Airborne shape measurement of parabolic trough collector fields

As the optical efficiency of the solar field has a high impact on the overall performance and economics of a solar thermal power plant, qualification methods determining the geometrical accuracy of solar concentrator systems have gained high importance. However, it has not been possible yet to measure the geometrical accuracy of larger fractions of the solar field, resolving the relevant single characteristics like local mirror slope deviations, panel alignment and gravitational deformation. This paper describes the development and assessment of a measurement technique for the qualification of parabolic trough collector modules based on the distant observer method called TARMES (Trough Absorber Reflection Measurement System). Instead of a stationary camera at ground level taking pictures of a turning collector, the new approach called QFly makes use of an airborne camera vehicle which allows a completely automated and fast measurement of large numbers of collectors under relevant operating conditions. The new approach was validated against a stationary TARMES and photogrammetric measurement, supplemented by an extended uncertainty analysis. This analysis includes an assessment of the uncertainties of input parameters and their influence on measured local slope deviations. By applying a Monte Carlo approach, the effects on the RMS values of the local slope deviations of mirror panels and collector modules were investigated. Furthermore it includes an evaluation of the influence of the measurement sample rate. The results suggest an absolute measurement uncertainty for the RMS of slope deviations at module level of about ±0.1 milliradians. 2013 Elsevier Ltd. All rights reserved.