Ffestiniog power station is a 360 MW pumped storage hydroelectric scheme, near Ffestiniog, in Gwynedd, northwest Wales. The power station at the lower reservoir has four water turbines, which can generate 360 megawatts of electricity within 60 seconds of the need arising. The station, commissioned in 1963, was the first major pumped storage system in the UK. The upper reservoir is Llyn Stwlan which drops 27 cubic metres per second of water to the turbine generators at the power station on the bank of Tan-y-Grisiau reservoir.
The plant is operated by First Hydro and has an average efficiency of 72-73% – i.e. it uses 28% more electricity (when pumping the water back up to the Llyn Stwlan) than it actually produces.