View source

A capacitor bank is used in fixed-speed or limited variable speed wind turbines.  It is an electrical component that supplies reactive power to the induction generator.  These generators require current from the electrical grid to create a magnetic field inside the generator in order to work. As a result of this, the alternating current in the electrical grid near the turbine will be affected (phase-shifted). This may at certain times decrease (though in some cases increase) the efficiency of electricity transmission in the nearby grid, due to reactive power consumption. 

In most places around the world, the power companies require that wind turbines be equipped with switchable electric capacitor banks which partly compensate for this phenomenon.  Thus the reactive power absorbed by the generator from the grid is minimized.  

The capacitor banks are usually mounted at the bottom of the tower or to the nacelle.  They may be heavy loaded and damaged in the case of excessive voltages on the grid and thereby may increase the maintenance cost of the system.