Summary
Electric Mountain Dynorwig, a pumped storage power station in North Wales, is undergoing a significant £1 billion refurbishment to extend its operational life by at least 25 years. Originally constructed in the 1970s, the facility is now replacing its aging turbines and generators, with the first of six units scheduled to return online by 2028. This upgrade aims to maintain the station's critical role in balancing the UK's energy grid, particularly as the country transitions to renewable energy sources.
The construction of Dynorwig was groundbreaking, involving the excavation of vast caverns and tunnels within the mountain, which required innovative engineering solutions and the removal of millions of cubic meters of rock. The project, completed in 1984, revolutionized the UK's electricity system by enabling rapid response to demand fluctuations and providing essential storage for excess energy, particularly from nuclear power stations. Today, the facility can deliver its full generating capacity of 1,728 megawatts within 16 seconds, a feat that remains unmatched globally.
As the refurbishment progresses, engineers reflect on the original construction's challenges and successes, including the development of new standards for rock reinforcement and concrete design. The project not only created local jobs but also transformed the region's economy after the closure of nearby slate quarries. The ongoing upgrades are set to ensure that Electric Mountain continues to play a vital role in the UK's energy landscape for decades to come.
Show Notes
In late 1973 the UK’s Central Electricity Generating Board gained parliamentary approval to build the largest and most difficult pumped storage hydroelectric power station in its history. It was the largest civil engineering contract ever awarded by the government and became the biggest construction project in Europe. Engineering teams had to burrow 750m deep into the Cambrian slate of Elidir Fawr mountain at Dinorwig, North Wales to create the underground power station and a 16km labyrinth of tunnels up to 10.5m in diameter linking upper and lower reservoirs.
It’s scale and complexity pushed the limits of design and construction with engineers developing state of the art practices for rock reinforcement and concrete design and pioneering new construction methods. As the station celebrates 40 years of operation and looks ahead to a bright future as a battery for renewable energy, we speak with the people that planned, designed and constructed electric mountain hearing stories that have never been told before.
Guests
Kin Almond, supervising civil engineer, James Williamson & Partners
John Armstrong, station manager Dinorwig and Ffestiniog, First Hydro
James Arthur – senior engineer, James Williamson & Partners
John Cowie – associate, James Williamson & Partners
Chris Roberts, commissioning engineer, Central Electricity Generating Board (CEGB)
Dyfrig Roberts – assistant engineer, James Williamson & Partners
Robin Thomas – civil engineering technician, James Williamson & Partners
Ian Waite – project surveyor, James Williamson & Partners
Musical recording of “Tydi a Roddaist” used with the permission of the Caernarfon male voice choir who performed in the excavated machine hall in 1979.
Partner
Mott MacDonald is a global engineering, management and development consultancy focussed on improving society by considering social outcomes and relentlessly focussing on excellence and digital innovation. James Williamson & Partners became part of Mott MacDonald in 1990.
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