Hydrogen has good energy per kilogram, but bad energy per square meter even in its liquid form [1]. Liquid hydrogen is less than 10 times as dense as water.
Synthetic fuels either require considerably greater arable land and water consumption to grow biofuel, or the use of things like algae cultivation and accelerated decomposition. It's probably more effective on a $ / CO2 mass basis to just sequester carbon and keep using refined fossil fuels. Airplanes account for a single digit fraction of the CO2 emissions from transportation, though, as their mass and drag are both tiny as compared to cargo ships.
Reply to your post below, HN is not letting me respond:
Those synthetic fuels are effectively the same as biofuels. You're using energy to sequester carbon out of the atmosphere (or a body of water, in the case of algae based biofuels) and using that carbon to power a machine.
You can either do this by using electricity generated from another artificial power source, as in your example. Or you can do this by harnessing natural energy, like setting up transparent pipes to collect solar energy into algae or by farming biomass on land. Since most energy decarbonization plans assume modest energy consumption growth, and sometimes even an overall energy consumption reduction the former plan is less feasible than harnessing naturally occurring energy.
Synthetic fuels either require considerably greater arable land and water consumption to grow biofuel, or the use of things like algae cultivation and accelerated decomposition. It's probably more effective on a $ / CO2 mass basis to just sequester carbon and keep using refined fossil fuels. Airplanes account for a single digit fraction of the CO2 emissions from transportation, though, as their mass and drag are both tiny as compared to cargo ships.
1. https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...
Reply to your post below, HN is not letting me respond:
Those synthetic fuels are effectively the same as biofuels. You're using energy to sequester carbon out of the atmosphere (or a body of water, in the case of algae based biofuels) and using that carbon to power a machine.
You can either do this by using electricity generated from another artificial power source, as in your example. Or you can do this by harnessing natural energy, like setting up transparent pipes to collect solar energy into algae or by farming biomass on land. Since most energy decarbonization plans assume modest energy consumption growth, and sometimes even an overall energy consumption reduction the former plan is less feasible than harnessing naturally occurring energy.