You can use heat pumps to heat water... in fact, it's a very good form of energy storage for off-grid homes in cold climates: You put in a 100 gallon water ta

You can use heat pumps to heat water... in fact, it's a very good form of energy storage for off-grid homes in cold climates: You put in a 100 gallon water tank, use a heat pump water heater to bring it up to 150deg F when the sun is shining. You use fail safe mixing valves to provide hot water for the taps/showers (which greatly increases the effective size of the hot tank), and the hot water can be used more directly for heating. Retrofits can be hard though, since the water loop may be designed for a rather high temp... though there are some heatpumps that get to rather high temps.