In 2001, voters in the city of San Francisco approved Propositions B and H, which directed the city to develop renewable energy resources for city-owned buildings. San Francisco now has its first results of that effort -- 30,000 square feet of photovoltaic panels on the roof of the Moscone Convention Center, across the street from the SF Museum of Modern Art. The 675 kilowatts of power the panels can produce at peak are not quite enough to meet the full electricity needs of the Moscone Center, but (coupled with efficiency improvements in the building) they're enough to help the facility save $210,000 annually.
According to Metropolis magazine, San Francisco is the first of what promises to be many cities pushing solar:
According to Adam Browning of Vote Solar, a San Francisco-based advocacy group, measures similar to San Franciscos are appearing across the country: on January 29, New Mexico passed a solar bond for its government buildings; New Jersey has what Browning calls a "perfect storm" of legislation in the works; and last December, the city of Austin, Texas unveiled a $5/watt rebate for solar energy, as well as passed legislation mandating that the city produce 20% of its energy needs from renewable sources by 2020.
There's a popular enviro-meme that nearly all of America's electrical needs could be met by installing solar on city rooftops. It will be very interesting to see the real-world result of urban solar installations. As the cost of solar continues to drop, we'll see more and more locales eager to cut their power bills in this way.