  Large scale renewable energy integration is being planned for multiple power
grids around the world. To achieve secure and stable grid operations,
additional resources/reserves are needed to mitigate the inherent intermittency
of renewable energy sources (RES). In this paper, we present formulations to
understand the effect of fast storage reserves in improving grid reliability
under different cost functions. Our formulations and solution schemes not only
aim to minimize imbalance but also maintain state-of-charge (SoC) of storage.
In particular, we show that accounting for system response due to inertia and
local governor response enables a more realistic quantification of storage
requirements for damping net load fluctuations. The storage requirement is
significantly lower than values determined when such traditional response are
not accounted for. We demonstrate the performance of our designed policies
through studies using real data from the Elia TSO in Belgium and BPA agency in
the USA. The numerical results enable us to benchmark the marginal effect on
reliability due to increasing storage size under different system responses and
associated cost functions.
