Glendoe Hydro Electric Scheme

Occupying land owned by the Glendoe and Garrogie Estates in the Monadhliath Mountains above Loch Ness, 2 miles (3 km) east of Fort Augustus, the Glendoe Hydro Electric Scheme is Scotland's first large-scale hydro-power development since the 1960s and represents its largest recent civil engineering project. Officially opened on 29th June 2009 by HM Queen Elizabeth II, accompanied by HRH The Duke of Edinburgh, the £150-million development generates 100 megawatts of electricity from a single underground power station. This is the second-largest conventional hydro-power station in Britain, next to the Sloy Power Station, and is particularly effective in meeting major fluctuations in the demand for power because it can generate at full capacity within 30 seconds of starting. It will generate 180 GWh of electricity in a year of average rainfall and the value of this electricity, taken together with the income from Renewable Obligation Certificates, will ensure a pay-back period for the scheme of around twelve years.

Design work was by engineering group Jacobs, while the contractor was the German construction company Hochtief. Workers were housed in a substantial on-site accommodation camp. The start of the project was marked in 2006 by an explosion triggered by Prime Minister, Tony Blair (b.1953) and First Minister, Jack McConnell (b.1960), which began the process of reshaping the valley. Water is collected from an area of around 29 sq. miles (75 sq. km) via existing streams, fourteen purpose-built intakes, 3 miles (5 km) of pipeline and 4½ miles (7 km) of underground tunnels. This water is diverted into Glendoe Reservoir at the head of Glen Tarff, which is retained by a dam 35m (114 feet) high and 905m (2969 feet) in length, the longest in Scotland. Another First Minister, Alex Salmond (b.1954), attended the plugging of the dam on 1st September 2008 and pressed the button to begin filling the reservoir. The drop from the reservoir to the power station near Loch Ness is 609m (2000 feet), the largest of any hydro scheme in the UK. Given that the efficiency of a hydro station increases with the size of the head, this makes Glendoe the most efficient in the country.

A further 5 miles (8 km) of large tunnel carries the water to the turbine and finally out into Loch Ness. A mile-long (1.3-km) tunnel provides access to a large cavern, lying 250m (820 feet) below the hillside, which contains the six-jet Pelton turbine and generator units. An adjacent smaller cavern contains a transformer which raises the voltage in readiness for injection into the national electricity grid. Although some tunnelling was undertaken via the drill-and-blast method, much was completed using an immense specialist tunnel-boring machine, christened Eliza Jane by local school-children, which took 15 months to complete the task.

Disaster struck in August 2009, less than a month after the official opening, when a major rock-fall blocked the upper section of the aqueduct connecting the reservoir to the turbine hall, causing the scheme to be shut down. The problem was said to have been caused by failure to effectively line the aqueduct tunnel and the solution has involved the building of two new tunnels at a cost of £10 million; the first some 600m (1968 feet) in length to divert water around the blockage and a second shorter access tunnel (550m / 1804 feet). The contractors for the repairs were construction engineers BAM Nuttall and the accommodation camp had to be re-established. The reservoir began to be refilled in June 2012, with the scheme becoming operational once again in August.

The scheme is operated by Scottish and Southern Energy plc, the Perth-based utility company.

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