Energy storage systems for unmanned underwater vehicles

The power source of an underwater vehicle is the main component that determines its range of travel and the tasks that it can perform. Until recently, the choice of practical power sources for most applications has been limited to lead―acid and silver―zinc batteries are a well-established technology and are available at low cost. However, they have a low energy density (~25 Wh kg -1). Although silver―zinc batteries have a high energy density (~120 Wh kg -1), they are very expensive, costing 20 times the price of lead―acid. They also have a very short life of 40―1-- cycles compared with 1000 cycles for lead―acid [1]. In recent years considerable research and development work has been done on advanced power sources for road electric and hybrid vehicles. This ongoing work is motivated by environmentally driven legislation aiming at reducing the harmful emissions of conventional internal combustion engine vehicles (e.g. [2, 41]). The power source should ideally have a high energy density, high power density (higher charge and discharge rates), low cost, long life, low maintenance, high efficiency and wide operating-temperature range. It should also be safe and recyclable. In addition to these requirements, which are similar to those for a road vehicle, there are additional considerations imposed by working in the underwater environment. Ideally, the power source should be non-gassing and, in the case of batteries, the electrolyte should be spill-proof. the operation of the power source should be independent of depth. This paper presents a review of the features of different types of batteries (primary and secondary) and fuel cells that have been used in autonomous underwater vehicles (AUVs), highlighting their merits and operational and engineering issues that need to be considered when using them. It also presents a survey of potentially promising alternative types of batteries and energy-storage systems including flywheel electromechanical batteries and supercapacitors