Hi bosh,
this is my first time on here, I have been window cleaning for over 40 years so I must be getting something right as I have a very successful business.
R E pricing solar panels I have been looking at this myself. I think it is like all jobs you have to take all of the elements - Height, degree of difficulty check your insurance to see if you are covered for solar panels, could be a bit expensive if you drop your brush on one, distance travelled, material cost, etc. Lets say you charge £15.00 for a house & it takes you 20 mins if you think you will do solar panels in the same time & you are happy then charge the same price. At the end of the day if you can earn £40 plus per hour then you are not doing to bad. If you have to travel for 30 mins then this will have to be costed into the price. I hope this helps.
Regards
Rick