How Does a Power Plant Work?

You are listening to ShiftKey Heat Maps weekly podcast about decarbonization and the shift away from fossil fuels. Session Shift Key Summer School continue. is teaching us his introduction to the electricity system. And on this class, what are the two machines that make the power grid work? Where do they come from? It's the basics that you didn't know, you didn't know, and it's all coming up after this. Shiftkey is brought to you by the Yale Center for Business and the Environment.

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Hi, I'm Robert Zemeyer, the founding executive editor of Heatmap News. And you are listening to ShiftKey, Heatmap's weekly podcast on decarbonization and the shift away from fossil fuels. On this week's show, it is the second episode of our new series, Shift Key Summer School. Well, as I mentioned last class, we know that people come to this podcast with a lot of different backgrounds. You know, everyone presumably cares about climate change, decarbonization, this set of issues, but

You know, people have a lot of different occupations, a lot of different backgrounds. You do a lot of different things. Everyone encounters the energy system in some way, either because you turn on the lights or you drive somewhere, maybe you pay a power bill. Uh but you may not all have a technical background in it. And so this week and next week and last week, we're going back to basically.

Jesse Jenkins, my co-host, as you know, is a professor at Princeton University and he's taking us to class. He's gonna introduce us to some of the uh basics about the energy system and specifically the electricity system. that professionals know, but that, you know, as a listener to the show, you may not know. And this week we are going back to the beginning. How do power plants work, particularly the earliest forms of power plants? Jesse, let's get into it.

Let's start at the basics of how do we actually generate electricity from most sources. We'll put aside more modern sources like wind and solar power that are connected to the grid with power electronics. Other resources, whether it's hydropower or thermal power plants like coal, nuclear, natural gas, geothermal, etcetera. They all basically work by s doing some kind of work that is converted into mechanical motion that spins around a hunk of magnets.

inside some electrical cable or coil, some copper coil or something like that, or vice versa. And that rotation of the electric of the magnetic field Induces a current to flow in those conductors, in the cables. And that's what pushes the electricity out onto the grid.

That's called the dynamo, that process of converting that rotational motion of some magnetic field into an electrical current. And those were invented way back in the late nineteenth century in the kind of eighteen seventies, I think, by folks like Siemens. And Tesla. And the first power plants used hydroelectric power to do that. So we used water falling from a height behind a dam.

through a turbine that was designed to then capture that water and spin to transfer that rotational energy into the dynamo to produce electricity. And we started then adapting steam engines like the kind that were used in in locomotives, trains at the time. to generate the first thermal power plants, including the Edison Electric Light Station in London, which was the first coal-fired power station in in eighteen eighty two.

And then the Pearl Street station, which was constructed later that year in New York City, which is the first commercial power plant that was selling electric lighting effectively to a chunk of businesses and buildings in Lower Manhattan. So they all do the same thing. They're all kind of built around the same concept of gotta spin a hunk of magnets around inside a bunch of copper cables.

And the way you generate the motion and energy, the rotational motion to do that depends on your original source of power or your prime mover, um, whether that's hydro, combustion, geothermal heat from the ground, heat from a nuclear power plant, etcetera. One note which is I think the dynamo was invented way earlier. I think it was like eighteen thirties. But then the power plants come later.

Yes. You're right. Yep. Well goes all the way back to the eighteen thirties and Faraday. Yep. I don't think it was Turned into anything practical until much later. Yeah. Like nineteen sixties. I mean it is this gets at the core thing, right? Which is most energy on the power grid, even today, is coming from the same basic generator technology of a copper wire spinning around a magnet, or vice versa. Yeah.

That's right. And I think I guess the difference between a dynamo and a modern generator is the dynamos produced direct current. Um, this is what Edison was originally working on. And then Tesla and Westinghouse worked on a practical generator to produce alternating current power. Which is what we use today on the grid. What's the difference between those two generators?

I think the basic difference is that the dynamo is rotating the copper coil, the conductor for the electrical field itself, inside of a magnetic field. And that consistent motion is generating a con a consistent current that flows in one direction down that conductor. In contrast, if you think about a an alternator or a synchronous generator that we use today for alternating current power, you can think of a big disc with magnets in the middle.

spinning around and on the outside at every one third of the way around the outside of that circle, you have a copper conductor. And as the magnetic field spins around it gets closer to that the poles of that magnetic field, north and south, get closer to the each of those three cables or conductors. And as they do so, the strength and polarity of the current that they're inducing changes. So when the when one of the poles is directly lined up with one of those

one of those conductors, the current is at its highest strength and it's tr going in one direction. And when the south pole comes around, it's inducing the strongest current in the opposite direction. So this spinning of the magnetic field creates the alternating current because you have the north and south poles inducing current flow in opposite directions as they spin around.

And that three conductor setup is why we have three phase powers. We're actually generating three different sine waves along three different conductors that we then kind of blend together on our grid. And that's why if you look out the window

at a power line coming down the the street or elsewhere they typically come in threes and that's actually the three separate phases of one effective conductor, alternating current conductor. So that it's not three different power lines. It's one alternating current power line with effectively three different phases that then can supply a constant effective average power to whatever's consuming on the other end.

