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WIND ENERGY
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CERTIFICATE
This is to certify that the student Mr. Devendra Singh of final year, have successfully completed the seminar presentation on “Wind Energy” towards the partial fulfilment of the degree of Bachelors of Technology (B. TECH) in the Mechanical Engineering of the Rajasthan Technical University during academic year 2018 under my supervision.
The work presented in this seminar has not been submitted elsewhere for award of any other diploma or degree.
Prof. Lalit Chouhan Counter Signed by:
Deptt. of Mechanical Engineering Prof. Shailendra Bohra
VIET, Jodhpur. HOD Mechanical Engineering
VIET, Jodhpur
ACKNOWLEDGEMENT
First of all, I thank the God Almighty for His grace and mercy that enabled me in the finalization of this seminar. Secondly I would also like to thank my Parents and Teachers who helped me a lot in finalizing this Seminar within the limited time frame.
Every seminar big or small is successfully largely due to effort of a number of wonderful people who have always given their valuable advice or lent a helping hand. I sincerely appreciate the inspiration, support and guidance of all those people who have been instrumental in making this seminar a successful.
I wish to express of gratitude to my guide to Prof. Lalit Chouhan, Mechanical Engineering Department to give me guidance at every moment during my entire thesis and giving valuable suggestion. He gives me unfailing inspiration and whole hearted co-operation in caring out my seminar work. His continuous encouragement at each work and effort to the push work are grateful acknowledged.
I am also grateful to Prof. Shailendra Bohra, Head of the Department, Mechanical Engineering for giving me the support and encouragement that was necessary for the completion of this seminar.
Devendra Singh
ABSTRACT
Seminar Presentation: Wind Energy
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his report describes about the wind power and its potential that can be harnessed in the future to meet the current energy demand. With detailed description of the wind turbine and the wind generator focus has been given on the wind blades or blades with the grid and the problems associated with it. The use of power electronics inn the circuitry and their applications have also been emphasized.
NAME: DEVENDRA SINGH
Mechanical Engineering (VIII SEMESTER)
Submitted to: Guided By:
Prof. Shailendra Bohra Prof. Lalit Chauhan
Head of Department
Mechanical Engineering
CONTENT
1. Introduction
2. Wind Energy
3. History of Wind Energy
4. Basic Principle of Wind Energy conversion
4.1 The Nature of The Wind
4.2 The Power in the Wind
4.3 Wind Energy Conversion
4.1 The Nature of The Wind
4.2 The Power in the Wind
4.3 Wind Energy Conversion
5. Wind Data Energy Estiomation
6. Site Selection Consideraton
7. Basic Componenets of Wind Energy
1) Rotor
2) The Windmill head
3) Transmissions
4)Generator
5) Controls
6) Towers
1) Rotor
2) The Windmill head
3) Transmissions
4)Generator
5) Controls
6) Towers
8. Classification of Wind Energy
1) Vertical axis wind turbine
2) Horizontal axis wind turbine
1) Vertical axis wind turbine
2) Horizontal axis wind turbine
9. Material for Wind Energy
Materials for blades
Glass and carbon fibers
Hybrid reinforcements
Natural fibers
Nano-engineered polymers and composites
10. Comparison with fossil-fuel turbine
11. Records
12. Operability
1. Introduction:
Wind: Wind results from air in motion. Air in motion arises from a pressure gradient. On a global basis one primary forcing function causing surface winds from the poles towards the equator is convective circulation. Solar radiation hears the air near the equator, and this low density heated air is buoyed up. At the surface it is displaced by cooler denser higher-pressure air flowing from the poles. In the upper atmosphere air near the equator the air thus tend to flow back toward the poles and away from the equator. The net results are a global convective circulation with surface winds from north to south in the northern hemisphere.
It is clear from above that the wind is basically caused by the solar energy irradiating the earth. This is why wind utilization is considered a part of solar technology. The wind is much more complex than solar because earth is rotating that causes Coriolis force resulting in an easterly win velocity component in the northern hemisphere. More complexity caused by the mountains, hills, trees and similar obstruction.
It has been estimated that 2% if all solar radiation falling on the face of the earth is converted to kinetic energy in the atmosphere and the 30% of this kinetic energy occurs in the lowest 1000m of elevation. It is thus said that the total kinetic energy of the wind in this lowest kilometer, if harnesses can satisfy several times the energy demand of a country.
