99% Invisible - Service Request #4: How Does the Grid in Phoenix Work?

Episode Date: April 3, 2026

In a place where losing power can turn deadly, keeping the lights on is a high-stakes balancing act. What infrastructure mystery keeps you up at night? Submit your Service Request by recording a voice memo with your question and emailing it to [e-mail]. Service Request is a production of 99% Invisible and Campside Media. Subscribe to SiriusXM Podcasts+ to listen to new episodes of 99% Invisible ad-free and a whole week early. Start a free trial now on Apple Podcasts or by visiting siriusxm.com/podcastsplus.  Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

A couple years ago, in the summer of 2023, I was in Phoenix doing some reporting. And that summer turned out to be the hottest on record, not just for Phoenix, but for the entire planet. September greeted millions of Americans with some of the hottest weather of the summer. Here in Phoenix, we are definitely used to this extreme heat. We are not used to experiencing 110-plus-degree days this many dates in a row. For 31 days, from the end of June until the end of July, temperatures exceeded 110 degrees. Sowaros were dropping dead from heat exposure. People were spending days and then weeks inside.

Playgrounds were empty because the playground equipment would burn a kid's skin. The unrelenting sun high above Phoenix seems to be taking its toll on all living things. And what struck me, walking around the city during that time, was how totally dependent Phoenix is on air conditioning. Everywhere you went, every building was cooled to the temperature of a refrigerator. And it was an enormous relief to walk into

one of those crisp buildings after struggling through the hot air outside. No matter where you live, the electrical grid is essential infrastructure. But in Phoenix, it's not an overstatement to say that the city cannot exist without it. If power goes out in the summertime, if all those air conditioners cannot run, people will die.

Which made me wonder, how does the city know how much energy they'll need to provide on the hottest summer days? I'm Delaney Hall and this is service request, a show from 99% Invisible and campside media. Each episode, we investigate a question about infrastructure, the vast and hidden machinery of modern life. We're looking at the pipes, the wires, the systems beneath your feet that you never really think about until they stop working. Today, I'm submitting a service request. How does the grid in Phoenix actually work? What an excellent question. And the answer takes us into the enormous and complex machine that sends us our power.

So it's weirdly local, even though it's also. incredibly immense. It's often called the largest machine in the world. This is Gretchen Bocke. She wrote a book called The Grid. She's a cultural anthropologist who's studied the work of electrical engineers, regulators, utility operators, and energy traders, trying to understand what they do. And I'll be honest right here at the start of this episode. The grid is not easy to describe. Electricity itself is not easy to describe. The system that delivers it to our homes is not something that we really see. And it's meant to be illegible. I mean, it's really, it's this, you don't have any access to a power plant. Like, you cannot like just go wander

into a nuclear power plant or to a coal-burning power plant or even a hydroelectric dam. Instead, the way most of us interact with electricity is when we get our monthly utility bill. So you just get this thing in the mail, and it doesn't seem to relate to anything. It's in some sort of unit that you have no idea what it actually means. It doesn't seem to matter whatsoever what you turn on and what you turn off. It's like going to the grocery store for the whole month and then just getting the bill at the end of the month. Did you buy pomegranates and were they really expensive? You don't even know, right? You don't know why your electricity bill goes up and down. So it's illegible in every way. But we're going to do our best to make this whole system that generates and transmits our power

more legible, starting with where electricity comes from. No matter how big of an electricity system you're talking about, there's always this, more or less the same set of components. But let's talk big. Big is power plants. Power plants were originally mostly coal burning, with time the transition in the 2000s was toward natural gas. But wind is a power plant. Solar panels are a power plant. They're just scattered everywhere. And the electricity that flows to your house has to come from one of these sources. It could be a natural gas plant or a nuclear plant, a wind turbine, a solar array, a hydroelectric dam.

Someone had to generate that electricity. Let's say you're on a coal system. So there's a coal burning factory somewhere, not too far away, within a couple hundred miles probably. And it's flash-combusting coal powder, cold dust. So it's doing that. and there's a magnet stuck on the piece of a rotating piece of metal. The coal dust is producing heat. That's producing steam.

