Angular Extent of the Heliostat Field in Solar Tower

Abstract

 In solar tower systems, the mirrors located on the ground reflect and concentrate the solar radiation on the receiver to increase the enthalpy of the heat transfer fluid. The mirrors can be placed surrounding the tower or limited in a direction, based on which the receiver is chosen to be external or cavity type, respectively. The overall performance of the system largely depends on the choice of the arrangement of the mirrors and the choice of the receiver. In this study, the angular extent of the heliostat field around the tower is studied at different latitudes. The field domain is discretized into square grids. The cosine and the attenuation efficiency are evaluated based on the position of the grid element and the aim point. The receiver aperture is idealized to be the outer surface of a cone and is denoted by the tilt angle. The interception efficiency is predicted with the angle made by reflected radiation on the slanted receiver aperture surface. No specific dimension for the heliostat is assumed and the amount of mirror area is expressed with the help of mirror density, which facilitates the prediction of the shading and the blocking efficiency. The amount of mirror area in each discretized field location is optimized for maximizing the optical performance. The results indicate that, with increased latitude in the northern hemisphere, the heliostat field tends to be limited towards the northern direction.