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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.

Deployed on a commercial airplane, proton exchange membrane fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they offer a performance advantage for the airplane as a whole.Through hardware analysis and thermodynamic and electrical simulation, we found that while adding a fuel cell system using today's technology for the PEM fuel cell and hydrogen storage is technically feasible, it will not likely give the airplane a performance benefit. However, when we re-did the analysis using DOE-target technology for the PEM fuel cell and hydrogen storage, we found that the fuel cell system would provide a performance benefit to the airplane (i.e., it can save the airplane some fuel), depending on the way it is configured. 3 AcknowledgementsThe authors of this study had a great deal of enthusiastic support from both within and outside of Sandia National Laboratories.Dr. Joe Breit of The Boeing Company directly or indirectly provided most of the information about airplane electrical systems and issues in current airplane design that might be able to leverage the capabilities of a fuel cell. In the rare cases he could not answer our frequent questions, he referred us to others at Boeing who were just as happy to help: Andy Bayliss for issues concerning airplane performance, Trevor Laib for information on the existing environmental control systems, and Farhad Nozari and Casey Roberts for more electrical system details.Ryan Sookhoo of Hydrogenics was gracious in his support of our project, offering details on their PEM fuel cell technology to assist us in making reasonable estimates for the current state of the art as well as predictions of what may be possible for future aviation-designed fuel cell systems. His insight into the European world of aviation fuel cells was also useful to help put this study into perspective.Dr. Andy Lutz of Sandia (now at the University of Pacific) provided his extensive knowledge on the Simulink thermodynamic models that were used in this study.Of course, this project would not have taken place without the support of the Department of Energy's Fuel Cell Technologies Program, Pete Devlin and Nancy Garland in the Market Transportation group in particular. The encouragement and suggestions we received from them was invaluable. 4 SummaryFuel cells have become increasingly important as alternative sources of power, offering the potential for drastic reduction in emissions in particulate matter (PM), nitrogen oxides (NO x ), and CO 2 . In addition, they offer exceptionally quiet operation, highly efficient use of the fuel energy, and a high energy storage density compared to batteries. For a number of years, the manufacturers of commercial aircraft, most notably Boeing and Airbus, have realized that fuel cells may offer advantages for commercial aircraft operation. Apart from emissions reductions and thermal efficiency...