Innovative instrumentation and methodology to characterize long distance heliostat beam quality in commercial solar power tower plants

The characterization of the whole solar field of a solar tower power plant is a time consuming labor that has to be performed to know the optical quality of each heliostat in the field. This allows to correct some deviations of each heliostat, leading to an improvement in its individual performance, and thus, improving the final performance of the whole field. The current methodology to characterize the optical quality of a heliostat is based on using a lambertian target, in which the solar beam is focused and its reflected radiation is captured using cameras. This leads to important measurement inaccuracies due to the non-uniformity of the lambertian target and the behavior of the camera. But the fact that the sun beam can overflow the size of the target, and its power density can be almost in the order of the ambient light, implies that a huge part of the heliostats in a plant cannot be well-characterized by these systems. These issues are even more important taking into account that plant size tends to grow even larger, increasing the distance of the furthest heliostats, and that small heliostats begin to be introduced in solar fields, whose reflected power is lower than that of common heliostats. Those issues will be overcome thanks to a new measurement system based on a non-tracking way to scan the sun spot, using an array of optoelectronic detectors which can be installed in new plants and even in plants that are now in operation.