When is a battery cheaper than a power plant?

There are nuke reactors which can throttle based on the load - the Navy uses them - but I don't think they're used much by POCO's.

I thought one of the advantages of NG was the ability to throttle based on demand. Is that not true?

Any source which can respond quickly allows for effective use of variable RE, not just conventional. That's why all the R&D into energy storage. Imagine if the POCO had energy stored and knew they wouldn't need a boiler for at least 24 hours - it might become economically viable to turn the boiler off until potentially needed again. Still years away (if not decades) from that scenario though.

The typical Nuke plant in the U.S. is old and designed well before interest in RE was common. If nuke plants could typically be throttled quickly the famous accidents would have been a lot less severe.
I guess machines like gas turbines only scale so big. It is the the need to indirectly create mechanical motion from steam that makes scaling difficult, AFAIK.

donald - Don't guess where you have zero idea!

There are reasons the nuke plants don't "throttle" down and it has nothing to do with RE. Your concept of the accidents is a bit off!

The "need to indirectly create mechanical motion from steam" - a cute but meaningless statement - were you an English major?

There's nothing indirect about it. That's why they're called Prime Movers. Scaling in terms of physical dimensions is not a part of Thermodynamics and has little, if anything, to do with process control.