that takes into account various combinations of intersecting sections between the cone beam's irradiation area on the collector surface and its absorption/reflection area. The inclusion of shadow blocking considerations along with categorizing intersections between beam illumination areas and collector absorption areas enables more universal, accurate, and practical calculations of optical efficiency. To evaluate our proposed method's performance, we calculate and compare the annual average optical efficiencies in a specific scenario using both our approach and traditional methods.