Challenging assumptions: a fast fuel cell ferry
Echandia Marine’s award-winning 'BB Green' has been transporting Stockholm’s commuters in an environmentally friendly fashion since 2016 but despite its success “there is a limitation when it comes to battery vessels”, admitted Magnus Eriksson, Echandia’s founder and CEO.
“The problem is total range: we see many potential projects where there’s a longer single journey or smaller frequent trips and no time to recharge.” To answer this, Echandia has set out a fuel cell concept based on the BB Green vessel technology - FC Green.
There are a number of attributes that have been retained: it’s an air-supported (ASV) hull, the cushion of air reducing the wet area by as much as 80%, bringing the energy budget down by 40%.
Again, the FC Green is capable of a 28kn cruise speed, identical to its battery driven sister “but the fuel cell has increased the range from 25km to 125km, that’s five times the distance” said Eriksson, talking at the at the 2018 Electric & Hybrid Marine Technology event. “Also, the refuelling times are between four and eight minutes – that’s less than the battery option and there’s no emissions,” he added. “From a naval architect’s perspective it’s fascinating as it seems we can keep the same total weight but increase the energy storage five times.”
The fuel cell plant has been designed by Canadian firm Redrock Power and this shatters a few assumptions: according to Paul Paterson of Redrock, each one of the pair of RR-2 fuel cell units have a nominal power rating of 300kW peak power of 450kW, “with this it can go a long way to reducing hybridisation and battery installation as it can handle manoeuvring and other short-term high-power requirements”.
Most importantly “while there seems to be a preconceived notion that fuel cells are slow to respond, this system can ramp up from idle to full power, that is from 30kW to 300kW, in under two seconds”.
Paterson explained that what really governs the ramp-up profile is nothing more than the volume of air that is fed to them by the compressors, and pointed out that in automotive applications the time to full power “is less than half a second”.
However, while most fuel cell propulsion plants are at present designed for buses, marine designs can steal a march on their automotive cousins as buses have to cope with high ambient temperatures while in the cooler marine environment, the fuel cells last much longer, it’s easier to keep them hydrated, and the whole design can be optimised for cooler running. Further, a bus system has to be very dynamic when it comes to loading, while a marine installation can be designed without the same response requirement.
More, he pointed out “a bus system has to be as small as possible but our system is quite a bit larger per kilowatt, allowing us to operate more efficiently”. In fact, these RR-2 units have a 56% rated power efficiency.
Durability of this marine system is likewise high: “We put the lifetime of the RR-2 system somewhat north of 25,000 hours, after which you recore the cells: that means replacing the membranes - but this only costs you about 20% of your original investment,” said Paterson.
There’s also an interesting business concept for the provision of the compressed hydrogen fuel: these ferries would probably be working between cities and putting it bluntly, where there are cities, there’s sewage.
Therefore Echandia is working with hydrogen supplier Metacon and daughter company Helbio which run catalytic steam reforming of biogas to hydrogen: while CO2 results from the process, it’s a renewable and the carbon is recirculated.
Compare this with the electrolytic creation of hydrogen: the production cost from this method stands between €6.5 and €7.0 per/kg, “but the biogas reformer cuts this in half” said Eriksson.
Moreover, while both systems require a similar and quite substantial hardware investment he underlined that the average lifetime of the electrolysis kit is just 10 years while the biogas reformer’s expected life is 25 years “which obviously reduces the capital burden substantially” he said.
“The business case does depend on local energy prices... and support for the refuelling station,” he concluded.
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