The county plans to ramp up the renewable share of its energy portfolio from 33 percent to 50 percent in 2017, if the rate structure allows — renewable energy is generally more expensive than conventional sources. It also would offer a voluntary 100 percent renewable portfolio at a higher monthly premium; a similar proposal by PG&E is pending before the California Public Utilities Commission.

For the first several years under the county program, about half of the renewable energy would be "delivered" or "bundled" energy — electricity purchased from a renewable source and delivered to the county's customers. Until a final contract is signed, county officials said they won't know where that power will come from.

The purchase of offsets, called renewable energy credits or certificates, would allow the county to claim green status for the other half of its renewable power while actually getting it off the grid from standard sources, including fossil-fuel-based suppliers.

The credits are purchased by companies and governments, through brokers, from energy producers that have unsold green power. Some critics have called the credits "empty bragging rights" that don't spur investment in renewable energy like contracts for actual delivered power.

Advocates for local energy generation have not objected to the credits, which would be used in about the same proportion as the Marin County program.

Hancock, the Climate Protection Campaign director, called the credits a "transitional tool." But her group and others have voiced concerns that a short-term focus on cheaper out-of-county sources leaves local generation projects in the lurch.

"I understand that the first thing they need to do is get a power supply and make that competitive," said Marlene Soiland, a representative of Sonoma County Alliance, the business coalition, and president of Soiland Management Co., the Santa Rosa firm that oversees various development and real estate businesses in the Soiland family.

"I'd like to see the local supply be a higher priority. That's what I've heard from the business community," Soiland said.

Aside from a 20-megawatt, $100 million solar-panel system planned for 50 acres at Charles M. Schulz-Sonoma County Airport, county officials were not able to specify last week what other projects they had on the drawing board. They cited the opportunity to purchase power from household and commercial projects, known as a "distributed" or community-scale energy grid.

The higher potential costs for customers of that power and the risk of taking on too much debt in an overly ambitious startup remain a crucial financial and political concern, county officials conceded.

"We can't just go up willy-nilly from 33 percent," Stillman said.

But with an estimated 355 megawatts needed at full rollout, and endorsements from some business, environmental and labor interests hanging in the balance, advocates said they will continue to push for a quicker transition.

"How are we planning, in a methodical way, to increase the use of renewable local resources?" said Woody Hastings, renewable energy implementation manager for the Climate Protection Campaign. "We've heard some of the elected officials asking for the same thing. We don't have the details on that."

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.