A battery-free non-intrusive power meter for low-cost energy monitoring

As highlighted by the Intergovernmental Panel for Climate Change (IPCC), providing clean, reliable and affordable energy for people everywhere will require the reduction of gas emission in the energy domain by 90%, compared to 2010 emissions, between the years 2040 and 2070. In addition, to a change in choices, preferences and behavior of individuals and households in energy demand and consumption, to achieve a successful transition to a more sustainable energy system, the adoption of new metering solutions to foster a wide range of sustainable actions by diverse people across the globe will be required. In this paper, we discuss the development of an ultra-low-power energy meter exploiting a single current transformer (CT) sensor for harvesting energy from the same load under monitoring. Starting from the hypothesis that the node activation rate increases monotonically with the primary load draw, and assuming that the node consumes fixed energy quanta during each activation, it is possible to infer the load power from the interval between activations. With this approach, we can provide a device that lowers maintenance cost related to installation and battery replacement; does not need to deal with high main voltage; and does not introduce any additional energy consumption overhead as it draws zero-power under zero-load condition. Energy budget is guaranteed also thanks to the use of a LoRa radio for data transmission.