Evidence room for a neighborhood emergency planner. Question dated ; packet frozen as of that date.
Should ERCOT's published winter reserve be represented as a guarantee for an extreme cold event?
Answer
No. Treat it as a planning estimate, not a guarantee.
ERCOT's final winter SARA for December 2020 through February 2021 shows 16,198 MW of capacity available for operating reserves in the forecast case, but only 1,352 MW in its extreme peak load and extreme generation outage case. ERCOT labels that row “Capacity Available for Operating Reserves, Normal Operating Conditions” and builds it from historical averages and percentiles. ST1 ERCOT SARA
If every other extreme-case assumption stayed fixed, that reserve would reach zero when thermal forced outages total 11,231 MW, which is 1,352 MW more than the 9,879 MW the SARA assumes in that column. ST1 ERCOT SARA
In 2011, FERC and NERC staff wrote that ERCOT and others “had adequate reserve margins, based on anticipated generator availability” but “those reserves proved insufficient.” ST2 FERC/NERC 2011
Decision: before , adopt a neighborhood extreme cold plan that assumes rotating outages can happen during a multi-day freeze even when published reserves look adequate. Specific actions below. No probability is assigned to any storm, and no motive is alleged.
- 16,198 MWforecast case operating reserve ST1
- 1,352 MWextreme load and extreme outage case ST1
- 11,231 MWthermal forced outage total that would exhaust it (computed) ST1
- 29,729 MW2011 ERCOT loss, cumulative over two days, not simultaneous ST2
Remaining operating reserve in each SARA column
Reconciliation: every baseline number
All four columns share Total Resources 82,513 MW, Peak Demand 57,699 MW and Reserve Capacity 24,814 MW. Each column then subtracts its own adjustments; the recomputed totals match the printed rows [d] and [e] exactly in all four columns. ST1 ERCOT SARA
The 19 listed resource lines sum to 82,514 MW, 1 MW above the printed total, consistent with rounding; the published reserve uses the printed total. ST1 ERCOT SARA
The extreme peak forecast of 67,208 MW equals Peak Demand plus the 9,509 MW Seasonal Load Adjustment, and the SARA bases it on the 2011 winter. The summary outage forecast of 8,616 MW equals forecast case maintenance plus typical forced outages. ST1 ERCOT SARA
Wind: the 6 wind lines contribute 7,070 MW; the low wind level is 1,791 MW; the difference is the printed 5,279 MW Low Wind Output Adjustment. ST1 ERCOT SARA
| Line | MW | Source |
|---|---|---|
| Operational Resources (thermal and hydro), MW | 67,529 | ST1 line 9 |
| Switchable Capacity Total, MW | 3,710 | ST1 line 10 |
| Less Switchable Capacity Unavailable to ERCOT, MW | -568 | ST1 line 11 |
| Available Mothballed Capacity, MW | 0 | ST1 line 12 |
| Capacity from Private Use Networks, MW | 3,631 | ST1 line 13 |
| Coastal Wind, Peak Average Capacity Contribution, MW | 1,480 | ST1 line 14 |
| Panhandle Wind, Peak Average Capacity Contribution, MW | 1,411 | ST1 line 15 |
| Other Wind, Peak Average Capacity Contribution, MW | 3,251 | ST1 line 16 |
| Solar Utility-Scale, Peak Average Capacity Contribution, MW | 269 | ST1 line 17 |
| Storage, Peak Average Capacity Contribution, MW | 0 | ST1 line 18 |
| RMR Capacity to be under Contract | 0 | ST1 line 19 |
| Capacity Pending Retirement, MW | 0 | ST1 line 20 |
| Non-Synchronous Ties, Capacity Contribution, MW | 838 | ST1 line 21 |
| Planned Thermal Resources with Signed IA, Air Permits and Water Rights, MW | 0 | ST1 line 22 |
