I believe Tesla decided to generate all the power in one place--to cluster the panels together in an ideal location. This makes much more sense than spreading panels all over the country. They can be easily maintained, can be placed in an ideal location for solar, require less grid-tie hardware, and can be protected from vandals.
They said that they'll eventually be generating the equivalent power used by the Superchargers, and that's certainly feasible...although I think their expense priorities are elsewhere right now--and rightly so.