Okay, here is my ideal system to eliminate fossil fuel and maximize the use of the sun for heat and hot water: solar hot water panels on the roof with a photovoltaic pump. A marathon 80 gallon hot water heater in the basement. This is an expensive, well made ard very well insulated electric hot water heater with a lifetime warranty and a good reputation. Beside this I would put 700+ gallon round water storage tank from Tarm to provide a heat dump and heat storage. This would allow me to go many days with no sun and still have hot water. Alternatively I could build a storage tank out of insulated concrete forms and a pond liner. ( the tarm system uses a pond liner) Into this tank goes several large coily loops of copper for heat exchange. The water in the tank is just a heat storage medium, not drinking water. I could then run a loop off this storage tank to radiant heat where I wanted it, a loop for domestic hot water, and I could even use a garage slab or a hot tub as additional heat dump capacity if the panels on the roof are collecting too much heat. The large storage tank gives me a large float time for when the sun is not out for many days and should allow me to get 100% of my hot water from the sun. It also should allow me to have fewer panels on the roof. The electric element on the Marathon is a last resort to add heat to the hot water if necessary. I am not an engineer with the skills to calculate whether and how well this system would work but hopefully I will get a client soon who is willing to look into it.