Energy company ENGIE, who are pumping £1billion into Dinorwig and Ffestiniog pumped storage hydro stations, has announced the release of £300m for the next phase of the programme.

ENGIE is in a joint venture with La Caisse, and have approved the investment for the next stage of the programme.

This will enable the first two units at Dinorwig to be replanted in a c.£300 million project, with units expected to reach commercial operation in 2028 and 2029. During this period, the remaining four units in Dinorwig will remain fully operational.

Located around 500 metres beneath the mountain, the works will see major components replaced in Dinorwig, including turbine and generator shafts of around 160 tonnes and generator motor rotors of up to 460 tonnes. The cavern itself is large enough to house St Paul’s Cathedral, and the station can generate up to 1,800MW of power, enough to supply around 1.5 million homes at peak output.

This investment will support a highly skilled workforce in north Wales, with peak construction activity expected to involve more than 250 people. The project will draw on local expertise alongside national and international supply chains, creating opportunities for Welsh businesses and workers.

The announcement follows the company’s recent agreement to acquire UK Power Networks, one of the UK’s largest electricity distribution companies, a 6,500 strong, best-in-class, organisation serving 8.5 million customers across London, the South East and East of England. The deal, expected to complete by mid-2026, is widely seen as transformational in scale and strategic importance.

Miya Paolucci, UK CEO of ENGIE, said: “Wales plays a central role in ENGIE’s UK strategy. Reaching financial close on this latest tranche of our pumped hydro investment demonstrates our long-term confidence in these vital assets and in the role flexible storage will play in delivering a secure, low carbon power system.”