Comparing Indoor and Outdoor Soiling Experiments for Different Glass Coatings and Microstructural Analysis of Particle Caking Processes
Klemens K. Ilse1,2,3, Jorge Rabanal4,5, Lukas Schönleber1, Muhammad Z. Khan1, Volker Naumann1, Christian Hagendorf1, Jörg Bagdahn2
1Fraunhofer Center for Silicon-Photovoltaics CSP, Halle, Germany
/2Anhalt University of Applied Sciences, Köthen, Germany
/3Department of Physics, Martin Luther University Halle-Wittenberg, Halle, Germany
/4International Solar Energy Research Center - ISC Konstanz, Konstanz, Germany
/5Centro de Desarrollo Energético Antofagasta, Universidad de Antofagasta, Antofagasta, Chile

The natural deposition of dust on glass surfaces of PV modules leads to shadowing effects, which can cause cumulative energy yield losses of more than 1% per day, especially in desert regions. Accordingly, soiling is addressed as one of the major concerns of component and system reliability of PV modules in desert environments throughout the world. Within this study, we present the results of outdoor and indoor soiling experiments with 4 differently coated glass samples. The outdoor experiments were conducted at the Solar Platform of the Atacama Desert (PSDA) over a duration of about 5 months. The samples showed huge 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 within a soiling test chamber and reproduced the outdoor behavior of the different coating types. The way of water interaction during dew events was found to be the key influence factor for 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 µm) are 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 important soiling mechanism increasing dust adhesion.

Area: Sub-Area 8.3: PV Performance Degradation and Spectral Impacts Due to Soiling (Joint between Topic to Areas 8, 9 and 11)