The business of wind generation is less than breezy these days for clean-energy producer NextEra Energy Resources.

In Saginaw County, Mich., in late June, a blade on a 160-ft turbine snapped and was left dangling from its rotor (ENR 7/10 p. 4). The turbine is one of 75 at the 120-megawatt Tuscola Bay Wind Energy Center. Earlier in June at the Steele Flats wind farm in Nebraska, one of 44 turbines collapsed.

On June 5, a 2.5-megawatt turbine at the Endeavor I Energy Center in northwestern Iowa caught fire, and one of its blades fell to the ground. On May 31, near Enid, Okla., another blade fell from a turbine at the 98-MW Breckinridge Wind Energy Center.

NextEra would not comment on potential causes of the failures, but spokesman Bryan Garner says, “These are four different issues at four different sites involving two different equipment manufacturers. Two of the issues involved turbine blades, one was a tower, and one was a fire in the nacelle. Yes, we are investigating each incident, as we would with any equipment issue. … We view these as isolated equipment issues. I should also point out there were no injuries.”

NextEra’s runs General Electric-manufactured turbines at its Tuscola Bay, Breckinridge and Steele Flats facilities. Cedar Rapids, Iowa-based Clipper is the manufacturer of the turbines at Endeavor.

NextEra Energy Resources owns and operates nearly 10,000 wind turbines across the country. Of the turbines’ combined 30,000 blades, there are only five or six blade failures a year, so two in a month is out of the ordinary, Garner notes.

“There is nothing to indicate there are more than would be expected for the volume of turbines we have in operation,” Garner says.

Juno Beach, Fla.-based NextEra, the largest owner and operator of wind turbines in the U.S., has 117 wind farms in the U.S. and Canada that generate more than 13,850 MW of net power a year.

By the Wind-Turbine Numbers

There are currently about 53,000 turbines in the U.S. Wind-turbine rotor blades fail at a rate of approximately 3,800 a year, 0.54% of the 700,000 or so blades that were in operation worldwide at the time of a 2015 study by renewable-energy insurance underwriter GCube.

The National Renewable Energy Laboratory’s 2013 review of drive-part failures in wind turbines found that electrical systems had the highest failure rate of internal turbine parts.

“We work with the respective manufacturers to investigate each incident and replace the impacted equipment. We site the turbines safely and responsibly and diligently maintain the equipment, so failures are rare,” Garner notes.

“We don’t have any specific data points on this, but I can say wind-turbine failures are extremely rare. Wind turbines consist of rugged, sophisticated equipment that enables them to operate reliably under near-constant wind conditions,” says Evan Vaughan, media relations officer of the American Wind Energy Association, Washington, D.C. “And wind farms are resilient. Should one turbine fail in a project, the others continue to operate.”