MODULE - II.pdf

WIND POWER What is it? How does it work? Efficiency Examples WIND POWER - WHAT IS IT? All renewable energy (except tidal and geothermal power), ultimately comes from the sun The earth receives 1.74 x 1017 watts of power (per hour) from the sun About one or 2 percent of this ener...

WIND POWER What is it? How does it work? Efficiency Examples WIND POWER - WHAT IS IT? All renewable energy (except tidal and geothermal power), ultimately comes from the sun The earth receives 1.74 x 1017 watts of power (per hour) from the sun About one or 2 percent of this energy is converted to wind energy (which is about 50-100 times more than the energy converted to biomass by all plants on earth Differential heating of the earth’s surface and atmosphere induces vertical and horizontal air currents that are affected by the earth’s rotation and contours of the land  WIND. ~ e.g.: Land Sea Breeze Cycle  Winds are influenced by the ground surface at altitudes up to 100 meters. Wind is slowed by the surface roughness and obstacles. When dealing with wind energy, we are concerned with surface winds. A wind turbine obtains its power input by converting the force of the wind into a torque (turning force) acting on the rotor blades. The amount of energy which the wind transfers to the rotor depends on the density of the air, the rotor area, and the wind speed. The kinetic energy of a moving body is proportional to its mass (or weight). The kinetic energy in the wind thus depends on the density of the air, i.e. its mass per unit of volume. In other words, the "heavier" the air, the more energy is received by the turbine. at 15° Celsius air weighs about 1.225 kg per cubic meter, but the density decreases slightly with increasing humidity.  A typical 600 kW wind turbine has a rotor diameter of 43-44 meters, i.e. a rotor area of some 1,500 square meters.  The rotor area determines how much energy a wind turbine is able to harvest from the wind.  Since the rotor area increases with the square of the rotor diameter, a turbine which is twice as large will receive 22 = 2 x 2 = four times as much energy.  To be considered a good location for wind energy, an area needs to have average annual wind speeds of at least 12 miles per hour. DMILL DESIGN A Windmill captures wind energy and then uses a generator to convert it to electrical energy. The design of a windmill is an integral part of how efficient it will be. When designing a windmill, one must decide on the size of the turbine, and the size of the generator. LARGE TURBINES: Able to deliver electricity at lower cost than smaller turbines, because foundation costs, planning costs, etc. are independent of size. Well-suited for offshore wind plants. In areas where it is difficult to find sites, one large turbine on a tall tower uses the wind extremely efficiently. SMALL TURBINES:  Local electrical grids may not be able to handle the large electrical output from a large turbine, so smaller turbines may be more suitable.  High costs for foundations for large turbines may not be economical in some areas.  Landscape considerations Wind Turbines: Number of Blades  Most common design is the three-bladed turbine. The most important reason is the stability of the turbine. A rotor with an odd number of rotor blades (and at least three blades) can be considered to be similar to a disc when calculating the dynamic properties of the machine.  A rotor with an even number of blades will give stability problems for a machine with a stiff structure. The reason is that at the very moment when the uppermost blade bends backwards, because it gets the maximum power from the wind, the lowermost blade passes into the wind shade in front of the tower.  Wind power generators convert wind energy (mechanical energy) to electrical energy. The generator is attached at one end to the wind turbine, which provides the mechanical energy. At the other end, the generator is connected to the electrical grid. The generator needs to have a cooling system to make sure there is no overheating. SMALL GENERATORS:  Require less force to turn than a larger ones, but give much lower power output.  Less efficient i.e.. If you fit a large wind turbine rotor with a small generator it will be producing electricity during many hours of the year, but it will capture only a small part of the energy content of the wind at high wind speeds. LARGE GENERATORS:  Very efficient at high wind speeds, but unable to turn at low wind speeds. i.e.. If the generator has larger coils, and/or a stronger internal magnet, it will require more force (mechanical) to start in motion. Wind Turbine Tower: Made from tubular steel, the tower supports the structure of the turbine. Towers usually come in three sections and are assembled on-site. