SONOMA COUNTY -- Sonoma County's startup public power agency is drawing closer to the onset of service in May, seeing higher-than-expected enrollment and savings for its first round of customers compared to Pacific Gas & Electric Co.

The renewable energy-focused agency, Sonoma Clean Power, announced that 5.4 percent of those first-phase customers had opted to remain with PG&E as of March 20. The agency originally projected a 22-to-25 percent opt-out rate for its first round of customers by the end of 2014, but current participation suggest a 3-to-5 percent greater rate of enrollment, according to materials for the agency's board of directors.

That enrollment comes as an anticipated PG&E rate increase works its way through the approval process with the California Public Utilities Commission, one expected to allow Sonoma Clean Power to beat PG&E's overall electricity rates by 4-to-5 percent.

While the agency has cautioned that it may not always provide a cheaper option compared to PG&E, those early rates are expected to add to its appeal as the agency rolls out service throughout the majority of Sonoma County in the coming years.

As California's second "community choice aggregation" power agency, Sonoma Clean Power will purchase electricity for its customers and deliver it over the power grid largely maintained by PG&E. MCE Clean Energy, which currently serves all of Marin County and the city of Richmond, began serving customers in 2010.

State law allows those CCA-type agencies to enroll their customers on an "opt-out" basis, meaning that those who wish to remain with PG&E will be required to take some kind of action prior to the onset of service. Sonoma Clean Power will mail opt-out reminders for its first wave of customers through June 20.

Around 20,000 customers -- 14,000 commercial and 6,000 residential -- are considered eligible for enrollment in the agency's first phase. Approximately 80 percent of Sonoma County ratepayers will ultimately be eligible for service, currently excluding those in Petaluma, Rohnert Park, Cloverdale and Healdsburg.

City councils in Petaluma, Rohnert Park and Cloverdale all voted to not allow service to their municipality in Sonoma Clean Power's first year. The agency in March approved a measure that would waive an approximately $85,000 fee for those cities if joining by Aug. 31, which would make ratepayers there eligible for service as part of "phase two" and "phase three" enrollment in 2015 and 2016.

Healdsburg operates its own power utility, including maintenance of infrastructure, and is thus not considered eligible for service.

Sonoma Clean Power will launch with a baseline "CleanStart" product made up of 33 percent renewable energy. It is a strict definition that excludes some low-carbon sources like hydroelectric power, though low-greenhouse-gas emitting sources also represent a large portion of that power mix.

A 100 percent renewable product, "EverGreen," will be offered at a 20 percent premium, drawing entirely from geothermal power produced at the Geysers geothermal field straddling Sonoma and Lake counties. Sonoma Clean Power said 192 accounts have already signed up for the EverGreen program.

The agency will also offer an incentive program for renewable energy producers known as "net energy metering," which provides credits for production from solar photovoltaic and other systems to offset overall energy costs.

MCE Clean Energy has seen around 80 percent of residential and 75 percent of commercial accounts sign up for its program.

Sonoma Clean Power signed a primary power supply contract with Baltimore, Md.-based Constellation Energy in November, and a separate contract for geothermal energy from Calpine Energy Service. The agency is expecting to purchase just shy of 500,000 megawatt-hours of electricity by 2016.

Those currently eligible for service or contemplating participation in subsequent phases can find more information at www.sonomacleanpower.org.