The Coire Glas project in the Scottish Highlands has achieved a milestone with the completion of a 1.2km exploratory tunnel construction.  

This milestone is part of SSE Renewables' ongoing efforts to establish what is said to become the UK's first large-scale pumped storage scheme in 40 years.  

The proposed facility, located at Loch Lochy in the Great Glen, is expected to have an installed capacity of 1,300MW and provide 30GWh of long-duration electricity storage. 

SSE Renewables anticipates making a final investment decision on the Coire Glas project by late 2025 or early 2026.  

If successful in securing an investable cap and floor mechanism, main construction is slated to begin in the second half of 2026.  

STRABAG UK has been at the forefront of the exploratory works, which started in December 2022. 

The project received a boost earlier in 2023, with SSE announcing a £100m ($127.60m) investment to further develop Coire Glas, including the construction of the exploratory tunnel.  

The ground investigation programme, designed and supervised by technical partners Stantec and COWI, is being executed by STRABAG.  

Construction of the tunnel, approximately 5m in height and 4.5m in width, is claimed to be required for acquiring precise geological data to inform the detailed design of the main works. 

SSE Renewables Coire Glas Development director Mike Seaton said: “This phase of the project is an engineering challenge in itself and we are learning a huge amount as we progress the works.  

“The findings of the tunnelling works, alongside our wider site ground investigation works completed by Fugro in December 2023, will be used to inform the final design, including the detailed design of underground structures, and will be a key consideration in any final decisions related to the project.” 

With the tunnel construction now complete, the project team will proceed with a three-month programme of exploratory drilling and testing.  

This phase will examine the ground conditions around the site of the proposed underground powerhouse excavations.