One of my customers is a solar panel installer, so I thought I'd ask his advice on cleaning them etc. He told me that the panels need switching off in 2 places and tested before and after the cleans to make sure they are working correctly before and after the job. Or the customer could put the onus on you should there be a fault occur. Bearing in mind the price of replacing a faulty panel and the price of erecting scaffolding is very costly. What precautions do you take if any and do you any of you follow this route bearing in mind to have a qualified tester present would be approximately £50.