The county of Napa has taken a public step towards exploring future electricity service from a Marin County-based public power agency, setting in motion a process that could one day give ratepayers in Napa County's unincorporated areas access to an alternate utility.

The board of directors for MCE Clean Energy -- formerly Marin Clean Energy -- are set to discuss at the Dec. 5 meeting taking early steps on a proposal to add Napa County and three other municipalities to its growing service area.

It would be the next geographic expansion for California's first "community choice aggregation" power agency, which delivers renewable energy-focused power service over the electric grid largely maintained by Pacific Gas & Electric Co. The agency currently offers service to every municipality in Marin County and expanded in July to include Richmond in Contra Costa County.

With an MCE strategic planning session looming, the Napa County Board of Supervisors recently authorized letter of interest, asking the power provider to "conduct exploratory negotiations with our county, to determine the practicality of such an arrangement and propose a framework whereby we could work together to develop a plan of action for moving forward, should our discussions prove fruitful."

"It seemed like it was good timing for an exploratory letter," said Brad Wagenknecht, chairman of the board and author of the one-page letter to MCE Executive Officer Dawn Weisz, during the Sept. 17 meeting.

It was not the Napa county government's first communication with MCE. Informal discussions had started following the power provider's presentation at a joint meeting of the Napa, Solano, Sonoma and Marin boards of supervisors in June, according to Mr. Wagenknecht.

Yet it was the first action item on the subject to go before Napa supervisors. It passed unanimously with all but one supervisor present.

Adding Napa County to MCE could take around two years and benefit from lessons learned while bringing on the city of Richmond, according to Jamie Tuckey, a spokesperson for MCE.

So-called "affiliate member" municipalities are required to fund a feasibility study, at a cost of around $20,000, to determine if their membership would have a net positive effect for the current customer base in terms of rates and renewable-energy opportunities, Ms. Tuckey said. Membership is ultimately authorized by the California Public Utilities Commission, and potential customers are given several opportunities to opt out and remain with PG&E.

Affiliate membership is considered for municipalities that are no more than 30 miles from MCE's current service area and have a potential customer base of 40,000 or less, though special consideration is possible in some cases. The cities of El Cerrito and San Ramon in Contra Costa County and the city of Albany in Alameda County are also exploring a service relationship with MCE, Ms. Tuckey said.

While county of Sonoma also is forming a community choice aggregation--type power agency known as Sonoma Clean Power, the Napa supervisors chose to begin talks with MCE due to the power provider's existing operations, Mr. Wagenknecht said.

MCE launched to a limited number of Marin County municipalities and customers in 2010, and has gradually grown to offer service countywide. The provider offers energy that is at least half from renewable sources, purchasing electricity from a variety of sources while launching programs that incentivize renewable-energy projects in its service area.

Rates currently average 1.15 percent more than PG&E for residential customers consuming 500 kilowatt-hours per month, or $79.04. For commercial customers consuming 1,225 kilowatt-hours during summer, rates currently average 3.1 percent less, or $253.66 per month.