Xcel Energy Inc., Colorado's largest utility, and five other Western utilities said Thursday they're seeking proposals to build a solar power plant that will concentrate the sun's energy and can generate 250 megawatts of power.

The plant, to be located in either Arizona or Nevada, would be the second-largest solar power plant of its kind in the nation, according to the Solar Electric Power Association in Washington, D.C., which has been eagerly anticipating the utilities' announcement.

"In terms of what's online right now, they would be toward the top [in size]," said Julia Hamm, executive director of the solar power association. "But there are more than 2,500 megawatts of this type of technology under contract right now, too."