Miniaturized Solar Scavengers for Ultra-low Power Wireless Sensor Nodes

Recently, solar energy harvesting circuits have been proposed to increase the autonomy of wireless sensor nodes. When the size of the photovoltaic module is very small, optimizing the efficiency of energy collection and tracking the Maximum Power Point (MPP) becomes hard and less effective. This paper tackles the challenge of powering a sensor node with miniaturized photovoltaic modules of some mm and capacitors or supercapacitors as energy storage devices, proposing an inductor-less solution suitable for on chip integration. We supply sensor nodes equipped with ultra-low power MCUs and ZigBee-compliant transceivers, focusing on the harvesting efficiency under poor light irradiance. Simulations and experimental results show the impact of light intensity variations and energy buffer capacity on the activity of the sensor node.