Can I clean my own solar panels, or use a window cleaner or pressure washer?

Your panels look grubby, there's bird mess along the bottom row, and you already own a hose and a long brush. Or your window cleaner has offered to do the panels too. Here is what the panel makers allow, and where doing it yourself stops.

Can I clean my own solar panels? Yes, from the ground

You can clean your own solar panels if you can reach them safely from the ground. Use a soft brush on a pole and plain water, at a cool time of day, and nothing stronger.

That is all the manufacturers ask for. LONGi's installation manual suggests a sponge dipped in clean water or a soft cloth, and JA Solar's manual says to wipe the glass with a wet sponge or soft cloth. A soft brush on a water-fed pole does the same job without a ladder.

As for how often, we recommend one to two cleans a year, depending on the area your panels are in and what your panel warranty asks for. Tony Beckett, our director, says "it all depends on the warranty of the panels, what they dictate as well."

Rain does a lot of the work, but not all of it. Even the Energy Saving Trust says a light clean every 12 to 24 months can help a system run at its best. Bird droppings, tree sap, farm dust and grime on shallow roofs tend to stay put, and our guide to whether solar panels need cleaning covers which roofs get dirtiest.

What to check before you clean your own solar panels

Your panel maker's manual. The cleaning rules are set by whoever made your panels, and some makers tie them to the warranty. JA Solar, the make we fit most, says in its manual: "Failure to comply with the requirements listed in this manual will invalidate the Limited Warranty".

What to do: find the panel make in your handover pack and read the cleaning section of that maker's manual before you start.

Water pressure. The Energy Saving Trust warns that a high-pressure power washer can interfere with the seals and wiring on your panels and lead to water damage. LONGi's operation and maintenance manual caps the water pressure on the surface of its panels at 0.7 MPa (7 bar).

What to do: use a soft brush on a pole, or a hose on a gentle spray. Never a pressure washer or a jet nozzle.

What goes in the water. The Energy Saving Trust says washing-up liquid can leave a residue on the glass. LONGi says detergents should only be used when water can't clean the panel, and rules out abrasives, polishes, acids and alkalis. JA Solar rules out any cleaning agent containing acid or alkali.

What to do: use plain water. LONGi allows mains water but warns that water high in minerals leaves deposits, so in a hard-water area purified water gives a cleaner finish.

The temperature. LONGi says the water should be within 10°C of the panel's temperature, and that its panels shouldn't be cleaned when it's below 5°C. The Energy Saving Trust adds that water dries fast on hot panels and leaves streaks.

What to do: clean early in the morning or in the evening on a mild day, never in midday sun or a frost.

How you reach them. The Energy Saving Trust advises staying on the ground if you don't have the training or equipment for working at height. JA Solar's manual says "Standing on the module or bracket for cleaning works is forbidden", and LONGi says not to stand or walk on its panels.

What to do: if a pole from the ground can't reach every panel, stop there and leave the rest to someone with access equipment.

Switching off. The Energy Saving Trust suggests turning the system off before you clean. LONGi points out that panels have no switch of their own and still produce electricity in daylight.

What to do: follow the isolation steps in your manual, and keep water away from the inverter, isolators and cables.

Damage. LONGi says not to clean panels with damaged glass or exposed wires, and the Energy Saving Trust says to stop and report any damaged cabling.

What to do: leave a damaged panel alone, photograph it from the ground and get it looked at.

A window cleaner offering to do them. A window cleaner can do a good job on panels if they work the way the panel maker says. Before they start, ask:

• What water do you use: purified, or straight from the tap?
• Will you work from the ground with a water-fed pole, or go on the roof?
• Will you add any soap, detergent or chemical? The answer should be no.
• Are you insured for working on or near the roof?

What to do: if they would stand on the panels or bring a pressure washer, say no.

What we see on real jobs

One to two cleans a year is the advice we give our own customers, homes and businesses alike. For commercial arrays, Tony puts it as once or twice a year, "to keep up with the warranty and the efficiency."

Bird fouling is the most common reason a home array really needs cleaning. Droppings don't rinse off in rain the way dust does, and pigeons nesting underneath keep adding more.

Cleaning alone doesn't fix that. The panels need clearing and bird proofing as well, or the mess comes back.

Our own cleans use purified water and soft brushes on water-fed poles, from the ground wherever the roof allows. Nobody walks on the roof unless there is no other way, and then only with access equipment and a method statement. We follow each panel maker's instructions on isolating.

What a professional clean costs

Commercial and farm cleaning is priced by the day, typically £800 to £1,500 depending on the size of the system and how dirty it is. As Tony says, "it depends how dirty they are."

Home cleans are priced individually, so there's no single figure to publish. What moves the price:

• how we reach the panels: a pole from the ground is quick, scaffolding or a platform isn't
• how many panels there are and how they're laid out
• what's on them: a light film is a wash, baked-on droppings, lichen or sap take longer
• the height and pitch of the roof
• whether bird proofing is needed at the same time

When to call someone, and what to send

Call a professional when:

• the panels can only be reached from a ladder, scaffold or the roof
• droppings are baked on, or birds are nesting underneath
• you can see cracked glass or damaged cabling
• generation has dropped and you don't know why: dirt is only one cause, and a solar health check looks at the rest

What to send us on WhatsApp:

• a photo of the panels taken from the ground
• a photo of the roof edge or underside of the array if you can see it, showing any nesting material, feathers or droppings
• the panel make, from your handover pack, if you have it
• a screenshot from your monitoring app if output has dropped
• your postcode

We'll tell you whether they need doing and what it would cost, and if they're fine, we'll say so. We're based in Warrington and clean homes, businesses and farms across the UK: see our solar panel cleaning service.

Key points

Yes, you can clean your own solar panels. Do it from the ground, with a soft brush on a pole and plain water.

Never a pressure washer, detergent or scourer. And never stand on the panels: JA Solar forbids it for cleaning, and LONGi says not to stand or walk on its panels.

Your panel maker's manual sets the rules. JA Solar says breaking them invalidates the warranty, so read the cleaning section first.

We recommend one to two cleans a year. How many depends on the area and what your panel warranty dictates.

Stop where the ground stops. Ladders, roofs, nesting birds and damaged panels need someone with the right kit.

Questions people also ask

Not sure your panels need doing? Send us a photo on WhatsApp and we'll tell you.