  This paper presents a framework for deriving the storage capacity that an
electricity system requires in order to satisfy a chosen risk appetite. The
framework takes as inputs user-defined event categories, parameterised by peak
power-not-served, acceptable number of events per year and permitted
probability of exceeding these constraints, and returns as an output the total
capacity of storage that is needed. For increased model accuracy, our
methodology incorporates multiple nodes with limited transfer capacities, and
we provide a foresight-free dispatch policy for application to this setting.
Finally, we demonstrate the chance-constrained capacity determination via
application to a model of the British network.
