How Is Wind Turned into Electricity?
- According to the Bernoulli principle, air moving at a higher speed has a lower pressure than air moving at a lower speed. Mechanical parts such as airplane wings, propellers, and windmill blades feature a cross-sectional design known as an "airfoil." When air passes around this shape, the curve of the top surface forces the air to move at a faster speed than the air moving along the bottom surface. As a result, greater air pressure is exerted on the bottom surface, creating upward force or "lift." When wind blows into a wind generator, the airfoils convert the wind's force into lift, which rotates a massive axle.
- Two types of wind power generator designs currently exist: horizontal-axis "propeller" models and vertical-axis "cyclone" models. Although the propeller designs have lower efficiency than vertical-axis ones, they are typically less expensive to build and maintain. Therefore, wind farms of five or more generators will generally use propeller units. Regardless of design, the ultimate mechanical goal is the same: converting the wind's linear force into rotational force applied around a single axle.
- For a wire coil exposed to a magnetic field, changes in the strength and polarity of that field will cause electrical current to be induced within said wire. If you take a strong permanent bar magnet (e.g. neodynium, samarium-cobalt, alnico), mount it perpendicularly to the end of an axle and place a coil of wire at a stationary point close to one end of the magnet, rotating the axle will change the orientation of the magnetic field with respect to the coil. From the coil's perspective, however, the field will appear to be changing, thus inducing electrical current. Hence, the mechanical energy required to turn the axle gives rise to electrical energy within the wire.
- The internal design of the wind power generator's turbine takes this basic mechanism and builds on it considerably. First, the main rotating axle is attached to a gear assembly, which rotates another axle at a faster rate. The permanent magnet (literally, the "rotor") is mounted on this second axle. The rotor turns freely inside of a tube (literally, the "stator") lined with several pairs of long, densely-wound copper coils.
As the rotor's field passes through each coil, the magnitude of the current it induces with each revolution follows a sinusoidal curve. However, because several separate coils are arranged around the circumference of the stator, the net induced current flowing from the generator looks like a series of connected, bouncing peaks. - Although wind power is a "renewable" source of electrical energy, it presents engineers with a number of significant limitations. First, there is a reliability factor. Spring and Autumn can yield especially windy weather, but storing this energy between seasons can be very expensive. Second, the geographical areas with the greatest wind power density are often far from the areas of greatest power consumption (i.e., cities), which requires the construction of new (and expensive) power transmission lines, transformer stations, and other energy-related infrastructure.
