[MUSIC] That's the electricity part, but that's not the whole power plant. If we remember our water, it's now lost a lot of it's heat, a lot of it's energy content. But we still have a bit cooler steam, I mean, it's still steam, it's still past the boiling point. At lower pressure, we've gotta do something with it, we could just let it go into the atmosphere. You might say well, that wouldn't be very good, I'm sure that's bad for something. Well it certainly would warm up the intervening air and the stuff around it, throwing out steam afterall. It certainly means you'd have to keep putting more water in like you do with a steam engine because a steam engine does leak steam out but there's a most important reason is, because if you want to clean water really, really well, you distill it. And by distilling it, that means you boil it, you turn it into steam, and you condense it again, and that water is pure and no impurities are left. This contraption called the turbine that has the stators and the rotor. The tolerances are small, the balance is precise and if e put a whole lot of impurity of scale, things building up over time as this thing is constantly used years after year, decade after decade you could destroy it. So you really want high purity water to go through the system. And that's another important reason why we will take this theme, this low pressure, cooler steam that comes out of the turbine, and we will condense it back into water and circulate that water back through the boiler to be turned into steam again. The device which does this is called a condenser because it condenses the steam back into water. Now, it's going to need an outside source of heat to do that. Actually, an outside source of being a heat sink. Some type of cool body of water. All power plants are built on some type of water source, for this very reason. It could be a river, a pond, a lake, the ocean, but you're going to have some source of water that you can suck out run through the condenser and run, well, let's talk about where you're going to put it next. You're going to take out this lake water or ocean water and you're going to warm it up slightly, condensing that steam back. Notice that the water that you cull out of the lake never went into the power plant. If this is a nuclear power plant, that water you use for the condenser never gets exposed to anything. All it's doing is cooling off the steam. What about the slightly warmer ocean water or pond water or river water? Well, in many place sit's just put back in and let's face it, if it's the ocean as huge and deep as they are and this is a few degrees, probably doesn't make much of a difference at all. Of course maybe right around the inlet, or right around the bay, maybe that would change the ecology. Certainly if you were in a small lake or a pond and you put that water back in constantly being a little warm or a little warmer, that would have a big change in the ecology. Kill the fish, promote algae growth, ruin the beautiful lake shore home's view. So, we go through one more step and that's the cooling tower. These are this large cement objects that are shape like an hourglass, and many people see this. And they see the white bellowing clouds out and they would say my god look at that power plant or worst look at that nuclear power plant with that cooling tower, isn't that terrible? Look at all of that air pollution it's making. Well that's just wrong on so many levels. All right so first, what's in the cooling tower? Basically it's a bunch of concrete, it's drip trays. Water comes in at the top and it drips down the sides. Often it goes on little shelves. It drips on one shelf to another shelf to another shelf. And lots of exposure to the air as that water trickles down through the cooling tower. There is holes in the bottom of the cooling tower to let air in. Just the outside air, no fans, no electricity used. Hot air rises and since this water is warm, it's going to warm up this air and there'll be a suction. And it will draw in the air and the air will come out now slightly warmer and slightly wetter out the top of the cooling tower with some evaporated water in it. You're basically making a cloud. And the water ends up being the same temperature as the air, which is usually the same temperature as the surface of the ocean, or the water, or the lake, or the river. And now you put it back into the lake, so we dealt with that water. And we have the water that's circulating and becoming steam, and one question you may have is how efficient is this? In the last topic, or two, we discussed thermo efficiency. Carnal efficiency. And we came up with a formula. 1-T cold/ T hot. You can do the same thing to find out what is the maximum efficiency of the power plant. The hot temperature will be the temperature that you get the steam up to. The cold temperature would ultimately be the temperature of your condenser, the temperature that the water gets down to before it goes back through that cycle. You put those numbers in, and you typically get a value about one third. 33%, maybe some are 35%, some other things may be 38, 39% but they're in that range. That is the efficiency at making electricity through a thermal plant, through a plant that boils water. What happens to the other two-thirds of the energy? Goes into waste heat. It just goes into heating up the environment. So on the face of it, you might say this is awful. All these electric power plants, it's throwing away two-thirds of the energy. Well, not so fast remember the automobile engine, that was throwing away more than two-thirds of the energy. Heat engines are not perfect, and physics tells us, unless we go down to absolute zero, they aren't perfectly efficient. But we are turning thermal energy into an extremely useful media, and that is the medium of electricity. When you use the electricity, on the other hand, often it's near 100% efficiency to do the task you have at hand. If you pay the penalty in the efficiency cost back at the source where you make the electricity. Or you could pay for it at the end use if instead, you're shovelling coal into your blender in your kitchen, or whatever purpose in the end you have electricity for. The bargain is do it at the power plant. Because the power plant can control all the side-effects of burning the primary energy source. Much better than you can do back in your home. And you are going to lose that heat engine efficiency in one place or the other. [MUSIC]
