indoor solar energy harvesting for sensor network router nodes · 2011-10-28 · challenge the...

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Indoor solar energy harvesting

for sensor network router nodesAbhiman Hande, Todd Polk, William Walker,

Dinesh Bhatia – University of Texas at Dallas

2007

Speaker: Victor Spiridon

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Free Solar EnergyWhy not harvest it for WSN

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Harvesting solar energy

• Solar panel size

• Duty cycle

• Energy storage• Rechargeable batteries

• Capacitors

• Backup energy.

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Harvesting solar energy… indoors

• Light intensity:• Outdoor: 100-1000 W/m2

• Indoor: 1-10 W/m2

• Cell efficiency:• Monocrystaline silicon cells: 1-3%

• Amorphous silicon cells: 3-7%

• Trade-off: price vs. panel size (no. of panels).

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy application

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Suited ApplicationsBuildings with “always on” lights

• Hospital & industrial environments

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Harvesting system:

Hardware

• Crossbow MICAz• Chipcon CC2420, Zigbee radio

• ATMega 128L

• Size: 2.5” x 2.25” x 1”

• Solar Cell• Solar World 4-4.0-100 monocrystaline

• Size: 3.75” x 2.5”

• Ultracapacitors:• 2 x Maxwell PC5-5, 5 Vdc, 2 F, in parallel

• Philips 34W fluorescent lights.

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Harvesting system:

Solar cells

• Output: 2 mA @ 3.2 VDC

• Needed: 25 mA @ ~3 VDC

• V – I profile @ 1 cm

from the light source

12 cells

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Harvesting system:

Dual Router Algorithm

• 100% availability for receiving sensor packets

• Minimize no. of solar cells / router node

• 50% duty cycle

• Alternative Sleep/Wake Routine

• Partner searching

• 1 second interval (reasons?).

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Start Initialize RouterNode Parameters

Locate Network

Determine shortest path to Base Station

Acquire ID from Base

Find a Route Partner

Start/Resume Sleep/Wake Routine

Forward message

Already Received

ID?

Route Partner stillAvailable?

Message to be

forwarded?

Lost network

connection?

No

No

No

No

Yes

Yes

Yes

Yes

Router Node Flowchart

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Start

Initialize SensorNode Parameters

Locate Network

Determine shortest path to

base

Send Sensor Reading

Go to SleepWake Up

Sensor Node Flowchart

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Harvesting system:

Circuit + battery back-up

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Prototype router node

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Experimental results

• Determining the no. of solar cells• Experiment with a variable power source

• Current 12 mA, 14mA (with PM circuit)

• 8 solar cells – just to be sure

• PM circuit efficiency @ 25 mA load• Drop of 60 mV & 5 mA 82%

• Q1 pmos (on): 50 mV drop @ 25 mA

• Leakage through Zener diode: 10 mV

• Ripple through a charge/discharge cycle• 15 mV – 0.5%. – due to high capacity.

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The solar cell set up

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Testing application

• 1 sensor node, 2 router nodes (1 pair)

• Sensing data: Vload reading• Sensor: each 10s

• Router: each 25s

• Results over 24h confirmed the system’s robustness

• Vload stabilized at 3 Vdc

• Similar results with 2 router pairs.

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Conclusions

• The harvesting technique is effective

• 50% duty cycle – reduced no. of solar cells

• Efficiency of power management circuit: 82%

• The network protocol – fairly robust

• Vload stabilized at about 3 Vdc

• Future Work: Interface the MICAz sensor node• A&D Medical UA767PC BP monitorBlood pressure, heart rate.

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Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions

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Personal conclusions

• No. of solar panels fairly large

• Router node – always close to light source• Why not use power from the grid?

• 100% routing availability is not needed• Same functionality: sync-ed nodes

• TinyDB

• Thorough system testing.

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Requiered experiments

• Power w.r.t. the distance from light

• Node survival on back-up power

• Influence of temp over solar cell efficiency• Above 40°- 1% less power / degree

• Network protocol testing over a complex topology

• Power usage at low / high traffic

• Is initial capacitator charging time neglectable?.

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Questions…

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R1

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R1 – Ch 2, 3 ; R2 – Ch 1, 4

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Test app

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No. of solar cells testing circuit

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Solar panel power – temperature

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