Learn wind energy

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Wind energy conversion to Electric power is an interesting multidisciplinary engineering task.

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Learn wind energy

  1. 1. WIND ELECTRIC CONVERSION Basic Questions for Wind System Design Monitor speed, direction and temperature Wind resource Evaluation Components of WECS, their Functions Operating characteristic speeds Gear for turbine to generator speed conversion Energy Flow and Control in WECS Generators
  2. 2. Basic questions for Wind System Installation • Is there enough wind ? • Are tall wind towers allowed in your area? • Do you have enough space? • How much electricity do you need or want to produce? • Do you want to connect to the utility grid or be grid-independent? • Can you afford a wind energy system? 2
  3. 3. Basic questions for Wind System Installation • What does it take to install and maintain a system? Is there enough wind where you install it ? • How much electricity do you need or want to produce? 3
  4. 4. Kinetic > Mechanical > Electric Wind is created by the unequal heating of the Earth’s surface by the sun. Wind turbines convert the kinetic energy in wind into mechanical power that runs a generator to produce clean electricity. 4
  5. 5. Wind resources evaluation • Apart from having a good wind turbine, the most critical aspects for the success of investment in the wind energy sector are (i) having a good site and (ii) an accurate assessment of the wind resource at the site over the season of active wind. Wind Resource Monitoring consists of following activities (i) Siting, (ii) Wind Monitoring (iii) Wind Resource Mapping 5
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  7. 7. On farm tower for Pumping Water • One- to 10-kW turbines can be used in applications such as pumping water. • Wind-electric pumping systems can be placed where the wind resource is the best and connected to the pump motor with an electric cable. 7
  8. 8. Turbine Component Function Nacelle Contains the key components of the wind turbine, including the gearbox, yaw system, and electrical generator. Rotor blades Captures the wind and transfers its power to the rotor hub. Hub Attaches the rotor to the low-speed shaft of the wind turbine. Low speed shaft Connects the rotor hub to the gearbox. Gear box Connects to the low-speed shaft and turns the highspeed shaft at a ratio several times (approximately 50 for a 600 kW turbine) faster than the low-speed shaft. High-speed shaft with mechanical brake Drives the electrical generator by rotating at approximately 1,500 revolutions per minute (RPM). The mechanical brake is used as backup to the aerodynamic brake, or when the turbine is being serviced. Electric generator Usually an induction generator or asynchronous generator with a maximum electric power of 500 to 1,500 kilowatts (kW) on a modern wind turbine. Yaw mechanism Turns the nacelle with the rotor into the wind using electrical or other motors. 8
  9. 9. Electronic controller Continuously monitors the condition of the wind turbine. Controls pitch and yaw mechanisms. In case of any malfunction (e.g., overheating of the gearbox or the generator), it automatically stops the wind turbine and may also be designed to signal the turbine operator's computer via a modem link. Hydraulic system Resets the aerodynamic brakes of the wind turbine. May also perform other functions. Cooling system Cools the electrical generator using an electric fan or liquid cooling system. In addition, the system may contain an oil cooling unit used to cool the oil in the gearbox. Tower Carries the nacelle and the rotor. Generally, it is advantageous to have a high tower, as wind speeds increase farther away from the ground. Anemometer and wind vane Measures the speed and the direction of the wind while sending signals to the controller to start or stop the turbine. 9
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  11. 11. Some definitions: • Solidity: In reference to a wind energy conversion device, the ratio of rotor blade surface area to the frontal, swept area that the rotor passes through. • wind rose: A diagram that indicates the average percentage of time that the wind blows from different directions, on a monthly or annual basis. • power curve: A plot of a wind energy conversion device's power output versus wind speed. • power coefficient: The ratio of power produced by a wind energy conversion device to the power in a reference area of the free wind stream. 11
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  13. 13. WIND Wind Speed at 10 m height SPEED SCALE Beaufort scale Wind 0.0-0.4 m/s (0.0-0.9 knots) 0 Calm 0.4-1.8 m/s (0.9-3.5 knots) 1 Light 1.8-3.6 m/s (3.5-7.0 knots) 2 Light 3.6-5.8 m/s (7-11 knots) 3 Light 5.8-8.5 m/s (11-17 knots) 4 Moderate 8.5-11 m/s (17-22 knots) 5 Fresh 11-14 m/s (22-28 knots) 6 Strong 14-17 m/s (28-34 knots) 7 Strong 17-21 m/s (34-41 knots) 8 Gale 21-25 m/s (41-48 knots) 9 Gale 25-29 m/s (48-56 knots) 10 Strong Gale 29-34 m/s (56-65 knots) 11 >34 m/s (>65 knots) 12 13 Hurricane
  14. 14. Requirements: wind to electric Conversion • Force of wind needs turbine area, height and direction control: • turn turbine and generator shaft, produce electricity • wind resources at 50meter height • Wind translational > rotational > electric 14
  15. 15. How Do Wind Turbines Work? • Today’s turbines are versatile modular sources of electricity. • Their blades are aerodynamically designed to capture the maximum energy from the wind. The wind turns the blades, which spin a shaft connected to a generator 15
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  17. 17. The formula for calculating the power from a wind turbine is: 17
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  19. 19. Turbines today are horizontal axis upwind machines with two or three blades, made of a composite material like fiberglass. The amount of power a turbine will produce depends on the diameter. The diameter of the rotor defines its “swept area,” or the quantity of wind intercepted by the turbine. The turbine’s frame is the structure onto which the rotor, generator, and tail are attached. The tail keeps the turbine facing 19 into the wind.
  20. 20. Tip Speed Ratio  The tip-speed is the ratio of the rotational speed of the blade to the wind speed. The larger this ratio, the faster the rotation of the wind turbine rotor at a given wind speed. Electricity generation requires high rotational speeds. Lift-type wind turbines have maximum tip-speed ratios of around 10 20
  21. 21. number of blades    The number of rotor blades and the total area they cover affect wind turbine performance. For a lift-type rotor to function effectively, the wind must flow smoothly over the blades. To avoid turbulence, spacing between blades should be great enough so that one blade will not encounter the disturbed, weaker air flow caused by the blade which passed before it. It is because of this requirement that most wind turbines have only two or three blades on their rotors 21
  22. 22. Operating Characteristics All wind machines share certain operating characteristics, such as cut-in, rated and cut-out wind speeds. • 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. 22
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  24. 24. Rated Speed… 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. 24
  25. 25. Generators     The generator is what converts the turning motion of a wind turbine's blades into 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), and they are available in a large range of output power ratings. The generator's rating, or size, is dependent on the length of the wind turbine's blades because more energy is captured by longer blades. 25
  26. 26. It is important to select the right type of generator to match your intended use. Most home and office appliances operate on 120 volt (or 240 volt), 60 / 50 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. 26
  27. 27. Generators that produce AC are generally equipped with features to produce the correct voltage (120 or 240 V) and constant frequency (60 / 50 cycles) of electricity, even when the wind speed is fluctuating. 27
  28. 28. 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. 28
  29. 29. Towers: Tall structures  Tower on which a wind turbine is mounted is not just a support structure. It also raises the wind turbine so that its blades safely clear the ground and so it can reach the stronger winds at higher elevations.  Maximum tower height is optional in most cases, except where zoning restrictions apply. The decision of what height tower to use will be based on the cost of taller towers versus the value of the increase in energy production resulting from their use. 29
  30. 30.  Studies have shown that the added cost of increasing tower height is often justified by the added power generated from the stronger winds. Larger wind turbines are usually mounted on towers ranging from 40 to 70 meters tall. 30

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