Do all three phases come into your home? This is actually something I had no idea about. So I think at the household level we often actually have a single phase, but then we split it back into three phase power in the home somehow. Um ask him about that. Uh for large consumers, the reason you would want three phase power

There's a couple of reasons you want three phase power. We're kinda getting ahead of ourselves in the the curriculum here too of transmission lines, but a couple of reasons you want three phase power, one of which is that if you have an electric motor

If you just have single phase power, the strength of that current is always changing following a sine wave up and down. And so you would get these little pulses of power into your motor every sixtieth of a second, that sixty hertz that which that spins around in the US. And if you have three phase power, you're getting a constant average mean from all three of those phases because they're thirty degrees or thirty percent out of sync with each other.

So that provides constant energy or constant current flow to in on average between the three phases to an electrical motor or something like that. You might have an industrial facility or an a compressor or something like that.

The other reason is that you don't need a large ground wire or return wire, I should say, for the current flowing in the other direction. So if you have a direct current, current's gotta flow one way for between the power plant and your consumer. Then it's also gotta flow back to complete the circuit.

And so you actually have two big wires of equal size conductor to transfer that power. Whereas if you have the same amount of average current flowing down the three phases, On average, the phases are canceling each other out.

Some of the phases are going forward, some of the phases are going backwards, and the net flow is effectively zero. And so they don't need a large return wire. And that's another reason why it saves. The the main reason though that we use alternating current is because it's very easy to step up and down the voltage.

from lower voltages to very high voltages so we can transmit power over long distances. This is what Tesla and Westinghouse demonstrated with the Niagara Falls generating station, sending power about I think fifty miles or a hundred miles into nearby cities, Rochester and Buffalo and others. And the reason you do want high voltages for that is that losses on a power line go down with the voltage squared. So if you double the voltage you have one fourth the losses on that line.

And so we want to send power over long distances at very high voltages. And then we step them back down to lower voltages at which the devices actually consume power. For big industrial facilities that could be pretty high, you know, kilovolt scale, thousands of volts. But in your home

Most of your devices run on either one twenty or two hundred and twenty volt, two hundred and forty volt. So we have to step things way back down and that's what all the transformers on the distribution poles are doing in series on the way back to your house. Got way off from generators and how we actually send the power down the line. So maybe that's in a whole other episode. Okay, that's great. No, that's I loved it. You actually answered a lot of questions.

Okay, so the first generating station is in London, developmental station, and then Pearl Street station in New York opens in eighteen eighty two. Let's just go down the history. So the Niagara station Which I bel think is the first hydroelectric station, opens eighteen ninety five. And that's the first time that a hydroelectric dam was used to generate electricity.

In the United States. No, I think that's the first in the United States. Actually the first hydroelectric power station was also in England in eighteen seventy eight in Cr Cragside, England, that was built by Lord Armstrong at his estate there using water flowing from a lake. to provide a couple of lights and produce hot water. Even ran an elevator apparently in his estate.

And that was all, I think, direct current using a classic kind of dynamo setup. That was followed then in January eighteen eighty two by the Edison station in London and then in September of eighty two, Pearl Street Station in New York City. Both the Edison Electric Station in London and the Pearl Street station basically adapted the kind of steam engine you would find in a locomotive.

So that's a reciprocating engine or a piston driven system where the expansion of steam drives a piston forward and then another piston is moving backwards at the same time. And then you convert that into rotational motion the same way you would. in the wheels of a locomotive by kind of having this

fixed rod connected to a spinning wheel at the end. And so then that ran the dynamo from there. That's different from the modern steam turbines that we use now, which didn't come along until a bit later and were largely popularized by Westinghouse as well. So Niagara cla uh has the claim to fame to being the first large scale alternating current power station that used that alternating or synchronized generator that we talked about earlier.

at Niagara Falls, which opened in August 1895. It was opened by Westinghouse Electric Corporation, which was the big proponent of alternating current. There's a couple of movies about this. I think one's called The Current Wars. You can go see the dramatization of uh Tesla and Westinghouse battling it out with Edison and his crew between alternating and direct current. I'm sure some of our listeners are the the right target audience for that movie if you're listening to this show.

And so from there on, really alternating current won out and Westinghouse went on to become a major supplier both of generation from hydropower and eventually from steam turbines. which use a set of kind of blades similar to what you would find in a hydroturbine to convert the expansion of steam into rotary motion by pushing on those blades and spinning it kind of like a fan or a pinwheel, you know, in the wind. Similar sort of concept.

Again, you can use any source of steam you want to generate power from a steam turbine. It's also called the Rankin cycle. That steam could come from combusting coal or diesel, natural gas, it could come from the heat that comes from nuclear fission in a reactor, and it come from geothermal energy coming from the ground. All of those are using the same effective cycle, the Rankin cycle.

to produce steam and then expand that steam through a turbine, condense it on the other end back down to water, and then pump that water back into the boiler or your nuclear reactor or into the ground for your geothermal plant and start the cycle over again.

And from then on, basically almost every except for hydroelectric dams, basically every form of electricity generation up through I wanna stop for a second when we get to combined cycle, but like through the beginning of the twentieth century, whether it's coal, oil, natural gas Or nuclear. basically every form of electricity and every form of power plant is just producing steam, using heat to produce steam, which we then shot through one of these rank and cycle generators, right?

