Optical Performance and Weight Estimation of a Heliostat With Ganged Facets

Abstract

In standard heliostat design, the usual strategy of cost reduction is to increase the mirror area of the heliostats. This not only leads to a reduction of specific drive cost but also to an increase of the torques caused by the wind loads, resulting in higher specific weight and higher specific drive power. These drawbacks are avoided when small heliostats are coupled. At the torque tube heliostat (TTH), the mirrors are mounted on torque tubes to simplify the coupling mechanism for the elevation angle. Ray tracing calculations were done to obtain optimized heliostat configurations and to compare the energy yield of a heliostat field built of 288m2 TTHs with a conventional heliostat field. To get an idea of the weight reduction potential of the TTH, the dimensions of the torque tubes, the secondary axis tubes, and the mirror support structure were weight optimized via finite element method. The layout criterion was a mean mirror error of 2.5mrads under wind load and gravity.