Conversion of the kinetic energy of the wind into mechanical energy that can be utilized to perform useful work, or to generate electricity. The most machines for converting wind energy into mechanical energy consist basically of a number of sails, vanes, or blades radiating from a hub or central axis. The axis may be horizontal, as in more familiar windmills, or vertical, as it is in some cases. When the wind blows against the vanes or sails they rotate about the axis and the rotational motion can be made to perform useful work. Wind energy conversion devices are commonly known as Wind Turbine.
Because of the wind turbines produce rotational motion, wind energy is readily converted into electrical energy by connecting the turbines to an electric generator. The combination of wind turbine and generator is sometimes referred to as an aero generator.
2 Wind Energy
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inetic energy present in the wind is a promising source of renewable energy with significant potential in many parts of the World. The energy that can be captured by wind turbines is highly dependent on the local average wind speed. Regions that normally present the most attractive potential are located near coasts, inland areas with open terrain or on the edge of bodies of water. Some mountainous areas also have good potential. In spite of these geographical limitations for wind energy project sitting, there is ample terrain in most areas of the world to provide a significant portion of the local electricity needs with wind energy projects.
3 History of Wind Energy
Sailboats and sailing ships have been using wind power for at least 5500 years, and architects have used wind-driven natural ventilation in buildings since similarly ancient times. The Babylonian Emperor Hammurabi planned to use wind power for his ambitious irrigation project in the 17th century BC.
The first practical windmills were in use in Sistan, a region in Iran and bordering Afghanistan, at least by the 9th century and possibly as early as the 7th Century. These ‘Panemone Windmills’ were horizontal windmills. Vertical windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s. By 1000 AD, windmills were used to pump seawater for salt making in China and Sicily.
Development were going on and in 19th century the first wind turbine used for the production of electricity was built in Scotland in July 1887 by Prof James Blyth of Anderson’s College, Glasgow. Blyth’s 10m high, cloth-sailed wind turbine was installed in the garden of his holiday cottage at Marykirk in Kincardineshire and was used to charge. Accumulators developed by the Frenchman Camille Alphonse Faure, to power the lighting in the cottage, thus making it the first house in the world to have its electricity supplied by wind power.
In 1941 the world’s first megawatt-size (1.25MW) wind turbine was connected to the local electrical distribution system on the mountain known as Grandpa’s knob in Castleton, Vermont, United States. It was designed by Palmer Cosslett Putnam and manufactured by the S. Morgan Smith Company.
The development of wind power in India began in 1986 with the first wind farms being set up in coastal areas of Maharashtra (Ratnagiri), Gujarat (Okha) and Tamil Nadu (Tirunelveli) with 55 kW Vestas wind turbines. These demonstration projects were supported by the Ministry of New and Renewable Energy (MNRE).
Although windmills have been used for more than a dozen centuries for grinding grain and pumping water, interest in large scale electric power generation has developed over the past 50 years. A largest wind generator built in recent times was the 800KWe unit operated in France from 1958-1960. The flexible 3 blades propeller was about 35m in diameter and produced the rated power in a 60km/hour wind with a rotation speed of 47rpm. The maximum power developed was 12MWe.
In India the interest in the windmills was shown in the last fifties and early sixties. Apart from importing a few from outside, new designs were also developed, but it was not sustained. It is only in the last few years that development work is going on in many institutions. An important reason for this lack of interest in wind energy must be that wind, in India are relatively low and very appreciably with the seasons. Data quoted by some scientists that for India wind speed value lies between 5km/hr. These low and seasonal winds imply a high cost of exploitation of wind energy. Calculations based on the performance of a typical windmill have indicated that a unit of energy derived from a windmill be at least several times more expensive than energy derivable from electric distribution lines at the standard rates, provided such electrical energy is at all available at the windmill site.
Now a day the world using 19% power by wind and India using wind power as 9.87%.
ITALIAN DESIGNERS PROPOSE SOLAR WIND BRIDGE
4 Basic Principle of wind Energy Conversion
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ind turbines operate on a simple principle. The energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a generator to create electricity.
The wind having kinetic energy that kinetic energy is used to rotate the blade of the windmill. Due to rotation of the blades the turbines rotate and the electricity is produced.
The wind strikes with the rotor blade and the blades rotate. Since wind don’t flows with a uniform order of speed, a gear box is used who takes the power from a shaft connected to the blades. The gear box gears up the power or the speed of the further rotating shaft with uniformity. This shaft is connected to a generator in which it rotates the turbine and cut the flux between the two magnetic poles and produce the electricity.
