Windmills: One type of wind turbines is the windmill. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is ...
Report About Wind Turbines Prepared by 4th year Mechanical Engineering Students
Lebanese University Faculty of Engineering Roomieh
EliaTohme WadihKhater
Jamil Chibany
INSTRUCTOR
Elias Kinnab, PhD Professor Professor Department of Mechanical Engineering 1
History of wind turbines
For human development to continue, sources of renewable or virtually inexhaustible energy ultimately needed to be found. It's difficult to imagine this, but even if we find several hundred or even thousand years of coal and natural gas supplies, what will humans do for the next 250,000 years or so after they are depleted? Even the most apparently "inexhaustible" sources like fusion involve the generation of large amounts of waste heat -- enough to place damaging stress on even a robust ecosystem like Earth's, at least for the organisms that depend upon stability of the system to survive. “Wind Energy Conversion” is a fascinating field, if only because its past has been so checkered and its exact future is so uncertain. Wind energy -- the leading mechanically-based renewable energy for much of man's history -- unlike many other industries, it has been around for thousands of years. It's a technology that has been reinvented numerous times. It is left with the promise and the drive to succeed despite daunting (and sometimes puzzling) obstacles, such as the vast areas needed and the one important one, the noises caused by large wind turbines. 2
Definition: A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy.
Types of wind turbines: Windmills: One type of wind turbines is the windmill. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill.
3
Wind Turbines: If the mechanical energy is then converted to electricity, the machine is called a wind generator. Wind turbines are classified into two general types: horizontal axis and vertical axis. A horizontal axis machine has its blades rotating on an axis parallel to the ground. A vertical axis machine has its blades rotating on an axis perpendicular to the ground. There are a number of available designs for both and each type has certain advantages and disadvantages. However, compared with the horizontal axis type, very few vertical axis machines are available commercially.
Vertical Axis Wind Turbine
Horizontal Axis Wind Turbine
4
Vertical Wind Turbines Although vertical axis wind turbines have existed for centuries, they are not as common as their horizontal counterparts. The main reason for this is that they do not take advantage of the higher wind speeds at higher elevations above the ground as well as horizontal axis turbines.
Savonius Wind Turbine: The Savonius turbine is S-shaped if viewed from above. This drag-type VAWT turns relatively slowly, but yields a high torque. It is useful for grinding grain, pumping water, and many other tasks, but its slow rotational speeds make it unsuitable for generating electricity on a largescale.
5
Flapping Panel Wind Turbine: This illustration shows the wind coming from one direction, but the wind can actually come from any direction and the wind turbine will work the same way.
Darrieus Wind Turbine: The Darrieus turbine is the most famous vertical axis wind turbine. It is characterized by its C-shaped rotor blades which give it its eggbeater appearance. It is normally built with two or three blades. The Darrieus turbine is not self-starting. It needs to start turning before the wind will begin rotating it.
6
Horizontal Axis Wind Turbines A horizontal Axis Wind Turbine is the most common wind turbine design. In addition to being parallel to the ground, the axis of blade rotation is parallel to the wind flow.
Up-Wind Turbines: Some wind turbines are designed to operate in an upwind mode (with the blades upwind of the tower).
Wind
Large wind turbines use a motor-driven mechanism that turns the machine in response to a wind direction. Smaller wind turbines use a tail vane to keep the blades facing into the wind.
Down-Wind Turbines:
Wind Win d
Other wind turbines operate in a downwind mode so that the wind passes the tower before striking the blades. Without a tail vane, the machine rotor naturally tracks the wind in a downwind mode.
Shrouded Wind Turbines: Some turbines have an added structural design feature called an augmenter. The augmenter is intended to increase the amount of wind passing through the blades.
7
Characteristics: Turbine size: There are different size classes of wind turbines. The smallest having power production less than 10 kW are used in homes, farms and remote applications whereas intermediate wind turbines (10-250 kW) are useful for village power, hybrid systems and distributed power. The largest wind turbines (660 kW – 2+MW) are used in central station wind farms, distributed power and community wind.
