Last year, Winter Storm Uri walloped Texas like no other winter storm in memory. Like everyone else, we spent several days hunkered down without power or water, wondering when the lights would come back on. Sure, we’ve all heard the Texas grid is now better prepared to weather extremes. But recent weather events have got us and our customers wondering about how events during the big Texas Freeze unfolded, why the grid failed, and what happened in the aftermath.
As an energy provider, part of our job is to help customers understand Texas electricity. For that reason, we’re going to review what happened in the big Texas Freeze in three parts. In this way, we hope to help customers better understand how weather and grid operations affect their Texas electricity bills and what could happen in the future.
Part 2: Why It Broke
To understand how the grid broke during Winter Storm Uri, it’s key to bear in mind that the number of customers needing electricity in Texas has long been an expanding problem. Even before deregulation in 2002, ERCOT’s job of wrangling enough power to meet demand is of pivotal importance. And as long as fuel flows to generators and turbines turned, ERCOT usually can gather enough electricity to keep Texas energy customers safe and warm.
However, the biggest failure in the big Texas Freeze lay with both ERCOT and energy companies not only failing to recognize the grid’s vulnerabilities to extreme cold but also in not preparing for it.
Never Underestimate the Weather In Texas
It is a fact that Texas is no stranger to bitterly cold weather.
Between 1899 and 1999, Texas experienced multiple episodes of widespread extreme cold weather events where temperatures fell to record lows; 5°F in Houston (1930), -1°F in Dallas (1989), -8°F in El Paso (1962), and even -17°F in Lubbock (1933).
To be sure, global warming has played a significant role in climate change for the past 50 years. The past 20 years have been noticeably warmer than last century. However, current research on how the Polar Vortex interacts with warming global temperatures now suggests that the Arctic actually goes through a chain of atmospheric processes that disrupt the Polar Vortex. These events send blasts of extremely cold weather blowing down into the northern mid-latitudes…including Texas.
So, it should come as no surprise that before 2021 there have been four major events where extreme cold did not cause the ERCOT grid to fail.
December 22-23, 1989, bitterly cold temperatures. On the morning of December 22, ERCOT power system peaks at 38,300 MW, 18% above forecast. High demand, combined with weather-related forced outages of generators and curtailed natural gas fuel supplies to generators pushed ERCOT to invoke system-wide load shedding for the first time ever. Rolling black outs lasted 30 minutes.
February 25, 2003, about 5,500 MW fell off line due to gas supplier freeze offs. ERCOT’s frequency falls from 60 Hz to 59.81 Hz and reserves fall below 2300 MW. ERCOT issued an Emergency Electric Curtailment Plan (EECP) Step #1 to bring all available generation on line. System re-balances to 60 hz within 30 minutes.
February 1-5, 2011, temperatures dropped for 5 consecutive days, causing freezing rain on Feb. 3. From February 1 – 4, a total of 210 individual generating units in ERCOT failed. Freezing weather shut at least 600 million cubic feet per day of natural gas production. Generation losses caused black outs affecting 3.2 million customers.
January 2014 Polar Vortex
January 6-7, 2014, due to demand, Luminant’s electric generators fail more than a dozen times in 12 hours. Of the approximately 19,500 MW of capacity lost due to cold weather, over 17,700 MW failed from frozen equipment.
A Snowball’s Chance in Hell
Texas generator companies have long been reluctant to invest in winterizing their power plants. Estimates for upgrading insulation and heat tracing equipment for pipes ranged from $50,000 to $500,000 per generating unit. And with global warming supposed to moderate Texas winters, the notion sounds a bit like buying insurance you weren’t going to use.
Following the 1989 blackout, the Public Utilities Commission of Texas issued recommendations for generators to improve insulation and freeze protection equipment. These were ignored by the industry. Similarly, in reports from both 2011 and 2014, the Federal Energy Regulatory Commission (FERC) and the North American Electric Reliability Corporation (NERC) also showed that ERCOT and Texas electric and natural gas systems continued to be vulnerable to extreme winter conditions. In fact, many of the same generators that went out in 1989 failed again in 2011 from the same problems.
FERC and NERC also recommended that Texas should pass laws to develop best winterization practices and make winterization plans mandatory. Instead, the Texas legislature authorized the PUCT to file a Report On Extreme Weather Preparedness Best Practices.
Though ERCOT has held annual winter weatherization workshops, up until February, 2021, legislation to require winter preparedness has had as a much a chance as a snow’s ball chance in hell.
