Here is the clearest justification for energy storage we've yet seen, from Citi's Jason Channell: Solar generates its electricity when most households are empty or have limited demand. Saving that electricity for later would dramatically offset consumption prices. He continues: "The potentially greater value is in terms of avoided capacity payments, and the grid stability which storage could provide. If storage could be combined with smart metering and demand response, we could conceivably move to a situation where load is managed (i.e., by dishwashers etc. being turned on automatically when demand was lowest and vice versa) and supply is being managed by storage. This could significantly reduce the amount of stranded capacity and hence wasted cost on an electricity system, as well as improve its reliability."
Insane stat: In the first quarter of 2014, solar and wind combined generated 28% of German electricity.
Relevant graphic: Here is the breakdown of the potential market size for different storage technologies.