Hydroelectricity is now an accepted part of Scottish scenery and way of life. This is largely due to the vision of one man, Tom Johnston, the Labour Secretary of State for Scotland in former UK Prime Minister Winston Churchill’s wartime coalition government. It would be good to think that somewhere Tom Johnston would be smiling at the prospect that 60 years later the now privatised owners, Scottish and Southern Energy, would be embarking on a £250M (US$357.6M) programme of refurbishing its hydroelectric stations. Whilst the longevity of his vision would have been no surprise to Johnston, he could not have foreseen the pivotal role Scottish and Southern Energy’s hydro generation would have in helping it to compete successfully in the UK’s emerging competitive electricity markets.

Scottish and Southern Energy is one of the largest energy companies in the UK, supplying around four million electricity and one million gas customers. It is one of the top five electricity generators and one of the country’s largest generators of renewable energy, with about 50% of the UK’s capacity. The company has a total installed hydro generation capacity in excess of 1300MW, with an average annual output of over 3000GWh.

Supporting Scottish and Southern Energy’s 54 main hydroelectric power stations and 24 smaller stations, there is an infrastructure of 93 dams, 78 reservoirs and around 600km of underground rock tunnel and a similar length of aqueducts and pipelines. Most of this was constructed in the 1940s and 1950s, and the company has recently announced an ambitious refurbishment programme for such facilities.

To understand the timing behind the company’s announcement, it is worth looking at the UK Government’s strategy to encourage the development of renewable energy. Recognising the sometimes unfavourable economics of investing in renewable energy, the Government has introduced an obligation on electricity suppliers to provide a percentage of their electricity supplies to customers from renewable resources, starting at 3% in 2002 and rising to 10.4% by 2010. The suppliers will have to demonstrate that they have purchased sufficient output from accredited renewable sources to cover their renewables obligation, or pay a premium of £30 (US$43) per MWh to cover any difference between this and their total obligation. Accredited generation will receive a Renewables Obligation Certificate (ROC) for each MWh produced, which is likely to be worth around US$43 in the supply market.

In July 2001, the Government announced the categories of generation which would be eligible for ROCs, and therefore attract a premium for the energy they produced. Of particular importance to Scottish and Southern Energy was the inclusion of refurbished hydro generation up to and including 20MW installed capacity.

‘After 50 years of operation, routine maintenance is no longer enough to ensure the continued efficient operation of our hydro-electric power stations. The time is fast approaching when many are due for major refurbishment,’ says David Lee, hydro generation manager for Scottish and Southern Energy. ‘Unless the stations had been eligible for ROCs this investment would have been uneconomic. We would simply have continued to run the stations until they were no longer operationally viable.

‘Happily, we are now able to commit to a ten-year

programme which will significantly extend the working lives of these assets, improve their efficiency and in so doing, secure around 200 jobs in rural Scotland and support manufacturing jobs in the turbine technology industry,’ he adds.

The company has already released details of the first year of its refurbishment programme, which will involve six of its hydro stations (see table). Although the work required at each will vary, in general terms refurbishment includes replacing the turbine runner/blades, inlet guide vanes, the controls and DC equipment, the generation circuit breaker and the auxiliary power distribution system. In addition, the turbine casing and shaft, generator rotor, stator frame and casing, the main inlet valve and hydraulic gates are refurbished to an ‘as new’ condition. All cabling and pipework associated with these systems will be replaced unless it is found to have a residual life at least equal to the equipment it serves.

Details of the stations to be refurbished during the first stage of the programme are as follows:


Aigas power station nestles in a gorge on the river Beauly and has two 10MW Kaplan turbo-generators. Aigas dam is of mass gravity construction, 91.5m long and 26m high with a capacity of 49,000m3. Borland fish lifts have been installed to allow fish to pass.


Ceannacroc power station was the first to be built underground in the UK. The river Doe feeds the power station directly or can redirected to Loch Cluanie for storage. The construction of the Cluanie dam was another first for the UK. Blast furnace slag, wet ground by the Trief process, was used, saving 70% of the cement which would otherwise have been needed. It is some 675m wide and over 40m high. Its construction raised the level of water level of the loch by almost 30m.


Gaur power station was the first hydro station to be fully automated and controlled from a remote control centre, now located in Perth. Its catchment area includes the Rannoch Moor, and is fed by pipeline with water stored behind the Gaur dam. The dam is of concrete gravity construction and is 110m wide, 13m high and has a capacity of over 7000m3.


The generating set at Invergarry power station is driven by a Kaplan turbine under a head of 50m which, at the time of installation in 1956, was a particularly high head for this type of turbine. Fed from Loch Garry by tunnel, the station is situated near the mouth of the river Garry in Loch Oich. The Garry dam has a Borland fish lift installed. Of mass gravity construction, its vital statistics are 47m wide, 17m high with a storage capacity of around 6500m3.


The river Orrin is held back by two dams to form Loch Orrin. The main dam is mass gravity, 315m wide, 51m high and has a capacity of 178,000m3. Orrin power station is on the southern shore of Loch Achonachie in Strath Conon and is fed by almost 5km of tunnel.

Torr Achilty

Torr Achilty power station is built into the dam of the same name behind which lies Loch Achonachie, formed by its construction. The dam is of mass gravity construction, over 245m wide, 23m high, has a capacity of almost 37,000m3 and is bypassed by a Borland fish lift. Orrin and Torr Achilty form part of Scottish and Southern Energy’s Conon scheme. During the development of the scheme, a mainline railway station and over 3km of railway track were replaced, and about 48km of public and private roads were constructed.

Whilst Scottish and Southern Energy’s announcement that it is to invest US$357.6M is good news for the future of hydro generation in Scotland, it is keen to stress this is not a new process. ‘We’ve been investing in a hydro refurbishment programme since the 1980s,’ Lee adds. ‘Originally refurbishment was undertaken on key systems but since 1995 we have moved to the principle of complete station refurbishment. We anticipate the additional output from the refurbished stations will be in the region 115GWh.
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