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