The circulation of air in the atmosphere is caused by the non-uniform heating of the earth’s surface by the sun. The air immediately above a warm area expands, it is forced upwards by cool, denser air which flows in form surrounding areas causing a wind. The nature of terrain, the degree of clover and the angle of the sun in the sky are all factors which influence this process. In general, during the day the air above the land mass tends to heat up more rapidly than the air over water. In coastal regions this manifests itself in a strong onshore wind. At night the process is reversed the air cools down more rapidly over the land and the breeze therefore blows off shore.
The main planetary winds are caused in much the same way: Cool surface air sweeps down from the poles forcing the warm air over the tropics to arise. But the direction of these massive air movements is affected by the rotation of the earth and the net effect in a large counter-clockwise circulation of air around low-pressure areas in the northern hemisphere, and clockwise circulation in the southern hemisphere.
Wind speed increase with height. They have traditionally been measured at a standard height of 10m where they are found to be 20-25% greater than close to the surface. At the height of 60m they may be 30-60% higher because of the radiation in the drag effect of the earth’s surface.
Wind possesses energy by virtue of its motion. Any device capable of slowing down the mass of moving air, like a sail or propeller, can extract part of the energy and convert it into useful work. Three factors determine the output from a wind energy converter:
I) The Wind Speed
II) The cross-section of wind swept by rotor
III) The overall conversion efficiency of the rotor, transmission system and generator of pump.
No device, however well-designed, can extract all of the wind’s energy because the wind would have to be brought to a halt and this would prevent the passage of more air though the rotor. The most that is possible is for the rotor to decelerate the whole horizontal column of intercepted air to about one-third of its free velocity. A 100% efficient aerogenerator would therefore only be able to convert up to a maximum of around 60% of the available energy in wind into mechanical energy. Well-designed blades will typically extract 70% of the theoretical maximum, but losses incurred in the gearbox, transmission system and generator or pump could decrease overall wind turbine efficiency to 35% or loss.
The power in the wind can be computed by using the concept of kinetics.
Where
D = Diameter
v = Velocity of wind
The fraction of the free-flow wind power that can be extracted by a rotor is called the Power-Coefficient; thus
Traditional windmills were used extensively in the Middle Ages to mill grain and lift water for land drainage and watering cattle. Wind energy converters are still used for these purposes today in some parts of the world, but the main focus of attention now lies with their use to generate electricity. There is also growing interest in generating heat from the wind for space and water heating and for glass-houses but the potential market is much smaller than for electricity generation.
The term “Wind Mill” is widely used to describe wind energy conversion systems, however it is hardly an opt. description any more. Modern wind energy conversion system is more correctly referred to as ‘WECS’, ‘aerogenerators’. ‘wind turbine generator’, or simply ‘wind turbines’.
However, for many of the uses to which electricity is put, the interruption of supply may be highly inconvenient. Operators or users of wind turbines must ensure that there is some form of back-up to cover periods when there is insufficient (or too much) wind available.
Small Producers: Private citizens in several countries have won the right to operate wind generators and other renewable energy system and to export power to the grid. For most small wind generators this requires that the output is conditioned so that it conforms to the frequency and phase of the mains supply. Power conditioning is readily achieved using an electronic black-box called a ‘synchronous inverter’, and although this is an expensive item of equipment, it does eliminate the need for batteries and for conversion of home appliances to run on DC.
Large Producers: Large and Medium sized wind generator are designed to give a stable and constant electrical output over a wide range of wind speeds and to feed current directly into the grid. They operate primarily as fuel savers, reducing the utility’s total fuel burn.
The choice of generator type depends on the size of the local distribution grid and its associate generating capacity. An induction generator would normally be used where there is a significant amount of other generating capacity. Inducting generators are robust and reliable and require minimal control equipment. For isolated networks where, other local generating capacity is limited, and where a high degree of autonomous control is required, a synchronous generator is more appropriate. Synchronous generators are more complex and therefore more expensive than induction machines.
Lift & Drag: The basis for wind energy conversion, the extraction of power, and hence energy, from the wind depends on creating certain forces and applying them to rotate a mechanism. There are two primary mechanisms for producing forces from the wind:Lift and Drag.
