This February of 2021, a major winter storm made its way through the U.S. central plains, setting all-time records for low temperatures across the country. One of the biggest impacts of the storm happened here in Texas where people across the state suffered extended outages of electricity and water. It was one of the worst winter weather events in history, creating loss-of-life and economic impacts that will take years to unfold. When disaster strikes, the flurry of political positioning and fingerpointing can make it difficult to understand what really happened. This is especially true for the complex systems of infrastructure like the power grid where most people really need a little more context and background than can be provided in a 500-word news story, but a little more boiled down than the discussions between economists and electrical engineers on twitter.

So - for the first time ever, by the way - I’m talking about a current event. This is a developing story, and we’re still learning the details and consequences of what happened during the storm. But, I’ve received a lot of requests for a video like this, and I hope it can provide some clarity and technical knowledge to elevate the dialogue surrounding this disaster. I’m Grady and this is Practical Engineering. Today’s blog is the story of the 2021 Texas Power Grid Emergency.

Before diving into the chronology of events, I want to provide just a quick overview of some important technical topics. I actually have a series of videos explaining the power grid in greater detail linked below, so check that out if you want to learn more. A wide-area interconnection, which is the technical term for a power grid, is the solution to the number one problem of the supply and demand of electricity: volatility. There aren’t many feasible ways to store large quantities of electricity, so for the most part, the supply and demand have to be matched simultaneously. Electricity is produced, transmitted, and consumed all in the exact same instant. Managing those ebbs and flows is a very difficult thing to do unless large groups of power producers and users are connected together, smoothing out the volatility of demands (making them more predictable) and the supply (making it possible to have larger, more efficient generation facilities). Interconnection increases the efficiency and reliability of electricity supply, and the majority of Texans are served by a single interconnection that covers most of the state. I’ll be referring to it as the Texas Power Grid.

Just because there are so many power producers and users interconnected doesn’t mean that there is no volatility in supply and demand. These are some example demand curves on the Texas grid. You can see that demand is always changing throughout the day. When power demand drops due to mild weather or at night when people are asleep, we need generators to shut down. Otherwise, the frequency of the AC power will speed up above 60 hertz. When demand spikes, we need generators spun up to match it. Otherwise, the extra load will bog down the physical generators, and frequency of the AC power will fall below 60 hertz. The consequences of the AC frequency deviating by too much are massive because every generator in the entire system is magnetically coupled. If parts of the system lose synchronization, both generators and equipment connected to the grid can tear themselves apart. Because of that, most parts of the grid (including generation facilities) have breakers that trip to isolate equipment if the frequency deviates too far. The breakers in your house monitor electrical current. If you plug in too many things to one circuit, the breaker will trip. These work the same way except they monitor frequency. And unlike in your house where restoring power is a quick fix, large power generating stations don’t turn on and off with a flip of the switch. So, matching supply and demand to maintain a stable frequency is the most critical part of managing the power grid.

In Texas, the entity in charge of this task is ERCOT, the Electric Reliability Council of Texas. This is a non-profit corporation with board members representing basically every segment of the electricity market from generators to utilities to consumers. ERCOT’s job is to oversee the entire system. They don’t own or operate any facilities themselves, but they tell the operators of generation facilities when to start and stop running depending on the electrical demand. ERCOT also manages scheduled outages. Owners have to have approval from ERCOT before they take facilities offline for maintenance. Finally, ERCOT manages the wholesale market of electricity by setting prices and handling the transactions between power sellers and buyers.

The week before Valentine’s day 2021 had already been a wintry one in many parts of Texas, but as the weekend drew near, the forecasts started to make clear that the next week would be extraordinarily cold. On February 8, a full week before things really hit the fan, ERCOT had already started issuing public communications about very high expected electrical demands across the state. They canceled or delayed approval for a large number of scheduled outages to make sure as much electrical infrastructure as possible would be in service in anticipation of the storm. They worked with the Texas Railroad Commission, which confusingly is in charge of the oil and gas industry, to increase the priority of delivering natural gas to power plants. They also worked with the U.S. Department of Energy to get permission for some power plants to temporarily exceed their emission limits from the EPA during peak needs for electricity. All this to say, the folks managing the power grid were expecting exceptional strain on the system and had already started working the week beforehand to prepare.

