Prior module, we talked about the components of the electricity system. There's generation, transmission, and distribution. We talked about some of the power plants themselves. In this module, we'll talk about what we call grid operations. How does the electricity system actually function? How does it work in an operative sense? To remind you, there are different pieces of the system, but at a higher abstract level, there's the power plant, there's the transmission lines, there's the distribution lines, and then there's a house where electricity is actually used. Now the fundamental issue, perhaps the theme for the course, and some ways is something you have to understand as a starting point it's really difficult, not impossible, but difficult to store electricity. Later in the course, we'll talk about how we start and figure how to do that. But for now, let's just exclude that option. The amount of electricity produced must be exactly as much electricity is consumed, exactly, like 99.9 percent. You can't really tolerate any difference. That's always true. Every second, every minute, every hour, every day, every week, month, year, you get the idea. It always has to be the same. That is really hard to do. What that means is at least in theory, if I turn on a fan, plug in my computer, somewhere, some power plant has to turn up just a little bit to make sure there's enough electricity. Now, somebody else may turn off their fan at the same time and it all nets out. But that's the idea. You have to make exactly as much as use all the time. That's not easy. That really explains why electricity system are difficult to operate, and we'll talk about why renewables are actually, maybe in some ways make that job even a little bit harder. But let's work up to that. For now, the fundamental idea is power consumed has to equal power supply all the time. Let's talk about power consumed or what's called the demand for electricity. Why electricity? Because we do useful things with it. We dry heat space, heating, space cooling, we run motors, we charge our batteries, we all the things we do with electricity. That's the demand for electricity or need for electricity. That varies all the time as well as you can imagine. Your home, you turn things on, your turn things off, the amount of electricity your house needs changes all the time. There are a lot of factors, things that influence demand. I want to just talk about just a few now so you have a sense of essentially the challenge of making electricity system work. Electricity demand or need for electricity follows what's called a load curve. Now, throughout this course, as we talked about, we'll be introducing new terminology bit by bit. This is what's called the load curve or a peak demand curve. As I've mentioned, one of the challenges in the energy business, particularly electricity's the terminology, it's not consistent. Different people use terms at different times. As I've said, I'm not going to teach you the right way to do that. There is no right way, but gets you comfortable with these different terms so you can interpret from the context of what they're talking about. That said, this is a typical load curve over the course of the day. In the morning, electricity demand for the system. Not talking about a house, but imagine a city or a state, or a bunch of villages, or just any area of land where there's a bunch of electricity users. This is a typical peak demand curve where in the morning, where people get up and they turn things on and they turn out in a coffee pot, and they turn on lights, so they turn on a heater, it tends to climb over the course of the day because people go into offices or go into buildings, and maybe at home, there's no one home and there's less electricity use. But in the office, the heating and cooling is on, the lights are on the computer is running, industry is doing whatever industry does, and generally, you find the peak demand, that is the maximum demand or need for electricity to insist them is usually in the afternoon. Though not always, we'll talk about a few exceptions just a minute. At night, it starts to come back down. The office closes, the lights turned off, people come home, they do what they do, but eventually they go to sleep. Everything's dark and quiet and you have minimum demand at night. That's a typical load curve for an electricity system. Now, different regions of the world have different types of load curves. I'll show a few characteristics just so you can get a sense of this. This is for a New England portion of the US. A number of states in the US and the Northeast part of the US are called New England. That electricity system is run as a whole. Later in the course, we'll talk about how that works, but for now, just look at the load curve for a typical day in New England region of the USA. It's low at 4:00 AM, not surprising, not much going on, climbs up to up to 8:00 AM as everybody gets up, turned on the light, plugs in the coffee maker and so on. Then least at this day in New England, it was flat over the course of the day. But notice there's something called the morning ramp. Electricity demand climbed up fairly steeply in the morning. Then it was fairly flat. Then this area showed an interesting nighttime peak where the peak demand, the maximum over the course of the day it was about 18:00 hours, 6:00 PM because everybody came home and turned on lights and turned on the oven and so on. That's just the way it happened to look in New England at that time. Different regions show different demand curves. Let me show one more. This is the US State of California, which is a famous demand curve, for reasons we'll talk about shortly. But notice how it minimum at 3:00 AM, climbs up until 8:00 AM, and actually goes down, which is characteristic of California. Different regions show different demand curves. But this one decreases over the course of the day, reaches at afternoon minimum, in essence, at 14:00, 2:00 PM. Why does it show that curve? Has to do with the climate and the way could you use electricity in California. Then you climb up to this very high peak at about 6:00-7:00 PM, 18:00, 19:00 hours. That's because everybody was back home and they are cooking and lights are on. This is in fact 10th of February of 2020. You have this high peak demand in the early evening, which is characteristic of California. Just how it happens to work in California. That shows how demand varies throughout the day. This curve shows how a couple of things going on here, how demand varies during the day, but it varies by the day of the week. This is in Great Britain, which shows a typical week in the Great Britain, and days of the week on the x-axis. Notice we have a California like peak in the late afternoon, and it's similar Monday through Friday, but on Saturday and Sunday, the whole thing shifts down. Make some sense because many offices and buildings are closed on the weekend and therefore using less electricity, the lights are on, the temperature setting may be different. The whole thing shifts down on the weekend but still has a somewhat similar shape. That's how it looks in Great Britain. Further adding complexity, there are seasonal variations in load. This shows for a set of US states, how that daily load curve varies by the season. It's highest in the summer because in this region of the US, there's a lot of space cooling, air conditioning, and everybody has their air condition. Many people have their air conditioners on during the day, but in the winter, they don't. You'll see the blue curve is lower than the green curve. The spring curve is even lower, this gets into subtle reasons of how things work there. But the major reason why you have lowest demand in the spring is because you also have less heating in the spring. There's some electric heating, or for example, natural gas heating powered by electric fans. In this region of the world, the lowest electricity demand is in the spring. Again, point is it varies by time of day and season. Here's a characteristic, this is for the UK again, national grid, showing, interestingly, that the summer is the lowest demand and winter is quite a bit higher. Now, why is that? That's because the UK Climate, this is 2011, things are slightly different now, is fairly mild. There is space conditioning, but not a lot of residential space condition. You don't find a lot of air conditioners in homes in UK. That's changing, this is true in 2011. Notice that winter is the highest because largely of space heating, but also because of lighting. Again, point being, it changes quite a bit over time. Take a short break here, pick up in the next video.