Blades are mostly made of glass-fibre reinforced composites; recycling end-of-life blades is one of the sector's priorities.
Most turbines have three blades: three offers the best balance of efficiency, stability and cost.
Wind speed increases with height, which is why towers keep growing and hub heights now exceed 100 metres.
On offshore turbines a single blade can exceed 100 metres, close to the length of a football pitch.
On large turbines the blade tips travel at close to 300 km/h, even though the rotor seems to turn slowly.
Modern turbines typically start generating at around 3 m/s and are shut down for safety in storms above about 25 m/s.
A wind turbine can theoretically capture at most 59.3% of the kinetic energy in the wind. This is known as the Betz limit.
Wind power rises with the cube of wind speed: double the wind speed and the available power increases eightfold.
