Cwm Dyli

Cwm Dyli is the location of a hydro-electric power station on the southern flank of the Snowdon range in North Wales. At the time it was built, it was the largest hydro-electric power station in the United Kingdom. It is Britain's oldest power station, and is believed to be one of the oldest Grid-connected hydro-electric stations in the world.

Cym Dyli hydro-electric power station
Cwm Dyli is located in Wales
Cwm Dyli
Location of Cym Dyli hydro-electric power station in Wales
LocationCwm Dyli, Wales
Coordinates53°03′57″N 4°00′41″W / 53.0659°N 4.0115°W / 53.0659; -4.0115Coordinates: 53°03′57″N 4°00′41″W / 53.0659°N 4.0115°W / 53.0659; -4.0115
Opening date1905
CreatesLlyn Llydaw
Power Station
Installed capacity9.8 MW


The station was built in 1905 by the Porthmadog, Beddgelert and South Snowdon Railway company, backed by North Wales Power and Traction Co Ltd to supply electricity to its own electric railway and connected slate quarries and mines. The railway was planned to run through the same valley as the power station and be fed with an electrical feeder, but the enterprise ran short of funds and the attempt was abandoned.[1] The company was renamed the North Wales Power Company Limited.[2]

In August 1906, power from Cwm Dyli was used to power the Oakeley Quarry in Blaenau Ffestiniog carried over the Crimea Pass by a long overhead transmission line at 10,000 volts. It also supplied Dinorwic and Pen-yr-Orsedd quarries. Cwm Dyli was claimed to be the largest electricity generating plant of its kind in Great Britain at the time.[3]

Electricity produced here was also used to power the Long Wave Wireless Telegraph transmitting station built by Marconi in 1912 near Waunfawr.

Supplying power directly to the National Grid, it is Britain's oldest power station, and is believed to be one of the oldest Grid-connected hydro-electric stations in the world. It was first commissioned in 1906 and has been in fairly continuous operation since then, although it was closed for upgrading in 1990. A single turbine now produces up to 9.8 megawatts (MW).

Known locally as the "Chapel in the valley", on account of its exterior design, it employed 13 men. Today, however, it is controlled remotely from Dolgarrog in the Conwy valley.

Water for the site primarily comes from Llyn Llydaw, some 320 metres above the power station, where rainfall is very high. The water is carried from the lake through a tunnel and two 30-inch (0.762 m) diameter, 2 kilometres (1.2 mi) long pipelines.[4]

The pipeline featured in the James Bond film The World Is Not Enough.

Technical detailsEdit

The generating equipment at Cym Dyli up to 1989 comprised:[4]

  • 2 × Ganz Pelton wheels
  • 2 × Boving Pelton wheels, together these aggregated a capacity of 900 horse power (6.619 MW)

The four wheels drove:

  • 1 × 1 MW Bruce Peebles alternator
  • 1 × 1.5 MW Bruce Peebles alternator
  • 1 × 3 MW Bruce Peebles alternator

The total electricity generating capacity was 6.5 MW, at 10 kV.

The following graph shows the annual electricity output in MWh from Cym Dyli:[4] [5] [6] [2]

See alsoEdit


  1. ^ Johnson, Peter (2002). An Illustrated History of the Welsh Highland Railway. Hersham: Oxford Publishing Co. ISBN 9780860935650. OCLC 59498388.
  2. ^ a b Electricity Commissioners (1925). Electricity Supply 1920-23. London: HMSO. pp. 228–231, 514–19.
  3. ^ "Festiniog Quarries Electrified". North Wales Express. 31 August 1906.
  4. ^ a b c Garrett, Frederick C. (1959). Garcke’s Manual of Electricity Supply vol. 56. London: Electrical Press. pp. A-50, A-141.
  5. ^ CEGB Annual report and Accounts, 1961, 1962 & 1963
  6. ^ CEGB Statistical Yearbook 1972 to 1986 Central Electricity Generating Board

External linksEdit