FUEL CELL FOCUS
POWER DENSITY IMPROVES, BUT CAN NEVER MATCH DIESEL When fuel storage volumes are included, lower power density is an inevitable trade-off, Paul Gunton hears Achieving a zero- or even low-carbon ship “is not business as usual”, Ed Fort, global head of engineering systems at Lloyd’s Register, told The Motorship. Even though fuel cell power density has improved, largely led by the automotive industry’s use of low temperature polymer-electrolyte membrane (PEM) technology, “compromises will need to be made if ambitious decarbonisation targets are to be realised”, he said. Although fuel cell generators proposed for marine applications “are beginning to ‘compete’ with conventional diesel gensets,” they will have an increased footprint once both the fuel cell and its fuel storage are considered. An alternative solution would be to increase bunkering frequency, but otherwise a corresponding reduction in cargo or passenger carrying capacity may have to be considered, he said. An alternative technology, the solid oxide fuel cell (SOFC), is less mature than PEM, he said, and its power density is currently significantly lower than that of conventional diesel gensets “but with development, it could offer significant advantages which potentially include extremely high electrical and thermal efficiencies and, recognising a large number of ships are likely to be operating on natural gas for many years to come, a potential solution for the methane slip issue”. Lloyd’s Register classed the world’s first SOFC installed on a deep sea vessel in 2010. The 20kW, EU funded demonstration unit was developed by Wärtsilä and installed on the Wallenius-owned PCTC Undine and operated successfully connected to the ship’s main power network.
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We are convinced that in a few years, you will be able to obtain 500kW out of a 20ft container That was a year after the 92m platform supply vessel Viking Lady was fitted with the first large scale marine fuel cell system and fuel cells’ power density has come a long way since then. It used LNG as fuel and generated 330kW, but took up a lot of space. The fuel cells themselves were housed in a purpose-built container measuring 13m x 5m x 4.4m while other components occupied a standard 20ft container. The whole installation weighed 110 tonnes. That trial formed part of a DNV-led project called the FellowSHIP project (Fuel Cells for Low Emissions Ships). Now, 12 years later, DNV gave approval in principle in October to the Norwegian company TECO 2030 for a hydrogen fuel cell system and to three versions of its FCM400 fuel cell module, which it has developed in conjunction with AVL of Austria. Each module can generate 400kW and they can be joined together to provide higher outputs, TECO 2030 reports on its website. An assembly fitted into a standard 40ft container would provide 6.4MW of electrical power, which approaches the power density of a typical diesel engine of similar output, based on a review by The Motorship of data from engine manufacturers.
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Jostein Bogan, product manager for energy storage and fuel cells at ABB, confirmed that some fuel cells are now comparable in size to equivalent diesel gensets, with improvements especially coming from the development of PEM fuel cells, which have found applications in land transport. But, like Fort, he noted that when fuel storage volumes are considered for hydrogen and conventional fuel, the comparison changes, since hydrogen has a much lower volumetric energy density. But other aspects of a vessel’s design can make up for this, he suggested. With no exhaust treatment systems needed, for example, space becomes available above the machinery room. Fuel cells are also more efficient than engines in recovering energy from fuel, he pointed out. Power density will continue to improve, believes Philippe Gorse, director for fuel cell solutions at Rolls-Royce Power Systems. As mentioned elsewhere in this feature, the company has built a 250kW demonstration installation, which is housed in a 20ft container, along with batteries and other equipment. “We are convinced that in a few years, you will be able to obtain 500kW out of a 20ft container”, he said. But he also said that the power density of an entire propulsion system is as important as that of the fuel cell itself. “You have to consider the hydrogen or methanol storage volume as well” and noted that, because they are more efficient than combustion engines, a fuel cell system will need a smaller tank than a hydrogen-fuelled combustion engine. Compared with conventional diesel engines, however, “you will never get to the to the same power density as you will not able to compress hydrogen enough”. But “if you want to go to zero carbon, you have to accept that”.
8 TECO 2030’s 400kW fuel cell secured approval in principle from DNV in October
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