Dinorwig's very rapid response capability significantly reduced the need to hold spinning reserve on part loaded thermal plant.

When the plant was conceived the CEGB used low efficiency old coal and oil fired capacity to meet peaks in demand.

[4][5][6] A 50 MW pumped storage facility at nearby Glyn Rhonwy in disused slate pits was approved in 2013, with an expected cost of £120 million.

Additionally, however, Dinorwig PHES receives a steady income for maintaining a permanent on-call capacity for urgent frequency regulation; in 2016 this was approximately £10.8 million.

The project – begun in 1974 and taking ten years to complete at a cost of £425 million[10] – was the largest civil engineering contract ever awarded by the UK government at the time.

[12] The power station is connected to the National Grid substation at Pentir by 400 kV cables that are buried for approximately 10 kilometres (6 mi), rather than using transmission towers or pylons to transmit the electricity across an area of outstanding natural beauty.

The generators are vertical-shaft, salient-pole, air-cooled units each having 12 electromagnetic poles weighing 10 tonnes each, producing a terminal voltage of 18 kV; synchronous speed is 500 rpm.

[16][17] It fills an important need in the system by responding to sudden surges in electricity demand because of its rapid ability to deliver power on load spikes.