Sloy Power Station, on the banks of Loch Lomond, was the first hydro scheme to be developed under the North of Scotland Hydro-Electric Board and it has just celebrated 70 years of power generation.
Sloy is the largest conventional hydro-electric power station in the UK. It has an installed capacity of 152.5 MW generating enough electricity to power over 80,000 homes.
It can operate at full load within five minutes of a standing start and it is this almost instant availability that makes it ideal for use during times of peak demand.
The North of Scotland Hydro Electric Board (NOSHEB) was established by an Act of Parliament in 1943 and was responsible for generating, transmitting, distributing and supplying electricity throughout the north of Scotland, including the Highlands and Islands. NOSHEB’s purpose was to develop abundant cheap electricity for the people living in the north of Scotland whilst attracting new industries to the area and the export of surplus power to consumers in the south.
The profit from this sale of surplus power was used to subsidise the costs of distributing power to the more remote areas of the Highlands and would be used to support economic development and social improvement in the north of Scotland.
The region, which covers an area of 21,750 sq m, contains Britain’s highest mountains and largest inland lochs combined with high rainfall levels making ideal conditions for hydro generation.
Sloy was the first scheme to be built following the Act of Parliament. Driven forward by the then Secretary of State for Scotland, Tom Johnston, the first sod was cut on 11 June 1945 by his wife, not with the usual polished spade, but an 18 tonne bulldozer. The sod cut was a strip of turf about 12 feet wide and 100 feet long, an act that was acknowledged later as a ‘fitting prelude to a big job”.
Nestled on the western shores of picturesque Loch Lomond, perhaps Scotland’s most famous loch, and gazing up past Sloy Power Station to the four huge pipes that feed its turbines, it is hard to imagine that Glasgow is less than 30 kilometres to the south-east.
The power station is fed from Loch Sloy, just four kilometres away but, crucially, over 277 metres higher than the power station.
This huge difference in height within a short horizontal distance is what provides the power to produce an annual average of over 120 million units of electricity – that’s about one million units for every inch of rainfall in its catchment area.Loch Sloy is contained by Sloy Dam which, at 357 metres long and 56 metres high, attracts from areas to the north and south via a system of tunnels and aqueducts.
The dam was the first of nine buttress dams to be constructed for the North of Scotland Hydro-Electric Board, this being the first of four which were designed by James Williamson and Partners.
A 3 km tunnel carries water from Loch Sloy through Ben Vorlich, to the valve house immediately above the Power Station. From here the water plunges down the side of the mountain through its four large pipelines and into the power station where four turbines drive four vertical shaft generating sets – 3 rated at 40MW and one at 32.5MW totalling 152.5MW. each developing 32.5MW.
There is also a 450kW Pelton wheel generator for emergency supplies.
When brought into service at times of peak demand – Sloy Power station can operate at full load within five minutes from a standing start.
With an installed capacity of 152.5MW Sloy has the largest capacity of Hydro-Electric's conventional hydro stations and when the four machines are running at full load nearly a million gallons of water pass through every minute.
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