Note that "standby" is burning power to keep the turbines spinning without flow, so that they don't have to accelerate when the stopcocks are opened. Dinorwig's purpose is smoothing demand spikes, so its 75% roundtrip efficiency is acceptable and its duty cycle somewhat predictable, but it must be a tricky optimization problem to maximize efficiency while never failing to meet the load.

(Interesting side note - when I took a tour of Dinorwig some years back, the guide said that when the facility was built it rarely needed to run more than 1 turbine - now they routinely fire up all 6. At some point it will run out of capacity...)

Dont forget the person who watches the telly to know when to turn it on. https://www.google.com/url?sa=t&source=web&rct=j&url=https:/...