The wind has its kinetic energy as it nothing but the flow of atmospheric air. A wind turbine is a machine which utilizes the kinetic energy of wind to produce rotational mechanical energy in its shaft. The rotational motion of the shaft turns an electrical generator to generate electricity. There are mainly two types of wind turbine available one is the horizontal axis type another is vertical axis type. The turbines are also available in different sizes depending upon their mode of applications. In many places of the modern world, people use small-sized wind turbines to charge batteries for auxiliary power supply to boats, caravans etc. Many electric utility companies use medium-sized wind turbines to supply a portion of the domestic load when sufficient wind is available so that they can sale back the surplus demanded power to the electrical grid. The stock of fossil fuels on that planet is becoming nil day by day, so there is a significant need for renewable sources of energy to produce electricity to meet up the on-growing demand for electricity. The wind power generating station is one of the solutions for that. The wind power generating stations, use many giant wind turbines to produce required electricity. The wind turbines can have either horizon shaft or vertical shaft depending on their design criteria. The horizontal design is more common as it produces more power compared to a vertical one.
Horizontal Axis Wind Turbine
We call the wind turbines that have horizontal shaft as horizontal axis wind turbines or in short HAWT. In HAWT the turbine rotor couples the electrical generator and this turbine generator set is placed on the top of the turbine tower. A wind sensor with servomotor keeps the axis of the turbine along the path of the wind. Although in small turbine a wind vane does the purpose. The turbines commonly have a gearbox in between the turbine shaft and the generator shaft. The functions of this gearbox are to provide mechanical coupling between these two shafts and to step up the slow rotating speed of the turbine blades to a high rotating speed of the generator.
A wind electric power generating station uses three blades horizontal axis wind turbines (HAWT). Three blades design is more mechanically stable and can have less torque ripple. The blade-length may be from 20 m to 80 m and usually of bright white colored so that any aircraft can view comfortably. A turbine with the blade length of 80 m may have rating up to 8 MW. The height of the large commercial turbine may be up to 70 m to 120 m and may be up to 160 meters in the extreme. The modern wind turbine systems use steel tubular supporting poles. The RPM of a large wind turbine may be from 10 to 22. Such large turbine blades, cannot achieve rotational speed more than that. As we told earlier, we use a gearing arrangement (gearbox) to step up this slow speed to required high speed of the generator.
Although, there are some designs in which the turbine rotor shaft directly couples the generator. As the rotational speed of a wind turbine varies with the variation of wind pressure, the modern wind turbines use solid-state converters to convert the generated electrical energy to a required voltage level and frequency to feed the electrical grids. No one can control the wind pressure on the blades by any means it entirely depends on nature. The designers provide a protective system to all large wind turbine which aligns the blade-edge faces depending on the speed of the wind so that we can avoid breakage of the blades during high wind pressure. We call this technique the feathering.
Vertical Axis Wind Turbine
There is another type of wind turbine which uses vertically aligned rotating shaft. We call this turbine Vertical Axis Wind Turbines or VAWTs. As it has the vertical axis, it does not have to align itself with the wind and hence using these turbines are more suitable where the direction of wind significantly varies. We can install this turbine even on the rooftop since the height of this turbine is much lesser than that of HAWT. Another significant advantage is that as the shaft is vertical, we can extend it to the bottom level where we can couple a generator with the vertical shaft with the help of ground-based gearbox which facilitates easier maintenance.
In spite of so many advantages over HAWT, we do not use VAWT for bulk power generation as the power output is quite less in VAWT compared to HAWT.