Cruachan Power Station

Coordinates: 56°24′23″N 05°06′47″W / 56.40639°N 5.11306°W / 56.40639; -5.11306
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Cruachan Power Station
Dam at Cruachan reservoir.jpg
The dam containing the upper reservoir
LocationArgyll and Bute
Coordinates56°24′23″N 05°06′47″W / 56.40639°N 5.11306°W / 56.40639; -5.11306
Construction began1959[1]
Opening date15 October 1965
Owner(s)Drax Power
Upper reservoir
CreatesCruachan Reservoir
Total capacity10,000,000 m3 (350,000,000 cu ft)[2]
Lower reservoir
CreatesLoch Awe
Power Station
Hydraulic head396 m (1,299 ft)
Installed capacity440 MW (590,000 hp)
Annual generation705 GWh (2,540 TJ) (2009)[3]

The Cruachan Power Station (also known as the Cruachan Dam) is a pumped-storage hydroelectric power station in Argyll and Bute, Scotland. The scheme can provide 440 MW of power and produced 705 GWh in 2009.

The turbine hall is located inside Ben Cruachan, and the scheme takes water between Cruachan Reservoir to Loch Awe, a height difference of 396 metres (1,299 ft). It is one of only four pumped storage power stations in the United Kingdom, and is capable of providing a black start capability to the National Grid.

Construction began in 1959 to coincide with the Hunterston A nuclear power station in Ayrshire. Cruachan uses cheap off-peak electricity generated at night to pump water to the higher reservoir, which can then be released during the day to provide power as necessary. The power station is open to visitors, and around 50,000 tourists visit it each year.


The power station is on the A85 road, about 8 km or 5 miles west of Dalmally, on a branch of Loch Awe leading to the River Awe, which is the outflow from the loch, at its NW corner. There is a seasonally open Falls of Cruachan railway station nearby.


Construction commenced in 1959, and the power station was opened by Queen Elizabeth II on 15 October 1965.[1] The concept was designed by Sir Edward MacColl, who died before it opened.[1][4] The civil engineering design of the scheme was carried out by James Williamson & Partners of Glasgow, and the main project contractors were William Tawse of Aberdeen and Edmund Nuttall of Camberley. Consulting electrical engineers were Merz & McLellan of Newcastle upon Tyne.[5][6] At the peak of the construction, there were around 4,000 people working on the project.[7] Thirty-six men died in the construction of the power station and dam.[8] The cost of the scheme was £24.5 million,[7] about £335 million in 2021 value.

Cruachan was one of the first reversible pumped-storage systems, where the same turbines are used as both pumps and generators.[5] Previous pumped-storage systems used separate pumps with a network of pipes to return water to the upper reservoir, making them much more expensive to build than conventional hydroelectric systems.[9] Cruachan is predated by the smaller 232 megawatts (311,000 hp) Lünerseewerk (de) of 1958 and the 360 megawatts (480,000 hp) Ffestiniog Power Station of 1963.[10] It is one of four pumped storage schemes in the United Kingdom.[11]

Its construction was linked to that of Hunterston A nuclear power station, to store surplus night-time nuclear generated electrical energy.[7] The power station was originally operated by the North of Scotland Hydro-Electric Board, before being transferred to the South of Scotland Electricity Board.[12] It was owned by Scottish Power from the privatisation of Britain's electricity industry in 1990 until Drax Group purchased it along with other Scottish Power assets on 1 January 2019.[13]

Maintenance of the penstocks, which formerly required them to be drained, is now done using a remotely operated underwater vehicle.[12]

To commemorate the 50th anniversary of the station's opening, a 2015 BBC radio documentary Inside the Rock covered the history of construction.[14]

In June 2021, Drax applied to build a further 600 MW pumped storage capacity using the same reservoir, to a combined 1 GW for seven hours of storage.[15] Several financing modes are possible.[16]


The Cruachan station temporarily stores energy at times of low demand, and releases it at times of high demand, when electricity prices are higher,[3] reducing the maximum power that must be provided by power stations. It is also used to cope with sudden surges in the demand for electricity, such as at the end of television programmes.[17] Despite the use of some rainwater, Cruachan is not a net generator of electricity: it uses more energy for pumping water and spinning its turbines than it generates.[3]

