Comparison and Optimization of Heliostat Canting Methods

Heliostat canting (alignment of mirror facets) is known to have a major influence on the optical efficiency of heliostat fields and therefore on the power output of solar tower plants. In recent years several canting concepts were used, mainly on- and off-axis canting. Several new canting concepts, like stretched-parabolic or target aligned canting, were proposed in order to improve the performance of heliostats. As solar power plants become economically more attractive, knowledge about the influence of canting becomes more important. In this context, the influence of several factors on the canting method is discussed and optimal canting strategies are described. The considered factors comprise plant power level, heliostat position in the field, heliostat area, receiver dimension and site latitude. It is concluded that the target aligned tracking method is superior to all other variants in the majority of cases. As for the standard azimuth-elevation tracking methods, no one of these exhibits a clear advantage. It is only the on-axis method that performs worst in all cases.