How do Wind Turbines work?

Windmills have been assisting mankind to convert the energy contained in wind to many other useful forms for the last 2,000 years. Today's wind turbines are capable of converting a great amount of energy in the wind into electricity. This is due to the blades, which are developed using state-of-the-art aerodynamic analysis and the other performance-enhancing equipment. In this video, we will explore these different sets of technology in a simple, yet scientific way. First, let's get into its basic working. If the blowing wind can turn the wing, we will receive electricity from the generator that is attached to it. However, how does the blowing wind turn the wing? Let's have a close look at the blade. The blade has a lot of airfoil cross-sections consisting of different sizes and shapes from the root to tip. The simple airfoil technology makes the wind turbine blade turn. That means that a lift force is produced when a fluid moves over an airfoil. This way, the wind turbine achieves the basic rotation we are accustomed to seeing. Just as in a moving train, you experience things relatively, the moving wind turbine blade also experiences the wind relatively. For the moving blade, the relative wind velocity is as shown. Therefore, the wind turbine blade is positioned in a tilted manner in order to align with the relative wind speed. As the blade velocity increases to the tip, the relative wind speed becomes more inclined towards the tip. This means that a continuous twist is given to the blade from the root to tip. However, this rotation cannot be directly coupled to a generator because the wind turbine blades typically turn at a very low rate of RPM due to the issues of the noise and mechanical strength. Considering this slow speed rotation, we cannot produce any meaningful electricity frequency from the generator. So, before connecting to the generator, the speed is increased in a gearbox. The gearbox uses a planetary gear set arrangement to achieve the high speed ratio. A brake also sits in the nacelle. The function of the brake is to arrest wind blade rotation during excessively windy conditions. Consequently, the electricity that is produced is transferred through the cables towards the base where a step-up transformer is situated. The wind turbine should face the wind normally for maximum power extraction. But, the wind direction can change at any time. A velocity sensor fitted on the top of the nacelle measures the wind speed and direction. The deviation in the wind's direction is sent to an electronic controller, which in turn sends an appropriate signal to the yawing mechanism to correct the error. You can see how the yaw motors turn the nacelle. Thus, the wind turbine will always be aligned with the wind direction. According to the wind speed, the relative velocity angle of the wind also changes. A blade tilting mechanism tilts the blades and guarantees a proper alignment of the blades with the relative velocity. Thus, the blades are always at the optimum angle of attack with the relative wind flow. Efficiency of a wind turbine is a really interesting topic. To gain a good insight into wind turbine efficiency, assume that you are measuring wind speed at upstream and downstream of a wind turbine. You can note that the wind speed at the downstream is much smaller than the upstream. This is because the blades absorb some kinetic energy from the wind. The same amount of energy is converted as mechanical power of the wind turbine. It is interesting to note that a wind turbine absorbs 100 percent of the available kinetic energy only if the downstream wind speed becomes zero. However, zero wind speed at downstream is a physically impossible condition. This cartoon animation clearly depicts this fact. Zero downstream speed simply means that the whole flow is stuck. This physical reality of the flow demands a certain amount of exit wind speed. That means that there is a theoretical maximum efficiency a wind turbine can achieve. This limit is known as Betz's limit. Essentially, it means that no wind turbine in the world can ever cross the efficiency limit of 59.3 percent. We hope you have now developed a good insight of the operation of wind turbines. Thank you.