Did you know there are two different types of wind turbines? The two types can easily be distinguished from one another. We’ll try to explain the fundamental differences between air resistance of the rotor (drag) and horizontal axis wind turbines (lift).
Air resistance wind turbines are propelled directly by the wind, and the (vertical) rotor moves along with it. This means that it’s impossible for the turbine to rotate faster than the wind. In a way, it works against the wind. This results in a very low efficiency. Additionally, the volume of material needed to build an air resistance wind turbine is much higher than for a lift turbine. More material has negative consequences for performance, price and installation. Both theoretical analyses and field tests have consistently proven air resistance wind turbines have a maximum efficiency of only 15%.
Lift propelled wind turbines have blades that resemble wings you see on airplanes. These blades move at right angles to the wind direction, at a higher speed than the actual wind speed. They work with the wind, like a sail, instead of against the wind. This is why these kind of turbines are fundamentally more suitable for harvesting wind energy. Moreover, the blades cover only a fraction of the rotor surface. This means much less material is needed for the rotor. Aside from the these advantages, the most important feature of the lift propelled turbine is its high efficiency. The maximum efficiency is 59%, also called the Betz limit – this is the maximum power that can be extracted from the wind in open flow.
To summarize, a horizontal axis wind turbine, such as The Windleaf, is the sensible choice. Economically, practically and environmentally.