The impact of the sampling time interval for energy demands on the optimal operational planning of residential cogeneration systems without electric power export was analyzed. To improve their operational flexibility, focus was also placed on battery installation. First, an optimal operational planning problem was modeled on the basis of a mixed-integer linear programming. The features of the model are to consider the operational constraints of the cogeneration units, i.e., a daily maximum number of start -stop cycles, minimum up- and downtimes, and starting and shutdown energies, and to introduce a battery in consideration of electric power consumption in a built-in bidirectional inverter. Then, the developed model was applied to an energy-saving analysis of the following residential cogeneration systems under 5-60 min sampling time intervals for the simulated energy demands. A gas engine-based cogeneration system is operated at a constant power output; a polymer electrolyte fuel cell-based cogeneration system employs daily start stop operation; and a solid oxide fuel cell-based cogeneration system is operated continuously. The results revealed that optimal operational planning under a sufficiently short sampling time interval is required to evaluate not only the energy-saving effect of the residential cogeneration systems without electric power export, but also the effectiveness of battery installation. (C) 2014 Elsevier Ltd. All rights reserved.