And, as you mentioned, having fossil in reserve for edge cases is definitely a viable option.
Wind can work but also partially has the same problem but to the same extent. Usually the colder it gets the less windy it gets. Basically in Finland during the winter it gets cold when there is no wind bringing warm air from the Atlantic (gulf stream) usually as a result of a high pressure zone parking itself over the country.
It does mean you depend on processes you have little say in. Somebody else specifies and builds much of the transmission line, and all of the generating capacity.
https://www.fingridlehti.fi/en/ja-kantaverkkokeskuksesta-soi... (this article is from summer about moving it the other way but the same happened now during the winter but other direction)
This is one of the reasons why the electricity prices hiked up as high as they did here. Basically Norway and Sweden do have some electricity available for cheaper then running reserve gas plants in Finland but they can't get that electricity from the south all the way up north.
And being that reliant on another nation is not good for the national safety of a country. Imagine if a significant portion (like lets say 30%) of the electricity used in US came from solar farms in Mexico (or even further south being transmitted through multiple countries). This would make US economy and national defense really vulnerable (both require massive amounts of energy to really function)
> "It does mean you depend on processes you have little say in. Somebody else specifies and builds much of the transmission line, and all of the generating capacity."
Overcapacity has its issues. It does not remove the dependency on fossil fuel, and you still need to have independently the same capacity in fossil fuel plants. A big part of the fossil fuel cost in term of economics is have them standby and operational, which today is paid primarily through subsidies. Having a bunch of wind turbines running at 20% efficiency while at the same time paying a fossil fueled power plant be ready to step is not cheap. Is it _still_ cheaper than nuclear? Hard to say. All the comparisons I have seen are done on the theoretical cost per watt produced, not what the grid costs to operate on a year to year basis in order to provide the service of a stable grid.
Looking at the day prices per local zone around Sweden and Finland, the prices goes down the closer you get to hydro and nuclear and goes up the closer you get to wind and fossil fuels, with as high as 10x. Economically that makes the case for wind + fossil fuels a bit harder to buy, through I am not blind to the fact that its previous generations that enabled it. Living next to wind+fossil fuel is right now very expensive, with industries moving north as a direct result.