Cut-in Speed: Cut-in speed is the minimum wind speed at which the wind turbine will generate usable power. This wind speed is typically between 7 and 10 mph.
Rated Speed: The rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a “10 kilowatt” wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph. At wind speeds between cut-in and rated, the power output from a wind turbine increases as the wind increases. The output of most machines levels off above the rated speed. Most manufacturers provide graphs, called “power curves,” showing how their wind turbine output varies with wind speed.
Cut-out Speed: At very high wind speeds, typically between 45 and 80 mph, most wind turbines cease power generation and shut down. The wind speed at which shut down occurs is called the cut-out speed. Having a cut-out speed is a safety feature which protects the wind turbine from damage. Shut down may occur in one of several ways. In some machines an automatic brake is activated by a wind speed sensor. Some machines twist or “pitch” the blades to spill the wind. Still others use “spoilers,” drag flaps mounted on the blades or the hub which is automatically activated by high rotor rpm’s, or mechanically activated by a spring loaded device which turns the 8
machine sideways to the wind stream. Normal wind turbine operation usually resumes when the wind drops back to a safe level. The graph below represents the variations of power in kilowatts with respect to steady wind speed in meters per seconds of a typical wind turbine.
Also, obviously wind power varies with wind speed as location varies; the graph below shows these variations.
9
Betz’s Law: Betz's law calculates the maximum power that can be extracted from the wind, independent of the design of a wind turbine in open flow. It was published in 1919, by the German physicist Albert Betz. The law is derived from the principles of conservation of mass and momentum of the air stream flowing through an idealized "actuator disk" that extracts energy from the wind stream. 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. Practical utility-scale wind turbines achieve at peak 75% to 80% of the Betz limit. The Betz limit is based on an open disk actuator; if a diffuser is used to collect additional wind flow and direct it through the turbine, more energy can be extracted. However, such shrouded turbines are costly to build in utility-scale units because of the extra structure required.
1 Ud Ud 2 η=1 = (1 − ) (1 + ) 3 Uu Uu ρAt Uu 2 power
2
10
Equations Available Wind Power: 1 2
The kinetic energy of a stream of air: E mV 2 1 2
The kinetic energy of the air stream available for the turbine E a V 2 Where = Volume of air parcel available to the rotor
A
V
The air parcel interacting with the rotor per unit time has a cross-sectional area equal to that of the rotor ( AT ) and thickness equal to the wind velocity (V).Power is the energy per unit and expressed P
1 a AT V 3 2
Major Factors: Air density, area of wind rotor and wind velocity The most important factor is Wind Speed(Power varies cubic power of velocity) - As the velocity doubles, the power is increased by 8 times. - The rotor area is reduced by a factor of 8. The selection of site is very critical for the success of a wind power
11
Wind Turbine Power and Efficiency: A wind turbine converts a fraction of the wind energy into mechanical energy - A part is transferred to the rotor of the wind turbine ( PT ) - Rest is carried away by passing air The efficiency is the ratio of actual power developed by wind turbine rotor to the available wind power - defined as power coefficient and expressed as Cp
PT 1 a ATV 3 2
The power coefficient or the power picked up by the wind turbine rotor is influenced by many factors: -profile of the rotor blade -number of blades -blade arrangement Wind Turbine Torque The thrust force developed by the rotor is F
1 a AT V 2 2
The rotor torque is T
1 a AT V 2 R 2
Maximum Theoretical Torque
Where R is the radius of the rotor
12
Rotor Torque: The torque developed by the rotor shaft is less than the maximum theoretical torque and given in terms of coefficient of torque as: CT
Tr 1 a ATV 2T 2
Rotor Tip Relative Speed: The rotor power at given wind speed depends on the relative speed between the rotor tip and the wind. Higher relative speed between the rotor tip and the wind leads to poor interaction the rotor and the wind. - For high speed wind approaching a slower moving rotor, a portion of the wind passes the rotor without transferring energy. - For low speed wind approaching a faster moving rotor, the wind deflects from the rotor and energy is lost due to turbulence and vortex shedding. Relative speed is defined as velocity of rotortip and wind speed as Vrw
R V
2NR V
N = Rotor rotational speed, rpm = Angular velocity
Also, it can be shown that power coefficient and torque coefficient is related by relative speed: CP R Vrw CT V
13
Power Generated by Wind Turbine: Power = ½ (ρ)(A)(V)3
ρ = Density of air = 1.2 kg/m3 (.0745 lb/ft3), at sea level, 20 oC and dry air A = swept area = (radius)2, m2 V = Wind Velocity, m/sec.
