Free Calculator
Is Cleaning Your Solar Panels Worth Paying For?
Cleaning companies quote the loss figure. They rarely quote the payback. Put in your roof tilt, your environment and your electricity rate, and see whether the electricity recovered covers the bill.
Roughly 900 in the UK, 1000 in Germany, 1400 to 1600 in Spain, Australia or California.
A paid clean does not pay for itself. It recovers about 3 of electricity against a 200 bill, so you are down 197. Break-even would need the price to fall to 3. Rain is doing this job for free.
Rain does the cleaning for free. Published field studies in northern Europe and the north-eastern US repeatedly find annual soiling losses of 1 to 3%, which is inside the noise of a normal year.
How this is calculated, and what it deliberately leaves out
- Loss starts from a published annual figure for the environment at a 30 degree reference tilt, then scales by tilt — shallow roofs self-clean far less.
- A clean recovers only the share of the year before the next natural wash, not the whole annual loss. Dirt starts accumulating the next day.
- Bird droppings and leaf litter are not modelled. They are localised rather than uniform, and a single dropping across a cell can cost more output than a season of dust by forcing a bypass diode.
- No allowance for panel damage or a fall. On a steep or high roof the safety case usually decides this before the arithmetic does.
- Losses above roughly 15% a year almost always mean something specific — a nesting site, a construction site next door, a farm track — rather than ordinary dust.
In most temperate homes, the answer is no
That is not a popular thing to publish, but the field studies are consistent: in a climate with regular rain, annual soiling losses sit around 1 to 3 percent. On a typical domestic array that is worth less than a single professional clean, so paying for one is a net loss and rain is doing the job for free.
The exceptions are real though, and the calculator is built to find them rather than to argue a line. Long dry seasons, agricultural dust, coastal salt and traffic soot all push losses to a point where cleaning clearly pays.
Tilt matters more than people expect
A steep panel sheds dirt. A near-flat one holds it, and holds the water that carries it, so the residue dries into a film instead of running off. Between a 5 degree and a 40 degree array in the same street, the shallow one can lose more than twice as much output to the same dust. If you are still at the design stage, that is worth knowing before you choose a mounting system for a flat roof.
If you do clean them yourself
Plain water and a soft brush. Never a pressure washer, which can force water past the frame seal, and never cold water on hot glass, because the thermal shock can crack a cell. Do it early morning or evening while the glass is cool. And if the roof is steep or high, the safety case decides this long before the arithmetic does — a fall costs more than twenty years of soiling.
Related reading
Our solar panel maintenance guide covers the full annual routine, and why cleaning matters goes into the cases where it genuinely does.
Soiling is one of several losses between the datasheet and your meter. The rest are in increasing solar PV yield, and if your output has dropped suddenly rather than gradually, that is a different problem — see how to tell if panels are damaged.