The change of a centralized to a decentralized and fluctuating energy supply infrastructure that bases on renewable energies poses grand challenges for mains operation to guarantee supply and flexibility.
A recent survey from the Faunhofer Institute für Solare Energiesysteme (ISE) states that there are 1.5 Million photovoltaic power (PV) systems with a total capacity of approx.. 40 GW installed in Germany (status 2015). Of these PV systems 70 % run on low voltage and 90% run on low- and medium voltage grid levels.
The large portion of decentralized renewable energy plants that supply at low and medium voltage levels causes weather dependent power flows. During peak feed-in periods when the output power of local renewable generation units exceed the local demand, a great amount of power flows from lower grid layers to upper grid layers.
This violates the limits for voltage and frequency tolerances of the power grid. As a result the Erneuerbare Energien Gesetz (EEG §9) in Germany regiments since 2012 the feed-in from distributed generation units.
However, an absolut or partial shut-down is not an efficient way to integrate more energy from renewable resources into the energy mix. It needs more effective technologies within smart grids to integrate renewable energy resources in our grid structure.