Danish shipping company tests flywheel on ferry: “Could be extraordinary”


A ship arrives loaded. But what? Magnetic flywheels. The Danish Molslinjen puts a spin on “mechanical batteries” to get environmentally friendly electric operation.

Many shipping companies install electric batteries to be able to replace fossil fuels with electricity. So does the Molslinjen. But the Danish shipping company is also investing in magnetic flywheels, where a rotating mass stores kinetic energy.

In mid-November Molslinjen invested in Wattsup Powera Danish startup company that manufactures flywheels for various purposes.

– This has the potential to be something extraordinary if we make it work, says Molslinjen CEO Carsten Jensen to the Danish newspaper Ingeniøren.

The flywheel’s rotor is built into a vacuum-filled cylinder, where it hangs freely floating in a magnetic field. In the rotor there is a combined motor and generator. The system is charged by the motor taking electricity from the grid and accelerating the rotor to a higher speed. Thanks to the vacuum, there is almost no friction at all, which allows the rotor to spin without losing its kinetic energy. When the electricity is needed, the process is the reverse compared to charging; the rotor slows down while driving the generator that provides electricity.

The faster you can get the rotor to spin, the more energy the flywheel can store.

– In theory, you can store a much larger amount of energy than in an electric battery, so we will try to get them up in faster rotations, says Carsten Jensen to Ingeniøren.

Now Wattsup’s prototypes will be tested in the US to see if the theories hold. The next step will be to do a test installation on the high-speed catamaran Express 4, which operates the Kattegat route between Aarhus on Jutland and Odden on Zealand. The idea is that the system should initially supply power to simpler functions, for example a ventilation system. In the long term, Molslinjen hopes that a number of flywheels will be able to power an entire ferry.

Light, long-lived – and expensive

The shipping company sees more advantages with flywheels compared to batteries in addition to large storage capacity. The flywheels, for example, have a longer service life and lower weight.

But the cost can be an Achilles heel. One of the challenges is to build the systems at a reasonable price without sacrificing either security or reliability. That’s the assessment made by Nikolaj Zangenberg, who is innovation coordinator at the Danish Technological Institute and has previously collaborated with WattsUp Power in the development of flywheels.

– My guess is that it will be a hybrid solution together with, for example, e-fuels or perhaps also electric batteries. I don’t know if the flywheel will be able to stand alone, he tells Ingeniøren.

The amount that Molslinjen has invested in Wattsup Power has not been made public. The company, which was founded in 2014, has been manufacturing since before flywheels in two size classes. One of 70 kWh which, for example, can store excess energy from solar power and one of 250 kWh for industrial applications. The company states that their fastest rotor spins up to 50,000 revolutions per minute.


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