Wind Power plant:
Basically a power plant is a place where electricity is produced. Wind energy describes the process by which wind rotates the blade of the turbine the wind consists of kinetic energy when it rotates the blades of the turbine then this energy is converted into mechanical energy with help of generator mechanical energy is converted into electrical energy. The mechanical energy is in the form of rotation.
Wind energy possesses kinetic energy due to which mariners used sails with the help of wind. Wind energy was used by the farmers to draw water from the wells and to grind their grains with the help of windmill. Now day’s electric energy is produced with the help of wind turbines. More than 25 percent per year wind energy usage is increased, in recent years but still, it only provides a small fraction of the world’s energy.
How do winds form?
The earth’s surface has both land and water let suppose that we have two places in which on one place the sun rays are falling while on other place sun rays are not falling. When the sun comes up, the air over the land heats up quickly when the air heats up it becomes warm the air rises up in the sky and hence low-pressure zone is created in the land than that over water. The heated air is lighter and it rises. Now in the second place, the sun rays are not falling hence the air in that place will be colder and it stays on the ground thus high-pressure zone is created in that area. As we know that air flows from the high-pressure zone to the low-pressure zone so air from the high-pressure zone will rashes to the low-pressure zone and hence wind will be formed.
The same process occurs between land and sea. The air on the sea is denser and having high pressure it replaces the air over the land this process happens in the morning time. In the night the land cools much faster than the sea so at this time the reverse process will occur the land will become a high-pressure zone and the sea will become a low-pressure zone. The movement of the airflow will be from land to sea.
During day time: air flows from sea to land
During night time: air flows from land to sea
Wind energy is utilized by various civilizations for various purposes. Sailors used wind energy to sail their boats in the ocean by wind energy. Wind energy is used as a windmill to draw water from the wells. We also used wind energy to dry clothes. Wind energy is used to make electricity. This purpose is served by the windmill. The basic principle of it is the same as every power plant. The turbine rotates the generator and electricity is being produced.
The kinetic energy in the wind turns the blades which are connected with the shaft. The shaft is connected with the gearboxes which are connected with the generator. When the wind will strike the blades it will start rotation which will turn the shaft and the shaft will turn the generator and generator will produce electricity which is sent through distribution and lines transmission to a substation, from the substation this energy is transmitted to our homes, schools, and business.
Parts of the wind turbine
The blades design is efficiently designed it can be mono blade, twin blade, and triple-blade for capturing the energy of strong, fast winds.
Mono blade turbine:
Mono blade turbine has a vertical tower for giving the required height to the mono blade horizontal axis turbine and an enclosure that enclose the generator and the gearbox. The shaft is connected with the blade gearbox and generator. If the air comes from the left side then it is called an upward direction and when the air comes from the right side then it is called a downward direction. When the air strikes the blade it will starts rotation which will rotate the shaft of the gearbox which will further rotate the generator. So the generator will produce electricity by converting mechanical energy. The length of the rotor is 15-25m. It requires counterweight to balancing purposes because it consists of one blade.
Twin blade horizontal axis turbine:
It works on the upward side direction of the blade when the air will strike the twin blade it will starts rotation which will turn the shaft which connected with the gearbox and generator and produce electricity. The vibration occurs due to force on the upper blade will high as compare to the lower blade at high speed. While the two-blade need to teeter unbalanced.
Triple blade horizontal axis turbine:
When the air strikes the blades the shaft will rotate and the generator produces electricity. No vibration problem occurs in triple-blade HAWT. Its production capacity is 15KW-3MW. Three blades turbine has smoother power output and balance gyroscopic force compare to two blade machine. Three-blade rotors have a simple rigid hub. The blade may be cross-linked for greater rigidity.
It is the central portion of the rotor wheel. All the blades are attached to the hub. The pith angle control mechanism is also provided inside the hub.
It houses the gearbox, generator, hydraulic system and yawing mechanism.
To capture the maximum surface area of wind the rotor is designed aerodynamically in order to spin the blades with high speed. The blades are made up of corrosion-resistant material, lightweight and durable. The best materials are composites of fiberglass and reinforced plastic
A gearbox magnifies or amplifies the rotor speed to the required generator speed rate. The gearbox is connected with the rotor through the shaft which is then connected with the generator.
