There’s lots of sites on the internet answering “Yes, you do need to clean your solar panels”. Many of these sites also offer cleaning services – perhaps a potential conflict of interest? Strangely none of these sites give numbers for the performance loss caused by dirt. There are several scientific papers investigating both surface and atmospheric dust effects on solar panels but a quick scan doesn’t show much consensus plus many of them are undertaken in dusty regions – not the UK.

Other sites suggest that as long as the panels are sloping at more than 5, 10, 20 degrees then rain does a decent job of cleaning the panels of dust. This is what the manufacturers of our panels have to say:

If your panels are covered in lots of bird droppings which rain isn’t great at clearing then yes they need cleaning! The above REC document goes into lots more detail and includes this pic of panels subjected to dustfall – no one is going to argue these panels need cleaning.

We have nearly three years worth of figures from our solar panels and can’t see any evidence of decline – could just be difficult to spot with the natural variability in the amount of sun – the super sunny first lockdown in Mar, Apr, May 2020 dominates the numbers. Don’t forget the performance of panels declines as they age – our REC panels are warrantied to decline by no more than 0.7% per year for 24 years – ending up at 80.7% of their original power after 25 years.

Let’s try another approach – if there is degradation what is it costing? Most production is in summer – Apr- September. In summer we use about 87% of the solar production – charging EV and battery, heating hot water and general consumption. If cleaning boosts performance then more will be exported – it won’t affect what we use.

Actual solar production Apr- Sep 2022 3019 kWh

Actual export Apr- Sep 2022 381 kWh

Actual solar use Apr Sept – 2022 2638 kWh

Let’s assume our panels have degraded by 5% due to not being cleaned

Potential (clean) production 3019/.95 = 3177 kWh

Potential clean export 3177 – 2638 = 539 kWh

Extra export due to cleaning 539 – 381 = 158 kWh

Octopus pay us 4.1 p per unit for power exported so the potential additional export from cleaning is worth around £6.50! Not completely happy that the above thinking is 100% correct – we probably would use some of the additional generation so saving could be more but don’t see it covering the cleaning cost. We’ll keep and eye on the yearly output – if there’s signs of it falling then give cleaning a go.

These are our back of the envelope calculations – yours will almost certainly vary – but at least try to get a feel for things before forking out on cleaning. Maybe cleaning could improve your solar production by a few percent but is it cost effective?