A methodology for optimum sizing of battery integrated biomass gasifier based distributed power generation systems is discussed. Typically, biomass gasifier systems are sized considering peak demand resulting into lower operational efficiency due to part load operation during low demand period. The proposed methodology using design space approach enables designer with multiple combinations of gasifier engine and battery systems for given load profile from which an appropriate combination may be identified considering specific objective or constraints if any. Two gasifier operational strategies are discussed and compared using cost of energy. The methodology is further extended for sizing of hybrid systems incorporating gasifier, solar PV and battery system. The proposed methodology is illustrated using a realistic load profile generated through a structured household survey of an un-electrified hamlet. For given load profile, battery integrated gasifier engine system in intermittent operation mode has the lowest cost of electricity followed by gasifier engine system alone, hybrid system and solar PV battery system. Sensitivity analysis is done to incorporate uncertainty related to variation in key input parameters. The proposed sizing methodology may be helpful in wider replication of gasification systems by providing cost effective sizing of such systems.