Measuring the state-of-charge — Analysis and impact on wireless sensor networks

Wireless sensor networks (WSNs) are typically used in application areas without wired infrastructure or mobility. Therefore, each sensor node needs its own energy supply unit. Sustainable WSNs are powered by energy harvesting systems (EHSs). These systems harvest and buffer the energy from the environment into rechargeable batteries or double layer capacitors. Due to the fact that the connectivity of the WSN depends on every single sensor node, it is important to know the state-of-charge (SoC) of the buffer to determine the remaining operating time. Therefore, each node has to measure its SoC, calculate the remaining operating time and populate this information through the network. The measurement is usually done by an integrated analog-to-digital converter (ADC) of the microcontroller. Each ADC has a specified error that has to be taken into account at the calculations of the remaining operating time. This work presents the error analysis of the SoC measurement using different energy storage components.