Power and Propulsion

Storing power for propulsion and other purposes


Paul Gunton
Paul Gunton
ShipInsight

05 December 2018

Storing power for propulsion and other purposes

For some time now, there has been intense discussion about the ability of shipping to decarbonise. In 2018, IMO adopted an ambitious plan to achieve significant advances in this direction through to 2050 and beyond. In the short term, the bridge to this target will be achieved through the use of lower carbon fuels such as LNG or methanol but in the longer term new means of storing and producing power on board will need to be developed.

One that is already being used and which is rapidly achieving acceptance as a useful concept is battery power. To avoid being a useless deadweight, batteries need a means of charging. This can be done by connecting to a shore power supply or feeding excess power from engines to the battery.

Battery power provides for emission-free operation but unless the power used to charge the batteries from shore comes from renewable, the pollution is merely moved upstream. Norway, which is self-sufficient in hydroelectricity, is therefore better positioned than many nations to make use of battery technology when it is the sole power source for the vessel. This is one reason why the country is a front runner in wholly battery- powered vessels – mostly ferries.

Battery power as waste energy storage has a much wider sphere of application and offers advantages for many ship types. In these situations, the battery allows auxiliary or main engines to be run at optimum speeds and excess power to be stored in the battery. This stored power can be used either to level out load demand from systems such as dynamic positioning or it can be used to provide emission-free operation in ports and harbours.

Another use for batteries on any type of vessel would be as an alternative to compressed air for starting main engines. All ships are obliged to be able to produce sufficient compressed air for six starting attempts of the main engine but occasionally more attempts are needed. A battery system can provide for many more attempts and can even provide all necessary power to run a get- you- home propulsion system. Batteries can only store electricity but even on mechanically- propelled vessels, a power- take- in device can be attached to the gearbox or direct to the shaft – effectively a shaft generator running in reverse.

Most of the in-service ships fitted with batteries have had them retrofitted as additions to existing equipment although in a small number of cases, including a quartet of 1997-built Scandlines’ ro-pax ferries, one of the multiple original engines was removed.