The ESB has opened its Turlough Hill generating station to the public and is offering free tours throughout the summer to mark the 40th anniversary of the State’s first and only hydro- electric storage station.

Set high in the Wicklow mountains and almost invisible to prying eyes the station – which can generate up to 292 MW of electricity in 70 seconds – is located 500 metres inside the hill itself.

Some 300 metres above the turbines is the upper reservoir on the top of Turlough Hill, its flat top the only sign from the nearest public road of man made intrusion in the landscape. It is approached by a small winding road over rocky outcrops known as the Wicklow Gap, seeming populated only by sheep.

However, 300 metres off the road, like a scene from a James Bond film, the tunnel appears with workers going in and out of the mountain in small golf buggy-like vehicles.

The station operates all year round but comes into its own typically at about 5pm on a wet February evening when household cookers across the country are switched on, lights come on and home heating fires up. Turlough Hill can deliver its 292 MW of electricity to the national grid, ramping up to full power in just 70 seconds ensuring the State’s lights don’t even flicker.

Almost invisible

Turlough Hill can stay at full power for about five hours. It does this by opening sluice gates allowing up to 2.3 billion litres of water drop through the pipework inside the mountain hitting the turbines at a depth of 300 metres. The water then exits into a lower lake, originally a corrie, a geographical feature which ensures the facility remains almost invisible in the landscape.

At night when the demand for electricity across the State is lowest the turbines switch into reverse, taking excess electricity from the national grid and sending the water back up the pipes to the upper lake, ready for the next day’s peak boost.

Engineering student Ger Murphy who has been taken on by the ESB as a summer tour guide says wind energy is now routinely used to pump the water back up to the upper lake overnight, completing a virtuous cycle – a sustainable loop utilising renewable wind and hydro power.

Turlough Hill was built by the ESB using a range of contractors including Irish company Public Works Ltd and German multinational Siemens which provided the equipment.

Station manager David Sexton says any comparable engineering job in these times – including a suggested tidal hydro storage facility proposed for Killary fjord in Co Mayo, would take longer to build because of ecological concerns and would cost hundreds of millions if not billions of euro.

Statistics

Mr Sexton runs through the statistics: The cavern where the heads of the turbines are visible is about 15 metres below the lower lake – the water falls 300 metres and then rises 15 metres to the outflow.

The mean difference in height between the two lakes is 285 metres. The station now incorporates the control centre for all the ESB hydroelectric schemes from Ballyshannon in Donegal to Ardnacrusha, as well as those on the Lee and the Liffey. But Mr Sexton is also keen to dispel a myth.

“It wasn’t always Turlough Hill and Dermot O’Riordan whose vision it was, did not call his son Turlough after the job. “Many people think that because “Turlough is the Irish for a dry lake, but in fact Mr O’Riordan called the storage station project after his son”.

He adds that this Thursday evening a private concert will be held inside the mountain to mark the 40th anniversary at which Turlough O’Riordan, currently working in the energy business in Norway, will be guest of honour.

For everybody else Turlough Hill will be open until September from 10am to 3.30pm. Those in groups of 10 or more are advised to book on the website esb.ie/turloughhill

Also, two “open weekends” will be held on Saturday 12th and Sunday 13th of July and on Saturday 9th and Sunday 10th of August. Tours are available from 10am to 3.30 pm each day.