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Interest in electrical energy storage systems is increasing as the opportunities for their application become more compelling in an industry with a back-drop of ageing assets, increasing distributed generation and a desire to transform networks into Smart Grids. A field trial of an energy storage system designed and built by ABB is taking place on a section of 11 kV distribution network operated by EDF Energy Networks in Great Britain. This paper reports on the findings from simulation software developed at Durham University that evaluates the benefits brought by operating an energy storage system in response to multiple events on multiple networks. The tool manages the allocation of a finite energy resource to achieve the most beneficial shared operation across two adjacent areas of distribution network. Simulations account for the key energy storage system parameters of capacity and power rating. Results for events requiring voltage control and power flow management show how the choice of operating strategy influences the benefits achieved. The wider implications of these results are discussed to provide an assessment of the role of electrical energy storage systems in future Smart Grids.

The class of completely simple semigroups forms a variety when considered as semigroups with the additional unary operation x ↦ x −1 , x −1 being the inverse of x in the subgroup H x . We present a Rees matrix representation for the -free product of any family of completely simple semigroups and for the -free product of any amalgam of completely simple semigroups. From the former, a description of the free semigroups in and of certain free idempotent-generated semigroups in is easily deduced. We then consider the lattice of subvarieties of . Also discussed are injectives and projectives in and a problem concerning the Hopf property.