Tesla's Superfactory could produce that. In about 12,000 years.
Even if the capacity's excessive by a few orders of magnitude, that's a hell of a lot of battery.
http://physics.ucsd.edu/do-the-math/2011/08/nation-sized-bat...
Assuming 56 kWh Tesla batteries. Half a million battery packs is 28 GWh of total storage capacity. That's the energy equivalent of 16,000 barrels of oil. Assuming a modest 30% Carnot thermal generation efficiency, you'd need 55,000 bbl of oil to actually generate that electricity.
Yeah, batteries are a hard sell.
If each battery is 2m x 3m or 6m in area, the Nation Sized Tesla Battery would cover 36,000 km^2, or an area 190 km on a side. Maybe we'll stack them.
(The actual measurements are smaller, around 1.5 x 2.5 m or so, so that's an overstatement.)
A buddy of mine working at ORNL claims there's interesting stuff on the storage front that's competitive with pumped storage, but can't say just what yet. I'm highly curious myself.
