Investigation of soiling on mirror and glass samples with regard to power losses in CSP and PV technologies

Abstract

This work undertakes a direct comparison of the influence of natural soiling on CSP and PV technologies by investigating outdoor exposed mirror and glass samples over a timespan of several weeks during summer in Évora, Portugal. Weather data as well as SEM and EDS analyses are used to support the investigations. It is shown that the measured relative soiling losses are approximately 8 to 14 times higher for CSP than for PV considering the same gravimetric density. Mean daily soiling rates are approximately 8 times higher (0.35%/d and 0.04%/d) for CSP and PV respectively. The results are used to create an optical model based on Mie scattering theory to successfully reproduce theses significant differences as well as the relation between soil gravimetric density and soiling losses for both technologies. The model is further extended to predict AOI responses for soiled PV modules. Calculations are made that recontextualize soiling loss measurements taken under normal AOI into an annual time frame with respect to the multiplicity of occurring AOI during the course of a year. Those calculations show that soiling loss measurements taken under normal AOI are not necessarily representative and suggestions are made to measure the soiling losses under specific angles with a corresponding weighting pattern based on the presented results.