Designing battery-powered vessels

As environmental protection continues to influence major business decisions in the marine industry, green technologies continue to advance. Impressive gains in cost, cycle life, charge rates, and energy densities are making the use of lithium-ion technology on vessels more practical.

Lithium-ion battery technology has already found many niches in the marine world. Vessel safety can be greatly improved with the large spinning reserve that energy storage inherently provides during vessel maneuvering. Applications in support of dynamic positioning are quickly gaining acceptance. Battery energy storage can decrease diesel consumption and emissions through peak shaving. The level of safety, the knowledge of how to manage these systems and diagnose developing problems with modules, and the way in which battery management systems alert onboard crew have all improved.

Of special focus to Elliott Bay Design Group, battery power for passenger and vehicle ferries or other vessels with short and repetitive routes, is proving to be even more economically viable. Many areas in the U.S. enjoy electric utility rates below 10 cents per kilowatt-hour (kWh). Diesel used for propulsion power has historically approached 24 cents per kWh in just operational cost, exclusive of capital expenses. This big 14 cents difference presents a unique opportunity for energy storage.

Obviously, if lithium-ion batteries were free and lasted forever the choice would be simple. As recent as six or seven years ago, one kilowatt-hour of lithium batteries would cost over $1,000 and could only supply 2,500 cycles. The cost of this energy storage would work out to be about 40 cents for every battery cycle used. That would not come close to beating the 14 cents savings, but such technology can now achieve costs as low as $600/kWh and supply over 6000 cycles. Suddenly, such a 10-cent per kWh-cycle cost beats that shore power differential. And, at this point, payback can be both big and fast.

Additionally, the growing international support of green shipping is pushing technical advances in automated shore power connections. Ferries have already been put in operation, with others soon to follow, that make quick connections at lower voltages. But HH Ferries in Sweden has begun making fully automated 10,000-volt connections for some of the largest ferries in Europe. These ferries will charge in as fast as five minutes and make crossings by battery power only.

Current state-of-the-art lithium-ion battery technology can achieve a watershed event in the marine world. Battery storage can now compete financially with diesel-generated electricity by utilizing even lower cost shore power. The payback is direct and without any subsidies or social costs factored in.

It is in the best interest of the ferry fleets and other short-haul vessels to investigate the financial benefits of energy storage. While operators may enjoy substantial financial benefits, the public will also benefit from the other advantages such as lowered emissions and reduced greenhouse effects.

About the author

Will Ayers

Will Ayers has been an electrical engineer in the marine field for almost 20 years. He is currently chief electrical engineer at Elliott Bay Design Group, Seattle. His prior experience includes 11 years at Washington State Ferries and five years with GE Automation Systems.

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