If you can put the hot water heater in conditioned space, how about a tank (50 gal? 80 gal?) electric HWH on a day night timer, heating the water once a day during the early hours of the morning still within the night rate. If you have a well insulated tank, or you insulate a cheaper tank, with your low usage rates you should have plenty of hot water all day. On those rare days you need more, you can manually switch the HWH on until the tank heats up, then switch it off. This way you get minimal standby losses, are not heating water you don't need, always have hot water, are heating it at the night rate, heats the whole tank at least once a day to avoid legionella, and can work fine with solar hot water.
I have had this setup for the last 20 years or so with a 20 plus year old 80 gal Bradford White 240V electric HWH. My entire electric usage at night (house, office building and barn) is 5kwh per day, which includes several items on standby, electric heater in the stock tank, air circulation fan, 2 freezers, refrigerator and all the other bits and pieces that use electric at night. Since I have the tank in conditioned space, I consider the tank heat loss, additional heat for my old leaky house. Of course there is no reason you can't use the same method with a gas system as long as it has electronic ignition, not a standby pilot.
-Rosalinda |