| Work Detail |
A European group has studied the impact of dirt on photovoltaic modules in Oman. They have collected 60 samples, depending on the season, month and angles of inclination.
Scientists from Imperial College London and the Karlsruhe Institute of Technology have investigated the impact of dirt on the glass surfaces of solar modules in semi-desert regions.
They analyzed how dirt can affect the performance of photovoltaic panels in optical and electrical power. “We have also carried out an economic analysis of the dirt, but we have not published it yet. The results indicate that economic losses depend largely on each location,” explains Christos Markides, co-author of the research, to pv magazine .
The study is based on 60 samples collected at a fouling station in Muscat (Oman).
“Estimating the energy performance of real photovoltaic installations remains a challenge due to overestimation or underestimation of dirt losses. Fouling losses largely depend on the size and shape of the particles, as well as their associated spectra, which significantly influence photovoltaic performance.” “In this work, we present the results of an extensive outdoor fouling experimental test campaign, apply detailed characterization techniques, and consider the resulting losses.”
In the article, “ Characterization of soiling on glass surfaces and their impact on optical and solar photovoltaic performance ,” recently published in Renewable Energy, Markides and their colleagues explained that the samples analyzed were glass coupons with low iron content. These coupons are commonly used in the solar industry to encapsulate the top layer of a photovoltaic module. The glass samples were collected at the end of each month during 2021 and in two seasonal periods, in the wet season and in the dry season. In each collection period, the researchers collected four samples, at 0, 23, 45 and 90 degrees, respectively.
The samples were sent to London for optical transmittance testing. The analysis showed that the relative transmittance of the horizontal samples decreased by 65% ??in the wet season, 68% in the dry season and 64% throughout the year.
“In comparison, vertical coupons showed a decrease in relative transmittance of 34%, 19% and 31%, respectively,” the research group added. “The mean decrease in relative transmittance at all tilt angles was 44%, 49% and 42% for the wet, dry and one-year coupons, respectively.”
Based on these results, the researchers calculated the expected electricity loss under a standard test condition of 1,000 W/m2 radiation and a temperature of 25 °C with a monocrystalline photovoltaic module.
“The relative transmittance reductions measured in the wet season, dry season, and full-year horizontal samples correspond to expected relative reductions in electrical power generation of 67%, 70%, and 66%, respectively,” they added. “Based on a local inclination angle of 23 degrees, the relative transmittance losses are estimated at around 30% per month, which translates into an equivalent relative reduction in photovoltaic power of around 30% per month at the location studied” .
Next, the scientists used X-rays and electron microscopes to characterize the soil particles. Since all the glass samples were located in the same place, the scientists assumed that their dirt would have the same material characterization. Therefore, they analyzed only horizontal glass coupons from the wet and dry seasons and throughout the year.
“According to the results of X-ray diffraction (XRD), the year-round horizontal dirty coupon has a variety of minerals such as silicon dioxide, calcium carbonate, calcium magnesium carbonate, titanium dioxide, iron carbide and aluminum silicate”, they stressed. “The elemental map highlights the chemical compounds indicated by the XRD analysis. Silicon (Si) is the most dominant element, while the rest are carbon (C), oxygen (O), sodium (Na), magnesium (Mg), aluminum (Al), calcium (Ca) and iron (Fe) ”.
The researchers also found that the dry season sample had more PM10 particles - these are particles with a diameter less than 10 µm - than the wet season sample. “It was also shown that natural cleaning due to periodic rains can eliminate the accumulation of larger particles, but not smaller ones,” they explain in the work. |