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity. Winds at elevations of 30 meters (roughly 100 feet) or higher are also less turbulent. Wind Vane: The wind vane measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind Anemometer: The anemometer measures wind speed and transmits wind speed data to the controller. Blades: Most turbines have three blades which are made mostly of fiberglass. Turbine blades vary in size, but a typical modern land-based wind turbine has blades of over 170 feet (52 meters). The largest turbine is GE's Haliade-X offshore wind turbine, with blades 351 feet long (107 meters) – about the same length as a football field. When wind flows across the blade, the air pressure on one side of the blade decreases. The difference in air pressure across the two sides of the blade creates both lift and drag. The force of the lift is stronger than the drag and this causes the rotor to spin. Land-Based Gearbox Turbine: The drivetrain on a turbine with a gearbox is comprised of the rotor, main bearing, main shaft, gearbox, and generator. The drivetrain converts the low-speed, high-torque rotation of the turbine’s rotor (blades and hub assembly) into electrical energy. Nacelle: The nacelle sits atop the tower and contains the gearbox, low- and high-speed shafts, generator, and brake. Some nacelles are larger than a house and for a 1.5 MW geared turbine, can weigh more than 4.5 tons. Yaw System: The yaw drive rotates the nacelle on upwind turbines to keep them facing the wind when wind direction changes.The yaw motors power the yaw drive to make this happen. Downwind turbines don’t require a yaw drive because the wind manually blows the rotor away from it. Pitch System: The pitch system adjusts the angle of the wind turbine's blades with respect to the wind, controlling the rotor speed. By adjusting the angle of a turbine's blades, the pitch system controls how much energy the blades can extract. The pitch system can also "feather" the blades, adjusting their angle so they do not produce force that would cause the rotor to spin. Feathering the blades slows the turbine's rotor to prevent damage to the machine when wind speeds are too high for safe operation. Hub: Part of the turbine's drivetrain, turbine blades fit into the hub that is connected to the turbine's main shaft. Gearbox: The drivetrain is comprised of the rotor, main bearing, main shaft, gearbox, and generator. The drivetrain converts the low-speed, high-torque rotation of the turbine's rotor (blades and hub assembly) into electrical energy. Rotor: The blades and hub together form the turbine's rotor. Low-Speed Shaft: Part of the turbine's drivetrain, the low-speed shaft is connected to the rotor and spins between 8–20 rotations per minute. Main Shaft Bearing: Part of the turbine's drivetrain, the main bearing supports the rotating low-speed shaft and reduces friction between moving parts so that the forces from the rotor don't damage the shaft. Main Shaft Bearing: Part of the turbine's drivetrain, the main bearing supports the rotating low-speed shaft and reduces friction between moving parts so that the forces from the rotor don't damage the shaft. High-Speed Shaft: Part of the turbine's drivetrain, the high-speed shaft connects to the gearbox and drives the generator. Generator: The generator is driven by the high-speed shaft. Copper windings turn through a magnetic field in the generator to produce electricity. Some generators are driven by gearboxes (shown here) and others are direct-drives where the rotor attaches directly to the generator. Controller: The controller allows the machine to start at wind speeds of about 7–11 miles per hour (mph) and shuts off the machine when wind speeds exceed 55–65 mph. The controller turns off the turbine at higher wind speeds to avoid damage to different parts of the turbine. Think of the controller as the nervous system of the turbine. Brake: Turbine brakes are not like brakes in a car. A turbine brake keeps the rotor from turning after it's been shut down by the pitch system. Once the turbine blades are stopped by the controller, the brake keeps the turbine blades from moving, which is necessary for maintenance. o A windmill built so that it too severely interrupts the airflow through its cross section will reduce the effective wind velocity at its location and divert much of the airflow around itself, thus not extracting the maximum power from the wind. o At the other extreme, a windmill that intercepts a small fraction of the wind passing through its cross section will reduce the wind’s velocity by only a small amount, thus extracting only a small fraction of the power from the wind traversing the windmill disk. o Modern Windmills can attain an efficiency of about 60 % of the theoretical maximum. P/m^2 = 6.1 x 10^-4 v^3 *The power in wind is proportional to the cubic wind speed ( v^3 ). WHY? ~ Kinetic energy of an air mass is proportional to v^2 ~ Amount of air mass moving past a given point is proportional to wind velocity (v) * An extra meter of tower will cost roughly 1,500 USD.  