San Francisco passed legislation this week that will require all new buildings under 10 stories tall to be outfitted with solar panels. The California city will become the largest municipality in the U.S. with such a mandate. "By increasing our use of solar power, San Francisco is once again leading the nation in the fight against climate change and the reduction of our reliance on fossil fuels," Scott Wiener, the city supervisor who introduced the legislation, said. The legislation makes explicit references to combating climate change and expresses concern about the city's future. Smaller California cities already have similar laws in place. Beginning in 2017, all new San Francisco buildings with 10 or fewer floors must have either solar photovoltaic or solar water panels. The measure builds on a California law that mandates new buildings have at least 15 percent of their roof space exposed to sunshine for solar panel use in the future.