The Efficiency Estimation Method for Harvesting Energy Charged into Capacitor

The purpose of this study is to give the estimation diagram of the direct charging efficiency by the energy harvesting. The energy generated by energy harvester is very small. In many cases we can't use DC/DC converter because the generated power is very small comparing to the power of the device driving or the converting efficiency is very small at those region. In such case, we sometimes use the method of the direct charging into the capacitor. But it is so hard to estimate the energy charging efficiency intuitively. The average efficiency is fundamentally related to the open voltage and the short current of the energy harvester and depends on the initial voltage and charged up voltage of the capacitor. We have derived the energy charging efficiency on the capacitor by using only four parameters. By using those relationships I have given the simple diagram for estimation of the charging efficiency. It is remarkable that the charging duration and the charging capacitance are not concerned with that result. Then we can use any capacitor for the efficiency estimation. Finally I have examined this diagram validity by the charging measurement of energy harvester.