To retrofit existing is still very cost prohibitive. Your best bet is to start new. For example instead of buying roofing for a new house you could pay a little more and buy some of the solar panel shingles available. The cost to replace an existing roof with them is a lot but for a new build you subtract the cost putting normal roofing on and it gets better.
Then design the house smarter and eliminate all the waste you can and you can get the price down reasonable.
If only I could find reasonbly price land in central OH where I could build.