Dinorwig is comprised of 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.

Dinorwig's reversible pump/turbines are capable of reaching maximum generation in less than 16 seconds. Using off-peak electricity the six units are reversed as pumps to transport water from the lower Llyn Peris reservoir to the higher Marchlyn Mawr reservoir. Llyn Peris (lower reservoir) rises during the day, then falls back overnight. The smaller and higher Marchlyn Mawr reservoir up in the hills does the reverse, dropping as much as 121ft (37 metres) during the day.

Closed-loop Pumped Hydro Storage