That seam is causing this thing to rotate. And there's tiny little brushes on the outside, and those brushes touch those magnets, and they produce what we call an alternating current. And that alternating current is sort of going, you can't see me, but it's sort of like forward, forward, back, forward, back, forward, back, forward. So it's not a constant stream. It's this motion forward, forward, forward, back, forward.

back forward, back of electrons that are jumping from atom to atom. Is this too much shit tail? No, I mean, honestly, this is like poetry. I'm loving this. Those electrons are not moving steadily in one direction, like water flowing downhill. Instead, as Gretchen said, they're jiggling back and forth, back and forth 60 times a second, and that back and forth motion is what's traveling through the wire. What we have now are transmission lines, which are the really, really big lines that children watch happily through the window on cross-country driving trips.

I have been that kid, yes. Exactly. They're beautiful in their way. They really are. They're striking in how they sort of hold their wires up. They're a decorative piece of the grid in some ways or the piece we're most likely to notice. Those big transmission lines carry high voltage electricity over long distance. It's way more power than anyone would need to run their household appliances.

It's enough power to kill an elephant, actually. And so the transmission lines eventually run into substations. Which is the piece where it least likely to notice, which is essentially a kind of gray industrial-looking kind of Lego built box, sometimes in a box, but it's often just a square of land with a fence around it. And what happens at the substation is that the electricity is stepped down in voltage. And it goes onto a totally different system, which is called the distribution network. And that's what goes into the house. Before it goes into the house, it's stepped down once again by a transformer, which is often located on top of a utility pole outside your home.

Again, this is for safety so that an elephant-killing dose of electricity isn't flowing into your house. So all of this stepping up is to move. electricity long distance and stepping down is to keep it from being entirely lethal. You can still kill yourself with it, but it's harder to do. Okay. The amazing thing about this system, the generation of power, and then the movement of electricity through power lines to the home, is that it happens incredibly fast. Electricity is always very, very fresh.

If you flip on your light switch or turn on your air conditioner about a minute before, that was a piece of cold. or cold dust, that tends to be what we burn. Wow. Or a drop of water or a gust of wind, right? It's a very fast system. And it will go simultaneously anywhere it's called. And we call that a sink.

So if you turn on your air conditioner, all of the electricity in the system will say, ooh, a pathway. And it will all come to you. Wow. And then it comes, poof. And your air conditioner goes on. And here's another amazing thing about this system. Historically, the grid has not had much storage capacity.

This is changing quickly. Grid-scale battery storage is a very hot field right now, and it's important for renewables. But for most of the grid's history, electricity has typically been consumed almost the instant that it's produced. As Gretchen says, it's fresh. And it makes sense to do it that way. If you can deliver electricity on demand, it doesn't really make sense to spend billions of dollars building giant batteries to store it. It would be like running a restaurant and deciding to build a massive warehouse to stash the meals when you could just cook them to order instead. This metaphor doesn't totally work because electricity doesn't go bad like food, but you get it.

But when you're delivering electricity on demand, the grid has to stay in perfect balance. meaning the amount of power being generated has to match the amount being used, pretty much exactly every second of every day. Because what's really being maintained is that precise frequency of 60 back and forth cycles per second. Forward back, forward back, forward back. That frequency of 60 hertz synchronizes every power plant, every transformer, and every home on the grid. If demand suddenly exceeds supply, the frequency drops, and the whole system gets out of whack. Cascading failures can knock out the grid entirely. That's why the supply of

electricity must always meet the demand. Not too much, not too little. But here's what makes this whole system even more complicated. The grid isn't just one power plant serving one city. It's a massive group project, an interconnected system that stretches across huge distances with many power plants and many utilities, all trying to balance supply and demand in real time. In the U.S., there are actually three grids. The eastern grid, the Texas grid, and this is the grid that matters most for Phoenix, the Western grid. It's my favorite grid. Oh, good.

The Western grid is huge. It stretches from Western Canada down to Mexico and from the Pacific coast to the Rocky Mountains and beyond. The Western grid includes coal plants, and the deserts. solar farms and hydroelectric dams, and it ties together dozens and dozens of utilities across multiple states. Some are for profit, some are municipal, and some are co-ops. The thing to understand is that the grid is not just physical infrastructure. It's an immense web of social, political, and economic relationships. There are deals at every possible level. There's state governance, there's companies that are making deals for electricity across that space. So you have different business

models. You have different utilities. You have different states. And you have a set of federal regulations. And you have two countries. What could go wrong? The fact that it works at all is just completely phenomenal. Within the Western grid is Phoenix, Arizona. And a central piece of Phoenix's relationship with the larger grid is a utility called the Salt River Project, or SRP. When you flip on your air conditioner in Phoenix, that electricity might come from a hydroelectric dam in Oregon or a solar farm in the Arizona desert or a natural gas plant somewhere in between. SRP's job is to coordinate all of that, taking power from neighboring utilities when Phoenix needs it and managing the moment-to-moment balance between what the city demands and what the

