Solid oxide fuel cells (SOFCs) are high-temperature, high-efficiency, combustionless electrochemical energy conversion devices that have potential for combined cycle applications. This paper intends to clarify and expand the efficiency discussions related to SOFC when operating in combined cycle (CC) systems. A brief analysis of the first and second thermodynamic laws is conducted and, building upon a previously developed SOFC dynamic model, operating fuel heating values are determined by utilizing the semi-empirical gas phase heat capacity method. As a result, accurate SOFC stack operational simulations are conducted to calculate its efficiency based on actual thermodynamic parameters. Furthermore, an analysis is conducted of a combined SOFC-CC system using dynamic modeling. Simulation results are given, which are intended to aid researchers in evaluating hybrid SOFC-CC generation systems.