E-ferry evaluation: Electric propulsion cheaper than diesel

By Halfdan Abrahamsen
For the Bay Journal News Service

As part of the team that works with the fully electric “E-ferry” Ellen in Denmark, it was exciting for me to get requests from the Chesapeake Bay area for information, and I was intrigued when I found out that the Ellen was featured in a Maryland study about the potential use of a ferry for crossing the Bay. (See “Maryland officials zap electric ferry proposal for Chesapeake crossing,” Bay Journal, April 2020.)

With that in mind, I wanted to share that the company I work for, Ærø EnergyLab, recently published its performance data and calculations on the costs of building and operating an electric ferry. Everyone is invited to make use of it. We hope this will help managers make decisions on the basis of valid and current figures. The lack of data in connection with building fully electric ferries has been a real hurdle to getting projects under way, and we hope that our data will fill a void.

Our conclusion is clear: It is cheaper to build and operate a fully electric ferry than a diesel or diesel-electric hybrid ferry.

The homeport of the E-ferry Ellen is Søby, a small town on the island of Ærø (Aeroe) in the southern Danish seas, inhabited by 6,000 people. The only connections to the mainland are by ferry, so ferry sailing and ferry building is both a matter of necessity and pride to the islanders.

The Ellen was built with support from the EU’s Horizon 2020 program, and has been in operation since August 2019, making five round trips a day — and seven trips is an option. Ellen spends around 1600 kilowatt hours as she travels the route of 22 nautical miles (25 miles) and carries a maximum of 31 cars. She is fast, and typically “sails” just short of 13 knots (nautical miles per hour).

Moreover, the Ellen travels a route that is seven times longer than any other electric ferry in operation. She covers the 22 nm without a recharge, and can actually go at least 45 nm. After being fully charged during the night, she only needs quick spot charges during turn-arounds in Søby Harbor.

Our calculations show that fully electric sailing is the best solution, economically, for a local or regional ferry operator. Investment costs are higher, but the savings in operation offset those costs after four to eight years. Thus, as the lifespan of a ferry is typically 25 to 30 years, an operator can look forward to perhaps two decades significant savings after the initial investment is recouped.

An E-ferry is also good for the local and global environment, because it releases neither greenhouse gases nor dangerous particles. We save the atmosphere from more than 2,500 tons of carbon dioxide per year compared with the diesel ferry it replaced.

How does Ellen perform so well? The local ship architects, Jens Kristensen Aps, designed the ferry for fully electric operation from the start. It has pointy ends and a slight bulge in the middle, which lets her slip through the water very effectively. Also, the passenger salon sits close to the waterline, on the same level as the car deck — most of which is uncovered to cut down on weight.

The design also eliminates the extra weight of diesel fuel tanks and emergency generators. Instead, the Ellen has two independent battery rooms, each connected to one of the dual propellers. This makes the systems fully redundant, and she can always get home on just one battery room and propeller.

Passengers love the Ellen. We offer light food and drinks, but elaborate kitchen facilities, cabins and electronic entertainment items have been left out. Such things are superfluous on short crossings, and there seems to be no great demand for them among passengers. Instead, they often praise the sundeck, where there’s none of the usual smog, no noise and no rumbling.

The captains also love the ship, in part because the power is instantaneous. This makes it easier to navigate tight ports and gives them greater confidence in maneuvering.

Many people are surprised to learn that the Ellen’s system is more environmentally sound than diesel propulsion even if you charge the batteries with electricity from fossil fuels. This is because the energy efficiency of the total system is 85%, which is more than twice that of a diesel ferry. That results in direct savings to the operator.

Furthermore, the fundamentally simple technology means that Ellen is certified to sail without a ship engineer onboard. This also translates into savings.

Thus, for both environmental and economic reasons, we are confident that our new data will be a positive surprise to many and change conventional wisdom on going fully electric in the maritime world.