How do powerplants adjust to the constant change in the demand of electricity?

Question

I have heard that electricity comes directly from powerplants to our homes. No storage or battery of any kind. If I turn on an extra light, how does the powerplant adjust for such a small change in the demand? Does that mean every other device that is turned on and getting electricity from this powerplant gets a little less energy to compensate for my light?

In: 24

Answer 1

Powerplants react to changing demand, they follow a multiple stage plan (depending how much extra power is needed)

If the demand suddenly changes at first the missing/additional power is caught up by the rotational inertia of the generators of the whole electrical grid. They slow down or speed up wich changes the frequency of the grid but compensates the power balance. (Your extra lightbulb would slow all generators in your country by an extremely tiny bit)

Then powerplants are paid to run a control curve to get back to the desired frequency, the steeper it is, the more money they receive for that. That means, if the frequency is too low they will gradually increase power output to speed the generator up again.. Slow coal powerplants aren’t able to do that very steeply (lots of extra power on short demand) but gas powerplants are able to.

If that isn’t enough to restore the grid frequency withing minutes the grid operator calls on the control reserve, powerplants that are paid to stand ready to increase power on demand (so they are already fired up but deliberately only doing half load)

If that reserve looks like it’s going to be exhausted as well the grid operator can phone additional poweplants to power up outside of this planned program, or drop some load (ask industrial consumers to consume less, or in an emergency trigger a partial blackout)

Within the powerplant you can usually temporarily increase power output very easily, just Close/open a valve to push more steam towards the turbine. But longterm changes take a lot longer, heating up a new block from being completely cold takes about 8 hours, so it has to be coordinated properly who will fire up their boilers ahead of time so when the load comes they are ready already.