news / 2013-04-18

Collector qualification from the air

A quadrocopter carries out deflectrometric measurements of parabolic trough concentrators from the air. (Source: DLR)

Air-based measurement systems help when optically examining entire solar arrays. QFly is a measurement system consisting of a flying drone that can carry either a CCD or infrared camera. Depending on the assignment, QFly flies over the solar array using different routes and takes photographs in the visible or infrared range of the spectrum.

Based on the images in the visible spectral range, the accuracy of the mirror surface can be determined using deflectometric methods. To supplement this, photogrammetric methods are used to detect, among others, deviations of the absorber tube from the focal line. This in turn enables deformations in the structure to be identified. This data also enables the optical efficiency of the entire plant to be determined using ray tracing.


The infrared images can be used to determine the surface temperature of the glass envelope tubes in the absorbers. Even with a 400 °C operating temperature, these envelope tubes are in the ideal case only “hand warm” thanks to the selective coating and the vacuum inside. With defective absorbers the envelope tube temperature increases, which can then be identified in the IR images.

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