ScottishPower said it would be possible to double the capacity of its Cruachan Pumped Storage hydro plant near Oban — with investment of £300 million to £400 million — but that the UK Government would need to help.

ScottishPower, the operator of the 440 megawatt Cruachan plant, has completed a two-year feasibility study to determine whether it is possible to expand the station.

The findings show that it would be possible to develop additional capacity of 400-600 megawatts.

A new cavern would need to be excavated within Ben Cruachan, and new dams could be constructed to increase the capacity of the upper reservoir.

“A new generation of pumped storage hydro would be a major asset for electricity systems worldwide as more renewable electricity continues to come on line,” said Hugh Finlay, generation director at ScottishPower.

“As well as being able to further support peak demand, expanded pumped storage would also be able to effectively store greater levels of electricity at times when renewable energy output is high but demand is low.

“Pumped storage hydro is the most cost effective and well-developed large-scale electricity storage technology in existence. We will now take forward our Cruachan findings with government and regulators.”

ScottishPower said it will now consider the next steps for the project, “including discussions with government on potential support mechanisms.”

Any project to expand Cruachan would include a building programme of up to 10 years involving 800 workers.

At full operation Cruachan can currently meet the power demands of more than 200,000 homes. ‎

Cruachan can also act as a ‘battery’ — when the turbines are reversed they use excess electricity from the national grid to pump water back in to the upper reservoir, effectively storing this energy.

Widely regarded as an engineering masterpiece, and often referred to as “The Hollow Mountain,” Cruachan was devised by Sir Edward MacColl and built by a workforce of 4,000.