Photo: Stadtwerke Konstanz

Car ferry: Wireless power supply via induction

At the suggestion of the Constance public utility company, students at the HTWG University of Applied Sciences Constance Technology, Economics and Design have developed a concept for supplying the Lake Constance car ferries between Constance and Meersburg with local emission-free power via induction over the ferry bridge. This can potentially save up to 20 tonnes of CO2 per ferry per year. Stadtwerke Konstanz wants to implement the concept.

Car ferries shuttle across Lake Constance between Constance and Meersburg around the clock, seven days a week. During rush hour, they are in the port of Meersburg or Constance-Staad for eight minutes, and at night for up to 45 minutes. Even during this time, the ships need energy, after all, all the measuring instruments on the bridge, the lighting on deck, the WLAN supply and the coffee machine for the on-board catering are to remain in operation. Currently, the required electricity is generated by a diesel generator on board. At the suggestion of the Stadtwerke Konstanz (Constance public utility company), HTWG students have developed a concept for an emission-free on-board power supply via induction over the ferry bridge.

“It’s well thought out, smart and absolutely convinced us,” says Christoph Witte, technical manager of Stadtwerke ferries. He announces his intention to implement the concept with a first ferry. At present the subsidies for this are still being applied for. “It will be a first component of our measures to save CO2 emissions in ferry operations,” he explains. “The big idea behind this is to develop automatic charging technology for the ferries of the future, which means all-electric ships where the batteries are automatically recharged during the short turnaround times.”

Every time the ferries enter the harbour, they have docked accurately at the landing stage for decades, so that vehicles and pedestrians can drive or walk ashore comfortably. In the process, the landing stage lowers onto the deck of the ferry. If an induction plate is now installed on the ferry bridge and on the deck respectively, the contactless power supply to the ferry can be provided directly via the jetty itself from landing to departure.

High security in the special ferry environment

“The procedure is impressively simple and convinces with its high level of security,” says Daniel Kirch, project manager at Stadtwerke Konstanz. The power supply without exposed electrical contacts is the ideal solution in an environment exposed to the elements. “There are no open contacts, no sparkover, no short circuit without plugs and sockets,” lists mechanical engineering student Tarek Sadek.
The positioning is optimal regardless of the water level, as the ferry bridge adapts to the water level. In addition, the induction device is robust and has a long service life, and the maintenance effort and the probability of failure are low, emphasizes mechanical engineering professor Dr. Peter Stein. This would be different, for example, with a robotic arm that makes a connection to the ferry after each entry: it would be prone to failure and, in the case of a plug-in connection, high wear and tear would occur on the sockets due to the repeated plugging in and unplugging several times a day. In addition, water, dirt and air could penetrate. Prof. Dr. Heinz Rebholz, Faculty of Electrical Engineering and Information Technology, adds: “The power supply by induction meets the legal requirements, so that health hazards are excluded.”

Successful interdisciplinary cooperation

Eight HTWG students, Bachelor and Master students from the Faculty of Mechanical Engineering and the Faculty of Electrical Engineering and Information Technology, developed the concept. “The project demonstrates the innovative power of HTWG. It is an exemplary combination of practice-oriented teaching, applied research and transfer for the benefit of regional companies and a resource-conserving society,” says Prof. Dr. Gunnar Schubert, Vice President for Research, Transfer and Sustainability. The power supply via induction was not the only focus of the students’ work at the beginning. Among other things, they had considered supplying electricity via photovoltaic cells on the ferry roof – which is still conceivable as a supplement to the power supply.

Onboard gastronomy closed due to Corona pandemic

“The students first measured the power consumption on the ferry during a few crossings and calculated the energy consumption from this,” explains electrical engineering professor Dr. Heinz Rebholz. Since the on-board catering remains closed due to the pandemic restrictions, the students had to additionally estimate the consumption of the refrigerators, coffee machine and cash register systems. Then it was a matter of defining the requirements for the inductive charging system and designing it with all its parameters. Transmission losses also had to be estimated. In parallel, the students researched offers on the market. “The interdisciplinary collaboration as well as the cooperation with the employees of the municipal utilities was enriching for everyone involved. The students learned to see the topic through different lenses,” says Prof. Dr. Heinz Rebholz.

The Meersburg car ferry will be the test vehicle

“It was a great project. If our idea is now implemented, I’m incredibly happy,” says mechanical engineering student Tarek Sadek, who wrote his bachelor’s thesis on the topic. The car ferry FS Meersburg is suitable as a test vehicle for the endurance test. The energy supply of this ferry is modular. It has two separate power circuits or diesel generators. In this way, the generator, which is not connected to the main drive, can be switched off while the ship is at berth.

Savings potential: 20 tons of CO2

The next step is to develop a suitable induction plate in cooperation with an industrial partner. It could initially be attached to a ferry bridge in Staad, and later another one in Meersburg. “If we replace the use of the power generator with shore power while the ferry is moored at the jetty, we can save up to about 50 percent of the diesel consumption needed to power the ferry during daytime course operations,” Daniel Kirch calculates. With the now measured consumption of 25kW and two crossings per hour with a laytime of 15 minutes each, this would be approx. 20 litres of diesel per ferry and day, which in turn would correspond to up to 20 tonnes of CO2 per ferry per year.

Further expansion stages possible

The concept can be further expanded, says Christoph Witte: “For example, a battery on board could completely replace the diesel generator for the on-board power supply. “A battery of the size installed in the Renault Zoe would suffice for this,” says mechanical engineering professor Dr. Peter Stein. The next stage of development would be the loading of a ferryboat powered entirely by electricity.

And the research vessel of the HTWG also benefits from the concept

The HTWG research vessel “Solgenia” will also benefit from the developed concept. The inductive charging system will initially be tested on the ship with a photovoltaic-hydrogen hybrid drive.