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
It must be used. The exact amount generated is used. When demand fluctuates, it changes the load on the generators, which in practice changes the resistance to the spin of the turbines. Those are big and have a lot of inertia, so a slight increase or decrease in resistance can be absorbed by the system.
What happens is that the turbine speed changes, which changes the phase slightly. It averages out, but clocks that use phase to keep time drift a little as demand fluctuates.
A big problem with renewables is that they don’t have this feature. If you can’t increase usage by charging batteries etc, then you’ll oversuply the network, which will firstly make lightbulbs shine slightly brighter, and then start tripping fuses.
Traditionally power grids were comprised of baseload generators (coal, nuclear, etc), which could handle power fluctuations on the scale of hours to days via ramping up and down, and power fluctuations on the scale of seconds via the inertia of their turbines. Then things like hydro and gas turbines handled fluctuations on the scales of minutes.
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