A new generation of WTs has recently emerged where the rotor is connected directly on a single shaft to a special high-torque, low speed generator without the use of a gear box. Such WTs are generally variable speed and feature power electronic converters to convert the frequency of the generated power to the grid frequency. Direct-drive WTs offer higher efficiency and lower noise levels due to the absence of a gear box, but the complex generator and power electronics may make them more expensive.