Comparative modeling of optical soiling losses for CSP and PV energy systems

Soiling is a challenge for both concentrating solar and photovoltaic technologies. Measurement procedures and efficiency sensitivities to soiling for the same surface particle density differ due to the different optical characteristics of both technologies. For this reason, soiling investigations performed at a site for one technology are not necessarily applicable to the other technology. Soiling measurements have been performed mostly under fixed or rarely occurring angles of incidence. In this study parallel measurements of soiling loss and particle mass density found on the main optical surfaces of concentrating solar power (CSP) and photovoltaic (PV) technologies are presented. The measurements are taken on samples of CSP second surface mirror and PV solar glass with consideration of the main optical characteristics of both technologies. Optical soiling losses are found to be higher by a factor of 8-14 in CSP for the same particle surface densities compared to PV. A Mie-based model is presented and validated, that converts the particle mass density and a set of other inputs into the optical soiling loss for either technology for normal angle of incidence and varying angles of incidence. This method facilitates the transfer of soiling loss data from one technology to another. The method can significantly increase the knowledge on soiling for both technologies as more measurement data is made accessible. Additionally, the soiling losses for different angles of incidence can be used to estimate more realistic annual loss parameters for the technologies in question and give recommendations for optimized incidence angles to be used in soiling measurements for both technologies.