TOPIC #2
Winter System Performance
Winter Storm Elliott is analyzed, while winter 2024 has its moment on the edge.
FERC, NERC Release Joint Report on Winter Storm Elliott
In late December 2022, a bomb cyclone later designated Winter Storm Elliott impacted both the bulk power and natural gas systems in the Eastern Interconnection. At its worst point, December 23-24, there were 90.5 GW of unplanned generator outages (about 13% of winter resources in the interconnection).
- Dry natural gas production dropped by 23% to 54% during the event. This had downstream operational impacts on gas availability and pressure for elevated power generation and retail natural gas demand.
- 1,702 individual generating units, of which 825 units were natural gas-fired generators, experienced 3,565 outages, derates, or failures to start.
- As generator outages mounted, the grid was operating well beyond N-1* planning conditions. To preserve frequency, grid operators in the interconnection shed a total of 5.4 GW of load during the event.
In October 2023, NERC, FERC, and regional reliability authorities released a 167-page joint report, following regional and utility after-action reports issued earlier in 2023. The report contained the following key findings:
- Freezing issues, fuel issues, and mechanical/electrical issues were responsible for 96% of outages, derates, and failures to start.
- The impact of extreme cold weather on mechanical and thermal stress, thermal cycling fatigue, and other effects (such as embrittlement and fuel and lubricant gelling) outstripped freezing and fuel issues as non-performance causes, although all played a role.
KEY TAKEAWAYS
FERC and NERC’s joint report on Winter Storm Elliott revealed continuing gaps in extreme cold weather preparations of the bulk power system.
Closing gaps that were identified after 2021’s Winter Storm Uri is key in improving cold weather operations in both gas and power systems.
Recent weather events in January 2024 showed some improved performance, as thermal generation and strong winds met demand and provided grid support.
FERC and NERC continue to promulgate new cold weather standards, but given timelines for implementation and pending generation retirements, the next few winters may be sources of concern.
FERC and NERC’s joint report on Winter Storm Elliott revealed continuing gaps in extreme cold weather preparations of the bulk power system.
Closing gaps that were identified after 2021’s Winter Storm Uri is key in improving cold weather operations in both gas and power systems.
Recent weather events in January 2024 showed some improved performance, as thermal generation and strong winds met demand and provided grid support.
FERC and NERC continue to promulgate new cold weather standards, but given timelines for implementation and pending generation retirements, the next few winters may be sources of concern.
A Few Concerning Developments During Elliott
There were some concerning developments mentioned in the FERC/NERC report.
First, a substantial majority of units lost due to freezing issues occurred at temperatures above their documented operating temperature (see Figures 2.1 and 2.2).
Second, natural gas fuel issues—such as low gas pressure due to a drop in regional gas production and pipeline freezing—caused about 20% of lost generation, with 9.5 GW related to transportation or pipeline pressure and 24 GW due to market issues and price restrictions.
Figure 2.1: Incremental Unplanned Generating Unit MW Outages, Derates, and Failures to Start (Total Event Area by Cause)
Source: FERC, NERC, and Regional Entity Staff Report on 2022 Winter Storm Elliott, Fig. 7
- Both firm and interruptible gas were curtailed by force majeure. Failure of gas suppliers to satisfy firm supply commitment and/or pipeline firm curtailments accounted for more generation loss (16.5 GW) than interruptible service interruptions (14 GW).
- In New York City, LNG kept local pipeline pressure adequate after it fell to levels that may have caused a complete gas system outage. Restoring service could have taken months.
Third, 19 GW of black-start-designated units—which can restore the grid after failure—experienced outages, derates, or failures to start, with 23% of those being failures to start, a core capability for such units.
The joint report pointed to prior event analyses and recommendations, particularly for 2021’s Winter Storm Uri report, many of which had made limited progress when the Elliott event occurred. For example, frozen transmitters, sensing lines, and other instrumentation—encountered in Uri—accounted for 42% of generation loss (or 46 GW) in Elliott.
Figure 2.2: Unavailable MW Due to Freezing Issues – All Balancing Authorities (December 21-26, 2022)
Overall, units reported 1,030 distinct freezing issue-related unplanned outages, derates, or start-up failures, which, combined, caused 110,962 MW of generation loss at various times during the event.
Notes: *"Other freeze-related issue” includes freeze-related sub-causes external to the generating unit such as frozen coal or ice on transmission lines. **Total=100%
Source: FERC, NERC, and Regional Entity Staff Report on 2022 Winter Storm Elliott, Fig. 75
Same as It Ever Was
The Elliott event had the largest footprint of any examined in a joint FERC-NERC-regional entity inquiry. The joint entities pointed several times to the similarity of issues experienced during Elliott to those of prior winter events.
Some common elements of these extreme cold weather events were natural gas production losses, mechanical/electrical and fuel issues, and load forecasts falling short of predicting peak electricity demand during the coldest periods.
