Since, and unless electricity has properties I’m not aware of, it’s not possible for electric power plants to produce only and EXACTLY the amount of electricity being drawn at an given time, and not having enough electricity for everyone is a VERY bad thing, I’m assuming the power plants produce enough electricity to meet a predicted average need plus a little extra margin. So, if this understanding is correct, where does that little extra margin go? And what kind of margin are we talking about?
In: Engineering
Most power plants work by rotating a big turbine which spins a shaft that spins the magnets in a generator. In the generator the rotating magnets creates a rotating magnetic field. And the windings in the generator which is hooked up to the three phase AC of the grid also produce a similar magnetic field. When these spin the same speed no current is produced by the generator. But if the generator gets ahead of the AC phase it produce power which also makes the AC speed up. Similarly if the generator starts slowing down the AC generated magnetic field will pull it back up to speed which slow down the AC.
This all means that all the turbines in all the power plants in the grid is all connected together and spins at exactly the same speed. And they have quite a lot of energy stored as rotating mass. If a single power station generates too much power the generators will spin faster. This takes up any excess power that is generated. But when the grid controllers slow down that power station and make it produce less power then is needed all the generators will release this energy as they slow down.
So there is a tiny bit of energy storage in the electricity grid, in the form of these big generators and turbines. It does not last for many seconds though so grid operators need to constantly increase or reduce power to meet the demand as accurately as it can.
This can be compared to driving a car. In order to maintain a fixed speed the engine needs to produce exactly as much energy as the car lose in drag and resistance. So these is a throttle position which works for the speed you want to go. But if you push the throttle a bit too hard or a bit too soft then the car is not going to instantly go super fast or instantly stop. You have some time to notice that the speed is not right and correct your throttle. And when there are changes in the driving conditions, going up or down a hill or going around a curve, just like there are different loads being applied to the electricity grid, you have time to adjust the throttle to meet this changing demand.
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