That's right. The vast majority of them, with the exception of hydropower, are steam engines or rank and cycle turbines. The exception is hydropower and and of course there are a lot of early efforts around these same period in the late nineteenth century

early twentieth century to harness other motion natural sources of motion and energy. There were early efforts to use wave energy on the Pacific coast to convert the motion of waves into power. Those were unsuccessful. There were early wooden wind far wind turbines way back

uh that were partially successful demonstrations, but not commercially successful. The world's first rooftop solar array actually dates back to eighteen eight eighty four, so right around the same time as Pearl Street. Charles Fritz, who is an inventor in New York City created the first solar cell, which was a selenium gold cell, so coated selenium on the top of a layer of gold, and produced a solar power at o about a one to two percent efficiency.

and installed it on a roof in New York City, which provides some lights for that building. Again, not really a commercial success until much, much later, when the efficiency could be dramatically improved. And we can talk later in the episode about how solar panels work.

But there's a great book on this. Electrice Madrigal wrote about a decade ago, I guess, now, on Green Dreams that actually has these really interesting Chapters on the early histories of these technologies that I had no idea before reading the book that things that we think of as twentieth century technologies or late twentieth century technologies, like

solar or wind or wave power, actually all had early attempts around this same period. There are inventors out there trying all kinds of different things. with the basic idea that electricity is a new new technology and it's gonna be growing and we're gonna find new ways to to harness the energy around us to turn it into electricity. And so some fun, cool examples of Not quite commercially successful, but creative efforts that were then later built on by other

I want to stick with Steam for a second. So why in the Rankin cycle, why do we use Steam? Because basically what happens is for the next 50 years, every single form of generation, with the exception of hydro, is using a rank and cycle generator. And we'll stick in the show notes what what that looks like so you can open the diagram and see it. But why does the rank and cycle specifically emerge triumphant over any other kind of heat based generating technology. Um why is steam so important?

No, that's a great question. So there's a couple of things here. We'll start with the sort of the basics of a heat engine, which is what also a internal combustion engine or an external combustion engine like the Sterling engine. These all rely on basically on the principle that we can extract useful work from differences in heat and pressure.

So in all these cases, when we're trying to harness usable energy, we're effectively exploiting some kind of gradient in potential energy, right? We've got something that's hot, it naturally wants to flow into something that's cold. That's the second law of thermodynamics, it wants to reach an equilibrium at some point with maximum entropy. Or you could also think about the gravity gravitational potential energy of water uphill, it wants to flow downhill.

or the voltage differences you have in electrical devices. That's how solar photovoltaics work. In each case we're we've got sort of a natural gradient here where something wants to go from its high state to its low state. And we can extract some useful work out of that process if we can intervene somehow to turn that into some kind of useful work, usually some kind of kinetic energy that we use to do some work for humans.

So the basic idea of a heat engine is that the amount of work you can extract from that engine is proportionate to the difference in heat between your hot and your cold side. And so the hotter you get the hot side or the colder you get the cold side, the more usable energy you can get out of it.

Now, if you enter if you add pressure to the mix, pressure and temperature can both work to increase the available energy in the system. So if we can pressurize something, that's similar to increasing its temperature, and we can then extract useful energy from that as well. So in a steam engine the basic idea is we're gonna we're gonna heat water up to both high temperature and potentially pressure as well in in the modern turbines.

And the reason that steam is really useful is a couple things. One is that you can actually stick a whole bunch of energy into water as it transitions from water to steam. So that phase change from liquid to vapor requires a large amount of energy, about two point six megajoules per kilogram of uh water.

And basically as you bring the temperature up, you kind of see this when you boil water on the stove, right? It gets hotter and hotter. You start to see the initial bubbles form. And actually if you put a thermometer in there, it stays at about a hundred degrees Celsius until all of the water is vaporized. And so you can however much mass of water you've got, you can absorb a huge amount of energy without raising the temperature too much.

And then we can extract that energy later. So this has a lot of advantages. If you were to try to raise the temperature of water vapor itself by the equivalent amount that it takes to vaporize that water initially, it would go to over a over 720 degrees Celsius. So now you're dealing with really high temperatures to get the same amount of energy into the water.

Uh. So if you try to take that two point two six megajoules and add it to a kilogram of water vapor instead of liquid that you're boiling, it would raise the temperature of that steam to seven hundred and twenty seven degrees Celsius. as opposed from a hundred, as opposed to staying at a hundred as you vaporize all that water. In in other words, that moment, that phase change where water where liquid water becomes water vapor. is a unique position in waters State cycle.