By definition of lift forces act perpendicular to the air flow, while drag fprces act in the direction of flow. Lift forces are pruduced by changing the velocity of the air stream flowing over either side of the lifting surface: speeding up the air flow causes the presssure to drop, while slowing the air stream down leads to increase in pressure. In other words, andy change in velocity generates a pressure difference acress the lifting surfcace. This pressure difference produces a force that beegins to act on the high pressure side and moces towards the low pressure side o thelifting surface which is called an airfoil. A good airfoil has a high lift/drag ratio, in some cases it can generate lift perpendicular to the air stream direction that are 30 times as great as the drag force parallel to the flow. The lift increases as the angle formed at the junction of the airfoil and the air-stream becomes less and less actute, upto the point where the angle o the air flow in the low pressure side become excessive. When this happens, the air flow breaks away from the low pressure side. A lot of turbulence ensues, the lift decreases and the drag increases quite substantially; this phenomenon is known as stalling. For efficient operation, a wind turbine blade needs to functon with as much lift and as little drag as possible because drag dissipates energy. As lift does not involve anything more complex thandeflecting the air flow, it is usually an efficient process. The design of each wind turine specifies the angle at which the airfoil should be set to achieve the maximum lift todrag ratio.
5 Wind Data and Energy Estimation
The seasonal as well as instantaneous changes in winds both with regard to magnitude and direction need to be well understood to make the best use of them in windmill designs. Winds are known to fluctuate by a factor of 2 or more within seconds. This calls for a proper recording and analysis of the wind characterstics.
There are various ways the data on wind behaviour is collected depending on the use it is intended to be put into. The horuly mean wind velocity as collected by the meterological observation is the basi data used in a windmill designs. The hourly mean is the one averaged over a particular hour of the day, over the day, month, year and years. The factors which affect the nature of the wind close to the surface of the earth, they are:
a) Latitude of place
b) Altitude of the place
c) Topography of the place
d) Scale of the hour, month or year
Wind beign an unsteady phenomenon, the scale of the periods considered is an important set of data required in the design. The hourly mean velocity provides the data for establishing te potential of the place for tapping the wind energy. The scale of the month is useful to indicate whether it is going to beuseful durig particualr periods of the year and what storage is necessary is to be provided for. Thedata based on scale of the hour is useful for mechanical aspects o design.
The values of Vg and hg amd m depends on the nature of the terrain, which asre classified as
i) Open terrain with few obstacles (Open land, lake, shores, deserts, parairies etc.)
ii) Terrain with uniformly convered obstacles (Wood lands, small towns, suburbs, etc.)
iii) Terrain with large and irregualr objects (Large city centres, country with breaks o large trees etc.)
6 Site Selection Consideration
The power available in the wind increases rapidly with the speed, hence wind energy conversion machies shoulb be located preferable in areas where the winds are strong and persistent. Although daily winds at a given site may be highly variable, the monthly and especially annual average speeds are remarkably constant from year to year. The major contrubution to the wind power available at a given site is actually made by winds with speeds above the average. Nevertheless, the most suitable sites for wind turbines would be found in areas where the annual average wind speeds are known to be moderately high or hing.
i) High annual average wind speed. A fundamental requirements ot be successful use of WECS (wind energy converison system), obviously, is an adequate supply of wind as stated above. The velocity is the critical parameter. The power in the wind Pw , through a given cross-sectional area for a uniform wind velocity V, is
Pw = KV3;
ii) Availability of Anemometery data is another important siting factor. The principle object is to measure the wind speed which basically determines the WECS output power, but there are many practical difficulties with the instrumentation and measurement methods. The anemometer height above ground, accuracy, liearlrity, location on the support tower, shadowing and inaccurate readings therefrom, icing inertial of rotor whether it measures the horizontal velocity component or vertical, and temperature effect are a few of the many difficulties encountered. The anemometery data should be available over some time period at the precise spot whete any proposed WECS is to be built and that this hould be accomplished vefore a siting decision is made.
iii) Availability of wind Vt curve at the proposed site, this important curve determines the maximum energy in the wind and hence is the principal initially controlling factor in predicting the elecrical output and hence renenur return of the WECS machine. It is desirable to have average wind speed V such as V > 12-16 m/hr which is avout the lower limit at which present large scale WECS generators cut in i.e. start turning. Wind Vt curve also determines the reliability of the delivered WECS generator power, for if the wind curve goes to zero there will be no generated power during lower than if the calm periods are short. In making such reliability estimates it is desirable to have measured Vt cureve over about a 5 year period for the highest confidence level in the reliability estimate.
iv) Wind Structure at the Proposed site, the ideal case for the WECS would be a site such that the Vt curve was flat i.e. a smooth stead wind that blows all time; but a typical site is always less than ideal. Wind specially near th eground is turbulent and gusty, and changes rapidly in driection and in velocity. This departure from homogeneous flow is collectively referred to as “the structure of the wind”.
