Utilities and grid operators across the country were forced into overdrive over the holiday weekend as a fierce winter storm pounded various regions and sent power demand soaring to new levels.
Frigid temperatures drove electricity demand to record highs and led to both controlled and uncontrolled outages over Christmas, while power generators in others had to burn unconventional fuels to keep the lights on where natural gas supplies were constrained under peak demand conditions.
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Tennessee Valley Authority, which serves some 10 million customers across the Southeast, asked customers going into the holiday weekend to do things like lower thermostats by one or two degrees and to delay laundry in order to manage demand, but the utility went on to direct intermittent power outages beginning on Christmas Eve to reduce the load.
TVA saw superlative demand conditions, with much of its service area experiencing single-digit temperatures. TVA said it managed its highest ever single-day demand on Dec. 24, its highest winter peak demand hour at 7 p.m. on that day, and its highest weekend peak power demand in its history.
The Southeast has typically scored favorably in recent seasonal risk assessments put out by the North American Electric Reliability Corporation, or NERC, which regulates grids across the continents, illustrating how extreme the conditions were for the region over the Christmas weekend.
Grid operators in other regions were also forced to take extraordinary measures to keep electricity flowing and ensure adequate reserve margins.
ISO New England, overseer of grid operations in six states, has historically struggled to maintain reliability during peak winter demand conditions in large part due to natural gas supply constraints. Those supply issues led utilities to increase combustion of fuel oil over the weekend as the grid operator declared a precautionary alert thanks to tight operating conditions.
Fuel oil made up as much as 38% of the region’s resource mix on Dec. 24, surpassing other thermal resources, including nuclear and gas. Oil as a percentage of ISO-NE’s total resource mix has since fallen but remains its top resource as of Tuesday.
The Electric Reliability Council of Texas, which has been subject to immense scrutiny after February 2021’s winter storm Uri led to widespread outages and more than 200 deaths, marked its own new winter peak demand record on Dec. 23.
That led ERCOT to request the Department of Energy declare an emergency and dispense to power generators operating more than a dozen natural gas-fired units from certain environmental regulations so they could operate at maximum capacity if necessary.
Without permission to maximize those units, ERCOT said, it could have to order outages.
“The loss of power to homes and local businesses in the areas that may be affected by curtailments presents a far greater risk to public health and safety than the temporary exceedances of those permit limits that would be allowed under the requested order,” ERCOT said in its Dec. 23 letter to DOE.
The department granted ERCOT’s request through Christmas Day.
Regulators at NERC have concluded that extreme weather is increasingly threatening the nation’s power grids and are warning the sector to be careful about retiring “always-on” thermal resources like coal and gas in favor of variable resources, such as wind and solar.
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NERC’s recent long-term reliability assessment said the increase in wind and solar installations in Texas is increasing its on-peak planning reserve margins, but it said those additions are simultaneously “elevating concerns of energy risks that result from the variability of these resources.”
Proponents of a more aggressive transition to renewable sources have argued that utilities need to install more battery storage to capture renewable energy and manage the variability of wind and solar. They have also pointed to outages of thermal sources, including natural gas units, which NERC concluded failed at a higher rate than wind units during the 2021 winter storm in Texas.
ERCOT said its Dec. 23 emergency request to DOE was driven by the outage or derating of approximately 11,000 megawatts of thermal generating units, 4,000 MW of wind generating units, and 1,700 MW of solar units.
