Windmills at Iron Range wind farm grind to a halt after defects found

Minnesota Power’s Taconite Ridge wind farm isn’t producing nearly as much electricity as anticipated in recent months, with seven of the 10 wind turbines shut off for repairs.

The $50 million project, built on 450 acres of land overlooking U.S. Steel’s Minntac mine, came fully online early this summer. But this fall, inspectors with the turbine manufacturer discovered defects in seven of the wind turbines’ blades. Those turbines were shut down.

Some of the fiberglass blades have “wrinkles” that must be repaired for the blades to operate properly, said Amy Rutledge, communications manager for Minnesota Power. Repairing the blades is taking longer than anticipated.

“We had hoped they would be wrapped up by mid-December, but we’ve had a few issues with the weather,” Rutledge said. Ironically, windy weather kept the manufacturer from removing the rotors as quickly as they’d like, she said.

Repair crews are estimating all 10 turbines will be working by the end of January, Rutledge said. The work is covered under manufacturer Clipper Windpower’s warranty, she said, and the delay won’t affect Minnesota Power’s electrical supply.

The defects were discovered during a scheduled 500-hour inspection, conducted about three or four months after each turbine began operating, said Taconite Ridge project manager Andrew Remus. And while the wrinkles aren’t structural defects, they need to be fixed, he said.

“If we leave them the way they are, without taking any action, they will affect the way the blade operates,” Remus said, adding, “The blade is all one piece, and you need it to be perfect.”

The 153-foot-long blades are made of layer upon layer of fiberglass. Each layer should rest smoothly on top of the previous layer, Rutledge said, and any imperfection will gradually work its way to the blade’s surface to create that wrinkle.

“These are the largest blades out there on the market for inland units,” Remus said.

And in translating such large man-made components from the engineering stage to the real world, “there are some start-up issues, some design and engineering issues you work through.”

Some of the wrinkles will be sanded down and relaminated, Rutledge said, while others will be repaired with a premade “patch” that’s similar to using putty to repair a dented car.

The project is the first large-scale wind farm in northern Minnesota, and the first to be fully owned and operated by Minnesota Power. When running at full capacity, the turbines are expected to produce 25 megawatts of electricity, enough to power about 8,000 homes.

The wind farm is part of Minnesota Power’s plan to increase its renewable energy resources. In early 2007, Minnesota Gov. Tim Pawlenty signed into law a bill requiring electrical utilities to produce 25 percent of their electricity from renewable resources by 2025.