IIRC (though I'm not a chemist) a challenge with synthetic fuel generation is the continuous high power needed to drive those processes. Most renewables don't provide that yet (with the exception of hydro), at a sufficient level to make aviation fuel. There was a company mentioned here a while back that is trying to do that with small scale nuclear sited at airports, but that has other issues.
I'm not seeing the problem. Synthetic diesel is its own energy storage medium. If the plant was powered at night by burning its own daytime products, and powered in the day by solar, it would still be carbon neutral.
I think the problem is the need for uninterrupted high power input to the Fischer Tropsch process in order to maximize the utilization factor. You could get this in theory from a massive dedicated battery that kicked in when clouds rolled over and reduced solar output. It's doubtful that the economics of that work out.
Another problem is getting an uninterrupted supply of H2 and CO to feed the process. None of the convenient sources for those are carbon neutral, and obtaining either in a carbon neutral way (i.e. renewable electricity powered electrolysis) adds significant additional inefficiencies.
> Synthetic diesel is its own energy storage medium. If the plant was powered at night by burning its own daytime products, and powered in the day by solar, it would still be carbon neutral.
Yes, but why would you power it at night with the syn diesel you created during the day? You'd end up with at best 25% of the syn diesel you started the night with, because the Fischer Tropsch process is only 50% efficient, and running a diesel generator is at best 50%.
I'm not a process engineer of course, but my feeling is that abundant free energy changes these equations. It simply does not matter what the efficiency is when the energy input is free. Also you wouldn't burn the fuel for electricity, you'd burn it for direct heat. A lot of petroleum refinery equipment is heated by burning things that have just been made in the refinery itself. That doesn't seem very different.
