Best household energy storage
By selling the electricity, it can  be stored as money because the fungibility of money allows it to be exchanged for electricity. Furthermore, this is likely to be competitively efficient with various physical storage equipment. In addition money can be converted into reduced demand by allocating it toward more efficient load side equipment.

The goal is really sustained access to a particular level electrical service. Generating and storing electrical power on site are just two possible strategies for maintaining such access.