Northern Europe is much further from the equator than most of the rest of the world. To the point where rooftop solar stops being a great option. That said there’s a few ways to boost that 10%.
PS: Geothermal can also slash energy needed for heating. Ground sourced heat pumps are the only reasonable small scale solution, but in urban areas going a little deeper starts to make a lot of sense.
> To the point where rooftop solar stops being a great option.
Perhaps as a complete energy solution. But it is already the case today that a domestic rooftop solar in Europe (maybe not in the very north) has payback times <10 years. And that's without factoring in batteries which (as the OP describes) are rapidly approaching affordability.
PS: Geothermal can also slash energy needed for heating. Ground sourced heat pumps are the only reasonable small scale solution, but in urban areas going a little deeper starts to make a lot of sense.