The wind power capacity in the U.S. grew by almost 10 gigawatts in 2009, a 39-percent growth spurt from the year before, but wind turbine output from factories is waning, warned the American Wind Energy Association.

The total figure for new wind power for 2009 came to 9,922 megawatts. That's enough for 2.4 million homes, the AWEA claimed. Wind is notoriously fickle, though, and the actual output from turbines is closer to 30 percent of their rated capacity, but it's still an impressive achievement. Wind and natural gas accounted for around 80 percent of the new generating capacity in the U.S. By contrast,solarinstallations in the U.S. came to around 400 megawatts. (Solar, though, is expected to grow at a 50 percent a year rate for the next few years, according to GTM Research.)

The AWEA warned at the beginning of the year that 2009 might be a downer because of the economic climate. In 2008, wind capacity in the U.S. grew by 8.4 gigawatts, an annual record at the time.

Texas has more wind than any other state, with 9.4 gigawatts in the ground. That will likely continue to expand. A-Power Technologies from China has already announced plans to build one of North America's largest wind farms in the state. In second place is Iowa, with 3.7 gigawatts.

But the AWEA warned not to get too complacent. A lack of clear national policy and high inventories can lead to a drop in domestic wind manufacturing. The situation has been reversed from the picture in 2007 and part of 2008, when long waiting lists existed to get turbines.