In late January, as a severe polar vortex brought high winds and some of the coldest temperatures ever recorded in the Upper Midwest, residents who ventured out may have caught an unusual sight: The familiar distant turning of many of the region’s ubiquitous wind turbines had ceased.

Plummeting thermometer readings—minus-25 degrees Fahrenheit in many areas with wind chills approaching 60 below—began to trigger fail-safes that shut down the turbines to prevent damage from icing and frozen internal lubricants.

“MISO [the Midcontinent Independent System Operator] lost most of its forecasted wind capacity in its northern zone,” says Dan Walsh, NRECA’s senior power supply and generation director.

Fortunately, the diverse portfolios of the region’s power producers meant that even with the loss of wind, electricity supplies were adequate, and outages during the multiday cold snap were minimal. But experts say it and other extreme-cold episodes this year have tested the grid’s resilience and reliability and reinforced the need for fuel and generation diversity.

“Sustained periods of severe cold weather repeatedly spiked power demand across much of the nation,” says Paul McCurley, NRECA’s chief engineer. “The results should serve as a reality check for anyone who sees promotion of specific technologies and the exclusion of others as a realistic path toward energy security and independence.”

In addition to lost wind generation, MISO reported fuel shortages and cold-related mechanical problems for some gas-fired power plants. Other independent system operators reported similar problems. Circulating pump problems caused by ice even shut down a nuclear plant in New Jersey.

Despite the challenges, G&T cooperatives kept power flowing using a combination of coal and natural gas baseload generation, peaking plants, renewable energy, load management, and power purchased from other sources.

“The system performed reliably due to good planning and preparation and solid, real-time operations,” says Priti Patel, vice president and chief transmission officer of Maple Grove, Minnesota-based Great River Energy.

To concentrate resources, Patel says, planned maintenance and scheduled outages on some generation equipment were postponed, and routine transmission work was temporarily suspended.

Bismarck, North Dakota-based Basin Electric Power Cooperative, which serves 141 distribution co-ops, says its participation in the large, geographically diverse Southwest Power Pool (SPP) helped keep supply flowing and prices low.

“One of the advantages of the 14-state SPP market is the vast footprint and the diversification of weather events that it provides with more of a north-to-south diversity,” says Dave Raatz, Basin Electric’s senior vice president for asset management, resource planning, and rates. “Energy prices are set based on the total load in the entire market. The diversification of this load, along with the types and quantities of generation in the entire market, helps to temper energy prices during very cold snaps in the north.”

Natural gas-based generation functioned well during the cold snap, but sustained cold across the region drove above-average residential demand throughout the Midwest and boosted fuel prices. Great River Energy says its lignite-coal-fueled generation in North Dakota proved both economical and reliable.

“Coal Creek Station and Spiritwood Station operated well in the extreme cold,” says Rick Lancaster, Great River Energy’s vice president and chief generation officer. “Our crews worked through the night to ensure our generation facilities had ample fuel supplies to reliably operate the plants.”

Basin Electric coordinated with its plant operators during the event to monitor fuel stocks, including coal and natural gas supplies. John Jacobs, Basin’s senior vice president of operations, says coal-based generation played a particularly important role in meeting demand this winter.

“It’s the well-maintained, lowest-cost resources that are less susceptible to the elements that will be called on to run,” he says. “You can be the lowest cost, but if the wind isn’t blowing, or are not weatherized and well-maintained, you will not be available to generate during these times.”

G&Ts also got cooperation from industrial users, who curtailed some operations during the most extreme conditions to ensure that ample supplies of electricity and natural gas were available for essential uses. Residential load control programs, operated in conjunction with distribution co-ops, also helped reduce demand.

Great River Energy dispatched load control for dual-fuel and peak-shave water heaters, which resulted in demand reduction of 359 MW on Jan. 29. Full load control for interruptible commercial and industrial users was implemented the following day, resulting in a 459-MW reduction in peak billing demand.

During the two coldest days, Great River Energy’s estimated load management impact was about 3,112 MWh, Lancaster says.

“That helped the cooperative avoid additional real-time purchases from the energy market, saving money for all of our member co-ops,” he says.

Energy managers agree that flexibility and adequate fuel supply are essential to getting through sustained severe weather.

“Each event has its own set of issues,” Jacobs says. “You have to evaluate and prepare for anything that might come your way.”

Basin Electric’s Raatz adds that G&Ts need “different types of generation resources that can be dispatched under different situations.

“It comes down to having a balance.”