Energy officials told lawmakers Wednesday that studies are underway to determine how much generation capacity is needed in Southern California to replace the plant's output, and which sources would be the best options.
An official with Southern California Edison, which owns San Onofre, said the utility's greenhouse emissions rose last year after the plant shut down due to safety and equipment issues.
In 2012, 30 percent of the utility's electricity came from carbon-free resources, said David Mead, senior vice president for transmission and distribution planning. That's down from 2011, when San Onofre was still running and 50 percent of the utility's electricity came from carbon-free nuclear, hydroelectric and renewable sources, Mead said.
The utility has increased its use of natural gas and other fuels to replace the plant's power generation, Mead said.
Lawmakers expressed concerns about the long-term effects of replacing nuclear power with sources like coal or natural gas. Utility officials said they were working to meet renewable energy benchmarks and increase efficiency at other plant, but they acknowledged that the plant's absence will be felt as California attempts to meet its emission goals.
"There's no doubt that loss of (the plant) is going to have a dramatic impact in the region," said Jim Avery, senior vice president of power supply for San Diego Gas & Electric.
San Onofre was responsible for one-fifth of the electricity used by San Diego County and southern Orange County, powering 1.4 million homes.
Mead and Avery spoke at a state Capitol hearing of the Senate Energy, Utilities and Communications Committee. Also testifying were the chief executive of the California Independent System Operator, which manages the state's power grid, and members of the California Energy Commission and Public Utilities Commission.
Wednesday's hearing was the first of three scheduled to discuss the consequences of shutting down the San Onofre plant. Committee hearings on Aug. 13 and Sept. 24 will focus on the plant's decommissioning.
Edison announced June 7 that it was permanently closing San Onofre. Its twin reactors hadn't produced electricity since January 2012 after a small radiation leak led to the discovery of damage to hundreds of tubes that carry radioactive water in nearly new steam generators. The problems arose after a $670 million upgrade to the plant.
Edison is reducing the plant's staff from 1,500 to about 600 by September. Some employees could be hired at other Edison facilities, but Mead said the number of positions has not been determined.
Officials noted that the plant closure has affected the power grid. Units at a natural gas power plant that had been shut down in Huntington Beach have been reconfigured and came back online in June.
Democratic Sen. Alex Padilla of Los Angeles, the committee's chairman, said the plant's closure poses "a tremendous challenge."
"For starters, normally planning and generating 2,000 megawatts of generation would take several years," said Padilla, who has a mechanical engineering degree from Massachusetts Institute of Technology. "But in this instance, we must expedite those processes and work together to make sure that we keep the lights on."