Strabag UK completed the 1.2km-long tunnel in the Scottish Highlands after beginning exploratory works in December 2022. SSE’s technical partners, Stantec and Cowi, designed and supervised the ground investigation programme.
The works included building a tunnel approximately 5m high x 4.5m wide through the hillside around the proposed location of the underground powerhouse complex. The tunnel will allow the project team to gather accurate information on the geological conditions to inform the detailed design for the main works.
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.
SSE Renewables said the works went to plan, and samples of excavated materials were 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,” said Mike Seaton, SSE Renewables’ director of development for Coire Glas.
Located at Loch Lochy in the Great Glen, the proposed Coire Glas project would have an installed capacity of 1,300MW and provide 30GWh of long duration electricity storage.
The scheme would take excess energy from the grid and use it to pump water 500m uphill from Loch Lochy to an upper reservoir created by the construction of a 90m-high dam. The water could be released to power the grid when required, including 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, 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.
