As a step towards reaching its goal of 100 percent renewable energy by 2020, the City of San Francisco passed landmark legislation last week that requires all new buildings under 10 stories to have rooftop solar panels.  Some smaller cities in California already have such laws, but San Francisco is the first major city in the U.S. to mandate this new requirement.  Starting next January all new buildings with 10 floors or fewer must have either solar PV or solar thermal panels installed. This new rule builds on existing state law that requires all new buildings to have at least 15% of their roof space exposed to sunshine, in order to allow for solar panel installation.  Read More in the Guardian>