Technically almost all homes have a wonderful energy storage system already -- their hot water heater tank. One can imagine a setup where you've got a hot wate

Technically almost all homes have a wonderful energy storage system already -- their hot water heater tank. One can imagine a setup where you've got a hot water tank and a mixing valve that allows you to heat your water up to some very high temperature and then mix that down to "safe" hot water for the house. Have that run in "heat from grid if below this threshold, otherwise conditionally heat with surplus energy if the water's below this temperature"