grid can supply. SRP is one of the nation's largest public power utilities. We serve power and water to over 2.2 million people in the greater Phoenix metropolitan area. This is Angie Bond-Simpson. She works for SRP, and her job in essence is to make sure that Phoenix never. runs out of electricity, especially in the summer. My job is to do future infrastructure planning for the power system. I am the senior director of resource management. As we've learned, the grid has to stay in balance. And Angie has a view on how that actually works.

I'm curious, how do you know kind of minute by minute how much electricity Phoenix needs? And then how do you make sure you're generating exactly that amount? How does that balancing happen? Yeah, that occurs with really good planning and different planning horizons. So when we're talking about big infrastructure planning, that takes years. So when my group looks at planning for what's needed in the future, we're thinking about maybe six to 30 years out. For the long term, Angie's team looks at the same. stuff like population growth and climate data and new technologies like electric vehicles.

All of that information gets plugged into a long-term forecast that helps SRP make decisions about building new power lines and substations and finding new sources of power. But there's another planning horizon that is much shorter. I'm curious on a more day-to-day basis how you anticipate the energy-neutral. needs of Phoenix at any given moment. Sure. So they'll look at the next day and they'll say based on the weather, based on how customers have used electricity over years of data, here is our best prediction for what tomorrow will look like. Based on that prediction, the day ahead team will make an energy plan for the next

day. They look at what power plants are available and what the forecast says about wind and solar and they consider how much each source will cost to use. What they do is they essentially stack the generation in a way to meet reliability and to do the best economics for the system. So they're trying to solve for both reliability and economics. And when you say stack the generation, you know, they're handing them a plan that says you're going to get this much energy from this power plant. you're going to get this much energy from this wind farm.

Do I have that right? That's correct. The stack looks like a stacked bar chart, showing the cheapest energy on the bottom, with the more expensive sources layered on top, ready to be used if needed. And within that stack, different types of power plants play different roles. There are the weather-based sources like wind and solar, and if those are available, you want to use them. But they're not always there.

Sometimes things happen, right? Sometimes the wind doesn't blow. Sometimes there are clouds. When that happens, you want to turn to the sources that are called dispatchable. The ones that grid operators can turn on and off and ramp up or down on command. That's stuff like natural gas, coal, and hydroelectric. As Angie says, you can think of the weather-based resources as rain. When it's there, you can capture it and use it.

And you want to do that as much as possible. But your dispatchable resources are more like a faucet. You want to be able to go to that faucet to turn it on. And sometimes you need a large flow of water and sometimes you need just a trickle. So the day ahead team takes all of these resources, the rain and the faucets, and then proposes a stack for the following day. But of course, things happen. The weather might not cooperate or a power plant might go offline. And so the stack gets handed off to another team called the real-time team, which watches how the actual day unfolds and makes adjustments on the fly.

There are two groups within the real-time team. The first are the real-time operators. And they're working on something called the supply and trading floor. They're actually buying and selling electricity with other neighboring utilities. So they are working with other utilities in the West. and looking at what our demand is and what our generating portfolio and capability is. And if there's a surplus, that team is able to potentially sell into a market. And if there is a deficit, that team may have to purchase from another utility in the market.

And then there's, yes, another team. They're called the grid operations team. That is solely looking at the reliability of the system. So should something occur, they're the sort of ones that go in and can emergency respond. But that's sort of the last line of defense of you really want to have boring operations. So I'm curious, is there an actual control room where all of this balancing happens? There absolutely is. So take us inside.

What does the control room look like? Each power plant actually has its own control room that, then can communicate with a central control room at SRP. And what that control room actually looks like is a large room with screens, pretty much screens for as long as you can see. And then there are different pods of operators that are looking at different components of the system. One thing that was sort of shocking to me is it's pretty quiet in the control room. And I think that's by nature because you have a lot of people that are studying what is happening in real time.

