Generators could remove nearly a quarter of the natural gas-fired generating capacity on the California ISO's grid in 2018 without affecting the reliability of the state's primary transmission system, according to new research from the Union of Concerned Scientists.

In fact, retiring the roughly 5,500 MW at 28 combined-cycle and peaking plants could be "the lowest-cost way to manage the grid" because of the fixed costs required to keep the plants operational, according to the report, released Aug. 7.

The report's envisioned closures, which are identified by location but not by plant name or owner, go beyond the several thousand megawatts of gas-fired capacity already scheduled to retire over the next decade to comply with the state's restrictions on once-through cooling systems that rely on ocean water.

The study also found that no new gas plants are needed to meet the state's energy or reliability needs in 2030 when California is targeting a 40% reduction in greenhouse gas emissions from 1990 levels. Instead, the ISO grid could add 8,000 MW of new solar, 1,500 MW of wind, 1,000 MW of batteries and 600 MW of geothermal to help meet a power-sector carbon cap of 42 million tonnes by 2030.

The report comes as state regulators consider utilities' proposals for meeting the 2030 emissions target, including a proposal from Edison International subsidiary Southern California Edison Co. to lower the power sector's cap to 28 million tonnes. Under a similar scenario, the report quantified gas capacity retirements surging to more than 10 GW by 2030.

'Gas glide path'

Even with those shutdowns, however, nitrogen-oxide emissions may rise because of more frequent starting and stopping of the remaining gas fleet in response to the need for more flexible operations, the report said.

Laura Wisland, senior manager of Western states energy for the Union of Concerned Scientists and a report co-author, called for "a gas glide path, a roadmap for the state to figure out how we transition off gas in an orderly and equitable way." Twelve of the gas plants that could be retired are in areas "disproportionately burdened by air pollution."

While some state energy regulators, lawmakers and the ISO's board of governors have also called for an exit strategy for natural gas, three major projects totaling 2,537 MW are under construction, according to California Energy Commission data. The commission in 2018 suspended its review of two additional projects proposed by NRG Energy Inc. and Calpine Corp. Only one proposed gas power plant within the commission’s jurisdiction remains under active review.

California ISO spokesperson Steven Greenlee declined to comment on the report's specific findings. "We are still reviewing the report and working with the authors to fully understand the study's conclusions."