Exists, I forget the name of the company though. I distinctly remember a pic from a trade show where it looked like you had to wade through car batteries, they had that many.
But I didn't think they had implemented it perfectly -- they used it to generate A/C, and then you know 90% of the internal power supplies converted it back to DC -- why didn't they just run it at DC to begin with? Strikes me as more efficient, though I could be wrong.