Electric travel – a ferry good idea

This article originally appeared in the July '22 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Since 2018, an electric ferry, converted from diesel operation, has been running the Helsingborg (Sweden) to Helsingor (Denmark) route 46 times a day. It has a 4.1MWh battery and 6MW of power via four 1.5MW propellers and a diesel engine for emergency use. The route is just 4km (2.5 miles) but the battery would only last for 14km or 8.7 miles so fast charging via automated connection on the quayside keeps it topped up. Charge times are between five and nine minutes.

In Norway, a fleet of electric ferries operate on the Hareid to Selesund route and use smart charging at the dockside. Strong headwinds mean the electricity consumption can be high for the 16km (10 mile) journey. The rapid charging and grid supply system was developed by Norwegian Electric Systems (NES) using Danfoss’s Vacon NXP DC/DC converter, designed for hybrid systems, and the company’s Vacon NXP grid converter.

Terminal power

An automated charging tower on the shore connects to the ferry in seconds and charges 350kWh in six minutes. “This scale of charging places stringent demands upon the smart grid onshore at both ends of the route, in Hareid and Sulesund, which supports reliable power supply for the electric vessel rapid charging system,” explains Danfoss, Country Manager, Norway, Håvard Wolden.

It was soon realised that the ferry terminals in Hareid and Selesund required extra power to achieve the necessary charging power. NES strengthened the power grid on both sides, and retrofitted vessels with batteries, converter and power control technology.

“During charging, the system ensures the charging power adjusts to transfer exactly the energy required, not more and no less.

"By ensuring optimal charging power, the system avoids unnecessary wear on batteries and power electronics, both onboard and on shore,” explains Torbjorn Haygland, Vice President of Scandinavian countries are adopting electric ferries with gusto.

“The charging system reduces peak power consumption by drawing onshore battery power instead of energy from the grid, for short intervals of time, for example with the electricity price is high” he continues. The onshore power supply is supplemented with battery storage systems powered by Danfoss grid converters.

The electricity used to supply the system is supplied from renewable sources, to minimise losses and optimise operating costs. Replacing the diesel ferry fleet has saved an estimated 7,000 tonnes of CO2 emission each year, based on 32,000 vessel charging sessions.

Sweden’s super chargers

‘Super fast’ charging is in place for the Echandia Marine fleet of Green city Ferries, operating in central Stockholm, Sweden. The Movitz electric passenger ferry is equipped with a new battery system, Echandia LTO, based on battery technology that enables superfast charging. The ferry can be fully charged within 10 minutes with up to 500kW charging power.

The fast-charging station in central Stockholm provides considerably higher charging power than those available for charging electric cars, says Echandia Marine’s Bilal Malla. Movitz operates using ‘power as a service’ provided by Swedish power company, Vattenfall. The company supplies the charging station, battery system and drive line and also operates and maintains the system.

Flying ferries

Stockholm will also be the home for Candela’s P-12 Shuttle, an electric flying ferry with hydrofoils which lift it out of the water to ‘fly’ across the commuter Ekerö to the city centre. The 30-passenger ferry will travel at a top speed of 30 knots, using 0.1kWh per passenger kilometre, says the manufacturer. It should halve the commute of 15km from 55 to 25 minutes.

The carbon hulled vessel creates near-zero wake for a smooth crossing for passengers and without causing wave damage to other vessels or shorelines.

Next year, the capital will conduct a nine-month trial. If successful, the city’s fleet of more than 70 diesel ferries may be replaced with the P-12 Shuttles.

Currently there are two 200-passenger ferries operating, but they are less than a third full on each crossing. The two departures per day could be replaced with a P-12 Shuttle leaving every 11 minutes, says the Erik Eklund, chief, commercial vessels at Candela.

This article originally appeared in the July '22 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.