High-efficiency hybrid systems (HS) based on the coupling of solid oxide fuel cells (SOFCs) and gas turbines (GT) are analyzed in this paper through the use of two different approaches: simplified and detailed SOFC models. The simplified model, already presented by the authors, is very useful for HS design and off-design analysis. The detailed model, developed by the authors and verified through the use of available experimental data, allows the complete description of the SOFC reactor’s internal behavior to be obtained. The detailed model can also be utilized for HS modeling. Both models are presented and discussed in this paper, and they are compared to each other. The results obtained for the stand-alone SOFC reactor, and the HS design point configuration are presented and carefully discussed, also taking into account the nonlinear SOFC response.