  The preventative strategies for $N-1$ network security dominant in European
networks mean that network capacity is kept free in case a line fails. If
instead fast corrective actions are used to overcome network overloading when
single lines fail, this has the potential to free up network capacity that is
otherwise underused in preventive $N-1$ security strategies. In this paper, we
investigate the impact on renewable integration of a corrective network
security strategy, whereby storage or other flexibility assets are used to
correct overloading shortly after line outages. In this way, we find
significant cost savings for the integration of renewable energy of up to 2.4
billion euros per year in an aggregated 50-bus model of the German power system
utilizing these flexibility assets, so-called network boosters (NB). This
offers a role for storage beyond energy arbitrage or ancillary services like
frequency control. While previous literature has focused on the potential
savings of NB in the short-term operation, we focus on the long-term benefits
in systems with high shares of renewable energy sources, where the capacities
and dispatch of generation and NB are optimised. We demonstrate the benefits of
NB for various shares of renewable energy, NB and flexibility costs, as well as
different allowed levels of temporary overloading the lines in both (i) a
sequential model, where long-run generation investments are optimised
separately from the NB capacities, and (ii) a simultaneous model, where
generation is co-optimised with NB investment so that mixed
preventive-corrective approaches are possible.
