Hi nick.
What no one has mentioned is the nature, past and present circumstances of your marketplace.
Some residential clients had the panels put in for free. These are the ones you can charge more money to, as they have not had the initial outlay of installation. They don't have money to re-coup, but want the maximum yield from their panels.
The rest of the marketplace has paid for their panels. They are generally number crunchers. They know how much their panels cost, know how much money they will make annually and how much margin they have left for monitoring, maintenance and cleaning. They will also know which FiT they are on.
To get each client and maximise your financial benefit at the same time, you must know all the figures for the above. This is not saying if you do not know the above, you will not get the job. It means that if you and say "Yes, 12 panels is £30." And I go and ask about how long they have been installed, which FiT they are on, do they monitor their output, what are they hoping to achieve by having their panels cleaned, what plans do they have for future maintenance etc, I can charge maybe £40 and they will still go with me because I have bought their confidence as well as sold my service to them.
Getting people's confidence in such a new industry is very important. Whilst all the above info is not essential on every residential job, it is invaluable when pricing commercial jobs.
At the moment, our conversion rate from enquiry to cleaning is between 8-9 out of 10. It is not because we are the cheapest, we rarely are. It is because we know more and sell the service in a better way.
Don't focus just on price. It pays to spend time number crunching and reading about industry trends as a whole. If this is a service you are seriously looking to branch into, invest your time doing the research and you will be better placed than your lesser informed, cheaper competition.
If anyone has benefitted by the above, please let me know. If anyone wants to to fire off, I would like to know that too!