That’s inconvenient for nuclear reactors, I’m not sure how it works for coal.

Not a powerplant guy, but from the little I know, it's not a lot different, with the exception that a coal plant can reduce fuel consumption to the point that pressure stays at operational levels, turbines continue to spin under low load. For pairing with renewables, nat gas seems to be the winner as a gas turbine can spin up in minutes, although getting the steam turbine going takes longer, so it's running less efficiently for that period as the steam circuit is all about recovering energy not captured by the gas turbine. If the plant has MHD, that's near instantaneous.

I learned about how all this works back in HS (a probably-overambitious science fair project demonstrating MHD - stupidly long story, but I got to visit some power plants, learn how that part of the grid works).