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Here is a compilation of essays on ‘Wind Turbine’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Wind Turbine’ especially written for school and college students.
Essay on Wind Turbine
Essay Contents:
- Essay on the Meaning of Wind Turbine
- Essay on the History of Wind Turbines
- Essay on the Resources Needed by Wind Turbines
- Essay on the Types of Wind Turbines or Wind Mills
- Essay on the Performance of Wind Turbines
- Essay on the Wind Potential of Wind Turbines
- Essay on Wind Turbine Size and Power Ratings
Essay # 1. Meaning of Wind Turbine:
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A wind turbine is a rotary device that extracts energy from the wind. If the mechanical energy is used directly by machinery, such as for pumping water, or grinding stones, the machine is called a windmill. If the mechanical energy is instead converted to electricity, the machine is called a wind generator, wind turbine wind turbine generator (WTG), wind power unit (WPU), wind energy converter (WEC) or aero generator.
The following points further make the difference between:
Wind turbines and Wind mills:
i. Windmills have been in use since the 9th century and use the kinetic energy (energy of motion) of wind to do mechanical work, like crushing grain or pumping water.
ii. Wind turbines use a generator to transform the kinetic energy of the wind into electricity without producing any greenhouse gases. The generator is essentially a magnet that creates an electrical current in a coil of wires when it spins.
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iii. Windmills are much shorter than wind turbines and usually have many blades. The blades catch more wind causing the windmill to be able to do more physical work. The propeller blades are connected to an axle with gears. The gears are connected to a vertical shaft that runs down the length of the tower and is connected to other mechanical equipment.
Windmills do work such as pump water or grind grain, which is why they are a common site on farms where they are used in crop production. They are not built to produce electricity.
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Wind turbines, like aircraft propeller blades, turn in the moving air and power in electric generator that supplies an electric current. Simply stated, a wind turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity.
Essay # 2. History of Wind Turbines:
Wind machines were used in Persia as early as 200 B.C. The wind-wheel of Heron of Alexandria marks one of the first known instances of wind powering a machine in history. However, the first practical windmills were built in Sistan, a region between Afghanistan and Iran, from the 7th century.
These were vertical axle windmills, which had long vertical drive-shafts with rectangle-shaped blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn and draw up water and were used in the grist-milling and sugarcane industries.
By the 14th century, Dutch windmills were in use to drain areas of the Rihine River delta. In Denmark by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first known electricity generating windmill operated, was a battery charging machine installed in 1887 by James Blyth in Scotland.
The first windmill for electricity production in the United States was built in Cleveland, Ohio by Charles F Brush in 1888 and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24-metre (79 ft) towers with four-bladed 23-metre (75 ft) diameter rotors. Around the time of World War I.
American windmill makers were producing 1,00,000 farm windmills each year, mostly for water-pumping. By the 1930s, windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap and windmills were placed a top prefabricated open steel lattice towers.
A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30-metre (98 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 percent, not much different from current wind machines.
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In the fall of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont. The Smith-Putnam wind turbine only ran for 1100 hours. Due to war time material shortages the unit was not repaired.
The first utility grid-connected wind turbine operated in the UK was built by John Brown & Company in 1954 in the Orkney Islands. It had an 18-metre (59 ft) diameter, three-bladed rotor and a rated output of 100 kW.
Essay # 3. Resources Needed by Wind Turbines:
Wind turbines in locations with constantly high wind speeds bring best return on investment. With a wind resource assessment it is possible to estimate the amount of energy the wind turbine will produce.
A quantitative measure of the wind energy available at any location is called the Wind Power Density (WPD). It is a calculation of the mean annual power available per square meter of swept area of a turbine and is tabulated for different heights above ground.
Calculation of wind power density includes the effect of wind velocity and air density. Color-coded maps are prepared for a particular area described, for example, as “Mean Annual Power Density at 50 Meters”.
In the United States, the results of the above calculation are included in an index developed by the U.S. National Renewable Energy Lab and referred to as “NREL CLASS”. The larger the WPD calculation, the higher it is rated by class. Classes range from Class 1 (200 watts/square meter or less at 50 meters altitude) to Class 7 (800 to 2000 watts /square meter). Commercial wind farms generally are sited in Class 3 or higher areas, although isolated points in an otherwise Class 1 area may be practical to exploit.
Essay # 4. Types of Wind Turbines or Wind Mills:
Modern wind turbines fall into two basic groups; the horizontal-axis variety, like the traditional farm windmills used for pumping water and the vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor. Most large modern wind turbines are horizontal-axis turbines.
