Airborne Soiling Measurements of Entire Solar Fields with Qfly

Concentrating Solar Power (CSP) plants are often being built in regions with high dust loads such as the Middle East and North Africa. Current soiling measurement methods in solar fields are labor and cost intensive and they only cover small measurement spots. Even a high number of manual measurements can only cover a minimal portion of the total solar field mirror surface. Airborne measurement solutions such as Qlly have been developed in recent years to measure the geometry and tracking accuracy of the large CSP mirror areas. Soiling on solar mirrors is qualitatively visible in raw QFly measurement images. In this study we present a method to automatically derive the mirror cleanliness from aerial images taken with QFly. We present scattering investigations that correct for the directional particle scattering, illumination and camera viewing angles. A promising correlation was found between the thus corrected camera RGB signals and reference reflectance measurements that shows an RMSD of 3% for the investigated dust.