For Oakland (Calif.) Mayor Jerry Brown, renewable energy has always been a no brainer. As governor of California during the early 1980s, he lobbied hard for wind farms. So last June, after deregulation of the state's electric-power industry gave consumers, for the first time, a choice to buy "green power," Brown jumped right on the bandwagon. Now, towns, businesses and individual homeowners in California are free to buy electricity generated by solar arrays, wind farms, geothermal installations, and biomass fuels.