> Barring sources like steam methane reformation from landfill-reclaimed methane
You got this reversed: as a general purpose energy carrier, methane is far more useful than hydrogen. Because it is so much easier to handle (as you said), and because so much infrastructure is already in place.
But you can't produce methane from surplus electricity without having hydrogen as an intermediate step. All this talk about hydrogen is just about skipping the inefficient methanization step. Methanization would also have a hard scaling limit in how much concentrated CO2 can be captured. Ambient concentrations are far too low for methanization and carbon fuel applications like aerospace won't ever be able to capture.
Right now, the UK is getting 7% of its electricity from burning biomass, primarily woodchips. CO2 capture there seems eminently doable, as a source for methanization of hydrogen.
It seems unlikely that hydrogen will be a viable fuel for commercial aircraft, given the difficulties of keeping hydrogen liquid or storing it compressed without excessive mass. Liquified natural gas (primarily methane) is however a viable fuel: https://www.wired.com/2012/03/boeing-freezes-design-with-liq...
If we can generate hydrogen from wind and capture CO2 from biomass, and use them to generate methane, this seems a viable way to power aviation going forwards. For most other things, batteries or direct hydrogen use seem viable, but aviation is hard.
Wouldn't aircraft H2 storage just be low pressure insulated tanks that self maintain their temperature by the boiling of the H2? Insulation is mostly air and as a result is light.
Any vented excess H2 isn't a big issue. You can just dump it straight into the atmosphere with no environmental consequence. If that turns out to be unsafe in some situations you can run it through some sort of heated auto lighting burner.
The energy loss of liquefaction is worse than that of methanization. If you add liquefaction of methane it gets close and H2 might even be slightly ahead, but LNG handling would be so much easier. 190K and 33K are very different temperatures.
You are pretty much describing the end-game scenario I had in mind: the use cases where CO2 capture would be hard or impossible are mostly the same as the use cases where direct use of H2 (without methanization or even further synfuel steps) is prohibitive. Mobile (mostly aviation) and decentralized (upgrading distribution networks for H2 capability down to individual kitchen gas stove seems almost as unlikely as upgrading the
stoves to capture).
A post-fossil energy economy that combines H2 (where feasible) with methane (where necessary) won't see much if any of the methane's carbon captured. In a post-fossil economy CO2 sufficiently concentrated for methanization could easily be a limiting factor. Photosynthesis is the only scalable way to concentrate carbon from an atmosphere where CO2 is measured in hundreds of PPM, so all the post-fossil methane has to come either directly from biological processes or from biomass burning capture + H2.
You got this reversed: as a general purpose energy carrier, methane is far more useful than hydrogen. Because it is so much easier to handle (as you said), and because so much infrastructure is already in place.
But you can't produce methane from surplus electricity without having hydrogen as an intermediate step. All this talk about hydrogen is just about skipping the inefficient methanization step. Methanization would also have a hard scaling limit in how much concentrated CO2 can be captured. Ambient concentrations are far too low for methanization and carbon fuel applications like aerospace won't ever be able to capture.