The project would more than double the electricity generating capacity at its ‘Hollow Mountain’ Cruachan facility.

The up to 600MW power station will be located inside Ben Cruachan – Argyll’s highest mountain – and increase the site’s total capacity to 1.04GW. The plant will be housed within a new, hollowed-out cavern which would be large enough to fit Big Ben on its side. Around two million tonnes of rock will be excavated to create the cavern, tunnels, and other parts of the power station.

The new power station could be operational as soon as 2030 with construction work getting under way in 2024, creating hundreds of jobs across Scotland.

It will support around 900 jobs during six years of construction across the supply chain in a range of industries from quarrying and engineering, to transport and hospitality. Around 150 on-site local construction jobs will be created during the development.

The development – which could be the first newly constructed plant of its kind in the UK in more than 40 years – is designed to provide storage capacity to strengthen the UK’s energy security and enable net zero.

The new plant could be operational in 2030, providing critical stability services to the power system by acting like a giant water battery. It will use reversible turbines to pump water from Loch Awe to the upper reservoir on the mountainside to store excess power from wind farms and other low carbon technologies when supply outstrips demand and then use this stored water to generate renewable power when it is needed.

Wind farms are routinely paid to turn off when supply outstrips demand or there is insufficient capacity on the National Grid Transmission System due to a lack of energy storage creating local bottlenecks. In 2020, enough wind power to supply around a million homes went to waste because of this.

Ian Kinnaird, Drax’s Scottish assets director, said: “Drax’s plan to expand Cruachan will strengthen the UK’s energy security by enabling more homegrown renewable electricity to come online to power homes and businesses across the country, helping to end our reliance on imports and cut costs. This major infrastructure project will support hundreds of jobs and provide a real boost to the Scottish economy. Only by investing in long-duration storage technologies can the UK reach its full renewable potential, and Drax is ready to move mountains to do just that.”

Claire Mack, Scottish Renewables chief executive, said: “Pumped storage hydro is a critical technology needed to meet net zero. Over the last decade we have managed to develop the technologies to decarbonise the power system such as wind and solar, but what we really need now is greater flexibility to fully optimise those technologies. That’s why the success of long-duration storage projects such as Cruachan 2 is absolutely vital to Scotland and the whole of the UK.”

Drax must secure consent under Section 36 of the Electricity Act 1989 from the Scottish government – a process which will take around one year to complete from the application’s submission.

Alongside a successful Section 36 application, the project will also require an updated policy and market support mechanism from the UK government. The existing lack of a framework for long-duration electricity storage and flexibility technologies means that private investment cannot currently be secured in new pumped storage hydro projects, with no new plants built anywhere in the UK since 1984 despite their critical role in decarbonisation.

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