Short answer
Many solar panels benefit from occasional cleaning, because rain does not always remove bird droppings, lichen and traffic grime. Whether yours need it depends on where they are: panels near trees, busy roads, the coast or popular bird perches, and panels at a low pitch, tend to get dirtier. The best way to tell is to look at them from the ground and compare your system's output with similar weather in the past.
Don't panels clean themselves in the rain?
Rain does wash off some loose dust, particularly on steeply pitched panels. But it is less effective on dirt that sticks. Bird droppings dry hard and sit in one place, lichen grows into a crust, and the oily film from traffic and chimneys tends to cling rather than rinse away. Rainwater itself can leave a light layer of dirt as it dries, especially along the bottom edge of each panel where water collects.
So rain helps, but on many homes it does not keep panels fully clear on its own.
What makes solar panels dirty
Bird droppings are the most common problem, because a single dropping covers part of a panel completely. Panels below a favourite perch, a TV aerial or a chimney often see more.
Trees add leaves, pollen, sap and seeds, and shade the panels so they stay damp, which can encourage moss and lichen. Homes near busy roads, farmland, building work or industrial sites pick up more dust and grime. Near the coast, salt spray can leave a film. And panels fitted at a shallow angle let water and dirt sit on the surface rather than running off.
How to check whether your panels need cleaning
- Look at the panels from the ground, with binoculars if needed, ideally on a bright day. Note droppings, green or grey patches, leaves and a dirty band along the bottom edge.
- Open your monitoring app, inverter display or generation meter and look at recent output.
- Compare it with a similar period in a previous year, or with days of similar weather, rather than with yesterday. Output naturally varies with season, cloud and temperature.
- If output seems lower than you would expect for the conditions and you can see dirt, cleaning may help.
- If output has dropped suddenly or sharply, especially without visible dirt, contact your installer, as it could be a fault rather than dirt.
How often should solar panels be cleaned?
There is no single answer. Panels on an open site with a steep pitch may need very little attention, while panels near trees, roads or the coast, or with a regular bird problem, need more. One or two visits a year suits many homes, but a recurring problem with droppings or debris is worth bearing in mind when you decide.
Checking twice a year from the ground, for example in spring and after autumn leaf fall, is a sensible habit, and it will show you how quickly your panels get dirty.
Don't expect miracles from cleaning
Cleaning removes material that blocks sunlight. It does not repair a fault, change how the system was installed or make up for shading from trees and buildings. If clean panels still seem to produce less than they should, talk to your installer.
If you decide to clean panels yourself, our guide on how to clean solar panels safely explains what to do and what to avoid. The short version: only clean panels you can reach from the ground, and never climb onto a roof.
When to call a professional
Call a professional if your panels are on a roof you cannot reach safely from the ground, if they are visibly dirty with droppings or lichen, or if you would simply rather not handle it yourself. For a sudden drop in output, or any damage, contact your installer first.
We clean solar panels on house roofs, garages, outbuildings and commercial rooftops using pure water and soft brushes that leave no residue. Regular schedules are available, and we do not promise a fixed increase in output, because removing dirt is not a measurement of your installation's performance.
Rather have it done for you?
Pure-water cleaning to keep panels clear of dirt and droppings. Family-run by Jason and Lucas Prior, covering south Essex.
Frequently asked questions
Do solar panels really need cleaning?
Many do from time to time. Rain clears loose dust, but bird droppings, lichen and traffic grime often stay put, particularly on panels near trees, roads or the coast and those at a low pitch.
How often should solar panels be cleaned?
It depends on the location. One or two visits a year suits many homes, while panels with a regular bird or tree problem may need more attention. A look from the ground will tell you.
How can I tell if my solar panels are dirty?
Look at them from the ground for droppings, patches and a dirty bottom edge, and compare your system's output with similar weather in a previous year using your monitoring app or meter.
Related guides
- How to clean solar panels: safe cleaning for ground-level solar panels, and why roof-mounted arrays are best left to a professional.
- What affects the cost of solar panel cleaning: how the number of panels, roof height, pitch, access, droppings, lichen and regular visits change a solar panel cleaning quote.