Right now wind is leading the renewable energy surge and records for the largest turbines are being set. Just how big is the largest one? Siemens is creating a single blade that is 225 feet long, basically as wide as a 747 airplane.
The manufacturing process is incredible, from Wired UK:
Siemens manufactures the mammoth B75 blades in one, smooth, streamlined piece — with no joints — using its IntegralBlade process. The technique — which requires glass fibre-reinforced epoxy resin and balsa wood to be cast in a mould — renders the blades steadfast and less likely to develop faults while being beaten with 181 tonnes of air energy every second, when wind speeds are ten metres per second (30 mph). The huge strain it is put under means no blade can leave the factory without being carefully inspected for even minor cracks.
The size of these things is almost unimaginable, like trying to picture three 747’s spinning around a massive pole. They will also have to shoot up into the sky several hundred meters.
According to Siemens, when fully constructed this mammoth would generate 6-megwatt’s, while another group is looking into 20-megawatt versions!