Re water heating-
first, figure out how much you currently spend on heating water. That's the theoretical upper limit on savings. Secondly, consider how you currently heat water; if you're not heating with electricity, you may end up losing money with a solar water heater--the backup for the solar panels is invariably an electric heater (low standby losses) which is damned expensive to run.

Photovoltaics make sense if you can get some government subsidies. We've installed photovoltaic panels here in New Jersey, but the state is very supportive in terms of subsidies and credits for power generated. Even so, it's only marginally cost-effective (but should be more so when electric rates go up, as they're bound to.)