Exploratory tunnelling at the site of what could become the UK's first large-scale pumped storage project in four decades has been completed. The 1.2-kilometer tunnel is a key milestone in SSE's 1.3 gigawatt (GW) Coire Glas project, located in the Scottish Highlands near Loch Lochy in the Great Glen.
The Coire Glas project, once operational, would provide 30 gigawatt-hours (GWh) of long-duration electricity storage, enough to supply firm and flexible renewable power to three million British homes for up to 24 hours continuously, according to SSE Renewables.
SSE Renewables aims to make a final investment decision by late 2025 or early 2026, with main construction expected to begin in the second half of 2026, pending the outcome of the administrative allocation of an investable cap and floor mechanism.
The exploratory work, which began in December 2022, was carried out by mining and tunnelling contractor Strabag UK. In early 2023, SSE announced a £100 million investment to advance the project, including the construction of the major exploratory tunnel.
The tunnel, measuring approximately five meters in height and 4.5 meters in width, cuts into the hillside at the proposed site of the underground complex. This construction allows the project team to collect detailed geological data to inform the design of the main works.
Following the completion of the tunnel, a three-month programme of exploratory drilling and testing will continue to further investigate the ground in the area designated for the underground powerhouse.
Mike Seaton, SSE Renewables' Director of Development for Coire Glas, praised the completion of the tunnel, stating, “Completing the tunnelling is testament to the hard work and dedication of everyone involved and a positive step forward in de-risking the project.” He added that the findings from the tunnelling, alongside other site investigations, will play a crucial role in the final design and decision-making process.
Stantec and COWI, SSE's technical partners, have been instrumental in the design and supervision of this complex ground investigation programme. John Ord, Business Director for Energy at Stantec, expressed enthusiasm for the project, noting that the team is eager to move into the next phase, which involves defining rock quality more than a kilometre inside the mountain.
COWI's Managing Director in the UK, Andy Sloan, also highlighted the importance of this milestone, praising the collaboration between the joint Stantec/COWI team, SSE Renewables, and Strabag. “The joint Stantec/COWI site team have worked tirelessly with SSE Renewables and Strabag to reach this point and collaboration has been excellent,” Sloan said.
As the project progresses, the findings from the tunnelling and subsequent drilling will inform the detailed design of the underground structures, bringing the UK closer to enhancing its renewable energy storage capacity.
