Wind is the directional, string air movement in the earth’s atmosphere.
Movement of air mass is mainly caused by temperature difference and varying density and pressure. These variations are caused by radiation from the Sun, which depending on geographical location, time of the year and specific terrain factors is absorbed in different degrees causing the air to be heated up in varying degrees. Hot air has a lower density than cold air and rises up. Cold heavier air sinks and flows to the low pressure areas – the air masses begin to circulate. The wind direction s determined by the position of high and low pressure areas.
These moving air masses contain kinetic energy. The amount of energy depends on the air mass and its speed. Historically this energy was captured by windmills that transfer the energy directly into mechanical energy to drive machines. Modern wind turbines transform the kinetic energy into electricity. The greater the speed and mass of wind, the greater the amount of electrical current. Wind speed is the determining factor for current, as power increases to the third power.
Wind speeds are usually categorised in 12 wind strengths. The effects of each wind strength in nature are described in the chart on the right.
Wind speed is crucial for the economic effectiveness of wind turbines – as a rule a doubling of wind speed translates into an eightfold increase in electric power.