The anemometer monitors the air speed and sends the data to the controller, which starts up the system at a certain minimum wind speed (typically 8 to 16 mph) and shuts off the machine at high winds (typically above 50 mph). The moving part of the turbine has a set of graphite brushes that ride on the slip rings as the turbine yaws. To connect the output terminals of the moving alternator to the fixed cables that carry the electric current down the tower to the home, most models use copper alloy slip rings. DOE's Office of Energy Efficiency and Renewable Energy ( EERE). Downwind models don't need a yaw drive: the wind itself turns the rotor away from moving air. Upwind models have yaw drive to orient the rotor into the wind. To support the system as it swivels on its tower such models use sealed bearing called the yaw bearing (the swiveling motion is called yawing). The main rotor shaft and alternator at the top of a tower must change orientation when the air current changes direction. The rotors of most HAWT are located upwind of the tower. Upwind means it is pointed against the airflow. The picture below shows the inside of a large wind turbine. You can find more details including pros and cons of each type in this guide. Nevertheless, because of lower efficiency of vertical systems, HAWTs are more common nowadays. On the positive side, a small VAWT can be mounted on a home's flat rooftop, since the building generally redirects an air flow over the roof and this can increase its speed at the turbine. In addition to this, the Darrieus type is not self-starting. There are two brands of VAWT: Darrieus ("egg-beater") and Savnoius (S-type). Vertical-axis turbines (VAWT) do not have to be pointed into the wind, so their alternator and gearbox can be placed at the bottom of the tower. Their main disadvantages are the requirement of tall towers, which are difficult to transport and install, and the necessity to constantly align in the direction of the airflow. The main advantages of horizontal axis wind turbines (HAWT) are their higher efficiency and ability to self start. Both styles have their pros and cons and both are used in home wind generators. There are two main types of turbines based on the axis on which they rotate: horizontal axis ("propeller-type") and vertical-axis.
If the air motion is converted to mechanical energy that is used directly by machinery, such as a pump or grinding stones, such a machine is more often referred to as a windmill.
Such a system was first built in 1888 in US by Brush Electric and since then is being used widely for generating electricity. However, nowadays this term usually refers to an electro-mechanical system that converts the wind power to electricity. In a broad sense, a wind turbine is any device that converts the kinetic energy of the moving air into other usable forms of energy. THE GUIDE TO WIND POWER TURBINES FOR YOUR HOME
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