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Laboratory and outdoor fouling experiments conducted in Saudi Arabia have shown that increased particle resuspension by wind is one of the dominant factors for the high antifouling performance of photovoltaic glass.
A group of scientists has investigated the correlation between laboratory and outdoor fouling experiments on glass panels with anti-fouling coatings (ASC). Outdoor experiments were conducted over a year at eight locations in Saudi Arabia and compared with laboratory tests reproducing potentially relevant fouling mechanisms. “I am very optimistic about the possibility of generalizing the results to other arid and semi-arid areas with high soiling losses due to mineral dust,” Dr. Klemens Ilse, author of the study, told pv magazine .
“The laboratory tests consist of three main procedural steps: dry powder deposition, processes to modify the adhesion of the powder, and a cleaning process, which includes intermediate characterization steps,” the researchers explained. “This study is the first to comprehensively analyze a large number of coatings and samples, correlate and compare soiling patterns from indoor and outdoor experiment results, and identify key mechanisms for predicting ASC outdoor performance.”
Field tests took place from February 2019 to January 2020 in Al-Khafji, Solar Village, Al-Qassim, Riyadh, Makkah, Tabuk, Yanbu and Al-Ahsa. In all locations, glass samples were mounted at 25 degrees. The glass panels were changed and tested quarterly, except at Al-Khafji and Solar Village, where they were tested monthly. Different coatings were tested both in the laboratory and outdoors, some with hydrophilic properties and others identified as hydrophobic.
In laboratory tests, all experiments were performed with a sample tilt angle of 20 degrees, with Arizona A2 dust and a simulated wind speed of about 15 m/s. Scientists could control humidity from 20% to 80% and temperature from -5ºC to 80ºC. Four different tests were performed to reflect different fouling mechanisms.
In dry deposition tests, which mainly reflect the rebound process of particles, dust was simply deposited on the samples. Dry deposition and wind blowing tests, which represent the effect of particle resuspension, were performed by depositing powder on the samples and then blowing on them with an air knife. Spray tests were performed with light or heavy spray, to simulate caking effects. In these tests, dust was deposited and then light or heavy dew was simulated, followed by wind.
“In the correlation analysis of the annual average, taking into account the annual average of dirt losses, the dry tests after the wind blow and the light dew tests after the wind blow showed a strong correlation in the majority of places,” the scientists declared. “That is, while dry tests after deposition and heavy spray tests after wind blow indicated low correlation or anticorrelation respectively.”
Explaining the results, the scientists said that in desert conditions, increased resuspension of particles by wind is one of the dominant factors for high antifouling performance. “Laboratory heavy dew tests may be more feasible to predict soiling in locations with higher dew frequency and, above all, heavy dew capable of cleaning the surface, which are usually rare in the Middle East,” added the Dr. Ilse.
The scientists also analyzed the Al-Khafji and Solar Village cases for seasonal signatures. The tests were conducted monthly and showed a general trend in which heavy dew tests seemed to better predict soil behavior outdoors during the dry summer months, while light, dry dew tests might better predict soil behavior. dirt in the wet winter months.
“These results may seem counterintuitive at first, but they could be explained by the interaction of the dew with the hydrophobic and hydrophilic properties of the surfaces. “This includes caking processes, increased particle capture during wet surface conditions, and reduced capillary adhesion during dry seasons,” the scientists note. “However, more research is needed to better understand the observed effects, including outdoor and laboratory tests with various types of coating.”
The results were presented in “ Correlation between laboratory and outdoor soiling experiments with anti-soiling coatings ,” published in Solar Energy Materials and Solar Cells . The research was carried out by academics from the Anhalt University of Applied Sciences (Germany), the Fraunhofer Center for Silicon Photovoltaics (CSP), the Fraunhofer Institute for Microstructure of Materials and Systems (IMWS) and the Fraunhofer Institute for Silicate Research ( ISC), as well as the King Abdulaziz City for Science and Technology (KACST) of Saudi Arabia. |
