Comment The grid needs storage - not battery storage (Score 4, Informative) 334
There are many ways to 'store' electricity. Batteries are just one.
I rather like this one, a thermal storage solution. Putting air into and out of bladders under deep water is a very simple method, as is moving water up and down hills. Then there are flywheels and fixed volume compressed air storage. (The air bladders above are fixed pressure compressed air storage.) There other thermal storage possibilities, but getting good round trip efficiency is tricky.
There are non-traditional battery techniques too: flow batteries (liquid electrolytes in tanks, adding storage capacity is as easy as adding tanks full of electrolyte) and molten metal batteries (take the idea of aluminium smelting and make it reversible).
All the non-battery alternatives I can think of work at industrial scale, so if you're looking for a household/small business solution, I think that at least for now batteries are it.