Solar experts said the facility's successful first year of operation should help convince utilities that sun power can be a viable part of the U.S. generation mix, even though its costs are higher and its output more intermittent than traditional coal- and natural-gas-fired generators.

Xcel Energy is using the plant's power to help it meet the renewable-energy standards approved by Colorado voters and state legislators over the past four years.

"We have been very pleased with the amount of solar power the SunEdison plant has been able to deliver," said Karen Hyde, vice president of resource planning and acquisition for Xcel. "We continue to believe that solar power will be an integral part of our resource strategy."

Xcel customers pay about 2 percent more on their power bills to fund renewable energy, mostly from wind farms.

Among plants employing the technology of photovoltaics — direct conversion of sunlight to electricity — the 8.22-megawatt Alamosa facility is the largest in the nation to deliver power to a public utility.

Its size is exceeded only by the 14-megawatt photovoltaic generating station at Nellis Air Force Base in Nevada, where the power plant is used to meet a portion of the base's needs.

Yet the Alamosa plant's bragging rights may soon go by the wayside as larger solar plants begin to come on line.

Developers recently completed construction of a 10-megawatt photovoltaic plant in southern Nevada that will serve customers of Pacific Gas and Electric Co.

And construction of other plants using solar-thermal technology — harnessing the sun's heat to make steam to spin turbine generators — is expected to bring larger-scale facilities more suited to utilities' needs.

"Not to pooh-pooh Alamosa's size, but the industry is growing fast," said Mike Taylor, director of research for the Washington, D.C.-based Solar Electric Power Association.

"I'd almost call it entry-level," Taylor said. "But you've got to start somewhere. So kudos to the Colorado initiatives that got them out in front on this project."

Photovoltaics are best known for their use in solar panels installed on the rooftops of homes, stores, government buildings and parking structures. Large-scale solar arrays are in place at Denver International Airport and the Denver Federal Center.

"Solar power has come to maturity," said Rick Gilliam, managing director of Western states policy for Beltsville, Md.-based SunEdison. "Alamosa is helping us show that solar is a legitimate resource."