Yeah, phase changes. Yep. Where you can just dump energy into it and then you get energy out the back end, but in a different form. Yeah, exactly. And so then we do further superheat it beyond you know, we're not running a hundred degrees Celsius. steam through a turbine. We do superheat it beyond that to a dry vapor at a very high temperature. And in modern coal fired power plants, the super critical ones, we actually increase the temperature and pressure to very high levels where

the water enters another state, the kind of fourth state, where it's super critical. That means it flows like a vapor, so it's easy to move it around and through a turbine, but it acts more like a liquid in terms of its flow properties. And so that makes it a more efficient at transferring

its energy into rotational energy, kinetic energy. So Basics is if we can get a lot of dump a lot of energy to turn water into both high pressure and temperature steam, we can then let that steam do what it wants to do, which is to flow out and to expand and to cool off. And so we let it expand through a turbine uh and cool off as it does so. And we extract that usable energy out, part of it, right? Usually only

thirty to forty percent of the energy that we dump in to the front end. And we use that energy to spin the gear shaft and to spin the magnets inside the alternating current generator. Then it comes out the back end. It has to stay in steam form. Otherwise if it starts to condense, you've got very high velocity water.

that starts to destroy your turbine. It starts to create pits and corrosion. And so that limits the degree that we can extract energy out of that. We can't bring it all the way down to say zero. We've got to leave it above a hundred degrees Celsius or the equivalent temperature and pressure combination. And so we that limits how much we can extract from the steam. And then we have to condense it further on the back end all fully back into water.

And that's where you get the heat sinks that these plants all have, whether that's a cooling tower using evaporative cooling or running water through running through a lake or through the ocean where we're using the cool water of that water body to cool the steam back into water.

It's interesting thinking about the deployment of steam and these Rankin cycle generators in the late nineteenth century. For us as people who care about the power grid, right, these are interesting techniques as they're deploying electricity for the first time. But the use of coal to convert water into steam and the use of steam power actually comes way earlier

than any of this, right? Like it's steam that is actually the nineteenth century, the core nineteenth century and late nineteenth century, especially energy medium. And actually the history of the nineteenth century energy is switching from wood and hydropower. Two. Powered steam. And already by the time that the Pearl Street station is built in New York, the United States is crisscrossed with steam engines.

moving our economy already runs on steam. It's actually the application of steam and coal, w which at that point are old and fundamental technologies to economic function to power generation that is new, it's not it's not they didn't have to make any huge discoveries around steam and coal. They were already using steam and coal in factories. They just weren't intermediating it through the electricity grid, or through electricity wires at all.

Yeah, in all these cases you're just trying to convert that steam the expansion of that steam into motion, whether that's the pistons of a steam engine or the pistons of a reciprocating generator attached to a dynamo in Pearl Street. Or in a lot of factories, just a bunch of belts, right, that would then move equipment throughout the facility. It's just a lot easier to move energy around, either and more precise to do that as electricity.

And so over time the devices and industrial facilities all converted over to using electricity directly. And then you could generate your energy somewhere far away. And this is the other second advantage of steam turbines, what made Westinghouse so successful, is that they have large economies of scale.

So it's a lot cheaper to generate power from a big steam turbine than the equivalent amount of power from a lot of little steam engines. And that wasn't I mean, that's true for reciprocating engines, but they kind of top out given their complexity. The Pearl Street station generators were in the hundred kilowatt scale.

I think there were six of'em originally, so six hundred kilowatts. And they only powered a few hundred lights, which is remarkable. The original lights were incredibly inefficient, or so it took something like a thousand watts. or more per light bulb. Whereas again, now we're down to like ten to fifteen watts in an efficient LED bulb. But anyway, they were in that kind of hundreds of watts scale, and that kind of maxed out the scale of the reciprocation.

Steam turbines you can gen you you could increase and increase and increase into the megawatt scale. And by doing that, utilities or generators were able to lower the cost of energy while expanding customer base. And in fact, that is what gave rise to the early natural monopoly characteristics of the power grid. Both the fact that the grid itself is a network and network effects like the network is more useful the more people connected to it.

lends itself to a monopoly. But also the steam turbines themselves got bigger. So one of Westinghouse's deputies, Sam Insul, who started Consolidated Edison in Chicago, realized that they could gain an enduring advantage by harnessing bigger and bigger steam turbines.

And effectively bought out all the competitors one by one so that they could expand their customer base and install larger turbines, which then allowed them to lower their average cost, which then allowed them to buy out more competitors or undercut them in costs. and grow and grow and grow until they had a dominant position in the Chicago area. Others followed similar strategies in the early utilities around the country.

And this is what prompted the initial regulation of electric utilities was this recognition that It's actually better to have a single large utility. It's cheaper for everybody if that's the case. But if we let them stay unregulated, they're gonna become naturally monopolies on their own and then they're gonna abuse that position to make as much money as possible. And so we wanted to keep the benefits of the monopoly, but bring it under regulation to ensure that it wasn't abusing market power.

And so it's actually the kind of economies of scale inherent in steam turbines and also hydropower that led to the regulation of utility SaaS monopolies. Do you want to build critical skills that are transforming the clean energy sector? Then discover the Yale. And Equitable Energy Development Online Certificate Program from our sponsor, the Yale Center for Business and the Environment. This fully online five month program.

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One thing that's remarkable is the enduring nature of the Rankin cycle, the steam turbine. In the United States today, we still get about seventy or seventy five percent of our electricity from generators that use a Rankin cycle. That includes a bunch of combined cycles that we'll talk about later, so not all of the energy there comes out of a Rankin cycle, but they have them too. So that's all the coal, nuclear, oil fired steam turbines and gas combined cycles in the country.

