Wind Power Technology

Wind power is the conversion of the kinetic energy of moving air into useful work, most often electricity. A wind turbine captures this energy with rotor blades that the wind pushes into rotation; the rotating shaft drives a generator to produce electricity. Wind itself arises from the uneven heating of the Earth's surface by the Sun, and large-scale wind patterns are influenced by the planet's rotation through the Coriolis effect. As a renewable resource, wind produces no fuel cost or emissions during operation, but its output varies with weather and location.

Turbines are broadly divided into horizontal-axis and vertical-axis designs. The familiar three-bladed horizontal-axis turbine has its rotor shaft aligned with the wind and must be turned to face it. Vertical-axis turbines, by contrast, accept wind from any direction. The Savonius design uses curved scoops driven mainly by drag and is simple and self-starting, while the Darrieus design uses curved aerofoil blades driven by lift and can reach higher efficiency. A range of experimental concepts, including the Turby, the Warp turbine, and the laddermill, have explored alternative ways to capture wind, some at high altitude.

There is a fundamental limit to how much of the wind's energy any turbine can extract. Betz's theory, derived by Albert Betz, shows that a turbine can capture at most a certain fraction of the kinetic energy in the wind passing through it — about 59 percent — because the air must keep moving to leave the rotor. Real turbines achieve less than this ideal because of mechanical and aerodynamic losses, but the Betz limit defines the theoretical ceiling that designs work toward.

Frequently asked questions

What is the difference between horizontal-axis and vertical-axis turbines?

A horizontal-axis turbine has its rotor shaft pointing into the wind and must be turned to face it, while a vertical-axis turbine, such as the Savonius or Darrieus, accepts wind from any direction.

What does Betz's theory say about wind turbines?

It shows that no turbine can extract all the energy from the wind, with a theoretical maximum of about 59 percent, because the air must keep moving to pass through the rotor.

How does the Savonius design differ from the Darrieus design?

The Savonius rotor uses curved scoops driven mainly by drag and starts easily, whereas the Darrieus rotor uses aerofoil blades driven by lift and can be more efficient.