| Planned Coastal Wind with Signed IA, Peak Average Capacity Contribution, MW | 371 | ST1 line 23 |
| Planned Panhandle Wind with Signed IA, Peak Average Capacity Contribution, MW | 0 | ST1 line 24 |
| Planned Other Wind with Signed IA, Peak Average Capacity Contribution, MW | 557 | ST1 line 25 |
| Planned Solar Utility-Scale, Peak Average Capacity Contribution, MW | 35 | ST1 line 26 |
| Planned Storage, Peak Average Capacity Contribution, MW | 0 | ST1 line 27 |
| Sum of the 19 listed lines (computed) | 82,514 | computed from ST1 |
| [a] Total Resources (printed) | 82,513 | ST1 |
| [b] Peak Demand (printed) | 57,699 | ST1 |
| [c] Reserve Capacity [a - b] (printed; recomputed 24,814) | 24,814 | ST1 |
| Line | S1. Forecasted Season Peak Load | S2. Extreme Peak Load, Typical Generation Outages | S3. Forecasted Season Peak Load, Extreme Low Wind Output | S4. Extreme Peak Load, Extreme Generation Outages | Source |
|---|---|---|---|---|---|
| Total Resources [a] | 82,513 | 82,513 | 82,513 | 82,513 | ST1 |
| Peak Demand [b] | 57,699 | 57,699 | 57,699 | 57,699 | ST1 |
| Reserve Capacity [c] = a - b | 24,814 | 24,814 | 24,814 | 24,814 | ST1 |
| Seasonal Load Adjustment | 0 (printed as a dash) | 9,509 | 0 (printed as a dash) | 9,509 | ST1 |
| Peak demand used (b + seasonal adjustment) | 57,699 | 67,208 | 57,699 | 67,208 | ST1 |
| Typical Maintenance Outages, Thermal | 4,074 | 4,074 | 4,074 | 4,074 | ST1 |
| Typical Forced Outages, Thermal | 4,542 | 5,339 | 4,542 | 5,339 | ST1 |
| 95th Percentile Forced Outages, Thermal | 0 (printed as a dash) | 0 (printed as a dash) | 0 (printed as a dash) | 4,540 | ST1 |
| Thermal forced outages, total (typical + 95th) | 4,542 | 5,339 | 4,542 | 9,879 | ST1 |
| Low Wind Output Adjustment | 0 (printed as a dash) | 0 (printed as a dash) | 5,279 | 0 (printed as a dash) | ST1 |
| [d] Total Uses of Reserve Capacity (printed) | 8,616 | 18,922 | 13,895 | 23,462 | ST1 |
| [d] recomputed: seasonal + maintenance + forced + 95th + low wind | 8,616 | 18,922 | 13,895 | 23,462 | ST1 |
| [e] Capacity Available for Operating Reserves, Normal Operating Conditions (printed) | 16,198 | 5,892 | 10,919 | 1,352 | ST1 |
| [e] recomputed: c - d | 16,198 | 5,892 | 10,919 | 1,352 | ST1 |
Thermal forced outage total that exhausts operating reserve
In the Extreme Peak Load, Extreme Generation Outages column the SARA assumes 5,339 MW of typical forced outages plus 4,540 MW at the 95th percentile, 9,879 MW in all, and leaves 1,352 MW. With every other assumption fixed, each extra MW of thermal forced outage removes one MW of reserve, so reserve reaches zero at 9,879 MW + 1,352 MW = 11,231 MW. ST1 ERCOT SARA
Cross-check: the Extreme Peak Load, Typical Generation Outages column reaches the same point, 5,339 MW + 5,892 MW = 11,231 MW. ST1 ERCOT SARA
This is arithmetic on published assumptions. Zero is the point of mathematical exhaustion, not the point where trouble starts: the packet does not give a 2020/2021 minimum reserve requirement, and in 2011 ERCOT had a 2,300 MW minimum responsive reserve requirement and reserves that “eventually dropped below the level of safe operation.” ST1 ERCOT SARA ST2 FERC/NERC 2011
Sensitivity: hypothetical extra thermal forced outages
Sensitivity, not a measurement or prediction The control adds a hypothetical amount to the thermal forced outages of the extreme load and extreme outage column and holds everything else fixed. It does not report any measured outage and does not forecast one.
