Over provision the panels by a good margin and have them at a more southerly angle (for northern hemisphere). You can play around on nrel pvwatts to see what configuration produces the most even expected monthly output: https://pvwatts.nrel.gov/pvwatts.php
Most solar charge controllers allow a certain amount of PV overprovisioning.
It is often surprising that most of the US is south of most of Europe (the common reference is that Chicago and Rome are both 42N. The jet stream complicates the effect on overall climate, but latitude is pretty much the only thing that matters for solar power.)
Solar panels are mildly more efficient when colder, the same latitude in an area with similar cloud cover in north America is probably generally slightly better for solar than Europe because it is colder, not sure if it would ever be more than a rounding error though.
The difference between surface solar radiation levels in the US and Europe are wild[1], fully agree on the rounding error view. Anchorage seems to receive the same level of watts per area as Germany and Poland.
Need a renewables feasibility index that accounts for the amount of solar, wind, hydro vs climate and typical weather. And bin plot population vs that.
Seems obvious that Norway, Washington State have lots of hydro. Places like Spain and California have lots of steady sun. Scotland, no sun in the winter but lots wind all the time. Those places renewables aren't problematic.
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.
In southernmost Sweden, just above Germany, solar production is only 5% in December compared to June. In northernmost Sweden the sun doesn't even rise above the horizon for most of December.
Most solar charge controllers allow a certain amount of PV overprovisioning.