Recommendations: Redoubling Efforts on Cold Weather Reliability
The joint entities recommended 11 actions to improve cold weather reliability for each of generators, natural gas infrastructure, gas-electric coordination, and grid operations.
Several of these recommendations repeat those issued after Winter Storm Uri: in particular, strengthening generators’ abilities to maintain extreme cold weather performance. Those recommendations are summarized at Figure 2.3.
Figure 2.3: Winter Storm Elliott Report Recommendations and Recommended Timing
Note: Recommendations contain selected references to Uri joint entity report as referenced in the Elliott report at Appendix E.
Source: Joint Entity Winter Storm Elliott Report and staff presentation
Moving Ahead
Despite halting progress on implementation of recommendations from Uri and prior major winter events, bulk power system players and FERC are pushing along processes that will improve extreme weather preparedness.
A post-Uri analysis of black-start resources in Texas issued in December 2023 studied the causes of black-start resource outages. It issued seven recommendations, focused on the following three themes:
- Black-start system restoration planning and testing
- An assessment of natural gas availability to black-start and next-start resources, as well as improved electric and natural gas coordination
- The prioritization of natural gas supply and transportation to black-start and next-start resources
In mid-February, FERC approved NERC’s proposed cold weather standards, which require that each balancing authority have operating processes for “extreme cold weather conditions” and that transmission operators consider impacts of load shedding during emergency conditions on gas infrastructure.
Timing is an issue, however. As Commissioner Clements observed, the cold weather standards will take effect “no sooner than April 1, 2027—three years, and crucially, three winters from today [February 14, 2024]."
Fast Forward One Year
Entering the 2023-24 winter season, NERC’s pre-season assessment placed much of the eastern United States and Canada at elevated risk of insufficient power reserves during the winter.
The winter proved to be relatively temperate, except for two significant incursions of Arctic weather, named Winter Storms Gerri and Heather, which occurred approximately January 8-14 and January 13-18, respectively.
Although the storms were not as long and severe as Winter Storm Uri, they did entail significant increases in power demand. One analysis found that Winter Storm Heather set new single-day electricity demand records in SPP and ERCOT. The storm set records for the second-highest electricity demand in the Southeast (after Winter Storm Elliott), the third highest in PJM, and the fourth highest in MISO.
While freezing temperatures affected some thermal units, the grid relied heavily on coal- and gas-fired dispatchable generation and benefited from favorable wind speed conditions, a weather condition that was lacking during the Uri event.
Figure 2.4A: MISO (Minneapolis and Little Rock) Temperatures (in °F) and Net Generation by Fuel Type and Net Interchange (MWh) (Jan. 5-19, 2024)
Source: Weather Underground; EIA Hourly Electric Grid Monitor
Figure 2.4B: PJM (Pittsburgh) Temperatures (in °F) and Net Generation by Fuel Type and Net Interchange (MWh) (Jan. 5-19, 2024)
Figure 2.4C: ERCOT (Dallas) Temperatures (in °F) and Net Generation by Fuel Type and Net Interchange (MWh) (Jan. 5-19, 2024)
Source: Weather Underground; EIA Hourly Electric Grid Monitor
Improved Performance, but Caution Ahead
The January 2024 winter storms were an early indicator of whether the industry’s remediations to date after Uri are effective. Texas was a case in point.
- While gas production fell by about 8% nationwide, Texas authorities conducted infrastructure inspections to ensure key facilities (processing, pipelines, storage) were properly weatherized to ensure minimal impact to the gas system.
- Forced outages of dispatchable generation were a fraction of that experienced during Uri.
- Energy storage remains a small portion of Texas capability, but it may play a greater role if storage duration can be lengthened.
Midcontinent ISO avoided emergency operations but issued cold weather and conservative operations alerts during Winter Storm Heather, even as its South region hit an all-time winter peak.
- At system peak, unplanned outages totaled 36 GW, of which 17 GW were gas-fired units. This was attributed in part to gas supply availability.
- Wind provided key support, comprising 16% to 20% of the energy mix during the peak period of the storm.
PJM relied upon thermal resources for about 90% of its power, including 41% from gas generators. At its system peak of 134 GW on January 17, it was able to export 8 GW to neighboring regions.
NERC and FERC announced they would review bulk power system performance during the January 2024 storms, the results of which are expected in June 2024.
IMPLICATIONS
System operators and planners will need to focus on weatherization, preparation, inspection, and coordination—on both the power and gas systems—to meet winter demands on bulk power resources. Emergency and transmission operations practices in extreme cold conditions will be a focus of NERC over the next few years.
Some difficult decisions will remain for fossil generators. They have been the main source of energy during extreme weather in the past. While many are slated for retirement, those units are not easily replaced by intermittent resources, particularly solar, because of its non-coincident performance in winter peak conditions. Generation owners may face difficult decisions on investment in weatherization and other winter preparation.
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