1. Network and Systems Laboratory nslab.ee.ntu.edu.tw Jay Taneja, JaeinJeong, and David Culler Computer Science Division, UC Berkeley IPSN/SPOTS 2008 Presenter: SY

2. Network and Systems Laboratory nslab.ee.ntu.edu.tw Outline Introduction Micro-Solar Planning Model And System Design Node And Network Design Evaluation Conclusion

3. Network and Systems Laboratory nslab.ee.ntu.edu.tw 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. Network and Systems Laboratory nslab.ee.ntu.edu.tw About This Paper Show how they develop the micro-solar power subsystem -- systematically Modeling Design Evaluation System design experience sharing Real deployment evaluation

5. Network and Systems Laboratory nslab.ee.ntu.edu.tw The Challenges Capacity Planning Infinite power lifetime Mechanical Design Weatherproof with Correctly Exposed Sensors Incorporating off-the-shelf and custom-built pieces

6. Network and Systems Laboratory nslab.ee.ntu.edu.tw Outline Introduction Micro-Solar Planning Model And System Design Node And Network Design Evaluation Conclusion

7. Network and Systems Laboratory nslab.ee.ntu.edu.tw Storage Charge-Discharge All Ideal Components Half Hour of Exposure Per Day Micro-Solar Planning Model Regulator Efficiencies E in : E out 66% 2% 60%50%

8. Network and Systems Laboratory nslab.ee.ntu.edu.tw Application Load Application Load Starting point for capacity planning Most time is spent sleeping (~20 uA) with short active periods (~20 mA) DeviceAverage Current Sensors9 uA (550 uA at 1.67% DC) Radio0.206 mA (20.6 mA at 1% DC) MCU9.6 uA (2.4 mA at 0.4% DC) Quiescent15 uA Total0.24 mA (supply voltage 3.3V  79.2mWh)

9. Network and Systems Laboratory nslab.ee.ntu.edu.tw Energy Storage Energy Storage TypeLead AcidNiCadNiMHLi-ionSupercap Operating Voltage Range 5.0-6.1V0.8-1.35V0.9-1.4V3.0-4.2V2.2-3.0V* Volume Energy Density 67 Wh/L102 Wh/L282 Wh/L389 Wh/L5.73 Wh/L Charge/Discharge Efficiency 70-92%70-90%66%99.9%97-98% Self-discharge (Per Month) 3-20%10%30%<10%5.9%/day Charging MethodTrickleTrickle/Pulse Pulse Est. Lifetime (79.2 mWh/day) 98.5 days33.3 days (2)75.8 days (2)35.4 days3.8 days Straightforward charging logic

10. Network and Systems Laboratory nslab.ee.ntu.edu.tw 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. Network and Systems Laboratory nslab.ee.ntu.edu.tw Solar Panel Solar Panel Important parameters IV and PV Curves Physical Dimensions MPP: 3.11 Volts They choose – Silicon Solar #16530 (4V-100mA)

12. Network and Systems Laboratory nslab.ee.ntu.edu.tw 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. Network and Systems Laboratory nslab.ee.ntu.edu.tw Outline Introduction Micro-Solar Planning Model And System Design Node And Network Design Evaluation Conclusion

14. Network and Systems Laboratory nslab.ee.ntu.edu.tw HydroWatch Weather Node

15. Network and Systems Laboratory nslab.ee.ntu.edu.tw 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 and Systems Laboratory nslab.ee.ntu.edu.tw Network Architecture Used Arch Rock Primer Pack for multi-hop network stack, database for stored readings, and web-based network health diagnosis

17. Network and Systems Laboratory nslab.ee.ntu.edu.tw Forest Deployment

18. Network and Systems Laboratory nslab.ee.ntu.edu.tw Outline Introduction Micro-Solar Planning Model And System Design Node And Network Design Evaluation Conclusion

19. Network and Systems Laboratory nslab.ee.ntu.edu.tw 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. Network and Systems Laboratory nslab.ee.ntu.edu.tw Urban Neighborhood Energy Harvested Every node received enough sunlight

21. Network and Systems Laboratory nslab.ee.ntu.edu.tw Three Nodes, Three Solar Inputs

22. Network and Systems Laboratory nslab.ee.ntu.edu.tw The Forest Watershed 19 Nodes for over a Month Mounted on 4-ft stakes throughout the area

23. Network and Systems Laboratory nslab.ee.ntu.edu.tw Forest Watershed Site

24. Network and Systems Laboratory nslab.ee.ntu.edu.tw Forest Watershed Energy Harvested Watershed Most nodes struggle to harvest sunlight

25. Network and Systems Laboratory nslab.ee.ntu.edu.tw Three Nodes at the Watershed

26. Network and Systems Laboratory nslab.ee.ntu.edu.tw Reflected Light Though only minimally, a cloudy day helps a sun-starved node harvest solar energy. Sunny Overcast Sunny

27. Network and Systems Laboratory nslab.ee.ntu.edu.tw 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