Biomass gasification derived fuel gas is a renewable fuel that can be used by high temperature fuel cells. In this two-part work an attempt is made to investigate the integration of a near atmospheric pressure solid oxide fuel cell (SOFC) with a novel allothermal biomass steam gasification process into a combined heat and power (CHP) system of less than MWe nominal output range. Heat for steam gasification is supplied from SOFC depleted fuel into a fluidised bed combustor via high temperature sodium heat pipes. The integrated system model was built in Aspen Plus (TM) simulation software and is described in detail. Part I investigates the feasibility and critical aspects of the system based on modelling results. A low gasification steam to biomass ratio (STBR=0.6) is used to avoid excess heat demands and to allow effective H2S high temperature removal. Water vapour is added prior to the anode to avoid carbon deposition. The SOFC off gases adequately provide gasification heat when fuel utilisation factors are < 0.75; otherwise extra biomass must be combusted with overall efficiency penalty. For SOFC operation with U-f = 0.7 and current density 2500 A m(-2) the electrical efficiency is estimated at 36% while thermal efficiency at 14%. An exergy analysis is presented in Part II. (c) 2006 Elsevier B.V. All rights reserved.