Ffestiniog Power Station

Ffestiniog Power Station
The upper reservoir, Llyn Stwlan, and dam.
Country	Wales
Location	Tanygrisiau, Ffestiniog, Gwynedd
Coordinates	52°58′51″N 03°58′08″W / 52.98083°N 3.96889°W / 52.98083; -3.96889
Opening date	1963
Owner(s)	First Hydro
Upper reservoir
Creates	Llyn Stwlan
Lower reservoir
Creates	Llyn Ystradau
Power Station
Pump-generators	4
Installed capacity	360 MW (480,000 hp)

The Ffestiniog Power Station (Welsh pronunciation^ⓘ) is a 360-megawatt (MW) pumped-storage hydroelectricity scheme near Ffestiniog, in Gwynedd, north-west Wales. The power station at the lower reservoir has four water turbines, which can generate at full capacity within 60 seconds of the need arising. The scheme has a storage capacity of around 1.44 GWh (5.2 TJ) at maximum output for four hours, and the capacity to power the whole of North Wales for several hours.^[1]

The station, commissioned in 1963, was the first major pumped storage system in the UK.^[1] The upper reservoir is Llyn Stwlan, 170,000 cubic metres (6,000,000 cu ft), which discharges 27 cubic metres per second (950 cu ft/s) of water to the turbine generators at the power station on the bank of Tanygrisiau reservoir. The building of the lower reservoir increased the size of Llyn Ystradau and flooded the route of the Ffestiniog Railway which had to build a deviation around the reservoir and power station.

The plant is operated by First Hydro, a UK company owned by a joint venture of International Power and Mitsui & Co.,^[1] and has an average efficiency of 72–73%, i.e. it uses 39% more electricity (when pumping the water back up to the Llyn Stwlan) than it actually produces.^[2]