We're often asked whether you should clean your solar panels so I was interested to see two very different methods of keeping them in tip top generating condition at the Solar Power UK exhibition last week.
Anything that blocks the light transmission to your solar PV (or thermal) panels has the potential to lower the performance – and the financial return you get from them. How great the effect and how much you need to clean them will vary according to your local environment.
I live in rural Devon, where it has seems to have rained constantly (and hard) all this year, so mine are probably pretty clean. However, tests in farmyards have demonstrated that a regular cleaning can make a significant difference to the output of a system. Similarly the salt in seaside locations, or grime from busy roads or railways, can decrease output.
The first option is the obvious one – to wash them. But it's not as simple as that. According to Ionic Solar Cleaning Systems tap water doesn't do the job. It leaves deposits of salt and minerals on the panels which also reduce the performance. They showed me an example of a panel where half had been washed with tap water and the other half with their ultra purified water, and there was a definite difference.
Problems with birds on your solar panels? Read YouGen's blog on how to deal with this issue.
The Ionic Reach & Wash System consists of a soft-bristled brush with jets of purified water. The panels are then left to dry. There are various systems available ranging from a residential kit to industrial sized ones. Due to economies of scale, residential kits end up much more expensive per clean than the larger systems, so it may be more cost effective for people with small scale solar PV systems to find an installer to clean them, rather than invest in the kit themselves. This may not be the case if you have a solar field.
As every location is different, there is no one answer to the question about how often panels should be cleaned. Ionic recommend monitoring the output of your panels, and if the efficiency drops that's an indication that you might need to give them a clean.
The basic residential kit starts at (ex VAT):
purification system: £69.95
The second option doesn't involve washing at all. Instead SmartShield is a non-stick coating which is applied to the solar panels and stops the build up of any dirt. I was intrigued to learn that it also work on the inside of glass shower cubicles to keep the limescale build up at bay, and on the inside of an oven – I'm tempted to try it!
It's chemically inert and doesn't harm the environment, and is quick to apply. An application has a 10 year warranty, and data from Romag shows that when two identical arrays were tested, the one with SmartShield gave a 9.8% better yield than the untreated one. Neither panel was cleaned during the test, but it is recommended that you also clean the panels to optimise performance.
The cost of SmartShield is around £15-20 per panel, so a 4kW system will cost between £240 and £320. This includes the application of the coating.
As with the Ionic system, I wasn't just asked to believe the sales patter. They demonstrated it with a glass dome filled with dirty water. The bottom half was coated with SmartShield and, as you can see in the picture, the dirt didn't stick to it.
Both companies can put you in touch with installers in your area who can supply their product.