This paper presents a fully integrated solar energy harvesting system and power management unit (SEHS-PMU) for ultra-low-power Internet of Things (IoT) applications. The proposed system is implemented in 45 nm CMOS technology and employs a reconfigurable charge pump (RCP) architecture to achieve efficient energy conversion without using bulky inductors. A maximum power point tracking (MPPT) algorithm enables optimal energy extraction from the solar cell under varying illumination conditions. In addition, capacitor value modulation (CVM) is used for impedance matching, supporting compact monolithic integration. The proposed RCP-based DC–DC converter achieves a peak power conversion efficiency of 95%. Furthermore, on-chip low-dropout regulators (LDOs) generate regulated output voltages of 2.8 V, 1.3 V, and 0.7 V to support different subsystems of IoT, smart city, and IoMT sensor nodes. The proposed SEHS-PMU provides a compact, energy-efficient power management solution that enables sustainable operation of next-generation self-powered IoT devices.