@david999 ... just water, David, or do you add anything to it ?

When were your panels installed please?

I put some washing up liquid in when I clean mine, then rinse off with clean water.  It takes quite a bit to clean them I find, the grime is well stuck on!  Installed 2011, cleaned about twice a year when I notice that they look dusty.  I use a hose and a broom.

I have a near worst case scenario with 10 out of 16 panels at an elevation of only 15 degrees.  Rain only just washes stuff off and of course in winter with the sun low in the sky the scattering effect of any dust is elevated.  Panels on a sloping roof are less susceptible. 

@colinc my panels were installed two years ago and I clean them twice a year, but only because I have easy access.  I use water initially with hand soap, I’m sure washing liquid has salt in it and saline and electricity not good.  I then us glass cleaner with a soft cloth.  I am aware of thermal shock so be careful in warm weather and hot panels.  I read on here I’m sure of a bloke getting a shock from the panels , and at height not a good outcome.  Ladders is not an option, get a window cleaner to go them.

Posted by: @david999

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 I read on here I’m sure of a bloke getting a shock from the panels , and at height not a good outcome.

Best done when its not sunny!

My experiences bear out what @jamespa said about slope making a difference. Our roof has about a 25 degree pitch and so rain washes off quite easily. As a result, I've never cleaned them since they were installed about 5 years ago. My total generated in 2022 was 4.8MW and 2025 actually increased on that with just as smidge under 5MW. Given I'd expect a certain amount of degradation with age, that looks to me like pretty definite evidence that my panels on my roof don't need to be cleaned other than for cosmetic reasons. With a shallower slope, it might well be different.

Interesting perspectives.  I'm definitely not climbing on a roof so I'll see if I can reach them from a step ladder with a long washing pole and rinse them off.  I don't think they are particularly dirty but it's hard to tell from the ground with binoculars!  I don't have data for May last year but I don't think the generation has reduced.  It's a bit hard to tell as my export limit is 3.68kWh, the house has a background load of 0.5kW and my clipping strategy works with filling the battery with excess solar.

@david999 Thanks, I have read that some detergents are not adviseable. Salt is an abrasive, although saline, as used medically, has a very low % by volume and is considered non-abrasive. Obviously that would be expensive !

We have steep pitched roofs, according to our installer. He suggested to just let Nature do its thing for a year or two.

After the long dry spell through April, gulls had also been doing their thing; viz. target practise. However, after a couple of downpours last weekend the panels look good as new; albeit only 5mths since being installed.

Our 21 panel array (8.1 kWp.) is arranged over four distinct areas / orientations / inclinations. The five panels on our house pitched roof are out of reach and not accessible to any sane observer. There are a further 4 panels on a flat roof inclined at 15 degrees and again, inaccessible to all with life preservation in mind.

Two panels are on a single story pitched garage roof and the remaining ten sit in the garden inclined at 15 degrees. The latter 12 panels are lovingly washed perhaps twice a year with rainwater in a bucket and with an extendable glass cleaning mop/scraper. Those in the garden have the distinct advantage of being accessible from the sides and above. No detergent is ever used and rainwater is I am told, preferable to tap water and lower in lime etc. The first mentioned 9 panels are too high up for me to see any dirt on them and as a pitched roof is used for the first 5, I have turned my 1.75 blind eyes to the problem. 😉 The actual solar yield has actually increased over the last four years or so! Rewards, Toodles.

@toodles Good to know.  I will give it a go with my telescopic pole and if it works great.  I don't know what the cost is per panel, but if it comes to, say, £200 for the job (£10 a panel) that's equivalent to 714kW of peak energy or 1.67MW of export to pay for it.