A steam generation system comprises a main steam generator and a back-up steam generator (20) which are both in fluid communication with a super heater (3) for superheating the generated steam. The superheater comprises a main heat source (6) for heating up a flow of heating gas. A back-up evaporator (2) is provided as a back-up steam generator for evaporating supplied water into steam. The back-up evaporator is connected in parallel to the main steam generator. An auxiliary heat source is provided for heating up the back-up evaporator. By controlling the auxiliary heat source (9), it is possible to supply more or less heat energy to the back-up evaporator to compensate for fluctuations in steam production of the main steam generator. The back-up evaporator is positioned away from the flow of heating gasses departing from the main heat source.