A fundamental truth of the grid has been that electricity must be generated at the precise moment it is demanded. It is the ultimate just in time system, where the laws of physics prevent carrying inventory. This characterization is under challenge, as the development of large-scale energy storage technologies is accelerating. A growing group of engineers, grid operators, and regulatory agencies believe that energy storage will be a critical component of the grid of the future. Over the past several decades, large-scale hydro and pumped hydro storage facilities dominated the energy storage landscape. Today, new and evolving battery chemistries, primarily for electric vehicle and backup power applications, are emerging as potential solutions for some of the challenges that face the grid today. Both batteries and high-speed mechanical flywheelsconnected to the grid through power electronicsare enabling smaller and more modular energy storage systems. These storage systems are being considered for a variety of applications, from time-shifting wind © 2012 IEEE.
