£300m investment to upgrade ‘Electric Mountain’ approved

A major £300 million upgrade of one of Wales’ most iconic power stations has been approved, as energy firm ENGIE pushes ahead with a wider £1 billion investment programme in north Wales.

The funding will support the next phase of work at the Dinorwig pumped storage power station — known as “Electric Mountain” — near Llanberis, alongside ongoing investment at the nearby Ffestiniog facility.

The project will see two of Dinorwig’s six generating units replaced, with work expected to be completed by 2028 and 2029. The remaining units will continue operating throughout.

Dinorwig, which opened in 1984, is one of the largest and fastest-acting pumped storage hydro plants in Europe, capable of reaching full output within 30 seconds and generating enough electricity to power around 1.5 million homes at peak capacity.

Located around 500 metres beneath the mountain, the station’s vast underground cavern, which is  large enough to house St Paul’s Cathedral, will undergo significant engineering work, including the replacement of turbine shafts weighing around 160 tonnes and generator components of up to 460 tonnes.

The investment is being delivered through First Hydro Company, a joint venture between ENGIE and La Caisse, which operates both Dinorwig and the older Ffestiniog plant, opened in 1964.

ENGIE said the project would support jobs and skills in the region, with more than 250 people expected to be involved at peak construction.

The company said it would draw on local expertise alongside wider UK and international supply chains, creating opportunities for Welsh businesses.

Miya Paolucci, UK chief executive of ENGIE, said the investment reflected the company’s long-term commitment to Wales.

“Wales plays a central role in ENGIE’s UK strategy,” she said.

“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.”

Pumped storage facilities such as Dinorwig play a key role in balancing the electricity grid by storing energy and releasing it quickly at times of peak demand.

Water is released from an upper reservoir through high-pressure tunnels to generate electricity, before being pumped back uphill when demand is lower.

The new investment forms part of a broader £1 billion programme to modernise the two north Wales sites.

Around £250 million has already been invested since 2017, including upgrades at Ffestiniog and preparatory work at Dinorwig.

The plants together account for around 2.1 gigawatts of installed capacity — representing a significant share of the UK’s electricity storage capability.

ENGIE is also seeking to strengthen its presence in the UK energy sector more widely.

Universities

Earlier this year, the company announced plans to acquire UK Power Networks, one of the country’s largest electricity distribution operators, in a deal expected to complete by mid-2026.

Alongside infrastructure investment, the company said it is working with universities in north Wales, including Bangor and Wrexham, to support skills development and future careers in the energy sector.

This includes recruiting new apprentices and graduates, as well as engaging with students through careers events.

The Dinorwig facility has been a prominent feature of the local economy for decades, with the operator also supporting community initiatives and education programmes in the surrounding area.

The latest investment is expected to extend the lifespan of the site and reinforce its role in supporting the UK’s transition to low-carbon energy.