COURTENAY, N.D. — On any given day, the blades of 100 wind turbines that wrap around the central North Dakota town of Courtenay rotate softly over the prairie, generating enough energy to power 105,000 homes.

But when temperatures dropped below negative 20 degrees on Jan. 29, the white towers automatically came to a standstill and ceased to produce electricity. Until the air warmed up beyond that threshold, the turbines remained dormant.

Wind turbines here and elsewhere have software that senses when the air temperature drops below minus 20 and forces them to shut down, said Mark Nisbet of Xcel Energy, which owns the wind farm. It's an industry standard to protect turbines from damage during extremely cold weather.

Turbines across North Dakota shut down at times in the last week of January due to some of the coldest temperatures the area had seen since the mid-1990s. Wind power levels dropped significantly, more than experts anticipated.

Sen. Kevin Cramer, R-N.D., and others seized on the mid-winter lapse in wind power to criticize the Green New Deal, a policy proposal to reduce carbon emissions and address climate change. Cramer called the proposal "a fantasy."

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“What it did in my mind is it exposed a real vulnerability that we’ve often talked about over the years … of intermittent electric generation,” he said of the turbines shutting down.

Despite the recent outage, wind energy experts say turbines rarely shut down in North Dakota, so rarely that it doesn't affect the overall bottom line. It wouldn’t be economically feasible to develop turbines to handle lower temperatures, said Brian Draxten, manager of resource planning for Otter Tail Power Co., a utility based in Fergus Falls, Minn., that draws wind energy in North Dakota.

“The additional costs you have to incur for the very few times probably wouldn’t make it worth it,” he said.

Draxten said turbines have trouble operating below minus 20, much like a vehicle when fluids don’t stay warm enough to move through an engine properly. The systems use some energy to keep oil and components heated so they can start up again, he said.

ND has over 1,500 turbines

Wind provides about 6 percent of the power in the U.S., but it makes up about 25 percent of North Dakota’s electrical grid mix, according to the U.S. Energy Information Administration. The state has more than 1,500 wind turbines that can produce more than 3,000 megawatts, or enough to power almost 500,000 homes.

North Dakota feeds energy into a grid overseen by Midcontinent Independent System Operator (MISO), which manages 200,000 megawatts of energy in 15 states in the central U.S.

Based on feedback from electric companies, MISO predicted turbines would be able to produce 9,000 megawatts on Jan. 30, half of MISO's total capacity for wind power, Draxten said. But the extreme cold that forced turbines to shut down meant the companies feeding into MISO could only produce 4,000 megawatts, according to a MISO report released in late February.

The grid pulled from other resources to reduce the risk of electrical outages. Minnesota Power, Xcel Energy and Otter Tail said no homes in their systems lost power because of the wind turbine shutdown.

The Bison Wind Energy Center near New Salem, N.D., the largest in the state, only went down for one to two hours on Jan. 30, according to Minnesota Power, which owns the wind farm.

All-of-the-above policy

Other sectors in the energy industry also experience issues in extreme temperatures, said Michael Goggin, vice president of Grid Strategies, a Washington, D.C., consulting firm that helps companies integrate renewable energy into electric grids. He noted equipment in nuclear power plants can break down and coal piles can freeze.

“You can’t rely 100 percent on any one energy source,” he said.

Minnesota Power, Xcel Energy and Otter Tail get about 20 percent of their energy from wind, and the rest comes from other sources, including coal, natural gas and biomass. Thanks to diversified energy portfolios, grids in the Midwest were able to draw energy from other parts of the country during the January wind turbine outage, Nisbet said.

As the cold air moved out of North Dakota and into the Great Lakes region, wind turbines came back online and the Peace Garden State provided energy to those grids, Goggin said. “That type of event shows a strong grid is a key part of how we deal with events like this,” he said.

Cramer served on the North Dakota Public Service Commission from 2003 to 2012, when the body approved numerous wind projects.

He said he doesn’t regret signing off on those projects and is pleased about the energy mix the state produces. An all-of-the-above policy is the best plan, he said, but he doesn’t want to see services duplicated.

“What we have to be careful to do is not, in the name of diversity, kill baseload electricity,” he said.

Draxten said he doesn’t believe the U.S. will ever be 100 percent dependent on renewable energy. There are shortcomings to wind, but the cold won’t stop the industry from developing turbines in North Dakota, he said.