Sorry this is a late reply. I can see that mentioning molten salt was a bit left-field, However, it is one of the more realistic ways to store the huge amounts of power needed to fuel an economy for a couple of weeks (which you need in northern europe if you want to use solar/wind). Here’s a link about it:

https://onlinelibrary.wiley.com/doi/10.1002/cite.202000137

I am pro nuclear, but if we are going to descend into this renewable hell, then we need to actually think about how you store terawatt-hours of power. I really think that this kind of storage might be the nearest we have to a solution. we’ll only need it once we try to turn off the gas turbines, of course. It is fascinating that so many smart people don’t see that the whole jigsaw is missing vital pieces.

The fact that you descend into complete science fiction should give you pause for thought. I doubt it will, but please think about how fantastical your proposed solutions are - “a massive lake of molten salt under every city” (I actually like that one!)…