We had our installation done via ZLC energy in 2012 - we had got quotes from 3 separate outfits and ZLC, although not the cheapest, was most forthcoming in answering questions etc. We also managed to get a slightly larger array with their help.
We didn't enquire further into how the warranty was backed.
We found ZLC to be helpful and they worked hard to sort out an issue that we had regarding Western Power and a local transformer that kept tripping out.
We're in West Cornwall