China installed a record amount of renewable energy last year, data from the National Energy Administration (NEA) showed on Tuesday. VIDEOGRAPHIC
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00:00A wind turbine produces electricity using the force of the wind.
00:12It's a source of renewable, inexhaustible and free energy.
00:17There are two types of wind farms, onshore and offshore.
00:21The turbine tower can be up to 100 meters high.
00:25The propeller is generally made up of three blades, shaped like the wings of an aeroplane.
00:30They measure between 35 and 60 meters in length.
00:34They begin to rotate under the effect of a wind speed of under 10 km per hour.
00:40The nacelle rotates automatically, so that it's always facing the wind.
00:44Optimal wind speed is about 50 km.
00:48Beyond 90 km, the propellers stop spinning for safety reasons.
00:53The spinning propeller turns a low-speed shaft inside the nacelle.
00:58The rotation speed of the shaft is not high enough to produce electricity.
01:02However, a gearbox increases the speed to 1500 revolutions per minute and transfers
01:08it to a second shaft, connected to a generator.
01:12The generator transforms the kinetic energy into electricity.
01:18Inside the tower, a transformer raises the voltage to 20,000 volts.
01:24Electricity is sent by underground or undersea cable to a substation, where the voltage is
01:29increased again, so that it can be injected into the power grid.
01:34Wind farms are clean and sustainable and can be built quickly.
01:38However, they have their drawbacks.
01:40Wind energy is intermittent, depending on the weather and environment.
01:45Wind turbines are noisy, don't always fit happily into the landscape and represent a
01:49danger for birds.