Here’s What Happened: Seeking Answers For the Winter 2021 Texas Blackouts

We’re still unraveling what happened in Texas to cause rolling blackouts for millions of people. One of the most interesting pieces I’ve seen on the power outages is from Dr. Brent Bennett of Life:Powered, which I have reproduced below. You can read the piece on their website by clicking here.

The Texas blackouts were a tragic reminder of how crucial electricity is to our daily lives, especially in dealing with harsh weather. When we lose what we so often take for granted, it is normal to be left bewildered and searching for answers. Unfortunately, it is hard for Texans to sort through the competing narratives.

Two prevailing narratives need to be mentioned right away. First is that the sole reason for the capacity shortage was the extreme nature of this weather event and that even climate change is playing a role. While these cold temperatures were unprecedented in recent memory, this shortage was entirely predictable and preventable. Second is the false rumor that a large number of coal and gas plants “froze” due to the extreme cold. Though there were some plant failures due to the weather, it is still apparent that the primary cause of failures was ERCOT not initiating rolling blackouts soon enough, which caused power plants to go offline as the grid frequency dropped dangerously low. Ultimately, the problem with these narratives and the debates over “what broke” during this event is that they obscure the long-term policy decisions that made it inevitable.

Electricity demand in Texas has grown at a rate of about 2% annually over the past decade, requiring a comparable growth in generation to meet that demand. However, as shown below, only 2,186 MW of gas generation was added from 2015 to 2020, compared to 16,197 MW of wind and solar, a number which has grown to over 20,000 MW as of this month. Several thousand MW of coal plants were also retired over that time. Comparing ERCOT’s Seasonal Assessment of Resource Adequacy (SARA) reports from 2015 to 2020 shows a net loss of about 1,000 MW in reliable capacity for peak winter demand periods. In other words, Texas has been relying entirely on wind and solar to meet our demand growth since 2015 and now has less gas and coal generation in total than it did five years ago. 

Figure 1: Annual capacity change of natural gas, wind, and solar since 2015

Source: ERCOT

The causes of this shift toward only wind and solar for new generation in Texas are myriad and will need to be discussed in depth as future changes to the ERCOT market are considered. However, the point is that the stage was set for a situation combining high demand with low wind and solar generation to lead to blackouts. In fact, Texas experienced Level 1 emergencies on August 13 and August 15 of 2019, which required conservation measures but not blackouts to balance the grid. Life:Powered wrote about these events and predicted a crisis was on the way. An emergency may have occurred again on August 14, 2020, if not for reduced demand due to COVID-19. The only real surprise is that the blackouts came first in the winter and not in the summer.

With that said, ERCOT knew that such a situation could occur in the winter. The latest winter SARA report (in the first table on page 2) shows a massive 43% reserve margin for an average winter peak demand of 57,699 MW. However, the second table details the true risks to the system. In an event combining record demand of 67,208 MW with exceptional outage rates and low wind production (see the fifth column in the table below), demand would exceed supply. Even without the 95th percentile level of forced thermal outages (fourth column in the table below), the system would only have 613 MW in reserves, which would still lead to a Level 3 emergency and rolling blackouts. The latter situation is roughly where the Texas grid stood on the night of February 15, the night before the blackouts.

Figure 2: Range of potential risks from ERCOT Winter 2020/2021 SARA  

Winter Resources Available 82,513 82,513 82,513 82,513 82,513
Winter Peak Demand 57,699 57,699 57,699 57,699 57,699
– Seasonal Load Adjustment 9,509 9,509 9,509 9,509 9,509
– Typical Maintenance Outages, Thermal 0 4,074 4,074 4,074 4,074
– Typical Forced Outages, Thermal 0 0 5,339 5,339 5,339
– Low Wind Output Adjustment 0 0 0 5,279 5,279
– 95th Percentile Forced Outages, Thermal 0 0 0 0 4,540
Total Uses of Reserve Capacity 9,509 13,583 18,922 24,201 28,741
Capacity Available for Operating Reserves 15,305 11,231 5,892 613 -3,927

Demand reached a peak of over 69,000 MW at 8 PM on the night of the 15th (blue line in Figure 3) and dipped to 65,268 MW by 1 AM on the 16th, which is when the blackouts started. Wind generation, which the SARA says should reach 7,070 MW on an average peak winter day, was only 5,350 MW and falling when the blackouts started. Therefore, the demand on reliable generation (grey line in Figure 3) was about 60,000 MW at that point. Eventually, wind generation would bottom out Monday night at 649 MW, or 2% of its installed capacity, roughly consistent with a previous forecast of about 1,200 MW.

In concert with the decline in wind production, demand was forecast to exceed 74,000 MW by 8 AM Monday morning, 71,000 MW Monday night, and 75,000 MW Tuesday morning (dotted blue line in Figure 3). At all three of those times, the demand on reliable generation was forecast to meet or slightly exceed 70,000 MW. The SARA indicates that about 75,000 MW of reliable generation could have been available prior to the event, but at least 10,000 MW was unavailable due to planned maintenance outages, another mistake in forecasting on ERCOT’s part. In conclusion, it was inevitable that this weather event was going to cause demand to exceed supply, even if no wind or fossil fuel generators had failed due to the weather.

Figure 3: ERCOT wind and solar generation and system-wide load from 2/12 to 2/16/21

Note: Dotted lines based on forecast prior to the initial blackout.

There is evidence that some unexpected outages with a few power plants—the so-called “freezing” referenced above—caused demand to exceed supply earlier than expected and caught grid operators off guard. Because controlled rolling blackouts were not initiated soon enough, low grid frequency caused a large number of coal and gas plants to “trip” and shut off to avoid destroying their equipment. This grid management error, not problems with the power plants, is likely the primary cause of over 16,000 MW in thermal generation going offline during this event.

These errors likely turned what should have been more manageable rolling blackouts into sustained and catastrophic blackouts for millions of Texans, , but the blackouts would still have occurred without these mistakes. Even if every possible thermal resource were online, roughly 75,000 MW per the SARA report, the situation would have been precarious at best, with three periods over the course of 24 hours requiring maximum output to maintain an operating margin above emergency levels. It is impossible to run a reliable electric grid when every resource must be available and perform perfectly during times of peak demand and irresponsible to plan as if that will happen.

It is critical that policymakers understand that the primary causes of this tragedy were not technical or management errors but rather policy choices that favored unreliable wind and solar over reliable gas and coal generation. Poor real-time decisions made the problems worse, but it was these long-term policies that left the grid vulnerable to any event combining high demand with low wind and solar output and made this event almost inevitable.

Unfortunately, with ERCOT predicting a surge of new wind and solar generating capacity over the next few years along with very little new reliable generation, the threat of blackouts will only increase unless wind and solar generators are required to pay for the reliability costs they impose on the grid. Life:Powered has repeatedly called on policymakers to require wind and solar purchase a certain amount of reliable generation, energy storage, or demand response to firm up their capacity during peak demand periods. We will now amplify those efforts in order to prevent this tragedy from happening again.