Sloy Hydroelectric Plant, Scotland

Background to the Sloy Hydroelectric Power Plant

In May 1945 construction began on the Sloy Hydroelectric Power Station on the banks of Loch Lomond in Scotland. The power station was completed 5 years later and was opened on 18th October 1950 by the late Queen Mother. Even today it is still the largest conventional hydroelectric power plant in the UK. The Loch Sloy Dam, built as part of the project, is 56m high and 357m long and raised the surface level of the loch by approximately 47m. The resulting Sloy Reservoir has a 17km2 direct catchment area, although various pipes and intakes have provided a further 63km2 of indirect catchment area. The total volume of water held in the reservoir by the dam is approaching 36million m2, and the potential energy contained within this mass of water is equivalent to 14million kWh of useful electrical energy. A 3km long tunnel takes water from Loch Sloy to a valve house positioned approximately 197m above the tank. From the valve house, four 2m steel pipes carry the water down into the powerhouse that is situated on the west coast of Loch Lomond.

Extending the Sloy Hydroelectric Power Plant

When the plant was initially built, a vertical Francis turbines was installed in each pump and these were rated at 32MW giving the plant a total output capacity of 128MW, however in the late 1990s a £113m refurbishment resulted in three of the turbines being replaced with larger 40MW turbines. As a result of this refurbishment, the total output of the plant now stands at 152MW. In Sept 2010, Scottish & Southern Energy was given planning permission to extend the Sloy Hydroelectric Power Plant by installing a pumping station, which will give the plant pumped storage capability. The proposed pumping station will house two 30MW pumps each capable of pumping 10m3 / second of water. These would be adjoined to two of the existing pipes, allowing water to be pumped back from the powerhouse on Loch Lomond all the way to Loch Sloy. With the 2 pumps running for 6 hours at a time, 432,000 m3 of water would be pumped out of Loch Lomond, resulting in only a 6mm fluctuation in the water level! The purpose of this pumped storage extension will be to take advantage of excess energy in the grid during evenings and times of low demand, to help the grid in times of especially high demand. The cost of this proposed work is £40m and it would provide an extra 200GWh to the grid. Work on this installation is due start in late 2012 and is due for completion within 27 months.

Environmental Impact of Sloy Hydroelectric Power Plant

One final point to highlight is the risk to wildlife by installing this new pumped storage facility within the Sloy Hydroelectric plant. Ruffe which were introduced by Anglers into Loch Lomond are actually a pest species, however the new facility creates the possibility of these fish being pumped into Loch Sloy, which would threaten the established population of Powan fish in the higher Loch as the Ruffe feed on Powan eggs.