Turlough Hill

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Turlough Hill
(Cnoc an Turlaigh)
Tomaneena (Tuaim an Aonaigh)
Turlough Hill.jpg
The upper reservoir on Turlough Hill, viewed from Tonelagee
Elevation 681 m (2,234 ft)[1]
Prominence 54 m (177 ft)[1]
Location County Wicklow, Ireland
Range Wicklow Mountains
OSI/OSNI grid T063982
Coordinates 53°01′27″N 6°24′59″W / 53.02417°N 6.41639°W / 53.02417; -6.41639Coordinates: 53°01′27″N 6°24′59″W / 53.02417°N 6.41639°W / 53.02417; -6.41639[1]
Topo map OSI Discovery No. 56
Easiest route Access road to north of summit
Turlough Hill Pumped-Storage Scheme
Lough Nahanagan.jpg
Lough Nahanagan, the lower reservoir
Turlough Hill is located in island of Ireland
Turlough Hill
Location of Turlough Hill in Ireland
Coordinates 53°01′43″N 6°24′23″W / 53.02861°N 6.40639°W / 53.02861; -6.40639
Status Operational
Construction began 1968
Commission date 1974
Construction cost IEP £22 million
Owner(s) ESB Group
Pumped-storage power station
Upper reservoir Turlough Hill
Upper res. capacity 2,300,000 cubic metres (81,000,000 cu ft)
Lower reservoir Lough Nahanagan
Hydraulic head 549 metres (1,800 ft)
Pump-generators 4 x 73 MW
Power generation
Make and model Karlstad Mekaniska Werkstad (pumps),
Siemens (generators)
Nameplate capacity 292

Turlough Hill (Irish: Cnoc an Turlaigh, meaning "Hill of the Turlach"),[2] also known as Tomaneena (Irish: Tuaim an Aonaigh, meaning "mound of the assembly/fair"),[1] is a 681-metre (2,234-foot) high mountain in County Wicklow in Ireland and site of Ireland's only pumped-storage hydroelectricity plant. The power station is owned and operated by the ESB and can generate up to 292 megawatts of electricity at times of peak demand.

The mountain[edit]

The historian Liam Price recorded that the mountain was known locally as Tomaneena;[3] Turlough Hill is the name given to it by the ESB when they surveyed the site for the pumped-storage scheme.[4] It is 681 metres (2,234 feet) high and is the 136th highest summit in Ireland.[1] The summit is located to the south-west of the upper reservoir and is easily reached via the tarmac access road that begins at the top of the Wicklow Gap.[5] It is also possible to reach the summit from Glendalough or from the summits of neighbouring Camaderry and Conavalla mountains.[6]

The underlying geology of the mountain is granite, covered with blanket bog, which is a habitat for heather, purple moor grass and Sphagnum moss.[7] A number of alpine plants grow near the summit: dwarf willow, cowberry, crowberry, fir clubmoss and common bilberry.[8] To the north-east of the summit, at the head of Glendasan valley, is Lough Nahanagan (Irish: Loch na hOnchon, meaning "Lake of the Water Monster"),[9] a corrie lake carved by a glacier at the end of the last ice age.[10]

The pumped-storage scheme[edit]

The Turlough Hill power station is owned and operated by the Electricity Supply Board (ESB).[11] Like all pumped-storage hydroelectric schemes, it makes use of two water reservoirs connected by a pressure tunnel: in this case an artificial reservoir near the summit of the mountain and the naturally occurring corrie lake, Lough Nahanagan, at the foot of the mountain.[12] Water is pumped up from the lower reservoir to the upper reservoir, using surplus power available at times of low demand, and then allowed to fall by gravity from the upper reservoir back into the lower reservoir, passing through turbines along the way to generate electricity.[13] The generating plant resides inside the mountain in a cavern measuring 250×70×90 feet (76×21×27 metres),[12] which houses four reversible pump turbines with a combined capacity of 292 megawatts.[14] The upper reservoir is 19.4 metres (64 feet) deep, has a capacity of 2.3 million cubic metres (81 million cubic feet) and covers an area of 160,000 square metres (40 acres).[14][15] The power station is designed to generate electricity at times of peak demand and is instantly dispatchable: it can go from standstill to full generation within 13 seconds, compared with 12 hours for some thermal plants.[16] It can generate electricity at full load for up to six hours per day and has a round trip energy efficiency of 75%.[17] Since 2004, Turlough Hill has been the Hydro Control Centre (HCC) for the entire ESB hydroelectric portfolio, which comprises 19 generators in total.[11] An overhaul of the plant was planned for 2011[18] following the failure of Unit 1's stator bars. A subsequent investigation led to serious defects being discovered, which led to the refurbishment of all four generating units.[19] This was being carried out[20] by Voith Hydro and by mid-2012 was nearing completion.[19]


