New Circuit Activated for UK's Biggest Hydropower Station

National Grid PLC said Tuesday it has energized the second of three new high-voltage circuits linking the 1,800-megawatt Dinorwig hydroelectric power station with the transmission network in North Wales.

The first new circuit was switched on in January 2025. The projects are part of the gird operator's broader project to replace infrastructure built in the 1970s between the Dinorwig pumped storage plant in the Elidir Fawr mountain in Gwynedd and the Pentir substation.

"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", National Grid said in a press release.

"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 percent by 2030", National Grid added.

"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.

"As part of these ongoing works, a temporary road closure is in place on the lane between Brynrefail and Fach-wen to ensure the safety of the community and project teams while construction activity in the area continues.

"A diversion via Deiniolen - agreed with Cyngor Gwynedd - is currently signposted, and alternative footpath routes are also signposted on affected parts of the Llyn Padarn circular walk. National Grid is maintaining regular communication with local residents and businesses about the diversions".

Dinorwig's owners, French utility ENGIE SA (operator with a 75 percent stake) and Canadian pension fund manager La Caisse (recently renamed from CDPQ), have committed GBP 1 billion ($1.35 billion) over 10 years to extend the life of the Dinorwig and Ffestiniog plants in North Wales.

Ffestiniog's refurbishment was scheduled for completion last year, according to a statement by ENGIE May 17, 2025. Earlier in 2026 ENGIE and La Caisse reached financial close for a portion of the investment, amounting to around GBP 300 million, to enable the first two of Dinorwig's six units to be replanted in 2028 and 2029.

"During this period, the remaining four units in Dinorwig will remain fully operational", ENGIE said in an online statement March 30.

Dinorwig is Europe's biggest and fastest-acting pumped storage station, capable of reaching full output in 30 seconds, according to ENGIE.

"Wales plays a central role in ENGIE’s UK strategy", said ENGIE chief executive for the UK Miya Paolucci. "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".

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