The utilization of renewable energy has become a crucial solution to address the global energy crisis and climate change. One such technology is the solar heater, which converts solar energy into thermal energy for heating purposes. However, the efficiency of conventional solar heaters remains limited and not fully optimized. This study aims to improve the efficiency of solar heaters by integrating a Thermoelectric Generator (TEG) to harvest waste heat, and developing an Internet of Things(IoT)-based monitoring system for real-time observation of key parameters. The solar heater used is of the box type, with a reflector design to concentrate sunlight into the heating chamber. TEG modules are installed at the bottom of the heating surface and are combined with Heatsinks to maintain the necessary temperature gradient, essential for generating electrical voltage. The monitoring system includes DS18B20 temperature sensors and INA219 current-voltage sensors connected to an ESP32 microcontroller. Temperature and electrical output data from the TEG are wirelessly transmitted to the Arduino IoT Cloud platform and displayed locally on an LCD screen.The results show that the TEG successfully generates electrical energy from the absorbed heat, with varying output depending on the recorded temperature. The IoT monitoring system operates stably in transmitting real-time temperature and voltage data, with an accuracy of ±0.5°C for temperature and a margin of error of 2% for the INA219 sensor. This research demonstrates that the integration of TEG with the IoT system can enhance the efficiency of solar heaters, providing a more efficient and environmentally friendly renewable energy solution, while enabling optimal performance monitoring, especially in remote areas or regions without access to conventional electricity.