The first commercial offshore wind turbine that Siemens created 30 years ago had 5m long blades and produced a paltry 30kW. A lot can change over three decades. The company’s newest offshore model isn’t just the biggest in the sea; it’s the biggest anywhere.
Known by an alphanumeric jumble (STW-6.0-154), the turbine produces a whopping 6MW of power — nearly 25,000 times as much as Siemen’s original mode — and utilises a trio of 75m turbine blades — the world’s largest — for a rotor diameter of 154 metres — equal to the wingspan of an Airbus 380 and a humongous 18600sqm sweep area. In all, each turbine can produce 25 million kilowatt hours of energy. That’s enough to power 6000 homes.
Siemens developed the 6MW turbine exclusively for use at sea, which presents an entirely different set of problems and opportunities than on land. Offshore turbines need to be lighter, more robust and more reliable given their distance from nearby mechanics. That’s why Siemens replaced two-thirds of the traditional drive train — the main shaft, gearbox and high-speed generator — with its proprietary Direct Drive system that instead uses a low speed generator connected directly to the low-speed shaft. If the part isn’t there to break, you won’t need to send someone out to fix it.
What’s more, the Direct Drive system also frees up a significant amount of space in the turbine’s nacelle (the main body housing), enough to fit a small crane for lifting heavy generator components and a coffee machine for lifting servicemen. This system also makes the STW-6.0-154 the lightest turbine in its class, with a 200 ton nacelle and a 350 ton total masthead weight. “At the same time, the turbine delivers an increased energy yield and offers greater profitability over its life cycle,” Henrik Stiesdal, CTO of the Wind Power Division within the Siemens Energy Sector, said in a press release.
Part of this weight savings comes from the turbine’s IntegralBlade technology which generates a 20 per cent savings over conventional production methods. The 6 MW turbine is capable of using either a specially built 154m rotor for maximum power generation or a slightly shorter 120m long blade, the same that the 3.6MW model uses, for areas near airports and flight paths that have a 150m tip-height restriction.
The first 6MW turbine with the 154m rotor was recently installed in Østerild, Denmark at the new Danish new national test centre. This followed a July 2012 announcement that Danish energy giant DONG had ordered 300 of the massive turbines with plans to install them along the UK coast in the upcoming years. For its part, the UK has invested more than £75 billion in offshore power development to date in an attempt to derive 25 per cent of its total power consumption from the wind by 2020. [Siemens 1, 2 – NA Wind Power 1, 2 – New Scientist – DONG Energy]