Future declines in the selling price of surplus electric power, and the cost of PV systems and storage batteries are expected. Autonomous operations like self-consumption of surplus electric power may, therefore, become cost-effective. In addition, self-consumption may reduce excessive power backflow, which can reduce the power generation efficiency in cities. Both energy savings and improvements to thermal comfort are important to support the spread of zero energy houses (ZEH). This study aims to understand the utility of autonomous operations. Through measurements and simulations, we show that thermal comfort is improved, and peak load reduced by precooling. In addition, we show that using a heat pump water heater during the day is efficient. We proposed different combinations of PV systems and storage capacity for different regions and household composition and confirmed their economic efficiency. Finally, we confirmed the possibility that using surplus electric power can improve quality of life during low load periods.