MidAmerican Energy says it has idled nearly four-dozen electricity-generating wind turbines while workers check them for safety after blades broke off of two similar turbines over the past two months.
Those blade failures follow a break earlier this year and one in 2019.
MidAmerican, a Des Moines-based subsidiary of Warren Buffett-owned Berkshire Hathaway, said Tuesday it has paused the use of 46 turbines it has identified as having blades like the ones that broke.
The blades, upwards of 175 feet long, broke somewhere along their length and not at the base, the company said.
On Thursday, MidAmerican said, a technician discovered that a turbine blade had fallen into a harvested field southeast of Paton in Greene County. The technician went to the Beaver Creek wind farm after its monitoring system detected a problem with the turbine, the company said in a statement.
MidAmerican said a blade also broke off a turbine and fell into a cornfield in September at its Arbor Hills wind farm in Adair County.
MidAmerican experienced earlier problems with blades that broke from turbines in April of this year and October 2019, both at the company’s Orient wind farm, also in Adair County.
No one was injured in any of the incidents.
MidAmerican spokesman Geoff Greenwood said in a statement Tuesday that the company – which has more than 3,000 wind turbines in Iowa – had isolated the issue to blades made by Danish manufacturer Vestas.
In each case, MidAmerican’s weather data show lightning strikes occurred close to the turbines, the company said, with the blades in the earliest two failures taking direct hits.
The blades all had the same lightning protection system, which is designed to channel the energy from any nearby strike safely into the ground.
The company said the turbines it has idled potentially could be affected. They will remain out of service while “full analysis and inspections” are under way and until “corrective actions are complete” if necessary, it said.
MidAmerican said it began the inspections a year ago, after the first blade broke. Typically, the investor-owned utility inspects about a third of its turbines each year.
“We are looking for any sort of structural damage and will do whatever is necessary to ensure they are safe, including blade repair or replacement,” MidAmerican said.
The company said it is working with Vestas “to ensure that all of its blades within MidAmerican’s wind fleet are safe.”
It said it’s addressing gaps in its monitoring system to better ensure the company quickly identifies and inspects blades that may be damaged by lightning strikes.
“Though a blade failure remains an extremely rare occurrence, even one incident is not acceptable, which is why we’ve immediately enacted these additional precautions,” Greenwood said in the company’s statement.
The company introduced wind energy in Iowa in 2004 and now generates about 60% of its electricity from turbines. Overall, Iowa got 42% of its energy from wind in 2019 – more than any other state.
But wind energy has become controversial in rural areas where turbine farms are located. Residents have voiced safety concerns, and some say low-frequency noise and light flickering from the blades have made them ill. Some counties have sought temporary moratoriums on new turbine construction.
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