Extending the life of Europe’s largest pumped storage hydro scheme

Dinorwig Refurbishment and Modernisation

Hidden deep within the mountains of Eryri National Park, Dinorwig quietly performs as one of the UK’s most critical pieces of energy infrastructure. Europe’s largest pumped storage scheme, Dinorwig is capable of delivering nearly 1.8 gigawatts of power in seconds, playing a vital role in balancing the UK’s electricity grid.

After more than four decades of operation, owner Engie is investing up to £1 billion in a 10-year, major refurbishment programme to modernise the station while reducing outage time. We are supporting Engie as part of an integrated delivery team, providing multidisciplinary engineering and advisory services across the programme. Our role spans civil, mechanical, and electrical engineering, alongside technical review, contractor interface management, and project-wide management and coordination.

A key part of our work has been developing the strategy for dewatering and refilling the station’s waterway system, enabling the first full outage since commissioning in 1984. With an operating flow of up to 60 tonnes of water a second passing through deep shafts, high-pressure tunnels and turbines, dewatering required careful planning and assessment to manage the risks. The phase of work was successfully completed in 2025.

Our role also includes supporting digital delivery, helping to establish collaborative digital environments to manage information and design reviews.

Through project and technical roles embedded within the client team, we’ve supported replacement of the main inlet valves, and continue to support multi-stage mechanical and electrical replant programme extending to 2035—while keeping generation online. This includes coordination across multiple contractors and interfaces, applying structured programme management, risk management, and governance processes to keep the effort on track.

The refurbishment will extend the life of critical components, including turbines, generators, and associated systems, allowing the station to continue to respond rapidly to fluctuations in supply and demand.