The combination of biomass gasification with fuel cells is commonly referred to as Biomass-Integrated gasification fuel cell systems (B-IGFC). In this two-part system analysis, we investigate seven B-IGFC systems and four solid oxide fuel cell (SOFC) designs with a system power output of around 1 Mw(el). In this part, we define the B-IGFC systems and asses their technical feasibility using a finite volume based SOFC model and ASPEN PLUS (TM) models for the simulation of the gas processing. It is found that the low operational temperature of the ZnO employed for the H(2)S removal in all systems requires an additional humidification of the producer gases (PG) to avoid carbon deposition. Diluted PGs require highly active anode catalysts to yield low activation losses and satisfying mean current densities. The air-to-fuel ratio required to maintain the operational temperature of the different cell designs generally increases with decreasing internal reforming potential of the producer gases. In this respect, counter-current cells are less sensitive than co-current cells. The maximum solid temperatures and temperature gradients resulting from the operation of SOFCs with producer gases are lower than with pre-reformed natural gas. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.