This chapter discusses various energy storage devices, comparison among them, and the use of energy storage devices in minimizing fluctuations in line power, frequency, and terminal voltage of wind generator systems. It describes the output power leveling of wind generator systems by pitch angle control, power quality improvement by flywheel energy storage system, and constant power control of doubly fed induction generator wind turbines with supercapacitor energy storage. The chapter deals with fluctuation minimization of power, frequency, and voltage by energy storage devices, especially using super-conducting magnetic energy storage (SMES) systems. Various promising energy storage systems are available on the market battery, such as energy storage, supercapacitor energy storage, SMES, flywheel energy storage, and compressed air energy storage. An SMES unit consists of a large superconducting coil at the cryogenic temperature. SMES is a large superconducting coil capable of storing electric energy in the magnetic field generated by direct current flowing through it.