ZEROe: Hydrogen-hybrid aircraft concept

Society uses absolutely mind-gobbling amounts of energy, mostly from fossil fuels. There's just not enough land available to produce even a significant fraction of that from biofuels. Never mind the ecological devastation that would be caused by converting the little wilderness left to intensive biofuel cultivation.

That is not to say biofuel don't have a role to play. Agriculture and forestry wastes, municipal biowaste, etc. can all be used for energy. And yeah, it makes sense to use the available biofuel for sectors that are otherwise very hard to decarbonise, such as aviation.

Algae, well, that has been researched for decades with very little to show for it. It has great potential, but it seems very difficult to make it actually work.

> Perhaps the efficiency to produce methane is not so bad, but a chain with 6 or 7 carbons like gasoline is very complicated.

The Fischer-Tropsch process is almost a hundred years old, and has been used on an industrial scale. E.g. Nazi Germany used it to produce a non-trivial fraction of their liquid fuels during WWII. Similarly South Africa used it during Apartheid. Now FT itself is better suited for producing mostly straight hydrocarbon chains like diesel or jet fuel rather than the branched ones seen in high octane gasoline.

The efficiency of traditional FT is around 40%, but by adding extra hydrogen to the process it can be increased by around a factor of 3 (the efficiency meaning the energy content of the carbon carrying feedstock vs the output, so over 100% is possible as hydrogen provides some of the energy in the final product).

The problem is to get the CO needed for FT in a carbon-neutral manner. Biomass is limited, capturing and reducing CO2 is expensive and requires a lot of energy.

Well the answer to that is that it is not that simple. We know how synthesize hydrogen and scale it and what it will cost because companies are already doing that today. Synthesizing other fuels may be long term feasible but are simply not commonly done right now. More importantly, there don't seem to be many companies planning to do that right now. Airbus is not in the business of producing fuel so it would need such a company to step up and do it before they can start designing products for it.

E.g. liquid methane would be a good alternative for hydrogen. The appeal of both hydrogen and methane would be that converting engines to burn it seems doable and given that rockets can use either as propellant there is no question about their suitability as a fuel from an efficiency point of view. The difference of course is that with methane it would end up coming from fossil reserves which from the point of view going carbon neutral kind of defeats the purpose of making these planes carbon neutral. Swapping out kerosene for methane kind of just moves that problem. IMHO it's still worth exploring (and some companies have actually done that). Also, I imagine synthetic methane is eventually going to happen and kill the market for natural gas. Just not in the next decades.

The key here is a combination of becoming carbon neutral and doing it in a cost effective and timely way. Synthetic methane may or may not actually become a thing but the simple reality is that it's an industry that simply does not currently exist. Clean hydrogen production on the other hand exists today (at small scale) and seems to be on a feasible path to scaling in the next 15 years or so. Additionally hydrogen infrastructure is something that is attracting lots of investment currently. Airbus is targeting a launch in the mid to late 2030's. So they need to be targeting a fuel source that they can reasonably expect to have some supply for by then so they can actually fuel the planes where-ever they need to fly. So the supply and infrastructure for hydrogen are not a certainty but at least on a path where it could be there in 15 years. The rest is just solving engineering problems. They seem to believe they can do it.

But are batteries more efficient for long distance planes?

Conversion losses may be lower, but a battery-powered plane doesn’t lose weight during flight. That makes the impact on landing harder, so planes will have to be made stronger and, thus, heavier.

And yes, that should make quite a difference. Reading https://en.wikipedia.org/wiki/Fuel_fraction, 40% of the take-off weight of long-haul flights is fuel. Not all of that will be gone at landing, but if 10% of fuel is reserve, such an airliner still will be a third lighter at landing time.

Also, commercial planes have turnaround times of about an hour, sometimes half of that (https://simpleflying.com/turnaround-time-importance/). I would think pumping in hydrogen would be easier to do in that time than charging batteries. Batteries could be replaceable, but that would add more weight.

I never addressed the lifespan of containers, that's not same as hydrogen leakage.