Ok how do you use solar in Northern Europe during the winter? For 3 months you get less than 1% of the normal summer output (in most cases you will spend more energy just to melt the ice and snow off the panel)
Also hand waving the storage problem away with “just buy it from someone else using transmission lines” is naive. Basically that just makes you ultra reliant on those other countries that the line goes through of and whoever is on the other end of it. At least with coal and gas you can just ship it from some other party if politics block you from getting it from your current provider.
Where in Northern Europe? Norway, e.g., has lots of hydro. Iceland has geo. Different places will need different solutions. Wind is viable in many places. Tides, in some. Ships full of ammonia synthesized elsewhere will be right for some places, at times. (Norway is right now building a major industrial-scale ammonia synthesis plant.) And transmission lines will be important and unproblematic in many places (e.g. Sweden), even if not all.
The "storage problem" is solved by building out storage. Some places will need more storage than others; where you need a lot, underground or deep-water compressed air might be best. Transmission lines are a backup plan. You need to use everything. Cost matters.
Also hand waving the storage problem away with “just buy it from someone else using transmission lines” is naive. Basically that just makes you ultra reliant on those other countries that the line goes through of and whoever is on the other end of it. At least with coal and gas you can just ship it from some other party if politics block you from getting it from your current provider.