Wind energy is the process of harnessing the mechanical energy of the wind and transforming it into electrical energy. If you have dabbled around in green and sustainable energy, or perhaps taken a class in the subject, then you know that the reputation of wind energy is right up there with solar and hydro. Its one of the cleanest forms of energy – 100% per cent emission- and residue-free energy production. It is also estimated to be producing nearly 20% of the world’s electricity. Before we investigate the working of a windmill, let’s first look at how wind turbines produce electricity.
How do turbines produce electricity?
A turbine is a machine designed to capture some amount of energy from a moving fluid (such as a liquid or a gas) so that it can be put to use. The turbine in a windmill is one of the simplest kinds of turbine. The huge rotor blades that you see on the front of the windmill are the turbine part of the windmill. The blades are engineered into a special curved shape, similar to that of the airfoil wings on an airplane.
When the wind blows past the wings of an airplane, it provides an upward force called lift. The same wind that blows across the blades of a windmill produces a rotational effect on them. The amount of kinetic energy the wind loses is almost the same as the amount of kinetic energy the windmill picks up, excepting the fact that certain losses of energy do occur (such as friction). The amount of energy a windmill produces is directly proportional to the area the rotor blades sweep through. In other words, the longer the blades, the more energy the turbine of a windmill will be able to produce. The factor that plays a key role in the production of wind energy is the speed of the wind itself. In fact, if the wind speed doubles, the turbine will be able to produce 8 times the amount of energy it produces at the standard wind speed (1/2 the speed). The other term used for the turbine is “rotor blades”.
Key Parts of a Windmill
Although there are different kinds of windmills, we will primarily look into the working of a horizontal windmill in this section. As we have already seen, the turbine blades spin around by harnessing the kinetic energy of the wind. Although the rotor blades spin at very high speeds, they are supported by a central drive shaft that supports the blades. The central axis or the drive shaft does turn quite slowly in comparison to the turbine.
In more modern turbines, the blades can swivel around on the hub at the front in order to meet the wind at the best angle or pitch so that it will be able to harness the energy from the wind in the best way. This swiveling of the blades to meet the wind at the correct angle is known as the pitch control mechanism. The pitch control mechanism of the blades is achieved with the help of small electric motors or hydraulic rams that control the swivel with precise electric control. Smaller turbines have more mechanical control over their swivel, while some others do not have any swivel at all.
Next, we move onto the main body of the windmill, known as the nacelle. The nacelle contains two main components within it – the gearbox and the generator. The gearbox converts the low-speed rotation of the drive shaft into high-speed rotations that are fast enough to successfully run a generator. The usual conversion rate of the gearbox is about 16 rpm (rotations per minute) of the drive shaft to around 1600 rpm for the generator. The generator is placed right after the gearbox in the nacelle. The generators in windmills can produce 2 million watts of power at 700 volts at maximum capacity under high wind speeds.
The next important part in a windmill is the Anemometer. The anemometer is an automatic speed-measuring device that is placed on the surface of the nacelle at the back. The anemometer provides measurements regarding wind speed and direction. Using these parameters, the entire nacelle, along with the blades, can be moved around with the help of a yaw motor. The yaw motor is mounted between the nacelle and the tower.
If it’s too windy or if the weather is turbulent, brakes are applied to prevent any damage from happening to the windmill. This is employed for safety reasons, as the windmill apparatus may encounter damage at such high speeds. The brakes are also applied when safety checks and maintenance work are to be done on the wind turbine. The electric current produced from a windmill is then taken to a step-up transformer, which steps up the voltage of the electricity many times. This is so that it can be effectively transmitted over large distances to the grid. From the grid, electricity is transmitted to various smaller sub-stations, which distribute the electricity for household and industrial consumption.