[rich_sasha]

How long do the batteries last? What happens after a week or cloudy winter weather?

Battery storage typically seems to smooth out production over about 24hrs, not multiple days and certainly not seasons.

[pfdietz]

Dunkelflauten (and seasonal leveling) are covered by use of an e-fuel like hydrogen.

You can see this effect in action at the optimization/simulation site https://model.energy/ Go there, solve for Germany (2011 weather data, 2030 cost assumptions), then disable hydrogen and try again. The optimum cost nearly doubles.

[ZeroGravitas]

Interestingly, this simulation also suggests a 95% cost increase if Germany tried to do it without e-fuel/power-to-X (which it estimates would need to cover about 8% of demand)

https://www.wartsila.com/static/energy-vision/#/country/DE