Technology group Wärtsilä Corporation on Thursday (24 August) published an insight article breaking down the basics of hybrid ships. It also shares experts’ predictions on what they see in the coming years for hybrid ships and what those predictions mean for ship owners: 

Are you already sailing a hybrid ship and wondering what the next decade will bring? Or maybe you’re interested in investing in a hybrid vessel and want more insight? Let’s dive into the hottest trends in hybrid and find ways to save fuel while increasing vessel performance.

What trends do we have to look forward to in the world of hybrid ships? Experts predict that the coming years will see:

• New battery types
• More powerful batteries
• Batteries being chosen based on function, not size
• An increase in the use of fuel cells
• More DC hubs – which might not always be the right choice
• Standardised shore power
• Hybrid retrofits in the ferry segment

Want to start with the basics? In the next section you can get up to speed with how hybrid ships work – and the benefits they bring.  

What are hybrid ships?

Hybrid ships are vessels that use two power sources, usually a conventional combustion engine and a rechargeable battery. They can be as small as a local ferry or as large as a Pure Car and Truck Carrier (PCTC). The number of hybrid ships is growing across all segments. The offshore industry used to be the biggest market for ships with hybrid systems, but today there are hybrid versions of small merchant vessels, PCTCs, RoRo and RoPax ferries, smaller ferries, and special vessels like tugs and research ships.

How do hybrid ships work?

Hybrid electric ships can instantly switch between engine and battery when required, or they can be used simultaneously. The battery is used in one of two ways:

• For optimising the propulsion train – the battery is used for functions like spinning reserve, peak shaving, black out prevention or load ramp-up support
• For zero-emission sailing – the battery is the sole power source for the vessel in manoeuvring or harbour operations.

The key to maximising the benefits of a hybrid system is a dedicated energy management system (EMS) that both optimises the interaction of the different power sources and safeguards the battery by directly controlling the converter that determines the charge and discharge rate. A standard power management system (PMS) cannot do this.

Will hybrid save me money?

Running a hybrid ship can provide fuel savings of 15–25% compared to an equivalent diesel-powered vessel. Gensets are subject to less wear and tear because they can be powered down when the battery takes over, meaning maintenance costs are lower too.

Running a hybrid ship can provide fuel savings of 15–25% compared to an equivalent diesel-powered vessel. 

What are the benefits of hybrid ships?

Aside from the cost and efficiency benefits, hybrid ships are also better for the environment, with up to 25% lower emissions than comparable diesel-powered vessels. This makes it easier to comply with strict emissions regulations and makes the vessel more attractive for charterers or passengers.

Running on battery power also reduces noise and vibration, so the vessel is quieter and more comfortable for passengers and crew. Less noise and lower emissions also have a positive impact on coastal communities and ecosystems – for example, with a hybrid vessel it is possible to sail with zero emissions when manoeuvring in harbour. If batteries are charged from shore side, the electricity already comes from up to 50% renewable sources.

What are the latest trends for hybrid ships?

Let’s look at what the future holds for hybrid vessels. Here are the top seven trends that we’ll see over the next decade – and what they might mean for you.

1. New battery types are becoming available 

All marine batteries are lithium-ion batteries, similar to ones from the automotive and energy industries. Now we’re starting to see the introduction of new lithium-ion battery chemistries for marine use alongside the common nickel-manganese-cobalt (NMC) batteries, including:

• lithium-ferro-phosphate (LFP) batteries, and
• lithium-titanium-oxide (LTO) batteries.

What does this mean for ship owners?

These new battery types offer varying advantages depending on the application area, such as a longer lifespan, lower weight or lower cost. Every manufacturer has their own claims about their product, and the number of battery suppliers is growing all the time. If you want a full market overview and recommendations for your specific vessel application, talk to a large marine electrical integrator like Wärtsilä. They will be able to advise you on the best battery chemistry and the optimal solutions for your vessel.

