Nuclear power's output stability isnt worthless but it requires some pretty impressive mental calisthenics to convince yourself that it's worth quintupling the price tag when you can just build a battery.
7 hours is apparently enough 99% of the time.
Overproducing a bit and turning it into windgas would probably work for the rest.
It’s nowhere enough and there aren’t any places to build more.
For reference current energy production is 7500MW in Finland.
That being said, Finland has a wild excess of solar energy in the summer, and I'd like to see the gov't get serious about nationwide schemes to store up that energy for wintertime use. Air-water heat pumps, sand batteries, it's a start... capture that summer heat and squirrel it away.
Periods with low wind and low sun do happen but theyre rarer and shorter than people think. It's much more common that availability of wind and sun anticorrelate (even in winter), which is why the storage needed to get to 99% is normally measured in hours rather than days.