Spurred by the advances in battery technologies and the commercialisation of electric and hybrid cars, the maritime industry is asking itself: Do these propulsion solutions make sense for ships? Performance benefits, fuel savings and emissions reduction is being weighed against capital investments, practicality, limitations in range and safety. DNV plays a vital role in enabling the safe introduction of large battery packs in ships. With the world's first class rules for ship propulsion batteries and related projects being brought to life, the company aims to pave the way for battery and hybrid solutions.
As demonstrated by the safety issues experienced by the Boeing Dreamliners, a battery pack can represent a hazardous component unless all safety aspects are properly handled. Through participation in developing the first hybrid offshore supply vessel, Viking Lady, DNV has produced the world’s first class rules for ship propulsion batteries. The rules play a vital role in enabling the safe introduction of battery and hybrid solutions.
Cost benefit
The payback time for pure battery and hybrid systems depends on the capital investment as opposed to their operational cost savings. Even if the capital costs related to pure battery or hybrid systems for cars are significantly less than for ships, the payback time may be significantly less for a ship due to the much higher energy requirements. Estimates show that whereas a hybrid car may not pay back the additional investment within its lifetime, a hybrid offshore supply vessel can have a payback period of less than two years. In addition, one pure battery or hybrid ship may contribute to reductions in emissions similar to emissions from thousands of cars. Pure battery or hybrid systems for relevant ship types therefore clearly make sense.
Battery propulsion
A pure battery ship will be subject to the same range constraints as an electric car, even if space and weight constraints are not as strict. The distance it can travel before the battery needs recharging will therefore be limited, making the availability of charging infrastructure a key factor. Current battery technologies restricted the application to ships operating over short distances between fixed locations. In such conditions, however, it is becoming a reality. As a result of a contest between various technical solutions, organised by the Norwegian Ministry of Transport and Communications and facilitated by DNV, the first pure battery-driven ship, a ferry, will go into operation on the route between Lavik and Oppedal in Sognefjorden, western Norway, in 2015. The ferry will have access to cheap and renewable electricity at both ports.
Hybrid systems
The actual fuel and emissions reduction gained from a hybrid power system depends on the optimisation of its energy production efficiency. For internal combustion engines, energy efficiencies are normally significantly decreased and the specific emissions increased at low and varying loads. Hybrid power systems avoid operation at these loads by using the battery as an energy buffer that absorbs the load variations. The benefit of hybrid power systems is therefore closely associated with the operational profile. A car driving in urban areas at low and varying engine loads will have a significantly higher benefit from a hybrid power system than one driving on the highway. Similarly, these systems will be beneficial on ships when the requirements for power variations are high, while the average power requirements are low. This operating profile is relevant for both tugs and offshore supply vessels. Foss was the first to commission a hybrid tug in 2009. The first hybrid offshore supply vessel, Viking Lady, will be commissioned in 2013.
Source: DNV