In the communities in my neighborhood the talk is about having the various HOA's install solar and the solar energy companies put it on a lease.
The cost model they're looking at is net zero to the HOA and people who live in the homes since the net energy savings goes to the solar install company until the install + interest is repaid. It's an interesting model, and makes much more sense than having to pre-pay the entire install up front (which is cost-prohibitive for most people).
first of all lets post some common sense you are not going to save $100 on a 12,000.00 water heater solar installation. You will have to install a solar unit to supply more than just one unit which will cost a lot more. The only way one could possibly make it a prudent investment is getting a substantial credit with both the govt tax incentives and the providing power company, with out both of you are just being a good citizen for clean energy.