Do Solar Panels Need Cleaning? A London Guide

Usually not often. On a typical pitched roof in the UK, rain washes off most dirt, and the Energy Saving Trust says panels generally need very little maintenance. Cleaning helps when something rain can’t shift builds up: bird droppings, lichen, leaves, or grime from a busy road. If you do clean, do it from the ground with water and a soft brush, or use someone trained to work at height. Never climb on the roof or stand on the panels.

Key points

• Rain keeps most tilted rooftop panels clean enough.

• Bird droppings, lichen, leaves and heavy traffic grime are the usual reasons cleaning helps.

• Use water and a soft brush or sponge. No washing-up liquid, no pressure washer, no abrasive tools.

• Never stand on panels or work at height without training and equipment.

• The Energy Saving Trust suggests checking panels every year or two and cleaning if you see a build-up.

• If output has dropped, dirt may not be the cause. Check the monitoring first.

Why rain usually does the job

Panels on a pitched roof are tilted, smooth and glass-fronted. Rain runs straight off and takes most dust and pollen with it. The Energy Saving Trust says that in many cases rainfall will wash away most dirt and debris.

The steeper the panels, the better this works. Panels mounted at a low tilt, such as on flat roofs, can collect more dirt along their lower edge, where water pools briefly before running off.

When cleaning does help

Bird droppings. A dropping blocks light completely from the cells underneath it, and rain doesn’t always shift it. Pigeons are a particular problem in London, especially where they nest under the panels. Our guide to pigeon-proofing solar panels explains how to stop that.

Lichen and moss. These grow slowly on the frame and lower edge of panels, especially in shade or under trees.

Leaves and debris. Trees nearby can drop leaves that collect along the bottom of the array. Keeping branches trimmed also reduces shading.

Traffic and building grime. The Energy Saving Trust notes that homes near busy roads or other dusty environments may need cleaning more often. That applies to many London streets.

How to clean solar panels safely

The Energy Saving Trust’s advice, which we agree with:

• Use water and a soft brush or sponge. Avoid washing-up liquid, which can leave a residue.

• Don’t use a pressure washer. High pressure can damage seals and wiring and let water in.

• Don’t stand on the panels. They aren’t built to take a person’s weight and can crack.

• Work from the ground where possible. Long-handled brushes with a water feed reach many low roofs from the ground.

• Don’t work at height without training and equipment. For most two-storey London houses, that means using a professional.

• Clean when it’s cool, early morning or late afternoon, to avoid streaks.

• Report damaged cabling to your installer rather than touching it.

Also check your panel manufacturer’s instructions. Some warranties set out how panels may be cleaned, and using the wrong method could affect your cover.

Is it dirt, or something else?

If your output has dropped, dirt is only one possible cause, and often not the main one. Before paying for cleaning, look at your monitoring app:

• A gradual decline over months can be dirt, but it can also be new shade from a growing tree, or normal ageing.

• A sudden drop points to a fault, such as a tripped breaker, an inverter problem or a failed string of panels. Cleaning won’t fix that.

• Lower output in winter is normal. Compare with the same month last year, not with summer.

Our guides to solar generating less than it used to and solar panels not generating go through the checks.

What a service visit covers

The Energy Saving Trust suggests a visual check every one to two years and a fuller professional service every few years. A service is a good time to clean panels that need it, because the access is already in place. Our solar servicing visit can include checking the panels, mounting, cabling and inverter, and bird-proofing where it’s needed.

Frequently asked questions

How often should solar panels be cleaned in the UK?

Often not at all, because rain does most of the work. Check every year or two and clean if you can see a build-up of droppings, lichen or grime.

Can I clean my own solar panels?

Only if you can reach them safely from the ground, using water and a soft brush. Don’t climb onto the roof or stand on the panels.

Can I use a pressure washer on solar panels?

No. It can damage seals and wiring and let water in.

Does dirt reduce solar output?

Yes. Dirt, droppings and lichen block light from reaching the cells. But a large or sudden drop is more likely to be a fault, so check the monitoring first.

Will cleaning affect my warranty?

Using the wrong method could. Follow the manufacturer’s instructions and avoid abrasive tools, detergents and pressure washers.

Book a solar system inspection. We’ll check what’s really affecting your output, and clean and bird-proof the panels if they need it.