What we know: TVA ordered rolling blackouts for the first time in 90 years amid freezing temps

The Tennessee Valley Authority called for temporary energy load reductions, or rolling blackouts as some call them, to stabilize the regional power grid for the first time in its 89-year history amid subzero temperatures Friday morning.

TVA Chief Operating Officer Don Moul told The Tennessean Friday the power operator had to reduce strain on its grid as demand for energy ran nearly 35% higher than expected on a normal winter day, while at the same time a few of its coal and gas energy facilities were down because of the freezing temperatures.

"We've restored a number of those in each category, but we still have some work to do to build additional margin," Moul said.

TVA is working to build up some of its energy margin as temperature settle into the high single digits and low teens across the state.

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"We're optimistic, but also realistic," Moul said. "We have some real cold temperatures through the next 48 hours, and we're expecting peak [energy use] in the evening tonight into tomorrow morning, similar to what we've already seen."

On Thursday night and Friday morning, temperatures dipped below zero across much of Tennessee, with wind chills making it feel significantly colder. High temperatures are expected to rise into the 20s on Saturday, and stay there through Christmas Day.

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TVA previously said it wouldn't need to do rolling blackouts

Last year, TVA said it would take temperatures of negative 10 across the Tennessee River valley for it to have to use all of its generations at once, and still, rolling blackouts would be unlikely unless a nuclear unit suddenly went offline.

A nuclear plant did not go offline, but Moul said the temperatures were some of coldest every recorded by TVA in Tennessee in its history.

"The National Weather Service has called this a once in a generation event," Moul said. "So, pretty extreme conditions."

How many people are without power in Nashville?

More than 22,000 customers of Nashville Electric Service reported outages as of 6:15 p.m. Friday. That number was down from more than 50,000 an hour earlier.

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The largest group of outages was in the Cane Ridge neighborhood, where an unrelated equipment failure fire impacted 20,000 customers. NES said power had been restored to 8,000 customers in the area.

When will my power come back in Nashville?

Some of Nashville's outages are expected to last until Saturday, Jack Baxter, vice president of operations, NES, said.

NES crews have been working around the clock in the frigid temperatures, he said, and they'll continue to do so, come what may.

"Keep our workers in mind," he said. "We understand for our customers without power, it's very cold. It's very frigid conditions. Our crews are out in this working so please keep them in your thoughts."

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Between 25 and 30 crews have been working all day Friday, he said, and 15-20 are scheduled to work overnight.

Who lost power in Nashville?

NES is responsible for managing its own grid load, Baxter said. The company began asking high-usage commercial customers to voluntarily shut down some power usage around 9 a.m.

The order from TVA came in around 9:45 a.m. and lasted until 11:45 a.m.

Baxter couldn't estimate how many customers were included in the rolling blackouts. The company divides the city into 12 parts, identifies and removes critical infrastructure like hospitals and water treatment plants from the regions and then begins the process of switching off power for 10 minutes on a rotational basis as needed.

"They did notify us pretty early that the load curtailments were working and the system had stabilized. So everything was going well," Baxter said.

A plan in case of need like this has been in place for decades, he said. This was the first time it was implemented.

Why didn't I get warning of the rolling blackouts?

Nashville residents expressed dissatisfaction with the limited warning given to customers before the blackouts began Friday morning.

But the company had a matter of minutes to act, Baxter said. The operations team notified NES' communications team, which later shared a news release and social media posts.

"When demand exceeds generation capacity, it's imperative that we that we bring that demand below generating capacity as quickly as we can," he said. "We literally have minutes to make that happen to keep from causing other problems."

Other regional electric companies did use social media to announce the plan sooner than NES did.

Why is my power out?

Baxter said the majority of ongoing Nashville outages were weather related, although some indirectly.

At least five poles were damaged by automobile collisions, he said. Otherwise, high winds and fallen trees or branches impacted equipment.

What you can do to reduce energy, but stay safe

Moul said it was important for people to balance safety, but that they can do simple things like not running their dishwashers or doing laundry until it's the warmest part of the day.

He added people should also open blinds on the sunny side of their house because it can cut down on of the heating energy load.

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Reach reporter Mariah Timms at mtimms@tennessean.com or 615-259-8344 and on Twitter @MariahTimms.

Adam Friedman is The Tennessean's state government and politics reporter. Reach him by email at afriedman@tennessean.com

This article originally appeared on Nashville Tennessean: Why Tennessee Valley Authority ordered rolling blackouts in Nashville