A typical 600 kW turbine costs about $450,000.  Installation costs are typically $125,000.  Therefore, the total costs will be about $575,000.  The average price for large, modern wind farms is around $1,000 per kilowatt electrical power installed.  Modern wind turbines are designed to work for some 120,000 hours of operation throughout their design lifetime of 20 years. ( 13.7 years non-stop) Maintenance costs are about 1.5-2.0 percent of the original cost, per year. Advantages of Wind Power The wind blows day and night, which allows windmills to produce electricity throughout the day. (Faster during the day) Energy output from a wind turbine will vary as the wind varies, although the most rapid variations will to some extent be compensated for by the inertia of the wind turbine rotor. Wind energy is a domestic, renewable source of energy that generates no pollution and has little environmental impact. Up to 95 percent of land used for wind farms can also be used for other profitable activities including ranching, farming and forestry. The decreasing cost of wind power and the growing interest in renewable energy sources should ensure that wind power will become a viable energy source in the United States and worldwide.  Wind Turbines and the Landscape - Large turbines don’t turn as fast  attract less attention - City dwellers “dwell” on the attention attracted by windmills  Sound from Wind Turbines - Increasing tip speed  less sound - The closest neighbor is usually 300 m  experiences almost no noise  Birds often collide with high voltage overhead lines, masts, poles, and windows of buildings. They are also killed by cars in traffic. However, birds are seldom bothered by wind turbines.  The only known site with bird collision problems is located in the Altamont Pass in California.  Danish Ministry of the Environment study revealed that power lines are a much greater danger to birds than the wind turbines.  Some birds even nest on cages on Wind Towers.  Integrating Wind Energy into the Grid GRID: An electric grid is a network of synchronized power providers and consumers that are connected by transmission and distribution lines and operated by one or more control centers. When most people talk about the power "grid," they're referring to the transmission system for electricity. The five biggest challenges that solar and wind pose to the grid 1) Variability 2) Uncertainty 3) Location-specificity 4) Nonsynchronous generation 5) Low capacity factor There are solutions for integrating solar and wind into the grid... Improved planning and coordination: This is the first step, making sure that VRE is matched up with appropriately flexible dispatchable plants and transmission access so that energy can be shared more fluidly within and between grid regions. Flexible rules and markets: Most grids are physically capable of more flexibility than they exhibit. Changes to the rules and markets that govern how plants are scheduled and dispatched, how reliability is assured, and how customers are billed, says NREL, "can allow access to significant existing flexibility, often at lower economic costs than options requiring new sources of physical flexibility." Flexible demand and storage: To some extent, demand can be managed like supply. "Demand response" programs aggregate customers willing to let their load be ramped up and down or shifted in time. The result is equivalent, from the grid operator's perspective, to dispatchable supply. There's a whole range of demand-management tools available and more coming online all the time. Flexible conventional generation: Though older coal and nuclear plants are fairly inflexible, with extended shut-down, cool-off, and ramp-up times, lots of newer and retrofitted conventional plants are more nimble — and can be made more so by a combination of technology and improved practices. Grid planners can favor more flexible non-VRE options like natural gas and small-scale combined heat and power (CHP) plants. Flexible VRE: New technology enables wind turbines to "provide the full spectrum of balancing services (synthetic inertial control, primary frequency control, and automatic generation control)," and both wind turbines and solar panels can now offer voltage control. Interconnected transmission networks: This one's pretty simple. Wind and solar resources become less variable if aggregated across a broader region. The bigger the geographical area linked up by power lines, the more likely it is that the sun is shining or the wind is blowing somewhere within that area. https://www.youtube.com/watch?v=sb4uX8xCacY https://www.youtube.com/watch?v=y6fG-aIP_PU https://www.youtube.com/watch?v=CyHOl-hetbU https://www.youtube.com/watch?v=Zy9u5_AcM0w