To understand how a wind turbine works, we must first have a clear idea of what a wind turbine is.

In this article, we discuss the basic principle and conversions involved in the operation of a wind turbine. The following areas will be covered;

How Does A Wind Turbine Work? Working Principle of A Wind Turbine

How Does A Wind Turbine Work? The Functions of Individual Components

How the Different Parts of A Wind Turbine Function

Summary of the Functions of Wind Turbine Components

What Conditions are Required for A Wind Turbine to Produce Electricity?

How the Wind Turbine Changes Orientation

Limitations and Disadvantages of Wind Turbines

Conclusion

References

 

A Wind Turbine is simply a renewable energy device which is used to produce electricity by converting wind (kinetic) energy through a series of linked processes. Wind turbines first convert kinetic energy from wind into mechanical energy, and then subsequently convert mechanical energy into electricity [6].

The wind energy is captured by rotor blades [19]. These blades are usually two or three in number, and may each have an average length of 50 meters [16]. In wind turbines, the rotor usually has a diameter of about 130 to 170 meters. The length of the rotor blades usually determines the electrical productivity of the wind turbine.

Wind energy causes the blades of the turbine to rotate, driving a generator which produces electricity. Because the blades often turn slowly, a multiplier may be used to increase the speed of rotation that reaches the generator, to about 2000 rotations per minute (rpm).

A summary of the working principle of a wind turbine is given in the following section of this article.  

 

How Does A Wind Turbine Work? Working Principle of A Wind Turbine

As mentioned earlier, wind turbines generate electricity by converting wind energy, through a relatively simple mechanism.  

Wind energy turns the blades of a rotor, which is directly connected to the shaft of the wind turbine [13]. The rotation of the blades and the rotor itself, represents the conversion of kinetic energy from wind, to mechanical energy that moves the parts of the wind turbine.

A gear box is in turn connected to the main shaft of the wind turbine. This gear box links the shaft to a generator [14]. When the blades and rotor are made to rotate by wind energy, the gear box and generator also rotate, because they are connected to the rotor by the shaft.  The rotation of the generator generates an electromagnetic field, which helps to produce and transmit electricity.

We can summarize the working principle of a wind turbine in the following points;

1). Wind energy (Kinetic) moves the rotor blades, causing the rotation of the rotor and all its connected components

2). The rotor begins to spin, making the shaft and gear box (which are connected to the rotor) to spin as well. Kinetic energy is converted to Mechanical energy in this stage

3). Mechanic energy from the rotor causes the generator to rotate, and an electromagnetic field is created. This stage involves the conversion of Mechanical energy to Electricity

4). The current which has been generated is transmitted to a converter, to make it usable for power supply

Based on the discussion so far, it is not difficult to understand that the amount of electricity produced by a wind turbine is proportional to the strength of the wind in any given place or time. Other factors that determine the performance of a turbine include the size and length of the rotor blades, the location of the turbine, and the efficiency of the generator.

 

How Does A Wind Turbine Work? The Functions of Individual Components

When it comes to producing electricity, the generator can be viewed as the main component of a wind turbine. This component is responsible for the final conversion of mechanical energy to electricity [7]. The generator in a turbine works on the principle of electromagnetism, which implies that when a conductor material is rotated within a magnetic field, it produces electricity by electromagnetic induction [8].

The role of generating electricity in a wind turbine is shared mainly between the wind, the rotor and the generator. While the wind provides the initial kinetic energy and torque to move the rotor; the rotor itself provides the mechanical energy to drive the generator, which produces electricity.

As we have earlier stated, the performance of a wind turbine depends on the intensity and speed of the wind. A controller is usually used to ensure that the wind turbine is making maximum use of the available wind energy, by orienting the blades and face of the turbine in the direction of best wind speed and intensity.

The controller in a wind turbine is equipped with an anemometer and a wind vane. These components help to detect the speed and direction of wind, respectively.

In most cases, wind turbines function optimally between wind speeds of about 8 and 55 miles per hour (mph). At speeds of more than 55 mph, most turbines are shut off, in order to prevent the parts from being damaged.

To produce electricity, the generator requires a fairly high rate of rotation. This is usually provided by a gear box, which multiplies the rotations of the rotor and the shaft from tens of rotations to thousands or rotations per minute.

The electric current produces by the generator is rectified to produce direct current DC, which is in turn converted to alternating current (AC), and is fed to the utility grid for the purpose of supplying power to electrical appliances. A step-up transformer is used in the transmission of the AC after it has been converted.

