Sea Technology

JUL 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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auxiliary functions such as lighting. As with the traditional hybrid model, the batteries work with the boats' diesel engines, storing energy and providing propulsion as needed. The Saft batteries charge overnight from the local grid with high-capacity energy storage capabilities that provide the boats with six hours of autonomous, fully electric operation during the two busiest periods of the day—three hours in the morning and three hours in the evening. Overall, the hybrid design has reduced fuel costs and CO2 and NOx emissions. Batteries are also providing propulsion power for zero-emission electric shuttle ferry services in La Rochelle, France, and on Paris's Saint-Denis canal. Lithium-Ion Advantages Compared to other battery technologies, such as nickel, lead and silver, lithium ion has several advantages. Because lithium is the lightest metal and has a high electrochemical potential, lithium ion provides more energy per volume and operates at higher voltages to maximize the power-to-weight ratio of a battery. The batteries can also be recharged repeatedly, which reduces their life cycle costs compared to other makeups. Saft teamed up with GE Power Conversion (Paris, France), an engineering specialist in converting electrical energy into mechanical performance, to develop a theoretical scheme for a passenger ferry with hybrid propulsion and energy storage. Saft offered lithium-ion energy storage systems while Power Conversion contributed knowledge of systems that combine rotating machines and variable speed drives with automation and process controls. A typical 15,000-gross-tonnage ferry that is used for short-distance operations requiring frequent rotations in and out of harbor was used in the scheme. Calculations were for a ferry that would carry 300 cars and 1,000 passengers, with a length of 130 meters, beam of 23 meters, draft of 6.2 meters and a nominal speed of 21 knots. The main propulsion was delivered mechanically by a diesel engine twinned with a variable pitch propeller, together with diesel-electric pods that offered improved maneuverability, greater energy effciency and lower noise. Hotel loads include general ship services such as lighting, ballast pumps and HVAC, as well as cargo and duty services such as pumps, winches and actuators. A ferry such as this would typically have four modes of operation: open sea, when the lithium-ion energy storage system is charged as the ferry runs on mechanical power from the genset; channeling and maneuvering operations, when the vessel is propelled by the energy storage system, which also powers the hotel loads; call (docked in harbor), when hotel loads are supplied via cold ironing or the energy storage system; and night call, when cold ironing supplies residual hotel load and charges the energy storage system. Considering the sizes of loads, it was calculated that the hybrid system for such a vessel would require a battery capable of delivering a peak power of 4.5 megawatts and 1.75 megawatt-hours of energy to achieve 10 and 5 minutes each of channeling and maneuvering operations at 1.5 and 0.5 megawatts, plus support for hotel loads, which demand around 2 megawatts. In this case, the energy storage system was based on the overall energy requirement. With weight- and spacesaving lithium-ion technology, a battery for this application would have a total mass of less than 20 metric tons and take up around 10 meters cubed of volume. Advancing the Technology Saft manufactures various lithiumion chemistries, of which its lithiumion Super-Phosphate has shown advantages for maritime applications. Compared to traditional lithium-ion batteries, lithium-iron phosphate (LiFePO4) offers increased abuse tolerance because the product is less prone to reactivity under harsh conditions. Additional benefts of iron phosphate include a longer cycle life, faster recharge and lower cost of raw materials. LiFePO4 batteries are rechargeable lithium-ion batteries that use LiFePO4 as the cathode material. This low-cost, naturally occurring mineral offers excellent thermal stability, very fast charge times and a long cycle life. Compared to traditional metal-oxide-based lithium ion, the iron phosphate solution provides less energy for a given volume and weight, more sensitivity to storage at elevated temperatures (although better than lead acid, nickel-cadmium or nickel-metal 12 st / July 2013 www.sea-technology.com

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