Sandstorm erosion on solar reflectors: Highly realistic modeling of artificial aging tests based on advanced site assessment

Kurzfassung

In this work a guideline is developed which allows for a highly realistic laboratory simulation of sandstorm effects on glass components for the solar industry. So far no standardized test procedure is developed to test components against each other and predict their lifetime in the field to a realistic extent. One important reason for that matter is the strong variation from one site to another which would have to be addressed in a standardized test procedure. To overcome this issue, the meteorological and geological parameters of five outdoor sites are investigated in this work regarding their erosion potential, and additionally state of the art silveredglass reflector samples are exposed. A special focus is laid on the relative humidity, rh, and wind velocity, u, present at the same time (here named as u-rh couple). It is shown that strong winds accompanied with low relative humidity are more often measured at sites where the reflectors are more severely damaged by impacting sand particles. Apart from the u-rh analysis, the mineralogical characteristics of the sites are investigated and both the particle size distribution and the chemical composition of the soil are presented. In total, six erosion determining factors are identified and the five investigated sites are qualitatively ranked and sorted into three erosivity classes. The input parameters of a laboratory erosion setup were tailored in order to meet the conditions of the three erosivity classes. Therefore state of the art reflectance measurements are used, but also a novel method, based on image processing of microscope pictures of the mechanical defects on the glass surface is presented. This method enables the determination of a defect size density distribution (DSDD). The test parameters of the laboratory setup are adjusted in order to achieve a similar DSDD like observed outdoor for the three different erosivity classes.