  Power generation in Germany is currently transitioning from a system based on
large, central, thermal power plants to one that heavily relies on small,
decentral, mostly renewable power generators. This development poses the
question how transmission grids' reactive power demand for voltage management,
covered by central power plants today, can be supplied in the future.
  In this work, we estimate the future technical potential of such an approach
for the whole of Germany. For a 100% renewable electricity scenario we set the
possible reactive power supply in comparison with the reactive power
requirements that are needed to realize the simulated future transmission grid
power flows. Since an exact calculation of distribution grids' reactive power
potential is difficult due to the unavailability of detailed grid models on
such scale, we optimistically estimate the potential by assuming a scaled,
averaged distribution grid model connected to each of the transmission grid
nodes.
  We find that for all except a few transmission grid nodes, the required
reactive power can be fully supplied from the modeled distribution grids. This
implies that - even if our estimate is overly optimistic - distributed reactive
power provisioning will be a technical solution for many future reactive power
challenges.
