began supplying grid inertia in 2020. Turbine hall There are four Francis turbines, which operate as both pumps and generators. These are housed in a cavern within Ben Cruachan, which is long, wide and high, with an adjacent transformer hall. The chamber is at a depth of around , and is located within a hard granite intrusion. Construction of the power station required the removal of of rock. Access to the hall is gained by a road tunnel long, high and wide, which is warm and humid enough to allow tropical plants to grow. The transformers step up the voltage from 16 kV to 275 kV for transmission. Six oil-filled cables carry the electric current up a cable shaft to a point in front of the dam, and from there it is carried on pylons to Dalmally to the east. The staircase in the cable shaft has 1,420 steps, making it the tallest in Britain. After passing through the turbines, the water enters a surge chamber designed to balance fluctuations in the level of water before entering the tailrace tunnel to Loch Awe, which is in diameter and long. Reservoir The Cruachan Reservoir is above Loch Awe, and is contained by a dam long. The reservoir has a catchment area of , and is capable of holding of energy. Environmental restrictions meant that the dam had to have a "clean" structure, so the operational equipment is located within the dam wall itself. The penstocks are a pair of tunnels, long and inclined at 56° from the horizontal with a diameter, which then bifurcate into four steel lined long, diameter shafts. The penstocks underwent a major inspection and refurbishment in 2003. Tourist attraction The power station was listed by the conservation organisation DoCoMoMo as one of the sixty key monuments of post-war Scottish architecture. In November 2012, the power station received the Institution of Mechanical Engineers' Engineering Heritage Award. A visitor centre, refurbished in 2009, is situated at the outflow to Loch Awe and receives around 50,000 visitors a year. The power station houses a three-section modernist mural in wood, plastic and gold leaf by English artist Elizabeth Falconer. The mural includes Celtic crosses, pylons, mythical beasts, and men of industry. The first section depicts the mythical Cailleach Bheur, who guarded the spring underneath the mountain. The middle panel commemorates fifteen workers killed when the roof of the turbine hall collapsed,