SSE is marking 75 years of operation at Sloy Power Station, Scotland’s largest conventional hydroelectric plant and one of the UK’s most significant renewable energy sites.
Opened on 18 October 1950 by Queen Elizabeth, the station has supplied renewable electricity to the national grid for three-quarters of a century. With an installed capacity of 152.5MW, Sloy generates around 130,000MWh of electricity annually – enough to power about 48,000 homes. The station can reach full capacity in under five minutes, providing valuable flexibility to the grid during periods of high demand.
Built between 1945 and 1950 under the Hydro Electric Development (Scotland) Act 1943, the project was a major post-war engineering effort. Water from Loch Sloy travels through a 3km tunnel beneath Ben Vorlich before descending four steel pipelines to the generating hall at Inveruglas Bay on Loch Lomond.
Robert Bryce, SSE Renewables Director of Hydro, said the anniversary recognises the station’s importance to Scotland’s energy history. “Sloy Power Station is a remarkable achievement of Scottish engineering. It has provided fast, flexible and reliable renewable power for 75 years and continues to play a vital role in supporting the UK’s move toward a net zero energy system,” he said.
Gillian O’Reilly, SSE’s Head of Heritage, said the milestone also honours the workforce behind the station. “For 75 years, Sloy has been maintained by generations of skilled engineers and operators. Their work has kept it running efficiently and ensured it continues to deliver clean, reliable power for communities across Scotland,” she said.
Construction of the station was completed in challenging conditions, with only 21 dry days recorded during the four-year build. The 357m-long, 56m-high dam raised Loch Sloy by 155ft and required 1,700 blasting operations and 180,000 tons of rock excavation.
Today, Sloy remains the UK’s largest conventional hydroelectric station and continues to play a key role in supporting renewable energy generation and the transition to net zero.
Earlier this year, SSE Renewables submitted a Section 36 planning application to the Scottish Government to convert Sloy into a pumped storage hydro scheme. The proposal would add up to 100MW of pumping capacity and allow the site to store and release energy depending on grid demand, providing up to 1 GWh of long-duration electricity storage.
If approved, SSE aims to reach a final investment decision by late 2027, with the upgraded station operational by the end of 2030. The plans also include an upgrade to the existing 32.5MW G4 turbine, increasing total capacity from 152.5MW to 160MW.
The development phase could support around 70 full-time equivalent jobs and contribute to the local economy, alongside a new community benefit fund linked to SSE’s £10m Hydro Community Fund.
