Underwater Turbine Harvests Tidal Energy

The company has recently secured a stake in SeaGen, the world's first commercial power plant to generate electricity from tidal energy. Commissioned in 2008, the 1.2 MW plant is located in the Irish Sea and can provide around 1,500 households with electricity.

This power is generated by two large underwater rotors driven by the strong tidal currents that flow during ebb and flood. Siemens acquired a ten percent holding in the operator company, Marine Current Turbines, in 2010.

A larger plant, with an output of 8 MW, is due for completion off the coast of Scotland by 2014. This will be able to supply some 8,000 households with electricity generated from tidal energy.According to the International Energy Agency, as many as 800 billion kilowatt-hours a year could be generated worldwide by means of marine currents.

That is around one-third more than Germany’s annual power production and enough to supply 250 million households.

SeaGen is located off the town of Strangford, in Northern Ireland, where powerful tidal currents flow through a narrow strait. The plant consists of a tower three meters in diameter, which is anchored to the seabed at a depth of 30 meters and rises to a greater or lesser extent above sea level, depending on the tide.

Below the surface, the tidal current drives twin rotors of 16 meters in diameter fixed to the tower. Together, these cover an area of around 400 square meters. In order to be able to exploit the tidal current in both directions — ebb and flood — the rotor blades are pitched through 180 degrees when the tide turns.

Despite being around twice as expensive as a comparable offshore windpark, tidal energy systems do have a number of advantages. Matching the 6,000 megawatt-hours a year generated by SeaGen would require an offshore wind turbine of almost twice the rating. Moreover, tidal energy and other marine currents can be predicted with considerable accuracy and are therefore much more dependable than wind or solar power. The holding in Marine Current Turbines forms part of the Siemens environmental portfolio, which generated around €28 billion in sales for the company in fiscal 2010.