Fuel cell arrangement having an improved efficiency. The arrangement comprises one or more fuel cell units 110 and a methanation unit 200 and a control unit 300. The fuel cell unit comprises a water inlet 111, a hydrogen outlet 112 and an oxygen outlet 113. The methanation unit comprises a catalyst 222, a hydrogen inlet 213, a carbon oxide inlet 214 having a first controllable valve 215 and a methane outlet 216, wherein the hydrogen outlet of the first fuel cell unit is coupled to the hydrogen inlet of the methanation unit, and the methanation unit is adapted to convert hydrogen and carbon oxide into methane, wherein the control unit is adapted to control the first controllable valve so as to obtain an optimum converting process to convert hydrogen and carbon oxide into methane.