Generators come in various sizes, Grid-connected has large wind turbine have induction generator relative to the output you wish to generate. Medium capacity has a synchronous generator to electrify villages and remote areas. Small capacity turbines use permanent magnet DC generators which supplies power to microwave stations and illuminating lighthouses. The nacelle is the housing or enclosure that seals and protects the generator and gearbox from the elements.
Brakes used to stop the rotor when power is not desired. Hydraulic disc brakes fitted to the shaft of the gear box.
Maximum wind energy is gain by the wind turbine with the help of tail vane. The tail vane maintains proper rotor pointing.
The tower supports the rotor and nacelle. The modern wind turbine generator is installed on tubular towers. The tower is much larger than the rotor diameter. Steel and concrete towers are being used.
How wind turbines work:
Windmills have been assisting mankind to convert the energy contained in wind to many useful other forms for the last two thousand years. Today wind turbine is capable of converting a great amount of energy in the wind into electricity. This is due to the blades which are developed using state of the art aerodynamic analysis and the other performance-enhancing equipment. The blade of the windmill has a lot of airfoil cross-sections consisting of different sizes and shapes from root to tip. The simple airfoil technology makes the windmill blade to rotate. Lift force is produced over an airfoil. For moving blade the relative wind velocity is:
Therefore the wind turbine blade is positioned in a tilted manner in order to align with the wind speed. As the blade velocity increases to the tip the relative wind speed becomes more inclined towards the tip. The blade requires a continuous twist from the root to the tip. However, this rotation cannot be coupled directly to the generator because the wind turbine blades typically turn at a very low rate of rpm due to the issues of noises and mechanical strength. Considering this low-speed rotation we cannot produce any meaningful electricity from a generator. When the gearbox is not connected with the generator its speed is maximum. The gearbox uses plenty of gear set arrangement to achieve a high-speed ratio. The speed ratio is approximately 1:90. A brake also sits in a nacelle. The function of the wind brake is to arrest wind blade rotation during excessively windy conditions. The cutoff speed is approximately 80 km/hr.
We always require some energy to rotate the turbine most wind energy comes from turbines that can be as tall as a 20-story building and have three 200-foot (60-meter)-long blades. We connect the windmill with the turbine; as the wind strikes the blades the wind mills start rotating, which turns a shaft of the turbine connected to a generator that produces electricity.
Consequently, the electricity that is produced is passed through cables towards the base where the step-up transformer is situated. The wind turbine should face wind normally for maximum power extraction. The wind does not flow always in one direction its flow is changing day by day. The speed and direction of the wind is measured by a velocity sensor on the top of the nacelle. The deviation in the wind direction is sent to the electronic controller which in turn sends an appropriate signal to the yawing mechanism to correct the error. The wind turbine will always be aligned with the wind direction because the yaw motor turns the nacelle.
The relative velocity angle of the wind will be changed according to the wind speed when the speed of the wind will be changing the velocity will also be changing. A blade tilting mechanism tilts the blades and guarantees a proper alignment of the blade with the relative velocity. When the relative wind flows the blades are always at the optimum angle of attack. To gain a good insight into a wind turbine efficiency assume that you are measuring wind speed upstream and downstream over wind turbines. The wind speed at the downstream is much smaller than the upstream.
Vout < Vin
This is because the blade absorbs some kinetic energy from the wind. This kinetic energy is converted into mechanical energy when the blades of the turbine rotate.
Pmechanical = 1/2mV2in – 1/2mV2out
It is an interesting fact that wind turbine absorbs 100 percent of the available kinetic energy only if the downstream wind speech becomes zero. However, zero wind speed at downstream is physically impossible condition. Zero downstream speed simply means that the whole flow is stock. This physical reality of the wind flow required a certain amount of exit wind speed to maintain the efficiency of the turbine. That means that there is theoretically maximum efficiency a wind turbine can achieve. This limit is known as Betz’s limit. The Betz’s limit is about 59.3%. it means that no wind turbine in the world can ever cross the efficiency limit of 59.3%.
