PLANS to convert the UK’s largest conventional hydro power plant – on the banks of Loch Lomond – into a renewables project have been announced.

SSE Renewables will seek permission to convert its Sloy power station and dam into a pumped-hydro storage scheme, which would store power generated at times of renewable excess for later use.

Finlay McCutcheon, the director of onshore Europe at SSE Renewables, said that the announcement meant it was “crucial” for the UK Government to step up and outline how it plans to help facilitate the deployment of such projects.

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First Minister Humza Yousaf, who visited the Sloy hydro plant on Monday, also renewed his call on the UK Government to take action. Yousaf had written to Prime Minister Rishi Sunak about the same issue over the weekend.

Loch Sloy is around three miles from the power station on the shores of Loch Lomond. The smaller loch is at an elevation around 277 metres higher than its larger cousin, making it an ideal location for pumped-storage hydro.

The technology works by moving water from low elevations up to higher ones during times of surplus, such as when the wind is blowing strongly and demand is low.

Later, when supply is low due to the variable nature of wind power, for example, the water can be allowed to flow back downwards, turning a turbine and generating power as it goes.

SSE Renewables said that a pumped-hydro facility at Sloy could “provide firm, flexible renewable energy for up to 160 hours non-stop, enough to power 90,000 homes for one week”.

As it stands, UK bill payers see hundreds of millions of pounds added onto energy costs because of the fees that have to be paid to wind farms to shut down.

If the excess energy could instead be generated and stored in technologies such as pumped-storage hydro, those fees – which totalled £807 million across 2020 and 2021 – could drop.

SSE Renewables director McCutcheon said: “We're delighted to announce new redevelopment plans for our landmark Sloy power station.

“In converting our existing Sloy conventional hydro power plant to a pumped-hydro storage facility, we can provide the additional large-scale, long-duration electricity storage we need as part of the country's future energy mix.

“With up to 25GWh of storage capacity, the scheme would be capable of powering 90,000 homes for an entire week, so bolstering our energy security and providing the balancing flexibility we need in a renewables-led energy system.

“The development of pumping capability at Sloy also complements our development plans for our other pumped hydro storage project at Coire Glas. Taken together and if approved for delivery, Coire Glas and Sloy can treble Britain’s current flexible electricity storage capacity.

“That’s why it’s crucial the UK Government urgently confirms its intention on exactly how they will help facilitate the deployment of pumped hydro storage projects as part of our future energy mix.”

SSE’s planned £1.5 billion Coire Glas scheme would sit between Fort William and Inverness.

It was one of six projects highlighted in a report commissioned by Scottish Renewables as having the potential to more than double the UK’s pumped storage hydro capacity to 7.7GW.

The BiGGAR Economics report further said that the six projects had the potential to create almost 15,000 jobs and generate up to £5.8bn for the UK economy by 2035.

SSE said it “awaits the UK Government’s decision on how it intends to support the deployment of long-duration electricity storage as set out in last year’s ‘British Energy Security Strategy’”.

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First Minister Yousaf said: “Scotland has vast natural resources which have helped us to become world leaders in renewable energy. Facilities like the Sloy power station continue to play a significant role in energy supply, providing flexible services to the grid and help to ensure a continued, resilient and secure electricity supply, by helping to balance our intermittent renewable electricity generation.

“Hydro power was the country’s original source of renewable energy and it has the potential to play a significantly greater role in the transition to net zero – both on a small-scale in co-operation with local communities and on a larger scale, to help to ensure a continued resilient and secure electricity supply.

“We continue to call for the UK Government to provide an appropriate market mechanism for hydro power and other long-duration energy storage technologies, to ensure this potential is fully realised.”

SSE Renewables said it will “refine its project design to convert the iconic Sloy plant from conventional hydro power to pumped-hydro storage technology”, and expects to submit a planning application by early 2024.