In article , David Hansen
writes
Strictly speaking Dinorwig was not designed as a backup generator,

It would also be slightly difficult to claim that any such scheme is
a generator, because it consumes more electricity than it generates
(unless there has been a change in the laws of physics since I
studied the things).

Sometimes it generates, sometimes it soaks power up. Just like a UPS.
--
"now, the thing you type on and the window you stare out of are the same thing"