[phreeza]

This is being done. Power companies have shipping containers full of batteries hooked up to their grids. I have read better stories but the first thing I found googling just now is this http://www.abc.net.au/news/2015-01-07/ausnet-trialling-new-s...

[sehugg]

That's still a pilot program, though. The Wikipedia article has a good summary of various tech and installed systems: http://en.wikipedia.org/wiki/Grid_energy_storage#Batteries