The Wind turbines - Know it all !

three blades supported by a hub constituting the rotor
three blades supported by a hub constituting the rotor

The Wind turbines

They generally consist of three blades supported by a hub constituting the rotor and installed at the top of a vertical mast. This assembly is fixed by a nacelle that houses a generator.
An electric motor makes it possible to orient the rotor so that it is always facing the wind. The blades make it possible to transform the kinetic energy of the wind (energy that a body possesses because of its movement) into mechanical energy (mechanical movement of the blades). The wind rotates the blades between 10 and 25 revolutions per minute. The speed of rotation of the blades depends on their size : the larger they are, the less quickly they rotate. The generator transforms mechanical energy into electrical energy. Most generators need to run at high speeds (1,000 to 2,000 revolutions per minute) to generate electricity. It is therefore first necessary that the mechanical energy of the blades passes through a multiplier whose role is to accelerate the movement of the slow transmission shaft, coupled to the blades, to the fast shaft coupled to the generator. The electricity produced by the generator has a voltage of about 690 volts that cannot be used directly, it is treated through a converter, and its voltage is increased to 20,000 volts. It is then injected into the electricity grid and can be distributed to consumers.
The horizontal axis wind turbine consists of a mast, a nacelle and a rotor.
The horizontal axis wind turbine consists of a mast, a nacelle and a rotor.

Description of a wind turbine

The base, often circular and reinforced concrete in the case of onshore wind turbines, which maintains the overall structure; The mast 6 or the tower at the bottom of which we find the transformer that allows to increase the voltage of the electricity produced in order to inject it into the network; Nacelle 4, structure supported by the mast housing the various mechanical elements. Direct drive wind turbines are distinguished from those equipped with gear trains (gearbox / gearbox 5 ) depending on the type of alternator used. Conventional alternators require an adaptation of the rotational speed in relation to the initial movement of the rotor; Rotor 2, a rotating part of the wind turbine placed high in order to capture strong and regular winds. It is composed of 1 blades made of composite material that are set in motion by the kinetic energy of the wind. Connected by a hub, they can each be on average 25 to 60 m long and rotate at a speed of 5 to 25 revolutions per minute.

The power of a wind turbine

Power is the amount of energy produced or transmitted in one second. The wind turbines currently installed have a maximum power of between 2 and 4 MW, when the wind is strong enough.
Consider a wind turbine whose blades have a radius r. It is subject to the acceleration of a wind of speed v.
The energy captured by the wind turbine is proportional to the kinetic energy of the wind that passes through the wind turbine. All of this energy cannot be obtained because the wind speed is not zero after the wind turbine.
The maximum power (energy per second) captured by the wind turbine is given by Betz's formula :
P = 1.18 * R² * V³
R is in meters V in metres per second P in watts
Knowing the dimensions of the wind turbine and the wind speed at a given site, we can, using this formula, evaluate the power of a wind turbine. In practice, the useful power of a wind turbine is less than P. This is due to the fact that, from wind to distribution, there are several stages of energy conversion, each with its own efficiency : wind towards kinetic energy of the propeller Generator of electricity to transformer rectifier to storage to distribution. The optimal efficiency is 60 - 65%.0 For commercial wind turbines, the efficiency is in the range of 30 to 50%.0

Wind turbine and load factor

Even if it does not always operate at full power, a wind turbine operates and produces electricity on average more than 905660f the time. In order to characterize the notion of "deliverability" of a wind turbine, energy companies use an indicator called load factor. This indicator measures the ratio between the energy produced by an electricity production unit and the energy it could have produced if it were continuously operating at its maximum power. The average wind load factor is 23%.0

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