Pumped storage development in Scotland

SSE Chief Executive Alistair Phillips-Davies has spoken in recent months about how he believes that accelerating offshore wind development is the cheapest and quickest route to a secure, clean and homegrown energy system in the UK. However, he warns that dramatically expanding wind power’s full potential will also require massive investment in grid infrastructure and amid all the debate one critical word is being overlooked – flexibility. 

Flexibility, Phillips-Davies says, holds the key to realising the full benefits of renewables. Put simply, “we need ways to capture wind power when there’s too much of it and store it for when it’s not windy enough”.

“Network investments will help,” he admits, “but there’s another established British technology that can have a massive impact: pumped hydro storage.” 

SSE’s Chief Executive explains that his company is building the first large-scale pumped hydro storage scheme in the UK for more than 30 years. The 150MW Coire Glas project in the Highlands of Scotland is big enough to power three million homes for 24 hours on its own. Critically, it can be built without any subsidy, subject to some tweaks to regulation. Located on the shores of Loch Lochy near Invergarry, the scheme would double the current amount of electricity storage capacity in Great Britain and could deliver 1.5GW and 30GWh of long duration storage by 2030.

After a rigorous tendering process, in May 2022, SSE Renewables selected Strabag UK to undertake the exploratory works for the scheme. Scheduled to begin at the site this summer, the works will provide essential information on the nature of underground conditions at the location. The findings will be used to inform the final design of the project and will be an important consideration in SSE Renewables’ final decision on whether to proceed.

The work will see the creation of a tunnel approximately 4m wide and up to 1km long, which will cut into the hillside towards the proposed location of the underground powerhouse complex. Samples of the materials within the hill will be analysed, and survey and assessment work will be carried out to give a detailed understanding of the geological conditions. The information will then be used in detailed design of the tunnel and cavern support structures. 

In June 2022, it was announced that six short-listed tenderers from around the world are taking part in the Invitation To Tender process to conduct the civil engineering and mechanical and engineering works at Coire Glas. 

Reviews of the submitted tenders are now underway, following which, it is anticipated a preferred tenderer will be selected for the mechanical and electrical scope and two tenderers will be selected for the civil engineering scope.

The preferred tenderers will work with the Coire Glas team on a programme of extensive ground investigation works, running until autumn 2023, which will allow them to refine their proposed project designs. The construction phase of the project is scheduled to commence in spring 2024 and, is expected to support up to 500 jobs.

The six tenderers shortlisted for the main construction works were:

• Bechtel, Acciona Construcción S.A. and Webuild S.p.A consortium.
• BAM Nuttall, Eiffage Génie Civil SA and Marti Tunnel AG consortium.
• Dragados S.A and BeMo Tunnelling UK Ltd consortium.
• Strabag UK Ltd for the civil engineering scope
• Andritz Hydro GmbH and Voith Hydro GmbH & Co KG partnership
• GE Hydro France for the mechanical and electrical plant scope.

“These kinds of hydro projects played a huge role in the UK’s post-war recovery, harnessing the power of the glens and creating green jobs for soldiers returning from war” Phillips-Davies said. “This is the kind of solution we need as part of a national effort to boost investment in infrastructure, deliver a green economic recovery and build the homegrown energy on which our future generations can depend.”

Finlay McCutcheon, SSE Renewables’ Director of Onshore Europe, added: “In response to the current situation in the energy markets, the UK needs to not only supercharge cheap renewables but also home-grown, long-duration storage technologies to cost-effectively decarbonise the grid and reduce our dependence on imported gas.

“The swift introduction of an adapted Cap and Floor mechanism by government this year could unlock billions of pounds of investment in these vital technologies and create thousands of skilled jobs. As the UK’s clean energy champion, with our consented and shovel-ready 1500MW Coire Glas pumped storage project in the Scottish Highlands, we stand ready to play our part.”

Panoramic view from Ben Cruachan of Cruachan reservoir, dam and loch. Photo courtesy of Draz

Cruachan expansion

Renewable energy company Drax has submitted an application to expand Cruachan Power Station in Scotland and build a new underground pumped storage plant. The new power station could be operational as soon as 2030 with construction work getting underway in 2024.

The major infrastructure project will support around 900 jobs during six years of construction across 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 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 with around two million tonnes of rock being excavated to create the cavern, tunnels, and other parts of the power station.

Turbine hall, Cruachan Power Station. Photo courtesy of Drax

When operational, the new plant will provide critical stability services to the power system. 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.

“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,” Ian Kinnaird, Drax’s Scottish Assets Director, said.

In order to deploy this critical technology, 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 this, the project will also require an updated policy and market support mechanism from the UK Government. No investment decision has yet been taken and development remains subject to the right regulatory framework with the UK government.