SSE has successfully completed the exploratory tunnelling phase for what could become the United Kingdom’s first large-scale pumped storage project in four decades.
The recent achievement involves the completion of a 1.2 km exploratory tunnel, which is a significant development in the ongoing progress of SSE’s Coire Glas project, located in the Scottish Highlands.
Overview of the Coire Glas Project
Situated at Loch Lochy in the Great Glen, the proposed Coire Glas project is designed to have an impressive installed capacity of 1,300 MW.
This facility is expected to offer 30 GWh of long-duration electricity storage, sufficient to provide consistent and flexible renewable power to approximately three million British households for up to 24 continuous hours.
Future Steps and Investment Decisions
SSE Renewables aims to make a final investment decision on this ambitious project by late 2025 or early 2026.
If approved, main construction could begin in the second half of 2026, contingent upon securing a favorable administrative allocation of an investable cap and floor mechanism.
Exploratory Works and Collaborations
The exploratory works at Coire Glas began in December 2022 and have been executed by STRABAG UK, a global leader in mining and tunnelling.
In early 2023, SSE announced a substantial £100 million investment to further the development of Coire Glas, which included the creation of a major exploratory tunnel as part of an extensive site investigation initiative.
SSE’s technical partners, Stantec and COWI, played pivotal roles in designing and supervising this complex ground investigation program, carried out by STRABAG.
The tunnelling work involved creating a tunnel approximately 5 meters high and 4.5 meters wide, cutting into the hillside near the proposed underground powerhouse site.
The purpose of this tunnel is to enable the project team to gather accurate geological data essential for the detailed design of the main construction works.
Ongoing Exploratory Drilling and Testing
With the tunnelling phase now complete, the project moves into a new stage, focusing on a three-month-long program of exploratory drilling and testing.
This phase aims to further investigate the geological conditions in the area designated for the underground powerhouse.
A Significant Engineering Achievement
Mike Seaton, SSE Renewables Director of Development for Coire Glas, emphasized the importance of this milestone: “Completing the tunnelling is a testament to the hard work and dedication of everyone involved and a positive step forward in de-risking the project. The works progressed as planned, and the materials excavated from within the hillside are currently under analysis. This phase of the project is an engineering challenge in itself, and we are gaining valuable insights as the work progresses. The findings from the tunnelling, along with the broader ground investigation works completed by Fugro in December 2023, will be instrumental in shaping the final design, including the detailed design of underground structures. These results will be critical in making any final decisions related to the project.”
Stantec and COWI’s Contributions
John Ord, Business Director for Energy at Stantec, highlighted the company’s involvement: “The Stantec team has thoroughly enjoyed working on this stage of the Coire Glas project, delivering award-winning work alongside COWI, STRABAG, and SSE Renewables. We look forward to continuing our support as it moves into the next phase, defining rock quality more than a kilometre inside the mountain. This crucial work will inform the design of the main pumped storage scheme, bringing the project closer to providing a significant boost for the UK’s renewable energy storage.”
COWI’s Perspective
Andy Sloan, Managing Director of COWI in the UK, expressed his satisfaction with reaching this milestone: “At COWI, we’re delighted to have reached the important milestone of completing the tunnelling phase for the exploratory tunnel. The joint Stantec/COWI site team has worked tirelessly with SSE Renewables and STRABAG to reach this point, and collaboration has been excellent. The Stantec/COWI team will now proceed to supervise the underground drilling, which includes complex testing rarely seen in the UK.”
This collaborative effort and the successful completion of the exploratory tunnel mark a significant step forward in the Coire Glas project, potentially setting the stage for a new era of renewable energy storage in the UK.