Pumped hydro. Britain has four. Cruachan in Scotland near Oban you can visit, not sure about the others. When we all watched the same two TV channels, pre-emptive spin up was a thing to handle "put the kettle on love, Dallas has finished" power surges.
The hydro in the article - its IMMEDIATE activation still allowed a million people to experience a 45 minute blackout. Trains stopped etc . Pumped hydro will take anywhere from approximate 60 seconds to several minutes to generating power. It also obviously needs to always kept in reserve for such generator dropouts
It was commissioned in 1984. It's not always kept in reserve. It has a component for black start, it also has a component for surge demand management.