We have been proposing the concept of “i-Energy” as a new energy management scheme to realize efficient and versatile control of e-power flows among decentralized energy generation/storage devices and appliances in homes, offices, and neighboring communities. The i-Energy concept is best characterized by a novel energy control method named “Energy on Demand (EoD).” The novelties of EoD rest in (1) the explicit demand-based power supply control, (2) the best-effort power distribution based on appliance priorities, and (3) the ceiling control of power consumption. With EoD, people can attain the guaranteed reduction of energy consumption without damaging their quality of lives. Moreover, when utility companies are allowed to set and modify ceiling values based on contracts with consumers, EoD systems work as smart demand response systems. This paper first describes the protocol for EoD: power request demands named “Quality of Energy (QoEn)” and appliance priority descriptions. Then, the demand mediation algorithm based on appliance priorities for a single power source is introduced. Experiments using real world everyday-life data in a smart apartment room demonstrated the effectiveness of EoD.