Insufficient supply in winter times due to electric heating, mostly. Nuclear power plants are relevant insofar that they (in particular the older generation of power plants) are bad at providing energy on-demand. So while everyone worries about Germany and the issues associated with variable availability of solar and wind power, there are also documented cases where Germany had to fire up its coal plants to meet nuclear posterchild France's electricity demands.

I used to read German online magazine Telepolis regularly. They've got a writer who advocates for renewable energy, hence I used to come across related articles every now and then.