Monday, May 25, 2009
The Earth is unevenly heated by the sun resulting in the poles receiving less energy from the sun than the equator does. Also, the dry land heats up (and cools down) more quickly than the seas do. The differential heating drives a global atmospheric convection system reaching from the Earth's surface to the stratosphere which acts as a virtual ceiling. Most of the energy stored in these wind movements can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere.Humans have been using wind power for at least 5,500 years to propel sailboats and sailing ships, and architects have used wind-driven natural ventilation in buildings since similarly ancient times. The use of wind to provide mechanical power came somewhat later in antiquity.
The Babylonian emperor Hammurabi planned to use wind power for his ambitious irrigation project in the 17th century BC. The ancient Sinhalese utilized the monsoon winds to power furnaces as early as 300 BC evidence has been found in cities such as Anuradhapura and in other cities around Sri Lanka The furnaces were constructed on the path of the monsoon winds to exploit the wind power, to bring the temperatures inside up to 1100-1200 Celsius. An early historical reference to a rudimentary windmill was used to power an organ in the 1st century AD. The first practical windmills were later built in Sistan, Afghanistan, from the 7th century. These were vertical-axle windmills, which had long vertical driveshafts with rectangle shaped blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmilling and sugarcane industries. Horizontal-axle windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many Dutch windmills still exist.