KNOXVILLE, Tenn. - The Tennessee Valley Authority, looking outside the region to boost its renewable energy portfolio, said Thursday it will buy 450 megawatts of wind power capacity from the Great Plains.

The nation's largest public utility has signed 20-year power purchase agreements with Maryland-based CVP Renewable Energy Co. and Chicago-based Invenergy Wind LLC for electricity generated by wind farms they are building in McIntosh County, N.D., and Roberts County, S.D., respectively.

The added wind power should reach TVA's seven-state system in 2012, said Belinda Thornton, TVA's general manager of power and origination. It will be enough to supply 140,000 homes.

"We are very pleased that TVA is growing its renewable energy portfolio," said Steve Smith, executive director of the Southern Alliance for Clean Energy. "We think it is long overdue."

TVA's call in December to buy up to 2,000 megawatts in renewable energy attracted more than 60 proposals. With negotiations continuing, three more wind contracts could be announced by year's end, Thornton said.

TVA wouldn't reveal the value of the contracts, but Thornton said "the purchase price had to be competitive with forecasted market prices. For many of the projects, including all of the solar proposals, this was an insurmountable hurdle."

The 20-year power purchase TVA signed with Invenergy in 2004 to add 15 wind turbines to TVA's wind farm on Buffalo Mountain near Knoxville was valued at the time at $60 million. That was for 27 megawatts.

CPV will be providing TVA with 200 megawatts from 87 wind turbines at its planned Ashley project in North Dakota, and Invenergy will be providing 250 megawatts from 167 turbines at its proposed Hurricane Lake project in South Dakota.

TVA was the first utility to develop a commercial wind farm in the Southeast when it erected three turbines on the reclaimed strip mine on Buffalo Mountain in 2000. But it has been slow to add capacity.

The utility's total renewable capacity now is about 50 megawatts - mostly from the wind farm, several demonstration-scale solar collectors and landfill gas recycling.

This doesn't count some 4,300 megawatts from its clean hydroelectric generation - out of a total TVA capacity of more than 32,000 megawatts. TVA gets most of its power from coal-fired and nuclear plants.

Thornton said the new renewable purchases should make TVA's "green power" portfolio one of the largest in the region.

Smith agreed that it certainly "puts TVA back into a much better position among its peers."

TVA officials say biomass and solar energy have the greatest potential in the utility's territory, which includes most of Tennessee and parts of Kentucky, Mississippi, Alabama, Georgia, North Carolina and Virginia, although Smith argues that the valley also has more wind power available.

TVA is participating in the state of Tennessee's $31 million, five-megawatt solar farm planned for Haywood County.