Energy

Wind generator

The most important way to use wind power is to produce electric power through wind generators, namely aerogenerators. Electric power is obtained by exploiting wind kinetic energy: airflows move at more than 10 km/h speed making the blades of a propeller turn. They are connected to a generator that transforms mechanic power into electric power. There are different types of aerogenerators, that differ in shape and dimension. They can have one, two or three blades, of different length. Those with 50 cm length are used as battery chargers, while those with 30 cm blades can supply 1,500 kW power, managing to satisfy the daily power need of around 1000 households. The most popular aerogenerator is made up of a steel tower of 60-100 meter height, with two or three blades that are around 20 metres long. It generates a power of 600 kW, which equals the daily power need of 500 families. The blades of the wind generator are fixed on a mechanical element called hub and form the rotor. According to the position of the axis, it is possible to distinguish between horizontal and vertical axis rotors. The first ones are the most common and popular; while the second ones have been used since ancient times but only recently they have been subject to studies and researches to improve their efficiency (the main advantages of vertical axes are: their constant functioning regardless of the wind direction, a better resistance even when the wind is strong and turbulent). The structure of a wind generator with horizontal axis is simple: a support (foundations and tower) with a gondola or nacelle on the top. Inside there is a slow-driving shaft, as well as a turn multiplier, the fast shaft, the power generator and auxiliary devices (braking system and control system). The rotor (consisting of the hub, on which the blades are mounted) is fixed at the extremity of the slow shaft. The shape of the blades is designed in such a way that the incoming airflow activates the rotor. From the rotor, the wind kinetic energy is transmitted to a power generator. The wind generator works according to the strength of the wind. Under 4/5 metres per second it cannot start. The minimum speed allowing the device to provide power is 10/12 metres per second to produce a few hundred kilowatts. When the speed is high (20/25 m/s) the generator is switched off for safety reasons. The progress made in the design of aeolian rotors in the last 10 years allow them to work at lower wind speed, catching a higher quantity of energy also at higher levels, increasing the quantity of wind power that can be exploited. Rotors with “mobile” blades have been created: by changing the blade inclination with a different wind speed it is possible to keep the quantity of power produced by the aerogenerator constant.