Hydroelectric: Case Studies
Large-scale hydroelectric scheme - Sloy/Awe, Scotland
This large-scale hydroelectric scheme is in the mountains of Argyllshire, Scotland. The reservoir is 338 metres above sea level and was created by building a dam 725 metres long and 45 metres high across Glen Shira.
Water released from Loch Shira passes through the 5-megawatt Sron Mor power station sited on the shore of Lochan Sron Mor, a smaller reservoir just in front of the main dam.
This smaller loch acts as a headpond for the main power station in the scheme. Its level is controlled by a dam centred on a rocky knoll in the middle of the glen. This dam has two distinct parts: a concrete structure on one side of the knoll and an earth embankment on the other. Water is carried from this headpond by tunnels and pipelines to Clachan power station over 7 kilometres away at the head of Loch Fyne.
The Allt na Lairige scheme uses the water resources of upper Glen Fyne in an area lying between Sloy and Shira. This dam is 425 metres long and 24 metres high, and is anchored to its rock foundation by high-tensile steel rods. Water is carried by tunnel to the 6-megawatt power station on the River Fyne 240 metres below.
Small-scale hydroelectric scheme - Garbhaig, Scotland
Operated by Garbhaig Hydro Power Ltd, the small-scale hydroelectric site is within a National Scenic Area, adjoining Loch Garbhaig in Slattadale Forest, south of Lake Maree, Rosshire, Scotland. The water source is natural water storage at Loch Garbhaig, enhanced by a 2-metre weir at the loch’s mouth. From there, it is supplied through 1,400 metres of buried pipeline to the 1,000-kilowatt Newmills Hydro Pelton Turbine, driving a synchronous generator of the same rating.
The scheme feeds into the power grid via a 415-volt to 33-kilovolt transformer. By December 1994, it had supplied 9 gigawatt hours to the grid – sufficient electricity to meet the average needs of 750 homes. When compared with the equivalent output from a fossil-fuelled power station, the scheme has saved 2,200 tonnes of carbon dioxide, 130 tonnes of sulphur dioxide and 15 tonnes of nitrous oxide gases.
Highland Regional Planning Authorities, Scottish Natural Heritage, the Forestry Commission and the Highland River Purification Board were all involved in planning consultations. Tree screening was used at the turbine house and transformer yard, mounding was used to hide the access road, and local stone was used for the intake structure and access road. Local opinion is supportive – access to a site of natural beauty improved without disturbing the attractiveness of the area. Fishing is unaffected and the loch is more accessible for fishermen.
An electricity purchase contract, including a premium for renewable energy, was awarded in July 1991. This enhanced its financial viability and revitalised the original project. Original construction work cost £555,000, with a further £600,000 invested in 1992/93.
Micro-hydroelectric scheme - Isle of Eigg, Scotland
Four out of the five households that make up the Kildonnan settlement on the east coast of the island are now connected to a shared hydroelectricity scheme installed by the Isle of Eigg Heritage Trust, which is responsible for the development of the island since it came into community ownership in 1997.
The small community is not connected to the national grid power supply and the villagers relied on private diesel generators for their electricity needs. However, the generators were noisy, costly and dependent on regular shipments of diesel to the island. In addition, the generators had to be switched off at night and produced oil waste as a by-product. The Trust was keen to switch to a cheaper and more reliable source of electricity.
This is the last stage in a major renovation project to improve the quality of life for the residents of these houses. Four out of the five houses have been completely rebuilt, with damp-proof courses, proper heating systems, renewed water and sewerage supplies and new electricity circuits.
The hydroelectric scheme is supplied from a nearby stream, which is used to power a small turbine. Four houses are supplied at the moment, including a guesthouse, and a fifth will be connected once renovation work on it is complete.
The turbine is capable of producing in the region of 6 kilowatts of power for the bulk of the year and has sufficient capacity to power additional households in the future if needed. The residents installed the hydroelectric scheme themselves, and they will also be responsible for maintenance and repairs. The £40,160 project received a total of £9,200 from Lochaber Enterprise and the Community Economic Development programme, as well as funding from the Scottish Land Fund, the Scottish Clean Energy Efficiency Demonstration Scheme and the Gordon Fraser Trust.