An electromagnetic ‘plug-and-play’ charging technology will allow electric vessels to charge offshore without direct physical connections.

Currently, battery-powered offshore vessels rely on charging infrastructure located at ports, limiting how far they can travel between charges. 

It would make sense if electric service operation vessels (SOVs), such as those used to maintain offshore wind farms, could tap into the electricity directly generated from wind turbines. However, using plug-based connections in harsh, salty waters is very challenging. 

To address these challenges, Norwegian shipbuilding company Vard launched the Ocean Charger project to develop and test offshore charging technologies. One of its key research partners is SINTEF, a Norwegian independent research institute. 

Giuseppe Guidi, a senior research scientist at SINTEF, said: “We’ve looked at a lot of solutions here, and we’ve tested a possible solution that works almost like a regular electrical contact. But we can avoid all the problems because we transfer the power inductively by encapsulating the plug itself in materials that can withstand just about anything.”

The charging system uses no direct physical contact between exposed metal components. Instead, an inductive charging coil, mounted on a cable from an offshore wind turbine, for instance, is sealed in a waterproof casing. A similar coil, equally well protected, is mounted on the vessel. Current is then transferred between the two coils via a magnetic field.

Guidi said: “It won’t be necessary to be precise when lowering the plug into the receiver hole. It’s almost like putting a cup in a cup holder. It will fit no matter which way it is turned. Very plug and play.”

While a magnetically-coupled fast-charging solution may sound simple in theory, in practice there are many technicalities to consider. For instance, alternating current is converted to direct current, sent at high voltage through a flexible cable, and then converted to high-frequency current that can be transmitted via magnetic fields. On board the ship, the power must be converted again before being transferred to the battery.

According to the research team, the two areas that required the most work were the electromagnetic design, enabling the system to provide high power in a compact space, and the control system, ensuring energy loss was kept to a minimum.

Håvard Vollset Lien, vice-president of research and innovation at Vard, who heads the Ocean Charger project, said: “The genius of charging at sea in this way is that the electrical energy produced locally is used directly to charge the ships, which ensures that very little energy is wasted.”

Even if the wind is not blowing and the turbines are not generating power, the ships can still be charged via an electrical storage hub located at the wind farm. 

In the long term, Vard envisions that this type of charging solution could be used to establish a charging infrastructure along the entire Norwegian coast. While the project has focused on SOVs, it could be used for a range of other vessels, including supply ships used in the oil industry.

Vollset Lien said: “Perhaps one day it will become a common sight for electric service vessels and coastal vessels to charge their batteries at sea and out in the shipping lane.”