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

1Challenge the future

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


Free Solar EnergyWhy not harvest it for WSN


Outline

• Challenges of Indoor solar energy harvesting

• Indoor solar energy applications

• Implementation

• Experimental results

• Conclusions

• Personal conclusions


Outline



• Implementation


• Conclusions



Harvesting solar energy

• Solar panel size

• Duty cycle

• Energy storage• Rechargeable batteries

• Capacitors

• Backup energy.


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).


Outline


• Indoor solar energy application

• Implementation


• Conclusions



Suited ApplicationsBuildings with “always on” lights

• Hospital & industrial environments


Outline



• Implementation


• Conclusions



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.


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


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?).


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


Start

Initialize SensorNode Parameters

Locate Network

Determine shortest path to

base

Send Sensor Reading

Go to SleepWake Up

Sensor Node Flowchart


Harvesting system:

Circuit + battery back-up


Prototype router node


Outline



• Implementation


• Conclusions



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.


The solar cell set up


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.


Outline



• Implementation


• Conclusions



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.


Outline



• Implementation


• Conclusions



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.


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?.


Questions…


R1


R1 – Ch 2, 3 ; R2 – Ch 1, 4


Test app


No. of solar cells testing circuit


Solar panel power – temperature

relations

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

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