San Francisco Chronicle: When it comes to renewable power, Californians tend to think big. Big wind farms sprawl across our hills. Big solar power plants will soon blanket acres of desert. Big new power lines will bring that electricity to our cities. This, Bill Powers insists, is exactly the wrong approach. He wants us to think small. Powers, an engineer and energy consultant, argues that California should cover every available rooftop with photovoltaic solar panels, especially commercial …