Denmark is known as the city of winds about 45% of electricity in Denmark is produced by the wind mills. In terms of output:
- Germany leads the world
- India ranks 5th on the ranking
The modern turbine works when the wind strikes the blade at a speed of 6 to 9 miles per hour which is known as the cut-in speed. Turbines will shut down when the speed of the wind is too hard with the help of brakes in the turbine to prevent equipment damage.
The amount of electrical energy production in a given time by the wind turbine is known as the capacity factor. When the speed of the wind is less than 3 m/s then the power production will be zero because the blades of the turbine will not rotate with high speed but when the speed of the windmill is increasing the energy production will also be increasing. At 10m/s to 30m/s speed of the wind the windmill will produce maximum energy but when the speed of the wind is increased from 30m/s then there is danger of generator damage when the speed of the turbine reach to 35 m/s we apply a brake and stop the production of energy. So we can see that when the speed of the wind is minimum no energy is producing and when the speed of the wind is maximum then also we not producing energy. So the speed of wind must be in range for the production of energy. The generation in the wind turbines is of two types:
- Synchronous generation
- Asynchronous generation
In a synchronous generation the turbine speed rotation is fixed. The output voltage is synchronized with the frequency, voltage, and phase of the grid. These parameters of both the wind turbine and the grid must be the same. Otherwise, we will not be able to connect the windmill with the grid.
Modern wind turbines use asynchronous generation in which the turbine speed of rotation varies with the wind speed to give maximum power output. The asynchronous generation is more efficient than a synchronous generation. As the speed of the wind is changing in the asynchronous generation due to which the voltage and frequency both will be changing.
The equation for Wind Power:
We know that air consists of particles which contain kinetic energy which is represented by the following equation:
kinetic energy= 1/2 mv2
As we know that power is the time rate of change of energy so by taking derivative on both sides we get:
dE/dt=1/2 v2 dm/dt
P=1/2 v2 dm/dt
The mass flow rate of the wind can be given by the:
dx/dt is the time rate of change of distance which is called speed. So by putting this vale we get:
Now put this equation in the power equation we get:
The amount of power production will be directly proportional to the cube of speed; If the wind speed doubles, the power of the wind turbine will be increase eight times. The speed of the wind turbine has a large impact on power when there are small changes in the speed of the turbine. The power of the wind turbine is greatly affected by the speed.
The density of the air
The density of the air decrease when the elevation of the wind is denser the air, the more energy received by the turbine. Air density varies with elevation and temperature. The density of the air can be determined from the height of the Air from the sea level; when the air is above the sea level it’s density decrease and when the air is below the sea level it’s density increases. As the density has a direct relation with the power so when the density of the wind will increase the power of the turbine will be increased. From the above, we assume that wind turbines will produce more power when it is installed at a lower elevation and with cooler average temperatures.
Area of the turbine:
The area of the blade is greatly affects the power when the area of the turbine blade will be large it will capture more wind.
Types of wind turbines:
There are two types of wind turbines:
Horizontal axis wind turbine:
The horizontal axis means the rotating axis of the wind turbine is horizontal to the ground which is lightweight and adequate strength. The advantage of horizontal wind is that its blades are made up of glass fiber and reinforced plastic and is able to produce more electricity from a given amount of wind.
Horizontal-axis wind turbines (HAWT) have an airfoil of the cross-section to create lift as the air flows over them and the main rotor shaft and electrical generator at the top of a tower and may be pointed into or out of the wind. Forces like wind turbulence, gust, gravitational forces, and direction changes in wind considered while designing the turbine.
Vertical axis wind turbine:
Vertical axis wind turbines the system of the turbine stands vertical or perpendicular to the ground. It can be of two types:
- Darrious rotor in which rotor is D-shape
- H-type darrious rotor in which rotor is H-shape
The blade is attached to the shaft. The constructions of both types are similar. The shaft is attached to the gearbox. The gearbox is then attached to the generator. In the vertical axis, wind turbine blades can accept wind from any direction. This type of turbine was design by French engineer Darrien in 1972. Vertical axis turbines are powered by the wind coming from all 360 degrees means that its blades rotate when the wind came from any direction. This type of turbine is used in such places where the wind is not consistent.
