Wind blows on the blades and makes them turn, which turns a shaft inside the nacelle (the box at the top of the turbine). The shaft goes into the gearbox which increases the rotation speed enough for the generator, which then uses magnetic fields to convert the rotational energy into electricity. The electricity goes into a transformer which converts it into a higher voltage, for distribution through the national grid.

Turbines rotate to face the direction that the wind is coming from. At the top of the turbine are instruments to measure wind speed and direction. When the wind changes direction, motors move the blades and the nacelle, so that they are facing into the wind. There are also brakes fitted into the turbine so that it can be switched off in very high winds of about 25 meters per second (56 miles per hour), to prevent the turbine being damaged.

As wind speed increases, the power available from the wind increases at a more rapid rate; so that a little difference to the wind speed makes a big difference to the power output. The power output of a turbine depends on the diameter and length of the blade. The longer the blade, the more area is moved by the wind, and consequently the greater the output.

The trend now is for installing larger machines because of the lower cost of production and increased output. A typical modern turbine is rated at 1.8MW, which can generate enough electricity in a year for over 1000 homes, which saves over 4,000 tonnes of carbon dioxide emissions annually.  The most common wind turbine design is the upwind, three blades, stall control, constant speed design. More efficient designs are now available with very high outputs using variable speed rotation.

The above information is curtesy of Scottish Renewables