Ensuring that the Netherlands is fossil gas-free by 2050 and CO2 neutral is difficult. A substantial energy transformation is needed. Sustainable energy sources must be year-round to replace fossil fuels. Flow batteries store excess energy for periods of low energy generation.

Flow battery versions exist. Many active materials can store electricity. Organic and vanadium flow batteries. All have pros and cons. A long-lasting variation employs pricey materials. The cheaper one employs less efficient textiles. Dutch scale-up Elestor claims hydrogen and bromide are the best active materials. The company claims efficient, sustainable, and affordable.

Discuss flow battery operation first. This energy storage system uses two huge storage tanks, each with a closed circuit that circulates its contents. Membranes connect both circuits. This layer preferentially passes protons.

Elestor’s technology fills one tank with hydrogen bromide after the battery is entirely depleted. This material splits into bromine and hydrogen gas when charged. The membrane keeps the bromine in the tank with HBr, where it creates dibromine. The other tank holds hydrogen (H2) to drain the battery. The charging reaction is HBr electrolysis, not H2O. Elestor claims HBr electrolysis works better.

Hydrogen combined to bromine releases energy. Hydrogen and dibromine instead of hydrogen and dioxygen make the battery act like a fuel cell. The battery is an electrolyser when charging and a fuel cell when discharging.

Wiebrand Kout, founder, recommends this hydrogen bromine flow battery for large wind and solar farms. Thus, making the best general-purpose flow battery is not the goal. Kout admits that the American ESS iron flow battery may be better for neighborhood storage. However, this Dutch innovation looks promising. Last year, the company raised 30 million euros. That took eight years of scale-up.