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

2. 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

3. 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

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

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

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

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

8. 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 = W

9. 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

10. 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).

11. 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

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

13. 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

14. 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)

15. 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