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They plan to decarbonize the aviation industry in two ways: electric planes and hydrogen-powered planes. But in any case it implies fewer passenger seats and, as a result, a dramatic increase in ticket prices (if I understand it correctly). Does greener flights mean a lot less affordable flights? Is flying going to become a luxury? Is our world going to be less connected (in terms of international in-person connections)?

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  • also a 3rd plan, not necessarily sustainable, but presented as such: synthetic non-hydrogen fuel
    – njzk2
    Nov 25, 2022 at 23:13
  • insofar as current pricing doesn't account for externalities, and as most plans involve influencing the market by factoring costs for those, it would seem that yes. But keep in mind that the current state of very cheap flights is only a couple of decades old. This era of constant flying, if it ends in the near future, would have been only a very short period of time
    – njzk2
    Nov 29, 2022 at 19:58

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The fact is: nobody knows.

Electric planes could be very useful for short distances. For long-distance flights, the battery cost investment is rather high, the weight of the plane increases rapidly (meaning you need more batteries because of the weight, meaning you have more weight because of the batteries, meaning you need more batteries because of the weight, ...) so I really hope we don't have to resort to battery-powered electric planes in long flights. However, for short distances electric planes could be useful and maybe even they could not increase costs but rather reduce costs. To get there, lots of development and cost-reduction is needed though.

In electric cars, we have already seen that the total cost of ownership during the whole ownership period is lower for drivers that use their car a lot and choose electricity, if you buy a new car and drive it until it's no longer serviceable.

I think that in most applications what determines whether fossil fuels are better or whether electricity is better, is the number of cycles a battery gets per year. Electric cars usually have about one cycle per week. This means the battery lasts long enough, but you get actual usage for it (more usage = more fuel savings). A daily cycle wouldn't help because then the battery needs to be replaced early (in plug-in hybrids that have a cycle per day we have already seen early battery failures). In applications where cycles are rare and/or seasonal, for example in lawnmowers (maybe 12 cycles per year, so that's average of cycle per month), battery cost is dominated not by cycles but by battery aging, and it's expensive as hell to have an expensive battery and you won't get even 200 cycles out of it. Based on this, electric planes seem promising (presumably they would get multiple cycles per week), as long as the battery weight is not a showstopper.

For hydrogen in long distance flights, it depends on the technology. Electric motors operated by fuel cells that burn hydrogen might be too expensive as a system. Burning hydrogen directly in jet engines could work, but then the fuel costs will be a showstopper for at least 10 maybe 20 years. To get cheap enough hydrogen, at least massive reductions in hydrogen electrolyzer costs are needed, and we need to have massive amounts of intermittent weather-dependent renewable capacity that could be used to operate those electrolyzers with practically zero electricity costs at times when not all electricity is needed elsewhere and there's plenty of electricity available. Also hydrogen storage is hard, maybe liquid hydrogen could remove the need for huge pressure vessels, but then liquid hydrogen is less efficient and more expensive than compressed hydrogen.

It's a long way to go. Fuel in international flights has no fuel taxes and the CO2 produced needs no permits. To help make hydrogen and electricity more viable, we should at first decide that all aviation fuels will be taxed at the same taxation level that motor fuels are taxed in most European Union countries. Maybe then the incentives for electric and hydrogen planes would be larger.

About the only proof that we have hope is that maybe we don't actually have to do anything. There are already 100% fossil compatible biodiesel variants on the market. The main problem with biodiesel is that we can never produce enough of it to cover all of road transportation usage, because road transportation uses so much fuel. However, if we produced biofuels only to replace jet fuel (which is very similar to diesel so the 100% fossil compatible biodiesel techniques should work with maybe minor modifications), we could have 100% of aviation fuels be sustainable and not even have to use electric or hydrogen planes. Maybe it will be cheaper in short distances to use electric over sustainable fuels. Maybe it will be cheaper in long distances to use hydrogen over sustainable fuels some day. But if it isn't, the technology to produce enough sustainable fuels is existent.

The sustainable aviation fuels would be more expensive, though, and unlikely to ever become as cheap as fossil fuels.

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    There are at least two massive downsides to biofuels - firstly that they take land away from growing crops for food, and secondly it is likely that they take more energy to produce than the fuel actually generates when burned. It's hard to see how this is in any way "sustainable".
    – John M
    Jul 20, 2022 at 12:18
  • @JohnM I disagree. Next generation biofuels produced for example from waste don't have those limitations. They do have the limitation that we can never produce enough of them for all road transportation usage (but we can probably produce enough of them for only all aviation usage).
    – juhist
    Jul 20, 2022 at 15:41
  • Second-generation biofuels are indeed better in some ways, but there are still some significant issues depending on the sort of "waste" that you are talking about, such as the potential effect on soil quality and biodiversity
    – John M
    Jul 21, 2022 at 9:47
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    For short distances, we should be using trains, not planes.
    – gerrit
    Aug 17, 2022 at 11:43
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    @njzk2 True. Boats may be an option, but they're very slow, so the distance at which they become unfeasible for most will be shorter than for trains (and boats are also harder to do sustainably if we're not willing to go back to sailing).
    – gerrit
    Nov 27, 2022 at 11:33

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