What is a Horizontal Wind Turbine?
A wind turbine is a device that is used to convert the energy from the wind into electrical energy. If the wind energy is used for mechanical purposes like grinding stones, pumping water etc then the device is called a wind mill. The most commonly used type of wind turbine is the horizontal wind turbine.
The main parts of a wind turbine are rotor, tower, gear box and generator. In a Horizontal Axis Wind Turbine (HAWT), the rotor’s axis is parallel to the ground and the direction of wind flow. The rotor resembles the propeller of an airplane and consists of blades that are attached to the rotor. This propeller is built on a horizontal shaft. With the wind, the rotor rotates and this in return rotates the horizontal shaft and drives the generator attached to it.
The rotor blades have an aerodynamic design. The top side is curved and the bottom side is straight. When wind passes over the blade, due to the difference in shape on either side, air passes faster over the curved side creating a low pressure area on the curved side which is also the upper side. This pressure difference results in lift force that helps the airplane to rise and keep it afloat in the air. Because the blades of the turbine are connected to the rotor by a hub, the lifting of the blade is not possible; instead the blades rotate about the hub. The lift force has a perpendicular drag force that slows down the rotor. The higher the lift to drag ratio the higher is the efficiency.
The Horizontal Wind Turbines are used when electricity has to be produced from wind on a large scale. HAWT is mounted on towers so that it could raise high above the ground where there won’t be any obstructions for the flow of wind. Further the air flow at higher levels will be more steady and strong. These towers have to be supported firmly on the ground since varying forces are developed in the turbine during different wind speeds.
During horizontal wind turbines, there are chances that the blades, rotor and generator will get damaged. So safety devices are installed in these turbines that reduce the rotation of the rotors in case of high speed winds. The safety devices can disconnect the rotor from the generator at times of high speed winds.
The HAWTs have many advantages over the VAWTs (Vertical Axis Wind Turbine) HAWTs. The main advantage is the efficiency. Since HAWT is installed in the direction of the wind and steady wind flow is ensured, the maximum output could be achieved. Since the wind strikes the blades at a consistent angle, there won’t be much vibration or other noise.
The disadvantage is that HAWT used for commercial generation of electricity are massive structures. This makes them really expensive. Since the blades and towers are really huge, transportation charges comprises almost 20% of the equipment cost. Installation charges are also very high. The height of the tower makes maintenance difficult.