After you have built out enough renewables for day load and to charge storage, you build out storage. Not batteries, those are super expensive. Stuff that is super-cheap, instead. There are lots of choices. But you don't need to choose immediately. Prices are plummeting at different rates, and nobody knows which will be cheapest by then.
Ehhhh, sorta? Wind power can be useful as a base load generator if you over provision by a large amount. But the problem is that during the summer months you will get ridiculously high generation and then in winter it drops like a rock. What's worse is that solar follows this same trend.
Typically pricing per kwh is averaging across the year. But during the winter you will have terrible shortfalls. So you need to double or even triple that price because you will have to double or triple the wind turbines and solar panels to achieve the same stable load.
Unfortunately, power storage for months worth of power is even more expensive than just over provisioning. Batteries are great for grid stability, but not for long term energy storage.
You can get a good idea of what renewables look like over the year here: https://www.eia.gov/todayinenergy/detail.php?id=16851
So unless we want to keep running natural gas in the winter, or we want to pay 3x as much for renewables, geothermal and nuclear would make a lot of sense when paired with renewables.
The appealing quality of synthetic fuel like ammonia is that there is always an eager market for as much as you can produce, so once your local tankage is full, excess power produces reliable revenue. Your synthesizers are idle only when you are drawing down banked energy, and not necessarily even then if you have plenty.
Synthetic hydrocarbons will be used for a long time where those others can't be made to work, such as old cars and chainsaws, and air transport until LH2 fleets and infrastructure are built out; or are used too rarely to merit upgrading, like back-up generators.
It is hard to know which are like Energy Vault, just there to scam investors, and which are onto something. I bet Terraform Industries is, at least, on the level. Whether they have the sauce to compete is a whole other question, but it will be a seller's market for a long time. That means whoever does it cheapest gets most profit.
Probably whoever manufactures equipment cheapest wins, even if their thing is not the cheapest/most efficient to use.
[1]: https://www.energy.gov/eere/water/pumped-storage-hydropower
https://news.ycombinator.com/item?id=31485229
Energy storage, chemical methods aside, is freshman-level physics: pump against pressure, lift something heavy, draw down against buoyancy -- E = fx, E = mgh -- using processes already used at industrial scale in billions of cases. The only open question is what exact scheme will end up cheapest. But you don't need to know that to start building. You might switch over to building something cheaper, later, but anything already built still works.
(But NB: Energy Vault is the Theranos of storage. Steer clear!)
The Black Sea is deep, making underwater methods attractive. Romania also has high mountains, making conventional pumped hydro also practical. The reservoir for pumped hydro need not encompass a watershed, unlike regular hydro, so can be minimally disruptive, environmentally.