The cost for the plan approved by the Texas Public Utility Commission in a 2-1 vote exceeds US$5 billion.

If new power lines attract that much wind generation, it would exceed the nation's current wind generating capacity. Texas already leads the country in its capacity to generate greenhouse gas-free electricity from giant wind turbines.

The commission declined to approve a more ambitious scenario, supported by many wind developers, to build power lines to move 24,000 MW of wind power, saying more study was needed on how wind volatility affects safe operation of the electric grid.

"This is a big bite," Commissioner Paul Hudson said, calling the transmission plan "nothing short of extraordinary," despite criticism that it might not be ambitious enough.

New power lines are needed to transfer wind generation from sparsely populated West Texas to the state's biggest cities, such as Houston, San Antonio and Dallas, where demand is highest.

Texas has some of the highest wholesale electricity rates in the nation, giving wind developers even more incentive to build.

Regulators have spent three years identifying the state's best wind production areas to determine how much new transmission capability should be built to take advantage of the plentiful resource.

Texas currently has 5,500 MW of wind capacity, an amount expected to grow to more than 9,000 MW by the end of the year -- long before new power lines can be built.

Texas' wind boom has created congestion on the existing power grid, leading to price volatility in the wholesale market this summer and losses for small power retailers.

The amount of transmission approved by the commission "gets us ahead of the need," said Calvin Crowder, president of Electric Transmission Texas LLC, a joint venture formed by American Electric Power Co and MidAmerican Energy Holdings, a unit of Warren Buffett's Berkshire Hathaway Inc , to invest in Texas projects. (Editing by Chris Baltimore and Walter Bagley)