Milestone for SSE’s Coire Glas as exploratory tunnel now complete
The completion of the 1.2km tunnel marks a new milestone for the Coire Glas project which would provide 30GWh of long duration storage for the UK if constructed
Exploratory tunnelling at the site of what would be the UK’s first large-scale pumped storage scheme to be developed in 40 years is now complete. The completion of a 1.2km long exploratory tunnel is the latest milestone in SSE’s ongoing development of its landmark Coire Glas project in the Scottish Highlands.
Located at Loch Lochy in the Great Glen, the proposed Coire Glas project would have an installed capacity of 1,300MW and be capable of delivering 30GWh of long duration electricity storage – enough to be able to provide firm, flexible renewable power for three million British homes for up to 24 hours non-stop.
SSE Renewables hopes to make a final investment decision on the project in late 2025 or early 2026, allowing for main construction to commence in the second half of 2026, subject to being successful in the administrative allocation of an investable cap and floor mechanism.
Exploratory works at Coire Glas commenced in December 2022 and are being conducted by STRABAG UK, a world leader in mining and tunnelling projects.
In early 2023, SSE announced a £100-million investment boost to further develop Coire Glas to include the construction of a major exploratory tunnel as part of a comprehensive package of site investigation works.
SSE’s technical partners, Stantec and COWI, have designed and supervised the unique and complex ground investigation programme which is being delivered by STRABAG.
The works included the creation of a tunnel approximately five metres high and four and a half metres wide which cuts into the hillside around the proposed location of the underground powerhouse complex. Construction of the tunnel will allow the project team to gather accurate information on the geological conditions to inform the detailed design for the main works.
Now that tunnel construction is complete, a programme of exploratory drilling and testing will continue for the next three months to further investigate the ground in the area of the proposed underground powerhouse excavations.
“Completing the tunnelling is testament to the hard work and dedication of everyone involved and a positive step forward in de-risking the project.
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.”
“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 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.”
“At COWI we’re delighted to have reached the important milestone of the end of the tunnelling phase for the exploratory tunnel.
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.”
Once complete, Coire Glas would provide 30GWh of long duration electricity storage. The scheme would take excess energy from the grid and use it to pump water 500 meters uphill from Loch Lochy to an upper reservoir created by the construction of a 90m high dam. The vast reservoir could store enough water equivalent to nearly 11,000 Olympic-sized swimming pools. At the flick of a switch this water could be released to power the grid when required including at times when wind power output is low and customer demand is high.
Subject to being successful in the administrative allocation of an investable cap and floor mechanism for UK long-duration electricity storage projects, SSE Renewables hopes to make a final investment decision on Coire Glas (1,300MW) in late 2025 or early 2026, allowing for main construction to commence in the second half of 2026. Construction is expected to last up to seven years, which means the project could be operating in 2032 and fully completed during 2033.
The delivery of Coire Glas is at the heart of SSE’s Net Zero Acceleration Programme Plus, or NZAP Plus, which commits to investing around £10m a day on average on critical low-carbon infrastructure needed in the net zero transition.