 

How the Different Parts of A Wind Turbine Function

Function of the Nacelle in A Wind Turbine

In a wind turbine, the nacelle is usually installed at height ranging from 50 to more than 100 meters at the top of the tower. With regards to the use of wind (kinetic) energy, the nacelle is the most important part of the wind turbine. This is because it is composed of all the major components of the wind turbine, which include the shaft, generator, brake assembly, and gear box [15].

Wind speed and direction are measured by the anemometer and wind vane. The yaw drive helps to control and change the orientation of the wind vane, to face the direction of best speed and intensity [4]. The Pitch control system controls the orientation of the rotor blades. These three components; including the pitch control, yaw drive, anemometer and wind vane, are all housed within the nacelle.

The wind vane detects the direction of wind at any given time. By the help of the anemometer, the suitability of the wind speed is determined. Wind turbines turbines generally function best at wind speeds of between 8mph (12.9km/h) to 55mph (88 5km/h).

When the direction of suitable wind speed has been detected, the yaw drive moves the face of the wind vane in this preferred direction, while the pitch control moves the rotor blades in the preferred direction as well. By this mechanism, the orientation of the wind vane is always in the best position to capture wind energy.

Based on the prevalent direction of wind in any location, the design of the nacelle and rotor assembly may be either downwind or upwind [12]. Downwind turbine designs have the rotor positioned behind the nacelle; while the upwind turbine designs have the rotor positioned in front of the rotor. These designs ensure that the system is able to capture wind in the most optimal way.

 

Function of the Rotor (Blades, Hub) in A Wind Turbine

In a wind turbine, the rotor plays the important role of converting kinetic energy from wind, to mechanical energy in the system, which is used to drive the generator [5].

The rotor is typically composed of two parts, which are the turbine blades, and the hub.

The hub is the part which connects the turbine blades to the rest of the system, through the main shaft [17]. It ensures that the mechanical energy produced by the rotor is efficiently transferred to the generator.

The turbine blades are designed to capture wind energy through a lift-and-drag mechanism [10]. This is possible because of the airfoil-shape of the turbine blades, which is the same design used to provide the lift force in aircrafts.

Two aerodynamic forces are generated from wind energy, by the turbine blades. These are the lift force, which acts perpendicular to the direction of the wind; and the drag force, which acts parallel to the direction of the wind.

The lift force acts on the downside of the turbine blade, moving it upward; while the drag force acts on the upper face of the turbine blade, pulling it along. These two forces combined, produces a torque which acts perpendicular to the wind direction, and spins the rotor of the turbine.

Because of the direct interaction of the turbine blades with enormous amounts of wind energy, they are considered to be very important to determine the efficiency and life expectancy of the wind turbine.

Turbine blades are designed in the form of a thin, resistant aerodynamic structure, and this design is continuously being improved to balance the alternate forces and prevent vibration or damage of the system.

 

Function of the Main Shaft in A Wind Turbine

A tubular, metallic component of the turbine; a turbine shaft plays the role of support and conveyance.

The main shaft supports the rotor, which comprises of the turbine blades and the hub. It also conveys (or transmits) the mechanical, rotary energy from the rotor to the other parts of the turbine that include the gear box and the generator.

 

Function of the Gear Box in A Wind Turbine

Alongside the main shaft, the gearbox helps to transfer the rotational force from the blades and rotor, to the generator of the wind turbine.

Typically, the gearbox serves to amplify the rotational speed of the turbine blades and rotor. This is necessary because the rotor is driven by wind at a relatively low speed compared to that which is needed by the generator to set up an electromotive field and produce electricity. The gearbox therefore converts this low-speed rotation to the required high-speed rotation for the generator.

In many turbines, the conversion ratio of rotational motion by the gearbox is about 90:1 (each rotation by the blades and the rotor is multiplied by the gearbox produce 90 rotations for the generator). This helps to produce more 1,000 rpm from only 15 rpm of the rotor and turbine blades. The gearbox also helps reduce the torque of the system, thereby increasing efficiency.

 

Function of the Controller in A Wind Turbine

Basically, the controller in a wind turbine plays the role of power management [9]. This means that it in charge of determining when the turbine is turned on or shut off.

A wind turbine comprises of computers which continuously monitor the environmental and operational conditions of the turbine. These computers compile the data which is collected, using this data to determine the routine of operation of the system.

The variables which are usually measured include the speed and direction of wind, which must be known in order to optimize the performance of the turbine. By the function of the controller, the turbine is able to start up at about 8mph, and shut off at about 55mph. This ensures that damage and inefficiency are both prevented.

 

Function of the Braking System in A Wind Turbine

We may consider the braking system in a turbine to be a safety component. This is because it protects all parts of the turbine by regulating the time and conditions of their operations.  

