  We consider the problem of characterizing the locational marginal value of
energy storage capacity in electric power networks with stochastic renewable
supply and demand. The perspective taken is that of a system operator, whose
objective is to minimize the expected cost of firm supply required to balance a
stochastic net demand process over a finite horizon, subject to transmission
and energy storage constraints. The value of energy storage capacity is defined
in terms of the optimal value of the corresponding constrained stochastic
control problem. It is shown to be concave and non decreasing in the vector of
location-dependent storage capacities -- implying that the greatest marginal
value of storage is derived from initial investments in storage capacities. We
also provide a characterization of said marginal value, which reveals its
explicit dependency on a specific measure of nodal price variation. And, more
generally, we derive an upper bound on the locational marginal value of energy
storage capacity in terms of the total variation of the corresponding nodal
price process, and provide conditions under which this bound is tight.