Published SARA column (fixed)
Immutable Extreme Peak Load / Extreme Generation Outages During Extreme Peak Load
Thermal forced outages 9,879 MW
Remaining operating reserve 1,352 MW
Hypothetical sensitivity
Black line: zero crossing at 1,352 MW extra (total 11,231 MW). Orange mark: your setting. Green: reserve remains. Red: exhausted.
Extra (hypothetical): 0 MW
Total thermal forced outages: 9,879 MW
Remaining operating reserve: 1,352 MW
| Hypothetical extra thermal forced outages | Total thermal forced outages | Remaining operating reserve | State |
|---|---|---|---|
| 0 MW | 9,879 MW | 1,352 MW | above zero |
| 500 MW | 10,379 MW | 852 MW | above zero |
| 1,000 MW | 10,879 MW | 352 MW | above zero |
| 1,352 MW | 11,231 MW | 0 MW | zero crossing |
| 1,500 MW | 11,379 MW | -148 MW | exhausted |
| 2,000 MW | 11,879 MW | -648 MW | exhausted |
| 2,500 MW | 12,379 MW | -1,148 MW | exhausted |
| 3,000 MW | 12,879 MW | -1,648 MW | exhausted |
Normal operating reserve is not an instantaneous guarantee
The SARA row is titled “Capacity Available for Operating Reserves, Normal Operating Conditions (c-d)”. Its forced outage inputs are historical averages for December through February weekdays, hours ending 7 am - 10 am, over 2017/18, 2018/19, and 2019/20, and its 95th percentile row adds the fuel limitation derates of the January 17, 2018 event. ST1 ERCOT SARA
The SARA summary says ERCOT “anticipates there will be sufficient installed generating capacity available to serve system-wide forecasted peak demand this winter season”; its peak forecast is based on normal weather conditions during peak periods, from 2004 through 2018. That statement concerns forecasted peak demand, not the extreme columns. ST1 ERCOT SARA
An instantaneous operational guarantee would mean load is served at every moment of an event. The 2011 report shows why a positive planning reserve does not provide that: ERCOT started the first day with 3,100 MW of responsive reserves against a 2,300 MW minimum, and generator failures still “overwhelmed ERCOT’s reserves.” ST2 FERC/NERC 2011
The earlier FERC/NERC warning, in its own words
Exact sentences from the August 2011 staff report, printed pages 7 to 10. ST2 FERC/NERC 2011
“Going into the February 2011 storm, neither ERCOT nor the other electric entities that initiated rolling blackouts during the event expected to have a problem meeting customer demand.”
FERC/NERC staff, August 2011, packet line 4. ST2 FERC/NERC 2011
“They all had adequate reserve margins, based on anticipated generator availability.”
FERC/NERC staff, August 2011, packet line 4. ST2 FERC/NERC 2011
“But those reserves proved insufficient for the extraordinary amount of capacity that was lost during the event from trips, derates, and failures to start.”
FERC/NERC staff, August 2011, packet line 4. ST2 FERC/NERC 2011
“In the case of ERCOT, where rolling blackouts affected the largest number of customers (3.2 million), there were 3100 MW of responsive reserves available on the first day of the event, compared to a minimum requirement of 2300 MW.”
FERC/NERC staff, August 2011, packet line 6. ST2 FERC/NERC 2011
“But over the course of that day and the next, a total of 193 ERCOT generating units failed or were derated, representing a cumulative loss of 29,729 MW.”
FERC/NERC staff, August 2011, packet line 6. ST2 FERC/NERC 2011
“Combining forced outages with scheduled outages, approximately one-third of the total ERCOT fleet was unavailable at the lowest point of the event.”
