This scheme for hydro-electric power generation is located between the north end of Loch Lomond, Loch Fyne, Loch Awe and Loch Etive, an area with rainfall exceeding 3000mm (120 inches) per year ensuring a plentiful supply of water. The Sloy component, located between Loch Fyne, Loch Sloy and Loch Lomond was the first hydro-electric development by the North of Scotland Hydro-Electric Board. The Board had been created after World War II by Tom Johnston (1881 - 1965), Secretary of State for Scotland in Churchill's wartime coalition cabinet, who subsequently became the Board's Chairman.
The Sloy scheme was the work of engineer James Williamson (1881 - 1953), with Harold O. Tarbolton, Reginald Fairlie and James Shearer providing architectural advice. Operational since 1950, the stations forming the scheme now generate a total of 239 megawatts (MW) of power and are run by the privatised Scottish & Southern Energy Plc (previously Scottish Hydro-Electric), headquartered in Perth.
Completed in a series of phases, the first section around Loch Sloy was built between 1945-50. This was complemented by the section around Lochan Shira which was completed in 1959 and the Nant scheme on the northwestern shore of Loch Awe, commissioned in 1963, together with the Awe Barrage (in the Pass of Brander) and the Inverawe Power Station built 1959-65. The Cruachan pumped-storage system was commissioned in 1965 but this passed to Scottish Power Plc on privatisation in 1990 and is therefore no longer considered part of this scheme.
The section centred around Loch Sloy discharges into the northern end of Loch Lomond and the headwaters of Loch Fyne. It includes the Alt-na-Lairig dam, the first significant pre-stressed concrete dam in Western Europe, together with a complex system of aqueducts and tunnels. The Sloy Power Station is the largest conventional hydro station in Britain, with a head of 277m (909 feet) and an installed capacity of 152.5 MW.