The concept of the project is to create a new class of electrical energy storage system with the unique combination of characteristics of high energy density, modularity, fast response and low cost. To achieve these aims, the project will radically extend performance of a zinc – air batteries from small scale single primary cells to rechargeable redox flow battery modules, which at production scale can be stacked to give powers of 20 kW to MWs.At all stages of the project, a system approach will be adopted to develop a working and robust energy store from the individual components (flow battery, power conversion, grid interconnection, control system) which is suitable for industrialisation within a short timescale at the end of the project.The project will be steered by analysis of the user applications and requirements, leading to system specifications for potential applications, which will in turn define targets for the individual system components.The rechargeable Zn-air battery proposed here will overcome many of the problems of other storage technologies including conventional redox flow cells by the introduction of the following innovations: the use of an air electrode for one half-cell reaction (only half the reactant volume is required), increasing energy density, use of an alkali electrolyte in which the metal is highly soluble allowing high energy densities with fast electrode kinetics, fast response due to the fast electrode kinetics and the reactants being already present at the electrodes, decoupling of power and storage capacity due to the external electrolyte storage, low cost (due to the cheap electrolyte & simple material requirements), highly scalable and modular using distributed power electronics.A 10 kW demonstrator will be built which will be fully tested against worldwide grid connection standards and over a wide range of operating regimes, in particular those associated with renewable generation.