Water is pumped from Loch Awe to the upper reservoir, 396 metres (1,299 ft) above, during periods of low energy use (such as at night), and then released during the day.[3] The upper reservoir also receives rainwater, supplemented by a network of 19 kilometres (12 mi) of tunnels.[3][18] Around 10% of the energy from the station is generated from rainwater; the rest is from the water pumped up from Loch Awe.[3]

The station is capable of generating 440 megawatts (590,000 hp) of electricity from four turbines, two of 100 megawatts (130,000 hp) and two of 120 megawatts (160,000 hp) capacity, after two units were upgraded in 2005.[10][12][19] It can go from standby to full production in two minutes, or 30 seconds if compressed air is used to start the turbines spinning.[20] When the top reservoir is full, Cruachan can operate for 22 hours before the supply of water is exhausted.[20] At full power, the turbines can pump at 167 cubic metres (5,900 cu ft) per second and generate at 200 cubic metres (7,100 cu ft) per second.[20][21]

The power station is required to keep a 12-hour emergency water supply in order to provide a black start capability to the National Grid, to enable utilities to be restarted without access to external power.[12][20] It began supplying grid inertia in 2020.[22]

Turbine hall[edit]

There are four Francis turbines, which operate as both pumps and generators. These are housed in a cavern within Ben Cruachan, which is 91.5 metres (300 ft) long, 23.5 metres (77 ft) wide and 38 metres (125 ft) high, with an adjacent transformer hall.[20] The chamber is at a depth of around 300 metres (980 ft), and is located within a hard granite intrusion.[23] Construction of the power station required the removal of 220,000 cubic metres (7,800,000 cu ft) of rock.[20] Access to the hall is gained by a road tunnel 1 kilometre (0.62 mi) long, 4 metres (13 ft) high and 7 metres (23 ft) wide, which is warm and humid enough to allow tropical plants to grow.[5][24]

The transformers step up the voltage from 16 kV to 275 kV for transmission.[20] Six oil-filled cables carry the electric current up a cable shaft to a point in front of the dam, and from there it is carried on pylons to Dalmally 8 kilometres (5.0 mi) to the east.[5][20] The staircase in the cable shaft has 1,420 steps, making it the tallest in Britain.[20][25]

After passing through the turbines, the water enters a surge chamber designed to balance fluctuations in the level of water before entering the tailrace tunnel to Loch Awe, which is 7 metres (23 ft) in diameter and 935 metres (3,068 ft) long.[3][5]


The Cruachan Reservoir is 396 metres (1,299 ft) above Loch Awe, and is contained by a dam 316 metres (1,037 ft) long.[2][3] The reservoir has a catchment area of 23 square kilometres (8.9 sq mi),[3] and is capable of holding 7 gigawatt-hours (25 TJ) of energy.[26] Environmental restrictions meant that the dam had to have a "clean" structure, so the operational equipment is located within the dam wall itself.[5][20]

The penstocks are a pair of tunnels, 260 metres (850 ft) long and inclined at 56° from the horizontal with a 5.3 metres (17 ft) diameter, which then bifurcate into four steel lined 190 metres (620 ft) long, 2.5 metres (8 ft 2 in) diameter shafts.[27] The penstocks underwent a major inspection and refurbishment in 2003.[27][28]

Tourist attraction[edit]

The power station was listed by the conservation organisation DoCoMoMo as one of the sixty key monuments of post-war Scottish architecture.[5] In November 2012, the power station received the Institution of Mechanical Engineers' Engineering Heritage Award.[4]

A visitor centre, refurbished in 2009, is situated at the outflow to Loch Awe and receives around 50,000 visitors a year.[20][29]

The power station houses a three-section 48 by 12 foot (14.6 m × 3.7 m) modernist mural in wood, plastic and gold leaf by English artist Elizabeth Falconer. The mural includes Celtic crosses, pylons, mythical beasts, and men of industry. The first section depicts the mythical Cailleach Bheur, who guarded the spring underneath the mountain. The middle panel commemorates 15 workers killed when the roof of the turbine hall collapsed, and the final section shows the station working.[30]

Popular culture[edit]

In the Disney+ Star Wars series Andor episode six "The Eye", the Cruachan Power Station appeared as the Empire's supply hub on the planet Aldhani.[31]


