Scotland Approves UK’s Largest-Ever Pumped Hydro Storage Project

In a significant move toward strengthening the UK's energy resilience and decarbonization goals, SSE Renewables has officially lodged a planning application with the Scottish Government to transform the historic Sloy Power Station—Scotland’s largest conventional hydro facility—into a cutting-edge 100MW pumped storage hydro scheme.

Perched beside the serene banks of Loch Lomond, Sloy has quietly powered homes since 1950. Now, SSE envisions a dramatic upgrade that would breathe new life into the facility by unlocking 16 gigawatt-hours (GWh) of long-duration energy storage. In the context of the UK's growing intermittent renewable generation, this capacity could become a strategic national asset—storing excess wind and solar power during periods of low demand and releasing it when the grid needs it most.

The proposed transformation hinges on Section 36 consent submitted directly to Scottish Government ministers. Should the plan be approved, SSE Renewables aims to reach a final investment decision (FID) by late 2027, with full commissioning of the pumped hydro system targeted for 2030.

Unlike conventional hydro systems, pumped storage operates like a vast battery—reversibly pumping water uphill when energy is abundant and releasing it downhill through turbines when supply is tight. This is not just a technical enhancement for a grid rapidly pivoting toward renewables—it’s a strategic leap forward.

In tandem with the overhaul, SSE also plans to upgrade the station’s 32.5MW G4 turbine, aligning its output with its sister units. The improvement would add an extra 7.5MW, bringing the station’s total generation capacity to 160MW—a boost that could play a small but meaningful role in balancing the UK’s evolving energy mix.

Crucially, the project isn’t just about electrons and efficiency. It's also a local economic engine. Up to 70 full-time equivalent jobs could be created during the development and construction, injecting employment and momentum into the region.

Recognizing the social contract embedded in energy infrastructure, SSE Renewables has also pledged to launch a dedicated community benefit fund, complementing its recently unveiled £10 million Hydro Community Fund. The intent is clear: this isn't just a technical upgrade—it's an opportunity to anchor long-term value within the surrounding communities.

First commissioned in the post-war era, Sloy Power Station has long been a symbol of Scottish engineering ambition. With this proposed conversion, it stands poised to become a cornerstone of a new era—one defined not by coal and carbon but by flexibility, storage, and sustainability.

Robert Bryce, Director of Hydro – SSE Renewables, said: “The proposed pumped storage hydro scheme will play an important role in the UK Government’s Clean Power by 2030 ambitions, providing firm, flexible renewable energy for up to 100 hours non-stop at the flick of a switch.

“The existing Sloy Power Station has been operational since 1950 and, over the past seven decades, has played a significant role in our energy system.

“The new proposals will ensure this remains an important asset for decades to come.

“If consented, the scheme will provide an economic and employment boost to the local area and help provide balance to our increasingly renewables-led grid during times of peak demand.

“This latest proposal, alongside our other investments in the technology, are a further example of the importance of hydro as a key part of a homegrown UK energy system.”