The first of its kind: low-emission ship generator successfully trialled

• In collaboration with universities and industry partners, the DLR has developed and tested the first ship-suitable generator consisting of high-temperature fuel cells and batteries.
• The hybrid system provides both electricity and heat. The fuel cells can be powered by hydrogen, natural gas, methanol or synthetic fuels.
• The generator produces 30 per cent less CO₂ and 95 per cent less soot than marine diesel or gas engines even when using natural gas.
• Focus: energy, transport, hydrogen and climate-friendly shipping.

A low-emission generator for passenger ships has been developed and tested by the German Aerospace Centre (DLR) in collaboration with industry and research. The system is the first of its kind to be ship-suitable, being based on high-temperature fuel cells and batteries.

The remarkable attribute of these fuel cells is their versatility, rendering them compatible with a wide range of fuels. These include natural gas, methanol and hydrogen, as well as CO₂-neutral power-to-liquid fuels — synthetic fuels produced using renewable energies. Even when natural gas is used as fuel, the hybrid generator emits one-third less CO₂ and 95 per cent less soot than marine diesel and gas engines.

Such generators are not only suitable for passenger and cargo ships, but also for stationary industrial applications.

Lower limit values for emissions in shipping

By 2030, carbon dioxide emissions from shipping are to be reduced by 40 per cent compared to 2008, and by 70 per cent by 2050. Passenger ships are particularly affected by this. Unlike cargo ships, they often spend more than half their time in harbours due to the many stopovers. The engines continue to run during this time in harbour, which produces additional exhaust gases.

At the DLR in Stuttgart, the participants in the EU project NAUTILUS (Nautical Integrated Hybrid Energy System for Long Range Cruise Ships) have developed the first ship-suitable generator consisting of high-temperature fuel cells and batteries and tested it on land. Suitable for ships because all the components are designed to be stable enough for use at sea and function reliably even in heavy swell and in an inclined position.

The so-called hybrid generator system produces electricity and heat. The electrical output of the test system is 80 kilowatts. "Depending on the size and energy requirements of a ship, generators in the megawatt range are feasible," emphasises Dr Syed Asif Ansar from the DLR Institute of Engineering Thermodynamics.

30 per cent less CO₂ and 95 per cent less soot

DLR and the project participants have measured the CO₂ and soot emissions of the NAUTILUS generator when using different fuels. Even when running on natural gas and methanol, the generator emits around 30 per cent less carbon dioxide and 95 per cent less soot than conventional ship generators with diesel or gas engines.

The high-temperature fuel cells achieve a particularly high electrical efficiency of 60 per cent, which means that around two thirds of the energy contained in the fuel is converted into electricity. Compared to conventional fuel cells, which have an operating temperature of around 80 degrees Celsius and a lower efficiency of around 50 per cent, the operating temperature of high-temperature fuel cells is between 650 and 800 degrees Celsius. This accelerates the electrochemical reaction of fuel and oxygen in the cells and enables the direct use of liquid fuels.

In addition, the high temperature of the waste heat can be used specifically for heating or to produce hot water. "At our test facility, we have shown how the waste heat generated in the fuel cells can be fed back into the energy system. Through the targeted use of heat, we achieve an overall efficiency of more than 80 per cent," explains Dr Ansar. "This makes the NAUTILUS generator around twice as efficient as a diesel or gas engine."

Fuel cells work with hydrogen, natural gas and methanol

In addition to hydrogen, the solid oxide fuel cells of the NAUTILUS generator also work with natural gas and methanol, which are first chemically converted into hydrogen and carbon monoxide.

This enables the gradual conversion of ships for future operation with CO₂-neutral, synthetic fuels or hydrogen. "During a partial conversion, fuel cells and existing gas engines use natural gas or methanol as fuel at the same time. This means that parts of the infrastructure on board can continue to be used. This saves costs and is often easier to implement," explains Dr Ansar.

Another advantage of the technology is that, unlike a centralised marine diesel engine, the components of the generator system can be distributed on board. This means that the supply system can be optimally adapted to the conditions of a ship.

Ship manoeuvres, load changes and hotel operations

"At the NAUTILUS test facility, we tested various scenarios for the energy requirements of ships. These include overseas voyages, ship manoeuvres when docking and, in the case of cruise ships, hotel operations in port," says Dr Ansar.

The challenge is to optimise the performance of the fuel cells and batteries to the power consumption of the ship. To this end, the NAUTILUS team investigated what happens when the power requirement changes within seconds, for example when accelerating or during a turning manoeuvre. "The batteries temporarily compensate for the sharp increase in current so that the fuel cells always remain in the ideal operating state when their power is ramped up," says Dr Ansar. "The DLR Institute of Engineering Thermodynamics and the project team have developed a special energy management system for this purpose. We made sure that the interaction between fuel cells and batteries always achieves the highest level of efficiency."

Using a "digital twin" of the generator system and energy management, the NAUTILUS team simulates fully integrated energy systems on ships. The DLR scientists are developing technical proposals for systems with outputs of 5 to 60 megawatts. This corresponds to the requirements of passenger ships with 1,000 to 5,000 passengers. The computational model can also evaluate existing systems or those already in operation and make them more efficient.

Next step: sea trials

Following the successful test runs of the NAUTILUS demonstrator on land at the DLR Institute of Engineering Thermodynamics and subsequently at the DLR Institute of Maritime Energy Systems, the two institutes intend to test the hybrid generator system at sea.

Weiterführende Links

Project website NAUTILUS 

Video: NAUTILUS – a future propulsion of cruise ships

DLR-News: NAUTILUS – Reduzierung von Schiffsemissionen

DLR-News: Brennstoffzellen senken Schiffsemissionen