The Ffestiniog Power Station is a 360 MW pumped-storage hydroelectricity

Pumped-storage hydroelectricity

Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

 scheme near Ffestiniog

Ffestiniog

Ffestiniog is a community in Gwynedd in Wales, containing several villages, in particular the settlements of Llan Ffestiniog and Blaenau Ffestiniog. It has a population of 4,830....

, in Gwynedd

Gwynedd

Gwynedd is a county in north-west Wales, named after the old Kingdom of Gwynedd. Although the second biggest in terms of geographical area, it is also one of the most sparsely populated...

, north-west Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

, United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

. The power station at the lower reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

 has four water turbine

Turbine

A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

s, which can generate 360 megawatts

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

 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 discharges 27 m3/s of water to the turbine generators at the power station on the bank of Tan-y-Grisiau

Tanygrisiau

Tanygrisiau is a village in the upper end of the Vale of Ffestiniog in the county of Gwynedd, north-west Wales . It can be found along the southern side of the Moelwyn mountain range and dates to around 1750...

 reservoir.

The plant is operated by First Hydro, a UK company owned by a joint venture of International Power

International Power

International Power PLC is an international electricity generator formed in 2000 by the demerger of National Power. It is headquartered at Senator House, 85 Queen Victoria Street in the City of London...

 and Mitsui & Co.

Mitsui & Co.

Mitsui & Co., also known as Mitsui Bussan, is one of the largest sogo shosha in Japan, and also part of the Mitsui Group. Its business area covers energy, machinery, chemicals, food, textile, logistics, finance, and more.- History :...

, 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.