San Diego Mayor Kevin Faulconer is moving ahead with the city’s plans to buy power from someone other than San Diego Gas & Electric, but he’s given the power company a chance to make its case to preserve its monopoly. The city has an ambitious plan to fight climate change. It says 100 percent of electricity sold within city limits must come from renewable sources by 2035. Right now, SDG&E is the greenest major power company in the state but still gets most of its power by burning natural gas.