The braking system automatically carries out a series of emergency stops. The conditions under which these stops occur include when one or more of the system components becomes faulty; and when the environmental conditions are not suitable or optimal for operation.

During the average lifespan of a wind turbine (which is about 20 years or 175,000 hours), the braking system typically stops the turbine between 500 and 1,000 times.

The types of braking systems in wind turbines are mainly two. These are the aerodynamic and mechanical braking systems [3].

Mechanical braking system in a turbine comprises of a hydraulic, disc-shaped brake shoe system that acts as a supportive component for the aerodynamic braking system.

Aerodynamic braking systems on the other hand, consist of a mechanism that changes the orientation of the rotor blades. When there is need to shut-off the system, aerodynamic brakes cause the turbine blades to turn in a perpendicular direction to the direction of the wind, thereby making them resistant to induced motion.

The aerodynamic braking system is more efficient and effective than the mechanical braking system, because it provides a more rapid and less forceful way of shutting off the turbine, thereby preventing wear and tear of the system components [2]. As a result, it usually serves as the main braking system in turbines.

 

Function of the Generator in A Wind Turbine

In a wind turbine, the generator is simply the component which is used to generate electricity from the rotational motion of the turbine blades and rotor.

The turbine generator works by electromagnetic induction, and may come in any of different forms, which include;

-As an AC (Alternating Current) Generator

-As an AC Induction device or Alternator

-As a DC (Direct Current) device or Dynamo [1]

While the DC dynamo generator is most commonly utilized in small wind turbines, the AC generators are often used in larger wind turbines.

Wind speed is very important for running the generator of the wind turbine, as it directly determines the magnitude of mechanical energy which is supplied to the generator. This mechanical energy causes an electrical coil (conductor) to rotate within a magnetic field, producing electricity by electromagnetic induction, as outlined by Faraday’s Law.

Turbine generators operate based on minimum and maximum wind speed limits. The minimum wind speed is that below which the generator will not produce any electricity, because the rate of rotation of the rotor is too slow.

When the speed of rotation exceeds the maximum limit of the wind turbine, the generator will automatically stop. This mechanism is driven by the controller system, which protects the turbine from damage.

 

Function of the Pitch Control System in A Wind Turbine

Controlling and operating the angular orientation of the blades in a turbine is the main function of the pitch control system [11]. This function is important to ensure that the turbine is able to trap the maximum amount of wind energy possible. It is also helpful to protect the turbine from excessively high wind speeds.

The pitch control works as a closed loop system. This means that it is self-driven, without need for any external interference or operation. Pitch control systems comprise of a set of hydraulic devices, gears and electric motors, which detect and work on the basis of wind speed, and generator rotation.

 

Function of the Tower in A Wind Turbine

Turbine towers are tubular structures that may be composed of concrete or steel. They may also be a single structure or a composite of different sections.

The tower plays the role of supporting and hoisting the entire system. Components which are supported by the tower include the nacelle and the rotor of the turbine.

Performance of the turbine is dependent on the speed of available winds. This makes the tower very important to ensuring that the turbine functions optimally, because taller towers generally imply that the rotor and nacelle would have access to more wind energy at high altitude. This in turn leads to the generation of larger amounts of electricity.

 

Summary of the Functions of Wind Turbine Components

Of all its components, four are most critical to determine the successful working of the turbine. These components are the generator, nacelle, rotor blades, and turbine tower [18].

The Generator is responsible for producing electric current through the process of electromotive induction, by the rotation of a metallic conductor in the form of an electric coil, within a magnetic field.

As a result of differences in electric charge within the field, an electric current is induced in the coil. This current is subsequently converted from DC to AC and transmitted along power lines which help to distribute the power produced.

The Nacelle plays host to the rotor and generator. Based on the state of the rotary motion which is transmitted to the generator from the rotor, the turbine may be described as either direct-driven or gear-driven.

Direct-driven turbines are those in which the rotary motion is transmitted directly to the generator without any amplification or adjustment.

In a gear-driven turbine, efficiency is improved by multiplying the number of rotations provided by wind through the rotor. This multiplication is usually achieved using the gearbox, which produces up to 90 times of the rotor’s speed per minute, for driving the generator.

 

Rotor Blades of the turbine directly interact with wind. These components capture kinetic energy from wind, and drive the rotor using this energy.

Due to the exposure of turbine blades to harsh environmental conditions, they require a fairly robust design. These blades are usually made of carbon, resin, fiberglass or wood, and have a thin, airfoil geometry.

The Tower of a turbine usually ranges from about 50m to over 100m, while some large turbines may have towers that reach and exceed 200m. They are usually designed to be sturdy, resilient and resistant, therefore they have relatively large weight and are often coated with corrosion and radiation-resistant materials.

