KNOXVILLE, TENN. ? The Tennessee Valley Authority, founded in the 1930s to generate power from hydroelectric dams, has signed an agreement to expand its wind power generating facility, the public utility said Tuesday.

The country’s largest public utility has been operating three wind turbines on Buffalo Mountain, a reclaimed strip mine about 25 miles west of Knoxville, since 2001.

TVA will add 18 turbines to give the site a capacity of more than 28 megawatts, up from 1.8 megawatts. Invenergy, a Chicago-based energy development company, will build, own and operate the new turbines, which are expected to be in operation in November.

Although the TVA project pales compared to large wind farms in the Pacific Northwest, California and Texas, “this is a significant commitment to wind in our region,” said Stephen Smith, executive director of the Southern Alliance for Clean Energy watchdog group.

Nationally, wind power is the fastest growing electric power source — outpacing gas turbines, coal plants or nuclear plants, he said. The Energy Department lists 4,558 megawatts of U.S. wind power.

TVA’s Green Power Switch alternative energy program also uses electricity generated by solar collectors and reclaimed landfill gas.

TVA provides electricity to 158 distributors serving 8.3 million people in Tennessee and parts of Kentucky, Virginia, North Carolina, Georgia, Alabama and Mississippi.