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Comment by gary_0 | Hacker News Reader

I keep waiting for everyone to wake up to the hydrogen scam. Do you see any practical consumer hydrogen infrastructure going up? Has it even been invented yet? Electrical infrastructure is a solved problem, we need to scale it up anyways, and it hooks into everything (industry, consumer use, consumer solar panels, public transport, renewable generation) because it just wires together and there are lots of electricians and engineers you can hire. There is electrical infrastructure almost everywhere there is human settlement! But hydrogen is a bunch of exploding leaking embrittling bullshit, and it will only ever have niche uses.

Fun fact: currently 95% of hydrogen is produced from fossil fuels. This might be a clue as to why such a dumb idea is still around.

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Hydrogen becomes more attractive once electricity is decarbonized. It's really the only fuel that has both the energy density to power flight and transoceanic travel and does not emit carbon. Batteries are fine for cars, and trains can be electrified. But you'll never fly across the Atlantic on a battery powered passenger plane.

Synthetic methane and other hydrocarbons are also ideas that are floated. But those need hydrogen as an input anyway. They also need a source of carbon, which is too difficult to extract from the atmosphere. So using the hydrogen directly may be more feasible.

Long-haul flights are the one possible exception, but they're not the saving grace the fossil fuel companies are trying to manufacture. Tanks of hydrogen at the airport are not a "hydrogen economy". And since it's looking like air travel will be one of the last things to decarbonize, there's no guarantee hydrogen will be relevant. Long-distance flights don't account for a large portion of global CO2 emissions[0] which leaves room for various options.

Short-range aircraft will probably switch to batteries in the coming decades, because the prototypes are already flying[1] and battery and electric motor tech is ever-increasingly ubiquitous and mature.

[0] https://en.wikipedia.org/wiki/Greenhouse_gas_emissions#Aviat...

[1] https://www.cbc.ca/news/canada/british-columbia/vancouver-el...

It's not just long haul flights, it's really anything longer than a hundred miles or so. Battery powered aircraft are also very small and light with little passenger or cargo capacity. Then there's the issue of charging. Planes can't just sit idle for hours at th gate as they charge. Faster charging reduces the lifespans of the batteries, and a plane needing a new set of batteries after a few hundred flights due to aggressive wear from fast charging is unacceptable.

It's not just long haul flights out of reach of battery powered aircraft. Even a regional flight like Seattle to San Francisco cannot be feasibly done with batteries. This is fundamentally due to the energy density of lithium ion batteries, no amount of engineering can change the chemical limitations at hand: https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

> Faster charging reduces the lifespans of the batteries

As far as I understand, the problem is not just the speed, but the thermal management. IIRC the impact on battery life is not as bad if cooled properly.

> and a plane needing a new set of batteries after a few hundred flights due to aggressive wear from fast charging is unacceptable.

That's an economics question. How much does it cost to get that battery replaced and charged over its lifetime versus the alternative.

> This is fundamentally due to the energy density of lithium ion batteries, no amount of engineering can change the chemical limitations at hand

That's the beauty of battery technology, you can substitute. Cobalt a problem? Fine we can make batteries with out it. Lead-acid not suitable, fine here's lithium ion. Lithium ion not good enough, find we'll find a better battery.

Hydrogen however is just that: hydrogen. Notice how low it is on the energy per volume scale. You can't substitute it out for anything. The volume requirement is what's going to kill you with hydrogen.

> Lithium ion not good enough, find we'll find a better battery.

Well, then get back to us when you find that battery. Unfortunately, simply finding a new battery chemistry that has an order of magnitude better energy density is easier said than done.

> Hydrogen however is just that: hydrogen. Notice how low it is on the energy per volume scale.

You're looking at uncompressed hydrogen. Hydrogen at 700 bar has several times better energy density than lithium ion batteries, and over 1000x as much energy by mass. And lower mass means you need less fuel since the craft is lighter.

A point if and I seriously mean if in the I'm exceptionally dubious about hydrogen powered aircraft. If aircraft were hydrogen powered you'd generate the hydrogen on site at the airport.

