Within the Internet of Things (IoT) domain, the powering of the devices is still today an aspect that is often overlooked: efficient power management and energy self-sufficiency are targets that are still difficult to be achieved in several application scenarios. In this context, the use of energy harvesting systems, of limited dimensions and able to guarantee the autonomous operation of the devices, represents an ideal solution. However, while outdoors the use of small-size solar cells is able to guarantee the operation of most of the monitoring and data acquisition systems, also allowing the implementation of safe operating modes and data protection policies, in indoor environments the continuous powering of the devices is more difficult to be achieved due to the lower intensity of the energy sources: indeed, in these contexts there is no direct exposure to solar radiation, with a significantly lower energy availability.

The project aims to implement an integrated monitoring platform, equipped with wide area connectivity for data transmission, able to operate autonomously thanks to the implementation of an energy harvesting solution based on the use of solar cells, capable of generating energy by exploiting the presence of diffuse sunlight (therefore without direct irradiation) or artificial light. An application of this type can have a significant impact for the realization of monitoring platforms of limited size and low cost, to be used according to a plug-and-play policy in closed environments. Indeed, even in operational contexts where there is an available connection to the electricity grid, the possibility of installing wireless monitoring platforms in remote spots without the need to carry out infrastructural interventions, and without having to resort to frequent maintenance interventions, plays a crucial role in the diffusion of this kind of technological infrastructures.

The purpose of the project is thus to demonstrate the feasibility of an energy self-sufficient distributed measurement system powered by solar cells of limited size, analyzing the most suitable cell typology for energy scavenging in conditions of diffuse or artificial light, identifying an ideal trade-off between the amount of energy supplied by the cells, the architecture of the monitoring device, the level of data protection and the data transmission frequency, allowing to maintain a positive trend of the battery voltage level.

The structure of the project foresees a first experimental phase in which the performance of different types of solar cells (e.g., mono or polycrystalline and amorphous silicon, DSSC, etc…) will be characterized in conditions of both diffuse and artificial light, studying the behavior of such cells for different the spectral compositions. At the same time, a microcontroller-based monitoring platform equipped with local or wide area connectivity will be developed. The first prototype will be provided with Long Range Wide Area Network (LoRaWAN) connectivity and will integrate energy-hungry sensors for the acquisition of environmental parameters (e.g., concentrations of Particulate Matter (PM)).

Following the development of the prototype, the project will focus on the identification of a suitable battery management system and an energy storage architecture. In parallel, the operating policy of the device will be studied, identifying security protocols capable of guaranteeing the privacy of the acquired data. In particular, adaptive operating protocols will be studied, able to reduce the computational complexity in case of low energy conditions. At the same time, the relationship between the frequency of data acquisition and transmission and the available energy level will be analyzed, with the aim of identifying an operating mode capable of leading to maximum efficiency, keeping constant the energy level of the storage element.