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.
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.
This is in the american southwest so winters are very mild and the sun is still strong. Summer is the much more demanding part where AC is 90% of electricity use for the year. There would certainly be challenges in other locations but I think you could do the napkin math on it with panels being as cheap as they are. The solution to pretty much any deficit these days is to just add more panels. The biggest issue there is, is if you do not have sufficient space. My panels are ground mounted.
Using an overprovisioned quantity of cheap cells is part of it.
Insulating and air sealing your home well is part of it.
Thermal mass approaches are part of it. Without cheap batteries, it's very possible to store a great many kwh in volumes of soil, water, or sand riddled with pipes and resistive heaters.
This year it has been pointed out that vertical bifacial solar panels radically outperform tilted arrays if snow is a possibility. Expect this to be the new normal at high latitudes as cell area is very cheap now.
Most solar charge controllers allow a certain amount of PV overprovisioning.