Located on the shores of Loch Lochy, between Fort William and Inverness, the Coire Glas project is expected to require a capital investment of over £1.5 billion to construct and, if approved for final delivery, would be the first pumped hydro storage scheme to be built in the UK in 40 years.

The project, which received planning consent from the Scottish Government in 2020, would also more than double Britain’s total current electricity storage capacity – providing vital backup to an increasingly renewables-led system and bolstering energy security. SSE hopes to make a final investment decision on Coire Glas in 2024, subject to positive development progress and the prevailing policy environment, and to fully construct and commission the pumped storage scheme by 2031.

Once complete, Coire Glas would be capable of delivering 30GWh of long duration storage. The scheme would take excess energy from the grid and use it to pump water 500 meters up a hill from Loch Lochy to a vast upper reservoir equivalent to nearly 11,000 Olympic-sized swimming pools where it would be stored before being released to power the grid when wind output is low and customer demand is high.

At the flick of a switch, Coire Glas would begin generating enough renewable energy to be able to power three million homes in just under five minutes. Critically, the Coire Glas project could provide this level of firm, flexible power for up to 24 hours non-stop.

SSE’s £100m commitment to further developing Coire Glas comes as the leading low carbon energy infrastructure company awaits the UK Government’s decision on how it intends to financially support the deployment of long-duration electricity storage, as set out in last year’s British Energy Security Strategy.

This could include the introduction by the UK Government of a ‘revenue stabilisation mechanism’ in the form of an adapted Cap and Floor scheme to support investment in long-duration storage. This would also be alongside broader consideration of how the electricity market, including the Capacity Mechanism and the Flexibility Markets, value the contribution of low carbon flexible assets such as pumped storage.

Coire Glas is expected to be one of the biggest engineering projects in the Scottish Highlands since the 1943 Hydro Electric Development (Scotland) Act kickstarted the construction of major hydro-electric schemes across Scotland 80 years ago. At peak delivery, the project would create up to 500 full time construction roles.

During a visit to SSE’s Pitlochry Dam and Hydro Station, net zero and energy secretary Michael Matheson said: “Today’s announcement is a significant and important milestone on the journey towards delivering the Coire Glas project. If built, Coire Glas will more than double Britain’s long duration electricity storage capacity – allowing the grid to more flexibly deploy renewable electricity. The Scottish Government has long been supportive of pumped hydro storage capacity, which we believe will play a key role in the energy transition and is a vital component of a more flexible, resilient and secure electricity supply.

“However it is critical that the UK Government puts in place the appropriate market and regulatory arrangements to support the industry’s development as a matter of urgency. Only with a supportive policy environment can this sector realise its full potential.”

SSE plc finance director Gregor Alexander said: “Coire Glas will be one of the most ambitious energy infrastructure projects the UK has ever seen and is a key component of SSE’s commitment to helping lead Scotland and the UKs’ energy transition.

“The £100m investment we have announced today will help play a crucial role in further advancing the Coire Glas project towards a final investment decision in 2024, which will enable the project to move towards construction. If delivered around the turn of the decade, Coire Glas could play a crucial role in getting the UK to net zero.

“Our investment commitment today also signals a significant down-payment by SSE to keep this critical project moving forwards. And our ability to reach a positive final investment decision will clearly depend on the prevailing policy environment for long duration electricity storage and long-term infrastructure projects more broadly.

“Whilst Coire Glas doesn’t need subsidy, it does require more certainty around its revenues and it is critically important the UK Government urgently confirms its intention on exactly how they will help facilitate the deployment of such projects.”

The next phase of detailed project design and refinement, construction planning and procurement will progress through 2023 and into early 2024. Around half of the £100m development investment will now be allocated to the pre-construction refinement phase of the Coire Glas project, including a comprehensive package of site investigation works which have now commenced and will complete later this year.

These include the construction of a major exploratory tunnel to enable the project team to fully assess the geological conditions that will be encountered in constructing the scheme.

The delivery of Coire Glas is at the heart of SSE’s Net Zero Acceleration Programme, or NZAP, which commits to investing around £7m a day on critical low-carbon infrastructure needed in the net zero transition.