Batteries for Large-Scale Stationary Electrical Energy Storage by Daniel H. Doughty, Paul C. Butler, Abbas A. Akhil, Nancy H. Clark, and John D. Boyes arge-scale stationary battery There are many examples of large- modes of traditional lead-acid batteries.5 energy storage has been under scale battery systems in the field. Table In these applications, we would like to Ldevelopment for several decades I provides a short list of examples of have relatively deep discharges with with the successful use of pumped installed large battery systems. good cycle life. Recent studies at Sandia hydroelectric storage as a model. Secondary batteries, such as lead- have shown that new carbon-enhanced Several large battery demonstration acid, nickel-cadmium, and lithium-ion negative electrodes in valve-regulated projects have been built and tested batteries can be deployed for energy lead-acid (VRLA) batteries have under a variety of electric utility grid storage, but require some re-engineering improved cycle life up to a factor of 10 applications. In addition, renewable for grid applications. Two novel classes at significant rates (up to 4C).6 energy sources such as wind and of battery systems that are relevant to Lithium-ion batteries, which have photovoltaics may require energy storage new installations of large energy storage achieved significant penetration into systems. While these applications are systems are sodium/sulfur (Na/S) and the portable/consumer electronics new and expanding, the shift toward flowing electrolyte batteries. Each of markets and are making the transition an expanded role for battery energy these batteries is briefly described below, into hybrid and electric vehicle storage in the de-regulated electricity and information related to large battery applications, have opportunities in grid market became evident by the late applications is highlighted. storage as well. If the industry’s growth 1980s and early 1990s. Studies by in the vehicles and consumer electronics Sandia National Laboratories identified Secondary Batteries markets can yield improvements and opportunities for battery energy storage manufacturing economies of scale, in the generation as well as on the Grid stabilization, or grid support, they will likely find their way into grid transmission and distribution segments storage applications too. Developers 1,2 energy storage systems currently of the electric grid. Reports from consist of large installations of lead-acid are seeking to lower maintenance and these studies describe battery storage batteries as the standard technology. operating costs, deliver high efficiency, application requirements and provide The primary function of grid support and ensure that large banks of batteries a preliminary estimate of potential is to provide “spinning reserve” in the can be controlled. As an example, in costs and benefits of these applications event of power plant or transmission November 2009, AES Energy Storage for the U.S. electric grid. Applications line equipment failure, that is, excess and A123 Systems announced the fall into two broad categories: energy capacity to provide power as other power commercial operation of a 12 MW applications and power applications. plants are brought online. These systems frequency regulation and spinning Energy applications involve storage can take energy from the grid when reserve project at a substation in the system discharge over periods of either the frequency or voltage is too Atacama Desert, Chile. Continued cost hours (typically one discharge cycle high and return that energy to the grid reduction, lifetime and state-of-charge per day) with correspondingly long when the frequency or voltage begins improvements, will be critical for this charging periods. Power applications to sag. The current implementation can battery chemistry to expand into these involve comparatively short periods of provide a few minutes of energy, but grid applications. discharge (seconds to minutes), short overall grid management, including recharging periods, and often require shifting peak loads, and supporting Sodium-Beta High many cycles per day. renewables, will require longer Temperature Batteries Detailed performance criteria for durations of storage and therefore re- applications such as peak shaving and engineering of conventional storage Rechargeable high-temperature battery load leveling (energy applications) systems to handle greater energy/power as well as frequency and voltage technologies that utilize metallic sodium ratios. Some improvements can be made offer attractive solutions for many large- regulation, power quality, renewable by re-engineering of existing secondary generation smoothing and ramp scale, electric utility energy storage battery technologies; longer discharge applications. Candidate uses include rate control (power applications) are durations will generally require new 2 load-leveling, power quality and peak described elsewhere. Generally, the chemistries and system designs. most important requirements have shaving, as well as renewable energy The lead-acid battery chemistry can management and integration. A number been the need for low cost, flexible be modified for grid storage applications designs, proven battery technologies, of sodium-based battery options have beyond stabilization applications by been proposed over the years, but the and reliable performance. modification of the electrode structures. While many battery technologies variants that have been developed Lead-carbon electrodes are designed the furthest are referred to as sodium- have been proposed and developed for to combine high energy density of a electrical energy storage applications, beta batteries. This designation is used well-designed battery with the high because of two common and important only a handful have actually been used specific power obtained via charging in fielded systems. Technologies that features: liquid sodium is the active and discharging of the electrochemical material in the negative electrode, and are used in fielded systems include lead- double-layer. Lead-carbon electrode acid, nickel/cadmium, sodium/sulfur, the beta-alumina ceramic separator research has been focused on the functions as the electrolyte. Sodium/ and vanadium-redox flow batteries. extension of cycle life durability and Cost effective energy storage systems sulfur technology was introduced in specific power. Carbon is added to the 7 3 the mid-1970s. The advancement of have been identified for utility, end- negative electrodes; while the carbon user, and renewable applications. Other this technology has been pursued in a does not change the nature of the variety of designs since that time. battery technologies, such as the many charge-transfer reactions, it increases lithium-ion batteries, are less mature A sodium-sulfur (Na/S) battery specific power and reduces the incidence is a type of molten metal battery and not yet well-developed for these of sulfation during charging cycles, 4 constructed from sodium (Na) and applications. which is one of the principal failure The Electrochemical Society Interface • Fall 2010 49 Doughty, et. al. primary disadvantage is the requirement to sodium/sulfur cells. However, (continued from previous page) for thermal management, which is sodium/metal chloride cells include a necessary to maintain the ceramic secondary electrolyte of molten sodium sulfur (S). This type of battery has a separator and cell seal integrity. tetrachloroaluminate (NaAlCl4) in high energy density, high efficiency of In the mid-1980s, the development the positive electrode section, and an charge/discharge (89-92%), long cycle of the sodium/metal-chloride system insoluble transition metal chloride (FeCl2 9 life, and is fabricated from inexpensive was launched. This technology offered or NiCl2) or a mix of such chlorides, as materials.8 However, because of the potentially easier solutions to some of the positive electrode. The advantages operating temperatures of 300°C to the development issues that sodium/ are that the cells have a higher voltage, 350°C and the highly corrosive nature sulfur was experiencing at the time. wider operating temperature range, are of the sodium polysulfide discharge Sodium/metal chloride cells, referred to less corrosive and have safer reaction products, such cells are primarily as ZEBRA cells (ZEolite Battery Research products. suitable for large-scale, non-mobile Africa), also operate at relatively high From the time of their inventions applications such as grid energy storage. temperatures, use a negative electrode through the mid-1990s, these two Sodium β’’-Alumina (beta double-prime composed of liquid sodium, and use technologies were among the leading alumina) is a fast ion conductor material a ceramic electrolyte to separate this candidates believed to be capable and is used as a separator in several types electrode from the positive electrode. of satisfying the needs of a number of molten salt electrochemical cells. The In these respects, they are similar of emerging battery energy-storage Table I. Examples of installed large scale battery energy storage systems. Name Application Operational Power Energy Battery Type Cell Size & Battery Dates Configuration Manufacturer Crescent Electric Membership Peak Shaving 1987-May, 2002 500 kW 500 kWh Lead-acid, flooded 2,080 Ah @ C/5; 324 cells GNB Industrial Battery, Cooperative (now Energy United) cell now Exide Battery BESS, Statesville, NC, USA Berliner Kraft- und Licht Frequency Regulation 1987-1995