LOS ANGELES (AP) — California regulators Thursday approved a plan for two utilities to develop replacement power to help fill the void left by the closure of the San Onofre nuclear power plant, but environmentalists warned it could open the way for more dirty energy.

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.