Conservation-minded Seattleites may be able to put their money where their utility bills are beginning in January.

That's when Seattle City Light plans to kick off a program allowing the utility's 340,000 customers to voluntarily pay more to purchase power from renewable energy sources.

Residential customers can pay $3, $7 or $10 extra each month — about the amount surveys show customers are willing to pay for cleaner-burning fuels. That money would then go into a fund to buy everything from solar power to wind generation to geothermal power to landfill gas.

While not yet approved by the City Council, the program is required under a law passed by the Legislature this year. It gives residents a chance to replace some of their power with renewable energy, and it encourages utilities to experiment with some of the most well-known — if not cost-effective — "green power" sources.

Green power refers to forms of energy production that don't emit pollution, including nuclear or hydropower, even though both are often controversial among conservationists. Seattle City Light touts itself as primarily a green utility because little of its power comes from sources such as coal.

Under the program, customers would pay monthly for green power or offer lump-sum payments for any amount at any time. Sixty percent of the money would go toward purchasing renewable resources that cost no more than twice as much as wind power — the cheapest of renewable resources.

The remaining 40 percent would go toward pilot projects to encourage development and use of green-power technologies. Most of the 40 percent will be used for solar projects. Solar power is now the most expensive renewable resource.

"It's really more like research-and-development money to prime the pump," said Nancy Glaser, strategic-planning director for City Light. The difference in costs among some renewable-energy sources is staggering.

The cost of replacing the average customer's residential power bill with 100 percent wind energy is about 2 cents per kilowatt hour — roughly $14 a month. The cost to do the same with solar power is about 26 cents per kilowatt hour — $187 a month.

But, city officials said, there was a small but vocal minority that adamantly pushed for solar power in a 1996 survey of residents.

"It's a technology that's ripe for expansion," Glaser said. "People see potential over the long haul."

If 1 percent of customers participated in the green-power project — the low end of the scale among other cities that have tried such voluntary measures — the revenue would be roughly $324,000 for pilot projects, which could buy only about 11 solar panels.

The remaining 60 percent would go toward other types of renewable energy, such as King County's landfill gas-to-energy project at its Cedar Hills landfill.

Craig Welch can be reached at 206-464-2093 or cwelch@seattletimes.com.