|Rendering of the battery-electric car ferry. Click to enlarge.|
Siemens, together with the Norwegian shipyard Fjellstrand, has developed a battery-electric car ferry, the miljøferge (environmental ferry) ZeroCat. The 80-meter vessel can carry up to 120 cars and 360 passengers. From 2015 onward, it will serve the E39 route between Lavik and Oppedal, across the Sognefjord. The ship’s batteries will be recharged in the breaks between crossings, a procedure which only takes 10 minutes.
The vessel currently serving this route uses on average one million liters (264 thousand gallons US) of diesel a year and emits 570 metric tons of carbon dioxide and 15 metric tons of nitrogen oxides. The electrically powered ferry was developed for submission to a competition organized by Norway’s Ministry of Transport. As a reward for winning the competition, the shipping company Norled has been granted the license to operate the route until 2025.
The aim of the development section of the competition was to achieve at least 15-20% energy and environmental efficiency in the operation of development ferry. The award criteria for the choice of provider in the final competition was a weighted combination of development ferry’s energy and environmental efficiency (40%) and lowest price on the operation of the ferry route as a whole (60%).
The ferry has been specially designed to accommodate the requirements of an electric drive system. As a catamaran with two slim hulls, it offers less resistance in the water than a conventional vessel. Furthermore, the hulls are made of aluminum instead of steel, which is conventionally used.
Rather than a diesel engine, the ferry is equipped with electric motors to drive the ship’s two screws. These motors are powered by a Li-ion battery weighing 10 metric tons. All in all, the new vessel weighs only half as much as a ferry of conventional design. This saving has a direct impact on the specifications of the drive system.
Whereas the ferry currently serving the route has an engine with an output of 1,500 kW (2,000 hp), the battery in the new vessel will have an output of 800 kW (1,100 hp). In normal conditions, operating at a speed of 10 knots, battery power of 400 kW (536 hp) will suffice.
According to Fjellstrand, the energy required for a crossing of the route at 11 knots is 155 kWh, and at 13 knots, 201 kWh. A full day’s operation would consume 6,300 kWh.
The crucial feature of the new ferry is that it only takes 10 minutes to recharge the 1,000 kWh lithium-polymer battery pack, using a 1,000 kW charger. In the two small villages linked by the ferry, however, the local grid is not equipped to deliver such a large amount of power in such a short space of time. To deal with this problem, batteries have been installed at each port. These serve to recharge the ferry’s battery during turnaround and are then themselves slowly recharged from the local grid.
Hundreds of ferries link Norway’s mainland to the islands off its coast and provide routes across its many fjords. Using today’s battery and recharging technology, all crossings of up to 30 minutes in duration could be served by electrically powered vessels.
Fjellstrand miljøferge (presentation)