As wind turbines across Texas froze up during the recent cold snap, turbines in Minnesota kept turning.
Except for a few days on the Iron Range.
That's because wind turbines in the north are built for cold weather.
“The difference for us is when that Arctic weather blows through, we're used to it,” Josh Skelton, Minnesota Power chief operations officer said. “Our wind turbines have design features such as material selection, cold weather packages, different lubricants, and hydraulic heaters to keep fluids warm.”
While temperatures in Texas dipped below freezing, the thermometer in the north plummeted into the 30's and 40's below zero.
No problem for northern wind turbines.
All of Minnesota Power's 164 wind turbines at its 500-megawatt Bison Wind Energy Center in New Salem, N.D., continued to run, Skelton said.
It was pretty much the same on the Iron Range.
At Minnesota Power's Taconite Ridge Wind Energy Center at Minntac Mine in Mountain Iron, the 10-turbine, 25-megawatt facility, remained operational through almost all of the long cold stretch.
However, the turbines did shut down for three days due to the cold, Skelton said.
“They typically run to 22 below zero,” Skelton said. “They've got a little more range due to the cold weather package and the design.”
A high-tech temperature sensor inside each turbine nacelle at Taconite Ridge takes a temperature reading every 10 minutes, according to Skelton.
If the temperature inside a turbine nacelle reaches 22 below zero, the turbine automatically shuts down. The sensor continues to take a temperature reading every 10 minutes.
When the temperature inside the nacelle goes back above 22 below zero, and with sufficient wind blowing, the turbine automatically restarts.
Special cold-weather lubricants and an internal electric heater inside the nacelle, help keep the turbine internals operating.
The Taconite Ridge site, high atop a hill, is unique when it comes to temperature, Skelton said.
That means the Taconite Ridge turbines may continue to run even if its colder in other areas of the Iron Range, he said.
“There's kind of a temperature anomaly there,” Skelton said. “Even when it's 35 below in Tower, it doesn't reach 22 below at Taconite Ridge.”
Great River Energy distributes electricity to 28 rural cooperatives across the state from nine wind farms in Minnesota, North Dakota and Iowa. The wind farms are owned and operated by wind developers.
All the wind farms providing power to Great River Energy continued to operate during the cold snap, Mark Rathbun, Great River Energy manager of renewable resources said.
Wind turbine manufacturers design and build turbines to meet the expected weather conditions of specific geographical areas, Rathbun said.
“The key to operations in the Midwest is preparation,” Rathbun said. “Based on where the wind turbines are located, the wind turbine manufacturers anticipate those conditions and build them to operate in a wide range of temperature conditions. They could operate down to minus 22 and up to 95 to 100 degrees.”
Standard wind turbines without cold weather packages, are designed to operate down to five degrees Fahrenheit, he said.
Yet, as temperatures fall, the air changes, making a wind turbine more effective.
“The wind has more energy as it gets cooler,” Rathbun said. “The air gets more dense and you are going to get more power at zero degrees than at 70 degrees.”
Beyond bitter cold temperatures, icing on wind turbines can also create major problems, Skelton said.
“There's potential for ice to build up on the wings,” Skelton said. “The issue is that then it's like throwing a Volkswagen off the blades or breaking a blade. If there's an icing imbalance, you would try to de-ice it or knock it off.”
Technologies are being developed which in the future could help prevent icing of wind turbines, Rathbun said.
“As our power supply transitions, there will continue to be improvements to wind turbine technology,” Rathbun said. “Sometime in the future it's possible that there could be heating elements to prevent that type of issue. There's a lot of people working on those types of issues,”
There's more than 80,000 wind turbines operating across the United States, according to the American Clean Power Association. The turbines generate 111,808 megawatts of electricity, making it the third largest source of electricity generating capacity in the nation.
Minnesota is currently ranked eighth in the nation for wind power generation, according to the association.