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NETWORK / 37 / OCTOBER 2016 Redox fl ow Redox ow batteries are considered a viable next generation technology for highly e - cient energy storage. They use electrolytes – chemical components in solution – to store energy. A vanadium redox ow battery, for example, uses vanadium ions dissolved in sulphuric acid. Being separated by a mem- brane, two energy-storing electrolytes cir- culate in the system. The storage capacity depends on the quantity of electrolytes and can be increased or decreased depending on the application. To charge or discharge the battery, the vanadium ions are chemically oxidized or reduced while protons pass the separating membrane. Where are they now? In the UK, vanadium ow batteries are just reaching commercialisation. RedT a UK energy storage technology company, announced last month that the € rst large- scale containerised systems have passed the pre-testing phase at the Power Net- works Demonstration Centre in Scotland (see below). The systems will now move into € nal installation and commissioning on the Isle of Gigha to manage grid constraints. The future? A single solution: RedT has also embarked upon a three-year knowledge transfer partnership with New- castle University to develop the € rst hybrid storage system using the technology. The ow battery, ideal for long duration energy- intensive industrial applications, will be combined with a lead acid, lithium battery or super capacitor for short duration power- intensive applications. Membrane: A crucial element in a ow battery is the membrane through which the protons pass to charge and discharge the battery. The membrane must also separate the two electrolytes to prevent short- circuiting. Currently, Na€ on membranes are the benchmark, but this material swells when exposed to water and loses its barrier function for vanadium ions. Now scientists from the Leibniz Institute for Interactive Materials (DWI), RWTH Aachen University and Hanyang University in Seoul have developed a hydrophobic membrane that achieves an e ciency of between 85 and 99%, signi€ cantly improving on the 76% achieved by current vanadium systems. Electrolyte: While the use of Vanadium ow batteries is still in its infancy, work is already underway to improve the technology further. Scientists at Harvard University have taken inspiration from vitamin B2 to develop a new class of battery electrolyte. With just a few tweaks to the original B2 molecule – used by the human body to help store energy – this new group of molecules is well suited for use in alkaline ow batteries. The highly stable and soluble molecules are produced through simple synthesis, meaning it can be manufactured on a large scale at very low cost. Positive Negative AC/DC converter Electrode membrane Pump Pump Cell e e v 2+ v 4+ v 3+ v 4+ Electrolyte tank v 5+ /v 4+ Electrolyte tank v 2+ /v 3+ Isle of Gigha Like many remote islands oš the coast of Britain, the island of Gigha in the Inner Hebrides is the ideal location for harness- ing renewable energy. But, as is again the case in many of these locations, Gigha is hampered by grid con- straints, limiting the inhabit- ants' ability to make the most of natural resources to improve local energy security. The island, which is 70 miles long by a mile and a half wide, is powered by one of the € rst community- owned grid-connected windfarms in Scot- land. The farm consists of three installed turbines with a combined capacity of 775kW, but a fourth is being added. This new turbine will be constrained to 225kW of its full 330kW capacity, resulting in a loss of 3GWh over its 25-year life. Thanks to a £3.6 million funding award from the (now defunct) Department of Energy and Climate Change, the island is to get an energy storage system to alleviate grid constraints, allowing for a 20% mini- mum increase in wind energy generation and the option to connect further renewa- bles in future. RedT has completed pre-testing of a 1.68MWh version of its grid-scale contain- erised ow battery. The system will com- prise eight 20£ containers – seven RedT 15-240 modules and one for service equip- ment. This setup removes the need for a permanent building and simpli€ es installa- tion, transportation and decommissioning. The system could also provide extra revenue from the sale of wind energy, local backup power supply in the event of network faults, the ability to replace die- sel generators at local € sh-farms, electric- ity trading, network services, frequency response and short-term operating reserve. RedT is working with SSE, EA Technol- ogy, Community Energy Scotland and Gigha Green Power on the 2.5-year project, and installation and commissioning has started.