Investment in marine fuel cells has advanced rapidly in the first few months of 2019. But while fuel cell technology develops, there has been less progress on other factors likely to limit uptake. Key among them are energy storage and the supply of clean hydrogen.
For any but the smallest marine fuel cell application, energy storage is an essential part of the power system. If power produced by fuel cells cannot be used immediately, it must be stored. For some advanced fuel cell designs that must be turned on constantly, batteries are essential for taking the excess charge.
Battery technology is well developed in shipping, as evidenced by its continuing spread into new ship types. But cost and energy density remain barriers to uptake. On Hurtigruten’s battery-assisted cruise ships, Roald Amundsen and Fridtjof Nansen, the installed 1.35-MWh systems occupy just a fraction of the battery rooms designed to accommodate installations of up to 6.5 MWh. When those installations are complete they are expected to weigh around 80 tonnes. That is nearly half the total weight of the four Rolls-Royce B33:45 engine which cater for the majority of the vessels’ power needs.
It is not hard to see why big battery packs have yet to find applications on more weight-sensitive vessels. And technology advances that are expected to kick battery energy density to a new level are proving painfully slowly to emerge. According to research institute BloombergNEF solid-state batteries – the next great hope in scaling down battery technology – are not expected to have a 'meaningful impact' on the electric vehicle market by the late 2020s at latest. For the more conservative and challenging marine market, it could be much later.
Even more than batteries, it is answers to the hydrogen challenge that will determine the success of fuel cells in shipping. The difficulty of storing hydrogen in large volumes is well known. Even in its most compact, liquefied form, hydrogen takes up twice the space of LNG. For vessels taking long voyages between bunkering, this is a key issue. Storage concerns could be overcome only with major changes to vessel design. Adapting bunkering schedules would not be a possibility unless the availability of commercial liquefaction plant, in Europe in particular, is dramatically improved.
But there is a more fundamental issue than storage. Fuel cells can only cut greenhouse gas emissions from well-to-wake if they use clean fuel. There are technologies emerging which could supply renewable hydrogen. Large scale electrolysis plants have been designed for onshore use which would deliver many hundreds of tonnes per day. Hydrogen could also be produced cleanly by combining natural gas steam reforming with carbon capture and storage. And a recent breakthrough by Stanford University researchers could make seawater electrolysis effective at greater volumes.
But none of these solutions will be available at commercial scale imminently. The question therefore remains whether renewable sources of hydrogen can be scaled up rapidly enough to contribute to shipping’s relatively urgent need for decarbonisation.
Fuel cells will play a role in the decarbonisation of shipping. But the size and timing of that role will be decided largely by progress in the fields of batteries and renewable hydrogen.