Second to last paragraph of this article. Also note they still expect Panasonic to make the batteries or be a joint venture partner in the gigafactory. ZEN in Japan, home of Pansonic, ya gotta love it. Perfect storm on the demand side.
http://www.forbes.com/sites/uciliawang/2014/05/07/tesla-makes-fast-move-to-build-two-giant-battery-factories-simultaneously/