Re: magic thinking
"Both coal and nuclear power plants can be ramped over wide ranges quire quickly, and before Dinorwig and before CCGT that's how the grid was regulated. It not especially efficient, but its certainly possible. And the French do it all the time with their nuclear fleet."
Quickly relative to what?
With a response time of hours from warm (not hot) boilers, a large coal->steam station can just about cope with the daily cycle, but would struggle to follow e.g. the tea time peak.
Nuclear station response times depend on the design (both of the reactor and the steam circuit), but again hours is not untypical, and slower than that has historically been common - for engineering and financial reasons, nuclear stations like to be run at maximum output.
Dinorwic on the other hand is zero to maximum (a little under 2GW) in a few seconds when pre-warned a few minutes in advance, or maybe a minute or so without advance notice. In the current market-driven regime it's not used for night->day energy storage (which was its original purpose, because nuclear couldn't follow sufficiently well) but for short term frequency management.
The data at Gridwatch illustrates Dinorwig's role and capabilities quite clearly, as does the Dinorwic operator's website (fomerly First Hydro Corporation, now rebranded to something I can't remember), Wikipedia, etc:
https://en.wikipedia.org/wiki/Dinorwig_Power_Station
In between, in response time terms, are the combined cycle gas turbines and the open cycle gas turbines.
Gridwatch has lots of fact-based info for the UK and france.
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