This is the first in a series looking at battery technology in shipping. The series will cover the roots of the new technology, safety issues, research into future system configurations and the trend towards their use across the world fleet.
Shipping is often considered as somewhat backward when it comes to embracing new technologies and to some extent that is true. However, it needs to be realised that for much of its working life, an ocean going ship will be operating hundreds of miles from land with little if any immediate assistance available in case of need. That situation requires all the systems and equipment on board a ship to be robust, reliable and in some cases easily repairable by the crew with limited resources.
However, for smaller vessels that operate much closer to land being at the cutting edge of technology is not unusual. Within this century we have seen the debut LNG fuelled ferries, hybrid tugs and ferries, pure battery ferries and even prototype craft running on hydrogen.
Batteries have become a hot topic in shipping circles and although many consider the offshore vessel Viking Lady (2013) or the ferry Ampere (2015) to be the first battery equipped vessels there were earlier examples. Both vessels mentioned are Norwegian owned and operate in Norwegian waters leading Norway to be considered as the home of battery technology and hybrid ships, but the technology first gained traction in the US.
Foss tugs built the Carolyn Dorothy in 2009 as the first true hybrid tug. The tug had the same bollard pull as others in its class but much smaller twin main engines. The engines were complemented by a battery pack and two gensets. In its various modes of operation Carolyn Dorothy used battery power for low speeds and light running, and a combination of battery and generators for medium power operation.
For full power, the diesel main engines cut in and are coupled by clutches to the drive system in addition to the electric motors. Surplus power generated at any stage is used to recharge the battery packs. One significant difference to more recent hybrid craft is that the battery packs on the tug were heavy lead acid types and not the lithium ion systems now commonly used.
The year after Carolyn Dorothy was built, Foss retrofitted Campbell Foss an earlier built tug with a lithium ion battery system. In August 2012, an explosion and fire occurred in one of the lithium batteries on the Campbell Foss. Subsequent to that fire, Foss removed the remaining batteries from the tug and all of the lead acid batteries on Carolyn Dorothy.
Campbell Foss was returned to service in diesel configuration without batteries, and Carolyn Dorothy was returned to service in a modified hybrid configuration that did not require the use of batteries.
The fire was investigated by the US authorities and subsequently the Maritime Administration (MARAD) then provided $600,000 in funding to put batteries back into the two tugs, and a risk assessment incorporating lessons learned from the fire was carried out. The investigation resulted in several structural changes to the vessels and the installation of fire suppression system in the battery rooms. More lessons about fire suppression were learned in a later fire on board the Norwegian ferry Ytterøyningen in 2019.
Following that fire the Norwegian Maritime Authority warned shipowners, operators and other stakeholders and interested parties about the dangers associated with lithium-ion battery systems. The battery system maker Corvus also carried out its own investigation and made several recommendations, some of which related to the unique circumstances of the incident.
Given the novelty of installing high capacity lithium-ion battery systems on ships, a small number of incidents in the early days may not be surprising since fires have occurred in other unrelated uses including mobile phones, vehicles, and computers. Research is well advanced into replacement technologies but for the time being it is generally accepted that the benefits outweigh the risks especially as action is being taken to remedy shortcomings.
Systems for all situations
Battery systems come in two distinct types. That on the Viking Lady was mainly a prototype designed to store any excess power generated by the ship’s engines and use it as needed for any purpose. By contrast the system on Ampere was specifically designed to provide all the necessary propulsion power as well as all other requirements of the vessel. On the Carolyn Dorothy, the system was also specifically designed for adapting to changing requirements of the vessel type.
On all hybrid ships, the battery is an essential part of the power system but in most cases it will be secondary to the main engines which presently are most likely to be running on conventional fuels or be able to switch to one of the greener alternatives now being developed.
Power demands for ships change depending upon the operations being performed at any given time. This could be sailing in open waters, entering or leaving port, idling in port or at anchor, performing operations requiring dynamic positioning or carrying out cargo handling operations.
For most cargo ships, the main demand for power comes when sailing in open waters. If the ship has a typical mechanical propulsion system comprising one or two main engines directly linked to propellers, a battery system is unlikely to provide much in the way of fuel savings. Even so a PTO/PTI device could potentially produce enough energy during sailing to allow the ship to make its entry and departure to and from the port on battery power alone and thus reducing exhaust pollution in the port environment.
If the vessel uses its own cranes for cargo handling it may also provide enough power for that purpose and for ships carrying refrigerated cargoes some assistance to maintaining the correct temperature.
On a diesel-electric ship a battery system can allow better management of changing demands using peak shaving. Here the vessel’s gensets can always be run at optimum levels with excess power produced being used to charge the battery and when demand increases feeding energy from the battery into the electrical distribution system. Only when the battery is close to being discharged and demand increased does the need arise to bring an additional generator online.
It is in these types of ships – which often have dynamic positioning requirements – that hybrid design comes into its own. Most vessels of this type are either offshore vessels, shuttle tankers or passenger ships.
On a pure electric ship, the battery will need to be charged from shore power which requires sufficient power to be available from the local grid or some other arrangement to be made. This type of installation is suitable only for vessels such as ferries making short trips between points where dedicated facilities can be provided.
There are operational issues to be addressed here such as whether the batteries should be recharged during out of service periods or during the port calls which may be of very short duration. In some cases the draw on the grid may be too high for rapid recharges but this can be overcome by a shore battery which draws constantly on the grid and which can be used for a rapid recharge of the battery on the ship.
The hybrid fleet – a growing phenomenon
Considering the relatively short period since batteries first came to be seriously considered it is noticeable that the rate of take up has been more rapid than was the case with LNG as a fuel for example.
Currently there are almost 250 ships fitted with battery systems in service and a similar number under construction or on order. Around one in four of these are pure electric ships with no diesel engines.
Ferries make up around half of all ships with installed batteries and offshore and tugs accounting for almost 35%. The remainder are spread roughly equally between cruise ships and cargo ships.
Battery systems are not cheap and in addition to the cost of the battery pack itself there are ancillary requirements and power management systems to be accounted for. For pure electric ships or those planning to make use of shore energy for topping up batteries, the cost of electricity generated ashore must be taken into account. Generally this will be significantly higher than the cost of power generated by the ship itself using a conventional diesel genset and appropriate fuel.
However, the cost of shore electricity may be offset by ‘green’ incentives offered by ports such as reduced port fees for less polluting vessels and increased attractiveness of the vessel to charterers concerned about their green credentials.
Cost of systems might also be expected to reduce as take up increases and as system improvements develop over time.
Look out for part two of the series over the coming weeks.