The escalating global energy demand and the urgent need to reduce dependence on fossil fuels have accelerated research into intelligent hybrid renewable energy systems. A smart hybrid renewable energy management system was designed, implemented, and experimentally evaluated, integrating solar photovoltaic (PV) energy and piezoelectric energy harvesting as complementary renewable sources, managed by an ESP32 microcontroller with real-time IoT monitoring capability. The solar subsystem employs a Maximum Power Point Tracking (MPPT) charge controller to maximise energy extraction from a polycrystalline PV panel under varying irradiance conditions. The piezoelectric subsystem harvests kinetic energy from mechanical pressure through an array of eight 27 mm Lead Zirconate Titanate (PZT) discs mounted on a foam pressure pad, with a full-wave bridge rectifier conditioning the output for battery charging. Three lithium-ion 3.7 V cells arranged in a 3-Series configuration form the energy storage backbone, providing a nominal pack voltage of 11.1 V compatible with standard 12 V DC systems. The ESP32 performs continuous voltage and current monitoring via a resistive voltage divider and an ACS712 Hall-effect current sensor, executing a priority-based energy management algorithm that governs relay-controlled load switching and automatic grid backup activation. Experimental results demonstrate a solar-to-load system efficiency of 70.1%, an MPPT stage efficiency of 87.7%, and a piezoelectric rectification efficiency of 78.7%. All relay switching events occur within the 500ms design target.
Kumar et al. (Sun,) studied this question.