HEMS (Home Energy Management System) is the most important technology for saving energy. Because conventional HEMS is always mounted into wall of the house so can't satisfy the location free situation, HEMS is not spreading into the public life. Then I propose the novel concept of HEMS which is based on the sensor network technology. Sensor network nodes can be moved everywhere at anytime. This system is characterized as the free from communication wire. But its power source is battery. So we have to change the battery frequently. So as to get rid of the maintenance of changing battery, I introduce the energy harvesting into sensor network nodes. Room illumination and the temperature difference between human body and room atmosphere are regarded as the circumference energy resources. And we can get such energy by using Solar cell and Peltier element. We have to get more than 100 μW power as the average of consumption power of sensor network node by energy harvesting (room illumination and the difference of temperature). Then I've examined the amount of power. Account for room illumination, 100 μW can be obtained under the condition of 200 lx. And account for the difference of temperature, 20 μW can be obtained under the temperature. Considering room condition, the room illumination does not always exist for every room, and the difference of temperature always exist. But 20 μW is not enough for the system. Then I've tried to add the extra energy for using magnetic resonance typed wireless power transmission. The target specification for it is transmitting distance is more than 1 m and transmitting loss is more than 0.1% and the diameter of receiving coil must be less than 10 cm for realizing practical HEMS. In this paper we present the calculation result for satisfying the target specification for using different size coils (transmitting coil is very large and receiving coil is very small).
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