Photo Essay: Making the world’s largest turbine blades

As wind energy moves further offshore the quest is on to produce turbines that are bigger and more powerful. But this increased power leads to size and engineering challenges, not least of which is the size and weight of the rotor blades.

The Siemens SWT-6.0-120 wind turbine uses direct drive and proven rotor technology. Nacelle and rotor weigh together less than 350t, setting a new low-weight standard for large offshore machines.

Siemens has produced the first batch of its new 75m-long B75 rotor blades and these will be installed on the second prototype of the company's 6MW offshore wind turbine, which will be erected in the second half of the year in Denmark's Osterild Test Station.

If the B75 Quantum blade were produced using traditional technology, it would be 25-50 per cent heavier. Heavy blades are subject to higher loads and require stronger nacelles, towers and foundations.

1 The B75 blade is the world's largest fiberglass component cast in one piece. The manufacturing process posed several challenges for the project team. In particular, the mould had to consist of two parts so that it could be transported.

2 Siemens is the only wind turbine company that manufactures rotor blades in one piece without glue joints, which significantly improves the cost efficiency of wind turbines.

3 Wind power plants have evolved dramatically over the past 30 years. The first commercial wind turbine had a capacity of 30kW and 5m-long rotor blades, for a 10m rotor diameter. The latest turbine generation from Siemens has a 6MW capacity and 75m-long rotor blades for a rotor diameter of 154m - the largest in the world.

4 Before a rotor blade leaves the factory, it is carefully inspected for potential defects and cracks - the only way to ensure that a blade will be able to withstand the tremendous force of the winds. When operating at 10m/s wind speed, a 154m rotor extracts energy from 200t of air per second.

5 A special vehicle, traveling at 60km/hour, transported these giants over a distance of 575km from the blade factory in Aalborg to the Danish town of Nakskov on Lolland Island. By car, the trip is about 330km, but because of the length of the rotor blade some re-routing was necessary taking bridges and tunnels into consideration. In Nakskov the blades were painted - the painting cabin at the blade factory is currently limited to 58m blade length.

6 The SWT-6.0-120 has a swept area of 18,600 square metres – equivalent to almost two and a half football fields.

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