INTRODUCTION TO WIND ENERGY
Wind presents a vast source of renewable energy. For many centuries, wind mills have used wind flow, or motion energy (i.e. kinetic energy) of wind, for grain grinding, water pumping and still is extensively used for sailing and flying a kite.
Wind energy is in fact an indirect form of solar energy. Winds are generated due to heating of air by solar radiations during the day, at variable rates in different parts of the hemisphere and rotation of the earth. Heated air rises up and cooler air replaces it resulting in wind. Wind movement on the earth surface is influenced by the terrain, water reserves, deserts, forests, vegetation and habitat developments.
Wind or air in motion contains the "kinetic energy" which is converted into mechanical power by means of a wind turbine. The wind turbine is connected to a generator for producing electricity.
Wind turbines are installed on high level of more than 30 metres above the ground or a tower to capture the most energy and to take advantage of faster and less turbulent wind.
The modern wind turbines are of two basic types:
Vertical axis wind turbines have the vertical main rotor shaft. The main advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom, on or near the ground, so the tower doesn't need to support it, and that the turbine doesn't need to be pointed into the wind. Drawbacks are usually the pulsating torque produced during each revolution, and the difficulty of mounting vertical axis turbines on towers. This means they must operate in the slower, more turbulent air flow near the ground, with lower energy extraction efficiency.
Horizontal-axis wind turbines typically either have two or three blades. These three-bladed wind turbines are operated "upwind," with the blades facing into the wind. The other common wind turbine type is the two-bladed, downwind turbine. Horizontal axis turbines are the most common type used today.
In a horizontal axis wind turbine, the wind turns two or three aerodynamic blades mounted around a rotor shaft. The aerodynamic forces (lift and drag) of wind produce mechanical power. This power rotates the blades and the shaft connected to a generator, normally via a gearbox, which produces electricity. The rotor blades and shaft are connected to the nacelle, which contains the gearbox and other power/mechanical components and is mounted at the top of the wind turbine tower. The nacelle rotates freely to allow aligning of the wind turbine blades with the direction of the wind and optimising extraction of wind energy.
Capacity range of wind turbines varies from few hundred watts to several megawatts. Small capacity wind turbines, below 50 kW, are used mostly for stand alone applications such as homes, offices, telecommunications and commercial buildings.
Larger capacity wind turbines, above 50 kW, are used in multiple numbers in wind farms, which provide bulk power to the electrical grid.
The European Union continues to be the most advanced region of the world for wind power development.
An overview of the status of the wind energy technology developments in the European Union countries is given on the European commission's website , and that for India is available on the Indian Indian Ministry of New and Renewable Energy (MNRE) website.
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