Located on the southeast shore of Loch Ness, 19 miles (30 km) SSW of Inverness, Foyers is primarily a pumped-storage power station with a small amount of conventional hydro-electric capacity. Pumped-storage involves raising water to a high reservoir during off-peak periods and releasing it later to generate additional power during times of peak demand. The scheme was redeveloped to focus on pumped-storage in 1969, having been purchased by the Hydro Board from the British Aluminium Company (BAC). The scheme was originally built by BAC in 1896 and was the first large-scale commercial hydro-electric scheme in the UK, used to power an aluminium smelter also located here until this closed in 1967. BAC created a reservoir by joining two small lochs to form Loch Mhor, which lies 179m (587 feet) above Loch Ness and 2 miles (3 km) distant.
During the redevelopment, a modest 5-MW turbine was installed in the original power station building to replace the original plant and provide pure hydro-electric generation, while the tunnels and pipes which carried the water were reused. The River Fechlin was diverted into Loch Mhor to provide additional water and, to support the pumped-storage system, new tunnels and a further power station were built close to Boleskine House, made famous by the psychic experiments of Aleister Crowley in the late 19th C.
Water travels to and from Foyers through a near horizontal low pressure tunnel 2743m (9000 feet) in length, joining a vertical high pressure shaft and tunnel, with a surge shaft above. The high pressure shaft is 112.8m (370 feet) deep and feeds into a horizontal tunnel 117.3m (385 feet) long which then divides into two smaller tunnels 315.2m (1034 feet) long - the last 95.7m (314 feet) sloping down to the turbines.
A new power station was built to house two 150 MW (204,000 horse-power) Francis generation-motor sets, each weighing 914 tonnes, with 5m (16 feet) wide turbine blades, amongst the largest in Europe. The generators each occupy pits 36m (118 feet) in depth on the shore of Loch Ness, with 100 cubic metres (3531 cubic feet) of water passing through each turbine and out into the loch every second during generation. The turbines can be brought from a standstill to full power output in less than two minutes, which makes the station extremely responsive to demand. The new scheme became fully operational in 1975.
The scheme has a total capacity of 305 MW and is run by the privatised Scottish & Southern Energy Plc, headquartered in Perth, which has an annual turnover of £2.3 billion (2006).