A fuel cell power system including at least one fuel cell, a ram air system and a cooling circuit in which coolant is intended to circulate for regulating a temperature of the at least one fuel cell. The cooling circuit comprises a ram air heat exchanger in the ram air system and the ram air system comprises a nozzle. The fuel cell power system further comprises a water tank and the fuel cell power system is arranged to flow water from the water tank to the ram air system so as to spray water in ram air via the nozzle. Thus, dimensioning of the ram air system which includes the ram air heat exchanger is reduced.