And if you go to a place like India or China where seventy plus percent of the electricity comes from coal That's the Rankin cycle too. So here we are, you know, go from eighteen eighties all the way through to twenty twenty five, and the Rankin cycle is still the dominant way in which we generate electricity around the world. Let's just quickly hop past There's just a fancy way to boil water.

Right. So so basically okay, we've gotten to nineteen hundred in this mini history. What then proceeds to happen is a massive build out of the electricity grid. Through the first half of the twentieth century, the United States massively expands its power grid using both a massive expansion of hydroelectric facilities, which wind up generating

Just uh even more electricity actually by the middle of the century than they do today. And also a massive expansion of rankinsile plants. I wanna briefly stop in the nineteen fifties and just ask In nineteen fifty one, I believe, is the first time we get a com civil nuclear reactor. And my understanding of the history of nuclear energy is when we invent nuclear weapons first. have the sense that there's potential for a lot of other technological applications there. And then almost

There's big government efforts in the middle of the century to to find new things to do with the nuclear technology we have. But we kind of find a way to boil water with uranium and stop there. If we just get steam out of them and we then we feed it through a Rankincycle generator, the same we do with coal or Or anything else. Where is that steam coming from?

Yeah, so the principles of a nuclear reactor were developed as part of the Manhattan Project to figure out again, like you said, how to build a bomb. The key to building a bomb is to have a massive chain reaction of fission where you split a a large atom, uh uranium or plutonium, in half, and that releases both a bunch of energy and some neutrons.

And those neutrons run into some other atoms and split them and you get a chain reaction that in the case of a nuclear weapon produces an ungodly amount of energy and a massive nuclear explosion. But you can also have a much slower chain reaction and that's what was first demonstrated at the Chicago pile, which is the research reactor developed by Fermi.

in Chicago, famously I think underneath the bleachers of the football stadium at University of Chicago. And the basic idea there was that they observed very clearly that as this happens, there's heat generated in addition to the sustained reaction of atomic fission.

So we got a fancy way now to generate a bunch of heat. We can hook that heat up to a tea kettle and boil some water and now we've got a rank and cycle generator as well. And that's basically what a nuclear reactor is. All right. I'm skipping over all kinds of

important and impressive physics involved in operating nuclear reactors and controlling that chain reaction. The sort of unique special thing about a nuclear p reactor is not how it generates electricity. That's just a big Rankin cycle, the same type you would find in a large coal plant. The exciting or unique thing about it is its incredible energy density. So you get an enormous amount of energy out of that fission reaction.

And therefore you can get a lot of heat out of a very small nuclear core and a very small amount of fuel that sustains over years until it's used up. as opposed to coal that we're burning in the billions of tons per year. That's a just an important piece to to pause on a second for those who are concerned about nuclear waste. Because nuclear reactors are about seven orders of magnitude more energy dense than coal.

All of the waste and fuel production and management associated with the nuclear fleet also scales proportionately. So whereas we burn on the orders of billions of tons of coal every year, I think less in the US now or probably under a billion, but we used to burn around a billion a year and globally burn several billion. The entire history of the US nuclear fleet has consumed tens of thousands of tons of nuclear fuel.

And that's really important. That's that's the s sort of singular advantage of the nuclear reactor is just its incredible energy density. It means you can produce a lot of power in a small Container. You know, we talked last episode about how a typical nuclear plant today is about a gigawatt, a thousand megawatt scale. That's enough for a medium-sized city.

And so a single reactor you see out there is enough to supply energy for a medium sized city. You usually have two or more of those at a site. And they generate a lot of energy with a small amount, a tiny amount of fuel. That also means that the amount of fuel we have to dispose of or care for later is also very small. I think a lot smaller than most people have in their heads.

And in France they reprocess that to a smaller volume. In the US, we just have them sitting around in effectively in secured parking lots at the back of the nuclear reactors all around the country because we haven't agreed on a place to permanently store them. I love that in kind of a richly layered meta statement about not only America's nuclear policy, but America's land use, that our solution ultimately to nuclear waste was to store it in highly secure parking lots.

We love our parking lots in the United States. We love to store things that we love to store things that we don't quite know what to do with in parking lots. Okay, so that's nuclear. Then in the nineteen sixties the There's a new form of power generation that comes onto the scene. And this wounds winds up being extremely important to

Today's energy mix. And we're actually not talking about wind and solar here. We're talking about a natural gas combined cycle turbine. So can you explain what that is, where it gets invented, and why it's important?

Yeah, so this comes out of the military industrial complex as well, just like nuclear power and right around the same time, right? So in the nineteen fifties, we invent jet engines. as a way to build superior uh fighter aircraft or bombers. That then of course spills over into commercial aviation. But also now we've got another way to burn something to generate a lot of heat, to spin a turbine, to Convert some of that rotational motion into electrical energy.

How's a jet engine different than just like the normal turbine we were using in Rankin Yep. So here you're using air. Here's you're using air effectively or a fuel air mixture that is expanding very rapidly through the turbine to generate that rotational motion, as opposed to steam. And so in order to do that effectively, we not only have to get it really hot, but we also have to compress it to a high level. So a bunch of compressed air.

