National Grid has switched on the second of three new high voltage electricity circuits connecting the Dinorwig hydroelectric power station with the transmission network in North Wales, marking another major step in future-proofing a vital part of Britain’s grid.

It follows the energisation of the first new circuit in January 2025, and forms part of National Grid’s wider project to replace infrastructure originally installed in the 1970s between Dinorwig and Pentir substation.

Dinorwig pumped storage station is situated in Elidir Fawr mountain in Gwynedd, and provides fast-response power generation to help stabilise the transmission network. It is owned and operated by First Hydro, a company 75% owned by ENGIE.

Since autumn 2021, National Grid and delivery partners, Morgan Sindall, Infrastructure, and Siemens Energy have been upgrading the connection with the transmission network to ensure clean electricity from the power station continues to flow reliably for decades to come.

Work is also progressing on reinforcements at Dinorwig substation, which is housed within the mountain alongside the pumped storage station, connecting its output into the grid via the new circuits.

The upgraded substation features a new hybrid solution comprising SF6 and ‘clean air’ gas insulated switchgear (GIS) technology, contributing to National Grid’s efforts to cut emissions of the greenhouse gas SF6 from its network by 50% by 2030.

With the second circuit now in service, focus turns to completing the remaining new circuit and continuing work at Pentir and Dinorwig substations to further reinforce the network in the region.

Mark Brindley, Construction Director at National Grid, said: “Switching on the second new circuit is a major step forward for this project. We’re strengthening a vital clean energy link in North Wales and ensuring Dinorwig can continue to power homes, businesses and communities for years to come. We’re immensely grateful for the continued patience and understanding of local communities as we push ahead with the final phase of this complex once-in-a-generation project.”

Peter Kirk, Managing Director – Energy at Morgan Sindall Infrastructure, added: “We’re proud to be delivering this important work in North Wales, helping to bring cleaner energy onto the UK national grid and strengthen the resilience of the network. Energising the second circuit is the latest success story of strong collaboration, as we apply an innovative approach to upgrading existing circuits and boosting capacity between the Dinorwig and Pentir substations in a challenging environment.”

Delphine Cherel-Sparham, Managing Director of ENGIE Hydro UK, concluded: “It is fantastic to see the second circuit energised – another important step for Dinorwig’s future and enhanced reliability. As owner and operator, ENGIE is investing to extend the life of the station and is proud to be working with partners supporting its delivery; strengthening the flow of clean, flexible power from Wales to homes across the UK.”