And in some instances, making calls and doing checks and making sure that the right procedures are being followed. But in essence, it is a very calm environment and you want it to be calm. It's funny because I think I'm imagining something much more chaotic, almost like an open trading floor, you know, where it's like bring up the solar, call Utah, you know, just like a more out loud kind of situation. but what you're describing is something much quieter and much more focused. Yeah, and, you know, if you think about that, that's the way that you actually want it to be, right? Because as you were planning the grid, you are planning proactively for a number of conditions. None of us can predict the future. So we're trying to make sure that the right amount of infrastructure with a little bit of wiggle room for things that could go wrong is built.

So that was the basic overview of how SRP works, day-to-day and year-to-year. It's complicated. The whole grid is complicated. It's full of organizations and agreements that go by acronyms like FERC and NERC and ISOs and RTOs and IRPs. It's kind of a nightmare to describe. But I've also come to feel that the sheer density of acronyms involved is weirdly comforting because, each one represents a layer of oversight, a whole team of people who are there to keep the lights on and the AC running. Now, in Phoenix, all of this planning, the long-term forecasting, the day ahead stacking, the real-time operators, it all gets put to the test during one season in particular, summer. And specifically, the hottest day of the hottest week at the hottest hour. That's when come back.

So to move to reliability, grid reliability, it's obviously a huge issue. And I guess how do you prepare for the energy needs of Phoenix on what you know is going to be a really, really hot day? Yeah. The hot day, again, starts pretty far in advance with that forecasting. very far out. So the planners will actually look at the projection for the hottest day of the hottest time of the year and the hottest hour, and we'll essentially build the system for that time, that extreme time. And if we can meet that peak and have a little bit of reserves for contingency purposes, then the assumption is that the remainder of the year can be covered and that you use those times where it's not hot to do your proactive and preventative maintenance. So it sounds like

planning for summer is sort of a year-round project. Absolutely. Absolutely. What happens when something goes wrong? And I'm curious if there are any nightmare scenarios that keep you up at night when it comes to grid reliability. Well, sure, there are plenty of nightmare scenarios. But Just to be clear, you know, my job is to prevent those situations for actually coming to fruition or to at least give our real-time operations as many tools in their toolkit to manage those times. So having good planning, good standards, good training, making sure that if there is a small outage, that there's a response, that there's good relationships across the West so that if we need to purchase power, we have a good handle on who's selling and what's available.

And so there's just this constant hum in the background for preparedness. And I think that's what most people probably don't appreciate is that, you know, when you go home and you flip on the air conditioner or the light, you have an expectation of it being there. And there is so much that goes into actually planning and executing to make that come to fruition. at all times. Angie mentioned the recent blackout in Spain and Portugal, when the entire Iberian Peninsula went dark

after a small electrical disturbance turned into a massive cascading failure. That's the kind of nightmare scenario they are always trying to prevent. But she said the more likely risks are smaller and less dramatic and happen on a much more local scale. Because it's actually pretty mundane things that cause power outage Oftentimes, when a customer is without power, it's more something that has happened on that distribution or that neighborhood grid. And those are things like a car accident that runs into a power pole. Or there was a gender reveal party that popped confetti into the distribution lines,

or mylar balloons. And so it's, you know, it's things that everyday people are doing and they accidentally get into the distribution system. At SRP, we're very fortunate to have a lot of different redundancy to where we can try to minimize those outages and have fast response times, but it's almost impossible to prevent every outage and every Marlar balloon from getting in the power line. Those unpredictable gender reveal parties, you can't always know when someone's going to shoot confetti into a transformer or something. Exactly. Try to forecast that. So why might the power go out when there's a heat wave?

Why are heat waves a particular concern? Every piece of infrastructure for every, I'd say, major critical function, whether that's the airport or whether that's the power grid, has a temperature rating to it. So you may have heard there are temperatures where Sky Harbor airplanes, they can't land at Sky Harbor because the tarmac's not rated for that. Right. And, you know, that's the analogy I would use for the power grid is the power grid is not necessarily designed to run full tilt at those extreme temperatures without having the ability to cool off. So things like transformers and anything that has rubber or plastic components will degrade faster in the heat.

In the time you've been with SRP, have there been any close calls where, you know, for example, Phoenix almost had rolling black. out. You know, I can't think of any times that we got that close, you know, my awareness in this position, what I will say is you don't have to have the nightmare scenario happen for large amounts of stress within the operators to occur. So, you know, think about, in, in 2023, it was the hottest summer on record for Phoenix. We had over a month that temperatures were over 110 degrees. You know, consecutive days where our customers and our community had high heat, 110 degrees. Right.

