Wind turbine - Wind power unit (WPU)
- A wind turbine converts the energy of wind into kinetic energy. If the mechanical energy is used directly by machinery, such as pumping water, cutting lumber or grinding stones, the machine is called a windmill. If the mechanical energy is instead converted to electricity, the machine is called a wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aero generator.
- Wind turbines can rotate about either a horizontal or vertical axis, the former being more common.
Horizontal axis wind turbines ():
• HAWT have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.
• Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted forward into the wind a small amount.
• Downwind machines have been built, despite the problem of turbulence (mast wake), because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since cyclic (that is repetitive) turbulence may lead to fatigue failures most HAWTs are upwind machines.
Vertical-axis wind turbines (VAWTs):
• Have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable.
• With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque.
• It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life. However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.
Comparison table of two types of wind turbine:
Variable blade pitch, which gives the
turbine blades the optimum angle of attack. Allowing the
angle of attack to be remotely adjusted gives greater
control, so the turbine collects the maximum amount of
wind energy for the time of day and season.
The tall towers and blades up to 45 meters long are difficult
to transport. Transportation can now amount to 20% of equipment costs.
A massive tower structure is less frequently used, as
VAWTs are more frequently mounted with the lower bearing
mounted near the ground.
A VAWT that uses guy-wires to hold it in place puts stress on the bottom bearing
as all the weight of the rotor is on the bearing. Guy wires attached to the top
bearing increase downward thrust in wind gusts. Solving this problem requires a
superstructure to hold a top bearing in place to eliminate the downward thrusts
of gust events in guy wired models.
GRINOR provide the best products which have been awarded such international certificates: