Entwicklung und Validierung einer luftgestützten, kamerabasierten Messmethode für den Verschmutzungsgrad von Solarfeldern

Abstract

CSP (Concentrating Solar Power) plants are often built in regions with high dust pollution such as the Middle East and North Africa. Current soiling measurement methods in solar fields are labour- and cost-intensive and cover only a small part of the mirror surfaces even with a high number of measurement points. The airborne measurement solution QFly was developed at DLR in recent years to measure the geometry and tracking accuracy of the large CSP power plant. A drone is used to take pictures of a solar field, which are evaluated by an automated program. Soiling of solar mirrors is qualitatively visible in unprocessed QFly measurement images. The goal of this work is to develop a method for the automatic detection of mirror purity from aerial images taken with QFly. The number of particles per mirror surface determines how much light is scattered under constant lighting conditions. Part of the scattered light will enter the UAV camera and thus contribute to the pixel RGB value, which represents the mirror area, detecting higher values than a point with fewer particles. Disturbing factors such as geometric influences, background reflection and diffuse light must be separated from the RGB signal. The geometrical conditions between camera, sun and mirror as well as the particle size distribution and the solar spectrum considered in the respective scattering investigations. The camera internal settings such as gamma correction, white balance and vignetting are examined and corrected. A promising correlation between the thus corrected camera RGB signals and reference reflectance measurements was found. The presented investigations show that a soiling measurement method with sufficient measurement uncertainty by drone is possible. The method requires further development work and could, once completed, change and improve the soiling monitoring in power plants in the long term.