v) Altitude of the proposed site, it affects the air density and thus the power in the wind and hence the useful WECS electirc power output. Also, as is well known, the winds tend to have higher velocities at higher altitudes.
vi) Terrain and its aerodynamic, one should know about terrain of the site to be chosen. If the WECS is to be placed near the top but not on the top of a not too blunt hill facing the prevailing wind, then it may be possible to obtain a ‘speed up’ of the wind velicity over what it would otherwise be. Also the wind here may not flow hirizontal making it necessary to tip the axis of the rotor so that the aeroturbine is always perperdicular to the actual wind flow.
vii) Local ecology, if the surface is bare rock it may mean lower hub height hence lower structure cost. If trees or grass or vegetation are present, all of which tend to destructure the wind, then higher hub heights will be needed resulting in larger system costs than the bare ground case.
viii) Distance ot Roads or Railways, this is another rfactor the system engineer must consider for heavy machinery, structures, materials, blades and other apparatus will have to be moved into any chosen WECS site.
ix) Nearness of site to local centre/users, this obvious criterion minimizes transmission line length and hence losses and costs. After applying all the previous siting criteria, hope fully as one narrows the proposed WECS sites to one or two they would be relatiely near to the users of the generated electric energy.
x) Nature of ground, ground condition should be such that the foundations for a WECS are secured. Ground surface should be stable. Erosion problem should not be there, as it cold possibly later wash out the foundations of a WECS, destroying the whole system.
xi) Favourable land cost, land cost should be facourable as this along with other siting costs, enters into the total WECS system cost.
xii) Other conditions such as icing problem, salt spray or blowing dust should not present at the site, as they may affect aeroturbine blades, or environmental is generally adverse to machinery and electircal apparatus.
7 Basic Components of Windmill
The main components of a WECS are shown in figure, in block diagram form.
II) The Windmill head
III) Transmissions
IV) Generator
V) Controls
VI) Towers
Aeroturbines convert enery in moving air ot rotary mechanical energy. In general, they require pitch controal and yaw control (only in the case of horizontal or iwnd axis machines) for proper operation. A mechanical intercase consisting of a step up gear and a suitable oupling reansmits the rotary mechanical energy to an electrical generator. The output of this generator is onnected to the load or power grid as the application warrants.
Yaw control, for locatities with the praveliling wind in one direction, the design of a turvine can be greatly simplified. The rotor can be in a fixed rientation with the swept area perpendicular to the predominant wind direction. Such a machine is aid to be yaw fixed.
I) Rotor:
Rotors are mainly of two types:
i) Horizontal axis rotor
ii) Vertical axis rotor
One advantage of vertical axis machines is that they operate in all wind directions and thus need no yaw adjustment.
The rotor is only one of the important componenets. For an effective utilization, all the components need to be properly designed and matched with the rest of the components.
II) WindMill Head:
Windmill head supports the rotorm housing the rotor bearing. It also houses any contrl mechanism incorporated like changing the pitch of the blades for safety devices and tail vane to orient the rotor to face the wind. The latter is facilitated by mounting it on the top of the supporting structure on suitable bearings.
III) Transmissions:
The rate of rotation of large wind turbine generators operating at rated capacity or below, is conveniently contralled by varying the pitch of the rotor blades, but it is low, about 40 ot 50 revolutions per minute. Because optimum generator output requires much greater rates of rotation, such as 1800rpm, it is necessary to increase greatly the low rotor rate of turning. Among the transmission are mechnaical systems involving fixed ratio gears, belts, and chains, singly or in combination or hydraulic systems involving fluid fumps and motors. Fixed ratio gears are recommended for top mounted equipment because of their high efficiency, known cost and inimum system risk. For bottom monted equipment which requires a right-angle drive, transmission costs might be reduced substantially using large diameter bearing with ring gears mounted on the hub to serve as a transmission to increase rotor speed to generator speed. Such combination offers a high degree of design flexibility as well as large potential savings.
IV) Generators:
Either constant or variable speed generators are a possibility, but variable speed units are expensive and/or unproved. Among the ocnstant speed generator candidates for use are synchronous induction and permanent magnet types. The generator of choice is the synchronous system because it is very versatile and has an extensive data base. Other electrical component and systems are, however, under development.
