Generally solar panel arrays in the UK will not need heavy duty cleaning as they are designed to self-clean in the rain. However, depending on location, they may suffer from a high build-up of dirt, leaves, bird droppings or salt water if near the coast, etc. so cleaning the modules on a regular basis may be required, depending on the amount of soiling. The obvious danger is working at heights therefore we would recommend you hire a professional – window cleaners often offer this service. No abrasive chemicals to be used, warm soapy water is fine.