ρ = 1.16kg/m3, at1000 feet elevation ρ = 1.00kg/m3, at5000 feet elevation ρ = 1.203 kg/m3 at San Jose, at 85 feet elevation. The average wind velocity is 5 mph at 50m tower height
ρ = 1.16 kg/m3 at Altamont pass, at 1010 feet elevation and average wind velocity of 7m/s at 50m tower height (turbines need a minimum of 14mph, 6.25 m/s, wind velocity to generate power).
This is how the power generated by wind turbines varies with respect to their size:
14
15
Energy Conversion The Wind Power: The wind is created by the movement of atmospheric air mass as a result of variation of atmospheric pressure, which results from the difference in solar heating of different parts of the earth surface. It has different wind systems. Equator receives more solar radiation than higher latitude regions. The curvature of the earth surface causes oblique interaction with incoming suns ray with increased altitude. Hot air goes up and creates low pressure region
Cooler air moves from high pressure region
Wind Energy Conversion • Wind power describes the process by which the wind is used to generate mechanical energy or electrical energy. • Wind energy is the kinetic energy of the large mass of air over the earth surface. • Wind turbines converts the kinetic energy of the wind into mechanical energy first and then into electricity if needed. • The energy in the wind turns propeller like blades around a rotor shaft. - The rotor is connected to the main shaft, which spins a generator to create electricity. • It is the design of the blades that is primarily responsible for converting the kinetic energy into mechanical energy. 16
• The rate of change of angular momentum of air at inlet and outlet of a blade gives rise to the mechanical torque. - As the air flows over the aero foil-section of the blade, it induces a differential pressure distribution across the top and bottom surfaces of the blade.
Wind energy is created when the atmosphere is heated unevenly by the Sun, some patches of air become warmer than others. These warm patches of air rise, other air rushes in to replace them – thus, wind blows. A wind turbine extracts energy from moving air by slowing the wind down, and transferring this energy into a spinning shaft, which usually turns a generator to produce electricity. The power in the wind that’s available for harvest depends on both the wind speed and the area that’s swept by the turbine blades.
Rotor
17
Rotor The portion of the wind turbine that collects energy from the wind is called the rotor. The rotor usually consists of two or more wooden, fiberglass or metal blades which rotate about an axis (horizontal or vertical) at a rate determined by the wind speed and the shape of the blades. The blades are attached to the hub, which in turn is attached to the main shaft.
Generators The generator converts the mechanical energy of the turbine to electrical energy (electricity). Inside this component, coils of wire are rotated in a magnetic field to produce electricity. Different generator designs produce either alternating current (AC) or direct current (DC), available in a large range of output power ratings. Most home and office appliances operate on 120 volt (or 240 volt), 60 cycle AC. Some appliances can operate on either AC or DC, such as light bulbs and resistance heaters, and many others can be adapted to run on DC. Storage systems using batteries store DC and usually are configured at voltages of between 12 volts and 120 volts. Generators that produce AC are generally equipped with features to produce the correct voltage (120 or 240 V) and constant frequency (60 cycles) of electricity, even when the wind speed is fluctuating.
Transmission The number of revolutions per minute (rpm) of a wind turbine rotor can range between 40 rpm and 400 rpm, depending on the model and the wind speed. Generators typically require rpm's of 1,200 to 1,800. As a result, most wind turbines require a gear-box transmission to increase the rotation of the generator to the speeds necessary for efficient electricity production. Some DC-type wind turbines do not use transmissions. Instead, they have a direct link between the rotor and generator. These are known as direct drive systems. Without a transmission, wind turbine complexity and maintenance requirements are reduced, but a much larger generator is required to deliver the same power output as the AC-type wind turbines.
