German utility Ewe Gasspeicher announced plans on June 27 to build what it says could be the biggest battery in the world, to be housed in underground salt caverns off the northern German coast.

A giant redox flow battery will provide up to 700MWh by the end of 2023, communications officer Dietmar Bücker told BESB, at a cost of around $1,100/MW. The biggest flow battery in existence is believed to be Sumitomo Electric Industries’ flow battery in Japan, which can provide about 60 MWh of power.

Bücker said the battery would be built under a brine-for-power project consisting of three phases, the first and second of which would involve the installation of solar panels.

“Every kind of energy can be stored,” he said. “In future we want to store the renewable power of the north German wind parks. Storage will be scalable to market requirements.”

In the third phase, modifications of the caverns, which currently store natural gas, will be completed.

Ewe Gasspeicher is working with Friedrich Schiller University in Jena, 500 kilometres to the south of the coastal town of Oldenburg. The university has developed electrolyte materials for the project such as recyclable polymers dissolved in salt water, which are less polluting than conventional vanadium flow batteries.

“Not only is vanadium extremely expensive, but the solution is highly corrosive, so that a specific membrane has to be used and the life span of the battery is limited,” said Martin Hager, a lecturer at Friedrich Schiller University. The battery is expected to have about 20,000 charging cycles, the scientists claim.

The researchers have developed new materials without adding aggressive acids, saying the battery is based on polymers that in their core structure resemble polystyrene and can accept or donate electrons.

The pilot of the project will install two above-ground containers for the electrolytes before the end of this year.

“We have to underline that the brine for power project is still a research project and we need to carry out some more tests and clarify several issues before we transform it into underground caverns,” Bücker told BESB.

“But we are very confident that by about the end of 2023, we will have an operating cavern battery.”