Two new cogeneration systems (producing power and heating) based on solid oxide fuel cell fed by either the syngas or biogas are proposed. The performance of systems is analyzed and compared with one another from the thermodynamic and economic viewpoints. Applying the conservation of mass and energy as well as the exergy and cost balance equations for each system component and using the engineering equation solver software, the systems are modeled. Through a parametric study, effects of some key variables such as the current density and the stack temperature difference on the systems' performance are investigated. It is found that for power generation, digester based solid oxide fuel cell shows better performance (with a first law efficiency of 40.14% vs 20.31%); however, considering the combined power and heating system, the total efficiency is obtained 51.05% and 58.75% for digester and gasifier based systems, respectively. In addition, it is found that the digester based SOFC is more cost-efficient and has 54% less unit product cost compared to that of the gasifier based system. (C) 2016 Elsevier Ltd. All rights reserved.