Turlough Hill was first conceived by Dermot O'Riordan, Deputy Chief Engineer in the ESB's Civil Engineering Department.[21] In 1964, ESB engineers visited several locations in the Wicklow Mountains, digging trial pits and boreholes, looking for suitable sites for a pumped-storage station.[22] A shortlist of three proposals was drawn up by O'Riordan: an artificial upper reservoir at the summit of Tonduff mountain with an artificial lower reservoir in the Glencree valley; an upper reservoir using Lough Ouler, a natural corrie lake near the summit of Tonelagee mountain, with an artificial lower reservoir in the Glenmacnass valley; and an artificial upper reservoir at Turlough Hill with Lough Nahanagan as lower reservoir.[4]

The Turlough Hill site was chosen as the best of these options and work commenced on the scheme in 1968. The cost was estimated at IEP £12 million.[7] A loan of £6 million was secured from the World Bank to partially finance the project.[23] Contracts worth £2 million were signed with Karlstad Mekaniska Werkstad for four reversible pump turbines and with Siemens for four 73 megawatt generators in 1969.[24] The contracts for the civil engineering works were awarded to two German consortia: Beuscher-Teerbau for the upper reservoir and Alfred Kunz & Co. for the underground works in the lower reservoir.[25]

Concerns about the impact of the scheme on the scenery at the Wicklow Gap led to ESB engaging the services of landscape architect Sylvia Crowe.[7] She recommended that the upper reservoir be camouflaged by planting vegetation on its embankments and that the works on the lower reservoir at Lough Nahanagan be designed to fit into the background of rock.[7] The siting of the transmission lines that would connect Turlough Hill to the electrical grid was a matter of some controversy. Objections to the lines, planned to run from Turlough Hill to the village of Hollywood, came from several quarters, including Bord Fáilte, the Irish tourist board.[26] In the end, it was decided that they would run underground from Turlough Hill for c. 1 mile (1.6 kilometres), to preserve the view at the Wicklow Gap, before emerging overground on pylons along the King's River to Hollywood.[15] This added £600,000 to the cost of the project.[27]

At their peak, the construction works employed over 500 personnel: many of the workers lived in a temporary camp adjacent to the site, which provided food and lodgings.[28] During the initial exploratory works, a geological fault was discovered inside the mountain and the location of the cavern housing the generating plant had to be altered.[29] 1,400 pounds (640 kilograms) of gelignite were stolen from the site in an armed raid in 1972.[30] Archaeological investigations near the Wicklow Gap during construction uncovered part of Saint Kevin's Road, the ancient path that brought pilgrims from Hollywood to the monastery at Glendalough.[31] The first generator went on line in December 1973 and remaining three soon followed.[31] The scheme became fully operational in 1974.[11] At the time of completion, it was the largest civil engineering project ever carried out in Ireland.[14] The final cost of the project was IEP £22 million.[31]

Following the completion of Turlough Hill, the ESB considered a number of sites – in the Wicklow and Comeragh mountains as well as around Lough Derg – for further pumped-storage schemes.[32] However, Turlough Hill remains the only such scheme in Ireland to date, although the Commission for Energy Regulation has approved the construction of a 70MW facility at Knocknagreenan, County Cork.[33]



