The rising popularity of tankless water heaters as well as mod/con boilers, though arguably not merited from an economic standpoint, seems to indicate a desire on many levels for a modern substitute to generations old American tank type hot water technology. That said, I'm surprised we don't see more discussion, on this site at least, of solar hot water systems, especially from those plumbers plying their craft in the lower latitude "Sun Belt" of the US. Lots of sun and low ∆T's seem ideal for solar hot water. Some of the new solar systems seem attractive as far north as my 37.5º location. I've even got a customer whose had me sub meter his water heater just to see how much gas it consumes to get an idea of potential savings.