8 Classification of WECS
The world's tallest vertical-axis wind turbine, in Cap-Chat, Quebec
Vortexis Schematic
A vertical-axis wind turbines (VAWT) is a type of wind turbine where the main rotor shaft is set transverse to the wind (but not necessarily vertically) while the main components are located at the base of the turbine. This arrangement allows the generator and gearbox to be located close to the ground, facilitating service and repair. VAWTs do not need to be pointed into the wind, which removes the need for wind-sensing and orientation mechanisms. Major drawbacks for the early designs included the significant torque variation or “ripple" during each revolution, and the large bending moments on the blades. Later designs addressed the torque ripple issue by sweeping the blades helically.
A vertical axis wind turbine has its axis perpendicular to the wind streamlines and vertical to the ground. A more general term that includes this option is "transverse axis wind turbine" or "cross-flow wind turbine." For example, the original Darrieus patent, US Patent 1835018, includes both options.
Drag-type VAWTs such as the Savonius rotor typically operate at lower tip speed ratios than lift-based VAWTs such as Darrieus rotors and cycloturbines.
2. Horizontal axis
Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position
A turbine blade convoy passing through Edenfield, England
Offshore Horizontal Axis Wind Turbines (HAWTs) at Scroby Sands Wind Farm, England
Onshore Horizontal Axis Wind Turbines in Zhangjiakou, China
Horizontal-axis wind turbines (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 servomotor. 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.
Any solid object produces a wake behind it, leading to fatigue failures, so the turbine is usually positioned upwind of its supporting tower. Downwind machines have been built, because they don't need an additional mechanism for keeping them in line with the wind. In high winds, the blades can also be allowed to bend which reduces their swept area and thus their wind resistance. In upwind designs, turbine blades must be 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.
Turbines used in wind farms for commercial production of electric power are usually three-bladed. These have low torque ripple, which contributes to good reliability. The blades are usually colored white for daytime visibility by aircraft and range in length from 20 to 80 meters (66 to 262 ft). The size and height of turbines increase year by year. Offshore wind turbines are built up to 8MW today and have a blade length up to 80 meters (260 ft). Usual tubular steel towers of multi megawatt turbines have a height of 70 m to 120 m and in extremes up to 160 m.
Rotational speed
The blades rotate at 10 to 22 revolutions per minute. At 22 rotations per minute the tip speed exceeds 90 meters per second (300 ft/s). Higher tip speeds means more noise and blade erosion. 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 featheringthe blades into the wind which ceases their rotation, supplemented by brakes
9 Materials and recent developments
Materials that are typically used for the rotor blades in wind turbines are composites, as they tend to have a high stiffness, high strength, high fatigue resistance, and low weight. Typical resins used for these composites include polyester and epoxy, while glass and carbon fibers have been used for the reinforcing material. Construction may use manual layup techniques or composite resin injection molding. As the price of glass fibers is only about one tenth the price of carbon fiber, glass fiber is still dominant.
New designs
As competition in the wind market increases, companies are seeking ways to draw greater efficiency from their designs. One of the predominant ways wind turbines have gained performance is by increasing rotor diameters, and thus blade length. Retrofitting current turbines with larger blades mitigates the need and risks associated with a system-level redesign. As the size of the blade increases, its tendency to deflect also increases. Thus, from a materials perspective, the stiffness-to-weight is of major importance. As the blades need to function over a 100 million load cycles over a period of 20–25 years, the fatigue life of the blade materials is also of utmost importance. By incorporating carbon fiber into parts of existing blade systems, manufacturers may increase the length of the blades without increasing their overall weight. For instance, the spar cap, a structural element of a turbine blade, commonly experiences high tensile loading, making it an ideal candidate to utilize the enhanced tensile properties of carbon fiber in comparison to glass fiber. Higher stiffness and lower density translates to thinner, lighter blades offering equivalent performance. In a 10-MW turbine—which will become more common in offshore systems by 2021—blade lengths may reach over 100 m and weigh up to 50 metric tons when fabricated out of glass fiber. A switch to carbon fiber in the structural spar of the blade yields weight savings of 20 to 30 percent, or approximately 15 metric tons.
Some of the most common materials which are being used for turbine blades now and will be in the future are summarized below:
The stiffness of composites is determined by the stiffness of fibers and their volume content. Typically, E-glass fibers are used as main reinforcement in the composites. Typically, the glass/epoxy composites for wind blades contain up to 75 weight % glass. This increases the stiffness, tensile and compression strength. A promising source of the composite materials in the future is glass fibers with modified compositions like S-glass, R-glass etc. Some other special glasses developed by Owens Corning are ECRGLAS, Advantex and most recently WindStrandTM glass fibers. The WindStrandTM glass fibers show15 percent higher stiffness and up to 30 percent higher strength when compared to E-glass.
