MILPITAS -- Gov. Jerry Brown on Tuesday signed legislation requiring California utilities to get one-third of their power from renewable sources, giving the state the most aggressive alternative energy mandate in the U.S.

California utilities and other electricity providers have until the end of 2020 to draw 33 percent of their power from solar panels, windmills and other renewable sources. Brown signed the bill at a solar panel manufacturing plant near San Jose.

"There are people who think we can drill our way to happiness and prosperity," the Democratic governor told hundreds of plant workers and other supporters gathered to witness the signing. "Instead of just taking oil from thousands of miles away, we're taking the sun and converting it."

Previous California law required utilities to get 20 percent of their power from renewable sources. Supporters of the higher standard said it will reassure investors and keep money flowing to develop alternative energy sources. They say that will lead to cleaner air and job growth in the clean-energy sector.

U.S. Energy Secretary Steven Chu also attended the bill signing ceremony at the SunPower (SPWRA)-Flextronics solar manufacturing plant in the San Francisco Bay area city of Milpitas.

Critics of the legislation said sticking with traditional energy sources such as coal and natural gas would be cheaper, keeping costs down for business and residential ratepayers. Business groups point to estimates that the higher standard could drive up electricity costs for California ratepayers by more than 7 percent, despite language in the legislation to limit cost increases.

"Industry in California already pays electricity rates about 50 percent higher than the rest of the country," said Gino DiCaro, spokesman for the California Manufacturers and Technology Association. "With 33 percent, those rates are going to go up even more."