Harnessing the power of the wind

China installed a record amount of renewable energy last year, data from the National Energy Administration (NEA) showed on Tuesday. VIDEOGRAPHIC

Transcript

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.