18
Power Generated by Wind Turbine Wind turbines with rotors (turbine blades and hub) that are about 8 feet in diameter (50 square feet of swept area) may peak at about 1,000 watts (1 kilowatt; kW), and generate about 75 kilowatt-hours (kWh) per month with a 10 mph average wind speed. Turbines smaller than this may be appropriate for sailboats, cabins, or other applications that require only a small amount of electricity. [Small Wind] For wind turbine farms, it’s reasonable to use turbines with rotors up to 56 feet in diameter (2,500 square feet of swept area). These turbines may peak at about 90,000 watts (90 kW), and generate 3,000 to 5,000 kWh per month at a 10 mph average wind speed, enough to supply 200 homes with electricity. Homes typically use 500-1,500 kilowatt-hours of electricity per month. Depending upon the average wind speed in the area this will require a wind turbine rated in the range 5-15 kilowatts, which translates into a rotor diameter of 14 to 26 feet. Doubling the tower height increases the expected wind speeds by 10% and the expected power by 34%. Doubling the tower height generally requires doubling the diameter as well, increasing the amount of material by a factor of eight. At night time, or when the atmosphere becomes stable, wind speed close to the ground usually subsides whereas at turbine altitude, it does not decrease that much or may even increase. As a result, the wind speed is higher and a turbine will produce more power than expected - doubling the altitude may increase wind speed by 20% to 60%. Tower heights approximately two to three times the blade length have been found to balance material costs of the tower against better utilization of the more expensive active components.
19
The Inside of a Wind Turbine: Wind turbines harness the power of the wind and use it to generate electricity. Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. 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. This illustration provides a detailed view of the inside of a wind turbine, its components, and their functionality.
Anemometer: Measures the wind speed and transmits wind speed data to the controller. Blades: Lifts and rotates when wind is blown over them, causing the rotor to spin. Most turbines have either two or three blades. Brake: Stops the rotor mechanically, electrically, or hydraulically, in emergencies.
20
Controller: Starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 55 mph. Turbines do not operate at wind speeds above about 55 mph because they may be damaged by the high winds. Gear box: Connects the low-speed shaft to the high-speed shaft and increases the rotational speeds from about 30-60 rotations per minute (rpm), to about 1,000-1,800 rpm; this is the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring "direct-drive" generators that operate at lower rotational speeds and don't need gear boxes. Generator: Produces 60-cycle AC electricity; it is usually an off-the-shelf induction generator. High-speed shaft: Drives the generator. Low-speed shaft: Turns the low-speed shaft at about 30-60 rpm. Nacelle: Sits atop the tower and contains the gear box, low- and high-speed shafts, generator, controller, and brake. Some nacelles are large enough for a helicopter to land on. Pitch: Turns (or pitches) blades out of the wind to control the rotor speed, and to keep the rotor from turning in winds that are too high or too low to produce electricity. Rotor: Blades and hub together form the rotor.
21
Tower: Made from tubular steel (shown here), concrete, or steel lattice. Supports the structure of the turbine. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity. Wind direction: Determines the design of the turbine. Upwind turbines—like the one shown here—face into the wind while downwind turbines face away. Wind vane: Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind. Yaw drive: Orients upwind turbines to keep them facing the wind when the direction changes. Downwind turbines don't require a yaw drive because the wind manually blows the rotor away from it. Yaw motor: Powers the yaw drive.
