It could never be less expensive in the same way a a sled will continue to slide forever on a frictionless surface: theoretically. Material limitations, and te

It could never be less expensive in the same way a a sled will continue to slide forever on a frictionless surface: theoretically. Material limitations, and technical limitations may make it cheaper practically. As an example, let's look at rockets. Which is cheaper, removing the CO2 after release, or developing switching technologies, for instance, to using O2 and H. Well, for certain applications, where the energy density and logistics of the fuel matter, pulling the CO2 out afterwards makes more sense. Now, yes, that is a small example, but my point is just to show thermodynamic efficiency doesn't translate directly to cost effectiveness for all applications.