And if you think about what that's like, right, you can't open a window at 110 degrees. Even when it's nighttime and it cools to 87 degrees, you can't open a window then. And if the power goes out, you're not just going to write it out. You're trying to think about where am I going to go. So that's always in the back of mind in the summer. But when you have these consecutive days, you start recognizing the system I've been planning for the hottest hour of the hottest day of the hottest year. Those days are occurring back to back to back. And you're always thinking about is something going to happen, not a total system collapse.

Just is there a minor component that I'm going to have to repair quickly at night to get it back up and running for the next? day. Do I have good communication with the region? Is the region also experiencing a heat wave? Is there not enough capacity on the market? And, you know, what I can say is in 2023 and even in 2024, where we had over 100 days, over 100 degrees, the system behaved very well, but it was stressful. It was continued stress of making sure of double checking, of communicating, you know, with cities and and making sure they knew what our plans were. And I have no other way of describing it other than stressful. And that's on a successful year, right?

That's when all the plans were put into place and they worked and everybody did their job. And, you know, still, it was hard. Right, right. Yeah, what I hear you saying is in a summer like that, the margin for error is small. Exactly. It's everybody is holding their breath and waiting for. to cool off. And summers in Phoenix are only getting harder, not just because the heat is getting more intense,

but because of the growing demand on the whole system. Phoenix is one of the fastest growing cities in the U.S., even as it gets hotter and hotter. And major industrial customers, like data centers and factories, they're moving to Arizona, too. Angie told me that a single big customer can use as much electricity as 50, thousand homes. That pace is, to use a very technical term, bonkers. Because just to cite transmission lines can, you know, sometimes take three to five years, in some cases, a decade to cite generation and go through processes for public input and environmental compliance and working with a community and hiring a firm to go out and construct. That can take six years. And so you, you,

We've got this just growing year over year, over year demand and a lag in being able to site and construct infrastructure in that same timeframe. So to me, you know, making sure that we have the equipment, the generators, the transmission lines, the transformers, and all of that in place when customers need it, is going to be really challenging. The system Angie describes is resilient. It's been built and rebuilt. and adapted over more than a century.

But right now, it feels like the grid is facing its biggest challenge yet. Summers are getting hotter, and the infrastructure needed to keep the city cool can take a decade to build. This is such a classic infrastructure thing where, like, people don't think about it. You know, it's quite boring when it works because it just exists in the background and we take it all for granted. And it's really only when something goes, goes terribly wrong that, you know, we we wake up and pay attention to how very important something like the grid is.

Absolutely. Well, I do know that there are about 5,500 employees at SRP that think about it all the time. Right. Yeah. So that we don't have to. Exactly. We started with a question. How does the grid in Phoenix actually work? And we have an answer. Phoenix sits inside the Western grid, an enormous piece of infrastructure that coordinates the delivery of power to the Western states. Every summer, thousands of people who work within the system focus on keeping electricity flowing even on the hottest days. To do that, they plan 365 days a year. They maintain the infrastructure.

They stack energy sources the day before and then watch screens in a quiet control room to make sure that, nothing goes wrong. All so that when the temperatures outside hit 115 degrees, you can flip a switch on your air conditioner and know that the power will be there. With that, consider your service request resolved. Today on the show, you heard Gretchen Bocci, author of The Grid, the fraying wires between Americans and our energy. You also heard Angie Bond Simpson, the senior director of resource management at the Salt River Project. What infrastructure mystery keeps you up at night? It could be something you use every day but don't actually understand.

The switch you flip, the wire above your head, if you're curious how it works, we want to know. Submit your service request by recording a voice memo with your question and emailing it to service request at 99PI.org. Remember, if you're having a gender reveal party, Please don't shoot confetti into the power lines. I'm Delaney Hall. Infrastructure is everywhere, and we're here to help you decoded. Service Request is a production of 99% Invisible and Campside Media.

The show is produced and fact-checked by Julia Case Levine and edited by Shoshi Shmulevitz. Mix by Iwan Lai Trimuan. Theme song and music by Swan Rayal. Additional editing by Emmett Fitzgerald and Vivian Lay. show art by Aaron Nestor. Roman Mars is our boss at 99PI. Kathy 2 is 99PI's executive producer.

Matt Cher is the executive producer at Campside. We are part of the SiriusXM podcast family. You can find us on all the usual social media sites as well as our Discord server. There's a link to that, as well as every past episode of 99PI at 99PI.org.