A wind farm is a cluster of wind turbines (up to several hundred) erected in areas from each wind turbine we receive some power which will be step up and transmitted at medium voltage similarly all the wind turbines are connected with each other it is installed in such place where there is a nearly steady prevalent wind; such areas generally occur near mountain passes. This setup is known as the windmill.
How wind energy gets to you:
The turbines in a wind farm rotate at the speed of 15-20 rpm which are connected generators so the electricity they generate can travel from the wind farm to the power grid. The energy obtained from the wind farm is transmitted to the power grid. From the power grid, this energy is supplied to our homes.
Advantages of Wind Power
- Little to no global warming emission
- Unlike fossil fuels wind energy does not pollute air and water
- It is a renewable source of energy which is inexhaustible and resilient
- It is a cost-effective source of energy
- Wind energy resource is an infinite and reliable renewable energy resource
- Offshore wind farms producing energy, without affecting the landscape view.
- Reduces energy imports such as oil and gas from other countries
- Wind energy creates local and wealth employment
- Contributes to sustainable development
- Wind free source of energy which has no emissions
Production of Electricity by the wind turbine:
Currently, 2.5% of the electrical energy is produced by wind turbines in the world and further work is in progress to increase its production. Now days approximately 79 countries are producing electricity from the wind energy; In which 24 countries are producing high power more than 1,000 megawatts (MW). In terms of megawatt production of electricity in the world following countries have main markets
World largest turbines:
This list contains the turbines which physically exist. It does not include the turbines which are currently design.
The world’s largest wind turbine Vestas is located in the united kingdom with the capacity of producing electricity 8-9 MW and its height is about 220m. The rotor diameter of this turbine is 164m and the swept area is 21124. The root diameter is 4.6m. it is an offshore wind turbine.
Siemens SWT -8.0-154:
It is an 8MW wind turbine. It has a rotor diameter of 154m and a swept rotor area of 18600 This is an offshore turbine which is located in Germany.
Enercon E 126:
It generates about 7.58MW of energy. It is located in Belgium. It is the biggest direct-drive turbine in the world. Direct drive means that there is no gearbox in this turbine. it has very high hub height and relatively shorter blades which make it unique from the other wind turbines. The idea is that the turbine will apprehend it the higher elevation where the quality of the wind will be much better. The turbine has a hub height of 135m and a rotor diameter of 126m and a total height of 198m.
The rated power for this turbine is 7MW and the rotor diameter is about 171 m. one of the largest turbines is located in Scotland Methil, Fife.
Mingyang SCD 6.5:
This is the biggest two-bladed wind turbine which is designed by the Mingyang. It is located in China. It is offshore wind turbines produce 6.5MW power. It has a lightweight permanent magnet generator and it is adopted for China Typhon weather condition.
Spain has been one of the pioneering countries in Europe which are in onshore wind form installation and using the wind turbine to produce electricity. In Spain, the first wind turbine was installed about Thirty years ago. Spain is the first country which is producing maximum energy from the wind turbine approximately 20.9% of electrical energy is produced by the wind turbines in Spain.
Future of wind Turbine:
The wind industry has been shifting towards a large wind turbine over the past decade. The commercial wind turbine manufacture kick off their design rated 750KW and soon moves towards 2.3MW. Three years later the industry moves toward 3.2MW wind turbine. Now the turbine design is improved. The material and its behavior in real life windy condition engineer have been able to produce longer, more rigid and fatigue resistant blade. The direct-drive option has eliminated the gearbox. The gearbox maintenance is an essential part of the wind turbine. The gearbox failure can account for up to 80% of the incident that makes the turbine non-operational.
Limitation of windmills:
- Wind turbine requires such a place where the flow of wind is maximum and continuous
- The wind setup is very expensive
- The blades of the windmill are exposed to environmental factors like storm, sun, rain hence need higher maintenances increasing the further cost.