> Perhaps someone with more knowledge can comment on why solutions like these can't be used to solve the energy storage problem. Is it just economics?
Yes. If you round-trip energy through hydrocarbons, then you have to pay the "Carnot tax". Your heat engine will be at best around 50% efficient at transforming hydrocarbons into energy. This is then compounded with the inefficiency of reducing carbon dioxide to get maaaaybe 20% round-trip efficiency.
The tax is fine _as long as_ it doesn't have to be transported, assuming the energy would otherwise be wasted.
Which is why hydrogen solutions for stationary storage could be interesting, but the moment you start transporting them around they become less useful.
I'm not seeing that. Hydrogen requires a ton of very expensive infrastructure for storage. Its density is impractically low for storage in tanks, it can't be liquified under reasonable conditions, and reversible hydrogen-binding materials so far have all been duds.
If you happen to have an underground geological storage available, then it might be reasonable. Right now, there's a demonstrator project for that ongoing in Germany. I guess this qualifies as "local"?
So yeah, if you need storage for 3-12 hours of runtime, then batteries are fine. Sodium batteries are probably going to fit this niche once they become cheaper. Anything more than that is a big gaping hole in the renewable story with no good solutions.
Yes. If you round-trip energy through hydrocarbons, then you have to pay the "Carnot tax". Your heat engine will be at best around 50% efficient at transforming hydrocarbons into energy. This is then compounded with the inefficiency of reducing carbon dioxide to get maaaaybe 20% round-trip efficiency.
And all of this with a huge capital cost.