SSE has completed a 1.2km exploratory tunnel at the proposed Coire Glas pumped storage scheme in the Scottish Highlands, marking a significant milestone for the project. If fully developed, Coire Glas would be the UK’s first large-scale pumped storage facility in 40 years, with a capacity of 1,300MW and the ability to store 30GWh of electricity, enough to power three million homes for 24 hours.
The project, located at Loch Lochy in the Great Glen, aims to provide long-duration storage for renewable energy. SSE Renewables plans to make a final investment decision by late 2025 or early 2026, with main construction potentially starting in the second half of 2026, depending on the approval of an investable cap and floor mechanism.
The exploratory work, started in December 2022, has been led by STRABAG UK, with Stantec and COWI designing and supervising the ground investigations. The tunnel, which is about five meters high and four and a half meters wide, will help the project team gather detailed geological information necessary for the main construction.
With the tunnel now complete, further exploratory drilling and testing will continue for the next three months to assess the ground conditions for the underground powerhouse.
“Completing the tunnelling is testament to the hard work and dedication of everyone involved and a positive step forward in de-risking the project,” said Mike Seaton, SSE Renewables Director of Development for Coire Glas. “The works progressed to plan, and samples of the materials excavated from within the hillside are currently being analysed.
“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.”
John Ord, Business Director of Energy at Stantec, added: “he 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 important work will inform the design of the main pumped storage scheme, moving the project closer to offering a huge boost for the UK’s renewable energy storage.”
Andy Sloan, Managing Director of COWI in the UK, emphasized the importance of the achievement, noting, “The joint Stantec/COWI site team have worked tirelessly with SSE Renewables and STRABAG to reach this point. and collaboration has been excellent. The Stantec/COWI team will now move on to supervise the underground drilling, which includes complex testing rarely seen in the UK.”
