Evaluation of the Spot Shape on the Target for Flat Heliostats

The aim of this study is to evaluate the changes of the spot shape on the target in dependence of the variations of size and faceting of a flat heliostat or an array of heliostats. The flat heliostat, or a flat heliostat array, is a layout common for Concentation Solar Power (CSP) plants. The spot shape is evaluated by means of a numerical integration of an appropriate function; in order to confirm the results, both an analysis based on the Lagrange invariance and some simulations are performed. The first one validates the power density value in the central part of the spot, while the simulations assess the spot shape, which in its central part differs less than 3% from the calculated result. The utilized numerical method does not require specialized software or complex calculation models; it determines an accurate spot shape but cannot take into account shading and blocking phenomena.