2. Batteries are becoming more powerful

In the past, batteries were mostly used for spinning reserve, where the battery provides the entire load for the application. For example, the spare genset would be turned off and the battery would provide the power for station keeping in offshore applications. Batteries were smaller and they were also used for peak shaving and ramp-up support.

Today’s ship batteries of up to 40 MWh make it possible to achieve zero-emission manoeuvring. Such a battery can also provide power during harbour stays.

However, the size of the battery is not the only important factor to consider. The right battery depends on how it will be used and the operating profile of the vessel.

Lower prices are not the reason for the trend of more powerful batteries. Although we saw a steady decline before 2020, this has now stopped. With the increasing global demand for the cells and their raw materials the price is not likely to fall further.

What does this mean for ship owners?

Bigger batteries offer more flexibility for zero-emission operation as they can take on more energy-intensive tasks. Designing a hybrid propulsion system based on your operating profile can lead to new ways to operate your vessel and greater efficiency gains. 

For example, a variety of different modes can be added to a Wärtsilä-designed propulsion system so the vessel operator can automatically run the propulsion train at optimal efficiency.

A propulsion system designed around a battery is much more efficient than older propulsion designs and can deliver significant savings. For example, the hybrid Misje Vita bulk carrier has achieved up to 40% fuel savings compared to similar vessels in its fleet. 

Battery technology has proven its long-term reliability in the demanding world of shipping. A reliable marine battery is crucial for the smooth operation of ships, and Wärtsilä has been a pioneer in this field. Our marine batteries have been in use for over 10 years, and they continue to perform well. This makes us the only integrator to achieve such a level of reliability.

3. The function matters, not the size

Because the battery helps optimise the propulsion system, its ideal size depends on the vessel’s operational profile. Different modes make it possible for the vessel operator to choose the most efficient way to run the propulsion system. For example, when shore-side charging is required, sailing considerations are not as important for battery sizing as charging time and capacity.

Because the battery helps optimise the propulsion system, its ideal size depends on the vessel’s operational profile.

Designing the battery system based on function is becoming more common. This makes for better propulsion systems. It can also spark innovation in ways to operate a vessel more efficiently.

What does this mean for ship owners?

Adding a battery to a ship’s existing propulsion system will just add weight to the vessel. To get real benefits, the propulsion system must be redesigned based on the functionality of the vessel.

Rethinking ship design can lead to significant cost savings compared to the original designs. If a hybrid vessel does not have less installed power, you should involve an expert to re-evaluate the design.

4. Fuel cells are becoming more common

A fuel cell works like a battery that doesn’t need recharging. It will produce electricity and heat as long as it has fuel and an oxidizing agent. Both batteries and fuel cells provide direct current (DC) electric power. Batteries are good at variable loads, while fuel cells are best for stable base loads as they do not react well to load changes. This is why fuel cells are always accompanied by batteries. 

Today, proton-exchange membrane fuel cells (PEMFCs) are available for marine use. They have more than 50% efficiency when hydrogen is used directly. If a reformer is needed to make hydrogen from another fuel such as LNG, a PEMFC is still as efficient as a good combustion engine – but much more expensive.

The more interesting fuel cell technology – which is currently under development and not yet available for marine use – is solid oxide fuel cells (SOFCs). SOFCs can directly use methanol or ammonia to produce electricity.

What does this mean for ship owners?

Some ship owners will pilot this technology to gain experience, but for most owners it’s a case of watch and wait.

PEMFCs are an option for owners who are planning to use hydrogen. You will need more space to store the hydrogen, and the added weight will decrease the range of your vessel.

5. DC hubs are becoming a default choice – even when they shouldn’t be

A DC hub is a new integration concept for powertrains that uses direct current (DC) for electricity distribution.

Hybrid ships typically have: 

• an engine with a connected generator that produces electricity at alternating current (AC) 
• a battery that produces DC. 

Until recently, electricity has been distributed in AC where needed. However, the DC hub, a new electrical integration concept is now becoming popular. The DC hub uses DC for electricity distribution.

