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Comment by Qwertious | Hacker News Reader

It makes sense for large vehicles - a passenger plane from New York to London will never make sense for batteries, but could be done with hydrogen.

Similarly, cargo ships can't run on batteries, but could fairly trivially be switched to hydrogen with only minor loss in storage capacity (1-5%).

The benefit of hydrogen is that it was functioning just fine in the 1960s, there aren't any outright technical showstoppers here; just financial problems and technical problems that are hard to solve cheaply.

I'm not saying that hydrogen is the best solution (if synthfuel pans out then it'll be a perfect drop-in replacement for existing jet fuel), but it's a solution that exists today. It's there if we care.

Obviously we don't care, since coal plants are still around, but if we genuinely wanted to stop using fossil fuels ASAP then it would permit us to keep using planes/cargo ships.

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Liquid hydrogen takes 4x the volume of standard aviation kerosene. Coming up with on-jet liquid storage of hydrogen of that volume is a rather steep engineering hurdle. And hydrogen, liquid or not, will require some rather impressive storage and handling techniques at the airport.

If I were to bet, I would say that converting hydrogen to kerosene will be far cheaper and more efficient than trying to power long distance flight with hydrogen

> ...there aren't any outright technical showstoppers here

H2 molecules are extremely small -- storing them without loss is heavy and volumetrically expensive, making it implausible for any aircraft.

The same factors apply to ships, pipelines etc because space for fuel is space that does not contain high value cargo.

>The same factors apply to ships

Ships don't care about weight. The cooling infrastructure or heavy steel tanks are possible.

> Ships don't care about weight. The cooling infrastructure or heavy steel tanks are possible.

Have you looked at how high the containers are stacked on a container ship? Space taken up by fuel is space that can't be sold.

Source: we partner with commercial shipping companies and spend time not just talking to the commercial people but on the ships themselves.

The problem, just like for car, is the volume that hydrogen takes up, not the weight

The problem isn't doing one plane. It's doing enough of them to make a difference.

Jet fuel is ludicrously energy dense, to the extent that it's easy to underestimate how much energy you need: at any reasonably-sized airport, if you want to replace the current fleet then you need to be talking about roughly a power station's worth of continuous energy delivery into aircraft fuel tanks. That's doable with jet fuel because you're not climbing out of an energy well just to get hold of the fuel. You just separate it out, and the problem becomes pure logistics.

With H2, the volume you need and the added storage complexity means the current logistics becomes a rounding error in comparison to how on earth you get the gigawatts to churn feedstock into gas.

You could do it, but you'd want nukes on-site to do it.

Synthfuel apparently exists already and the US Navy has a solution. It's just very energy-intensive.

The shipping industry is investigating making ammonia from the hydrogen and then using that in fuel cells; it has the advantage that it's easier to handle. https://maritime-executive.com/article/highest-power-output-...

The Germans in WW2 made large quantities of synthetic fuel. It's not new, the same challenges continue to exist. Most of their military aviation fuel was apparently synthetic due to oil shortages.

https://en.m.wikipedia.org/wiki/Synthetic_fuel#History

The whole idiotic war would have been over the moment the free trade system of the US would have surplanted the pre-existing empires and their embargoes. Harber+Bosch + liquid gas is what feeds the world and creates the pre-requisite to all peace.

> the free trade system of the US would have surplanted the pre-existing empires and their embargoes

This doesn't make any sense: free trade is not a magic spell against the desires of imperialism, and the US embargoed Japan slightly before Japan attacked the US (but long into Japan's war with China).

Liquid gas may feed some of the world, but there are many left out with this centralized system.

I am glad that decentralised electrical from solar and wind can fully replace the old system and look foward to a new many-noded culture which can allow all humanity to flourish.

The best solution for large airplanes is remote meetings and realistic remote experiences.

Sorry. But there’s no reason so many people need to fly (consultants, I used to be one racked up a few hundred thousand miles) besides leisure or critical travel. And it should reflect in the price so tickets aren’t $150 to be crammed in like cattle.

And yes it should be rare to fly until we figure out cleaner fuel methods. Just my hot take.

Another place where it could make sense is trains. Building overhead power lines could be expensive, especially if we are talking about high speed trains. Because of the square cube law, large pressurized tanks could be economically quite efficient. A train could carry an extra car with a pressurized tank at 700 bar. At this pressure the hydrogen density is 42 kg/m3. A typical oil car has a volume of 131 m3, so assuming the same volume, we'd get about 5.5 tons of hydrogen. Hydrogen has about 3 times the energy density of diesel fuel, and hydrogen cells about twice the efficiency of diesel engines, so all in all 5.5 tons of hydrogen would be the equivalent of about 33 tons of diesel. That's more than enough to move a train from one train station to another one, even if the stations are hundreds of miles apart.

Couldn't cargo ships use wind? A wind turbine on the ship? A kind of modern re-imaging of how sailing ships of old were powered.

Is the problem that wind isn't reliable and you might go days without it? Or you wouldn't fit in ports or other areas with a big turbine sticking out? Or is there some other practical problem.

Several designs have been proposed for adding sails, of one shape or another, to ships in addition to an active mode of propulsion in order to reduce fuel consumption.

Further, the ships take a significant amount of energy to get going, so much of that initial acceleration could be handled by strong tug boats which would then be immediately recharged.

