The U.S. wind industry is growing again after taking a big step backward last year. Yet turbine makers and wind farm developers are finding few reasons to celebrate as the clean energy source struggles to secure long-term government support while facing stiff competition from cheap natural gas. Once the world's top wind market, the United States ceded that mantle to China last year as a weak economy halted its growth and cut new installations to half of the 10,000 megawatts of capacity built in 2009. Since then, business has picked up, but not for the reasons the industry would like. Energy demand is still tepid due to a gurgling economic recovery, and the low cost of natural gas is keeping power prices low. Pricing in long-term power sales contracts signed by wind developers has fallen 30 percent in the last two years and will fall further this year, according to IHS Emerging Energy Research. Currently, the market is being shepherded by developers who are scrambling to put turbines in the ground ahead of a 2013 expiration of lucrative federal tax credits for wind. Beyond that date, the industry's fortunes are hazy.