  1. ^ a b c d e "Tomaneena". Mountain Views. Retrieved 21 July 2011. 
  2. ^ "Turlough Hill". Placenames Database of Ireland. Department of Community, Equality and Gaeltacht Affairs. Retrieved 21 July 2011. 
  3. ^ Corlett & Weaver 2002, p. 310.
  4. ^ a b Munro, Hugh (4 November 1968). "The development of electricity in Ireland". The Irish Times (Dublin). p. 18. 
  5. ^ Dillon 1993, pp. 37-38.
  6. ^ Dillon 1993, p. 39.
  7. ^ a b c d Kelly, Tony (15 February 1969). "£12m ESB scheme begun in Wicklow". The Irish Times (Dublin). p. 9. 
  8. ^ Winder, Frank (2001). "Viewing Points for Alpine Plants in Wicklow". The Irish Naturalists' Journal 26 (12): 478–479. 
  9. ^ "Lough Nahanagan". Placenames Database of Ireland. Department of Community, Equality and Gaeltacht Affairs. Retrieved 22 July 2011. 
  10. ^ Colhoun, E. A.; Synge, F. M. (1980). "The Cirque Moraines at Lough Nahanagan, County Wicklow, Ireland". Proceedings of the Royal Irish Academy 80B: 25–45. 
  11. ^ a b c "Power Stations: Turlough Hill". ESB Group. Retrieved 22 July 2011. 
  12. ^ a b Power, Con (19 January 1971). "Turlough Hill, Co. Wicklow – Working for the Future". The Irish Times (Dublin). p. 16. 
  13. ^ "ESB project at Turlough Hill". Irish Independent (Dublin). 22 September 1969. p. 7. 
  14. ^ a b c "Turlough Hill a great success". The Irish Press (Dublin). 3 June 1975. p. 6. 
  15. ^ a b Fleming, Lionel (25 May 1972). "Turlough Hill". The Irish Times (Dublin). p. 12. 
  16. ^ "Something in reserve". The Irish Times (Dublin). 13 September 1977. p. A4. 
  17. ^ "Your frequestly asked questions". Spirit of Ireland. Retrieved 23 July 2011. 
  18. ^ ESB Group (2011). "ESB Annual Report 2010". p. 37. Retrieved 23 July 2011. 
  19. ^ a b "Turlough Hill Refurbishment Enters Final Stages". ESB Energy International. Retrieved 13 May 2013. 
  20. ^ "Turlough Hill refurbishments nearing completion". HRW Briefings. HydroWorld. Retrieved 13 May 2013. 
  21. ^ "Sunday Salute". Sunday Independent (Dublin). 5 August 1973. p. 9. 
  22. ^ "Power storage tests in mountains". The Irish Times (Dublin). 29 August 1964. p. 15. 
  23. ^ "£6m loan for ESB project". The Irish Times (Dublin). 20 March 1969. p. 1. 
  24. ^ "£2m jobs for power plant". The Irish Press (Dublin). 21 June 1969. p. 3. 
  25. ^ "Germans share ESB contract". Irish Independent (Dublin). 26 June 1969. p. 1. 
  26. ^ Fleming, Lionel (19 May 1970). "ESB power lines in Co. Wicklow. Bord Fáilte objections". The Irish Times (Dublin). p. 11. 
  27. ^ "Scenery goes on ESB bill". The Irish Press (Dublin). 6 October 1971. p. 1. 
  28. ^ "It's a happy site to work on". Irish Independent (Dublin). 19 May 1970. p. 13. 
  29. ^ "The power station inside the mountain". Irish Independent (Dublin). 19 May 1970. p. 13. 
  30. ^ "Turlough Hill raid inside job?". Irish Independent (Dublin). 7 February 1972. p. 5. 
  31. ^ a b c "The power station inside a mountain". Irish Independent (Dublin). 14 September 1977. p. 16. 
  32. ^ Fallon, Tom (30 July 1979). "In search of another Turlough Hill". The Irish Press (Dublin). p. 7. 
  33. ^ Department of Communications, Energy and Natural Resources 2010, p. 78.


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