  We investigate the problem of characterizing the economic value of energy
storage capacity to a wind power producer (WPP) that sells its energy in a
conventional two-settlement electricity market. The WPP can offer a forward
contract to supply power in the day-ahead market, subject to financial
penalties for imbalances between the contracted power and the power that is
delivered in real-time. We consider the setting in which the WPP has access to
a co-located energy storage system, and can thus reshape its wind power
production subject to its storage capacity constraints. Modeling wind power as
a random process, we show that the problem of determining optimal forward
contract offerings--given recourse with storage--is convex. We further
establish that the maximum expected profit is concave and non-decreasing in the
energy storage capacity, which reveals that the greatest marginal benefit from
energy storage is derived from initial investment in small storage capacity. We
provide a characterization of the marginal value of small energy storage
capacity to the WPP. The formulae we derive shed light on the relationship
between the value of storage and certain statistical measures of variability in
the underlying wind power process.
