Site and Construction

Opened by Royal Highness King Charles III on 9 May 1984, the station can generate 1728MW of power within 12 seconds to stabilise demand on the National Grid.

Dinorwig Power Station has been constructed on the site of the Dinorwig slate quarries, which closed in the 1960s. The slate tips were relocated to improve the aesthetic value of the area, and the plant was constructed within the Elidir Fawr Mountain, now part of the Eryri SAC.

Dinorwig’s reversible pump/turbines are capable of reaching maximum generation almost instantly. Using off-peak electricity, the six units are reversed as pumps to transport water from the lower reservoir back to Marchlyn Mawr.

Above-ground structures include the administration complex and security gatehouse.  A geological SSSI is located along the shores of Llyn Peris, showing the results of glaciation. Llyn Padarn, the lake into which Dinorwig releases excess water, is also a SSSI.

Environmental Restoration

Following construction, native ground cover, including grasses, shrubs, and wildflowers, was carefully replaced after the building works were complete. Local stone and slate, much of which was reclaimed from old quarry buildings, were used in the construction of external facings, walls, and buildings.

One of the main environmental problems that faced scientists was how to ensure the protection of the Welsh Arctic Charr, a native to Llyn Peris. This rare fish is found in only four lakes throughout Wales. A programme was devised to ensure safe relocation to Ffynnon Llungwy, a nearby glacial lake.

Engineering Achievements

When it was fully commissioned in 1984, Dinorwig Power Station was regarded as one of the world’s most imaginative engineering and environmental projects.

Today, Dinorwig’s operational characteristics and dynamic response capability are still acknowledged worldwide. Dinorwig is the largest site of its kind in Europe.

The station comprises 16km of underground tunnels, deep below Elidir Mountain. Its construction required 1 million tonnes of concrete, 200,000 tonnes of cement, and 4,500 tonnes of steel. The station’s six powerful generating units stand in Europe’s largest man-made cavern. Adjacent to this lies the main inlet valve chamber housing the plant that regulates the flow of water through the turbines.

Natural Life

We ensure continuous monitoring of environmental issues such as water quality and wildlife protection around Dinorwig. The habits and well-being of aquatic species are observed in both Llyn Peris and Marchlyn Mawr. The native populations of salmon, trout, and freshwater lamprey have open access to their chosen spawning grounds all year round.

A proportion of the site is within the Snowdonia National Park and is sheep-grazed upland grassland and old slate quarries. We also own and manage a small area of land on the outskirts of Nant Peris as a biodiversity park, where habitat creation schemes have been encouraged.