Surely the main issue with winter in more northern regions is the significantly reduced period of the day for which any solar-generation is even possible. During the daylight hours there's still more than enough total insolation to heat the small amount of air we need to inside our houses, but you obviously need some form of storage (or incredibly good insulation, arguably a form of storage too) to ensure buildings can remain a comfortable temperature throughout the day and night. From a purely technical feasibility point of view, there's always sufficient insolation somewhere/somewhen to provide all our energy needs, but whether it's practical or economical compared to alternatives such as nuclear is worth doing the sums on.