We are not trying to transfer green energy to less windy/less sunny places, the grid can take care of that.
It also seems like it can make use of existing infrastructure and save money there.
At first glance it seems reasonably transportable, but I'm worried about how you prevent it rusting in the air. Maybe it would be useful to blend it with biodiesel for that purpose.
But secondly, wind power makes a lot more sence in northern latitudes.
I imagine methane synthesis will beat some thinglike this out. Pipeline infrastructure exists, is convenient, etc.
Methane seems nice for the re-use of gas fired plants. I do think its gaseous nature has more downsides than upsides on the other two factors. There's also a gas-leak hazard with methane that doesn't exist here.
If the capital requirements are low enough, I could see a 40% efficient energy battery for smoothing out peaks being nicer than more complicated storage schemes.
For fuel that can be transported, methane is a winner. In addition to the distribution infrastructure, there's an awful lot of residential use, with lots of appliances that don't need replacement.
Yes for short term batteries are better but for say seasonal storage or when power is generated far away from where it is used then metal is better.