E-ferry Ellen: operational challenges and achievements unveiled

The world’s largest all-electric ferry in terms of battery power has been in operation a month. Its operator Ærø Kommune e-ferry project co-ordinator Trine Heinemann told Passenger Ship Technology “The downside is that we are still not using full battery capacity, the batteries are not yet properly balanced and we cannot get all the capacity in them that is needed for optimal operation. In principle the power/capacity is 4.3 megawatt hours, but because some strings cannot be charged more than 50% they cannot run on full capacity, so we are running on around 3.3 megawatt hours.”

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The operator’s aim to run Ellen on seven trips a day is therefore not possible, however this is not a critical problem at the moment as the operator only hopes to do this in high season.

Ms Heinemann said “The idea was that we start fully charged in the morning then charge a little less on the trip every time we charge so that at the end of the day it is empty. [The batteries are then fully charged as this is the optimal way to charge]. But we cannot really do that now and we have to charge for longer than calculated, maybe 10 minutes. We are doing four trips a day which is still good, and we have time to fix it and go up to seven trips a day.”

She explained that five strings out of 20 cannot charge to full capacity. “All cells in a string have to be very close to the same voltage and if there is too big a gap, either those with high voltage or those with low ones hold the others down. In one string a couple of weeks ago we replaced some modules, as the high cells were saying to the system that they do not want any more charge, and this means they hold back the lower cells from getting fully charged.”

Nevertheless a solution is being put in place – the higher modules will be disengaged from the system during charging so they do not affect the charging of the lower ones.

The ferry uses four charging lines, “which is good as it makes it more redundant, but occasionally one falls out or does not go in when we charge so we are only charging at half speed of the capacity on the affected room.” This can usually be solved by resetting the charging lines or connecting and reconnecting the charger. “It is not in that sense a big issue, but it takes time out and that is a challenge.” She said the issues relating to charging sounded like a software issue that should be easily resolved.

Despite small teething difficulties, the ferry is already a success. “It is really great it is actually sailing and we can sail a full trip and know it is working and in that sense these are just teething problems. We are all very happy with the design, as it is lying very well in the water. It is a nice ride and so quiet.”
The project is supported by the European Commission’s nearly €80Bn (US$90.5Bn) research and innovation initiative Horizon 2020 (H2020), and represents an important step in bringing carbon-free technology to the ferry sector, as the E-ferry is receiving the funding to provide a business case to encourage other operators to invest in fully battery-operated newbuilds.

As part of its EU funding, Ærø Kommune is required to log all data to provide concrete numbers on the operational costs of running a ferry.

Therefore Ærø Kommune has been recording how much energy is being used on each leg, how much it is using to charge and how long the charging takes. The figures are already good: “We are somewhere close to 800-900 kilowatt hours used on a leg and originally aimed for 790 and so we are pleased as it is very close. These are within the parameters we wanted to achieve so that is really good.”

Initial estimates suggested Ellen would be 40% cheaper to run operationally compared to a diesel alternative – and Ms Heinemann said the measurements recorded hold up with this estimate.

She commented “we need to think about how to present our recordings, whether that be very scientific, a business case or a mix of both.”

Another achievement is that the ferry has a crew of three approved – usually such a ferry would have four to six members of crew. This is because no engineer is needed on board, due to all systems being automated.