ABB has won an order to supply the first direct current (DC) power grid for use on board a ship. The equipment will allow a new offshore platform support vessel, being built in Norway, to cut its fuel consumption and emissions by up to 20%.

In traditional electrically-propelled vessels, multiple DC connections are made to thrusters and propulsion drives from an alternating current (AC) circuit, accounting for more than 80% of the vessel’s electrical power consumption. The new onboard DC grid will distribute power through a single DC circuit.

The ship`s engines will no longer need to run at a fixed speed, allowing the speed to be adjusted to optimise fuel consumption. By eliminating the need for bulky transformers and switchboards, the footprint and weight of the electrical system will be reduced by up to 30%, leaving more space for passengers or cargo, while also providing more flexibility in the positioning of equipment in the vessel.

The DC power network will also make it easier for vessels to obtain electricity from the shore when they are docked. At present, linking 50Hz shore grids to the 60Hz systems widely used on board ships, is difficult. DC sources such as fuel cells and photovoltaic panels could also feed power directly into the DC networks.

ABB announced the onboard DC grid technology last year as part of a revival of DC power systems. The technology is aimed at ships with low-voltage on-board circuits, such as offshore support vessels (similar to the one shown above), tug boats, ferries and yachts.

For a typical vessel, the emissions savings are equivalent to around 1,800 tonnes of CO₂ a year – similar to the annual CO₂ emissions from 680 cars.

The first order, placed by the ship owner Myklebusthaug Management, includes all of the power, propulsion and automation systems for a 93m-long, 5,000-tonne multi-purpose oil field supply and construction vessel, which is due to be delivered in the first quarter of 2013.

“With this solution, the vessel will be ready to maximise opportunities in energy savings with supplementary DC energy sources, such as solar panels, fuel cells, or batteries connected directly to the ship`s onboard DC grid,” says Veli-Matti Reinikkala, head of ABB’s process automation division. “The onboard DC grid will help the vessel operate from the very first day at the highest levels of fuel efficiency with low emissions.”