One possible form of energy storage is to separate a chemical compound AB into components A and B while adding energy. The reverse reaction at any point in time then allows the previously stored energy to be recovered. The water - hydrogen / oxygen system represents an interesting approach: by supplying electrical energy, water (AB) can be split into its components hydrogen (A) and oxygen (B) using an electrolyzer. These two components can then react again to form water at any time. The corresponding reaction in a fuel cell allows the energy released to be converted directly into electricity. If electrolysis is carried out using electricity generated from renewable sources, for example from wind generators or photovoltaic systems, this technology represents a promising approach to replacing the finite fossil energy sources such as oil and gas with the energy source hydrogen.