Calculation of the blocking factor in heliostat fields

摘要

This paper presents a method for the calculation of the blocking losses of a heliostat, in terms of a blocking factor, arising due to neighboring heliostats in a heliostat field. The proposed method is general in the sense that it is valid for any type of heliostat array and orientation. In the method the individual blocking elements are projected on the plane of the heliostat under consideration. The heliostat plane is defined in the heliostat coordinate system. An analytical expression for the geometry of the projection is presented, and a numerical iterative technique is developed for the solution. The solution procedure involves the subdivision of the heliostat surface into a suitable grid. An overlap test is developed to determine whether a particular sub-area is blocked. In a straightforward manner, all blocked sub-areas are subtracted once from the overall heliostat area. A program was written by using MATLAB to test the method. In initial runs on lap-top (Intel(R) Core(TM) i3 M380 2.53 GHz), typical rectangular heliostats (9.8x10.7 meters) were subdivided into 25x25 grids. Results for the instantaneous blocking factors for each of 99 such neighboring heliostats, were obtained in an average run time of less than 3.5 seconds.