Wind energy is a renewable energy resource blessed by nature. It is one the most abundant form of renewable energy resource, which is available throughout the year. It is cost-effective and a reliable source of energy. Unlike fossil fuels, it is environment-friendly, clean, and free from greenhouse gases. Wind energy system is more popular than a solar energy system because it can generate electricity 24 hours a day while solar systems can generate electricity only when the sun shines. The energy crisis faced by the world can be eradicated by the good utilization of renewable energy resource.
In this detailed post, you will get to know how wind energy is converted to electrical energy, various components a wind energy system and integration of a wind energy system into the conventional power system. Various parts of a typical Wind Energy Conversion System (WECS) are mentioned and elaborated.
- Brief historical background
- What is a wind energy system?
- Explanation of important terminologies
- Conversion of wind energy into electrical energy
- Factors affecting wind energy system
- Small wind energy system (for households)
- Frequently asked questions
The concept of
Today, scientists are using wind energy as a renewable source of energy to generate electricity.
What is a Wind Energy System?
Wind is movement different gasses or air in the horizontal direction flow from higher pressure to lower pressure region. Speed and direction are two parameters to specify wind. Have you ever thought, what causes the wind to blow?
Causes of Wind:
The wind blows because of the difference in air pressure and the rotation of the earth. Due to the uneven heating of the earth because of solar radiation some regions of the earth get warmer while the rest of the regions are colder. Warmer regions receive more light and heat from the sun while colder regions receive less light and heat from the sun. Warmer regions have warm air (lighter in weight) while colder regions have cold air (denser in weight). This causes a difference in air pressure and air temperature. Of course, higher the difference in atmospheric pressure, the higher the speed of the wind.
Wind energy or wind power is the process of generating electricity with the help of wind. As we discussed,
It is a power generating device, which converts
Wind farms are the dedicated area of land, where a large number of wind turbines are installed for generating electricity. The wind farms are designed in such a way that the land should not waste. For example
There is a calculated distance between the two turbines. The two turbines are apart from each other by 5 to 10 times the diameter of blades. For example, if the diameter of the turbine blades is approximately 15 meters. The two turbines are approximately 150 meters apart. The spacing between the turbines agricultural purposes visible in the figure below.
Offshore wind farms:
Offshore (on the sea) winds arise from the sea. Offshore farms generate electricity from sea breeze or install near the
Onshore wind farms:
Onshore (on land) winds arise from land. Onshore farms generate electricity from offshore winds.
Types of Wind Turbines:
Horizontal Axis Wind Turbines (HAWT):
HAWT is further classified according to the number of blades. That is single blade rotor, two blades rotor and three blades rotor.
Another classification of HAWT according to the position of a rotor. Upwind turbines and downwind turbines.
I am not going into the details of various kinds. You can easily understand the design and its properties here.
The article covers the design of 3 blades, upwind horizontal axis wind turbine.
So, let’s get started.
You have seen a wind turbine is mounted on a tower with a strong foundation. The connection to the grid is provided at the foundation. The nacelle and rotor are at the top of the tower. To access nacelle and rotor there are stairs inside the tower. The rotor consists of blades, blade pitch control and rotor hub.
Wind turbines have heavy, bulky and very tall structure, they need a strong foundation. Modern turbines are even taller, heavier and powerful. Onshore and offshore wind turbines need different types of foundations. Of course, the foundation should be strong and rigid enough to support such a huge structure. For example, GE-1.5 megawatt model whole assembly weighs 164 tons and a total height of 328 feet .
2. Connection to grid
Connection to the grid is necessary because if the wind is not enough to generate electricity. Grid supplies your electricity needs. When the
Tower height consists of 40m to 100m. Taller towers capture more energy and hence generating more electricity. If the tower height doubles then its diameter is also going to be doubled. Tubular steel, lattice steel or concrete towers are popular. For HAWT the tower height must be two to three times greater than blades length.
4. Stairs to access top of tower
In order to access the top of the tower, for maintenance and repairs, stairs are provided inside the tower.
5. Yaw mechanism
Yawning is the movement of the turbine along the vertical axis. Yaw mechanism consists of the yaw motor. Yaw mechanism orients turbines to move according to the wind direction and speed. It is a part of upwind turbines only. The yaw mechanism communicates with the wind vane (through the controller) and turns the nacelle with the help of motors.
The Nacelle is nothing but the housing of generator, gearbox, braking system, shafts etc. It is a lightweight box made from glass fiber. It connects the
7. Electrical generator
Of course, another most important part of wind turbines. Electrical generator gets input from high-speed shaft which rotates at the speed of (1000-1800 rpm). The generator converts rotational motion into electrical energy. The electrical generators used in turbines are either asynchronous generators or induction generators. Modern turbines can generate 600-3000 kilowatts (kW).
The frequency of the generator is proportional to the speed of prime mover. So modern turbines utilize induction generators. Also, induction generators have a simpler structure, low investment costs, and low maintenance. Majorly, two types of induction generators are used in the wind energy system: Self Excited Induction Generators (SEIG) and Doubly Fed Induction Generators (DFIG).
The frequency of electricity generated is proportional to wind speed. The output of the generator is AC (having variable frequency or mismatched with transmission line) is converted to DC. The DC voltage is then converted to AC (frequency matched with the power grid).
