The nuclear plant between San Diego and Los Angeles, which stopped producing power in January 2012, once generated enough electricity for 1.4 million homes. The unanimous vote by the California Public Utilities Commission opened the way for Southern California Edison and San Diego Gas & Electric to find ways to plug that gap.
Under the order, the utilities must obtain at least part of the power from renewable sources, conservation and storage. Commission President Michael Peevey said he would have preferred electricity that did not include natural gas-fired generation, but it wasn't yet possible to rely only on solar and wind power, customer conservation and other alternative sources.
California has been at the forefront among states in moving away from fossil-fuel generation, but solar, wind and other green energy make up only a fraction of overall production in the state.
Environmentalists say the decision increases the odds of seeing more polluting energy as California seeks to address climate change, but Commissioner Mike Florio said no one in the world has managed to run a complex electricity grid without some fossil-fuel energy to handle unexpected shortages.
Solar production, for example, surges during the day when the sun is shining, then ebbs.
A statement from environmental groups said the decision raises the risk of "new, gas-fired power plants that are often built in low-income communities of color." They said existing gas plants are contributing to ozone pollution that leaves the Los Angeles basin with some of the dirtiest air in the country.
While the decision "does require that a portion of the energy come from renewable sources, the utilities will ultimately get to choose where the bulk of the energy comes from, which could include natural gas," said the statement from the Sierra Club of California, the California Environmental Justice Alliance and Earthjustice.
The vote marked an initial step. The utilities are developing plans to generate or buy the power, which must be submitted to the commission for review.
Mark Nelson, Edison's director of integrated planning and strategy, said the company was planning to buy the power from the market, if needed. The company was earlier permitted to make major power purchases to compensate for older gas plants that are being phased out.
"Some gas is required to keep the system reliable," he said. He said newer, cleaner-burning gas plants are not "inconsistent with cleaning up the environment."
The San Diego utility hasn't finalized its plans for power, but it is expected that at least some of it will come from gas-fired generation.
NRG Energy has proposed a new plant in Carlsbad, near San Diego.
Production at the twin-domed nuclear plant stopped in January 2012, after a small radiation leak led to the discovery of damage to hundreds of virtually new tubes that carry radioactive water. It was closed permanently last year amid a long and costly dispute over whether it was safe to restart.
The plant was a key supplier to California's electric grid.