Will point out takes a decade now to produce a blue print aircraft. So if we started designing one now it would be flying when 2033? China rolled out a high speed rail network in ten years. You could do that in the US and other places.

Notable point. The complaints I hear about high speed rail in Europe is tickets cost more than airplane tickets and the trains are always full. The explanation is the ergonomics and logistics of passenger aircraft sucks.

You'd likely send via pipelines or tanker trucks instead.

Hydrogen doesn't make sense to transport. You contend with cryogenics / boil-off for tanker trucks or ships. Pipelines you're dealing with poor volumetric energy levels (you use comparatively more units of energy to move one unit of h2).

Boiloff is not that big of a deal if you are using the fuel right away. It is the same story as with LNG.

I replied to your comment that was talking about transportation... i.e. not using it right away.

H2 has a daily boil off 5 times greater than LNG. https://www.sciencedirect.com/science/article/pii/S277265682...

Not only that, liquid H2 has worse energy density than LNG. So again, you're spending more units of energy to comparatively more less units of energy.

You can liquefy hydrogen on the spot. You don't need to move LH₂ around. If that does become necessary, the solution is improved insulation. Modern materials can reduce boil-off to that of LNG's. In fact, LNG was once seen as impossible because of its boil-off concerns at one point.

You will need bigger tanks but the fuel is much lighter. It is a solvable problem.

>Boiloff is not that big of a deal if you are using the fuel right away.

>You can liquefy hydrogen on the spot. You don't need to move LH₂ around.

Why are you liquefying H2 if you are using it right away and or not transporting it? Liquefaction is to optimize for storage. You're all over the shop.

You liquefy H₂ for the density advantage, not for storage. You actually want to store hydrogen as a gas since it won't boil off.

If flights are carrying that much hydrogen around with them they should also just use them for "free" lift. I don't think hydrogen fuel tanks save the airplane, I think they return us to economic models where the blimp/airship make more sense.

Liquid hydrogen is significantly denser than air.

Right, which is why it "weighs" more and starts to make sense for a flying vehicle to store more of it as gas (less weight, more ballast) and the more you store as gas the closer you get to reinventing airships/blimps/zeppelins.

Hydrogen best case density is ~ 2.5 kWh/kg, definitely not that great considering this is in its liquid form. To stay in that form, you need to cool them to ~ 20˚K, which is about -253°C. Also, because the molecules are so small, the tank needs to be almost perfect. Even the crystal structure of metals is eventually penetrated by hydrogen. Hydrogen has many sensible uses in the production of many goods, filling powerful electrical generators etc. It would be great if we could produce it economically in a renewable fashion.

Actually, there are many carbon free fuels. It is hard for any to use as jet fuel. An example fuel that has much better properties than hydrogen is for instance sodium. Making a sodium fuel cell does not need any rare earth metals such as platinum, sodium is solid at room temperature, does not produce any fumes, better energy density than liquid hydrogen, the resulting NaOH sodium hydroxide can be recycled into sodium (with hydrogen as a byproduct) by the Castner process. Hard to say, if this could use the water vapor present in the atmosphere, if it did, you would also have to think about what to do with the caustic hydroxide solution. Probably, that would be neutralized quickly in the atmosphere but at ground level or above cities could "raise eyebrows" even though burning leaded petroleum in aviation still seems to be a thing...

The best density is 33.3 kWh/kg. That's simple physics.

Yes, sorry. It should've been per litre. (https://en.wikipedia.org/wiki/Energy_density#In_chemical_rea...) The intuition about volume/ weight is out of the window with hydrogen, because it's so light. Thank you for the correction.

Of course, for almost all uses, the volumetric efficiency is important because you have to create bigger tanks, which if they have to contain liquid hydrogen, are usually heavy and costly.

> Do you see any practical consumer hydrogen infrastructure going up? Has it even been invented yet?

It has been invented, the majority are in China and Japan if I remember rightly.

Yeah, my Canadian girlfriend works there.

We don't care that she's Canadian

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