Airborne Soiling Measurements in Operating Solar Fields

Kurzfassung

Soiling is an issue receiving increased attention over the last years. Currently solar field soiling levels are measured with handheld reflectometers that need a technician to operate and are limited to measuring small sections of the vast mirror surfaces present in CSP solar fields. Earlier we presented a method to determine the soiling levels over parabolic trough solar fields using a drone and image analysis techniques in combination with particle scattering simulations [1]. This previous method evaluated those areas of a mirror that showed the black absorber tube in the direct reflection. The light reaching a given pixel of the camera sensor consists of light scattered by the dust on the mirror and the so-called “background contribution” showing the object reflected in the observed section of the mirror. As the reflections of the absorber tube were used in [1] the background contribution could be neglected. Then scattering simulations were used to correct for the effect of different incidence and viewing angles on the intensity of the scattering signal. A good agreement between the scattering corrected RGB camera signal and reference reflectometer measurements could be shown. In operating power plants the parabolic trough field needs to de-focus in order to realize the black absorber tube background. In tower plants a black target would be required. In this study we present an enhancement of the method that allows evaluation of mirror areas that show the sky as a background. Thus, the enhanced method facilitates soiling measurements during full solar field operation and for all CSP technology options. The approach to determine the sky background to be subtracted from the scattering signal is presented and a feasibility study using a test dataset including reference soiling levels will be given.