22
Residential Wind Turbine
Bergey wind turbines operate at variable speed to optimize performance and reduce structural loads. Power is generated in a direct drive, low speed, permanent magnet alternator. The output is a 3-phase power that varies in both voltage and frequency with wind speed. This variable power (wild AC) is not compatible with the utility grid. To make it compatible, the wind power is converted into grid-quality 240 VAC, single phase, 60 hertz power in an IGBT-type synchronous inverter, the GridTek Power Processor. The output from the GridTek can be directly connected to the home or business circuit breaker panel. Operation of the system is fully automatic. It has a rotor diameter of 23 feet and is typically installed on 80 or 100 foot towers. 10kW Turbine 100 ft. Tower Kit Tower Writing Kit Total cost:
23
$27,900 $9,200 $1,000 $38,100
24
Blades Design: Calculation of Wind Power: 1
Power of wind = A = ρAV 3 2
Effect of swept area, 𝐴 = 𝜋𝑅2 Area of the circle swept by the rotor (𝑚2 ) Effect of wind speed, V Effect of air density,
Number of Blades 1) Number of Blades : One Rotor must move more rapidly to capture same amount of wind. Gearbox ratio reduced. Added weight of counterbalance negates some benefits of lighter design. Higher speed means more noise, visual, and wildlife impacts. Blades easier to install because entire rotor can be assembled on ground. Captures 10% less energy than two blade design. Ultimately provide no cost savings.
25
2) Number of Blades : Two Advantages & disadvantages similar to one blade. Need teetering hub and or shock absorbers because of gyroscopic imbalances. Capture 5% less energy than three blade designs.
3) Number of Blades : Three Balance of gyroscopic forces. Slower rotation. Increases gearbox & transmission costs. More aesthetic, less noise, fewer bird strikes.
26
Blade Composition 1) Wood Strong, light weight, cheap, abundant, flexible. Solid plank. Laminates. Veneers. Composites.
2) Metal Steel: Heavy & expensive. Aluminum: Lighter-weight and easy to work with. Expensive. Subject to metal fatigue. 3) Fiberglass Lightweight, strong, inexpensive, good fatigue characteristics Variety of manufacturing processes: Cloth over frame. Pultrusion . Filament winding to produce spars. Most modern large turbines use fiberglass.
27
Manufacturing Process
The blade mold (left) is lined with layers of fiberglass, then injected with epoxy resin. To enhance stiffness, a layer of wood is placed between the fiberglass layers. The two molds are joined and adhered together using a special liquid epoxy, which evenly joins the two sides of the blade. Finally, the whole mold is baked like a cake! 8 hours at 70 degrees C.
Before delivery, samples of the rotor blades have to go through a variety of static and dynamic tests. First, they are subjected to 1.3 times the maximum operating load. To simulate 20 years of material fatigue, the blades are then mounted on special test beds and made to vibrate around two million times, before the endurance of the material is again tested with a final static test. The blades are painted white, then shipped to wind farms all over the world.
28
Lift & Drag Forces The Drag Force is parallel to the direction of motion. We want to make this force small. The Lift Force is perpendicular to the direction of motion. We want to make this force BIG.
α = low
α = medium 0.80) = low speed, high torque
33
Pitch Control Mechanisms
Wind turbine pitch control system can change incidence of rotor blades in a wind power generation system based on real-time wind speed for the purpose of adjusting output power, achieving higher utilization efficiency of winder power and providing protection for rotor blades. When wind speed is not higher than the rated speed, the blade incidence stay near the angle 0° (highest power point), which is similar to that of a generator with constant pitch, generating an output power that changes along with wind speed. When wind speed is higher than the rated speed, the pitch control mechanism changes blade incidence so that the output power of generator is within the allowed range.
34
Location for a small or micro-scale wind turbine Many residential areas are not suitable for wind turbines as buildings and trees shade the wind and create turbulence which can reduce the efficiency and lifespan of a turbine considerably. Generally speaking, the ideal location is on top of a high mast on a south westerly facing hill with gently sloping sides surrounded by clear countryside which is free from obstructions such as trees, houses or other buildings. Here the wind flows relatively smoothly and steadily enabling it to drive wind turbines with greater efficiency. Wind turbines operate less efficiently in areas where obstacles interfere with wind flows. It is very important to understand and account for these reduced efficiencies when considering the use and economics of wind turbines in such areas. However, such areas, with less than ideal aspect and local conditions, may, with a good quality turbine system, have a sufficient wind resource to make an installation worthwhile. The predominant and most energetic winds in Ireland typically come from the southwest and west, so it is especially important that there are few or no obstacles to the turbine in these directions. Ideally, the turbine should be 10m above any obstacle within 100m. As a rule of thumb, a wind generator should be installed no closer to an obstacle than at least ten times the object's height, and on the downwind side. The preferred distance is twenty times the height of the object.
