Flux Density Measurement on Large-Scale Receivers

Kurzfassung

Commercial solar tower plants have much larger aperture surfaces than the receiver prototypes tested in earlier R&D projects. Existing methods to measure the solar flux density in the receiver aperture face new challenges regarding the receiver size. Also, the requirements regarding costs, accuracy, spatial resolution, and measuring speed are different. Flux density measurement delivers the spatial distribution of the concentrated solar radiation on a receiver aperture, measures receiver input power, and monitors and might control heliostat aimpoints. This paper resumes existent concepts, presents new ones and evaluates them against a catalogue of requirements. Direct and indirect moving bar techniques offer high measurement accuracy, but also have the disadvantage of large moving parts on a solar tower. In the case of external receivers, measuring directly on receiver surfaces avoids moving parts and allows continuous measurement, but is not as precise. This promising technique requires, due to specific reflectance properties of current receiver materials, proper scientific evaluation. Measurement-supported simulation techniques can also be applied to cavity receivers without installing moving parts. They have reasonable uncertainties under ideal conditions and require comparatively low effort.