Hi Alan. Many thanks for sharing your thoughts and experiences.
I agree I was lucky to get my panels cleaned for £60. Obviously if you have to pay for scaffolding, it will cost considerably more. Of course, as I said in my article, it might not be necessary to go on the roof if you/they use a long-pole system, as deployed by many window cleaners. I suspect this wouldn’t be quite as effective as cleaning the panels by hand, but it would be a lot better than nothing at all.
My feeling is that a lot depends on your location, e.g. whether you have a lot of trees nearby (as I do). I think the best strategy is to monitor your panels’ output year on year, and if you notice generation falling, consider having them cleaned. But yes, if you are able to compare your panels’ output with that of other installations in your area, that would be informative as well. Even so, every installation is different, e.g. I have a split-array as my house faces north-south rather than east-west. So you probably wouldn’t be comparing like with like, even in the same street. In addition, it might not be easy to access data on how much energy your neighbours’ systems are producing. Thank you for sharing yours, though!
I do agree that cleaning panels annually may not be necessary or cost-effective, and I certainly wouldn’t suggest doing it that often without very good reason.

Hi Nick, and thanks for an interesting article. I just wanted to say that it doesn’t seem to be a universal truth that it’s worth getting your panels cleaned. I’ve never had my panels cleaned, yet they don’t show a too dissimilar pattern to your’s, though I should confess that my yield for 2019 is the one year that does have a relatively low yield compared to your’s. The other difference between our systems is that I don’t have any overhanging trees. So, as you mentioned in your article, it may be that general dust gets washed off by rain but bird mess doesn’t. Also, you were very lucky to get your’s done for £60. I’m guessing it would be a lot more of it wasn’t for the pre-erected scaffold.
Despite not cleaning my panels, 2020 was my second highest yield to date and was only a little short of being a record year. If you’re interested in comparing, my output is automatically logged and stored on pvoutput.org. My system name on there is StratOGen.
I’m not saying that it isn’t worth paying to have them cleaned, I just think it’s important to compare your output with a similar system in your area before forking out on a regular basis.

Thanks, Rhian. Yes, the difference is remarkable, isn’t it? Of course, if you get panels now the amount you get paid under the Smart Export Guarantee (the successor to FIT) will be significantly lower than the FIT payments I receive. Even so, it will be well worth cleaning them every so often, especially if you can see that the amount of power generated is going down.

Thanks, Caz. Yes, it was £60 very well spent!