An accurate and cheaper method of estimating shading and blocking losses in a heliostat field through efficient filtering, removal of double counting and parallel plane assumption

Abstract

Evaluation of optical efficiency of a heliostat field is essential for central receiver tower plants. In the present study, an improved method is demonstrated to eliminate drawbacks of existing methods for evaluating shading and blocking efficiency. The proposed method obviates the parallel plane assumption with the immediate neighbours; hence improves accuracy. Moreover, the lack of flexibility introduced due to such simplifying assumptions in terms of altered field configuration is removed. The family of ray-tracing methods often provides accurate result only at the cost of large computational expense. The current method renders similar degree of accuracy at significantly lower cost by eliminating inefficiencies of a brute-force approach. At first, it identifies potential shader (blocker) neighbours through a two-level filtering. Secondly, the grids on a heliostat are checked from-edge-to-centre instead of a random order. Moreover, the grids already found to be shaded (blocked) by one neighbor are excluded from further checks. Such systematic approach reduces nonessential checking for shading (blocking) and hence improves computational efficiency. Furthermore, such approach also discards any possibility of double counting. Finally, the degree of accuracy as obtained through computationally expensive ray-tracing methods is achieved by the present method with far less number of grid points.