Measurement techniques for the optical quality assessment of parabolic trough collector fields in commercial solar power plants

The optical quality of the collector field of concentrating solar power plants is an essential factor for their profitability. High optical quality can be achieved and guaranteed when the manufacturing process is continuously monitored and adjusted in its essential steps. A stationary, automatic photogrammetry system has been developed for the shape accuracy control of concentrator structures. It uses a digital camera, automatically moved around the object, computer controlled automatic image evaluation and continuous calibration checks. It is robust and fast enough to be integrated in a solar collector production line. For on-site measurements of mirror slope in parabolic trough collector fields, a new method is presented. It uses a set of pictures of the reflections of the absorber tube in the concentrator. The slope errors of the mirror surface are calculated with high spatial resolution and accuracy. The effects of the reflector slope deviations on the optical performance are evaluated with ray-tracing. The results give detailed information about the optical quality of the concentrator, inaccuracies in the manufacturing process, and their optical performance penalty.