On the left is a (modified) aerial of Kramer Junction (Google Earth link) solar electric generating station in Southern California; on the right is an aerial of Central Park (GE link, again) in Manhattan.
According to Nova's "Saved by the Sun," Kramer Junction powers approximately 150,000 homes, or the equivalent of just under two Central Parks at Manhattan's population density of 66,940 people per square mile. Or to put it another way, turning Central Park into a solar electric generating station, like Kramer Junction (assuming, magically, the same solar conditions as the Mojave Desert), would power approximately 8-10% of Manhattan's households. While I don't think this comparison deflates the solar potential, it helps illustrate the enormous areas required, with current technologies, to achieve a more suitable way of creating energy than burning fossil fuels. Of course, this comparison also ignores demand (what I see as a -- if not the -- key to the current energy "crisis"), in which case the 150,000 might actually increase in Manhattan's denser and more compact living conditions.