Solar panel cleaning guide: frequency, methods and common mistakes

Solar panels are a long-term investment, and their performance depends directly on how clean they are. A layer of dust, bird droppings or plant debris can reduce a panel’s efficiency by 15 to 25 per cent. However, cleaning them incorrectly can be worse than not cleaning them at all.

How often should solar panels be cleaned?

The recommended frequency depends on location and environment. In rural areas with low pollution and no nearby trees, a biannual clean may suffice. In urban environments, industrial zones or very dusty areas, quarterly cleaning is ideal.

In any case, a monthly visual inspection is advisable to detect occasional build-ups of dirt, leaves or bird droppings. After episodes of Saharan dust, mud rain or strong dusty winds, an additional clean is recommended.

How to clean solar panels correctly

The correct method is simpler than it seems, but clear guidelines must be followed.

Use demineralised water or, failing that, tap water with a low lime concentration. Very hard water leaves white marks that over time become encrusted and reduce light capture. Apply the water with a low-pressure hose or a pole system with a soft brush.

Never use pressurised water directly on the panels. High pressure can damage seals, frames and the glass surface. Nor should scouring pads, hard brushes or abrasive products be used.

If there is adhered dirt, a neutral soap diluted in water and a microfibre cloth or soft-bristle brush can be used. Rinse with plenty of water and allow to air dry.

Common mistakes to avoid

The most frequent mistake is cleaning the panels during the middle of the day when they are hot. The thermal shock between cold water and hot glass can cause micro-cracks that over time reduce the panel’s lifespan. Ideally, clean first thing in the morning or late in the afternoon.

Another common mistake is walking on the panels to access difficult areas. The weight can damage the internal photovoltaic cells even if the glass does not visibly crack. If the panels are on a hard-to-reach roof, it is better to hire professionals with height-access cleaning equipment.

Using household cleaning products such as glass cleaner or degreasers is also a mistake. These products can leave chemical residues that degrade the panel’s anti-reflective coating.

Professional or DIY?

If you have a small installation on an accessible roof, you can do it yourself following the above guidelines. For large installations, on pitched roofs or at height, the safest and most effective option is to hire a professional service with safety equipment, demineralised water and specific tools.

The cost of a professional solar panel clean pays for itself quickly through improved energy performance.