you do know the 0% has been added into the cost of the deal, its never free.I'd check out Octopus and Ovo Energy. I went with Ovo over my local installers because I wanted a company that I knew would be around, and because they offered a 0% 3 year financing deal.
2 ways 0% makes sense, buying on a 0% 24 month credit card or getting a 0% green loan on your mortgage.
I looked at Octo and all the nationals and they were way too expensive for the kit you get