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SSE unveils redevelopment plans for Sloy hydro-electric Power Station

23 May 2023
  • Scotland First Minister Humza Yousaf welcomes plans to convert conventional hydro plant to new, flexible pumped hydro storage facility
  • If approved for delivery Sloy could provide firm, flexible renewable energy for up to 160 hours non-stop, enough to power 90,000 homes for one week 

SSE Renewables, as part of SSE plc, has unveiled plans to convert its 152.5MW Sloy Power Station, Britain’s largest conventional hydro power plant, into a new pumped hydro storage facility to bolster energy security and help provide the large-scale and flexible renewable energy back-up needed in a future UK net zero power system. 

The announcement was made yesterday during a visit by Scotland’s First Minister Humza Yousaf to SSE’s iconic power station on the shores of Loch Lomond in Argyll and Bute, central Scotland. The visit marks the 80th Anniversary of the 1943 Hydro Electric Development (Scotland) Act, which brought hydro-electric power to the Scottish Glens eight decades years ago.  

Now, 80 years later, SSE Renewables is announcing plans to convert its existing conventional 152.5MW Sloy hydro power station to pumped storage. As Britain transitions to a net zero power system, the development of additional pumped hydro storage projects will be crucial for energy security back-up and for balancing a renewables-led energy system during periods when the wind doesn’t blow and the sun doesn’t shine. 

Subject to final design, the converted Sloy scheme would be capable of delivering up to 25GWh of long-duration electricity storage capacity. At the flick of a switch, the converted Sloy scheme could provide firm, flexible renewable energy for up to 160 hours non-stop, enough to power around 90,000 homes for up to one week. 

SSE’s decision to announce plans for additional new pumped hydro storage capacity at its existing Sloy Power Station comes as the leading low-carbon energy infrastructure company 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’.

Humza Yousaf, First Minister 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."

Humza Yousaf First Minister

The First Minister continued:

"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."

Finlay McCutcheon, Director of Onshore Europe, SSE Renewables said:

"We're delighted to announce new redevelopment plans for our landmark Sloy Power Station, especially as we mark the 80th Anniversary of Hydro Power's contribution to homegrown power supply in Scotland and Britain.

"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 pumped storage plans for Sloy join those for a new pumped hydro storage scheme at Coire Glas between Fort William and Inverness, a potential £1.5bn-plus investment in what could be Britain’s biggest pumped hydro storage scheme in 40 years.

Pumped hydro storage would benefit from certainty as to how they would derive revenues, which is expected to be addressed in the UK Government’s upcoming decision on supports for long-duration electricity storage. 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, effectively without subsidy. This would also be alongside broader consideration of how the electricity market, including the Capacity Market and Flexibility Markets, value the contribution of low-carbon, flexible assets such as pumped storage.

Sloy pumped storage – next steps

Over the coming months SSE Renewables will refine its project design to convert the iconic Sloy plant from conventional hydro power to pumped hydro storage technology ahead of a period of public consultation later this year. Subject to the scoping opinion, it’s expected a planning application could be submitted to the Scottish Government by late 2023 or early 2024.

Subject to a positive consenting outcome and the prevailing policy environment, SSE hopes to make a final investment decision on Sloy in late 2025, and to fully adapt and commission the new pumped storage scheme by 2028.  

If approved for delivery, the project would require investment totalling the high tens of millions of pounds and would contribute to 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. SSE will provide an update on its future investment plans on Wednesday, alongside its full-year results.

Celebrating Scotland’s Hydro at 80

The construction of 54 power stations, 78 dams and over 300km of underground tunnels, beginning 80 years ago, resulted in affordable electricity for Highland communities, transforming the way people lived and worked. Now, eight decades later, SSE Renewables still owns and operates most of these sites, using ‘Scotland’s original source of renewable energy’ to provide cost-effective, low-carbon flexibility to Britain’s energy system.

Today, SSE’s almost 1.5GW of flexible hydro power and pumped storage capacity at sites across Scotland produces over 3TWh of renewable energy annually – enough to typically power over 1 million Scottish and UK homes each year. 

To celebrate Scotland’s landmark Hydro at 80 anniversary, SSE Renewables is planning a series of events and activities throughout the year. This will include the opening of a new Observation Point for visitors to Pitlochry Dam and Power Station, the publication of a biography of Scottish hydro pioneer Sir Edward MacColl, and a curated art exhibit showcasing images from SSE’s earliest hydro schemes.

Find out more about pumped hydro storage.