SELF-SUSTAINABLE SOLAR STREET LIGHT CHARGING Group No. 4 Anirban Banerjee, Priya Mehta, Surya Teja Tadigadapa

Introduction Three subsystems in overall streetlight design: Charging Circuit (Solar Panel to Battery) Discharging circuit (Battery to Light Source) User Monitoring (Mobile/Web Application) Our project: charging circuit for self-contained solar streetlight Circuit receives power from solar panel and uses it to charge battery Uses Maximum Power Point Tracking (MPPT) to maximise efficiency

Objective The streetlight should be: Solar-powered Portable Self-contained Self-sustaining In order to achieve this, the battery should be charged as efficiently as possible IV curve of solar panels make them very inefficient if used directly MPPT used to achieve efficiency

Overall Block Diagram Schematic Figure 1: Block diagram for Solar Streetlight

Charge Controller Block Diagram Schematic Figure 2: Block diagram of charge controller

Design Utilizes algorithm called maximum power point tracking (MPPT) Major components needed: Microcontroller and Algorithm Monitoring Components (Voltage/Current) Buck Converter Solar Panel Battery

Buck Converter Steps down the voltage produced by the solar panel to required voltage for charging the battery Figure 4: Buck Converter basic layout

Buck Converter Results Efficiency = (Output Power/Input Power) * 100 Efficiency = (0.612/0.775)*100 = 79.01% Input Voltage = 5V Input Current = 1.55A Input Power = 5*1.55 = 0.775W Output Voltage = 3.13V Output Resistance = 15V Output Power = (3.13)2/15 = 0.612W

Buck Converter Results Input Power Output Power Efficiency 0.775 0.612 79.01% 0.801 0.634 79.23% 0.832 0.661 79.44% 0.864 0.687 79.55% 0.896 0.714 79.65% 0.930 0.742 79.80% 0.958 0.766 79.95% 1.092 0.879 80.49% Figure 7: Graph illustrating buck converter efficiency

Microcontroller and MPPT Code Microcontroller: C2000 with Piccolo TMS320F28027 chip Generates PWMs that drives charging circuit MPPT Code: Reads in voltage and current from ADC pins on MCU Modifies duty cycles/PWMs accordingly The PWM signals are then used to drive the buck converter to step down the output voltage to a suitable level for the battery/output. Figure 3: PWMs generated by MCU code. Top: P-Mosfet (50% duty cycle) Bottom: N-Mosfet (25% duty cycle).

Monitoring Both current and voltage are monitored at the input (before the buck converter) and at the output (after the buck converter) This serves two purposes: Data from input and output is used to implement MPPT Data is also supplied to the mobile/web application team for user monitoring

Figure 5: Current Monitor basic layout Figure 6: Voltage Monitor basic layout

Monitoring Results Figure 8: Graph showing ADC results vs. Input Voltage for voltage reading Figure 9: Graph showing ADC results vs. Input Supply for current reading

Conclusion Results: Learned a lot! Buck converter fully functional Voltage monitoring fully functional: less than 10% error Current monitoring inaccurate No integration yet Learned a lot! Work that can be taken over and continued (see Future Work)

Future Work Individual sections of charging circuit are functional Integration and further testing required All subsystems Specific solar panel + battery Other teams’ work Another team next semester will take on the integration responsibilities Documentation and videos