The statistics tell me a different story. Seasonal differences in the renewable share are almost nonexistent. Maybe somewhere around +-20%. Sure we will need storage that lets us bridge weeks and if it is economic even up to a whole month but anything beyond that is not about trying to compensate energy shortages, it's about capturing the overproduced energy to sequester carbon.
Anything below the average of 40% is awful. The longest interval below 40% I have found was from 19.03 to 29.03. A month of storage is more than we would ever need. two weeks would be the sweet spot, one or zero weeks is doable if we use gas plants. Really the only amount energy storage that I would consider absolutely mandatory is 24 hours because we still want to use solar energy at night and wind power that is mostly generated at night during the day.
You still need 60% from somewhere. This is why France's new policy of replacing 20…25% nuclear out of 70…75% with renewables is good. Germany is just obliviously burning almost 50% coal instead.
https://www.energy-charts.de/ren_share.htm?year=2018&source=...
Also I recommend you to take a look at the daily variance.
https://www.energy-charts.de/ren_share.htm?year=2018&source=...
Anything below the average of 40% is awful. The longest interval below 40% I have found was from 19.03 to 29.03. A month of storage is more than we would ever need. two weeks would be the sweet spot, one or zero weeks is doable if we use gas plants. Really the only amount energy storage that I would consider absolutely mandatory is 24 hours because we still want to use solar energy at night and wind power that is mostly generated at night during the day.