One thing that everybody forget is that with agreement with the main power producers in Germany, the government of Gerhard Schröder (10 years ago) started the plan to built the network to link North Germany to the South for renewable energy production together with the agreed shutdown of the nuclear powerplants in 2020. Once the left/green government was replaced with the current one, the big power producers did a nice lobbying not to shutdown the powerplants and thus delayed the building of the network. But the laws to develop renewable energies (and the subsidies going with) were not changed. Thus, we ended up with a lot of individuals, small and medium companies building small "power plants" with wind and solar energy. A lot was done in the North because of good winds combined with cheap land. End result, power imbalance.
Also, the power network is still very "former East - former West" built, which is not helping. We had 3 years ago a blackout of the West while the East (which includes the part with most of the windmills) was still up.
At the end, the problem is mainly because of the delayed investment from the network operators and they are now affected by their own unwillingness to build the network. From a financial point of view, it is easy to understand because they are mainly coal/gas/nuclear producers and they would have had to build a network which would then be used by their competitors...