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Large scale central receiver systems typically deploy between thousands to more than a hundred thousand heliostats. During solar operation, each heliostat is aligned individually in such a way that the overall surface normal bisects the angle between the sun’s position and the aim point coordinate on the receiver. Due to various tracking error sources, achieving accurate alignment ≤1 mrad for all the heliostats with respect to the aim points on the receiver without a calibration system can be regarded as unrealistic. Therefore, a calibration system is necessary not only to improve the aiming accuracy for achieving desired flux distributions but also to reduce or eliminate spillage. An overview of current larger-scale central receiver systems (CRS), tracking error sources and the basic requirements of an ideal calibration system is presented. Leading up to the main topic, a description of general and specific terms on the topics heliostat calibration and tracking control clarifies the terminology used in this work. Various figures illustrate the signal flows along various typical components as well as the corresponding monitoring or measuring devices that indicate or measure along the signal (or effect) chain. The numerous calibration systems are described in detail and classified in groups. Two tables allow the juxtaposition of the calibration methods for a better comparison. In an assessment, the advantages and disadvantages of individual calibration methods are presented.

Es werden im DLR entwickelte Messmethoden vorgestellt, die der Qualifizierung von Heliostatfeldern dienen. Anwendungsbeispiel ist das Solarthermische Versuchskraftwerk Jülich. Des Weiteren werden Verwendungsmöglichkeiten der gewonnenen Daten (bspw. für Simulationen im Rahmen von Auslegungen und Betriebsbegleitung) aufgezeigt.

Two new test benches have been developed for the combined measurement of the thermal properties and overall optical efficiencies of receivers for the use in parabolic trough collectors. In the first test bench two receivers are simultaneously irradiated by natural sunlight via parabolic troughs that are mounted on a two axis tracking stage. Shutters enable the variation of the aperture for quasi constant solar input power over the test period. The second, the solar simulator test bench consists of an elliptical cylinder with flat end reflectors. Metal halide lamps (HMI) and the receiver are positioned in the two respective focal lines. The test benches are operated in two modes: Cold performance tests with water flow through the receiver at near ambient temperature in order to measure the optical efficiency in the stationary enthalpy increase, secondly hot testing with the empty receiver at typical operating temperature in order to compare irradiant power and steady state thermal loss power and calculate the efficiency. The test benches are operated in combination with classic heat loss measurement, together the three test benches form a complementary set. First comparative measurements with cold testing on the solar simulator test bench show high reproducibility and a measurement precision relevant for qualification and comparison of different receiver types at industrial and research level.