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Rheidol Hydroelectric Scheme
Cwm Rheidol, near Goginan, Ceredigion, Wales, UK
associated engineer
Peter Ibbitson
Freeman Fox & Partners
date  1957 - 1962
era  Modern  |  category  Power Generation  |  reference  SN707792
The Rheidol Hydroelectric power station is fed by a network of reservoirs watercourses that extract and discharge water into and out of the River Rheidol near Snowdon. Rheidol is the largest hydroelectric power generator in Wales. The total capacity of the scheme is 56MW — enough for 12,350 homes.
Rain falling on the Plynlimon uplands is collected in a series of aqueducts and fed into the Nant-Y-Moch Reservoir. Water from this reservoir drives a 13MW generator at Dinas Power Station, and then flows into Dinas Reservoir.
Water from Dinas Reservoir supplies the Cwm Rheidol Power Station, where there are two 20.5MW generators. The Cwm Rheidol Reservoir was constructed to avoid large variations in water flows, and it collects the water passing through the power station and releases it slowly through a turbine that drives a 1MW generator. Four other auxiliary generators provide a further 1MW total output.
There are three dams in the scheme — one for each reservoir — the largest is a 53m high concrete buttress dam 350m long. Two pressure tunnels were driven a total distance of 16km through the friable mudstone and shale bedrock. They allow water to travel between the scheme’s reservoirs.
Water released from the reservoirs flows through tunnels to penstock valves at the generating stations. When the penstock valves are opened, water flows through the turbines, which transfer rotational motion to the generators.
Electricity is generated at 11kV and cabled to the transformer. At the transformer it is stepped up to 33kV and sent to Rhydlydan sub-station. There are four lines from the sub-station — three supplying Aberystwyth and the surrounding area. The remaining supply is stepped up to 132kV and sent via Swansea to the UK's National Grid.
Extensive landscaping has ensured that the scheme blends into its surroundings. Wastes are recycled wherever possible, or taken to landfill. Rheidol was certified to ISO 14001 (Environmental Management) in April 1999.
The scheme covers some 16,000 hectares within the Cambrian Mountains Environmentally Sensitive Area and the Rheidol Woods and Gorge Special Area of Conservation. There is a ‘fish ladder’ 6m high with 14 pools that allows salmon and trout to bypass the power station to reach their spawning grounds. Rainbow trout are farmed in specially constructed tanks alongside Cwm Rheidol Power Station, and then released into Dinas Reservoir.
In 2001, the total water flow through the scheme was 169.8 million cubic metres — 0.7 million cubic metres through the fish farm.
Rheidol Hydroelectric scheme has been operated by E.ON, Powergen and now Statkraft Energy Ltd. Although it was completed in 1962, the official opening was not until 3rd July 1964.
A green power hub opened at Rheidol power station on 1st April 2004, with a control room to manage both the hydroelectric scheme and the nearby wind farm. This replaces the original control room.
Research: ECPK
"The Geology of the Dinas Cwm-Rheidol Hydroelectric Tunnel" by T.D. Adams
Geological Magazine, Vol.100, Issue 4, July 1963, pp.371-378

Rheidol Hydroelectric Scheme