By Jonathan Marshall
Siemens says its B75 wind turbine blade is the world’s largest fiberglass component cast in one piece. (Photos by Siemens.)
Two hundred years from now, an excited paleontologist discovers what appears to be an enormous fossilized bone—so big, it could only come from a giant prehistoric sauropod.
On closer inspection, this awe-inspiring, 25-ton object proves to be 75 meters long—longer than the biggest known dinosaur, Amphicoelias fragillimus, which extended at most 60 meters from its head to the tip of its tail.
However, tests show that instead of being formed of mineralized bone, it is composed of seamless glass fiber-reinforced epoxy resin and balsa wood. Its curved, aerodynamic shape suggests that it was used for capturing the wind, not anchoring a giant limb.
Research in old archives finally solves the puzzle: it was a type of wind turbine rotor called the B75, made by Siemens, which claimed it as the world’s biggest rotor blade way back in the year 2012.
The same archives will probably show that Siemens’ record didn’t last long. Ever since the early 1980s, when typical rotors were only 10 meters long, wind turbine manufacturers have engaged in an arms race to build ever-bigger machines. That’s because the amount of wind energy captured is proportionate to the square of the blade length.
Using the new blades, a 6-MW Siemens wind turbine can generate enough energy to supply nearly 6,000 European households with electricity, especially when mounted in windy offshore locations. Moving at a maximum tip speed of 80 meters per second, its blades sweep an area of 18,600 square meters, more than three times the surface area of an American football field. DONG Energy has plans to install 300 of these turbines off the British coast by 2017.
A 6-megawatt turbine has blades that are 75 meters long and the rotor has a swept area that’s the equivalent of two-and-a-half soccer fields.
Unfortunately, blade mass, or weight, increases with the cube of its length, creating all sorts of difficulties for manufacturing, transporting, erecting, and maintaining the latest generation of huge turbines.
That’s why manufacturers use the latest composite materials with glass or carbon fibers to cut weight while maintaining strength. That’s also why they’ve been much slower in recent years to one-up each other in turbine size.
Three years ago Clipper Windpower disclosed work on 7.5-MW turbine, and in 2010 a Norwegian company announced plans to introduce a 10-MW turbine with a rotor diameter of 475 feet. If such plans some to fruition, ocean sediments may someday yield even bigger fossils than the B75.
Email Jonathan Marshall at jonathan.marshall@pge.com.
