system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If electricity from natural gas power plants cant be stored, how do they know how much electricity to produce per day and where does the wasted electricity go to?
gpt
Lots of ways of making electricity have different benefits - nuclear is cheap but not very responsive if you need to increase or reduce supply, hydroelectric is expensive but very responsive, everything else is in between.

Power companies work HARD with big users in industry to manage the supply - for instance historically in the UK there are three 30' slots per year where domestic demand is so high that industry (eg foundries) can save a lot of money by keeping powered off during that slot (they pay variable pricing for power, btw).

What the grid needs is to know demand and be able to level it best possible.  To do that, the spare electricity from cheap nuclear overnight is used to pump the hydro plants water back uphill, or if there's a surge in demand (kettles going on at half-time in the football), the hydro plant can be brought online at almost no notice to cover a surge.  Gas plants take a littler longer to adjust, maybe a minute or so, so they can be brought up to cover the increased demand after the hydro has covered a gap at a price somewhere between the two.