For long term energy storage batteries are not ideal. Their costs increase linearly with time of storage and amount of storage. Peak shaving is an OK use for them, though.
What percentage of our global storage needs do you believe are "long term" in this dichotomy? Is this at the "electric cars can't do my daily commute" or "electric cars can't tow my boat 600 miles without stopping, once a year" stage? Seems like most of the world just needs solar to last until the next day with a decent chunk of that power needed immediately after the sun sets and any wind power available could get s…
Long term = weeks to seasonal
Batteries, especially that sort of cheaper battery, would be great for diurnal load leveling.
Long term storage is probably more hydrogen and mass thermal storage. The tradeoff would be capital cost per unit stored energy vs. efficiency.
Storage competes with and complements two other approaches: overinstallation of generation capacity w. curtailment, and dispatchable demand.
Curtailment involves installing more wind and PV than you need, and curtailing its output when supply > demand. A study in Minnesota found that this was cheaper than adding storage up to about 70% of the electrical power supply. Of course this creates dirt-cheap power during the curtailed periods that people can find use for (industrial thermal storage, production of hydrogen in low capital cost membraneless electrolyzers).
Dispatchable demand would involve redesign of industrial processes to operate in fits and starts. For example, today's aluminum cells do not respond well to inconstant power sources (their either freeze up or overheat and damage the lining). This was fine when the cheapest power sources were baseload sources. But perhaps an aluminum technology could be developed that would be more forgiving of variation and outages, to exploit the new situation where intermittent power is becoming the cheapest.
Of course, another approach is to move those industrial processes down close to the equator, where there is little seasonal variation in insolation. High latitude countries may become industrially disadvantaged in a renewable powered world.