The launch of Sonoma County's public power plan has long hinged on how its rates would compete with PG&E.

The county now says it has an idea of what an average residential and commercial customer would pay per month under its program. But its analysis of how those costs would stack up against PG&E already has triggered a dispute.

PG&E officials say the county gave an inaccurate average calculation of the utility's 2013 rates, resulting in a higher PG&E bill than what they said a typical customer might pay.

"We know what our rates are," said Jonathan Marshall, a PG&E spokesman. "Unfortunately, they don't understand our rate structure, apparently."

County officials and consultants with decades in the energy business defended their figures, which are based on annual rate estimates submitted by PG&E to the California Public Utilities Commission.

"We're comparing apples to apples according to their submissions to the CPUC," said Cordel Stillman, deputy chief engineer with the county's Water Agency, which is spearheading the proposal.

The difference boils down to alternate ways of computing an average customer's bill, composed mainly of electricity generation charges and delivery charges.

The county used a base rate on the delivery side that is an average for all the different price tiers that apply based on the amount of power used.

PG&E says its rate is more accurate because it factors in energy use at each of the different tiers.

While the county says an average residential PG&E bill for 2013 is $95.17, PG&E says it is $91.60.

The difference skews the rate comparison, PG&E officials said.

However, the point may be moot because PG&E still would be responsible for electricity delivery under a county program. If those costs are $3.50 less under PG&E they would also be so under the county program, county officials noted.

"In terms of the competitive comparison, it's irrelevant," said John Dalessi, an energy consultant to the Sonoma and Marin county power programs and a former manager at Southern California Edison. "It (the delivery charge) is going to be the same whether Sonoma Clean Power is serving the customer or PG&E is doing it. Hopefully people understand that."

You can reach Staff Writer Brett Wilkison at 521-5295 or