Network and Systems Laboratorynslab.ee.ntu.edu.tw

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

Jay Taneja, JaeinJeong, and David CullerComputer Science Division, UC Berkeley

IPSN/SPOTS 2008

Presenter: SY

Network and Systems Laboratorynslab.ee.ntu.edu.tw

OutlineIntroductionMicro-Solar Planning Model And System

DesignNode And Network DesignEvaluationConclusion

Network and Systems Laboratorynslab.ee.ntu.edu.tw

MotivationThey have a project – HydroWatch

Study hydrological cycles in forest watersheds

Sense temperature, humidity, and light

Forest environmentWant to design a device

Sense and transfer dataSolar powered

Infinite power lifetime

Network and Systems Laboratorynslab.ee.ntu.edu.tw

About This PaperShow how they develop the micro-solar

power subsystem -- systematicallyModeling DesignEvaluation

System design experience sharingReal deployment evaluation

Network and Systems Laboratorynslab.ee.ntu.edu.tw

The ChallengesCapacity Planning

Infinite power lifetime

Mechanical DesignWeatherproof with Correctly Exposed Sensors

Incorporating off-the-shelf and custom-built pieces

Network and Systems Laboratorynslab.ee.ntu.edu.tw

OutlineIntroductionMicro-Solar Planning Model And System

DesignNode And Network DesignEvaluationConclusion

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Storage Charge-Discharge 72:1120:1240:11:1All Ideal Components 48:1Half Hour of Exposure Per Day

Micro-Solar Planning Model

Regulator Efficiencies

E in : E out

66%

2%

60%

50%

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Application LoadStarting point for capacity planningMost time is spent sleeping (~20 uA) with short

active periods (~20 mA)

Device Average Current

Sensors 9 uA (550 uA at 1.67% DC)

Radio 0.206 mA (20.6 mA at 1% DC)

MCU 9.6 uA (2.4 mA at 0.4% DC)

Quiescent 15 uA

Total 0.24 mA (supply voltage 3.3V 79.2mWh)

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Energy StorageType Lead

AcidNiCad NiMH Li-ion Superca

pOperating

Voltage Range5.0-6.1V 0.8-1.35V 0.9-1.4V 3.0-4.2V 2.2-3.0V*

Volume Energy Density

67 Wh/L 102 Wh/L 282 Wh/L 389 Wh/L 5.73 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 Method

Trickle Trickle/Pulse

Trickle/Pulse

Pulse Pulse

Est. Lifetime (79.2 mWh/day)

98.5 days 33.3 days (2)

75.8 days (2) 35.4 days 3.8 days

Straightforward charging logic

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Solar PanelSolar cells composition

In serial and parallel

The panel characterized by its IV curveOpen-circuit voltage, short-circuit current, and

maximum power point

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Solar PanelImportant parameters

IV and PV CurvesPhysical Dimensions

MPP: 3.11 Volts

They choose – Silicon Solar #16530 (4V-100mA)

Network and Systems Laboratorynslab.ee.ntu.edu.tw

RegulatorsRegulators are “glue” matching primary

components50-70% efficiency for typical sensornet load

rangeInput regulator

Regulates voltage from solar panel to batteryCan be obviated by matching panel directly to

storageOutput Regulator

Regulates mote voltageProvides stability for sensor readingsModel estimates that load requires 28 minutes of

sunlight

Network and Systems Laboratorynslab.ee.ntu.edu.tw

OutlineIntroductionMicro-Solar Planning Model And System

DesignNode And Network DesignEvaluationConclusion

Network and Systems Laboratorynslab.ee.ntu.edu.tw

HydroWatch Weather Node

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Mechanical ConsiderationsEnclosure design is often application-driven

Sensor exposureWaterproofingEase-of-DeploymentRF in forestInternal mechanicals

Temp / RH Sensor TSR, PAR Sensors

Network and Systems Laboratorynslab.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

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Forest Deployment

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OutlineIntroductionMicro-Solar Planning Model And System

DesignNode And Network DesignEvaluationConclusion

Network and Systems Laboratorynslab.ee.ntu.edu.tw

The Urban Neighborhood20 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

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Urban Neighborhood Energy Harvested

Every node received enough sunlight

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Three Nodes, Three Solar Inputs

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The Forest Watershed19 Nodes for over a MonthMounted on 4-ft stakes throughout the area

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Forest Watershed Site

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Forest Watershed Energy HarvestedWatershed

Most nodes struggle to

harvest sunlight

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Three Nodes at the Watershed

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Reflected Light

Though only minimally, a cloudy day helps a sun-starved node harvest solar energy.

Sunny

Overcast

Overcast

Sunny

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ConclusionAlways surprises in real environmentReliability is important real application

But difficult to achieveIn their work

Systematic approach resulted in 97% collection of an unprecedented spatiotemporal data set

System design experience sharing