When the storm did hit on Valentine’s Day, it really was one for the history books. Three major facts to illustrate this point: First, it was extremely cold. The National Weather Service shows the departure from normal temperatures for three historical winter weather events in the southern U.S. plains. Essentially the entire southern U.S. had average temperatures more than 25 degrees Fahrenheit or 15 degrees Celsius below normal. All-time low temperature records were set in nearly every city across the region. It was the coldest many places had practically ever been. The next point is that it was not just a local event. The storm had significant impacts across the entire state of Texas and beyond. Finally, the duration of frigid temperatures was just so long. Large portions of the state were below freezing for more than 7 continuous days. That might not sound like a lot to those of you in northern climes, maybe even a welcome respite. But, in most parts of Texas, that is unheard of.

The state started Sunday with about a quarter of its total electrical capacity already out of service, mainly due to weather the week before. These outages were about half wind power and half natural gas generators. Even with that lack of capacity, as night began to fall that Sunday, Texas hit its all-time winter peak electrical demand of nearly 70,000 MW, and it met that full demand. The previous peak was 66,000. Everyone in the state was running their heaters to the max trying to stay warm. As the evening continued, though, it became clear to ERCOT and utilities that the amount of electricity available on the grid may not be able to continue to meet the demand. An advisory was issued that electrical reserves were low at around 11:30 PM. Not long after that, generation facility after facility started to trip offline reducing the capacity to meet the high demand.

Texas has a diverse portfolio of power generators. The largest segment of that is natural gas making up about half of the capacity. The second segment is wind turbines at about 30%. The rest of the generation fleet is made up mostly of coal powered plants, nuclear plants, and solar farms. This graph shows the outages of each generation type during the winter storm. You can see that wind and natural gas make up the majority of the lost capacity but no type of power plant was spared during the storm. The most important part of this figure is the natural gas line. Plant after plant went offline to the tune of 15,000 MW of capacity within the span of 8 hours. All the details are still coming out about what really happened, but there was a lot we know that went wrong.

Natural gas wells and pipelines are particularly vulnerable to cold temperatures. Not only does a gas stream contain water vapor that can freeze by itself, that water vapor can also combine with hydrocarbons to create hydrates that solidify at temperatures well above freezing. Combine this with the fact that many roads were completely impassable during the storm, it was nearly impossible for some gas suppliers to keep things flowing. That despite the fact that the wholesale price of natural gas during the storm skyrocketed to more than 100 times its normal price due to the incredible demand, with power plants competing with residential homes that use gas for heat. At that price, suppliers were doing essentially everything in their power to deliver gas to customers, but it just wasn’t enough. Or, in some cases, it was enough, but the generators couldn’t afford to operate their plants with such a high cost for fuel.

But it wasn’t just gas power plants that struggled, and it wasn’t just about fuel. Wind turbines were shut down due to icing. Solar panels were covered in snow. One of the few nuclear units in Texas tripped offline because of cold weather issues with its water supply. Basically, the entire system was ill-prepared for a storm of this magnitude. Texas does have a few connections to other power grids to help alleviate supply problems during emergencies, but those grids were suffering under similar conditions without much extra electricity to spare. This graph shows the total outages during the event. With that huge spike of generators going offline the morning after Valentine’s day, the state had nearly half of its total capacity gone during one of the highest periods of electrical demand on record. Without any remaining reserve of resources, ERCOT had only one option left to keep supply and demand in sync: shed load.

This is the technical term for what is essentially turning off parts of the power grid (in other words, disconnecting customers) to reduce total demands on the system. Here’s a simplified version of how it works: ERCOT tells the transmission operators they need to take X megawatts off the grid. Those megawatts are distributed roughly evenly between the operators you may have heard of, like Oncor, Centerpoint, CPS Energy, Austin Energy, etc. based on their share of the total load. Each operator has a plan in place for how to shed load within their own system when required. It’s not something they decide on the fly. Certain circuits critical to public health and safety like hospitals are prioritized. The other non-critical circuits are usually shut off in a rolling manner at 15-30 minute intervals. That way the inconvenience of lost service is spread out more evenly across the entire service area. Of course, in many places during the storm, that is not what happened.