35
Calculation of the energy produced over a year: The bottom line with a wind turbine is how much energy it produces. Do not confuse this with the maximum power output! Rated power output is only achieved at rated wind speed, which will only occur from time to time. The energy produced depends on the average power and not the peak power. This in turn depends mostly on the turbine’s physical size (diameter) and the site average wind speed. Most of the energy will be produced while the turbine it generating less than its rated maximum power. In these everyday winds, the power depends on the size of the turbine, and not its power rating.
Here is a chart that estimates annual energy production for different sized turbines in different annual mean wind speeds.
36
But if we consider The Evance R9000 is a three-bladed 5.5 meter diameter upwind wind turbine with a tail fin (which is basically a standard wind turbine). It uses a patented pitch control mechanism which it is claimed results in higher overall efficiencies than other small turbines and also limits the power output at high wind speeds to a constant level corresponding to the rated output of the generator of just above 5 kilowatts. It is a direct drive turbine (i.e. no gearbox) and the generator can also be used for emergency braking. The turbine does not have a cut-outspeed. The figure below shows the data from which the power curve (the green line) was obtained as an average of the binned power and wind speed readings. The peak power is obviously electronically regulated so that there is a sharp cut-off at 5.2 kilowatts.
37
The figure on the left below shows the power curve and the efficiency graph obtained from the WindPower program. The peak efficiency is about 35% which is plausible for a well-designed small turbine and occurs at about 7 meters/second. As can be seen from the previous web page, the peak efficiencies of large turbines are over 40% but this is probably not attainable from small turbines because the blade Reynolds numbers are much lower. The graph on the right shows the mean power produced for a range of mean wind speeds from 5 to 10 meters/second and is calculated for the Rayleigh probability distribution for the wind speed.
The table below shows the equivalent annual energy production in kilowatt-hours obtained by multiplying the mean power results by 8,760 the number of hours in a year. Annual energy production in kilowatt-hours Mean wind speed (m/s) = Power calculation
5
6
7
8
9
10
8,669 13,101 17,378 21,222 24,544 27,341 38
Economical Approach: Leading Manufacturers of Wind Turbine: 1. Vestas (Denmark) - 35,000 MW 2. Enercon (Germany) - 19,000 MW 3. Gamesa (Spain) – 16,000 MW 4. General Electric (USA, Germany) – 15,000 MW 5. Siemens (Denmark, Germany) – 8,800 MW 6. Suzlon (India) – 6,000 MW 7. Nordex (Germany) – 5,400 MW 8. Acciona (spain) – 4,300 MW 9. Repower (Germany) – 3,000 MW 10.
Goldwind (china) – 2,889
1.0 – 2.5 million per MW for large scale - Most commercial wind turbine are in the range of 2 MW $3,000 – 5000 per kW in range less than 10kW - $15,000 - $25,000 for residential home application
39
40
One may finally deduce as mentioned before that this is how “Wind Energy Conversion” is a fascinating field, if only because its past has been so checkered and its exact future is so uncertain. Wind energy -- the leading mechanically-based renewable energy for much of man's history -- unlike many other industries, it has been around for thousands of years. It's a technology that has been reinvented numerous times. It is left with the promise and the drive to succeed despite daunting obstacles. Here is a quick glimpse of wind turbines evolution throughout the early years as well as nowadays.
Wind Power's Beginnings (1000 B.C. - 1300 A.D.) The first windmills were developed to automate the tasks of grain-grinding and water-pumping and the earliest-known design is the vertical axis system developed in Persia about 500-900 A.D. The first use was apparently water pumping, but the exact method of water transport is not known because no drawings or designs.
Windmills in the (1300 - 1875 A.D.)
