The Electrochemical Society Interface • Fall 2010 49 L arge-scale stationary battery energy storage has been under development for several decades with the successful use of pumped hydroelectric storage as a model. Several large battery demonstration projects have been built and tested under a variety of electric utility grid applications. In addition, renewable energy sources such as wind and photovoltaics may require energy storage systems. While these applications are new and expanding, the shift toward an expanded role for battery energy storage in the de-regulated electricity market became evident by the late 1980s and early 1990s. Studies by Sandia National Laboratories identified opportunities for battery energy storage in the generation as well as on the transmission and distribution segments of the electric grid. Reports 1,2 from these studies describe battery storage application requirements and provide a preliminary estimate of potential costs and benefits of these applications for the U.S. electric grid. Applications fall into two broad categories: energy applications and power applications. Energy applications involve storage system discharge over periods of hours (typically one discharge cycle per day) with correspondingly long charging periods. Power applications involve comparatively short periods of discharge (seconds to minutes), short recharging periods, and often require many cycles per day.Detailed performance criteria for applications such as peak shaving and load leveling (energy applications) as well as frequency and voltage regulation, power quality, renewable generation smoothing and ramp rate control (power applications) are described elsewhere.2 Generally, the most important requirements have been the need for low cost, flexible designs, proven battery technologies, and reliable performance.While many battery technologies have been proposed and developed for electrical energy storage applications, only a handful have actually been used in fielded systems. Technologies that are used in fielded systems include leadacid, nickel/cadmium, sodium/sulfur, and vanadium-redox flow batteries. Cost effective energy storage systems have been identified 3 for utility, enduser, and renewable applications. Other battery technologies, such as the many lithium-ion batteries, are less matureand not yet well-developed for these applications.

Flywheels~~m. a~, A flywheel is an electromechanical storage system in which energy is stored in the kinetic energy of a rotating mass. Flywheel systems under development include those with steel flywheel rotors and resin/glass or resin/carbon-fiber composite rotors. The mechanics of energy storage in a flywheel system are common to both steel-and composite-rotor flywheels. In both systems, the momentum of the rotating rotor stores energy. The rotor contains a motor/generator that converts energy between electrical and mechanical forms. In both types of systems, the rotor operates in a vacuum and spins on bearings to reduce friction and increase efficiency. Steel-rotor systems rely mostly on the mass of the rotor to store energy while composite flywheels rely mostly on speed.

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The MC4169 Double-Layer Capacitor Assembly was developed in response to a request from the B61 Systems organization to provide interim power for the B61 Common JTA Development. The project has been successfully completed, and Lot 1 has been built by MMSC/GEND. Development testing showed that this assembly met all design requirements. This report describes the design configuration, environmental testing, and aging, reliability, and safety studies done to ensure that the design requirements were met.