In what could be one of the biggest power transmission breakthroughs in a half-century, a Houston company is proposing to build a new type of electrical connection between windmills in Oklahoma and Texas and power users in the Tennessee Valley.

The proposed $3.5 billion project would use direct current rather than the alternating current of most electric lines. It will require approval from at least four federal and state regulatory agencies.

But TVA officials say such a project could provide a major source of green power.

"We think this has great potential and, at the least, you have to respect the effort involved in trying to undertake a project of this scope," said David Till, TVA's general manager for transmission strategies.

A new Houston company known as Clean Line Energy Partners proposes to build four DC transmission lines to link windmills in the Midwest and West with power users east of the Mississippi River.

Jimmy Glotfelty, executive vice president of external affairs for Clean Line Energy, said the company is seeking to be classified as a utility, which would mean it could condemn property if needed.

Glotfelty said Clean Line has asked state regulators in Oklahoma and Arkansas for permission to pursue the project. As proposed, the transmission lines would stretch from Diamond, Okla., to the western edge of the TVA service territory in Memphis, he said.

"The goal is to work with TVA to drive down the price of wind energy and to make it more reliable and cost effective," Glotfelty said. "With the DC electric line, you will be assured that, when the wind blows, you will get that electricity almost instantaneously."

If regulators approve and contracts can be signed with power generators and users, Clean Line wants to build the first of two 3,500-megawatt lines by 2015.

Despite hefty upfront costs, Glotfelty said developers believe the DC lines will lessen power loss over the 800-mile distance compared with AC transmissions. High-voltage, direct current lines lose less power during transmission than their AC counterparts, although they do require more expensive converters to transform energy into usable power for local utilities. Glotfelty said Clean Line plans to build $250 million converter stations at each end of the DC line.

Construction is projected to generate 10,000 temporary jobs and open more long-term energy options for utilities, Glotfelty said.

"This could help dramatically reduce air emissions for TVA and other Southern utilities, and TVA could potentially even make some money wheeling power across its territory for other utilities," he said.

Till said Clean Line is one of several wind and transmission companies seeking interconnection agreements with TVA to boost the utility's renewable energy portfolio.

A draft version of TVA's 20-year energy plan calls for up to 3,500 megawatts of wind and other renewable power. The utility already has contracted to buy 1,380 megawatts of wind energy from seven wind generators in Illinois, Iowa, Kansas and North and South Dakota.

Clean Line Energy Partners' investors include the company's management team, the Houston-based Zilkha family and ZBI Ventures.

ZBI Ventures is a wholly owned subsidiary of Ziff Brothers Investments, the principal investment vehicle of the New York-based Ziff family, and focuses exclusively on private equity investments in the energy and energy-related sectors.