Ramez Naam has an opinion, backed up by some reasonable estimates:
For most of the US, this battery isn’t quite cheap enough. But it’s in the right ballpark. And that means a lot. Net Metering plans in the US are filling up. California’s may be full by the end of 2016 or 2017, modulo additional legal changes. That would severely impact the economics of solar. But another factor of 2 price reduction in storage would make it cheap enough that, as Net Metering plans fill up or are reduced around the country, the battery would allow solar owners to save power for the evening or night-time hours in a cost effective way.
That is also a policy tool in debates with utilities. If they see Net Metering reductions as a tool to slow rooftop solar, they’ll be forced to confront the fact that solar owners with cheap batteries are less dependent on Net Metering.
That same factor of 2 price reduction would also make batteries effective for day-night electricity cost arbitrage, wherein customers fill up the battery with cheap grid power at night, and use stored battery power instead of the grid during the day. In California, where there’s a 19 cent gap between middle of the night power and peak-of-day power, those economics look very attractive.
And the cost of batteries is plunging fast. Tesla will get that 2x price reduction within 3-5 years, if not faster.
Read the whole thing, and note the discussion of India too.