FERC/NERC staff, August 2011, packet line 6. ST2 FERC/NERC 2011
“These extensive generator failures overwhelmed ERCOT’s reserves, which eventually dropped below the level of safe operation.”
FERC/NERC staff, August 2011, packet line 6. ST2 FERC/NERC 2011
“Generators and natural gas producers suffered severe losses of capacity despite having received accurate forecasts of the storm.”
FERC/NERC staff, August 2011, packet line 12. ST2 FERC/NERC 2011
“However, the poor performance of many of these generating units and wells suggests that these procedures were either inadequate or were not adequately followed.”
FERC/NERC staff, August 2011, packet line 12. ST2 FERC/NERC 2011
“These recommendations were not mandatory, and over the course of time implementation lapsed.”
FERC/NERC staff, August 2011, packet line 14. ST2 FERC/NERC 2011
“Many of the generators that experienced outages in 1989 failed again in 2011.”
FERC/NERC staff, August 2011, packet line 14. ST2 FERC/NERC 2011
“At least another 12 percent were indirectly attributable to the weather (occasioned by natural gas curtailments to gas-fired generators and difficulties in fuel switching).”
FERC/NERC staff, August 2011, packet line 9. ST2 FERC/NERC 2011
Cumulative 2011 loss versus a simultaneous outage
The 29,729 MW figure is a cumulative loss: it adds up 193 units that failed or were derated over that day and the next. It is not a simultaneous outage, and it cannot be set against the 11,231 MW single-column threshold above. ST2 FERC/NERC 2011
The report’s simultaneous measure is a fraction: combining forced and scheduled outages, approximately one-third of the total ERCOT fleet was unavailable at the lowest point of the event. The packet does not give the 2011 fleet size in MW, so that fraction cannot be converted into MW here. ST2 FERC/NERC 2011
Timeline from the packet
- Cold weather caused many generators to trip, derate, or fail to start; non-mandatory winterization recommendations followed and implementation lapsed. ST2 FERC/NERC 2011
- Southwest cold weather event; rolling blackouts in ERCOT affected 3.2 million customers. ST2 FERC/NERC 2011
- FERC/NERC staff report on causes and recommendations. ST2 FERC/NERC 2011
- ERCOT releases the final winter 2020/2021 SARA, the date of this question. ST1 ERCOT SARA
- Season the SARA covers. ST1 ERCOT SARA
What the SARA does not prove
These outage definitions and common-cause risks cannot be bounded from this packet. Each item names what the packet does say.
- Outages beyond the 95th percentile. The outage rows are averages and a 95th percentile drawn from 2017/18, 2018/19, and 2019/20 plus one named fuel event; the packet gives no larger outage case, so a worse forced outage total cannot be bounded from it. Packet basis: Based on the 95th percentile historical average of forced outages for December through February weekdays, hours ending 7 am - 10 am, for the last three winter seasons (2017/18, 2018/19, and 2019/20) plus additional fuel limitation-related derates/outages at units in north Texas during the peak load hours for the January 17, 2018 cold weather event ST1 ERCOT SARA
- Outage definition window. Forced and maintenance outages are defined for December through February weekdays, hours ending 7 am - 10 am; the packet does not state outages for other hours, weekends, or a multi-day event. Packet basis: Based on historical average of forced outages for December through February weekdays, hours ending 7 am - 10 am, for the last three winter seasons (2017/18, 2018/19, and 2019/20); both Extreme Load scenarios include typical fuel limitation-related derates/outages at units in north Texas during extreme peak load hours ST1 ERCOT SARA
- Common-cause fuel supply loss. In 2011 at least another 12 percent of Southwest generator failures were indirectly weather-related, occasioned by natural gas curtailments and fuel switching difficulties; the SARA packet gives no statewide gas curtailment case. Packet basis: Only typical north Texas fuel limitation derates and those of the January 17, 2018 event are included. ST1 ERCOT SARA ST2 FERC/NERC 2011
