You quote, and I believe, 5x solar irradiation power difference between December, plus a second-order 10% power consumption difference. Doesn't this mean already a 5.5x difference - if X panels are sufficient in July, then 5.5X would be needed in December? And July itself probably already needs overprovisioning anyway - Polish summers are not guaranteed sunshine. If "July" is overprovisioned 1.5x and we add the 5x for December for a combined 7.5x overprovision, plus batteries, is it still cheaper than nuclear?
If nuclear gets dismissed as an expensive fantasy, well, at least it has been built and operated at massive scale. I am not aware of any large scale operating exports of solar energy from equatorial regions to Northern Europe, or similar distance.