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How electric ships can charge at sea
With a new magnetic charging plug for boats, it's about as easy as placing a cup in a cup holder.
It is challenging to set up charging stations at sea. But some companies have already made a start, including the shipbuilding group Vard.
“Movement and wear make charging at sea challenging when using a classic plug-based connection. Mechanical wear and tear, corrosion, and demanding maintenance increase the risk and costs,” says Håvard Vollset Lien at Vard. He heads the large Ocean Charger project.
We are primarily talking about electric maintenance vessels. These vessels maintain offshore wind farms, so called Service Operation Vessels (SOVs), according to Lien.
But the technology could also be used for other types of ships. For example, supply ships in the oil industry, known as Platform Supply Vessels (PSVs).
Magnetic magic replaces vulnerable plugs
We cannot control the weather and waves, but what about the connection plug itself? Could there be a smarter solution?
This is precisely what researchers and engineers in the Ocean Charger project have been working on.
“We’ve looked at a lot of solutions here," says Giuseppe Guidi, a researcher at SINTEF. “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.”
In principle, the concept is magically simple: classic contacts that corrode are swapped out for magnetic fields.
Charging without physical metal contacts provides good protection against nature’s corrosive elements.
Like placing a cup in a cup holder
A coil is mounted on the cable coming from the charging station. The charging station could, for example, be a wind turbine.
It is safely encapsulated in a waterproof material that is not affected by salt or algae. A similar coil, also well protected, is mounted on the ship.
Researchers at SINTEF have designed and tested what is essentially the heart of the charging system: the inductive charging coil.
Here, the current is transferred without physical contact through a magnetic field when the coils are close to each other.
A stable connection every time
“It won’t be necessary to be precise when lowering the plug into the receiver hole,” says Guidi. “It’s almost like putting a cup in a cup holder. It will fit no matter which way it's turned. Very plug and play.”
This new plug will provide a faster, safer, and more stable connection – every time.
A puzzle with many components
Transferring power wirelessly to a ship's battery may sound quite simple. In practice, it requires a whole chain of technical solutions. They must work in sync, be cost-effective, safe, and practical.
The power must first be converted from alternating current to direct current and transmitted at high voltage through a flexible cable.
It must then be converted into high-frequency current that can be transmitted through magnetic fields. On board, the power must be captured, converted again, and safely delivered into the battery.
For this to work efficiently, special cables, a smart control system, and components that can withstand both high power and rough conditions are essential.
Two areas have been especially challenging
Only when all these pieces fall into place does magnetically coupled fast charging at sea become possible.
Guidi says there are especially two areas the team has focused on.
One is the electromagnetic design. This concerns how the coil is wound and which materials are used so that the system can deliver high power within a small surface area.
The other is the control system. An intelligent management system is needed to ensure that energy loss is minimal.
Safe charging regardless of weather
The goal has been to achieve an efficiency level comparable to charging with an electrical contact, while gaining the enormous advantage of being maintenance-free and robust.
And they have succeeded.
“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,” says Vollset Lien.
Even when the wind is not blowing, charging can be ensured through intermediate storage of electricity in a so-called OSS hub.
Functions as an electrical hub
“The OSS hub functions as an electrical hub out at sea, collecting electricity from the wind turbines and making it possible to charge vessels directly, without travelling to shore,” says Lien.
In the long term, he envisions that this type of charging solution could be used to establish a charging infrastructure along the entire Norwegian coast.
“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,” he says.
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