  The application of the flow tracing method to power flows in and out of
storage units allows to analyse the usage of this technology option in
large-scale interconnected electricity systems. We apply this method to a
data-driven model of the European electricity network, which uses a
techno-economic optimisation to determine generation and storage capacities and
dispatch, assuming a 95% reduction of CO2 emission compared to 1990 levels. A
flow-based analysis of the power inflow into the different storage technologies
confirms the intuition that longer-term hydrogen storage is mainly utilised for
wind, whereas short-term battery storage mostly receives inflow from solar
power generation. The usage of storage technologies in general shows a
local-but-global behaviour: Whereas on average the power outflow from these
capacities is predominantly consumed locally inside the same node, when
exported it is also transmitted over long distances as a global flexibility
option for the entire system.
