This paper presents the design and implementation of an Internet of Things (IoT)-based Smart Energy Management System (SEMS) aimed at optimizing the utilization of both renewable and conventional energy sources. The proposed system is built around the ATmega328 microcontroller, which serves as the central processing unit for coordinating various components, including solar panels, batteries, sensors, and load management circuits. The primary objective is to enhance energy efficiency by prioritizing renewable sources such as solar power and intelligently switching to grid electricity only when necessary. The system also enables real-time monitoring and control through IoT integration, thereby improving energy utilization, reducing operational costs, and supporting sustainable development.