Comparing Indoor and Outdoor Soiling Experiments for Different Glass Coatings and Microstructural Analysis of Particle Caking Processes

Within the scope of this study, we present the results of outdoor and indoor soiling experiments with four differently coated glass samples. The outdoor experiments were conducted at the Solar Platform of the Atacama Desert (PSDA) over a duration of about five months. The samples showed large differences in soiling behavior and were characterized with respect to surface coverage of dust particles and transmission loss by light microscopy and optical transmission, respectively. Comparative indoor soiling experiments were performed in a soiling test chamber and reproduced the outdoor behavior of the different coating types. The mechanism of water interaction during dew events was found to be the key influencing factor for the soiling performance of the different coatings. To better understand fundamental soiling mechanisms in the Atacama Desert, soiled glass surfaces were investigated at a microstructural level using electron microscopy. It was found that the silt fraction of particles (>4 mu m) is caked by accumulation and compaction of small, platelet-shaped clay minerals during dew cycles. This caking process can be distinguished from particle cementation induced by water soluble salts and is regarded as an important soiling mechanism, which increases dust adhesion.