SSE will invest £100m in the UK’s first pumped hydro storage scheme in 40 years in a bid to support the UK’s renewable energy transition.

The project will take excess energy from the grid and use it to pump water 500m up a hill from Loch Lochy in the Scottish Highlands to a vast upper reservoir equivalent to nearly 11,000 Olympic-sized swimming pools.

The energy would be stored before being released to power the grid when wind output is low and customer demand is high.

Coire Glas could power three million homes and more than double the UK’s electricity storage capacity, with SSE arguing it could provide flexible power for up to 24 hours non-stop.

The project received planning consent from the Scottish Government in 2020, and is expected to require a capital investment of over £1.5bn to construct.

SSE hopes to make a final investment decision on Coire Glas in 2024, which is subject to development progress and the policy environment, with the aim to fully construct the pumped storage project by 2031.

The project could benefit an increasingly renewables-led system and bolster the UK’s energy security.

Once complete, Coire Glas would be capable of delivering 30GWh of long duration storage and would begin generating enough renewable energy to be able to power three million homes in just under five minutes.

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.

This includes site investigation works which have now commenced and will complete later this year, involving 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 Scottish government’s net zero and energy secretary Michael Matheson urged Downing Street to help stabilise the investment climate to help develop renewable energy.

He said: “If built, Coire Glas will more than double Britain’s long duration electricity storage capacity – allowing the grid to more flexibly deploy renewable electricity.

“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 finance director Gregor Alexander said: “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.”