In vertical-axis wind turbines, the axis of rotation is vertical with respect to the ground (and roughly perpendicular to the wind stream) and in Horizontal-axis turbines, the axis of rotation is horizontal with respect to the ground (and roughly parallel to the wind stream).
Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades and blade shape. Wind turbines convert wind energy to electricity for distribution.
A. Horizontal Axis Type Wind Turbine:
Horizontal-axis wind turbine (HAWT) have the main rotor shaft and electrical generator at the top of a tower and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.
Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted forward into the wind a small amount.
Downwind machines have been built, despite the problem of turbulence (mast wake), because they don’t need an additional mechanism for keeping them in line with the wind and because in high winds the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since cyclic (that is repetitive) turbulence may lead to fatigue failure most HAWTs are upwind machines.
Conventional horizontal axis turbines can be divided into three components:
i. The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low speed rotational energy.
ii. The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics and most likely a gearbox component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity.
iii. The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor yaw mechanism.
iv. Other equipment, including controls, electrical cables, ground support equipment and interconnection equipment.
Wind turbines can rotate about either a horizontal or a vertical axis, the former being both older and more common.
B. Vertical-Axis Wind Turbine:
Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable.
With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn’t need to support it and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque.
It is difficult to mount vertical-axis turbines on towers meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine.
Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life.
However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.
“Eggbeater” turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus. They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source or an additional Savonius rotor to start turning, because the starting torque is very low.
The torque ripple is reduced by using three or more blades which results in a higher solidity for the rotor; Solidity is measured by blade area divided by the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing.
Giromill is a subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting. The advantages of variable pitch are high starting torque; a wide, relatively flat torque curve; a lower blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight V or curved blades may be used.
Savonius wind turbine are drag type devices with two or more long helical scoops to give a smooth torque.
Advantages:
i. A massive tower structure is less frequently used, as VAWTs are more frequently mounted with the lower bearing mounted near the ground.
ii. Designs without yaw mechanisms are possible with fixed pitch rotor designs.
iii. The generator of a VAWT can be located nearer the ground, making it easier to maintain the moving parts.
iv. VAWTs have lower wind startup speeds than HAWTs. Typically, they start creating electricity at 6 m.p.h. (10 km/h).
v. VAWTs may be built at locations where taller structures are prohibited.
vi. VAWTs situated close to the ground can take advantage of locations where mesas, hilltops, ridgelines and passes funnel the wind and increase wind velocity.
vii. VAWTs may have a lower noise signature.
Disadvantages:
i. A VAWT that uses guy-wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guy wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guy wired models.
ii. The stress in each blade due to wind loading changes sign twice during each revolution as the apparent wind direction moves through 360 degrees. This reversal of the stress increases the likelihood of blade failure by fatigue.
iii. While VAWTs components are located on the ground, they are also located under the weight of the structure above it, which can make changing out parts very difficult if the structure is not designed properly.
iv. Having rotors located close to the ground where wind speeds are lower due to the ground’s surface drag, VAWTs may not produce as much energy at a given site as a HAWT with the same footprint or height.
C. Modern Wind Turbines:
Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of over 320 kilometres per hour (200 mph), high efficiency and low torque ripple, which contribute to good reliability.
The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 metres (66 to 130 ft) or more. The tubular steel towers range from 60 to 90 metres (200 to 300 ft) tall. The blades rotate at 10-22 revolutions per minute. At 22 rotations per minute the tip speed exceeds Fig. 1.57 Three bladed wind turbine. 300 feet per second (91 m/s).
A gear box is commonly used for stepping up the speed of the generator, although designs may also use direct drive of an annular generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system.
All turbines are equipped with protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes.
Advantages:
i. Variable blade pitch, which gives the turbine blades the optimum angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.
ii. The tall tower base allows access to stronger wind in sites with wind shear. In some wind shear sites, the wind speed can increase by 20% and the power output by 34% for every 10 meters in elevation.
iii. High efficiency, since the blades always move perpendicular to the wind, receiving power through the whole rotation. In contrast, all vertical axis wind turbines and most proposed airborne wind turbine designs, involve various types of reciprocating actions, requiring airfoil surfaces to backtrack against the wind for part of the cycle. Backtracking against the wind leads to inherently lower efficiency.
iv. The face of a horizontal axis blade is struck by the wind at a consistent angle regardless of the position in its rotation. This result in a consistent lateral wind loading over the course of a rotation, reducing vibration and audible noise coupled to the tower or mount.
