Automatic charging of an energy harvesting powered sensor node from controllable energy source
It is expected that the number of the Internet of Things (IoT) devices will grow significantly in the coming years. Batteries, which are today the most common source of energy supply for these devices, have many limitations. The limited capacity and the negative environmental effect of their production and recycling are among the most crucial ones. Energy harvesting has been proposed to overcome this problem. Over the past decade, the academia has produced thousands of papers on this topic, but it is still difficult to find a commercial sensor node operating solely with energy harvesting. One of the major reasons for this is the highly opportunistic and unreliable nature of the energy income from most of the available ambient energy sources. In this paper, we address this problem by proposing a control loop enabling an energy harvesting sensor to request a recharge whenever needed. Energy-wise, the proposed method effectively transforms the operation mode of a passive wireless device from opportunistic to proactive, thus enabling an application to operate in a more predictable manner. The feasibility and efficiency of the proposed approach is demonstrated by implementing a real-life prototype Bluetooth Low Energy capable sensor node equipped with photovoltaic energy harvester, which can communicate and request a recharge from a commercial indoor smart lighting system.