Solar panels accumulate dust, pollen, bird droppings, and general airborne soiling that reduces their output by limiting the amount of sunlight reaching the photovoltaic cells. Research suggests that heavily soiled panels can lose five to fifteen percent of their generating capacity. Regular cleaning maintains output and maximises the financial return on the installation.

How Often Should Panels Be Cleaned?

In the UK climate, panels typically need cleaning once or twice a year for most locations. Rainfall provides some natural cleaning, but horizontal and low-pitch installations accumulate more settled dust than steeply pitched ones. Properties near agricultural land, roads, or flight paths may accumulate soiling faster and benefit from more frequent cleaning. Monitoring the output of your solar system, if you have an inverter display or app, helps identify when cleaning is needed: a noticeable drop in output on sunny days compared with expected figures is a signal that the panels may need attention.

Cleaning Methods

The safest cleaning method for most homeowners is using a soft-bristle brush or squeegee mounted on a telescopic extension pole, allowing panels to be cleaned from the ground or from a short ladder without accessing the roof. Use clean water, ideally demineralised or purified water to avoid leaving mineral deposits as the water dries. Avoid hard bristle brushes, abrasive cloths, or pressure washers at close range, all of which can damage the anti-reflective coating on the panel glass surface.

Work on overcast days or in the early morning or evening to avoid thermal shock from cold water on hot panels, which could in rare cases crack the glass. Warm panels can also cause water to evaporate quickly and leave water marks.

Bird Dropping Removal

Bird droppings are acidic and can etch the panel surface if left for extended periods. They are also a more significant contributor to output loss than general dust due to their opacity. Soften dried droppings with water before removing them with a soft cloth or sponge to avoid scratching the surface.

What to Avoid

Do not use detergents or household cleaners, which can leave residues that attract dirt more rapidly. Do not use high-pressure jets at close range. Do not walk on the roof to access panels: most residential roof structures are not designed to be walked on and doing so risks both personal injury and roof damage. Check the panel manufacturer's guidance for any specific cleaning recommendations or restrictions that apply to your specific model.

Summary

Solar panels should be cleaned once or twice a year with a soft brush on an extension pole using clean purified water. Avoid abrasives, detergents, and close-range pressure washing. Bird droppings should be softened before removal. Professional water-fed pole cleaning services are a practical alternative, particularly for high or steep roofs. Never walk on the roof to access panels. Monitor system output to identify when cleaning is needed.