The successful use of battery-electric ferries dates back to the beginning of the 20th century. The Rhine ferry between Bonn-Bad Godesberg and Königswinter- Niederdollendorf successfully started operation on 08 July 1908.² In modern all-electric ferry shipping, as with alternative propulsion concepts in shipping in general, Scandinavia is a pioneer. In 2015, Norway put the world's first battery-electric ferry "Ampere" into operation since the Second World War; in 2019, Denmark followed suit with the largest battery-electric ferry to date, "Ellen".³

Ferries play an important role in local and (supra-)regional passenger transport: on the two Hamburg ferry lines alone, almost 5 million passengers were transported in the first half of 2019, and the trend is rising.⁴ On Lake Constance, just under 1.2 million passengers used the twelve ferry lines operating there in the period from April to July 2019.⁵ The most common reasons for ferry travel are leisure and holiday trips. In contrast, the use of ferries for work or business purposes is low.


Use of battery storage

In contrast to other types of ships, the special sailing profile of ferries suggests full electrification. Where the interplay of distance, schedule timing and shore-side power supply allow, batteries can take over the entire energy supply of the ships. The longer the journey, the greater the need for charging time and charging power in port.

For seagoing ferries, the use of fuel cells is also a promising option. Corresponding concepts also require battery storage to optimise energy efficiency, but are still at the research stage. A pioneering role is played here by the newly established European research project "HySeas III" with eight partners from six countries. Within the framework of this project, the first ocean-going ferry with hydrogen fuel cell propulsion is to be developed.⁶

One example of hybridisation of conventional combustion engines with battery-electric propulsion is offered by the Swedish shipping company Stena Line, which currently has 14 ferries that draw shore power while in port in Kiel and in four other ports of the route network. The annual savings of 13,000 t CO2 are remarkable.⁷ If this is related to the average CO2 emissions of 157 g/km of newly registered passenger cars in Germany in 2019, this saving corresponds to around 83 million car kilometres.⁸ In addition, hybridisation even completely avoids nitrogen oxide and particulate emissions in the ports.⁷  

Performance requirements

Battery storage in ferry shipping must above all be safe and robust. As in shipping in general, fires on ferries must be avoided at all costs, as extinguishing and rescue work, especially on seagoing ferries, is extremely difficult. Therefore, the batteries used should present the lowest possible risks in terms of flammability and explosion.

The ability to charge quickly is a factor that, in combination with a shore-side power supply, has a favourable effect on battery dimensioning and timetable planning: the faster the battery can be charged, the tighter the timetable can be timed and the smaller the batteries can be dimensioned for the given charging possibilities. In ferry operations, several charging and discharging cycles per day can often be assumed. The service life of the batteries, measured in charging cycles, is therefore of central importance for investment security.

With regard to the retrofit market, it must be considered that batteries have to be integrated into already existing hulls. Minimising the space required for the storage units can therefore be of crucial importance for feasibility. This can be achieved by the interplay of deep dischargeability, fast charging capability and high energy density. Equally relevant for the retrofit market are the requirements for the installation site: here, the safety of the battery storage unit determines whether an expensive explosion-proof room is dispensable.