It's not just that wind is unreliable, it's also very low energy density. You'd need a lot of sails to haul a small amount of cargo. There are applications using kite sails to supplement combustion engines, but that's just an opportunistic mitigation.

Cargo ships could use wind sure, it would just be much slower and each boat would have to carry far less stuff.

Might solve problems for countries that have lost their own manufacturing capacity because shipping products gets way less appealing.

It will make sense for nearly all transportation that can’t be directly electrified. The problem with batteries is that it is a massive resource hog, and one that is fundamentally unsustainable. It will have be abandoned. The only alternatives are ideas like synfuels or ammonia, but those require green hydrogen production anyways.

They are not the only alternative.

Ammonia (a toxic gas) as a fuel is an insane idea and will lead to needless deaths.

Efuels are incredibly inefficient. Hard to justify paying 10x the price.

Ammonia or synfuels are not the only alternative. The elephant in the room, the one fuel that is being used today is biofuel.

Biofuels are not green. It is purely greenwashing since the production of biofuels is very carbon intensive. It is also very environmentally destructive since it takes a lot of farmland to produce.

https://en.wikipedia.org/wiki/Cellulosic_ethanol

When they actually start producing that in any significant quantities, wake up me.

They will produce it as soon as it's economically viable to do so. Until then, (government subsidised) corn it is. Which some will call simply farming.

Imagine thinking corn ethanol is even remotely a good idea…

I'd appreciate if you at least tried to keep a non-condescending tone.

I was merely stating why cellulosic ethanol is not the major source of biofuel; because corn is heavily subsidized and produces a cheaper product, hence nobody wants to buy the more expensive product.

That's not a technical problem, it's an economic one. And the subsidies where to change we would see less from corn and more from other sources.

Government subsidized corn ethanol is an environmental disaster. If you hear it being brought up, you automatically assume the person is either confused or working for the corn lobby.

Cellulosic ethanol is an idea brought up as a solution to the problems of corn ethanol. Ironically, by the George W. Bush administration. Unfortunately, nothing has materialized in any meaningful quantity.

And FYI, they’d be subsidizing it heavily if any meaningful quantity of cellulosic ethanol could be produced. So bringing up that part doesn’t mean much. But cellulosic ethanol production never happened and so far there is no reason to believe it is possible.

> And FYI, they’d be subsidizing it heavily if any meaningful quantity of cellulosic ethanol could be produced.

I'm not so sure. That would introduce competition for the corn ethanol, and there's a fairly large constituency (those having their corn production subsidised) that would oppose this kind of measure.

The corn lobby are huge advocates for cellulosic ethanol because it means corn stover could also be made into ethanol.

It probably sounds like a great idea if you are a senator or congressman from a midwestern state.

BTW: Biofuels are ludicrously inefficient. Something like 1% of the solar energy actually ends up being usable at the end of the process. That’s not include all the other inputs like fertilizers or pesticides and the like. It is pretty resource intensive in reality. Which is why serious environmentalists reject them entirely.

Ah yes, No true environmentalist(TM).

This is not the true Scotsman fallacy. Biofuels are an environmental disaster, full stop. Anyone who promotes biofuels is aggressively undermining environmental policy.

How would a hydrogen powered passenger plane work? How big and or heavy would the fuel tanks need to be? As I understand it you either need very big tanks to store it as gas, or very heavy insulated tanks to store it liquefied. Would a passenger plane still work?

Hydrogen planes have been tested. The physics works out provided you have more room for the tanks.

Wing tanks won't work for hydrogen, and wing tanks are essential for weight distribution and reducing load on the wing roots. A hydrogen cylinder in the central fuselage will require a complete rework of the aircraft design and a new type designation, it's not something that can be retrofitted into current aircraft, even if converting the engines to hydrogen would be otherwise feasible.

Aircraft will remain liquid-hydrocarbon-fueled for the foreseeable future, even if the fuel production transitions to a synthetic process vs. refined crude oil.

Ah yes, it works if only it weren’t for those pesky economic considerations.

Making more room for the tanks means either less cabin/storage and/or bigger cross-section and increased drag.

The alternative is SAF, which has to be a synthetic fuel if the goal is to be honestly green. However, that requires enormous green hydrogen production anyways.

The alternative is electric and biofuels.

There will never be a long-distance battery powered plane. Not with any kind of battery we can conceive of today at any rate. And again, biofuels are not green.

> There will never be a long-distance battery powered plane.

"Long-distance" is a subjective term. There is an ever-increasing distance for which batteries are doable. Everything else is will be liquid biofuels, rather than efuels.

Biofuels are as green as the process making them. Electrify the equipment being used (something that's being done for reasons orthogonal to this) and you're already made the process more green.

Airplanes are not cars. Weight actually matters, even for short trips. There are not an “ever-increasing” number of routes that can be powered by batteries. You can’t even legally send passengers using batteries, because you can’t even get to reserve range minimums. It is basically zero today. And people have noted that even with miracle battery advancements, we would still not have a battery good enough to build a 737 or a320 equivalent. As a result, most of the aviation community has abandoned the idea altogether.

Again, biofuels are not green. The process that makes them involve vast quantities of land and resources. It is in fact a very inefficient and resource intensive idea. It is actually much worse than what it takes to make e-fuels.

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