What makes a wind turbine rotate

Friday 15 Sep 17

Have you ever thought about how modern wind turbines generate electricity? Find the answer here.

The way modern wind turbines generate electricity is inspired by the aerospace industry. One of the most important elements is the design of wind turbine blades. By using aerodynamically designed blades, the speed of the blades creates a negative pressure on the curved surface of the blades, thereby sucking the blade into rotation, in the same way the negative pressure on the top surface of aircraft wings keeps the aircraft in the air. To ensure optimal conditions, the rotor must be perpendicular to the wind direction. A wind vane is placed on the wind turbine nacelle to measure the wind speed and direction.

The wind vane activates a yaw motor which makes the nacelle rotate towards the wind direction to generate as much wind energy as possible.

Why three blades?
The vast majority of current wind turbines have three blades. It is possible to produce one- or two-bladed wind turbines, but the blade of a one-bladed wind turbine has to be three times wider to generate as much wind power as possible.

In addition, the components of a one- or two-bladed wind turbine must be more powerful than on a three-bladed wind turbine to counteract the uneven pressure on the wind turbine tower. The uneven pressure occurs because the winds are stronger at higher altitudes.

If a wind turbine only has one blade, the pressure on the tower will be intensified when the blade is pointing upwards and reduced when pointing downwards where the winds are less strong. If a wind turbine has two blades, the difference will not be as significant, but the pressure on the blade pointing upwards will still be greater than on the blade pointing downwards. If, however, a wind turbine has three blades with one blade pointing upwards and two downwards, the pressure will be distributed more evenly. Wind turbines with more than three blades can produce slightly more energy, but since the blades are expensive parts of a wind turbine, the total cost—and ultimately kWh rates—will increase.

Rotor size
The general aim/objective when designing a wind turbine is to reduce the cost of energy (CoE) to a minimum, i.e. to produce a wind turbine which generates large energy volumes at the lowest possible cost.

An important part of the process is the rotor design. The aim is not necessarily to achieve the highest possible output at a certain location or at a certain wind speed, but to generate as much energy as possible at the lowest possible cost. The rotor size is particularly important when taking into consideration the overall costs of a wind turbine.

A wind turbine can generate more energy with a larger rotor, and by avoiding heavy pressure and a larger generator, COE can be reduced. Wind turbine manufacturers continue to investigate rotor size in relation to wind turbine generators with the aim of developing wind turbines with the lowest possible COE.