The U.S. wind power industry had its slowest quarter since 2007 in the just-ended third quarter, as investors turned away from the sector after Congress did not pass a renewable power mandate, an industry group said.

The American Wind Energy Association (AWEA) said U.S. developers added 395 megawatts of electricity capacity at wind farms in the third quarter--the slowest quarter since 2007. Year-to-date installations of 1,634 MW, were down 72 percent versus the same period last year.

The U.S. Senate has not passed a national renewable energy mandate that would have required power utilities to generate minimum amounts of power from sources like wind and solar power.

Senator Jeff Bingaman, a Democrat who in September introduced a bill with a Renewable Electricity Standard, has said it has picked up support from Republicans.

But it could be tough to pass the legislation this year as Congress will have a full schedule after it returns following elections on Tuesday.

China and Europe already have mandates for renewable power which AWEA said will help lead to $35 billion in investment in 2010, or four times the amount that has been invested in the United States.

"U.S. wind energy can again lead the world," said Denise Bode, AWEA's chief executive. "But if federal policymakers do not act quickly to provide investment certainty...the U.S. wind industry will stall out."

Wind power supporters also want Congress to pass long term tax incentives that they say would give investors more confidence.

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