The cost moment to stop and start spinning metal is huge. These devices can't bid at 5min intervals let alone 30sec. They are precisely the ones which benefit from a method to store electricity, because making steam not exist means then spending time making it exist again, to spin the turbine. They bid into 30 minute supply price moments and then try to run at the highest contract bid price for as long as possible.

Gas turbines can start quickly but its said to be very expensive to do the startup. Its better to run them idle than have to cold start.

If the goal is to remove steam energy sources from coal and gas and oil, I get this. But if you have them, and you have efficiency from constant operating load, then rather than incurr start and stop cost, its better to store, even with wastage.

Back when I was a trainspotter, I used to hang at loco sheds and I asked a driver once why so many diesel locos ran idle doing nothing. he said that starting from cold was a pain. They costed it, and it worked out ok to run idle at their fuel cost, rather than have to restart. I think this is a similar moment.

So basically, I think you may have inverted the thing a bit. You can ignore free-energy inputs like wind and solar, but its wasteful so if you can't shed load in coal, its worth storing energy from solar and wind, meantime. If you have total excess energy from all sources, its worth storing it from anything which it is costly to stop-start, and you might as well store everything you can, to the capacity of storage.

Because wind and solar cannot guarantee supply in specific situations, storage can turn them into reliable power (albiet at lower intensity than the wallplate, because the storage either runs down too soon, or can't deliver as much peak)

Thats what I am reading anyway. This all feels like a classic complex linear programming optimisation problem for wiser people in power engineering economics.