Does Solar Panel Cleaning Actually Pay?What soiling costs, and the faults that cost more
Cleaning is the most-searched thing about solar maintenance and the least often necessary. Here is how to work out whether a clean is worth buying on your roof — and why the expensive problems are usually electrical rather than dirty.
- Rain deals with ordinary dust on a pitched roof; bird mess, lichen and sap are what stick
- Where soiling sits matters more than how much: a band along one edge clips the whole string
- At this quarter’s rates, every 100 kWh you fail to generate is worth about £16
- Purified water and a soft brush — never a pressure washer, and nobody walks on the array
- The faults that cost real money are silent: dead inverters, tripped isolators, failed optimisers
Most of the time, rain is your cleaner
The solar cleaning industry would prefer you did not know this, but on a pitched roof in a British climate, ordinary dust washes off. Panels are glass, set at an angle, in a country where it rains. A panel that looks dusty from the pavement is usually costing you very little.
What rain does not shift is the stuff that sticks: bird mess that has baked on through a hot week, lichen and moss creeping down from a ridge or an overhanging tree, sap and blossom fall, and the general film that builds on a shallow-pitched array where nothing runs off properly.
Where the soiling sits matters more than how much there is
This is the part that gets missed. Panels in a string are wired in series, so the current through the whole string is limited by its worst-performing cell. A narrow band of muck along the bottom edge of a row can therefore cost you more than a thin, even film over the entire array — because the band clips every panel it touches, while the film just dims everything slightly.
One well-placed dropping across a cell can do the same thing. It is why "how dirty does it look" is the wrong question and "where is it, and is one string reading lower than its twin" is the right one.
What the lost generation is actually worth
Before paying anyone, work out what you are buying back. At the rates in force this quarter, every 100 kWh you fail to generate is worth about £16 — assuming you use 30% of your generation at home at the 26.32p price cap and export the rest at 12p.
| What you lose | What it costs a year |
|---|---|
| 100 kWh | about £16 |
| A tenth of a 4 kW Havant array | about £74 |
| Electricity price cap, Oct–Dec 2026 | 26.32p/kWh |
| Outgoing Octopus export rate | 12p/kWh |
Ofgem price cap 1 Oct–31 Dec 2026 (Direct Debit); Octopus OUTGOING-VAR-24-10-26 region H from 1 March 2026; PVGIS 5.3 for a 4 kWp array at Havant. If you use more of your generation at home, a fault costs you more.
Put a cleaning quote against that arithmetic and the answer is usually obvious in both directions. If soiling is genuinely costing you a tenth of your output, a clean pays for itself quickly. If it is costing you two per cent, an annual wash is a subscription to a tidy-looking roof.
How it should be done — and what to refuse
Purified water and a soft brush, from the ground or a pole where access allows. No detergents, no abrasives, and never a pressure washer: forcing water past a frame seal or a junction box causes exactly the fault you were trying to prevent. Panels should be cleaned cold, early or late, not in the middle of a hot day.
And nobody should be walking on your array. A cracked cell or a trodden frame costs far more than any cleaning contract, and the damage is not always visible from the ground afterwards.
The faults worth more than the dirt
Here is the uncomfortable part for the cleaning industry: on most systems we are called to, the money is not in the glass. It is in an inverter that stopped months ago and nobody noticed, a tripped or water-damaged DC isolator, a failed optimiser dragging its string, or corroded connectors — which, on this coast, is a recurring theme.
None of those announces itself. The system simply earns less, quietly, until somebody reads the monitoring and compares it with the same months last year. An annual check exists to catch those; the cleaning is the bit you can see.
If you want someone to read the data first and clean only what is actually costing you output, that is what our solar panel maintenance plan is for — and it covers systems we did not install, including ones whose original installer has stopped trading.
Frequently Asked Questions
How often should solar panels be cleaned?
There is no fixed interval, and anyone quoting one is guessing. It depends on what lands on your roof: a house under trees or beneath a gull roost may need it yearly, while an exposed roof with a decent pitch may go years. The tell is in the data — a gradual drop against the same months last year, or one string reading lower than its twin.
How much output do dirty solar panels lose?
It depends entirely on what the soiling is and where it sits, which is why a single percentage figure should make you suspicious. A thin even film costs little; a band of bird mess along the bottom edge of a row clips the current for every panel in that string. Work from your own monitoring rather than from a number on a leaflet.
Is it worth paying for solar panel cleaning?
Do the arithmetic first. At the Oct–Dec 2026 price cap, with 30% of generation used at home and the rest exported at 12p, every 100 kWh you fail to generate is worth about £16. Compare that with the quote. If soiling is costing a tenth of your output, a clean pays quickly; if it is costing two per cent, it does not.
Can I clean solar panels myself?
From the ground with a soft brush and purified water, carefully, yes. What you should not do is use a pressure washer, detergents or anything abrasive, clean them hot in the middle of the day, or climb onto the array — a cracked cell or trodden frame costs far more than any clean.
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