Investing in future flexibility and clean power

ENGIE’s £1 billion investment programme is already underway and will keep Dinorwig and Ffestiniog in operation for at least another 25 years. These flexible generation assets, based in North Wales, are reaching end of life and the investment will ensure clean energy can continue to flow into the next few decades, helping the UK achieve Clean Power by 2030. 

The re-planting at Ffestiniog will be completed at the end of 2025, following an 8-year refurbishment, whilst at Dinorwig, work has only just begun. Due to the scale and complexity of the project, it will take up to 10 years to complete and a final investment decision on how many units to replant at Dinorwig is yet to be made.

Replanting involves replacing generating units and main inlet valves, some of the largest in the world, which control the flow of millions of litres of water. To carry out the work, the plants must be “drained down” – where water is stored in the lower reservoirs only. The water pressure in the shafts is higher than a nuclear submarine can withstand and so the drain down happens slowly and carefully, over the course of several weeks. Once empty of water, engineers climb inside the water shafts, carrying out thorough safety and integrity inspections.

Engie team at Dinorwig (2) (Resized)

Dinorwig, with its 1.8 GW capacity and Ffestiniog, with 0.3 GW, help keep the national electricity system balanced, offering instant system flexibility at short notice. The plants offer the flexibility needed to manage the day-night patterns of electricity consumption and support the integration of intermittent renewables onto the system.

Secretary of State for Energy Security and Net Zero, Ed Miliband said: Companies like ENGIE understand that clean energy is the economic opportunity of the 21stcentury, and are investing in the technologies the UK needs to support lower energy bills, protect our energy security, and create good local jobs.”  

First Minister of Wales, Eluned Morgan said: Investments such as these create high quality jobs for the local community. ENGIE is a longstanding investor in Wales, employing around 200 permanent staff and I’m pleased to support its replanting scheme, which will see the facilities continue to operate for another 25 years.”   

Assets on this scale are incredibly difficult to build today, so we believe it is essential to preserve and cherish the existing clean power assets we have in the UK if we are to achieve the energy transition.

Engie Team meeting with Welsh First Minister

Overview of First Hydro Company



Project Milestones

The Ffestiniog refurbishment will be completed by the end of 2025/early 2026.

The Dinorwig refurbishment project has only begun this year and is a more complex project that will take up to ten years. Replanting could see the complete refurbishment of up to all six generating units at Dinorwig and involves specialist technology, bespoke lifting systems, and expert contractors.

The first milestone is the replacement of its Main Inlet Valves (MIV’s) –  large valves that regulate water flow into a hydro turbine.

In early March the new MIV’s were transported from Porth Penrhyn to the Dinorwig site. Watch the video on the left hand side to see how we moved these giant valves, true feats of engineering, onto site. 

Before the new MIV’s can be installed the plant must be drained down, a once in a 40 year occurrence that began in April 2025.

This page will be updated throughout the project, please check back regularly for updates.

More information on our

Pumped hydro storage stations

Dinorwig - Drone shot from above

Dinorwig

Opened by HRH King Charles III in 1984, Dinorwig power station can generate 1.8GW of power within 12 seconds, offering the UK’s electricity system much needed flexibility.

Dinorwig Power Station
Ffestiniog

Ffestiniog

Commissioned in 1963, Ffestiniog Power Station was the UK’s first major pumped storage power facility. With four generating units units it can supply the entire power needs of North Wales for several hours.

Ffestiniog Power Station