WIND ENERGY

  Windmills have been used for centuries to grind grain and pump 
  water  in  rural areas. Winds  are  caused by  rotation of the 
  earth and heating of the atmosphere by the sun, and has global 
  patterns of a semi-continuous nature. It is affected significa-
  ntly by topography,and weather,with seasonal, daily and hourly 
  variations. The total annual kinetic energy of air movement in 
  the  atmosphere is estimated to be about 3 x 1015 kWh or about 
  0.2% of the  solar  energy  reaching  the  earth. The  maximum 
  technically  usable potential is theoretically estimated to be  
  30 trillion  kWh per year, or about 35% of current world total 
  energy consumption. The power in the wind blowing at 25.6 km/h 
  is  about  200  W/m2  of  the  area  swept  by   the  windmill. 
  Approximately  35%  of  this  power  can  be  captured  by the 
  windmill and converted to electricity. However,it is important 
  to note that the  power  output from the  windmill varies with 
  the cube of the wind speed. Consequently, only windy locations 
  on  mountains  and   coasts  are  suitable  for  the  economic 
  generation  of  electricity  by wind power. Harnessing of wind 
  energy  could  play a significant  role in the energy mix of a 
  region. Wind  energy is renewable  and  environmentally benign. 
  It  has  the  advantage  of   being  harnessed   locally   for 
  applications  in rural and  remote areas. Pumping of water for 
  agriculture  and  plantations  is  probably the most important 
  application  that  contributes  to  rural  development through 
  multiple  cropping. Wind  driven  electric generators could be 
  utilised  as  an independent power source, and for purposes of 
  augmenting the electricity supply from grids. 

  The  extent  to  which  wind  can  be exploited as a source of 
  energy  depends  on  the  probability density of occurrence of 
  different  speeds. To  optimise the  design of a  wind  energy 
  device, data on speed range over which the device must operate 
  to  maximise  energy  extractions are required, which requires 
  the knowledge of frequency distribution of the wind speed.