Wind Turbine Characteristics

A wind turbine is an engine that takes the kinetic energy of wind and converts it into mechanical energy. If energy is used directly by machinery, we usually call this machine a windmill. If the mechanical energy is not used directly but is converted into electricity, machine is called a wind generator.

There exist two types of wind turbines based upon direction of the axis turbine rotates around. Most commonly turbine rotates around a horizontal axis, while those rotate around a vertical axis are used less frequently. Wind turbines are also classified by the location where they will be exploited. Onshore, offset and aerial wind turbines have unique design characteristics each. Wind turbines may also be used together with a solar collector in order to extract the energy from the sunlight rises through a large vertical solar tower.

In a horizontal axis wind turbine the main rotor shaft and electrical generator are located at the top of a tower where they must be oriented towards the wind direction. Small turbines usually use a simple wind vane, while larger turbines tend to use a wind sensor along with a servomotor. Most of them include a gearbox turning the slow blades rotation into quicker rotation making them more suitable for electricity generation.

While tower creates turbulence, the turbine tends to be directed from the tower upwind. The turbine blades are made stiff so that they will not be pushed into the tower by high winds. In addition, the blades are usually placed quite at a distance in front of the tower and usually tilted slightly upward.

In spite of the turbulence problem, downwind machines are in existence because they need no additional mechanism to keep them in line with the wind. Additionally, the blades are allowed to bend in high winds, thus reducing their swept area and wind resistance. On the other hand, since turbulence leads to fatigue failures, most Horizontal Axis Wind Turbines are upwind machines due to the importance of reliability.

The main rotor of a vertical axis wind turbine runs vertically. This type of turbine is advantageous as far as the tower doesn’t need to support the generator and/or gearbox. So they can be placed near the ground because the turbine doesn’t need to be directed towards the wind. On the other hand, pulsating torque may be produced during each revolution along with drag created each time the blade rotates into the wind. Finally, while the vertical axis wind turbine cannot be mounted on a tower, it must operate within the much slower but more turbulent airflow near the ground. This causes extraction process less efficiency.

Although the horizontal axis wind turbine is more efficient generally, sometimes the vertical axis wind turbine may be preferable since it doesn’t require a tower construction. It is also more convenient in service and maintenance since most of its moving parts are located near the ground. They are also advantageous in areas do not allow the high structures construction, such as a tower to operate a horizontal axis turbine.

A horizontal axis wind turbine has advantages of its own and is used more widely than the vertical axis wind turbine. The fact it is connected to a tower allows it to be placed offshore and on uneven ground. Its height allows it to pick up the higher speed winds surface above the ground. Most importantly, they can be cheaper to operate because of higher production volume, larger sizes and general factors relating to both capacity and efficiencies.