  A Redox Flow Battery (RFB) is one of the promising energy storage systems in
power grid. An RFB has many advantages such as a quick response, a large
capacity, and a scalability. Due to these advantages, an RFB can operate in
mixed time scale. Actually, it has been demonstrated that an RFB can be used
for load leveling, compensating sag, and smoothing the output of the renewable
sources. An analysis on transient behaviors of an RFB is a key issue for these
applications. An RFB is governed by electrical, chemical, and fluid dynamics.
The hybrid structure makes the analysis difficult. To analyze transient
behaviors of an RFB, the exact model is necessary. In this paper, we focus on a
change in a concentration of ions in the electrolyte, and simulate the change
with a model which is mainly based on chemical kinetics. The simulation results
introduces transient behaviors of an RFB in a response to a load variation.
There are found three kinds of typical transient behaviors including
oscillations. As results, it is clarified that the complex transient behaviors,
due to slow and fast dynamics in the system, arise by the quick response to
load.