- Low wind combined with extreme load and extreme outages. Simple subtraction of the low wind adjustment from the extreme column would give -3,927 MW, but this is arithmetic only: the SARA neither publishes this combination nor states that the adjustments add. Packet basis: No printed column combines the 5,279 MW low wind adjustment with the extreme load and extreme outage adjustments. ST1 ERCOT SARA
- Cold beyond the 2011 basis. The extreme load case is anchored to the 2011 winter; demand above 67,208 MW is not modeled in the packet. Packet basis: Based on the 2011 winter and a revised economic growth forecast prepared in April 2020; the extreme winter forecast is 67,208 MW ST1 ERCOT SARA
- Winterization status of the 2020 fleet. The packet contains no 2020 winterization compliance or inspection data, so cold-related failure modes such as frozen sensing lines cannot be bounded. Packet basis: ST2 reports that 1989 winterization recommendations were not mandatory, implementation lapsed, and many units failed again in 2011. ST2 FERC/NERC 2011
- Resource lines no scenario stresses. None of the five adjustment rows reduces private use network, switchable, tie, or planned capacity, so their availability in a regional cold event is assumed, not shown. Packet basis: Switchable Capacity Total, MW 3,710 MW; Capacity from Private Use Networks, MW 3,631 MW; Non-Synchronous Ties, Capacity Contribution, MW 838 MW; planned resources total 963 MW. ST1 ERCOT SARA
- Operating reserve floor. The packet does not state the 2020/2021 minimum reserve requirement, so zero is only the mathematical exhaustion point; trouble can begin while the figure is still positive. Packet basis: The SARA row is 'Capacity Available for Operating Reserves, Normal Operating Conditions'. ST2 reports a 2011 minimum responsive reserve requirement of 2300 MW and reserves that dropped below the level of safe operation. ST1 ERCOT SARA ST2 FERC/NERC 2011
- No single-moment 2011 MW figure. The packet gives a fraction of the fleet at the lowest point, not a MW figure, and the 29,729 MW figure is cumulative over two days; neither can be compared directly with the 2020 thermal forced outage threshold. Packet basis: approximately one-third of the total ERCOT fleet was unavailable at the lowest point of the event ST2 FERC/NERC 2011
- Printed total versus line sum. A 1 MW difference, consistent with rounding of the listed lines; the published reserve uses the printed total. Packet basis: Printed Total Resources 82,513 MW; sum of the 19 listed lines 82,514 MW. ST1 ERCOT SARA
Proposed preparedness decision
Do not represent the SARA reserve as a guarantee. Before December 1, 2020, adopt a neighborhood extreme cold plan that assumes rotating outages can occur during a multi-day freeze even when published reserves look adequate.
- Build a roster of households that depend on powered medical equipment or electric heat, with a named check-in volunteer for each household.
- Designate one warming site with heat and backup power that does not depend on the grid, and test it before December 1, 2020.
- Set an activation trigger: a forecast of cold comparable to February 2011, or any grid conservation or emergency appeal.
- Keep a phone tree and printed contact sheet so outreach works without home power or internet.
Why: the extreme case leaves only 1,352 MW under normal operating conditions ST1; the extreme load basis is the 2011 winter ST1; and in 2011 reserves that looked adequate were overwhelmed by generator failures despite accurate forecasts ST2. This plan does not depend on knowing how likely a storm is, and it makes no claim about anyone’s intent.
Original official sources
- ST1 ERCOT SARA: Final Seasonal Assessment of Resource Adequacy for the ERCOT Region (SARA), Winter 2020/2021, ERCOT, November 5, 2020. Packet file sara.txt.
- ST2 FERC/NERC 2011: Report on Outages and Curtailments During the Southwest Cold Weather Event of February 1-5, 2011: Causes and Recommendations, FERC/NERC, August 2011. Packet file winter-2011.txt.
Each link stores the original address, so it survives offline; opening it needs a connection. This page names no individual people and makes no claims about any person.
Generated by model.py from the packet text and verified by check.py. Sensitivity values are hypothetical.