EnergyKeeper advanced the technology of metal-free, organic redox flow batteries from laboratory to large prototype scale. A 30 kW redox flow battery with a capacity of 100 kWh was constructed and demonstrated at the smart grid in ACRRES, Netherlands. In contrast to lithium, lead or conventional vanadium flow batteries, metal-free flow batteries use organic salts as active material. They do not contain heavy metals or rare elements. This means that no critical raw materials from unsafe countries are required for the production. All components can be produced in the EU, without the negative effects of battery metal mining. The technology shows its advantages especially in areas of application with high technical safety requirements, since the aqueous storage solutions are non-flammable. The metal-free flow battery is therefore a clean and sustainable alternative for stationary energy storage. Possible users include PV and wind farm operators, energy providers, infrastructure service providers, commercial and industrial companies and transport companies.