The engineering company CH2M Hill is now joining hands with the U.S. Department of Energy to provide Internet solar maps of 25 American cities, using Google Earth technology to chart the precise solar potential of neighborhoods, literally rooftop by rooftop. The company has just finished mapping all of San Francisco, allowing residents to enter their address and take the solar measure of their own home. "People in San Francisco think we don't have any solar potential,' says Gavin Newsom, the city's deep-green mayor. "But the map shows we have a lot more sun than you'd believe." Time Magazine Source.