Petaluma's city leaders Monday night dug into the structure and risks of the planned Sonoma Clean Power Authority, an alternative to utility giant PG&E promised to bring a greener product to county residents.

Council members offered no glimpse at whether they're likely to vote to join Windsor and unincorporated areas of Sonoma County in taking part in the power authority during two hours of presentation, discussion and comments at City Hall before an overflowing audience.

"This is a good discussion, and this is how people's questions are going to get answers," Mayor David Glass said. "In the last couple of weeks we've been bombarded with questions and concerns."

Sonoma County Supervisor David Rabbitt, the lone member of the board to vote against launching the power authority in April when it was approved, started Monday's discussion by emphasizing that he is a proponent of local, cleaner power and simply wants more time to vet questions.

"I want to know what I'm buying, there are questions I felt the public needed answered; I want to make sure Sonoma clean power will work as intended," Rabbitt said.

Petaluma was the fifth city to hear the county's public power pitch. Cloverdale was the first city to decline to take part, at least initially, and Windsor on Wednesday became the first to sign up. Sebastopol and Rohnert Park took no action.

Santa Rosa will consider the program today, with Cotati set to consider the matter on Wednesday and Sonoma on June 3.

Council members dug into questions about how the project will be financed and presenters explained lines of credit and the level of risk.

A long line of people spoke to the board, including environmentalists and residents, most in favor of the project. Customers will have the option to opt out and stick with PG&E.

Glass asked the presenters to explain the worst-case-scenarios and what they would mean for both customers and the cities.

If the power company failed, customers would be shifted back to PG&E, an unlikely scenario that nonetheless would not cause an interruption in service, Deputy County Counsel Steve Shupe said.

The power authority would not have any impact on a city's financial wellbeing or, more specifically, its general fund, said Cordel Stillman, the Sonoma County Water Agency's deputy chief engineer, who is among the presenters going from city to city.

Shupe explained that PG&E is subject to the same market conditions as a local utility. He reassured the crowd that he was a skeptic before he started examining the risks.

"The power providers that we are negotiating with have a big incentive to ensure we don't fail, they're interested in breaking into California market," Shupe said.

They estimate rates for residential customers could be between 1.8 percent lower and 1 percent higher than PG&E. For commercial customers, rates could be between 3 percent lower and 0.5 percent higher.

The county is urging cities to join by June 30.

Councilwoman Teresa Barrett wanted to know how their vote would weigh against a city like Santa Rosa, which has a larger share of customers .

Each city and the county would get a member on the board and one vote. However those with more customers, such as Santa Rosa with 35 percent of the county's electricity use, could call for a weighted vote in certain circumstances.

Shupe said that the larger jurisdictions wanted that provision.

"I'm sure they did," Barrett said.

"The joint powers agreement can be amended by a two-thirds vote of the governing board," Shupe said.

"Can they ask for weighted voting on that?" Barrett said.

The audience laughed.

"We're looking out for Petaluma so forgive us for that," Glass said.