Researchers in Finland found that dishwashing liquid reduces solar module transmittance and performance, leaving residues even after rinsing. They recommend avoiding its use for cleaning solar panels.
Image: University of Turku
Researchers at the University of Turku in Finland have investigated whether household cleaning products can be used to clean solar panels, finding that most – including glass cleaner and isopropanol – are suitable and do not affect module glass light transmittance.
Dishwashing liquid was the exception, as it was found to alter the optical properties of anti-reflective (AR)-coated solar panel glass.
The scientists noted that, although dishwashing liquid is unlikely to cause permanent damage, the transmittance of glass cleaned with it did not return to pre-cleaning levels, even after rinsing.
“Even though glass washed with dishwashing liquid appears clean, its light-transmitting capacity is noticeably diminished. A visually clean result doesn’t necessarily ensure peak performance,” researcher Julianna Varjopuro told pv magazine.
“It’s possible that the dishwashing detergent simply left stains on the glass rather than harming the AR coating. Regardless, it is recommended to avoid using it when cleaning solar panels,” added Professor Kati Miettunen.
The experiments were conducted using glass fragments taken from an unused silicon solar panel. Large glass pieces were immersed for 20 hours in various cleaning solutions, including ethanol, acetone, isopropanol, solar panel detergent, glass cleaner, and dishwashing detergent.
Image: University of Turku, Mikael Nyberg
A similar test was performed after growing algae on the glass for three days using a nutrient-sugar-moss mixture. Transmittance of cleaned glass was measured using a UV-vis spectrophotometer across 190–1100 nm.
Cleaning tests on unsoiled solar panel glass showed that all chemicals improved transmittance except for dishwashing detergent, which reduced the peak by about 1%. Solar panel detergent products, meanwhile, were found to perform only slightly better than generic cleaners. In soiled samples, cleaning restored transmittance and removed differences caused by algae, except when dishwashing detergent was used, which left the peak nearly 4% lower.
Atomic force microscopic (AFM) analysis confirmed the antireflective coating remained intact after cleaning, with scratches
attributed to earlier handling.
“Cleaning is rather evenly impacting the surface and PV power output decreases roughly proportionally to the decrease in optical transmittance,” said Miettunen. “On average, the transmittance of the soiled glass sample cleaned with dishwashing detergent was approximately 3% lower compared to that of glass cleaned with best suited cleaning agents. Thus, the impacts on PV output are
expected to be similar.”
“Currently, our group has started investigating soiling caused by snow,” Miettunen added. “In Nordic conditions, especially in late spring, solar radiation can already be significant while electricity demand still remains high. Therefore, we are interested to investigate power losses due to the snow accumulation on PV panels.”
Recently, other researchers at Germen research institute Fraunhofer CSP found that some widely used PV cleaning agents can damage anti reflective glass coatings, significantly reducing solar module efficiency. Their tests showed that while some cleaners are safe, others cause visible and permanent coating degradation, highlighting the need for careful selection of cleaning products to avoid long term performance loss.
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