If the energy you need is in the form of heating, it’s actually surprisingly viable to store energy for months. Heat batteries is probably the cheapest and easiest way to store energy for the long term. It’s just that it’s horribly inefficient to go back to electricity.

So it’s more of an issue when you want to use that excess solar to power your computer in winter.

If not nuclear, I think the northern regions need to focus on geothermal (Quaise?) and trash burning (yes, recycle first, but eventually everything non metal degrades and should be incinerated)