Windmill generators work by capturing the kinetic energy of blowing air and converting it to electric energy using copper coils and magnets. The wind pushes the wind turbine blades, which turn an axle. The axle, usually connected through a gearbox, turns an iron rod wrapped in copper coils and surrounded by magnets. Moving the copper wire inside the magnetic field causes electricity to flow through the wires.
The faster the wind turns a wind turbine's axle, the more electricity its generator produces. However, turbines must produce electricity at the right frequency and voltage to be compatible with the electrical grid. Wind turbines use a variety of measures to match frequency and voltage to the grid. Some wind turbines adjust their blades to the wind speed to run their generators at a constant rate. Other turbines change speeds with the wind and use secondary electrical controls to adjust frequency and voltage to the electrical grid.
Though variable-speed turbines operate at a wider range of wind speeds, all wind turbines have lower and upper speed limits, defined by the wind speeds at which the turbine produces the proper electrical frequency and voltage. Additionally, wind turbines must also shut off in very high winds to avoid damage to any components.
Manufacturers make wind turbines in two major styles, including horizontal axis and vertical axis formats. Horizontal axis turbines are the most common and turn to face the wind, similar to old-fashioned windmills. Vertical axis turbines use curved blades around vertical axes and do not need to turn into the wind.