Feature 3 | ENERGY GENERATION & STORAGE The VL45E Li-ion cell from Saft for


naval applications has a graphite-based anode, a nickel oxide-based cathode and an electrolyte that is a blend of carbonate solvents + LiPF6. Saft summarises the advantages of Li-ion batteries over traditional technologies as improved autonomy, greater reliability, longer sustained performance at speed, compactness, high capacity, long life and low life-cycle costs, and better stealth characteristics. In addition, they are said to be ideally suited as buffer batteries in AIP systems and for powering actuators. A ‘vast improvement’ in cycle life claimed over lead-acid technology fosters reduced maintenance costs. Li-ion technology is expected to be


A number of battery technologies have been investigated that could have applications on submarines.


foster improved performance in the mission-critical areas of energy density, response time and cycle life. A number of battery technologies have


been investigated as options to flooded lead-acid cell types, including Valve Regulated Lead Acid (VRLA), Lithium Ion, Lithium Titanate and Zebra. All of these use cells that are significantly smaller in capacity than current flooded lead-acid cells; submarine batteries would therefore require cells connected in series- parallel combinations, facilitating a wide range of battery voltages. Zebra


battery technology from


Rolls-Royce promises higher levels of performance and overall capabilities, safety and cost-effectiveness for surface ship and submarine applications from a high power density/high energy density design. Individual battery modules are available in configurations with ratings ranging from 24V to 1000V and 2kWh to 50kWh. Among the advantages claimed for


the Zebra battery in air-independent propulsion (AIP) submarine installations is that double the energy provided by lead-acid batteries can be supplied, depending on the compartment arrangements. Sprint speeds can thereby be increased or the additional space created used for extra equipment or for increasing AIP endurance. Other merits reported are: low through-


20


life costs, with long life and reliability; unaffected by external temperature; can be stored fully charged indefinitely; light weight


(40% of equivalent lead-acid


batteries); zero maintenance; and no emissions under any conditions. Lithium-Ion battery development


for marine applications is pursued by French specialist Saft, tapping its expertise in delivering advanced battery systems for the railway and automotive industries as well as underwater installations. Experience in the marine industry has been gained as a supplier of battery systems for emergency back-up, lighting, engine starting and other auxiliary systems. A number of merits of Li-ion


technology for marine installation designers cited by Saft include high power and/or energy storage from a compact space- and weight-saving package; high efficiency; a long calendar and cycle


life (even when operating


in extreme temperatures); and zero maintenance requirements. Li-ion cells – in which the negative


electrode (anode) is graphite and the positive electrode (cathode) is a lithium-bearing metal compound – are reportedly well suited to cycling thanks to their stable electrode structure. Charging and discharging involves an exchange of lithium ions between the electrodes via the electrolyte.


of special interest for hybrid propulsion systems in which the batteries work in conjunction with diesel (or possible gas turbine)-driven generators and electric motors. Li-ion batteries will significantly increase the underwater endurance and performance of submarines, but the associated diesel-driven charging unit technology needs to adapt to the new requirements, says German high-speed engine builder MTU. Tese requirements are more electrical power and the supply of rated power over almost the entire operational time to fully exploit the advantages of Li-ion technology. More powerful diesel gensets for


battery charging – the first scheduled for availability in early 2016 – will feature MTU’s Series 4000 engine design rather than its venerable V16-cylinder 396 SE model, examples of which are installed in numerous submarines. A major objective in designing the new V12-cylinder Series 4000-driven genset package was to ensure minimal changes to current installation envelopes. Smaller overall dimensions were


realised from a package with a power rating increased to 1300kW at 1800rpm; the intake air and exhaust gas volume flows are slightly higher but match those of the 396 SE84L solution. A lower specific fuel consumption and


improved emissions performance are also delivered along with greater flexibility in different operating scenarios, partly due to the Series 4000 engine’s common rail fuel injection system, advanced combustion process and modern electronics. WT


Warship Technology January 2012


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