The Tennessee Valley Authority is looking to buy enough renewable power to supply 978,000 homes in the next three years.

The nation’s largest public utility issued a request Tuesday for proposals for up to 2,000 megawatts of electricity from wind, solar, geothermal, biomass and hydropower by 2011. The move represents the biggest effort yet by TVA to buy more clean power and could bring a record amount of power generation into the valley from other sources.

TVA is targeting individual companies capable of producing at least 1 megawatt of electricity from renewable or clean energy resources and is interested in proposals that would provide the power supply from one to 20 years. Up to 1,000 megawatts of generation would be delivered to TVA by June 1, 2009.

Unlike its current Green Energy Switch program, TVA will entertain proposals from outside the Tennessee Valley in its newest clean energy plan.

“We expect this request for proposals to provide TVA with a variety of options to consider in acquiring efficient, cost-effective renewable and clean energy generation,” Van Wardlaw, executive vice president for power supply and fuels, said in a prepared statement.

The announcement was welcomed by both environmental groups and independent power producers.

“I think it’s very important for TVA to diversify its energy portfolio, and it’s a shrewd political move in recognition of the changes that are likely to come with a new administration,” said Stephen Smith, executive director of the Southern Alliance for Clean Energy. “It represents a real change.”

Two years ago, TVA distributors opposed a measure approved in the U.S. House of Representatives to require utilities to get at least 20 percent of their electricity from renewable sources. As a federal corporation, TVA was exempt from the requirement. But distributors worried that the measure later might be extended and prove costly in a region where wind and solar power sources are less abundant.

TVA’s environmental policy approved by utility directors earlier this year forecasts that more than half of TVA’s power generation will come from zero- or low-carbon-emitting sources by 2020, but TVA includes nuclear power and its fleet of 29 existing hydroelectric dams in that share.

Now only about 40 megawatts of TVA’s electricity capacity comes from wind, solar and biomass, agency spokesman John Moulton said.

Dan Dolan, vice president of policy research and analysis for the Electric Power Supply Association, said TVA’s announcement “is a very positive trend” toward bidding out future power supply.

“This is a recognition that the best value for consumers comes when a number of parties compete with each other to supply power,” he said.