I suggest your friend:
Does their research so they aren't told bull**** when they have a survey
Doesn't touch anyone using a salesman with a bargepole
Uses someone within a 50 mile radius in case anything goes wrong at a later date
Uses someone who knows that Sanyo panels have been Panasonic for almost 3 years now and understands that panels and inverters don't automatically go together but must be designed according to the home's specific requirements.
Doesn't use someone who sub-contracts the work, we're picking up a lot of repair work from this set-up at the minute. Host company goes bust, subbies can't be found anywhere and customer is left with cost of repairs.
Be patient and find the right installer for you. It's better to wait and find the right installer than to get a poor installation because you've been in a rush to get it in before FIT reduces.
Don't use anyone that doesn't use scaffolding - you may be liable if there's an accident.
You'll be lucky to find anyone to install if you've bought direct as well as it costing you more to do it because of vat (as Yellowvanman says) apart from which you're asking an installer to become responsible for a system that he/she hasn't designed.
Tell your mate to take his/her time and do it properly and it'll be well worth it. Cut corners cost money, this isn't one of those jobs you can save a bit of cash on - believe me, our margins are very low these days.
It's like anything the more you understand about it the more you have the ability to make an informed decision. The information is readily available.
