THREE-DIMENSIONAL FLUX PREDICTION FOR A DISH CONCENTRATOR CAVITY RECEIVER

This paper describes the development of ray tracing models for a 500 m2 dish concentrator. Two distinct types of model have been created: (1) a model in OptiCAD based on the generic dish design, which uses design values for mirror facet geometry, and averaged values for mirror facet slope and pointing error; (2) a model in Tonatiuh which incorporates measured values of these parameters, for the prototype dish completed in 2009. In both cases the goal is accurate prediction of the three-dimensional flux distribution in the focal region, in particular as an aid to receiver design. Inputs to the ray tracing models have included photogrammetry, flux mapping and Finite Element Analysis. Photogrammetry was primarily used to measure mirror panel geometry prior to installation on the dish, and mirror panel pointing error on the completed dish. On-sun flux mapping of the image produced by individual mirror panels gave information on panel slope error. The image of the moon created by the complete dish on a planar target gave a two-dimensional flux distribution which was used to calibrate the ray tracing models. The methodologies used can with suitable modification also be employed on other concentrator systems, such as heliostat / central receiver