These include E-glass/carbon, E-glass/aramid and they present an exciting alternative to pure glass or carbon reinforcements. that the full replacement would lead to 80% weight savings, and cost increase by 150%, while a partial (30%) replacement would lead to only 90% cost increase and 50% weight reduction for 8 m turbine. The world currently longest wind turbine rotor blade, the 88.4 m long blade from LM Wind Power is made of carbon/glass hybrid composites. However, additional investigations are required for the optimal composition of the materials
Natural fibers like flax, hemp, jute etc. are also used as materials for wind blades. The advantages of these are the low costs, availability and environmental friendliness. The disadvantages are the quality variations, high moisture uptake and low thermal stability of the raw fibers.
Additions of small amount (0.5 weight %) of nanoreinforcement (carbon nanotubes or nanoclay in the polymer matrix of composites, fiber sizing or interlaminar layers can allow to increase the fatigue resistance, shear or compressive strength as well as fracture toughness of the composites by 30–80%. Research has also shown that that the incorporation of small amount of carbon nanotubes/CNT can increase the lifetime up to 1500%.
Costs
While the material cost is significantly higher for all-glass fiber blades than for hybrid glass/carbon fiber blades, there is a potential for tremendous savings in manufacturing costs when labor price is considered. Utilizing carbon fiber enables for simpler designs that use less raw material. The chief manufacturing process in blade fabrication is the layering of plies. By reducing the number of layers of plies, as is enabled by thinner blade design, the cost of labor may be decreased, and in some cases, equate to the cost of labor for glass fiber blades.
Other materials
Materials for wind turbine parts other than the rotor blades (including the rotor hub, gearbox, frame, and tower) are largely composed of steel. Modern turbines uses a couple of tonnes of copper for generators, cables and such. Smaller wind turbines have begun incorporating more aluminum based alloys into these components in an effort to make the turbines more lightweight and efficient, and may continue to be used increasingly if fatigue and strength properties can be improved. Prestressed concrete has been increasingly used for the material of the tower, but still, requires much reinforcing steel to meet the strength requirement of the turbine. Additionally, step-up gearboxes are being increasingly replaced with variable speed generators, increasing the demand for magnetic materials in wind turbines., In particular, this would require an increased supply of the rare earth metal neodymium.
10 Comparison with fossil-fuel turbine
Advantages
Wind turbines are generally inexpensive. They will produce electricity at between two and six cents per kilowatt hour, which is one of the lowest-priced renewable energy sources. And as technology needed for wind turbines continues to improve, the prices will decrease as well. In addition, there is no competitive market for wind energy, as it does not cost money to get ahold of wind. The main cost of wind turbines are the installation process. The average cost is between $48,000 and $65,000 to install. However, the energy harvested from the turbine will offset the installation cost, as well as provide virtually free energy for years after.
Wind turbines provide a clean energy source, emitting no greenhouse gases and no waste product. Over 1,500 tons of carbon dioxide per year can be eliminated by using a one megawatt turbine instead of one megawatt of energy from a fossil fuel. Being environmentally friendly and green is a large advantage of wind turbines.
Disadvantages
Wind turbines can be very large, reaching over 140 metres (460 ft) tall and with blades 55 metres (60 yd) long, and people have often complained about their visual impact.
Environmental impact of wind power includes effect on wildlife, but can be mitigated if proper monitoring and mitigation strategies are implemented. Thousands of birds, including rare species, have been killed by the blades of wind turbines, though wind turbines contribute relatively insignificantly to anthropogenic avian mortality. For every bird killed by a wind turbine in the US, nearly 500,000 are killed by each of feral cats and buildings. In comparison, conventional coal fired generators contribute significantly more to bird mortality, by incineration when caught in updrafts of smoke stacks and by poisoning with emissions byproducts (including particulates and heavy metals downwind of flue gases). Further, marine life is affected by water intakes of steam turbine cooling towers (heat exchangers) for nuclear and fossil fuel generators, by coal dust deposits in marine ecosystems (e.g. damaging Australia's Great Barrier Reef) and by water acidification from combustion monoxides.
