Wind Power

Wind PowerPower Plant Seminar 1

S.N.Student NameID. No.

1Lemi Chala01165/03

2Abate Tasfaye01828/03

3Asnake Mitaw00551/03

4Ashenafi Abera00542/03

5Solomun Kidanemariam01517/03

6Asrat Alemayehu00553/03

7Kayo Babu01792/03

IntroductionWind turbine technology offers a cost-effective alternate renewal energy source. It is important to mention that a wind turbine is capable of generating greater amounts of electrical energy with zero greenhouse effects compared to other energy generating schemes including solar cell, tidal wave, biofuel, hydrogen, biodiesel, and biomass technologies. A wind turbine is the reverse of an electrical fan. A wind turbine uses wind energy to generate the electricity; a fan uses electricity to generate wind. In more sophisticated terminology, a wind turbine converts the kinetic energy of the wind into electrical energy.Wind turbines come in different sizes and types, depending on power generating capacity and the rotor design deployed. Small wind turbines with output capacities below 10 kW are used primarily for residences, telecommunications dishes, and irrigation water pumping applications. Wind turbine technology offers cost-effective solutions to eliminate the dependence on costly foreign oil and gas now used to generate electricity. Additionally, this technology provides electrical energy without greenhouse effects or deadly pollution releases. Furthermore, wind turbine installation and electricity generating costs are lower compared to other electrical energy generation schemes involving coal fired steam turbo-alternators, tidal wave turbines, geothermal-, hydrothermal-, biofuel-, and biodiesel-based electrical energy sources and nuclear reactor-based generators.Working principles of wind turbine

The operation is based on the scientific theory of fluid mechanics and some elements of aerodynamics. Modern wind turbines catch the wind by turning into or away from air flows. Wind moves the propellers mounted on a rotor and the movement turns a high-speed shaft coupled to an electric or induction generator. Air currents that blow over flat terrains or over-the-hill regions have wind velocities ranging from 10 to 65 miles per hour and are sufficient to turn large blades attached to a high-speed shaft coupled to a generator. Rotor blade design parameters such as chord, twist angle, and length are selected to achieve optimum aerodynamic performance and acceleration effects under various wind conditions at different tower height levels.

Aerodynamics

The blades of a wind turbine have an airfoil design such that the top half is curved and the bottom half is flat, as shown in Figure 1. When laminar wind flows over the thicker, curved section of the blade, the wind initially slows down and then speeds up to match the speed of the relative wind. The increased speed of the wind above the airfoil produces a low-pressure region while the air below the airfoil remains at a higher pressure. This causes a phenomenon called lift, where the turbine blade is lifted perpendicular to the wind flow, towards the low-pressure region. The turbine blade also experiences drag, which is caused by friction along the blade. Drag (D) causes the resulting direction of lift (L) to change, as seen in Figure 5. Both effects of lift and drag cause the turbine blades to rotate around a rotor, which generates kinetic, or mechanical, energy. To determine whether the turbine is mostly affected by drag or lift, the tip speed ratio can be calculated using where is the velocity of the rotor and is the velocity of the wind.

Equation 1: Tip Speed Ratio

If > 1, lift force allows the blades to turn faster than the speed of the wind and, therefore, allows the turbine to output more power more efficiently. If < 1, the turbine blades spin using drag force, which means that the maximum speed at which the blades can turn is the speed of the wind. The power produced by the wind can be calculated using Equation 2 where A is the cross sectional area of the rotor, is the air density, and is the wind velocity.

Equation 2: Power Production of a Wind Turbine

Figure 1: Laminar Flow over an Airfoil

Figure 2: The Effect of Lift and Drag on an Airfoil[footnoteRef:1] [1: ]

Advantages of wind turbine

Compared to other energy sources wind turbine technology offers affordability, pollution-free and maintenance-free operation. Major benefits of wind turbine technology can be briefly summarized as follows: It saves substantial money on utility bills; users face no power shortages or failures as experienced by customer. It delivers environmentally friendly and efficient electrical energy at lower cost, particularly, in areas where electrical grids are not available, for example in remote locations with difficult terrain features. Installation does not jeopardize the value of a home, office building, or commercial building. The installation can be easily undone and leaves no adverse visible effects at installation sites. The turbine does not require frequent or intermittent maintenance or employment of operations personnel; unlike steam and gas turbine-based alternator systems, no maintenance or operational costs are incurred. The technology essentially offers home-made electrical energy and off-grid living, which is not readily possible with other technologies.Despite these benefits, wind turbine technology has a few shortcomings. Damage to its tower structure or housing caused by strong winds may necessitate costly repairs or maintenance, particularly if a component must be replaced on a tower typically ranging from 50 to 70 m in height. Disadvantages It would be unfair not to identify the potential disadvantages or the imminent dangers. Consistent noise is the most annoying factor. For example, a constant high wind noise problem may be overcome by selecting installation sites away from residential areas, schools, and commercial buildings. It is important to understand that wind turbines are generally loud and the turbine blades represent a danger to birds flying less than 350 ft above the ground. Older turbines built 15 to 25 years ago are not only louder, but also less cost-effective. Turbine noise increases with operating height, rotor blade size, and power output. Most current wind turbine blades vary in length from 50 to 150 ft and the heights vary from100 to 300 ft, depending on ground surface roughness, vertical distribution of wind speeds, local terrain features, number of turbines on wind farm, and electrical power generating requirements.

Wind turbine installation cost depends on site selection, tower height, and output power rating. A typical 1.5-MW General Electric wind turbine costs around $2.5 million including parts, installation, and site selection. This cost will be much higher for wind turbines with higher output ratings. Other costly factors are site selection and tower structure. However, the cost of producing wind power has dropped four-fold since 1980, based on Electric Power Research Institute estimates.

A wind turbine normally sits about 30 stories above the ground at the hub, where three 130-ft blades are connected to the tower head. Although maintenance is rarely required after careful installation, an ordinary maintenance or erection technician is not qualified to perform the required tasks. Turbine installation and maintenance require intelligence, quick thinking, split-second decision making, stamina, strong knees, and the ability to function at dizzying heights. In other words, a technician must be hyper vigilant while working in tight spaces at heights exceeding 235 ft, in the presence of high-voltage electrical cables and spinning metal components. A turbine tower contains no elevator. Access to the top is only possible by climbing rung by rung on a narrow-steel ladder inside the tower. It is extremely difficult for an ordinary technician to perform tasks in such a narrow environment. However, an agile and experienced technician will be able to reach the tower top in 10 minutes or less several times a day. Wind turbine technicians require 8 weeks of rigorous training and classroom instruction covering installation, operation, and maintenance. Under working conditions, wind turbine technicians face inherent dangers while working alone almost 300 ft in the air with little support. However, crack wind turbine technicians earn annual salaries in six figures.

Wind Energy Projects In Ethiopia The Ashegoda Wind Farm, about 700 km, North of Addis Ababa has started generating 120 MW of electricity per year. It helps to start diversifying electricity generation, which would otherwise remain entirely from hydropower and thus susceptible to extreme weather events. Its construction was funded from both domestic and international sources. The Adama Wind Farm, which is also now operational, is about 80kms South of Addis Ababa. It produces 51MW of electricity per year.

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