All good points raised so far but IMO the most significant thing to investigate is the fact that the free PV company takes a lease on your roof for the length of the FIT scheme – 20 years currently.
The issue is that when you come to sell, I have heard that there are mortgage companies that wont give a mortgage on a building that also has a lease on it.
Check out this link for advice from Energy Savings Trust…
EST advice
If you have already decided to go for free PV, then I cant comment on a shade greener as I’ve not dealt with them, however I read an article on the lovemoney website a while ago that said their contract seemed reasonable one.
HTH