As we can store fossil fuels for weeks of demand, we can store the required energy in chemical form, no? Germany has huge natural gas storage, for ezample.

If you mean hydrogen, this video explains the issues better than I can: https://www.youtube.com/watch?v=Zklo4Z1SqkE

Doesn't need to be hydrogen - plenty of possible substances that could be used as storage (might not even need to be gaseous for some applications).