Sloy Power Station
We're proposing to convert our iconic 1950s hydro station to pumped storage hydro
In April 2025, we submitted a planning application to the Scottish Government to convert the iconic Sloy Power Station into a pumped storage hydro scheme.
Our proposals would bolster energy security and help provide the large-scale and flexible renewable energy back-up needed in a future UK net zero power system, helping meet the UK Government’s ambition of Clean Power by 2030.
If approved for delivery, the converted Sloy scheme would be capable of delivering up to 16GWh of long-duration electricity storage capacity.
It could provide firm, flexible renewable energy for up to 100 hours non-stop.
Sloy is Britain's largest
Sloy Power Station is Britain’s largest conventional hydro power plant and has been in operation since 1950. It currently generates around 130 million units of electricity in a year of average rainfall.
The current scheme makes use of the water of Loch Sloy, which is carried over 3km by a tunnel through Ben Vorlich before travelling down four high pressure steel pipelines to Sloy Power Station (shown below) at Inveruglas Bay on Loch Lomond.
Inside the power station, four Francis turbines drive four vertical shaft generating sets with a combined generating capacity of 152.5MW (shown left).
Pumped Storage Hydro
Pumped storage hydro uses excess electricity during off-peak hours. During this time, it pumps water from a lower reservoir to an upper reservoir. Water is released during peak demand periods. Water flows from the upper reservoir, downhill. As it moves, it passes through turbines to generate electricity.
One of the key advantages of pumped storage hydro is its large-scale storage capacity. This technology has the potential to store massive amounts of energy. This makes it easier to meet high supply demands than other technologies.
Our development proposals
Our proposals include the introduction of new pumps located in the grounds of the existing site, immediately north of the power station at Inveruglas on the banks of Loch Lomond.
The new pumps would enable water to be pumped from Loch Lomond to Loch Sloy through up to three of the existing four high pressure pipelines and tunnels, enabling the scheme to generate for longer periods of time, which would minimise the likelihood of renewable energy from other sources being constrained off the grid during times of low demand.
As part of our planning application, we are also including proposals to upgrade the existing 32.5MW G4 turbine to match its sister units, which would increase the station's generating output by 7.5MW to 160MW.
Subject to a positive consenting outcome, we hope to make a final investment decision on Sloy in late 2027 and to fully adapt and commission the new pumped storage scheme by the end of 2030.
Image : An architectural concept of the completed development
April 2025 - Section 36 Planning Submission
In April 2025, we submitted an application to the Scottish Ministers under Section 36 of the Electricity Act 1989 to convert Sloy into a pumped storage hydro scheme with a proposed pumping capacity of up to 100MW.
The Environmental Impact Assessment Report incorporates a robust assessment of the following environmental aspects: Aquatic Ecology; Terrestrial Ecology; Ornithology; Soils, Geology and the Water Environment; Landscape and Visual Amenity; Traffic and Transport; Noise and Vibration; Cultural Heritage; and Recreation.
Your feedback
We would like to thank everyone who joined us at our public exhibition events at the Three Villages Hall in Arrochar in July and November 2023.
Exhibitions like this are a very important part of the development process for us and we will continue to engage as the project progresses.
If you missed the events, or would like to read more about the proposed project, please download our event brochure here.
Please note that the project timeline has changed since the exhibitions took place in 2023.
Contact us
If you have any questions about our proposals or would like to provide any feedback to the project team, please contact:
Georgina Wardrop
Head of Hydro Stakeholder Engagement