Electric transport: ships

Where are we?

Stable Diffusion idea of a solar ship

Electric shipping prime need

Electric transport faces significant challenges with shipping. The problem is not in the motors but in energy storage.

Different ships, different needs

However, shipping includes several different vessels with various tonnages and distinct functions.

Outboard motors

There are already outboard battery-powered electric motors for small boats. Mercury, the traditional outboard motors company, sells one. See video 1.

Video 1: Electric outboard motor

The performance is lower, but it has better torque and is more efficient per kWh comparatively. The battery runs for around 45 m but is swappable and weighs 7 Kg (16 pounds), allowing bringing along spares to increase range.

A boat company even launched a boat designed to operate with Mercury’s electric motor.

Sailboats and electric propulsion

Sailboats rely on the wind as the primary propulsion system. Motors play an auxiliary role. Still, engines must work when requested.

Turning on motors on a sailboat means a necessity that sails can not meet at that moment. The need could be docking or ensuring propulsion after the masts broke on a storm.

The problem is where to store the energy. Batteries are too heavy and may discharge too fast. Sailboats can stay at high sea for long periods, with no chance to recharge.

Solar sails can help sailboats

One way to recharge the batteries is solar sails. Sailboats have relatively large areas of sails. Fitting sails with flexible solar panels can increase the space for PV generation.

Figure 1: Sail fitted with PV cells (source)

Theoretically, you could fit all sails with PV. AI image generator stable diffusion pictures it like this (figure 2).

Figure 2: Stable diffusion image IA rendition of a sailboat with sails totally covered with solar cells (source)

When PV coatings are commercially available, the sails may become solar panels instead of serving as a surface to latch on solar cells.

Some go further and add solar cells to the ship itself. See figure 3.

Figure 3: Sailboat fitted with solar cells on its hull (source)

It can seem utopic to power a boat solely from solar panels. Yet, some watercraft do it, albeit at a low speed.

Solar sails help up to a point

When the sun shines, that is.

The effectiveness of solar sails generating electricity depends not only on bright skies but the interaction of ship orientation, latitude, hour of the day, and solar altitude and water albedo interaction at a given time.

The wiring topology also matters. Microinverters will probably work best than large strings.

The difference between high seas and harbor ships

Solar sails can help recharge on high seas, but sailboats still must prepare for the worst. Solar sails could reduce the capacity of the battery.

In practice, you have to take into account long dark skies spells. The ship can not recharge, and power to motors will be vital if a storm comes.

Batteries have less energy density than hydrogen. They will need to be closer to ports and take time to recharge. Small ferries would be an example of an application.

Hence, hydrogen fuel cells allow large ranges for shipping.

Some experts argue that long-distance shipping will require synthetic ammonia or methanol, splitting the hydrogen and then feeding the hydrogen into fuel cells. This way allows compacting the fuel in smaller volumes.

At the moment, neither batteries nor hydrogen powers any long-haul ship.

Harbor boat

An example is electric tugboats working around harbors. The Nederlander ship maker Damen sells two models of electric tugboats. The tugboats use batteries that recharge in 2 hours with a life of 30,000 cycles.

One is already in operation in the port of Auckland, New Zealand, winning the award of tugboat of the year in 2022 (see figure 4)

Figure 4: Tugboat Sparky at Auckland Harbor (Source)

An electric ferry in works in Norway since 2015 (figure 5). It recharges 10 minutes between stops and then fills up during the night.

Figure 5: Ferry Ampere in Norway (Source)

A competitor line launched a bigger one in 2021 (figure 6).

Figure 6: A bigger Norwegian electric ferry boat (Source)

Norway also has the NL Hydra, a hydrogen fuel cell ferry (figure 7).

Figure 8: Another Norwegian ferry electric with fuel cell and hydrogen (source)

Currently, Norway is working on autonomous electric ferries.

In France, a river cargo ship Zulu 06, is supposedly in operation since September 2021 on the Seine river (Figures 9 and 10).

Figure 9: Zulu 06 hydrogen river cargo ship leaving its Romanian shipyard on route to Le Havre (Source)

Figure 10: Zulu 06 hydrogen river cargo ship in Budapest on route to Le Havre (Source)

To conclude

I could go on. I was amazed by the number of electric ships (mainly battery-operated and some fuel cells) already in operation.

Several viability studies for ship electrification vie for hydrogen, from national laboratories to naval engine manufacturers. Currently, the technology is ready to deploy: the problem is economic and regulatory.

The technology is ready but needs to scale up to become economically competitive. Portside refueling infrastructure needs addressing as regulation.

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