According to the British Hydropower Association (BHA), although the UK hasn’t witnessed new pumped storage capacity for over 40 years, there are now 11 schemes at various stages of development across Scotland and Wales, with a combined 10GW and 200GWh of storage capacity.
To help focus industry discussion on the future potential for this technology, in February the BHA met with developers, contractors and leaders in Scottish education and infrastructure, to highlight the opportunities and challenges that lie ahead.
Mike Seaton from SSE Renewables gave an update on a project his company has been working on – the 1.4GW and 30GWh, £2 billion Coire Glas scheme. Planning consent was given in 2020 and a 1km exploratory tunnel has already been dug. With the final investment decision expected in 2026, the scheme could be generating power by 2033.
Michael Matheson, a Member of the Scottish Parliament from the Falkirk West constituency, hosted this meeting about the future of Sottish hydropower. Admitting that the road ahead was going to be a long one to travel, he said: “Working alongside the British Hydropower Association, it is my ambition that frank and open engagement can take place between industry, developers, and communities to ensure that Scotland maximises it’s PSH potential while delivering real improvements for communities and driving towards a sustainable economy and energy mix.”
Scottish pumped storage experience
Travelling down this same road, Glen Earrach Energy (GEE) is awaiting approval for its 2GW Fearna pumped storage hydropower project near Loch Ness. If given, it would be one of the UK’s largest energy storage projects, delivering £20 million annually to Highland communities over a 125-year lifespan.
GEE says its proposal would account for nearly three-quarters of the planned pumped storage capacity for Loch Ness (34GWh of 46GWh) and two-thirds of the area’s generating capacity – using only half the water. The site’s natural topography and 500m elevation drop are key to its efficiency and the company claims the project could reduce the UK grid’s carbon footprint by 10%, delivering £2.9 billion in Net System Benefits over its first 20 years.
This 50:50 development joint venture project between SSE and Gilkes Energy is located at the western end of Glengarry and adjoins SSE Renewables’ existing Loch Quoich reservoir in the Great Glen hydro scheme.
Fearna PSH has a proposed installed capacity of 1.8GW with a capacity of up to 36GWh, providing 20hours of storage. Plans for the project envisage the development of tunnels and a new power station connecting SSE Renewables’ existing reservoir at Loch Quoich with an upper reservoir at Loch Fearna. Under the terms of the joint venture agreement announced in July 2024, Gilkes Energy will lead the project’s development under a developer services agreement with SSE Renewables.
GEE held four rounds of community consultations before entering the formal pre-application phase, and says it will continue to engage with local stakeholders during the planning process. Community feedback led to several changes to the project design, including reduced visual impact, less transport on the A82 road, and a decrease in above-ground infrastructure.
Roderick Macleod, Director of Glen Earrach Energy, said the project “is poised to become one of the UK’s largest and most advanced energy storage initiatives”. Richard Whitehead, AECOM Chief Executive for Europe and India, added: “The scale of Glen Earrach has the potential to meaningfully contribute to Scotland’s net zero ambitions, and those of the UK as a whole, while also delivering benefits to both the environment and local communities.”
In March this year, it was announced that the Earba Storage Project, a proposed pumped storage hydro (PSH) scheme with an installed capacity of 1800MW and a storage capacity of 40,000MWh, has received planning consent from the Energy Consents Unit of the Scottish Government. This makes it the largest PSH project ever approved in the UK.
Carl Crompton, Managing Director of Gilkes Energy, confirmed the approval, stating: “We are thrilled to share that our flagship pumped storage hydro project, Earba, has received planning consent from the Energy Consents Unit of the Scottish Government.”
The project is designed to store energy generated from renewable sources, particularly wind power, and release it when demand is high. With 22 hours of storage at full capacity, the facility aims to enhance grid stability as the UK transitions from fossil fuel-based power generation to renewable energy sources.
Planning application for the project was submitted back in March 2024. Known as a ‘Section 36’ Planning Application, it included considerable surveys, analysis, engineering design and consultation all summarized in an Environmental Impact Assessment report.
The need for large-scale energy storage has grown as the country moves toward net-zero emissions. Storage projects like Earba help integrate renewable energy into the grid by storing excess electricity and minimizing reliance on gas generation. Crompton emphasized the project’s benefits, stating that it would “support decarbonisation, strengthen energy security, and lower costs for consumers.”
Gilkes Energy is also working with the UK Government and Ofgem to implement the Long Duration Energy Storage (LDES) ‘Cap & Floor’ mechanism in 2025. This policy is expected to facilitate investment in PSH projects by addressing financial risks. Crompton noted that the mechanism has already attracted private investment for interconnectors and is expected to do the same for pumped storage.
With planning approval secured, Gilkes Energy will now focus on finalizing project design, securing investment, and preparing for construction.
