Nickel-cadmium batteries for energy storage applications

Battery energy storage (BES) is a catchall term describing an emerging market that uses batteries to support the electric power supply. BES may be implemented by an electricity provider or by an end user, and the battery duty cycle may vary considerably from application to application. For example, longer-duration capacity (MWh) availability is a requirement of load leveling, while high performance (MW) is needed for applications such as power quality and spinning reserve. At its low end, this market merges with conventional uninterruptible power supply (UPS) systems. High-end systems employ sophisticated power conversion devices and controllers to interface with the power grid, while nominal battery voltages can be measured in kilovolts. To date, only a handful of high-end systems have been deployed. However, the electric utility segment of this market in the USA is predicted to exceed 500 MW of capacity by 2010, and many more systems are likely to be installed by end users. Technologies that compete with BES include traditional generation methods (combustion turbines and diesels), pumped hydro, compressed air energy storage (CAES), superconducting magnetic energy storage (SMES), supercapacitors, flywheels, and fuel cells. This paper describes the various BES applications, and details how nickel-cadmium (Ni-Cd) batteries can provide particular benefits in many cases. The conclusion is that, despite its high initial cost, the Ni-Cd option often has the lowest cost of ownership, or life cycle cost.