Four energy companies have emerged from a group of 11 competing to become the main electricity supplier to Sonoma County's planned public power agency.
The short list of candidates, released Friday by the county, does not include Shell Energy North America, a subsidiary of the Dutch fossil fuel giant and the controversial main supplier to both Marin County's public power program and the proposed agency in San Francisco.
It also does not include Calpine Corp., the Houston-based operator of The Geysers, the geothermal field on the Sonoma-Lake county border that supplies about a quarter of California's renewable energy.
The four final candidates are:
; NRG Energy, based in Houston and Princeton, New Jersey, one of the country's largest power producers and retailers.
; Direct Energy, an energy retailer based in Canada and the U.S., a subsidiary of the British multinational Centrica.
; ConEdison Solutions, based in Valhalla, New York, a subsidiary of Consolidated Edison.
; Constellation, a power and natural gas supplier and subsidiary of Exelon, the Chicago energy producer, trader and distributor.
The list was disclosed four days before the county begins a series of public presentations before local city councils urging them to join the power agency. County officials have said they intend to award a power-supply contract by September and begin delivery to homes and businesses Jan. 1.
The county power plan has been under study since 2011 and was tentatively approved for the unincorporated areas of the county last week by the Board of Supervisors. It is built on the assumption that customers — who can opt out of the proposed system — prefer an alternative to Pacific Gas and Electric designed to rely more heavily on renewable energy, shrink the county's carbon footprint and promote local generation projects that provide jobs.