Renewable Energy - Wind Energy

The kinetic energy of wind and flowing water are indirect forms of solar energy and are considered renewable. Wind energy technology relies on gradients in physical properties such as atmospheric pressure to generate electrical power. Wind turbines harness wind energy and convert the mechanical energy of a rotating blade into electrical energy in a generator.

Wind Turbine

Moving air rotates blades attached to generator shaft in the machine cabin. The machine cabin is known as the nacelle. It contains the electrical generator wich converts the rotational energy of the rotating blades to electrical energy. Electricity is transmitted through a lini in the post that connects each wind turbine to the electric grid. Therefore, the generator produces electricity that is routed directly to the electric grid.

A typical horizontal axis turbine consists of a rotor with three blades attached to a machine cabin set a top a post that is mounted on a foundation block. The machine cabin contains a generator attached to the wind turbine. The rotor blades can rotate in the vertical plane and the machine cabin can rotate in the horizontal plane.

Most modern horizontal axis turbines have three rotor blades instead of two. Rotor blades attached to a generator shaft, or rotor, make up a rigid body with a particular moment of inertia. Rotational properties of a rigid body, such as angular momentum and torque, depend on moment of inertia. THe moment of inertia of the wind turbine depends on the number of rotor blades and their orientation. Turbines with two rotor blades have a higher moment of inertia when the blades are vertical than when they are horizontal.

The difference in moment of inertia between the horizontal and vertical configuration of two blades introduces a mechanical imbalance that can increase wear on the system. By contrast, the use of three equally spaced blades adds the cost of another blade but allow a symmetric palacement of blades that makes it easier to balance the blaes as they rotate. The improved stability of tubines with three rotor blades increases wind turbine realibility and reduce maintenance cost.

{source : Energy in the 21st century by John R. Fanchi,Christopher J. Fanchi}