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> ... but the task of greening the high seas fleet is far more daunting. I think large ocean-going vessels is one place where hydrogen might make sense. The b
by curtis 8y ago
> ... but the task of greening the high seas fleet is far more daunting.
I think large ocean-going vessels is one place where hydrogen might make sense. The biggest problem with hydrogen is storage, but when you start talking about really large fuel tanks storing liquid hydrogen becomes a lot more practical. All of the hydrogen powered automobiles I've heard of rely either on high-pressure gas storage (requiring heavy tanks) or metal hydride storage (requiring heavy metal hydrides) which pretty much make them inferior to modern battery-electric vehicles.
Storing cryogenic liquid hydrogen doesn't have the same weight penalty, but has a huge volume penalty, plus it has the additional problem of keeping the hydrogen really cold until you're ready to use it. However, on a cargo ship, the large volume of the tank probably isn't a big restriction, and keeping the hydrogen cold enough is going to be a much smaller problem. That's because heat-loss is going to be proportional to the surface area of the tank, rather than the volume.
Hydrogen still suffers from energy loss at production. Hydrogen production by electrolysis is nowhere near 100% efficient, nor is turning the hydrogen back into motive power, either with internal combustion engines or with fuel cells.
On the flip side, I think as long as wind power makes up a substantial portion of electrical generation capacity, there will be times when the cost of electricity actually goes negative. If you can do most of the hydrogen production at times when electricity is really cheap, and you are planning to store it for relatively long periods of time anyway, then most or maybe even all of this overhead can be offset.
- endymi0n 8y agoCame here to say the same thing. At the scale of container ships, almost all the disadvantages of hydrogen are gone. Storage, cooling and leakage should all be controllable, given large enough tanks. Interestingly enough, there's some prior art in the German Type 212 submarines, looks like it's production ready: https://en.wikipedia.org/wiki/Type_212_submarine https://en.wikipedia.org/wiki/Type_212_submarine It's probably only about cost and infrastructure. Does anyone have current details on the price of massive diesel engines vs. massive fuel cells and electric motors?
- curtis 8y agoI can't find anything that says how the Type 212 submarines store hydrogen. After thinking about it though, I think they must be using metal hydride storage. Submarines already have to be ballasted to offset the buoyancy of the crew compartment, and given the low density of liquid hydrogen, they'd need ballast to offset that too. Liquid oxygen is slightly more dense than water, but not enough to offer much compensation. It seems like you could use the metal hydride batteries as your primary ballast that you'd need anyway, and get the hydrogen storage pretty much for free (in the weight and volume sense, anyway).
- maxerickson 8y agoI wonder about just converting the hydrogen to methane for storage and transport. There seems to be a bit of serious research into it. Being able to reuse existing infrastructure is a pretty big win.
- adrianN 8y agoEvery conversion step loses a lot of energy I'd assume. Producing hydrogen instead of electricity to charge batteries is already wasteful.
- semi-extrinsic 8y agoAmmonia is a much better candidate, since it doesn't contain any carbon, so using it can't cause any CO2 emissions. But as others have said, the efficiencies are horrible, so its better if we just figure out H2 transport and storage. Edit: for large ships, my personal bet is on liquid H2 storage and then combustion in gas turbines. You get a lot of synergies between cryogenic fuel and a gas turbine. Tupolev even built and flew a liquid H2 fueled narrow-body jet in the 80s.
- maxerickson 8y agoIf you get the carbon from the air it doesn't cause any carbon emissions either. Or an existing stream that is currently being emitted into the air.
- semi-extrinsic 8y agoTo your first point: correct. But the concentration in air is so bloody low for any chemical process (air is <0.5% CO2) that you'll have to put in huge amounts of energy. It's not going to be economically feasible. To your second point: capturing CO2 and then re-emitting it is completely off the table. It will be (or already is, depending on your interpretation of Directive 2008/98/EC) banned in Europe, likely with an exception for greenhouses (where they need to use CO2 for growing plants, and currently get it from burning natural gas).