[maxerickson]

Methane synthesis is a potential solution. Simpler infrastructure/reuse of existing infrastructure.

Or potentially methanol (and better yet, butanol, which is easier to deal with than methanol, less corrosive, less hydroscopic).

[marmarama]

Hydrogen as a replacement fuel for vehicles is a dead duck. Batteries have won there.

Hydrogen, or zero net carbon hydrocarbons synthesized from it, is a good fit where energy density exceeds what current lithium chemistry batteries can provide, like aeroplanes, or rockets.

[maxerickson]

If we overbuild solar to store energy for winter heating, CNG may be pretty competitive for on road use (especially for larger vehicles).