So the way a Brayton cycle gas combustion turbine works, the same thing that's in a jet engine or in a combustion cycle power plant, is that you take fresh air in through a compressor. That's the blades you see on the front of a jet engine in the airplane. That's not a propeller blade that's providing you with thrust. It's actually a compressor that's sucking air in and compressing it down into a combustion chamber where it's mixed with fuel. on an airplane that's aviation gas or jet fueled.

in a combustion turbine for power generation that could be diesel or oil, but increasingly it's natural gas. And so we squirt some fuel in there with the high, high pressure air and we light it on fire. And that combustion reaction, effectively an explosion, leads to a very high pressure and temperature air that wants to expand very quickly and get out of that combustion chamber. And so we dump that

Rapidly expanding gas through a specially designed turbine, slightly different configuration than you'd use to harness the energy from steam. But same general idea as a pinwheel. You've got something moving real fast through this rotational blade, these through these angled blades, and they spin a turbine around. Now that termine is generating mechanical work that's doing two things here. One is it's actually driving the compressor.

So some of that energy that we get from the combustion is being used to compress the gas at the beginning of the cycle. That's worth it. You get more energy out from that than you use. And then it also spins a generator on the other on the back.

So that's the combustion turbine and same thing in a jet engine, right? Except in the jet engine we're just venting that gas right out the back, and so we're only using some of the energy to pr to run the compressor and then the rest of it is exhausted out the back to provide thrust.

for the airplane. So you're just shooting hot air out the back. And that's how you you get the plane to move. So instead of shooting all that hot air out the back, we take even more energy out in a stationary combustion cycle turbine and use that to generate more electricity.

So that's the Brayton cycle, or otherwise known as an open cycle turbine, because we are un unlike the Rankin cycle, we're not compressing the steam back into water and then starting the cycle over again. We're just venting that hot gas out the back. And it's very hot. Yeah.

Do we run natural gas? Do we run power plants like that today? Like are there just Braytoncycle plants? Yeah, there are a huge number of them and we use them primarily for peaking capacity. Because it's relatively small, you can have these in varying sizes all the way from the 10, 10 megawatt to hundreds of megawatt scale, and they're less expensive to build than a combined cycle or coal plant.

They are good for infrequent use when they're really needed. So that's what we typically call a peaker power plant. Although in a world with lots of renewables, maybe we don't always run them at the peak demand. We run them at the time when the demand minus wind and solar is greatest. And for a peaker, what you want is a generator that has a low fixed cost, and you're fine with a high variable cost because you only use it when electricity is really valuable.

And so a Brayton cycle is thirty to forty percent efficient. That's comparable to a Rankin cycle, but you're burning a much more expensive fuel. You have to burn a more energy dense fuel than coal. So you're burning either diesel or jet fuel or natural gas, all of which are more expensive per unit of energy per M M B T U million British thermal units or megawatt hours of heat content than coal. But they're more energy dense and so we can use them in this combustion chamber.

Is that still true by the way, post shale revolution? Like is it still the case that natural gas is more expensive than coal on a energy basis? Yeah, it is, but not as much. Not as much as it used to be. Yeah. It is more expensive. Coal's still the cheapest way to get heat. So you're burning this more expensive fuel at a comparable efficiency, and so the variable costs are higher than a coal plant.

So you really only want to use that combustion turbine when you've maxed out your cheaper variable cost generators, nuclear and coal. And that means we use them pretty infrequently. And so these are the power plants, these are the peaker plants that turn on right now, let's say, in a grid like the northeastern United States where there's not enough wind and solar to really be

significantly shape angle dynamics on a day to day basis. There's a lot of midday summer solar in the northeast, but there's not like so much. It's like California where you have to plan the rest of the grid around just how much midday solar you have. Let's say in the United States m uh northeastern United States, really hot summer day, it's four PM, it's a weekday, every office tower is full of people and cranking its AC. Homes have their air conditioning on.

absolute peak demand in the system. That's when these peaker plants right now, for instance, would be running. And I just want to also ask something, which is is it correct to understand that basically these are like I was familiar with Pika plants being the most polluting type of power plant, like the very polluting, but is it basically right to understand them as more or less like a jet engine? vertically under a smokestack and then they're just venting up out of the smokestack.

They're usually not mounted vertically, they're mounted parallel to the ground and then they just shoot their exhaust out of out of smokestack, which can usually contains some amount of emissions controls. And you know, a peaker power plant is not more polluting than a coal-fired power plant. We should be clear about that. Coal fired power plants are by far the worst polluting generators even now.

It's just that a combined cycle is a lot more efficient uh th than a combustion turbine. We'll talk about the combined cycle works in a second. But the more efficient gas generators that we run more often

are more efficient so they're burning less fuel per megawatt hour and they're also used more often so it's worth fitting them with more emissions controls. And so they tend to also control their NOx emissions as well, which contribute to smog and and pollution at the local level. So yeah, the gas turbines Pollu more per megawatt hour than a combined cycle turbine. It's also the case though, right, that because these are relatively smaller plants, because you can stick them in places because

My understanding is also that because you want them at moments of high demand, they tend to be jammed closer to high demand areas. Like these are the these are often the type of power plant you hear about in neighborhood I'm thinking in here in New York, there I think there are some in Queens, but like these are the type of power plants that run on hot days in the middle of residential neighborhoods and are responsible for criterion pollutants in those.

