  This paper considers the optimal dispatch of energy-constrained heterogeneous
storage units to maximise security of supply. A policy, requiring no knowledge
of the future, is presented and shown to minimise unserved energy during
supply-shortfall events, regardless of the supply and demand profiles. It is
accompanied by a graphical means to rapidly determine unavoidable energy
shortfalls, which can then be used to compare different device fleets. The
policy is well-suited for use within the framework of system adequacy
assessment; for this purpose, a discrete time optimal policy is conceived, in
both analytic and algorithmic forms, such that these results can be applied to
discrete time systems and simulation studies. This is exemplified via a
generation adequacy study of the British system.