Disadvantages:
i. The tall towers and blades up to 45 meters long are difficult to transport. Transportation can now amount to 20% of equipment costs.
ii. Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators.
iii. Massive tower construction is required to support the heavy blades, gearbox and generator.
iv. Reflections from tall HAWTs may affect side lobes of radar installations creating signal clutter, although filtering can suppress it.
v. Their height makes them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition.
vi. Downwind variants suffer from fatigue and structural failure caused by turbulence when a blade passes through the tower’s wind shadow (for this reason, the majority of HAWTs use an upwind design, with the rotor facing the wind in front of the tower).
vii. HAWTs require an additional yaw control mechanism to turn the blades and nacelle toward the wind.
viii. In order to minimize fatigue loads due to wake turbulence, wind turbines are usually sited a distance of 5 rotor diameters away from each other, but the spacing depends on the manufacturer and the turbine model.
Cyclic Stresses and Vibration:
Cyclic stresses fatigue the blade, axle and bearing resulting in material failures that were a major cause of turbine failure for many years. Because wind velocity often increases at higher altitudes, the backward force and torque on a horizontal-axis wind turbine (HAWT) blade peaks as it turns through the highest point in its circle. The tower hinders the airflow at the lowest point in the circle, which produces a local dip in force and torque.
These effects produce a cyclic twist on the main bearings of a HAWT. The combined twist is worst in machines with an even number of blades, where one is straight up when another is straight down. To improve reliability, teetering hubs have been used which allow the main shaft to rock through a few degrees, so that the main bearings do not have to resist the torque peaks.
The rotating blades of a wind turbine act like a gyroscope. As it pivots along its vertical axis to face the wind, gyroscopic precession tries to twist the turbine disc along its horizontal axis. For each blade on a wind generator’s turbine, precessive force is at a minimum when the blade is horizontal and at a maximum when the blade is vertical. The cyclic loading affects the design of the mechanical elements, structure and foundation of the wind turbine.
Essay # 5. Performance of Wind Turbines:
The overall η of an aero generator in calculated as follows:
η0 = ηA . ηg . ηc . ηgen
where η0 = overall conversion r| of an aero generator
ηg = η of gearing
ηc = η of coupling
ηg = η of generator
ηA = η of aero turbine
where Cp = Coefficient of performance.
The coefficient of performance of an aero turbine is 0.593 for horizontal axis wind machines. Wind speed plays an important role in power output.
The η of wind generator depends on the design of wind rotor and rotation speed expressed as:
Evaluating Wind Turbine Performance:
Wind turbines are rated at a certain wind speed and annual energy output.
Annual energy output = Power × Time
Example, for a 100 kW turbine producing 20 kW at an average wind speed of 25 km/h, the calculation would be:
100 kW × 0.20 (CF) = 20 kW × 8760 hours = 175,200 kWh
The Capacity Factor (CF) is simply the wind turbine’s actual energy output for the year divided by the energy output if the machine operated at its rated power output for the entire year. A reasonable capacity factor would be 0.25 to 0.30 and a very good capacity factor would be around 0.40. It is important to select a site with good capacity factor, as economic viability of wind power projects is extremely sensitive to the capacity factor.
Essay # 6. Wind Potential of Wind Turbines:
In order for a wind energy system to be feasible there must be an adequate wind supply. A wind energy system usually requires an average annual wind speed of at least 15 km/h.
The following Table represents a guideline of different wind speeds and their potential in producing electricity:
A wind generator will produce lesser power in summer than in winter at the same wind speed as air has lower density in summer than in winter.
Similarly, a wind generator will produce lesser power in higher altitudes – as air pressure as well as density is lower – than at lower altitudes.
The wind speed is the most important factor influencing the amount of energy a wind turbine can produce. Increasing wind velocity increases the amount of air passing the rotor, which increases the output of the wind system.
In order for a wind system to be effective, a relatively consistent wind flow is required, obstructions such as trees or hills can interfere with the wind supply to the rotors. To avoid this, rotors are placed on top of towers to take advantage of the strong winds available high above the ground. The towers are generally placed 100 metres away from the nearest obstacle. The middle of the rotor is placed 10 metres above any obstacle that is within 100 metres.
Essay # 7. Wind Turbine Size and Power Ratings:
Wind turbines are available in a variety of sizes and therefore power ratings. The largest machine has blades that span more than the length of a football field, stands 20 building stories high and produces enough electricity to power 1,400 homes.
A small home-sized wind machine has rotors between 8 and 25 feet in diameter and stands upwards of 30 feet and can supply the power needs of an all-electric home or small business. Utility-scale turbines range in size from 50 to 750 kilowatts. Single small turbines, below 50 kilowatts, are used for homes, telecommunications dishes or water pumping.