Upgrading Sloy
Back in April, SSE Renewables submitted a Section 36 planning application to the Scottish Government to convert the existing Sloy Power Station near Loch Lomond into a pumped storage hydro scheme. The proposal would see the station, which has operated since 1950, adapted to include a pumping capacity of up to 100MW, allowing it to deliver up to 16GWh of long-duration electricity storage. If approved, SSE plans to reach a final investment decision by late 2027, with the conversion completed and operational by the end of 2030.
The project would involve installing new pumps at the Inveruglas site, enabling water to be pumped from Loch Lomond to Loch Sloy during low electricity demand periods. This stored water would then be released to generate electricity when demand is higher. The application also includes a proposal to upgrade the station’s existing 32.5MW G4 turbine, which would raise the plant’s total generating capacity from 152.5MW to 160MW.
According to SSE, the development phase could support up to 70 full-time equivalent jobs and contribute to the local economy. A dedicated community benefit fund would also be created, adding to the recently launched £10 million Hydro Community Fund.
Robert Bryce, Director of Hydro at 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.”
Sloy Power Station is currently the UK’s largest conventional hydroelectric plant, producing approximately 130 million kilowatt hours of electricity per year in average rainfall conditions. The plant uses water carried from Loch Sloy through a tunnel and steel pipelines to power four Francis turbines.
The environmental impact of the project is addressed in a report covering areas such as ecology, water, noise, heritage, and transport, which is available on the SSE Renewables website.
Digging deep at Coire Glas
Located on the banks of Loch Lochy, near Inverness in Scotland, Coire Glas will be the first hydro storage project of its size to be constructed in the UK since Dinorwig Power Station in the 1980s.
Conwy-based provider of borehole geophysical and petrophysical logging technologies and services -Robertson Geo – was contracted by Strabag UK Ltd to collect a comprehensive set of geotechnical statistics for the development.
Driven by energy firm SSE Renewables, the site will have a potential capacity of up to 1300MW, generating enough power for up to three million homes in a matter of minutes.
Robertson GEO Managing Director Simon Garantini said the business – which also has locations in the US and Hong Kong – deployed a suite of geophysical probes in an exploratory tunnel more than one kilometre long and 700m below ground level.
A “challenging” task, he revealed the operation required equipment and new techniques they had never used before, including a 2,000m winch enclosed in a safety cage
“The exploratory work being undertaken for Coire Glas is among the most extensive ground investigations of its time, collecting and analysing a huge volume of geotechnical data before construction begins,” said Garantini. “The comprehensive scope of the ground investigation is not least required due to the site’s proximity to the Great Glen fault line, which is visible from outer space.
“The geotechnical data will observe ground conditions to inform on the potential risks and challenges posed to a successful delivery of the project, so this was a hugely important task, pivotal to them moving forward.”
The tunnel included three “galleries” from which a series of long, near horizontal and angled boreholes were drilled, and a series of short “televiewer” boreholes for imaging, deformability and stress testing.
Work continued 24/7 with two teams of two engineers alternating on back-to-back 12-hour shifts.
“Logistics underground could be difficult with equipment needing to be moved around underground whilst many other tasks were occurring simultaneously,” said Garantini. “The most challenging aspect of the logging operation was the development and deployment of a ‘push’ system to place logging tools in horizontal boreholes.
“Our team has considerable experience in using them on horizontal boreholes up to about 40m in length. However, these were up to around 280m so the magnitude of the task could not be underestimated.”
He added: “There were other challenges – notably in designing a push system for the raised boreholes up to 22m in length – but a manual arrangement using customised tubular push rods was engineered, which worked successfully.
“The work environment was noisy at times with the inevitable dripping water on sensitive equipment such as laptops, though together we resolved all these issues.
“The geophysical logging campaign we undertook formed a vital component of the overall ground investigation, providing high-quality calibrated data, not attainable by other means, at centimetre resolution in the boreholes.”
New ways to use water
As discussions at a recent webinar hosted by the International Hydropower Association highlighted, other technologies need to be able to step up to provide deep storage in locations where conventional pumped storage is unable to.
Gavin O’Leary is the Head of Electricity Storage Policy at the Department for Energy Security and Net Zero (DESNZ). Explaining that although the UK has 2.8GW of Long Duration Energy Storage (LDES) capacity installed in the form traditional pumped storage across four sites, he said: “We have not found the right model in a privatised electricity grid to incentivise development of storage.” And that’s why the country has gone over four decades without adding to its stockpile of long duration storage.
Admitting that although pumped hydro is established and “we know it works and is efficient”, O’Leary says the problem is “it takes a long time to build”.
“Construction is expensive and uncertain, and is something investors have not been willing to finance on a purely merchant basis so far,” he added.
Although alternatives to pumped hydro “might be quicker to build in principle and might be as, or even more, efficient and have other advantages”, O’Leary says it’s just not deployed in the same gigawatt scale anywhere. So as it’s uncertain you’re taking a leap into the unknown, and this means risk. And if you have risk, he added, risk means LDES is not being built and that’s a problem. The need for long duration flexibility is high and rising.
