You dont need to clean your solar panels.
However if you dont clean them, over time they will lose efficiency.
How much ?
You could be losing anywhere from 10-25 % depending on how long it has been building up on the surface.
How often ?
Between 6 to 12 months depending on environmental factors.
Getting your solar panels cleaned will make sure you get the most savings on your power bill putting more money in your pocket.
Getting an experienced professional to do it will help to get the best results and solve the problem of difficult access and safety.