A solid oxide fuel cell (SOFC) system integrated with an ethanol steam reforming unit is evaluated considering the first and second laws of thermodynamics. The ethanol reaction kinetic data and system architecture were developed in two previous communications. The irreversibility losses distribution and the plant energy and exergy efficiencies are studied at different reformer temperatures (823 < T < 973 K), water to ethanol molar ratios (5 < R-AE < 6.5) and fuel utilization factor (0.7 < U-f < 0.9). The post-combustion of the cell off gases for the heat recovery is also taken into account to maintain the system operation within the auto-sustainability boundaries. An increase of efficiency and irreversibility at the stack is reported when the reactants ratio is increased. The higher losses are placed at the steam reformer (280-350 kW) and the cell (400-590 kW) due to the combination of the chemical composition and stream conditions on chemical and physical components of the exergy. (C) 2010 Elsevier B.V. All rights reserved.