Looking to avoid power blackouts, California may turn to the one energy source it’s otherwise desperate to get rid of: fossil fuels.

A sweeping energy proposal Gov. Gavin Newsom signed Thursday puts the state in the business of buying power to ensure there’s enough to go around during heat waves that strain the grid. But some critics say the method of getting there is at odds with the state’s broader climate goals, because it paves the way for the state to tap aging gas-fired power plants and add backup generators fueled by diesel.

The debate highlights the challenge some states are facing as they scramble to address heat waves fueled by climate change without compromising on their pledges to transition to non-fossil fuel energy sources like solar and wind.

California gets most of its energy from renewable sources during the day, but doesn’t yet have the storage to dispatch enough solar power after the sun goes down. The bill aims to speed up the building of more renewable energy and storage facilities by removing local governments from permitting decisions. Supply chain issues are also slowing down building.

Democratic state Sen. Dave Min noted the tricky position the state is in by potentially needing to rely on fossil fuels and their planet-warming emissions to deal with the heat waves driven by climate change.

“That’s the obvious conundrum that we’re in,” said Min, who represents Huntington Beach, a coastal community home to a gas-fired power plant.

The problem isn’t unique to California. In New Mexico, a coal-fired power plant was slated to close its last two units Thursday. But a major utility asked the state to keep one unit open through September to meet demands during hot summer months since solar and battery storage projects that were meant to replace the lost capacity have been delayed.

State energy officials warned earlier this year that the state risks an energy shortfall equivalent to what it takes to power 1.3 million homes on the summer’s hottest days. Newsom and lawmakers are desperate to avoid a scenario like August 2020, when hundreds of thousands of people temporarily lost power because there wasn’t enough supply to go around.

Newsom’s solution centers on creating a “strategic reliability reserve” run by the Department of Water Resources. The water agency has been given that role because it is a major producer and user of power through its dams and operation of the state’s water pumping system. This summer, the department could reimburse utilities if they have to buy extra power and add temporary power generators, including those powered by fossil fuels. Any diesel-powered generators couldn’t be used past 2023.

Beyond that, the water department would be able to build new energy storage and zero-emission generating stations. It could also spend state money buying power from coastal gas-fired plants that are set to close in 2023. The plants were first set to close in 2020. Likewise the department could keep buying power from the state’s last remaining nuclear plant if it stays open beyond its 2025 closure.

Newsom said in a signing statement that he would direct state agencies to “ensure clean energy resources are prioritized over fossil fuels.”

Sen. Henry Stern, a Democrat from Los Angeles County, said while the bill doesn’t allow for the extension of fossil fuel plants, its a question lawmakers will have to address.

“What this bill is doing is buying time,” he said.

Republican state Sen. Shannon Grove, who represents fossil fuel-rich Bakersfield, said the legislation proves California needs oil and gas.

“If we don’t have these gas-powered plants to fire up when we need them you will not be able to flip the switch and get electricity,” she said.

Environmental groups, meanwhile, said the state wouldn’t need to rely on fossil fuels as a backup if it had moved faster to build up renewable resources and expressed concern that the bill doesn’t put enough guardrails on the water department’s power. The department would not have to comply with California’s landmark environmental law to move forward with new projects.

“The state is saying we need to rely on fossil power and they’re not fully admitting that it’s because of this lack of ambition,” said Alexis Sutterman, energy equity manager for the California Environmental Justice Alliance.

Andrew Campbell, executive director of the Energy Institute at the University of California, Berkeley’s Haas School of Business, said the water department’s new authority to buy power is “very expansive and open ended” and something that “really deserves scrutiny.”

California, he said, is likely on the forefront of a challenge that will probably hit other U.S. states as they move away from fossil fuels and boost how much energy is needed from the grid.

“Developing an electrical system that is very clean and doing that reliably is a challenge that hasn’t been solved anywhere,” he said. “And California, because it’s so far along with renewable energy development, is hitting that challenge sooner than some other places.”