8. Anemometer and wind vane
As you know anemometer is used to measure the speed of the wind. And wind vane tells us the direction of the wind. Of course, this is an important part for controlling the turbines automatically.
Wind turbines are designed to work in moderate weather. If there is wind speed greater than 25m/s then a signal from anemometer to the controller and controller shuts off the turbine. Similarly, turbines don’t work if the wind speed is as low as 5m/s. This system automatically takes the decision and protects the turbine in extreme weather.
9. Braking mechanism
Braking mechanism also provides safety of turbines in case of malfunctioning, over-speed (wind speed is unpredictable), overheating (generator).
Two types of braking mechanism available. These are aerodynamic and mechanical braking mechanism. Both of them work independently. Mechanical brakes are situated on between generator and gearbox. They are used as parking brakes
Aerodynamic brakes are used to turn the rotor blades perpendicular to the direction of the wind. All commercial HAWTs control pitch angle of their rotor blades, to minimize rotation speed.
The Low-speed shaft is connected to the left of
11. Rotor blades
The blades are foremost part of a turbine. Rotor blades are connected to the rotor hub. They face the wind, as the wind blows, blades try to rotate and lift according to the wind speed and power. The blades transmit power to the
12. Blade pitch control
Blade pitch control or blade angle adjustment. It is used to adjust rotation speed. Wind turbines have maximum and minimum speed limits. If the wind blows above or below these ranges turbines shut down. Pitch is an important part of large turbines. Wind turbines are designed to produce optimum output. But how this optimum output can be generated if the wind blows faster or slower than the optimum range. The speed and power of wind change frequently. The purpose of blade pitch is to adjust the blades (blades turn along the longitudinal axis) according to wind condition. For faster winds, it exposes less surface area to the wind.
13. Rotor hub
Rotor hub connects the rotor blades to the rest of the system. Rotor hub and rotor blades collectively called rotor. The rotor hub is connected to the
14. Low speed shaft
The rotor is connected to the low-speed shaft. And low-speed shaft is connected to the left of the gearbox. As the rotor spins, the low-speed shaft spins as well. In this way, the rotor transfers its mechanical energy (which is in the form of rotation) to the low-speed shaft. It can rotate up to low speed at 30-60 rpm.
15. High speed shaft
Gearbox low-speed to a high-speed shaft. And high-speed shaft drives the electrical generator. The h
This is an electronic controller effectively controls the turbines. You can optimize or control the power output of turbines by these control methods.
- Generator torque and speed
- Blade pitch control
- Rotation of the
Factors Affecting Wind Energy System:
There are certain parameters that can
- The shape and the length of turbine blades
- The speed of the wind
- Air density
1. The shape and the length of blades
The output of a
At higher altitudes, there are less obstruction like
3. The direction and speed of wind
The output of the wind turbine is dependent on both the speed and density of the wind. Of course, higher wind speeds tend to rotate blades faster. Due to the
P = 0.593*½*ρAV3
Where P = wind power
V = wind speed
A = rotor area
ρ = density of air
Betz Limit on Efficiency of a Wind Energy System
The constant 0.593 in the above equation is the Betz Limit. It was introduced by Albert Betz, a German physicist, in 1919. According to Betz’s law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind. The factor 16/27 (0.593) is known as Betz’s coefficient. So, the efficiency of a wind energy system can not surpass the theoretical limit of 59.3%. Practical utility-scale wind turbines achieve at peak 75% to 80% of the Betz limit.
The faster the wind speed, the greater the output of the turbine. It means wind speed is a major factor that can affect the efficiency of the whole system. Whenever someone decides to erect wind turbines, it is advisable to look into wind conditions at that place, for at least one year.
4. Air density
The third factor is air density, which is dependent on temperature, pressure
Frequently Asked Questions:
Difference between a windmill and a wind turbine/Wind Energy Sytstem
In essense, there is no difference in between the windmill and wind turbine. The windmill is an ancient term when wind energy used to drive mills (that is why it is named as windmill) and pump water. While a wind turbine (being a part a Wind Energy System) is used to generate electricity by converting wind energy into electrical power. Wind turbines have fewer blades than windmills. Windmills have to do more physical work, that’s why they are provided with more blades. Windmill converts wind energy into mechanical energy. While the wind turbines convert wind energy into electricity.
Do wind turbines produce noise?
HAWT are noisy and are popular in areas away from downtown. Commercial wind turbines produce noise just like a small jet plane. It causes health problems and noise pollution. In urban areas or home-based wind turbine systems utilize vertical axis wind turbines (VAWT). Vertical axis turbines are the first choice for homes because it requires less space and is less noisy. But the
How do wind turbines work when there is no wind?
If there is no wind, no electricity is produced. To derive a turbine the wind speed should be greater than the cut-in speed (that is approximately 4m/s). The anemometer is there to measure the speed of the wind.
Although, the Capacity Factor of a wind energy system is higher than many other renewable energy
We hope you’ve found out about the basic functioning of a wind energy system and how they convert wind energy into electric energy. There are other energy resources that need to be discussed in detail.
You may also want to read how electric energy is transmitted from generating stations to consumers and Load flow analysis of a power network.