My father-in-law showed me this a few years ago. Due to language barriers, I didn't understand him at first. I was VERY surprised at the efficiency of the storage... of course that is after it is built and powered.

That being said, for places that can't count on reliable sun/wind/water for renewables, this is a very good idea.

Now if they just made the whole thing look like a giant tree I'd be completely on board. I mean, how cool would that be?