Yeah, so the exposure is higher than coal-fired power plants that might be on the other side of the state, although the again the the air the particulate pollution from coal plants moves pretty far. But yes, because a lot of these Turbines are needed for reliability during times when power demand is high. That's also usually when the transmission grid is is congested, it's at its maximum transfer.

capabilities into the most populated areas where the demand is highest, like say New York City or Boston or somewhere else on the edge of the grid. And so we also have to locate these speakers close to the point of demand and that means they're in our cities and our suburbs and, you know, close to where a lot of people live. And that also contributes to their pollution impact.

All that said, coal plants still far worse, kill many, many, many more people, contribute far more to pollution than an open cycle gas turbine. Again, partly just because these turbines don't run very often. So while the exposure when they're generating a megawatt hour, it's bad because it's close to a lot of people. They operate on average in the United States at less than fifteen percent capacity factor.

Meaning full load hours meaning are the equivalent of fifteen percent of the hours of the year? And that means they generate very little electricity. So while we have over a hundred and thirty I don't know, a hundred and forty thousand megawatts or hundred and forty gigawatts of open cycle gas turbines operating in the US now, they generate only about four percent of our electricity.

So they're a large share of our capacity, maybe twenty percent of it or fifteen percent of it, but they only generate about four percent of our energy. And that does mean that, well, there are certain cases, right, like in New York where they are operated more often because of the grid is so congested.

For the most part, these turbines aren't huge contributors to urban air pollution. The big contributors are people driving their cars around all the time and the factories and other things that operate much more regularly and contribute to air pollution. NONONONONONONO

Just a fact. Um they get a lot of attention because there are alternatives and we could close them now and replace them with batteries in many cases, but yeah, they don't really contribute an enormous amount to say the the total air pollution exposure in New York City.

So this gets us to the combined cycle, which is the mainstay of our fleet today and the fastest growing contributor over the last decade. So picture your jet engine, right? You know, we've compressed our gas, we've lit it on fire, we've boosted it up into the range of fifteen hundred degrees Celsius, so really hot, and then we've expanded it out the turbine, and we've used that pressure and temperature to drive our turbine, generate some electricity, and run the compressor on the front end.

The exhaust gases that come out of the back of that open cycle or Brayton cycle turbine are still like six hundred degrees Celsius. That is equivalent to the combustion temperatures of a coal-fired power plant or a nuclear plant that generate electricity in the sort of 400 or generate heat in the sort of four hundred to six hundred and fifty degrees Celsius.

So it didn't take long for somebody to come up with a brilliant concept of why don't we run all those hot gases through a boiler and generate more steam, and then we'll just slap a Rankin cycle onto the back of our jet engine and we'll generate more electricity from that steam. That's what a combined cycle power plant is. The reason it's called combined is it has a Brayton cycle combustion turbine on the front end. Burning natural gas.

jetting hot air out the back, which goes through a heat recovery steam generator or a Herzig if you're in the biz. Which is basically just a big heat exchanger where we wrap a channel for the gas to flow through with some pipes that have water going through them. And we use that to boil the water instead of burning, you know, something directly in a boiler.

And because the hot gas is hot enough, we can extract even more energy out of the back of the combustion turbine, run a steam turbine, and generate more electricity with that steam turbine. And so the combined cycle combines a Brayton cycle and a Rankin cycle to be much more efficient than either of them are individually. So while Brayton and Rankin cycle turbines are about forty percent efficient, plus or minus, depending on how modern and high tech they are.

the most efficient combined cycle power plants are pushing sixty percent efficiency. So we get half again as much energy out of that billion cubic feet or whatever cubic meter of natural gas than you would if you were just running an open cycle or that vents the hot air right into the air, into the atmosphere.

And those are responsible for a lot of our electricity today. So something like forty percent of US electricity generation now is from combined cycle power plants. That's because they're more efficient and gas prices got cheap enough. in the US due to the shale boom, that they were able to actually push coal out of its typical role as the kind of mainstay on the grid. And so now a combined cycle power plant is the sort of

generator in the grid that we turn on after we've used up all our nuclear and hydro and renewables and it pushes out a lot of the less efficient coal plants. So they run less often. And whereas we got about fifty percent of our electricity from coal in the two thousands, that share is now down below nineteen percent. on par with what we get from nuclear power, whereas the share from gas combined cycles has gone up to about forty percent of our electricity over that same period.

And these are big much bigger facilities because the steam turbine part is a lot less power dense than the gas turbine, right? There's a reason why you don't put steam turbines on airplane wings. They're just too big. And so the gas turbine is very power dense, and that's why we used it for aviation, because it could put a ver relatively small turbine up on the wing of an aircraft.

It's actually you know, going back to our units, it's actually pretty remarkable to think about when you're sitting on an airplane, the jet engine that you see on the wing, each of those is probably on the scale of a twenty megawatt. Which is enough again, doing rough math in my head for something like fifteen thousand homes worth of electricity annually.