Energy harnessed by wind turbines is intermittent, and is not a "dispatchable" source of power; its availability is based on whether the wind is blowing, not whether electricity is needed. Turbines can be placed on ridges or bluffs to maximize the access of wind they have, but this also limits the locations where they can be placed. In this way, wind energy is not a particularly reliable source of energy. However, it can form part of the energy mix, which also includes power from other sources. Notably, the relative available output from wind and solar sources is often inversely proportional (balancing). Technology is also being developed to store excess energy, which can then make up for any deficits in supplies.
13. Records
Fuhrländer Wind Turbine Laasow, in Brandenburg, Germany, among the world's tallest wind turbines
Éole, the largest vertical axis wind turbine, in Cap-Chat, Quebec, Canada
Largest capacity conventional drive
The Vestas V164 has a rated capacity of 8 MW, later upgraded to 9 MW. The wind turbine has an overall height of 220 m (722 ft), a diameter of 164 m (538 ft), is for offshore use, and is the world's largest-capacity wind turbine since its introduction in 2014. The conventional drive train consist of a main gearbox and a medium speed PM generator. Prototype installed in 2014 at the National Test Center Denmark nearby Østerild. Series production began end of 2015.
Largest capacity direct drive
The Enercon E-126 with 7.58 MW and 127 m rotor diameter is the largest direct drive turbine. It's only for onshore use. The turbine has parted rotor blades with 2 sections for transport. In July 2016, Siemens upgraded its 7 to 8 MW.
Largest vertical-axis
Le Nordais wind farm in Cap-Chat, Quebec has a vertical axis wind turbine (VAWT) named Éole, which is the world's largest at 110 m. It has a nameplate capacity of 3.8 MW.
Largest 1-bladed turbine
Riva Calzoni M33 was a single-bladed wind turbine with 350 kW, designed and built In Bologna in 1993.
Largest 2-bladed turbine
The biggest 2-bladed turbine is built by Mingyang Wind Power in 2013. It is a SCD6.5MW offshore downwind turbine, designed by aerodyn Energiesysteme.
Largest swept area
The turbine with the largest swept area is the Samsung S7.0–171, with a diameter of 171 m, giving a total sweep of 22966 m2.
Tallest
A Nordex 3.3 MW was installed in July 2016. It has a total height of 230m, and a hub height of 164m on 100m concrete tower bottom with steel tubes on top (hybrid tower).
Vestas V164 was the tallest wind turbine, standing in Østerild, Denmark, 220 meters tall, constructed in 2014. It has a steel tube tower.
Highest tower
Fuhrländer installed a 2.5MW turbine on a 160m lattice tower in 2003 (see Fuhrländer Wind Turbine Laasow and Nowy Tomyśl Wind Turbines).
Most rotors
Lagerwey has build Four-in-One, a multi rotor wind turbine with one tower and four rotors near Maasvlakte. In April 2016, Vestas installed a 900 kW quadrotor test wind turbine at Risø, made from 4 recycled 225 kW V29 turbines.
Most productive
Four turbines at Rønland Offshore Wind Farm in Denmark share the record for the most productive wind turbines, with each having generated 63.2 GWh by June 2010.
Highest-situated
Since 2013 the world's highest-situated wind turbine was made and installed by WindAid and is located at the base of the Pastoruri Glacier in Peru at 4,877 meters (16,001 ft) above sea level. The site uses the WindAid 2.5 kW wind generator to supply power to a small rural community of micro entrepreneurs who cater to the tourists who come to the Pastoruri glacier.
Largest floating wind turbine
The world's largest—and also the first operational deep-water large-capacity—floating wind turbine is the 2.3 MW Hywind currently operating 10 kilometers (6.2 mi) offshore in 220-meter-deep water, southwest of Karmøy, Norway. The turbine began operating in September 2009 and utilizes a Siemens 2.3 MW turbine.
14. Operability
Maintenance
Wind turbines need regular maintenance to stay reliable and available, reaching 98%.
Modern turbines usually have a small onboard crane for hoisting maintenance tools and minor components. However, large heavy components like generator, gearbox, blades and so on are rarely replaced and a heavy lift external crane is needed in those cases. If the turbine has a difficult access road, a containerized crane can be lifted up by the internal crane to provide heavier lifting.
Repowering
Main article: Repowering
Installation of new wind turbines can be controversial. An alternative is repowering, where existing wind turbines are replaced with bigger, more powerful ones, sometimes in smaller numbers while keeping or increasing capacity.
Demolition
Older turbines were in some early cases not required to be removed when reaching the end of their life. Some still stand, waiting to be recycled or repowered.
A demolition industry develops to recycle offshore turbines at a cost of DKK 2–4 million per MW, to be guaranteed by the owner.
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