By Prof. Joerg Bagdahn, President of Anhalt University of Applied Sciences, Germany.
Dust accumulation on photovoltaic (PV) modules can lead to significant power losses due to absorbing or scattering the incoming sunlight. Depending on the location cumulative yield losses of more than 1% per day were reported in the literature for arid areas. In areas with high concentration of airborne dust as well as daily humid-dry cycles (frequently observed in most deserts regions of the world), the so called particle cementation process can strongly increase dust adhesion o the glass surface. This leads to costly subsequent cleaning procedures during the service of the PV modules.
To identify the underlying physical and chemical processes of cementation, glass samples were exposed to outdoor conditions at the PV test field of QEERI in Doha (Qatar). Subsequently the samples were investigated at microstructural level using electron microscopy (SEM and TEM) and elemental analysis with energy-dispersive X-ray spectroscopy (EDX). The microscopic investigations revealed the formation of nanoscopic needle-like structures, which were attributed to the Palygorskite minerals. It was shown, that the Palygorskite needles are responsible for the adhesion of other dust particles. Comparative indoor studies were conducted using a developed soiling test chamber which enables testing of glass samples under outdoor conditions. For the indoor soiling tests, different dust types were used, including standard Arizona and Aramco test dusts as well as dust collected from the PV field in Qatar. Within the test chamber, dew formation on glass surfaces and subsequent evaporation of the water was forced by cooling and heating of the samples. The lab results show the same nanoscopic Palygorskite needle-like structures as observed in outdoor conditions if dust from Qatar was used. Completely different nanoscopic adhesion mechanisms were observed for the used test dust (Arizona, Aramco). For the first time a realistic indoor test sequence for adhesion of dust particles was shown. This new indoor test enables the fast characterization of various glasses coatings (ASC) at different environment conditions. Further investigations of soiled PV modules from Morocco and Chile are underway and will presented at the conference.
Authors: Jörg Bagdahn1, Klemens Ilse1,2, Christian Hagendorf2, Volker Naumann2, Benjamin Figgis3
1 Anhalt University of Applied Sciences, D-06366 Köthen (Anhalt), Germany
2 Fraunhofer Center for Silicon-Photovoltaics CSP, D-061120 Halle (Saale), Germany
3 Qatar Environment & Energy Research Institute, HBKU, Doha, Qatar
Jörg Bagdahn is the president of the Anhalt University of Applied Sciences since September 2016 and has a professorship for “Photovoltaic Materials” at the University.
Jörg Bagdahn holds a diploma and a Ph. D. in material science from the Technical University of Chemnitz and Martin-Luther- University Halle, respectively. From 2000 until 2002 he worked as a postdoctoral fellow at the Johns Hopkins University on long term reliability of thin silicon films for MEMS applications. In 2003 he joined Fraunhofer and was responsible for various research activities in the area of microsystem technology, microelectronics and photovoltaics. From 2007-2016 he was the director of the Fraunhofer Center for Silicon Photovoltaics CSP.