A new study conducted at the University of Turku, Finland, investigated how household cleaning products affect the ability of solar panel glass to transmit light. The study showed that cleaning solar panels with a dishwashing detergent reduced the panel’s ability to absorb solar radiation.

For solar panels to work optimally, it is essential that they can absorb as much of the incoming solar radiation as possible. Soiling and, on the other hand, damage to the solar panel glass will reduce the panel's ability to absorb radiation.

A research team at the University of Turku in Finland investigated the best way to clean solar panels so that solar radiation would penetrate the panels as well as possible.

Most cleaning agents, such as glass cleaner and isopropanol, proved suitable for cleaning the studied solar panel glass.

The exception was dishwashing detergent and the results suggest that it should not be used when cleaning solar panels. Even dirty glass transmitted more light than glass cleaned with dishwashing detergent.

“Solar cell surfaces are usually made of glass, but typically have an anti-reflection coating and it is important to avoid damaging it. In this study, we did not test mechanical cleaning or pressure washers, for example, but I would not use them on panels,” cautions Professor of Materials Engineering Kati Miettunen.

The study found that the optical properties of the studied anti-reflective coating on solar panel glass did not deteriorate as a result of chemical cleaning – except when dishwashing detergent was used.

It is unlikely that dishwashing detergent damages the glass. However, rinsing does not seem to be sufficient, as the transmittance of the solar panel glass cleaned with detergent did not return to the pre-cleaning level after the rinsing.

“Even though the glass looks clean when cleaned with detergent, its ability to transmit light is significantly impaired. Therefore, a clean-looking end result does not guarantee optimal performance,” says Research Assistant Julianna Varjopuro.

The study conducted by the Solar Energy Materials and Systems (SEMS) research group at the University of Turku provides information on solar panel maintenance for users of solar power. In particular, the RealSolar project focuses on how to incorporate solar power into the Finnish energy system. Accessible information on solar energy solutions is important for an equitable green transition.

The results of the study were presented at the 41st European Photovoltaic Solar Energy Conference and Exhibition and in the conference proceedings.