The weather’s getting worse for wind-power companies, which are finding it increasingly difficult to attract venture backers.

U.S. investments in turbine farms and wind-energy businesses tumbled 38 percent last year to $9.7 billion, according to data from Bloomberg New Energy Finance. Venture capitalists have practically left the sector altogether. They invested only $177.6 million in wind startups last year, down 71 percent from the year before.

Wind power is bucking a broader trend for clean energy, which is seeing a surge of investment. Venture backers pumped $4.29 billion into the sector in 2011, up 13 percent from the previous year, according to the National Venture Capital Association. With wind, it’s harder for early investors to afford the large outlay of cash needed to get a business off the ground, said Jason Matlof, a partner at Battery Ventures in Menlo Park, Calif.

“We can’t compete as venture investors in capitalizing energy companies,” Matlof said.

There’s also a glut of turbine production – fueled by investments over the last half decade in the United States, Europe and Asia – and not enough demand. Global purchases of turbines will fall 14 percent this year from 2010 and won’t surpass 2011 levels for two years, Bloomberg New Energy Finance estimates.

Read the full story reported by Bloomberg in the San Francisco Chronicle …