  This study addresses the transmission value of energy storage in electric
grids. The inherent connection between storage and transmission infrastructure
is captured from a "cumulative energy" perspective, which enables the
reformulating of the conventional optimization problem by employing line power
flow as the decision variable. The study also establishes the theoretical
limitations of both storage and transmission lines that can be replaced by each
other, providing explicit closed-form expressions for the minimum capacity
needed. As a key departure from conventional practice in which transmission
lines are designed according to the peak power delivery needs, with sufficient
storage capacity, the transmission line capacity can be designed based on the
average power delivery needs. The models of this paper only rely on a few basic
assumptions, paving the way for understanding future storage as a transmission
asset market design. Numerical experiments based on 2-bus, modified RTS 24-bus,
RTS-GMLC, and Texas synthetic power systems illustrate the results.
