LOS ANGELES (AP) — Two retired generators at a Southern California power plant are back online, to help take up the slack from the shuttered San Onofre nuclear plant this summer.

The pair of natural-gas-powered units at the AES Huntington Beach plant will provide about 440 megawatts to the Los Angeles Basin, while giving voltage support to allow power to be imported into the San Diego area, the Los Angeles Times reported Sunday,

California’s energy grid operator says that without the backup, parts of LA County, south Orange County and San Diego County could face power shortages in the event of a heat wave or transmission outage.

“This is a critical component of the plan for summer should the San Onofre units continue to be offline, or even if there is a partial return to service,” Stephanie McCorkle, spokeswoman for the California Independent System Operator, told the newspaper.

The contingency plan also includes speeding up transmission upgrades. Customers will be called on to conserve power, as well.

San Onofre has been shut down for three months because of equipment issues. Southern California Edison officials are hopeful that it could be back at a reduced capacity in June.

The nuclear plant produces enough electricity for about 1.4 million homes. Officials said it also provides voltage support that allows power to be imported from elsewhere to serve Southern California, the Times reported.

The Huntington Beach units may operate through October, when they will have to be shut back down so the new Walnut Creek plant in the city of Industry can take over their emission credits.

San Onofre’s twin reactors have been idle since Jan. 31 in the midst of a federal probe into what went wrong with hundreds of tubes that snake through the generators. Some were so eroded after a brief run in operation that they can no longer function safely.