The 240-foot windmills are located on a hill in Rio Vista, where winds blow strong from May to September. The turbines will generate an additional 5 megawatts of electricity, which the utility will sell to local residents and businesses.

"Wind power is a very cost-effective alternative for us because there are no emissions and the fuel is free," said Dick Wallace, who manages SMUD's Solano Wind Project. "We're fortunate because in the Sacramento region, there's a direct match between when the wind blows and when we need more electricity."

The added power will not affect consumer rates, but increasing the amount of wind power to Sacramento's energy grid will help the utility prepare for a potential spike in demand for electricity this summer.

Since 1994, SMUD has operated the small wind power plant in the Montezuma Hills, little more than an hour from south Sacramento. In keeping with the national trend of substituting green power for more traditional power plants, such as those using natural gas, last year SMUD bought 16 new wind turbines.

About 5.5 percent of the Sacramento area's power supply comes from renewable energy sources, said Dace Udris, a spokesperson for SMUD.

In the long term, experts predict that using wind-driven generators will help create a more stable, affordable energy supply.

"I expect to see virtually all the municipal utilities moving toward more renewable energy," said James Sweeney, an energy expert at Stanford University. "Over the long run, wind energy will help lower consumer rates. In the short run, wind power is getting to a point where it is similar to the cost of natural gas."

SMUD projects that it will meet 10 percent of its electricity needs through renewable resources by 2006, and 20 percent by 2011. That means the windmills and other green power sources would eventually produce enough electricity to power 30,000 single-family homes.

State and federal programs that support the use of green power are helping utilities like SMUD make the switch.

"The more renewable energy sources there are in the mix, the less volatile prices will be," said Marwan Masri, who oversees the renewable energy program at the California Energy Commission. "We have a large wind resource in the state and it's a very cost- effective technology, so wind will play a large role for energy generation in California in the future."