It’s a good thing about the kettles, because as far as I can tell Dinorwig actually acts as a net drain on the UK grid.
Yes indeed, I do remember our visit to Dinorwig. Ironically, although my company has a similar pumped storage power station, Turlough Hill, I have never visited it.
Really Not All That Bright, the pumped storage stations do use more energy (pumping) than they generate, so in that sense you are right that they are a drain on the system. But their ability to store cheap electricity and release it at periods of high demand, displacing expensive peaking plant, is very valuable.