In this paper, a biogas fuelled energy system for combined production of electricity and hydrogen is considered. The system is based on a molten carbonate fuel cell stack integrated with a micro gas turbine. Hydrogen is produced by a pressure swing absorption system. A multi-objective optimization is performed, considering the electrical efficiency and the unit cost of electricity as the objective functions. The system operation is affected by variations in fuel composition, ambient temperature and performance degradation of the components occurring during its lifetime. These effects are considered while defining the objective functions. (C) 2010 Elsevier Ltd. All rights reserved.