Europe has more wind in the winters than in the summers
Fixing this with trans-European energy transfers is a neat idea, but if you want to send power from i.e. a solar panel on a roof in Spain to my house in Finland, or wind energy from Denmark to Poland, then we'll require infrastructure upgrades at scales that haven't been seen in much of Europe since the early 50's.
Fossil fuels aren't a solution, and nuclear energy only a smaller part of it. You can see that if you look at the cost and potential in the IPCC report.
There is no way around a massive build out of renewable energy.
PS: I just checked energy charts, and saw that Poland has more wind in the winter as well
Alas, at least in Northern Europe, the grids are largely in private hands, and investments are kept down to the legal minimum. There's no way we go all-renewable until someone kicks that hornet's nest.