How ERCOT Broke in 2021
Reports from both the University of Texas at Austin and the Federal Energy Regulatory Commission show that cracks in the ERCOT’s preparations appeared several days before Uri arrived. On February 8, the grid operator was already looking at 3,079 MW of planned generation outages, and 10,633 MW of unplanned generation outages and de-rates. That meant a total of 13,712 MW was already unavailable as the Arctic Vortex stormed into the Panhandle.
More outages would follow simply because generators and natural gas infrastructure weren’t prepared for the cold.
Beginning February 8, ERCOT saw its first wind outages and de-rates due to turbine blade icing. By February 10, freezing fog and drizzle in north Texas took out another 8,900 MW of nameplate (potential) supply. Conditions worsened and from noon on February 14 to noon on February 15, the outage capacity increased from 15,100 MW to 19,400 MW.
Natural Gas Wells and Supply
Natural gas wellheads in Texas are seldom insulated against cold. This lets water vapor in the gas condense and freeze up inside the wellheads, valves, and pipes. Icy roads also kept crews from repairing frozen equipment. As a result of the cold, production in the three basins fell nearly 50%. Output from natural gas processing plants shrank from 1.4 Bcfd on February 13 to just 0.257 Bcfd by February 16.
Several natural gas outages occurred when TDSPs cut power to natural gas infrastructure facilities simply because they hadn’t been identified as critical. Over 160 natural gas facilities had to be added to Oncor’s starting list of 35 by the end of the event.
Thermal Generation (fossil fuel)
On Sunday, February 14, about 8,400 MW of capacity was already offline due to scheduled, planned or mothballed outages, most of it (7,700 MW) from coal and natural gas power plants. By noon, another 15,000 MW went offline due to weather-related problems, including frozen water intakes, frozen sensing lines, condensation problems, and freezing equipment. Many couldn’t get natural gas delivered to them. By noon on February 15, the outage increased to 30,000 MW involving about 167 generator units.
Other equipment problems sidelined 1,900 MW on February 14. The next day, those outages had increased to 5,600 MW.
The Frequency Crisis
Maintaining the grid’s frequency at 60 hertz (Hz) keeps the load (demand) and generation balanced. If the load increases beyond the power output of a generator, the generator’s speed decreases and the frequency falls. If the frequency falls too low for too long, vibration and heat can damage the generator. To prevent this, ERCOT allows generators to automatically shut down and disconnect from the grid if their frequency gets too low. Generators can also trip off if the grid’s frequency drops below 59.4 Hz for more than 9 minutes.
At 7 pm on Sunday, February 14, the record peak demand on ERCOT hit 69,222 MW. But from 7 pm to 11:30 pm, several generators, renewable and thermal, rapidly fell off line. Though frequency stayed normal, ERCOT’s reserves fell under 3,000 MW. During the next 90 minutes, as over 1500 MW failed due to weather or tripped off-line, the frequency drew down further, reaching about 59.908 Hz.
At 1:07 AM, ERCOT declared an Energy Emergency Alert (EEA) Level 2 to warn customers to expect rolling black outs. Though ERCOT dumped its available demand response load, more and more generators fell off line over the next ten minutes.
At 1:18 AM, ERCOT’s operating reserves fell to 1,377 MW, triggering an EEA Level 3 alert. At 1:20 am, ERCOT ordered the state’s transmission operators to black out 1,000 MW of load.
For the next half hour, ERCOT fought to balance load shedding with frequency. Each time load was shed, a generator on the grid would buck at the increased strain and trip off. From 1:35 am through 1:51 am, 3,746 MW tripped off. Grid frequency fell below the 59.4 Hz automatic generator underfrequency relay trip level. This triggered the nine minute safety clock on the grid’s remaining generators.
By 1:55 am, ERCOT had shed 8,500 MW and had just under 5 minutes to recover frequency or lose about 17,000 MW of generation and black out the rest of ERCOT for weeks. ERCOT ordered another 3,500 MW of load blacked out. The frequency dipped but soon rose to 59.401 Hz. A moment later, 7 generators packed up, taking off 1,165 MW.
At 2:00 am, ERCOT dumped another 2,000 MW of load. With in 2 minutes, frequency rose to 60.0 Hz and then held steady. It would take another 30 minutes for the grid to stabilize enough for ERCOT to begin restoring load.
Many Texans would wait for days for their lights and heat to come back on.
At the peak, about 52,277 MW, roughly 48% of ERCOT’s capacity was still out on February 16. It would take ERCOT three more days to wrangle enough generation to end the black outs, even though 34,000 MW of generation remained off line.
Stay Tuned for The Texas Freeze Part 3: The Aftermath