Unpredictable natural fluctuations of blowing wind and solar radiation are well-known challenges for the breakthrough of renewables. This is for the simple reason that we need a continuity and reliable energy supply with stable electricity distribution networks. What to do with a surplus of electric energy generated by renewables? Or what to do if the demand for electricity will exceed the supply? These two questions can be answered in one: Developing and providing efficient energy storage devices on a large scale.
The World’s Largest Battery Is Allegedly Able to Power the German Capital Berlin for One Hour
EWE GASSPEICHER GmbH, a German-based utility company, intends to turn the answer into deeds. They officially announced to build the world’s largest battery by using salt caverns as electricity storage facilities. These caverns were used as gas storages before. “Since salt water in caverns is also known as brine and we intend to store power according to the redox flow principle, we have named the project brine4power, or b4p for short,” says Ralf Riekenberg, head of the brine4power project. He adds: “We need to carry out some more tests and clarify several issues before we can use the storage principle indicated by the University of Jena in underground caverns. However, I expect that we will have an operating cavern battery by about the end of 2023.”
“Two caverns, each with a volume of 100,000 m³, will be used for the world’s largest battery.”
With an electrical capacity of 700 megawatts hours, it is possible to power over 75,000 households with electricity for one day according to the initiator. The costs for the world’s largest battery are quite similar to that of a pump storage power plant.
The World’s Largest Battery Employs the Redox Flow Principle
“If everything works, this may fundamentally change the storage market, i.e. the market for control energy. The amount of electricity this kind of storage facility contains – consisting of two medium-sized caverns – is sufficient to supply a major city such as Berlin with electricity for an hour. It means that we will have built the world’s largest battery. In contrast to other energy storage facilities that convert the electrical current into other energy carriers – for example into compressed air – we are storing the electricity directly with brine4power,” says the Managing Director of the wholly owned subsidiary EWE GASSPEICHER GmbH, Peter Schmidt.
“This polymer-based redox-flow battery is ideally suited as energy storage for large wind farms and photovoltaic power stations,” Prof. Dr. Ulrich S. Schubert from the University of Jena explains.
EWE plans to use an advanced form of the redox flow battery. Researchers from the Institute for Organic Chemistry and Macromolecular Chemistry (CEEC Jena) at the Friedrich Schiller University Jena (FSU Jena) in Germany in collaboration with the spin-off JenaBatteries GmbH developed a more efficient redox flow battery. “What’s new and innovative about our battery is that it can be produced at much less cost, while nearly reaching the capacity of traditional metal and acid containing systems.” Dr. Martin Hager says. It is also safer and easier to handle due to its harmless saline solution and organic polymers instead of heavy metals like vanadium and aggressive acids. “Thus we are able to use a simple and low-cost cellulose membrane and avoid poisonous and expensive materials” researcher Tobias Janoschka explains. According to the scientists, novel synthetic materials like Plexiglas and Styrofoam for the structure are used.
How the Redox Flow Battery Works
A redox flow battery stores electrical energy in chemical compounds. Whereas this battery is a special kind of an electrochemical battery, it is able to generate electricity through chemical reactions with an electrochemical cell and store electric power by using liquid electrolyte solutions in two separate tanks – for the positive and negative battery pole. The electrodes of a redox flow battery are not made of solid materials, as in the case of conventional batteries.
Two pumps allow the circulation of the two separated electrolyte solutions between the tanks and the electrochemical cell. In case of an electricity demand, the cell generates electricity – a discharge occurs. In this state, the polymers are electrochemically oxidized. During a charging process, the polymers are electrochemically reduced. An unacceptable mixture of both electrolytes is prevented by a membrane which separates the electrodes.
“In these systems the amount of energy stored as well as the power rating can be individually adjusted. Moreover, hardly any self-discharge occurs,” Dr. Martin Hager from the University of Jena explains.
Common electrochemical cells without the opportunity of exchanging its substances are less complex compared to a redox flow battery which needs at least two tanks, pipes, two pumps to ensure the circulation of the electrolytes, some the control and monitoring devices. A real advantage of EWE’s world’s largest battery is the fact that the liquid with the dissolved compounds can be stored in arbitrarily large and separable liquid tanks which are non-flammable and scalable. The amount of energy stored doesn’t depend on the cell size compared to common batteries where the liquid is stored in the cells. The energy capacity depends on the amount of liquid electrolyte in the whole system (pipes, tanks, cell). All electrolytes can then be stored for several months. The surface area of the electrodes essentially defines the electric power. By replacing the polymer solutions, a flow battery can be recharged quickly. However, due to its complex structure, they are not suitable for small consumers.
EWE is a service provider based in Oldenburg, Germany, and active in the business areas of energy, telecommunications and information technology. With over 9,000 employees and sales of EUR 7.6 billion in 2016, the company is primarily owned by the local government and providing electricity to over 1.3 million customers mainly in Germany.