Drawing No. EH–CA–016 // Engineering Case Study
The February 2021 Texas power crisis, widely associated with Winter Storm Uri, caused widespread controlled blackouts as extreme cold, record demand, generation outages and natural-gas constraints affected the ERCOT power grid. This interactive ERCOT case study uses real Texas county contours grouped into eight weather zones to show how the emergency developed and how the system recovered.
Select a stage or run the event.
A crawlable summary of the same nine stages used by the interactive ERCOT replay.
Forecasts indicate an Arctic outbreak capable of producing widespread sub-freezing conditions and record winter electricity demand.
Severe cold expands across Texas. At hour-ending 20:00 on February 14, ERCOT reaches an all-time winter peak load of 69,871 MW.
Thermal, wind and other resources experience cold-related trips, derates and failures to start. Natural-gas production and delivery also deteriorate.
Operating reserves fall rapidly. ERCOT progresses through emergency alert levels and begins ordering firm load shedding.
A rapid sequence of generation losses drives frequency to its minimum. Emergency load shedding expands and arrests the decline.
Firm load shedding reaches approximately 20 GW in ERCOT while unavailable generation peaks above 50 GW. Millions of customers remain without electricity.
ERCOT averages approximately 34 GW of generation outages for more than two consecutive days. Cold, fuel constraints and equipment failures continue.
Improving weather and returning generation allow ERCOT to authorise restoration of emergency load, although some local customers remain de-energised.
ERCOT exits Energy Emergency Alert Level 3. System conditions stabilise, although some customer and infrastructure impacts continue.
Normal operation, emergency decline and recovery.
The emergency in five linked mechanisms.
Official milestones with educational interpolation.
| Stage | Demand (GW) | Available generation (GW) |
|---|---|---|
| 1. February 8–11, 2021 | 63 | 72.0 |
| 2. February 13–14 | 69.871 | 70.5 |
| 3. Late February 14 | 68.5 | 64.0 |
| 4. February 15 · 00:15–01:20 CST | 66 | 58.0 |
| 5. February 15 · approximately 01:51 CST | 60 | 50.0 |
| 6. February 15–16 | 50 | 47.0 |
| 7. February 16–17 | 53 | 49.0 |
| 8. February 18 | 57 | 61.0 |
| 9. February 19 · approximately 09:00 CST | 58 | 67.0 |
| Stage | Generation unavailable (GW) | Firm load shed (GW) |
|---|---|---|
| 1. February 8–11, 2021 | 12 | 0.0 |
| 2. February 13–14 | 16 | 0.0 |
| 3. Late February 14 | 23 | 0.0 |
| 4. February 15 · 00:15–01:20 CST | 30 | 1.0 |
| 5. February 15 · approximately 01:51 CST | 38 | 10.0 |
| 6. February 15–16 | 52.277 | 20.0 |
| 7. February 16–17 | 34 | 15.0 |
| 8. February 18 | 22 | 2.0 |
| 9. February 19 · approximately 09:00 CST | 14 | 0.0 |
| Stage | ERCOT frequency (Hz) | Condition |
|---|---|---|
| 1. February 8–11, 2021 | 60.000 | Controlled |
| 2. February 13–14 | 59.990 | Controlled |
| 3. Late February 14 | 59.950 | Controlled |
| 4. February 15 · 00:15–01:20 CST | 59.720 | Emergency |
| 5. February 15 · approximately 01:51 CST | 59.302 | Severe decline |
| 6. February 15–16 | 59.940 | Emergency |
| 7. February 16–17 | 59.980 | Controlled |
| 8. February 18 | 60.000 | Controlled |
| 9. February 19 · approximately 09:00 CST | 60.000 | Controlled |
| Stage | Normal | Cold watch | Stressed | Critical | Load shed | Restoring |
|---|---|---|---|---|---|---|
| 1. February 8–11, 2021 | 5 | 3 | 0 | 0 | 0 | 0 |
| 2. February 13–14 | 2 | 3 | 3 | 0 | 0 | 0 |
| 3. Late February 14 | 0 | 1 | 4 | 3 | 0 | 0 |
| 4. February 15 · 00:15–01:20 CST | 0 | 0 | 3 | 5 | 0 | 0 |
| 5. February 15 · approximately 01:51 CST | 0 | 0 | 0 | 4 | 4 | 0 |
| 6. February 15–16 | 0 | 0 | 0 | 0 | 8 | 0 |
| 7. February 16–17 | 0 | 0 | 0 | 3 | 5 | 0 |
| 8. February 18 | 0 | 0 | 0 | 0 | 0 | 8 |
| 9. February 19 · approximately 09:00 CST | 0 | 0 | 0 | 0 | 0 | 8 |
The crisis was not caused by one generating technology. Extreme cold simultaneously increased electricity demand and degraded natural-gas production, fuel delivery, generating equipment, water systems and distribution infrastructure. The common weather hazard made failures correlated rather than independent.
When generation losses outpaced the ability to replace supply, ERCOT ordered transmission and distribution utilities to disconnect firm demand. This reduced the power imbalance and stabilised frequency, but the available amount of switchable load was limited and many outages became prolonged rather than rotational.
ERCOT uses eight weather zones for load and weather information. The county contours are real; the zone assignments and outage progression are simplified to make the system-wide spread understandable. They are not an official county-by-county outage record.
Four concise conclusions.
A simplified barrier review.
Open each topic for the underlying system principles.
Cold reduced gas production and processing while heating demand increased. Some compressors and production facilities also depended on electricity, allowing disruptions in one system to worsen the other.
Firm load shedding is the controlled disconnection of customer demand that is not already participating as an interruptible resource. It is used only when voluntary conservation and operating reserves are insufficient.
The required load reduction was exceptionally large. Circuits serving critical facilities were often excluded, leaving a smaller pool of switchable circuits and limiting equitable rotation.
The broader FERC/NERC event analysis grouped reported causes into freezing, fuel issues, mechanical or electrical problems and other causes. These categories applied across multiple resource types and should not be interpreted as an hourly ERCOT generation mix.
Four transferable lessons.
Short answers to common questions.
No. Wind was affected, but the event also involved natural-gas, coal, nuclear and other generation, together with fuel and infrastructure constraints.
No. Fuel limitations were important, but freezing, mechanical and electrical failures, demand forecasting, winterisation and outage-plan limitations also mattered.
No. Frequency fell dangerously low, but emergency load shedding arrested the decline before uncontrolled system separation. A full collapse would have required a much slower black-start recovery.
No. County shapes are real, while weather-zone grouping and stage timing are educational approximations.
Approximately 20 GW refers to ERCOT's ordered firm load shed. The 23.418 GW figure refers to the largest combined firm-load-shed event across the wider South Central event area.
Compare the event with other EngineerHub disturbance replays.
Official references and educational boundaries.
Primary investigation: FERC/NERC February 2021 Cold Weather Outages Final Report.
ERCOT event archive: February 2021 Extreme Weather Event materials, including the legislative-hearing presentation and operational notices.
Weather-zone definition: ERCOT Weather Forecast and Weather Zones.
County geometry: Texas county map, cartographic boundary 1:500,000 SVG, published under CC0 on Wikimedia Commons.
County-to-weather-zone assignment, regional propagation, transmission corridors, intermediate system values and customer-impact timing are educational approximations. Official milestones include the winter peak, rapid generation loss, frequency nadir, firm load shedding, average outage magnitude and EEA3 exit.
Include the inputs and assumptions used.
EngineerHub.org