Powered entirely by batteries, Ellen is something of a Tesla among ferries. Fully charged, the 60m vessel can sail 22 nautical miles with up to 200 passengers and 30 cars onboard.
Totalling 4.3MWh this is the largest battery capacity at sea and equivalent to the average amount of electricity a UK household consumes each year.
After a 70 minute voyage, Ellen arrives at the harbour in Søby and moors alongside the charging station.
A mechanical arm plugs in and recharges the batteries in less than 25 minutes with clean energy supplied by local wind turbines.
"We are paying maybe 25% of what you would pay for running a similar diesel vessel." says Ms Heinemann. "So that's the significant saving."
Electric propulsion is beginning to spread from passenger cars to trucks and now ferries.