The Shannon hydroelectric Scheme was a major development by the Irish Free State in the 1920s to harness the power of the River Shannon. Its product, the Ardnacrusha power plant, is a hydroelectric power station located near Ardnacrusha within County Clare approximately 2.4 kilometres (1.5 mi) from the Limerick border. It is Ireland's largest river hydroelectric scheme and is operated on a purpose built headrace connected to the River Shannon. The plant includes fish ladders so that returning fish, such as salmon, can climb the river safely past the power station. Completed within 7 years of Irish independence in 1922 at a cost which was equivalent to one fifth of the Irish state's annual budget, the plant enabled an enormous surge in demand for electricity across the country and demonstrated the ability of the new government to develop during a difficult financial period. The plant was constructed by the German company Siemens-Schuckert, although much of the design was done by Irish engineers and Ireland provided most of the labour force. The scheme involved changes to the flow of the whole river, multiple dams and bridges and the construction of a national power grid. The generating plant at Ardnacrusha is composed of three vertical-shaft Francis turbine generators (commissioned in 1929) and one vertical-shaft Kaplan turbine generator (commissioned in 1934) operating under an average head of 28.5 metres. The scheme originally was designed for six turbines, with four turbines fitted. The 85 MW of generating plant in Ardnacrusha was adequate to meet the electricity demand of the entire country in the early years. The full output equates to about 332,000 MWh generated on an annual basis. Ardnacrusha generates at 10.5 kilovolts (kV) but this is transformed to 38 kV for local distribution and to 110 kV for long distance transmission.
Background
The first plan to harness the Shannon's power between Lough Derg and Limerick was published in 1844 by Sir Robert Kane. Inspired by Nikola Tesla's 1896 project at Niagara Falls, "Frazer's Scheme" proposed a head-race canal ending at Doonass, and was sanctioned by the Shannon Water and Electric Power Act 1901 (1 Edw. 7. c. cxxxvi). This envisaged a seasonal scheme with a back-up steam turbine to generate electricity in the summer, but the overall cost was considered too great and the scheme was shelved. In 1902 S. F. Dick proposed a sharper fall at Doonass. The British Board of Trade appointed a committee in 1918 which approved proposals by Theodore Stevens and published a report in 1922. This envisaged altering upper lake levels to create extra storage of 10,000 million cubic feet, at a cost of £2.6m.
At the end of 1923, the engineer Thomas McLaughlin approached the new Irish Free State's Minister for Industry and Commerce Patrick McGilligan with a proposal for a much more ambitious project. McLaughlin had started working for Siemens-Schuckert, a large German engineering firm, in late 1922, and his scheme would exploit the full height difference between Lough Allen and the sea. He drew on the analysis of 25 years of flow at the weir at Killaloe published by John Chaloner Smith, an engineer with the Commissioners of Public Works. McGilligan was enthusiastic although the President of the Executive Council, W. T. Cosgrave, was more cautious. The scheme was published by Siemens in September 1924 and the government appointed a team of experts from Norway and Switzerland to check its viability. It caused considerable political controversy as the cost of £5.2m was a large part of the new state's entire budget in 1925 of £25m and interests in Dublin preferred a more localised solution. But the experts supported the centralised solution which would require a distribution grid all over the country but recommended a two-stage implementation of the power generators. The government accepted this and by April 1925 had introduced the Shannon Electricity Act, 1925 in the Dáil.
Construction
In 1925 Siemens started the works with Dr. McLaughlin as managing director and Professor Frank Sharman Rishworth, who took a leave of absence from University College Galway, as chief civil engineer. A completion time limit of three and a half years, with penalty clauses for failure of adherence to this limit, was written into the contract. Around 150 of the skilled workers and engineers on the power station were Germans. A camp was set up for the workers that included living quarters for 750 men and a dining room that seated 600. Initially employment for 700 was provided, whilst at its peak there were 5,200 employed during the construction phase, with this dropping back to 2,500 near completion.
Siemens had to import a vast array of machinery from Bremen and Hamburg and built a 96 km narrow gauge railway to transport workers and supplies around the site, which included 76 steam locomotives. The government made good the local roads which were in an appalling state. The headrace involved building embankments up to 25m high over a distance of 10 km and many unforeseen geological problems were encountered. 7.6 million cubic metres (9.9×10^6 cu yd) of soil had to be moved and 1.2 million cubic metres (1.6×10^6 cu yd) of rock. Four major bridges were built and nine rivers diverted as well as numerous streams. Three large Parsons turbines were installed at the base of the dam which could generate 35MW, more than the entire public supply of the time. In addition a supply network of 110kV power lines was installed to Dublin, Cork and other centres. The construction project was not without controversy. Unskilled labourers were only paid agricultural wages producing strikes, national and governmental debate over wages, conditions, and spending over-runs. Despite this, there was a final cost overrun for Siemens of £150,000. The site attracted a huge number of sightseers, transported by excursion trains from all parts of Ireland. By 1929 it reckoned that 250,000 spectators had been guided over the works.
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