MrJazsohanisharma

Electricity Generation Using Wind Power


 1.1 Nature and Origin of the Wind

The wind is the motion of a mass of air. For the purpose of using wind energy,it is normally the horizontal component of the wind that is of interest. There is also a vertical component of the wind that is very small compared with the horizontal component, except in local disturbances such as thunderstorm updrafts.

At the earth surface, the atmospheric pressure is measured in the unit Pascal (Pa) and has an average value 101,325 Pa, which is sometimes called“one atmosphere”.Another unit of pressure used for meteorological calcula�tions is the millibar (mbar). There are exactly 100 Pa per millibar so that one atmosphere is about 1,000 mbar. On a map, regions of equal atmospheric pressure are identified by isobar lines such as those illustrated in Fig. 1.1.

A close concentration of isobar lines indicates a high pressure gradient or region of rapid pressure change. Wind speed is directly proportional to the pressure gradient.

The atmospheric pressure varies from place-to-place and from day-to�day, caused by the combined effects of solar heating and the rotation of the earth. As the earth spins, illustrated in Fig. 1.2, the atmospheric air surrounding it is dragged round with it at different levels depending on altitude. The mix of air forms turbulence causing wind at the earth surface.

An additional feature is the inertial force known as the Coriolis force,which occurs in rotational systems. When air moves over the surface of the earth as it rotates, instead of travelling in a straight line, the path of the moving air veers to the right. The effect is that air moving from an area of higher pressure to an area of lower pressure moves almost parallel to the isobars. In the northern hemisphere, the wind circles in a clockwise direction towards the area of low pressure but in the southern hemisphere,the wind circles in an anti-clockwise direction, as shown in Fig. 1.2.




The heating effect of solar radiation varies with latitude and with the time of day. The warming effect is greater over the equator causing less dense warmer air to rise above the cooler air, reducing the surface atmospheric pressure compared with the polar regions. The combined effect of the solar heating and the Coriolis force is to create the following prevailing wind directions[1]

.Latitude 90◦–60◦ N 60◦–30◦ N 30◦–0◦ N northern Direction NE SW NE hemisphere Latitude 0◦–30◦ 30◦–60◦ 60◦–90◦ southern Direction SE NW SE hemisphere In any particular location, the wind direction is much influenced by the presence of land masses and features such as mountain ranges. The general picture of sea winds for the north and south Atlantic regions is shown in

Fig. 1.3[1]

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