When the main power source is a battery producing DC, it can make sense to have the DC hub eliminate a transformation step. However, a DC hub is still not the right answer for every hybrid vessel.

What does this mean for ship owners?

More and more hybrid ships are being designed with only a DC hub, which may prove to be a mistake.

DC hubs can make sense for smaller hybrid vessels with small high-speed engines, but they will not be ideal for high-powered vessels with many engines or larger hybrid vessels.

Consider a ship with a diesel generator as the main power source, producing AC. If the main consumer of that power is an electric motor or the hotel load – both of which require AC – converting the power from AC to DC and back again will produce heat and electric losses.

DC hubs can make sense for smaller hybrid vessels with small high-speed engines, but they will not be ideal for high-powered vessels with many engines or larger hybrid vessels. Instead, these vessels should connect the gensets to an AC grid and connect the batteries and other AC consumers to small DC hubs that are part of the total diesel-electric hybrid power train.

Hand-picked content: Wondering whether a DC hub would be right for your hybrid ship? Read more in DC or not DC, that is the question.

6. New standard for shore power gains popularity

The IEC 80005 standard for high-voltage shore connection (HVSC) systems has been in place since 2011. HVSC systems allow ships to be supplied with electrical power from the shore. Their original role was to eliminate the need to use auxiliary gensets while in port.

Because HVSC systems can also be used to charge the batteries of hybrid vessels, all big RoPax, RoRo and PCTC vessels currently being built with hybrid propulsion are equipped with IEC 80005 shore power connections. These vessels can take shore power in any port that provides it – and by 2030, all major ports will.

The capability of IEC standard shore power is simple. For example, if a RoPax terminal provides 6.6MW of shore power and your hotel load while in harbour is 3MW, the rest of the available power – 3.6MW – is available for charging your battery.

The disadvantage of this solution is that connecting takes a few minutes. You will need a faster connection solution if charging time is critical. This is where the so-called “ferry chargers” come into play.

The Megawatt Charging System (MCS), designed for trucks, will bring a step change in ferry charger standardisation. MCS features standard plugs that are easy to handle by one person. The system can also transmit up to 3MW of power in a very short time.

For a good example of how well automotive standards can work for marine, check out how the MD Medstraum, the world’s first zero-emission fast ferry, is successfully powered with standard CCS2 chargers, the same type used for electric cars.

What does this mean for ship owners?

Standardisation means charging will become easier and faster. If your vessel is equipped to plug into IEC standard shore power the connection will take a few minutes. If you need a faster connection solution, a so-called ferry charger can connect within 30 seconds. These can connect automatically or manually but are currently manufacturer specific, so you can only use them for a vessel that always runs the same route.

Every year ferry chargers can provide more power: the largest can now provide 15MW AC medium voltage power to a ship, or over 8MW in DC with no further conversion needed on board.

7. Retrofits reach the ferry segment

Hybrid systems are available as retrofits – for example Wärtsilä has completed around 30 hybrid retrofits in the last 10 years. Most retrofits have included the standard HY Module.

Ferry owners also have choices:

• Changing a traditional vessel into a hybrid ferry
• Turning a diesel propulsion train into a full electric one.

Because some gensets can be removed, space and weight are usually no issue. Other changes can also be managed, especially if there is a diesel-electric propulsion train.

The available charging time and power usually define the sizing of the new system – more than the sailing considerations do. Another factor in the hybrid conversion business case is the available support from local authorities for the charging setup.

What does this mean for ship owners?

If you are interested in retrofitting your vessel to turn it into a hybrid ship, there are two main actions to take:

First, look at the charging options along your route. This often determines whether a retrofit is viable.

Next, speak to a reliable, leading systems integrator. Wärtsilä has the experience to retrofit your vessel in the most efficient and optimal way and can support you throughout its lifecycle.

Photo credit: Wärtsilä
Published: 28 August, 2023