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PATHS TO SUSTAINABLE ENERGY_2

The world's reliance on existing sources of energy and their associated detrimental impacts on the environment- whether related to poor air or water quality or scarcity, impacts on sensitive ecosystems and forests and land use - have been well documented and articulated over the last three decades. What is needed by the world is a set of credible energy solutions that would lead us to a balance between economic growth and a sustainable environment. This book provides an open platform to establish and share knowledge developed by scholars, scientists and engineers from all over the world about various viable paths. | Part 3 Energy Storage and Efficient Use of Energy 18 Understanding the Vanadium Redox Flow Batteries Christian Blanc and Alfred Rufer Laboratoire d Electronique Industrielle Ecole Polytechnique Federate de Lausanne Switzerland 1. Introduction Vanadium redox flow batteries VRB are large stationary electricity storage systems with many potential applications in a deregulated and decentralized network. Flow batteries FB store chemical energy and generate electricity by a redox reaction between vanadium ions dissolved in the electrolytes. FB are essentially comprised of two key elements Fig. 1 the cell stacks where chemical energy is converted to electricity in a reversible process and the tanks of electrolytes where energy is stored. end plate bipolar plate membrane end plate carbon felt b a Fig. 1. a The schematics of the vanadium redox flow battery. b View of the different components composing a VRB stack. The surfaces in contact with the catholyte are coloured in blue and in orange for the anolyte. The most significant feature of the FB is maybe the modularity of their power kW and energy kWh ratings which are independent of each other. In fact the power is defined by the size and number of cells whereas the energetic capacity is set by the amount of electrolyte stored in the reservoirs. Hence FB can be optimized for either energy and or power delivery. Over the past 30 years several redox couples have been investigated Bartolozzi 1989 zinc bromine polysulfide bromide cerium zinc all vanadium etc. Among them VRB has the best chance to be widely adopted thanks to its very competitive cost its simplicity and because it contains no toxic .