  1. ^ a b c "Cruachan: The Hollow Mountain: History". Visit Cruachan. Archived from the original on 28 October 2007. Retrieved 26 April 2014.
  2. ^ a b "Cruachan Power Station: Site Information" (PDF). Scottish Power. Retrieved 26 April 2014.
  3. ^ a b c d e f g h i "Cruachan Power Station: Site Information" (PDF). Scottish Power. Archived from the original (PDF) on 24 September 2015. Retrieved 26 April 2014.
  4. ^ a b "Engineering award for Cruachan power station's 'hidden' hydro scheme". BBC News. 30 November 2012. Retrieved 26 April 2014.
  5. ^ a b c d e f g Fleetwood, David (May 2009). "Ben Cruachan's hidden giant". Context. Institute of Historic Building Conservation (109).
  6. ^ "Cruachan Power Station". Gazetteer for Scotland. Retrieved 28 April 2014.
  7. ^ a b c James Freeman (19 May 2003). "Mountain of power to get £18.5m facelift". The Herald. Retrieved 26 April 2014.
  8. ^ Bill Ray (23 July 2013). "Boffins, Tunnel Tigers and Scotland's world-first power mountain". The Register. Retrieved 24 July 2013.
  9. ^ Fleetwood 2010, p. 70
  10. ^ a b Fleetwood 2010, p. 72
  11. ^ "Cruachan hydro power station output 'could double'". BBC News. 11 February 2014. Retrieved 28 April 2014.
  12. ^ a b c d Strettle, John (19 May 2010). "IET Presentation". The Institution of Engineering and Technology. Archived from the original on 27 April 2014. Retrieved 27 April 2014.
  13. ^ "Pumped storage: what are its prospects?" AECOM / International Water Power and Dam Construction. Global Trade Media, 13 June 2014. Retrieved: 21 January 2015.
  14. ^ "BBC Radio 4 - Open Art, Inside the Rock". BBC.
  15. ^ Lempriere, Molly (25 June 2021). "Drax to expand pumped storage hydro station Hollow Mountain". Solar Power Portal. Archived from the original on 25 June 2021.
  16. ^ "UK long-duration energy storage: 'Cap and floor' best investment mechanism available". Energy Storage News. 18 January 2022. Archived from the original on 18 January 2022.
  17. ^ Ian Smith (10 June 1998). "The key player behind the power of Scotland's passion". The Scotsman. Archived from the original on 19 June 2014. Retrieved 12 May 2014 – via HighBeam.
  18. ^ "Ben Cruachan". Outside Edge. Retrieved 27 April 2014.
  19. ^ "Case Studies". Varley Hydraulics. Archived from the original on 28 April 2014. Retrieved 28 April 2014.
  20. ^ a b c d e f g h i j k "Cruachan Hydroelectric Scheme". Retrieved 26 April 2014.
  21. ^ "Cruachan Power Station" (PDF). Sandia National Laboratories. Archived from the original (PDF) on 15 May 2014. Retrieved 14 May 2014.
  22. ^ "'First of its kind' Drax inertia contract commences with National Grid ESO". Current. 15 July 2020. Archived from the original on 27 June 2021.
  23. ^ Knill, J. L. (December 1972). "The engineering geology of the Cruachan underground power station". Engineering Geology. 6 (4): 289–312. Bibcode:1972EngGe...6..289K. doi:10.1016/0013-7952(72)90013-0.
  24. ^ "Cruachan Power Station". CANMORE. Retrieved 27 February 2014.
  25. ^ "Making a big splash: Hydro has the power once again". The Scotsman. 15 August 2008. Retrieved 27 April 2014.
  26. ^ Cruachan power station for FM3 (video). Archived from the original on 21 December 2021. Retrieved 27 April 2014 – via YouTube.
  27. ^ a b "Cruachan Power Station - Penstock Repairs" (PDF). BAM Ritchies. Archived from the original (PDF) on 23 May 2011. Retrieved 28 April 2014.
  28. ^ "Cruachan Hydro' Power Station; Penstock Access Platform" (PDF). ALPS. Retrieved 28 April 2014.
  29. ^ "Cruachan Power Station: Biodiversity Information" (PDF). Scottish Power. Retrieved 27 April 2014.
  30. ^ Oltermann, Philip (12 October 2015). "Hidden treasure: the modernist mural buried in a Scottish mountain". The Guardian. Retrieved 21 March 2023.
  31. ^ "When Star Wars took over a Scottish hydro scheme". BBC News. 5 December 2022. Retrieved 21 March 2023.


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