That also makes the open cycle gas turbines we put on our grid pretty small and so we can distribute them throughout the grid. Combined cycle power plants are typically in the scale of two hundred to six hundred megawatts. Sometimes they have two combustion turbines feeding one really big steam turbine.

So that's called a two on one combined cycle. Others are just single gas turbine for single ranking circ turbine. But they're very large and since we always have to bring this back to Jersey, if you're ever driving up to the Newark airport on ninety five, you'll pass an oil refinery on your left. And on your right, a massive power plant complex that is I think the largest in the state.

It has a huge, I think, gigawatt scale combined cycle with multiple units, I think four four or six units, and then a whole bunch of little combustion turbines in front closer to the highway. So For our Jersey fans, go on a sightseeing tour and you can see the industrial or the energy heartland of the New York metro area right there, with your oil refinery on one side and your gas plant on the other side. Yep. The Linden gas thermal. You'll see it say Linden cogeneration on

No, so that's the other one. Lyndon Kogen is actually Kogen from the response. I was about to say. Sorry, sorry, sorry. You'll be driving up ninety five, you'll see out of the well, let's say you're driving up ninety five, right? You're driving northbound into the city. Out of the right side of your vehicle, you'll see Linden Cogeneration plant, and it will have big signs, and it's clearly a refinery.

You're going north. Wait, you're going out of the city. South, you're going to the city. I'll bet you a I'll bet you a pork roll egg and cheese. The refineries on the left side of the power. Of ninety five. Oh yeah, you're so right. You're so right. Um, you'll be driving northbound. You're gonna see out of the left side of your vehicle a big industrial facility. It's clearly a refinery. It says Linden cogeneration plant on it. At that moment, you wanna look out of the right side of your vehicle.

Which is Linden Gas Thermal Power Station. It's nine hundred seventy two megawatts. It's enormous. What's interesting about Linden Can you tell that one time, Jesse, I was sitting on the northeast corridor going from New York to D C and I got bored, so I just googled all the energy infrastructure that you pass along the way. It's actually quite a lot. So uh let's just hit one last thing, which is the combined cycle plant I believe is invented in the nineteen sixties, right?

Yes, not too long after the combustion turbine,'cause it again, it doesn't really take a genius to say, Hey, we got a bunch of hot gas coming out of here at six hundred and fifty degrees Celsius, why don't we use that to generate some steam? The hard part was designing a heat exchanger that could work at such high temperatures.

And so those heat recovery steam generators are the key technology that enabled the combined cycle. And it didn't take too long for those to come around after the invention of the open cycle gas turbine. In nineteen sixty one, it looks like in Austria. Um yeah, so yeah, nineteen sixty one the first plant was a seventy five megawatts, a small one in Austria. They scaled up from there to become much larger as the gas turbines themselves got bigger.

No, they didn't really take off in the sixties and seventies because the US didn't have an abundance of cheap natural gas. Right. So if you think about the first ones are coming about in the nineteen sixties, you now fast forward to the nineteen seventies and eighties and the US is in its energy crisis era. And oil and gas are in short supply and quite expensive. And so they didn't really take off in the United States until the early 2000s. when two things happened.

the federal government deregulated interstate gas pipelines and in many parts of the country opened up generation of power plants or power generation to competition as well. And partly that was a result of the combined cycle plant, because they were smaller than coal plants and nuclear plants, you could build them with a smaller amount of capital and therefore you could enter the market without being a giant, super well capitalized utility.

And that created the opportunity for competitive independent generators to come into the market. There have been some experiments with this going back to the seventies with cogeneration of heat and power from industrial facilities and with the early wind. turbines that were offered some special contracts to generate power, but still had to sell to the same utility. The markets were deregulated and that's where we get our competitive markets like PGM or New York ISO or mid continent ISO.

in the early two thousands, right around the same time that the gas networks were opened up. And so that was the first wave of gas turbine construction. It was huge. We built I think a peak of almost sixty gigawatts of generators in a single year in like two thousand five or two thousand six.

Um gas prices were still quite high during that period though, and so they weren't run very frequently until the shale gas boom, which really took off in the twenty teens, where all of a sudden the cost of natural gas collapsed from six to ten dollars per MMBTU in the two thousands down to three to four dollars by the late twenty tens. And that's where they've stayed since then, which has allowed the combined cycle power plant to become the dominant generating technology in the US.

Well that brings us to the present day, but I was actually gonna say in the nineteen sixties, early nineteen sixties Just as the first combined cycle gas plants are being built and deployed in Europe and the United States, there is another process happening, and that is coming out of Bell Labs and coming out of some other energy RD outfits. Researchers and engineers are inventing the modern forms of what we now know as wind and solar.

This week, this episode, this class session was all about thermoelectricity. Next class session, we will talk about how wind and solar work. how they generate electricity at the engineering level and how they become the world's fastest growing sources of new electricity, especially, of course, solar. Thank you so much for listening to this special summer episode, summer school episode of Schifski. School is now dismissed. Go to recess.

Go to Recess. ShiftGe is a production of HBAP News. Our editors are Jillian Goodman and Nicol Oricella. Multimedia editing and audio engineering is by Jacob Lambert and by Nick Woodbury. Our music is by Adam Cromlow. Thank you so much for listening and see you next week.