Basic Theory of Wind Power

There is a great deal of power in wind. Where sufficient wind velocity exists, wind power can provide clean and cost-effective electricity.

1.  The cause of wind

Wind is simple air in motion. It is caused by the uneven heating of the earth by the sun. Solar heating varies with time and with the reflectance of the surface.

2.  Wind turbine components.

Blades, generator, tower and batteries (if energy is stored) are the basic components of a wind power system.

3.  Types of wind turbines

There are two primary types of wind turbines: horizonal and vertical.

a. Horizontal

Horizontal-axis wind turbines have blades that spin in a vertical plane like airplane propellers. The blades have a special shape so that when wind passes over them, it moves more rapidly over one side, creating a low pressure area behind the blade and a high pressure area in the front it .The difference between these two pressures creates a force which cause the blades to spin.

b. Vertical

The blades of vertical-axis wind machines works on the same principle as horizontal-axis machines: the shape of the blades causes a pressure difference when the wind blows over them and this cause the blade assembly to spin. In a vertical-axis machine, however, the blades spin in a plane that is parallel to the ground, like an eggbeater.

4.  Wind Turbine Siting

Finding the best site for a wind turbine is essential. The wind itself is rarely a steady consistent flow, and obstructions such as nearby building or hills can reduce the performance of the turbine. Furthermore, wind speed varies naturally with the time of day, the season, and the height of the turbine above the ground. The energy available in a stream of wind is proportionate to the cube of its speed. This means that a location where the wind speed is twice as fast as another location has eight times as much energy available. Especially good sites for wind turbines are:

a. Mountain passes.

Mountains act as a funnel for wind blowing through them ,causing the speed of the wind to increase.

b. Plains.

Since there are no natural barriers to slow the wind, large flat areas often have strong winds which can generate electricity.

c. Coastlines.

The temperature differences between the air over the ocean and the air over the land creates the predictable breezes which sailors have used for centuries.

5.  Minimum Wind Speed

Wind turbines have a minimum wind speed at which they can begin to generate electricity .For small turbines, this speed is about 3.5 meters per second (8 miles per hour). In general, average annual wind speeds of greater than this are required for users who are connected to the electric power grid. Large wind power plants require wind speeds of 6 m/s (13m/hr), but wind speeds higher than this are available in many locations.