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Products and solutions, 2016-01-12, 10:16 AM

Megawatt electricity storage system for the transition to renewables: Research project into redox flow batteries receives funding from Ministry for Economic Affairs and Energy

With demand for energy storage solutions rising rapidly in connection with the transition to renewables, the companies thyssenkrupp, Centroplast and Eisenhuth along with the research institutes Energie-Forschungszentrum Niedersachsen (EFZN) and Zentrum für BrennstoffzellenTechnik (ZBT) have launched a joint research and development project. The aim is to develop a new, low-cost process to manufacture one of the core components of redox flow batteries – bipolar plates – with surface areas in the m² range. Germany’s Ministry for Economic Affairs and Energy (BMWi) is providing 3.9 million euros over a period of three years as part of its funding measure “Extruded plate – new large-area bipolar plates produced by extrusion for redox flow batteries”. The new technology will substantially reduce the unit manufacturing costs of redox flow batteries and is expected to be marketed by thyssenkrupp from 2018.

The global market for energy storage systems is growing rapidly as renewables become increasingly established on the energy market. According to forecasts by the International Energy Agency IEA, electricity generation from renewable sources will roughly triple between 2012 and 2040. The problem is that wind and solar are volatile; the amount of energy they deliver fluctuates sharply. To store large amounts of energy from renewable resources, flexible storage systems such as redox flow batteries will be needed in the future.

From watts to megawatts: redox flow batteries have potential for large-scale applications

The special feature of redox flow batteries is that they do not store and convert energy in the same place, as is the case with other battery systems, but separately. Redox flow batteries store electricity as chemical energy in two large tanks containing electrolytic fluids – salts dissolved in organic or inorganic acids. The two tanks are connected to electrochemical cells that convert electricity into chemical energy or chemical energy into electricity. The power output and the amount of electricity stored can be scaled independently. Alongside their long lifetime this is one of the major advantages of redox flow batteries over other battery systems. Redox flow batteries are particularly suitable as stationary energy storage systems. They can respond very quickly to the supply situation, switching from storage to discharge in fractions of a second with efficiency levels currently of up to 80 percent.

The bigger the tanks, the more electricity can be stored. Power output, however, depends on the size of the active area of the electrochemical cells, and thus directly on the size of the bipolar plate. Increasing this size is the aim of the consortium. The latest commercial redox flow batteries have a cell area of roughly 0.1 m², providing only around 80 watts of power. To allow large scale industrial use in the future, the active cell area of redox flow batteries is to be increased to 2.7 m², more than 30 times the current size. Connecting hundreds or thousands of cells into larger units will provide batteries producing tens to hundreds of megawatts. This principle is not new and is already implemented today in other electrolysis applications, for example in chlorine production.

Innovation through cross-sector collaboration

thyssenkrupp Industrial Solutions has been working for some time to develop redox flow storage technology for large-scale use. The company’s know-how is mainly in the design of the electrochemical cells. The development of an improved cell design, which thyssenkrupp has patented, recently enabled the company to put a pilot redox flow storage system with cell areas up to 0.6 m² into operation at its research and development center in Ennigerloh. The newly developed bipolar plates will also be tested here under near-service conditions to see if they are suitable for use in redox flow batteries.

Under the newly launched project to develop a production process for a new kind of bipolar plate, Eisenhuth is responsible for transferring the research results to industrial production and for manufacturing small-area bipolar plates. ZBT, supported by Eisenhuth, will select and develop materials suitable for the new production technology.

Plastics specialist Centroplast will be responsible for scaling up the bipolar plates and demonstrating the feasibility of manufacturing plates on a m² scale using the new technology. The main focus will be on the ability to manufacture defect-free, high-quality bipolar plates in a robust and reproducible process. During the development process, the research institutes ZBT and EFZN will support the manufacture of the bipolar plates by Eisenhuth and Centroplast by means of extensive material characterizations and electrochemical analyses.

thyssenkrupp Industrial Solutions will then be responsible for integrating the newly developed bipolar plates into redox flow batteries and further optimizing the cell design with a view to large-scale applications. The joint project to produce the bipolar plates is being coordinated by Eisenhuth.

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