Comment by Maxion

You don't even need to open up R or Pandas to understand that solar is not viable in the winter.

Here's the official meteorology insitutions sunshine data: https://www.ilmatieteenlaitos.fi/1991-2020-auringonpaiste-ja...

Here's some solar production data over the seasons in visual form: https://profilesolar.com/locations/Finland/Helsinki/

What is also important to know is during the winter is that while production on average shows numbers every day, in practice that production comes only during the few actually sunny days in December when the panels aren't covered in snow.

Go even a bit up north from Helsinki and unless you keep your panels clear of snow manually, you'll hardly make anything between Nov and April.

EDIT: Here's a reddit thread where someone shares real production data: https://old.reddit.com/r/Finland/comments/1i6onkk/solar_ener...