The UK government’s Clean Power 2030 Action Plan sets out what needs to be done to achieve its goal of eliminating reliance on fossil fuel burning in the power grid by 2030.This means aiming for 4-6GW of long duration storage by end of the decade, and looking at 11-15GW by 2050. And these were, according to O’Leary, “really some quite substantial numbers we need to get to”.
“Given our historical dependence on pumped hydro which has many virtues but has long build times and geographical immobility, we are always interested in things that are quicker to build and can be built in wide variety of places. This will give us, Ofgem and the national energy system operator more tools to build the storage we need, wherever it’s needed,” he added.
Scalable solution
Stephen Crosher is the CEO of RheEnergise, a company that is developing High-Density Hydro. Based on traditional pumped hydro storage, it claims to be solving the challenges the technology faces, such as lack of sites, environmental and social issues around flooding valleys, water abstraction, the time taken to consent and construct, plus distances from generation or demand.
RheEnergise’s solution is a form of gravitational energy storage that pumps proprietary fluid uphill. And with the LDES market predicted to be US$4billion by 2040, with rapid scaling and exponential growth, Crosher says there is a “huge demand for solutions to solve the problems”.
With capacities ranging from 10-500MW, RheEnergise says it has a pipeline of projects in over 25 countries, with MOUs with utilities and developers. High Density Hydro, the company believes, is a scalable pumped storage solution for the future. And as it doesn’t need to abstract water in the same way as conventional schemes, it can be built in arid locations such as Texas where the demand for electrical power is set to grow by 50% in next five or so years. Such markets, Crosher says, will be a huge opportunity for them especially when the impacts of climate change and declining rainfall are taken into consideration.
Although they’re “looking for small hills and not mountains” for prospective project sites, Crosher admits that elevation can be a prohibiting factor. Consequently in the UK, flatter areas such as East Anglia, along with other countries such as The Netherlands, won’t provide favourable conditions. However a small hill or mine or mine shaft will suffice. In fact, he said the company is currently assessing a 280m mine shaft in Wales.
In the pipeline
The BHA recently gave a roundup of the UK’s pumped storage projects in the pipeline. Across Scotland these include:
- The 1.5GW, 45GWh Balliemeanoch in Argyll & Bute which is being developed by the ILI Group & AECOM. When fully operational it will have 30 hours of storage, feature a 110m high dam and a 2.8km, 9m wide headrace tunnel, a large catchment area and an upper reservoir storing 58Mm3 of water at a hydraulic head of 385m. The tail race will be into Loch Awe which is also used for the Cruachan project.
- Cruachan Expansion in Argyll and Bute will have a capacity of 0.6GW and 8.6GWh. Under development by Drax, the expansion encompasses the development of a new powerhouse, transformer cavern and tailrace tunnel adjacent to the existing power station to provide a further 600MW of generating capacity.
- Glenmuckloch in Kirkconnel, Dumfries & Galloway will have a capacity of 0.2GW and 1.6GWh, and is being developed by the Foresight Group. The site is on a partially restored open cast coal mine which forms the lower reservoir with 200m of head. As the scheme is near several operational wind turbines with more in development, it makes an ideal site to provide grid balancing and energy storage.
- Loch Kemp Storage in Whitebridge has a capacity of 0.6GW and 9GWh. Near Fort Augustus in the Scottish Highlands it is being developed by Statera Energy and is one of three proposed projects to use Loch Ness as the lower reservoir. The project plan is to generate for 15 hours at 600MW, with a total storage capacity of approximately 9GWh. The scheme involves four new saddle dams and four minor cut-off dams of 16-34m high around Loch Kemp to raise the current water level, enabling an upper reservoir of 21Mm3.
- Loch na Cathrach in Dores will have a capacity of 0.45GW and 4GWh and is under development by Statkraft. Formerly known as Red John, the scheme was approved by the Scottish Government in June 2021, and utilises Loch Ness as the lower reservoir and a newly constructed upper reservoir at 250m of head near Loch Duntelchaig. The system will employ three reversible pump turbines housed in an underground powerhouse, facilitating energy storage and generation.
And then over in Wales there’s the Moel Tryfan project in Gwynedd where Caernarvonshire Crown Slate Quarries is developing this 0.1GW, 0.6GWh scheme from twin quarries. The site would use Alexandra Quarry as the upper reservoir with a capacity of 1.2 million m3, with a hydraulic head of 250m and a headrace tunnel of around 1.3km. The scheme is rated at 100MW for ease of planning but could be marginally increased to better meet regional energy storage needs
Plus in Llanberis there’s the 0.1GW, 0.8GWh Glyn Rhonwy scheme which is under development by the Quarry Battery Company. Also known as Snowdonia Pumped Hydro, this 100MW project plans to form a new 1.3Mm3 reservoir in a former slate quarry. Planning consent, grid connection and an abstraction licence were achieved in 2017. A main investor has been secured but the project awaits the progression of the government’s cap and floor mechanism.
For more details see: https://british-hydro.org/pumped-storage-hydropower/
