How much efficiency do dirty solar panels lose?

Dirty solar panels typically lose 15–25% of their output. For a standard 4kW system, that's £120–250 per year in lost generation.

How often should solar panels be cleaned?

Once or twice a year for most installations — ideally in early spring and late summer. Properties with pigeons or overhanging trees may benefit from quarterly cleaning.

Solar Panel Cleaning: Is It Worth It?

Solar panels are a significant investment, and most homeowners want to know if cleaning them is genuinely worth the cost. The short answer: yes, but the savings depend on several factors.

How much efficiency do dirty panels lose?

Studies consistently show that dirty solar panels lose 15–25% of their output. In severe cases (bird droppings, heavy pollen, construction dust), losses can exceed 30%.

For a typical 4kW domestic system generating around £800–1,000 per year, that's £120–250 lost annually to dirt alone. A professional clean costs £60–100 for most domestic arrays, making the return on investment clear.

What causes the buildup?

Bird droppings — the biggest single cause of efficiency loss. They're opaque and don't wash off in rain

Pollen — creates a yellow-green film, especially in spring (April–June)

Lichen and moss — grows on panels that are shaded or north-facing for part of the day

Road dust and pollution — particularly for properties near busy roads

Agricultural dust — common across rural Somerset

Does rain clean solar panels?

This is the most common misconception. Rain removes loose surface dust, but it doesn't touch bird droppings, pollen films, or mineral deposits. In fact, rain makes things worse by leaving water marks as it dries — the same hard water staining you see on windows.

When should you clean them?

Once or twice a year is sufficient for most installations. The best times are:

Early spring (March) — clear winter grime before the high-output summer months

Late summer (September) — remove pollen and summer buildup before autumn

If you have a pigeon problem or your panels are under trees, quarterly cleaning may be worthwhile.

Can I clean them myself?

We'd advise against it. Solar panels are fragile, positioned on roofs, and damaged by the wrong cleaning products. Abrasive cloths scratch the anti-reflective coating. Pressure washers can force water under seals. And climbing onto a roof without proper equipment is dangerous.

Professional cleaners use pure water and soft brushes, applied from the ground with water-fed poles where possible. No chemicals, no pressure, no risk to the panels or to you.

The bottom line

If you have solar panels, annual cleaning is one of the simplest ways to protect your investment. The maths works out clearly: spend £60–100 on cleaning, recover £120–250 in lost generation. It pays for itself twice over.