Design, Modeling, and Capacity Planning for Micro-Solar Power Sensor Networks

1. Design, Modeling, and Capacity Planning for Micro-Solar Power Sensor Networks Jay Taneja, JaeinJeong, and David Culler Computer Science Division, UC Berkeley IPSN/SPOTS 2008 Presenter: SY

2. Outline • Introduction • Micro-Solar Planning Model And System Design • Node And Network Design • Evaluation • Conclusion

3. Motivation • They have a project – HydroWatch • Study hydrological cycles in forest watersheds • Sense temperature, humidity, and light • Forest environment • Want to design a device • Sense and transfer data • Solar powered • Infinite power lifetime

4. About This Paper • Show how they develop the micro-solar power subsystem -- systematically • Modeling • Design • Evaluation • System design experience sharing • Real deployment evaluation

5. The Challenges • Capacity Planning • Infinite power lifetime • Mechanical Design • Weatherproof with Correctly Exposed Sensors • Incorporating off-the-shelf and custom-built pieces

6. Outline • Introduction • Micro-Solar Planning Model And System Design • Node And Network Design • Evaluation • Conclusion

7. 72:1 Micro-Solar Planning Model Storage Charge-Discharge 1:1 E in : E out All Ideal Components 48:1 240:1 120:1 Regulator Efficiencies Half Hour of Exposure Per Day 60% 50% 2% 66%

8. Application Load • Starting point for capacity planning • Most time is spent sleeping (~20 uA) with short active periods (~20 mA)

9. Energy Storage Straightforward charging logic

10. Solar Panel • Solar cells composition • In serial and parallel • The panel characterized by its IV curve • Open-circuit voltage, short-circuit current, and maximum power point

11. Solar Panel • Important parameters • IV and PV Curves • Physical Dimensions MPP: 3.11 Volts They choose – Silicon Solar #16530(4V-100mA)

12. Regulators • Regulators are “glue” matching primary components • 50-70% efficiency for typical sensornet load range • Input regulator • Regulates voltage from solar panel to battery • Can be obviated by matching panel directly to storage • Output Regulator • Regulates mote voltage • Provides stability for sensor readings Model estimates that load requires 28 minutes of sunlight

13. Outline • Introduction • Micro-Solar Planning Model And System Design • Node And Network Design • Evaluation • Conclusion

14. HydroWatch Weather Node

15. Mechanical Considerations • Enclosure design is often application-driven • Sensor exposure • Waterproofing • Ease-of-Deployment • RF in forest • Internal mechanicals Temp / RH Sensor TSR, PAR Sensors

16. Network Architecture Used Arch Rock Primer Pack for multi-hop network stack, database for stored readings, and web-based network health diagnosis

17. Forest Deployment

18. Outline • Introduction • Micro-Solar Planning Model And System Design • Node And Network Design • Evaluation • Conclusion

19. The Urban Neighborhood • 20 Nodes for 5 Days • Mounted on house, around trees, and on roof • Meant to emulate forest floor conditions • Important for systematic approach -- provided validation of model

20. Urban Neighborhood Energy Harvested Every node received enough sunlight

21. Three Nodes, Three Solar Inputs

22. The Forest Watershed • 19 Nodes for over a Month • Mounted on 4-ft stakes throughout the area

23. Forest Watershed Site

24. Forest Watershed Energy Harvested Watershed Most nodes struggle to harvest sunlight

25. Three Nodes at the Watershed

26. Reflected Light Sunny Overcast Overcast Sunny Though only minimally, a cloudy day helps a sun-starved node harvest solar energy.

27. Conclusion • Always surprises in real environment • Reliability is important real application • But difficult to achieve • In their work • Systematic approach resulted in 97% collection of an unprecedented spatiotemporal data set • System design experience sharing