 

What Conditions are Required for A Wind Turbine to Produce Electricity?

For a wind turbine to function optimally, there are a number of conditions which must be satisfied. In general, the most important criteria for efficient performance of turbines are;

1. Optimal Wind Speed
2. Optimal Turbine Design

We may choose to call these the two main factors that determine wind turbine performance. However, the other required condition is;

3. Optimal Air Density

 

*Optimal Wind Speed

For a turbine to perform well, the speed of available wind should be sufficient to provide fast and consistent rotation of the rotor and generator. Increase in wind speed directly translates to an increase in rotary speed and electricity output.

Also, optimal wind speed should not exceed the bearable limits of the wind turbine, so as to prevent damage. The two limits of wind speed for optimal performance can be referred to as the cut-in and cut-out speeds.

*Optimal Turbine Design

The design of the turbine includes the geometry, efficiency and structural integrity of the various parts.

For optimal performance to be achieved, the design of the turbine should be made to suit the environmental conditions of the installation site. The rotor blades must have a large radius and airfoil geometry to capture as much wind energy as possible. However, the size of blades is determined by the size of the entire system and the conditions of the site of installation.

The generator and control systems must be efficient and effective at regulating the generation of electricity by the system.

*Optimal Air Density

Air density is controlled by temperature, altitude (or height), and atmospheric pressure. Higher density usually leads to higher energy output, because dense air is more capable of providing the lift-and-drag force to move the rotor blades, than light air.  

 

How the Wind Turbine Changes Orientation

As we have stated already, the orientation of the wind turbine usually changes to face the direction where the most wind energy can be captured. In general, two main changes in orientation may occur in a turbine. These are; change in the orientation of the rotor blades; and change in the orientation of the nacelle of the turbine.

The rotor blades can change orientation to face the most suitable wind streams at any given time. This change in orientation is controlled by the pitch control system of the turbine. The blades are connected to the hub which links them to the shaft and rotor. Pitch control may be either electrically or mechanically-driven.

Change in the orientation of the nacelle is controlled by the wind vane and anemometer, which help to detect the speed and direction of wind within the vicinity if the turbine. These data are monitored and evaluated by the main control system, which comprises of computers and microprocessors that activate the yaw motor, to cause the motion of the nacelle, as required.

 

Limitations and Disadvantages of Wind Turbines

1. Cost

Typically, the set-up stage of wind turbines involves significant expenses.

Huge investments are often required to manufacture and install the parts of a wind turbine. The need to transport large and heavy equipment to the installation site also incurs high cost.

2. Visual and Noise Pollution

In locations where wind turbines are installed, there is often the challenge of noise pollution, which is caused by the blades, rotor and generator of the turbine.

The imposing size of wind turbines is also a problem, especially in residential areas, so that their presence may cause visual or aesthetic pollution.

3. Unreliable Nature of Wind

Because wind energy is not always available, we cannot guarantee that a wind turbine will be able to provide electricity at any given time. This is a huge disadvantage, since energy supply must be reliable and secure to a fair extent for it to be trusted.

The unreliable nature of wind also means that wind turbines will most often need to be supplemented with electricity from the grid or any other source. This implies extra cost, and can be a relatively complex arrangement.

4. Environmental Impact

Because most wind turbines need to be set up in remote areas, their installation often requires the felling of trees and disruption of natural habitats.

Asides leading to deforestation, this poses a threat to wildlife which depend on their natural habitat to survive. The process of transporting equipment to the installation site can also have negative environmental consequences.

5. Geographic Restrictions

Wind energy is available in sufficient amount, only in specific geographical areas. This implies that the use of a turbine is possible in some locations only.

Another consequence of this is the need for elaborate transmission lines to convey the electricity from these remote locations, to the places where it is needed. The construction and maintenance of such transmission systems is usually expensive and complex.

6. Safety Challenges

Harsh environmental conditions, weather events, or vandalism can lead to the damage of wind turbines.

Such damage may involve the collapse of parts of the turbine, such as the blades and nacelle; or the collapse of the entire system. This is potentially harmful, especially if the turbine is situated in a human-occupied vicinity.

 

Conclusion

Based on the discussion in this article, wind turbines can be said to work in a series of three steps;

1). Wind (kinetic) energy is captured by the turbine blades

2). Kinetic energy is converted to mechanical energy by the rotor

3). Mechanical energy is converted to electricity by the generator

The parts of the turbine are each involved in the process of converting and amplifying wind energy to produce electricity. In the process of working, precautionary measures are taken by the safety components of the turbine, that include the braking and control systems.

 

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