Western
World
The first windmills to appear in Western Europe were of the horizontal-axis configuration. The reason for the sudden evolution from the vertical-axis Persian design approach is unknown, but the fact that European water wheels also had a horizontal-axis configuration -- and apparently served as the technological model for the early windmills -- may provide part of the answer. Another reason may have been the higher structural efficiency of drag-type horizontal machines over drag-type vertical machines which lose up to half of their rotor collection area due to shielding requirements. 41
20th Century Developments First Use of Wind for "Large-Scale" Generation of Electricity. The first use of a large windmill to generate electricity was a system built in Cleveland, Ohio, in 1888 by Charles F. Brush. The Brush machine (shown at right) was a post mill with a multiplebladed "picket-fence" rotor 17 meters in diameter, featuring a large tail hinged to turn the rotor out of the wind. It was the first windmill to incorporate a step-up gearbox (with a ratio of 50:1) in order to turn a direct current generator at its required operational speed (in this case, 500 RPM). Despite its relative success in operating for 20 years, the Brush windmill demonstrated the limitations of the low-speed, high-solidity rotor for electricity production applications. The 12 kilowatts produced by its 17meter rotor pales beside the 70-100 kilowatts produced by a comparablysized, modern, lift-type rotor. In Germany, Professor Ulrich Hutter developed a series of advanced, horizontal-axis designs of intermediate size that utilized modern, airfoil-type fiberglass and plastic blades with variable pitch to provide light weight and high efficiencies. This design approach sought to reduce bearing and structural failures by "shedding" aerodynamic loads, rather than "withstanding" them as did the Danish approach. Hutter's advanced designs achieved over 4000 hours of operation before the experiments were ended in 1968. Post war activity in Denmark and Germany largely dictated the two major horizontal-axis design approaches that would emerge when attention returned to wind turbine development in the early 1970s. 42
Nowadays, the 13,131 MW of wind power capacity additions in 2012 exceeded all forecasts presented in last year’s edition of the Wind Technologies Market Report. Key factors driving the record growth included the then-planned expiration of federal tax incentives at the end of 2012, improvements in the cost and performance of wind power technology, and continued state policies supporting wind energy. One of the latest innovations being investigated in the U.S. and Europe is the addition of a hinge at the nacelle-tower attachment, allowing the turbine to "nod" up and down in response to turbulence and wind shear (the difference in wind speed at the top and bottom of the rotor disk). This configuration has been tested at Riso and promises substantial reductions in rotor and drive-train loads and in control system costs. A model intended for commercial development operated in California for several years and has been investigated by the National Wind Technology Center. However, such innovations may not be necessary for wind to meet its cost goals for several years. Also, future outlooks suggest that the year 2014, is expected to be strong as developers’ commission projects that began construction in 2013. A forecasted range of wind power capacity additions of 6,000 to 10,100 MW is expected.
43
Acknowledgement: It is with our fervent enthusiasm and sincere hope that we would make merit to anyone who has contributed directly or indirectly to the development of this work. Thus, we wish to express our deep gratitude to our Professor Elias KINAB who gave us the will and patience to continue and complete this study. To all teachers who are contributing to our studies at ULFGII - Roumie throughout these few years, an expression of our sincere respects.
44
References: American Wind Energy Association (AWEA). 2013a. AWEA U.S. Wind Industry Annual Market Report: Year Ending 2012. Washington, D.C.: American Wind Energy Association. Anderson, D. A., Tannehill, J. C., Pletcher, R. H., 1984: Computational Fluid Mechanics
and
Heat
Transfer.
New
York:
Hemisphere
Publishing
Corporation, pp. 599. Wind Turbines Theory - The Betz, Equation and Optimal Rotor Tip Speed Ratio, Magdi Ragheb1 and Adam M. Ragheb2, 1Department of Nuclear, Plasma and Radiological Engineering, 2Department of Aerospace Engineering en.wikipedia.org IEEE PES Wind Plant Collector System Design Working Group National Energy Education Development Project (public domain) University of Tennessee, October 28, 2009 at 11:26 from IEEE Xplore University of Illinois at Urbana-Champaign, 216 Talbot Laboratory, USA www.telosnet.com www.whirlopedia.com www.windenergy.gov
45
Xcel Energy and EnerNex Corp. 2011. Public Service Company of Colorado 2 GW and 3 GW Wind Integration Cost Study. Denver, Colorado: Xcel Energy.
46
