The Blue Battery, is a battery that runs purely on water and table salt (Sodium Chloride), by storing electricity in a concentration difference between fresh and salty water. The Blue Battery can be used to facilitate the growth of renewable energy sources such as solar and wind power. The transition toward these sources is accelerating. However, the sources possess an intermittent character: the sun does not shine on every moment of the day unfortunately. At the moment fossil-fired power plants are still necessary to deal with these fluctuations. Hence, in order to facilitate this transition fully, energy storage is key. Conventional storage technologies, like Lithium-ion and lead-acid batteries, are not designed for storing vast quantities of electricity as power- and storage capacity are coupled, making storage unnecessary expensive. The Blue Battery allows to store electricity in a safe, scalable and environmentally-friendly way.