alt Hacker NewsWell, there's also burning regular fuel in a fuel cell, a FCEV. That doubles the efficiencies over ICE, so I guess that bumps it back up to 8x away?
Given the great energy densities and stability in transport of hydrocarbons, there's already some plants out there synthesising them directly from green sources, so that could be a solution if we don't manage to increase battery densities by another order of magnitude.
> there's already some plants out there synthesising them directly from green sources
I didn't realize that a "green" carbon atom is different from a regular carbon atom. They both result in CO2 when burned.