Austin's electric utility could soon reverse a long-standing practice of selling wind, solar and other renewable energy only to customers who choose to buy it, four Austin City Council members and a mayoral aide said this week.

The council's ambitious goal of getting 30 percent of the city's electricity from renewable sources by 2020 could be in jeopardy if Austin Energy relies exclusively on its landmark GreenChoice program, which offers wind-generated power at a cost that recently spiked to more than 50 percent higher than that of the standard electricity generated by fossil fuels.

Now, City Council members say, all Austin Energy customers may need to shoulder the cost of going green.

"If we have to spread the cost" to sell enough renewable energy, "that's something we should do," Council Member Sheryl Cole said. "Austin should move forward in its leadership role in heading off global warming."

The council oversees Austin Energy, the only electricity source for most Austinites.

Council members say it's too early to say how much utility bills could rise. In-depth council discussions will probably start later this year, when various advisory groups finish studying Austin's long-term energy options.

"Clearly, there is going to be some cost," Council Member Bill Spelman said. But he said he thinks renewables will probably be a good long-term investment. That assessment is shared by Council Members Chris Riley and Randi Shade and by Amy Everhart, a policy aide to Mayor Lee Leffingwell.

"But if it turns out (the city's renewable energy goals) will double or triple electricity costs," Spelman said, "then it's something I don't think (Austinites) would be willing to support."

For a decade, Austin's green ambitions have benefited from relatively cheap wind power in West Texas. The city has sold that power through GreenChoice. Under the program, customers can choose to sign a 10-year contract to get power from a particular wind farm. GreenChoice has sold the most renewable energy in the U.S.

At times, as the prices rose for coal, natural gas and nuclear fuel, GreenChoice was the cheaper option. And thanks to GreenChoice, the council has rarely had to face the prospect of selling renewable energy to Austinites who might not want it. When the question has come up, the council has been hesitant to ask all customers to pay.

In March, for example, some large businesses objected to a council plan to buy power from a solar array planned in eastern Travis County. In response, the council instructed Austin Energy to explore selling solar power only to willing GreenChoice customers.

But electricity from the solar array will be even more expensive than the current price for GreenChoice, which is now significantly more costly than the nonrenewable option.

The price of GreenChoice has nearly doubled since early 2008. A new GreenChoice subscription would now raise the monthly summer bill of an average Austin homeowner from $93.35 to $151.85, Austin Energy said. Businesses, which buy 83 percent of GreenChoice, could face bigger hits.

The latest GreenChoice offering has been on the market seven months, but only about 1 percent of it has sold, according to Austin Energy. Utility officials say they may be able to cut the price but caution that the drop may not be dramatic.

Roger Duncan, the head of Austin Energy and the architect of GreenChoice, first publicly raised the possibility of phasing out the program in an interview last week. He said GreenChoice may have outlived its usefulness.

Council Members Mike Martinez, who devised the idea of selling the city's solar energy through the GreenChoice program, and Laura Morrison did not return calls for comment..

The council can legally raise electricity rates as high as it wants. However, the 5 percent of Austin Energy customers who live outside the city limits could appeal any increase in the base rate to the state's Public Utility Commission, according to Austin Energy attorneys.

The commission cannot force the city to change its rates, according to state law, but it can restrict the utility's discretionary spending, potentially hindering its ability to pay for city services such as parks and libraries. About 9 percent of Austin Energy's revenue goes toward those services.

Some critics say Austin is overcharging for its wind, thereby undercutting GreenChoice. Mike Sloan, president of local renewable energy consulting firm Virtus Energy, says the city has overestimated various costs and packed in hidden fees.

In 2006, Sloan notes, the program sold renewable energy at the best price in the country, according to an annual top 10 list compiled by the Department of Energy's National Renewable Energy Laboratory. But by December 2008, GreenChoice had dropped off the list.

GreenChoice customers, like all Austin Energy customers, pay for the maintenance and upkeep of the city's coal plant, nuclear plant "and other facilities they don't get power from," Sloan said. "They're subsidizing power they don't buy, and they shouldn't be."

Austin Energy spokesman Ed Clark denied that the utility is charging extra fees. He also said GreenChoice customers rely on the other power sources when the wind isn't blowing and should therefore have to pay an equal share of the upkeep on those facilities.

"If they weren't getting power from those other sources," Clark said, "they wouldn't have electricity 24/7."