Ah, I see your source (and the origin of the energy-power confusions) is the Trehugger article. That one however is sourced to the article Map Shows New York City Rooftops' Potential for Solar Power in the New York Times, which didn't confuse the terms:

Map Shows New York City Rooftops' Potential for Solar Power - NYTimes.com

Over all, the images show that 66.4 percent of the city's buildings have roof space suitable for solar panels, said the CUNY team, which developed the map in partnership with the city and the federal Department of Energy. The rooftops could generate up to 5,847 megawatts from hundreds of thousands of buildings, the team said, compared with the negligible 6.5 megawatts yielded now from about 400 installations.

At those output levels, the panels could meet 49.7 percent of the current estimated daytime peak demand and about 14 percent of the city's total annual electricity use, the officials said. The figures consider typical weather conditions.

...Nationwide, the installed solar capacity is just 2,300 megawatts, less than half the rooftop potential of New York City.

_{*Lunatic*, n.
One whose delusions are out of fashion.}