Cruachan Power Station: 'The Hollow Mountain'

Cruachan Power Station, affectionately known as the ‘Hollow Mountain’, resides deep inside Ben Cruachan mountain in Argyll and Bute.

Winter snow scene around the Hydro electric Dam on Ben Cruachan,above Loch Awe, Argyll, Scotland

Bought by Drax in December 2018, the site is one of only four pumped storage hydro stations in the UK and has a capacity of 440 MW – enough to power more than 90,000 homes.

Pumped storage is one of the oldest forms of large-scale energy storage requiring two reservoirs based at different altitudes but close to each other.

Sitting on Loch Awe, Cruachan fits the bill perfectly and as the home to one of the wettest areas in Europe, it is a prime location for pumped storage.

Key facts

  • Cruachan power station can reach full generating capacity in less than 30 seconds
  • The reservoir has a capacity of 440 megawatts (MW) – enough to power more than 90,000 homes
  • Construction involved the excavation of 220,000 cubic metres of rock and soil and around 1,500 workers were employed at the peak of this major civil engineering project
  • The reservoir has a storage capacity of 10 million m³ of water and has a catchment area of 23km²

So how does it work?

Water released from the upper reservoir, flows through a turbine and into the lower reservoir. The flow of water rotates the turbine which in turn rotates a generator to produce electricity. Electricity from the grid can then be used to drive the turbine in the opposite direction, to pump water from the lower reservoir back up into the upper reservoir.

Pumped storage provides extremely quick back-up during periods of excess demand by maintaining stability on the National Grid. For example, Cruachan can reach full load in 30 seconds and can maintain its maximum power production for more than 16 hours if necessary. It can also help solve intermittency issues with other forms of renewable power, that is, when the wind doesn’t blow and the sun doesn’t shine. For these reasons, Cruachan recently won a six year contract to keep the electricity system stable.


The turbine hall is located 1 km within the hollowed-out mountain of Ben Cruachan and houses four generators. The plant has four primary modes of operation and can deliver a range of balancing and ancillary services.

Turbine hall, Cruachan Power Station

Turbine hall, Cruachan Power Station

Cruachan Power Station is also a popular tourist destination which has been rated five stars by Visit Scotland.

Guided tours are available through the Cruachan website with visitors and school groups welcomed between March and November. Unfortunately these are currently suspended due to the pandemic.