If actually cared about efficiently transferring to fight climate change, and not build a utopia. We would simply create a list of all coal power stations, order them by age and then start building a nuclear plant right next to one after the other as fast as possible.
If you did it that way, you could in less then 20 years basically make your grid green. Most people wouldn't notice anything what so ever. No new infrastructure would need to be build. It would be reliable in basically all situations. And it would give you a very large base of highly educated engineers and technicians.
Compare that to just importing tons of PV from China and putting up tons of new transition lines.
> but there are readily available seasonal storage choices
Are there? Non have been deployed and if you look at modeling these need to be essentially free to actually happen.
> Iron-air looks economically viable
One startup claims this, they have not shown a prototype or given specs, it will not be commercially deployed for a few years. Its a bit early to claim its viable.
Fact is, storage beyond 2h is totally unproven. Most companies that have worked in this direction have failed.
> Electrolysed hydrogen, either stored directly or as ammonia. Just need PV prices to fall a bit, which is expected, and the cost of electrolysis to fall, which is happening.
Using direct heat is simply a better option then electrolysis on large scale. With advanced nuclear you can use nuclear heat to crack steam. Far better option.