With the depletion of fossil fuel reserves and the rising levels of greenhouse gas emissions, global warming has become a critical environmental issue. In response, societies are increasingly focusing on developing renewable energy sources and promoting green technologies to reduce carbon footprints. Among these, solar energy stands out as a clean, sustainable, and abundant power source. In the field of lighting, LED technology has also gained widespread recognition due to its long lifespan, energy efficiency, safety, and eco-friendliness. Combining solar power with LED lighting offers an innovative solution for sustainable urban illumination.
This paper introduces a solar-LED streetlight system that automatically detects ambient light to control the operation of the lamps. It incorporates maximum power point tracking (MPPT) to maximize the efficiency of the solar panels, constant current control for the LEDs, and battery monitoring. Users can also set the operating time of the LEDs according to their needs.
Currently, most streetlights use high-pressure sodium lamps powered by the grid. These systems require complex wiring and suffer from low efficiency due to multiple conversion stages. In contrast, solar-LED streetlights eliminate the need for extensive cabling and offer higher system efficiency by directly using DC power from solar panels to drive DC-based LEDs. This not only reduces energy loss but also lowers installation and maintenance costs.
Figure 1 shows the structure of the solar-LED streetlight system. When sunlight hits the solar panel, it generates a DC current that is directed to the controller. The controller then charges the battery during the day and powers the LED at night. The controller ensures stable current for the LED and monitors its status while managing the charging and discharging cycles. On cloudy or rainy days, if the battery lacks sufficient charge, the system can activate a backup mains supply to ensure continuous operation.
Figure 2 illustrates the block diagram of the controller. The solar panel connects to a DC/DC converter through a MOSFET switch (KCHG), which regulates the battery charging process. The converter prevents reverse current flow and protects against polarity issues. The same DC/DC converter also powers the LED through a flyback topology, ensuring consistent current output. While this topology may not be as efficient as a buck or boost circuit, optimizing voltage relationships can enhance overall performance.
The controller is managed by an MCU, which handles MPPT algorithms, battery charging modes, LED current regulation, and day/night detection. It also includes monitoring and protection features, such as temperature sensing and user input detection. The STM32F101RXT6 microcontroller was chosen for its flexibility and compatibility with ADC, GPIO, and external interrupts, making it ideal for future expansion.
Table 1 outlines the peripheral assignments of the MCU in the actual circuit design.
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