Tennessee is vulnerable to winter blackouts. Here is a big reason why.

Last December, the Tennessee Valley Authority said it was prepared to handle 34 gigawatts of demand. When an Arctic blast dropped temperatures right before Christmas, demand peaked at about 33.4 GW.

But TVA failed to deliver the power it promised it could handle, and the utility was forced to order blackouts. More than a dozen fossil fuel plants faltered, and hundreds of thousands of Tennesseans lost power. It was the biggest test to date for TVA.

TVA says it is fixing the problem. But federal officials say the region remains vulnerable to power shortages — and, while TVA can weatherize plants, the fossil fuel system on which it relies extends past its control.

What happened last December? 

By mid-December 2022, TVA knew severe weather was coming. TVA communicated the threat across the organization and committed all available generation. On Dec. 22, temperatures dropped more than 40 degrees in just five hours. 

On Dec. 23, many cities in TVA’s seven-state region dipped below zero. By late morning, TVA had 6.5 GW of unplanned outages, equivalent to nearly 20% of peak demand, according to a recent report by the Federal Energy Regulatory Commission, or FERC.

TVA asked local power companies like the Nashville Electric Service to cut power by 10% through rolling blackouts. 

The blackouts were needed because of lost fossil fuel generation. TVA could not fully operate 10 of its 17 gas plants, three of its four owned coal plants and its one contracted coal plant in Mississippi. 

Courtesy Tennessee Valley Authority

At least 10 of the Tennessee Valley Authority’s methane gas plants failed during Winter Storm Elliott in December 2022. At least three of TVA’s four owned coal plants had failures, and one contracted coal plant had a failure.

(Note: TVA was also unable to generate power at one of its gas plants in Memphis, shown in the image above as being in operation, but TVA has since said that failure was caused by old age and not cold weather. Also, the image does not show the Gallatin Fossil Plant, a coal plant east of Nashville.)

What caused the power outages? 

The FERC report examined the entire region of the Eastern U.S. affected by power outages during the December storm, called Winter Storm Elliott, and identified the top three causes. FERC estimated that mechanical and electrical issues caused 41% of outages, while freezing issues caused 31% and gas fuel issues caused 20%. FERC noted that a “substantial majority” of generation loss from power plants occurred at temperatures above their documented minimum temperature thresholds.

Most power generation losses were related to gas, the report shows, following precedent: Fossil gas, also called “natural gas” or methane gas, has become the focus of scrutiny related to winter blackouts because gas has failed the most.

“Extreme cold weather events have repeatedly impaired the production, gathering, processing, and transportation of natural gas,” the FERC report says, referencing several events like the deadly Winter Storm Uri in 2021. 

Last year, gas was the largest source of electricity in the U.S, accounting for about 40%, and could be as bad as coal in its contribution to climate change. It is a fossil fuel comprised mostly of methane, a greenhouse gas that heats the planet about 80 times faster than carbon dioxide in a 20-year timeframe.

Courtesy Federal Energy Regulatory Commission

Gas failures represented the majority of lost generation in the U.S. during Winter Storm Elliott in December 2022.

Gas plants are particularly vulnerable to outages because cold weather affects its entire supply chain, including fracking sites, pipelines compressor stations and power plants. Last December, TVA reported an inadequate gas supply and insufficient pressure on pipelines in some locations.

Gas also overlaps with electricity, as the gas system requires electricity to make electricity. 

“We have an interconnected gas-electric system. What happens on one system does impact the other system,” Mark Lauby, the chief engineer at the North American Electric Reliability Corporation, or NERC, said at a meeting with FERC earlier this month. 

Both the physical components of the fossil gas system and their interconnectedness with the wider energy system present serious challenges. TVA can weatherize its gas plants — the utility says it has spent $8 million in recent months to do just that — but does not control what happens further up the supply chain. 

Federal officials have warned that there is no entity regulating the entirety of the fossil gas system at this time. 

FERC Chairman Willie Phillips, during a regular meeting this month, said the energy industry needs “an organization that has responsibility and authority for the natural gas system reliability.”

How bad is the risk? 

NERC estimated that Tennessee, and a portion of surrounding states, could fall about 5.7 GW short of capacity during a bad storm this winter — similar to last year. 

“Natural-gas-fired generator availability and output can be threatened when the fuel supply is insufficient or when infrastructure is unable to maintain the flow of fuel. As Winter Storm Elliott demonstrated, the rapid decline in natural gas production during periods of extreme cold weather can have wide-area consequences for the grid,” NERC said in its reliability assessment for the upcoming winter season.

In the Southern U.S., utilities have not added much new generation since last year. “Forecasted peak demand has risen while resources have changed little in these areas since Winter Storm Elliot caused energy emergencies across the area in 2022,” NERC said. 

This year, TVA added 1 GW of purchased power and 1.4 GW of new gas generation, spokesperson Scott Brooks said.

TVA does plan to build a lot more generation in the next few years. Based on public announcements and the most recent budget, most of that generation will be gas.