As more and more resources tripped offline so quickly, the frequency of the Texas power grid began to drop. ERCOT continued ordering additional load to be shed from the system trying to keep up with both the rising demand from the cold weather and the quickly failing power plants. At about 1:50 AM, the frequency fell below 59.4 hertz. It doesn’t sound that significant, but this is a critical threshold for grid stability. Power plant controls are set to automatically disconnect if the frequency stays below 59.4 hertz for more than 9 minutes. In such a situation, as each generator trips, the frequency would quickly plummet until just about every circuit breaker on the grid had disconnected. Four minutes and 37 seconds is all that separated Texas from a complete grid collapse. Without the urgent action to continue shedding load from the system, many might still be without power in Texas a month later. That’s because recovering from a complete collapse, called a “black start” of the power grid, is an immense technical challenge. So much equipment would need to be inspected, repaired or replaced from the damage caused by the collapse. Only then could we start bringing generators and customers online slowly but surely to maintain balance between supply and demand throughout the process. If anything goes wrong during a black start and frequecy deviates too far, breakers will trip to protect the equipment and you have to start all over.

I am not an economist, but the energy market is an important part of this story, so I’ll do my best to summarize the key points here. Unlike other markets that pay generators to secure capacity for the future, the wholesale electricity market in Texas is energy-only. That means if you put power on the grid, you get paid for it. You get no extra points for having generation capacity when it wasn’t needed. The only reason it’s feasible to invest in future capacity is the scarcity pricing of wholesale electricity. When demand is high, the price goes way up. In theory, this incentivizes generators to not only make short-term investments to ensure their facilities are up and running during peak demands but also long-term investments in plants that can spin up during these times when prices are sky high to capitalize on the energy scarcity. This type of price model also favors intermittent sources of electricity like wind and solar which would struggle to compete in a market that valued firm capacity.

While it normally varies between $30 and $50 per megawatt-hour on an average day, the wholesale electricity price went up to the cap of $9,000 per megawatt-hour during the storm and stayed that high for days. The result was that providers spent more money on wholesale electricity in a week than would normally be spent in 4 average years. That’s with the extreme load shedding that occurred and doesn’t include the incredible prices that some utilities paid for natural gas. Most energy users won’t see those massive costs, at least not right away. That’s because nearly every retail provider offers a fixed or at least tiered rate for electricity to their customers, bearing the dips and swings of the wholesale price using a wide variety of financial tools and long-term contracts to try and hedge against the extreme volatility. Prudent planning can only take you so far in an event like this, though, and at least one utility has already filed for bankruptcy protection after the extreme energy bill came due. Other retail energy providers used a different strategy to manage the market unpredictability: pass the risk on to their customers by offering direct access to wholesale energy rates for a monthly fee. The idea is that some users may prefer to manage their own demand, cutting back on electricity usage when rates are high and shifting usage to times when rates are low. Unfortunately, many of these customers were misled about or misunderstood the incredible volatility of the wholesale energy market to which they were being exposed, and there are many reports of residential energy bills in the thousands of dollars.

During the peak of the event, ERCOT ordered 20,000 MW of load to be shed from the system. That’s the equivalent of turning off half of Texas on a normal day. And the load shed orders lasted for three days straight from early morning on the 15th to the end of the 18th. What should have been rolling outages couldn’t roll because many utilities just didn’t have any non-critical circuits on their system left to turn off. The result was that millions of Texans were plunged into darkness, in some cases for days, without heat or light during one of the coldest winter storms on record. My house lost power in the middle of the second night of outages, and it was already 42 degrees Fahrenheit (6 degrees celsius) that morning before we relocated to a family member’s house. And, we were the lucky ones. Many were not so fortunate to have friends or family with power nearby or even to have roads clear enough to safely make the trek. The selection of which circuits were left on versus off seemed arbitrary or even capricious to many. Water utilities started losing service, both because of frozen lines and lack of power available for pumping, reducing the availability of yet another basic human necessity to huge swaths of the population. Even though we had avoided the catastrophe of a total grid collapse, we did not avoid a crisis. Many lives were lost, and the economic impacts of this emergency are untold.

I have my own opinions about what could have or should have been done better during the storm and by whom, but this is not the place. My goal with this video is to try and summarize the facts of this tragic event in a way that is approachable by people who don’t have a working knowledge of the intricacies of the power grid. Many are still recovering from the storm and will be for years to come. Please feel free to share your thoughts and opinions in the comments below. All I ask is that you please be kind and respectful to one another. Thank you, and let me know what you think!