Wind turbines also known as wind energy converter are used to convert the kinetic energy of the wind into electrical energy. They come in two types, vertical and horizontal. The smallest turbines are used for charging batteries for domestic use while the larger ones are used to generate electricity for homes. Wind farms which refer to a large array of turbines are used by countries as an alternative source of electricity to reduce their reliance on coal,fuel oil and other fossil fuels. Wind turbines are classified by the wind speed they are designed for from Class 1 to Class 3.Wind turbines can rotate from either a horizontal or vertical axis and can also include blades or be without blades. The horizontal axis blades are however more common than the vertical ones.
These large blades mounted at the top of the tower produce the majority of wind power electricity generated in the world today. The turbines have the main rotor shaft and electrical generator at the top of the tower and must be pointed to the wind. Small turbines are pointed by a simple wind vane,while large turbines use a wind sensor coupled with a yaw system. Most have a gearbox, which turns the slow rotation of the blades into quicker rotation suitable for electricity generation. Some turbines do not need a gearbox and are called direct drive meaning they couple the rotor directly to the generator without a gearbox as intermediary. These direct drive turbines are more advantageous compared with the turbine with gearbox. They eliminate the gear speed increaser which is susceptible to significant accumulated fatigue torque loading, reliability issues and high cost of maintenance.
These have the main rotor shaft arranged vertically. One advantage is that the turbine does not have to be pointed directly to the wind to be effective, which is an advantage on a site where the wind is highly variable. It is also an advantage when it is attached to a building where it is less steerable. The generator and gearbox can be placed close to the ground, using a direct drive from the rotor assembly to the ground based gearbox improving accessibility for maintenance. However it generates far less power overtime.
Wind turbine rotor blades are being made longer to increase efficiency. They are required to be stiff, strong light and resistant to fatigue. Materials with these properties are composites such as polyester and epoxy, while glass fiber and carbon fiber are used for reinforcements. Construction may employ manual layup or injection moulding. Wind turbine parts other than the rotor blades(including the rotor hub, gearbox,frame and tower) are largely made of steel. Smaller turbines have begun using aluminium alloys for the components to make the turbine lighter and more efficient. Prestressed concrete has been increasingly used in the material for the tower, but still requires much reinforced steel to meet the strength requirements of the turbine. Setup gearboxes are being increasingly replaced by variable speed generators, which require magnetic materials. This will require a greater supply of rare earth mineral called neodymium. These technological innovations point to a more reliable wind turbine with increased capacity for electricity generation.