I think Finland just has a large enough extent from south to north that solar might be starting to become viable in the south but not in the north. While Iceland already produces more electricity per capita than any other country, using only hydro and geothermal, so solar is pretty much non-existent.

Comparison of solar share:

https://ourworldindata.org/grapher/solar-share-energy?tab=li...

Solar potential:

https://en.wikipedia.org/wiki/Energy_in_Iceland#/media/File:...