Wärtsilä Corporation is developing SOFC systems for the power ranges of 200 kW and above. Currently the work is focused on a 5 kW test system and a 20 kW prototype unit. Reliable system development requires dynamic simulation, and APROS (Advanced Process Simulation Software) has been chosen as the tool for this work. Development work has been made for modeling fuel cell power plant by preparing modules for SOFC stacks, sulfur removal units, natural gas reformers, catalytic afterburners, and power conditioning systems. The implementation of a zero and one- dimensional SOFC stack model into APROS has been made and results are under validation. In this contribution, the functionality of modeling these test systems has been studied at the component and system levels. Measurement data is available from both Wärtsilä Corporation and VTT from their own 5 kW test systems that have been running for over 4000 h.