Develer Workshop:
A workshop focused on the principles and benefits of applying the Energy Harvesting techniques on Wireless Sensor Networks. The contents come from my Better Embedded 2013 talk.
From Event to Action: Accelerate Your Decision Making with Real-Time Automation
Development of a Wireless Sensors Network powered by Energy Harvesting techniques
1. DEVELOPMENT OF A WIRELESS SENSOR
NETWORK POWERED BY ENERGY
HARVESTING TECHNIQUES
Daniele Costarella
Develer – Campi Bisenzio, FI, Italy – November 6th, 2013
2. November 6th, 2013
Energy Harvesting Workshop
Outline
• Energy Harvesting Basics
• What are the benefits? Where is it useful? Important aspects.
• Piezoelectric, Thermoelectric and Solar Sources
• Selecting the Right Transducers, piezogenerator models,
capabilities, limitations
• Converting Harvested Energy into a Regulated Output
• Rectification, start-up, efficiency, and over-voltage concerns
• Integrated solution in a WSN
• Challenges Design of a EH-WSN node, prototyping
• Data analysis
2
4. November 6th, 2013
Energy Harvesting Workshop
4
Energy Harvesting Basics
• Energy Harvesting is the process by which energy readily available
from the environment is captured and converted into usable electrical
energy
• This term frequently refers to small autonomous devices, or micro
energy harvesting
• Ideal for substituting for batteries that are impractical, costly, or
dangerous to replace.
5. November 6th, 2013
Energy Harvesting Workshop
5
Common EH Sources
Energy Source
Performance
(Power Density)
Notes
Solar:
• Outdoor, direct sunlight
• Outdoor, cloudy
• Indoor
15 mW / cm2
0.15 mW /cm2
10 uW / cm2
Power per unit with a
Conversion efficiency of 15%
Mechanical
• Machinery
100-1000 uW /cm3
•
Human body
110 uW / cm3
Ex. 800 uW / cm3 @ 2mm e 2.5
kHz
Ex. 4 uW / cm3 @ 5 mm and 1
Hz
•
•
Acoustic noise
Airflow
1 uW / cm2 @ 100 dB
750 uW / cm2 @ 5 m/s
Thermic
• Temperature gradients
•
EM radiation
1-1000 uW / cm3
It depends on the specific
conditions with respect to the
Betz limit
Depends on the average
temperature.
Distance: 5 m from a 1W source
@ 2.4 GHz (free space)
6. November 6th, 2013
Energy Harvesting Workshop
6
Design challenges in conventional WSN
• Sensor node has limited energy supply
• Hard to replace/recharge nodes’ batteries once deployed, due to
• Number of nodes in network is high
• Deployed in large area and difficult locations like hostile environments,
forests, inside walls, etc
• Nodes are ad hoc deployed and distributed
• No human intervention to interrupt nodes’ operations
• WSN performances highly dependent on energy supply
• Higher performances demand more energy supply
• Bottleneck of Conventional WSN is ENERGY
7. November 6th, 2013
Energy Harvesting Workshop
7
Energy Harvesting in Wireless Sensor
Networks
• Wireless Sensor nodes are designed to operate in a very
low duty cycle
• The sensor node is put to the sleep mode most of the time and it is
activated to perform sensing and communication when needed
• Moderate power consumption in active mode, and very
low power consumption while in sleep (or idle) mode
• Advantages:
• Recharge batteries or similar in sensor nodes using EH
• Prolong WSN operational lifetime or even infinite life span
• Growing interest from academia, military and industry
• Reduces installation and operating costs
• System reliability enhancement
8. November 6th, 2013
Energy Harvesting Workshop
8
Wireless Sensor Node
Main subsystems
Power unit
Piezoelectric
generator
Sensing
subsystem
Sensors
Solar source
TEG
ADC
Computing
subsystem
Communication
subsystem
MCU
• Memory
• SPI
• UART
Radio
9. November 6th, 2013
Energy Harvesting Workshop
9
Wireless Sensor Node
Power consumption distribution for a wireless sensor node
25%
Computing Subsystem
Sensing Subsystem
60%
15%
Communication Subsystem
10. November 6th, 2013
Energy Harvesting Workshop
10
Energy sources
• Vibrating piezos generate an A/C output
• Electrical output depends on frequency and acceleration
• Open circuit voltages may be quite high at high g-levels
• Output impedances also quite high
• TEGs are simply thermoelectric modules that convert a
temperature differential across across the device, and
resulting heat flow through it, into a voltage
• Based on Seebeck effect
• Output voltage range: 10 mV/K to 50 mV/K
• A solar cell converts the energy of light directly into
electricity by the photovoltaic effect
• The output power of the cell is proportional to the
brightness of the light landing on the cell, the total area
and the efficiency
11. November 6th, 2013
Energy Harvesting Workshop
Energy Storage
Option 1: Traditional Rechargeable Batteries
• Inefficient charging (lots of energy converted to heat)
• Limited numbed of charging cycles
Option 2: Capacitors
• Efficient charging
• Limited capacity
Option 3: Super Capacitors
• Small size
• High efficiency
• Very high capacity ( from 1 up to 5000F or so)
11
12. November 6th, 2013
Energy Harvesting Workshop
Supply management: LTC3588
• The LTC3588 is a high efficiency
integrated hysteretic buck DC/DC
converter
• Collects energy from the piezoelectric
transducer and delivers regulated
outputs up to 100mA
• Integrated low-loss full-wave bridge
rectifier
• Requires 950nA of quiescent current
(in regulation) and 450nA in UVLO
12
13. November 6th, 2013
Energy Harvesting Workshop
Supply management: LTC3588
A simple circuit simulation
13
14. November 6th, 2013
Energy Harvesting Workshop
Supply management: LTC3588
A simple circuit simulation with a 47uF output capacitor
14
15. November 6th, 2013
Energy Harvesting Workshop
Supply management: LTC3588
We could increase the output capacitance to 2200uF
15
16. November 6th, 2013
Energy Harvesting Workshop
Supply management: LTC3588
And if we choose an even larger capacity? Ex. 1F
16
20. November 6th, 2013
Demoboard Project
• Design of a multisource Energy
Harvesting Wireless Sensor Node
• Development of a demoboard with
Energy Harvesting capabilities,
including RF communication and
Temperature sensor
• Additional supercap for longer
backup operation
• Very customizable to the end users’
needs
Energy Harvesting Workshop
20
21. November 6th, 2013
Energy Harvesting Workshop
Power supply circuit
Piezo
Solar
TEG
Primary Charge
Supercap
21
22. November 6th, 2013
Energy Harvesting Workshop
Prototyping
On board:
• 40-Pin Flash Microcontroller
with nanoWatt XLP Technology
• Low Power 2.4GHz GFSK
Transceiver Module
• Low Power Linear Active
Thermistor
22
23. November 6th, 2013
Energy Harvesting Workshop
Signal analysis
Fig. A: Duty cycle
Fig. B: TX pulse length (Zoom View)
23
26. November 6th, 2013
Data analysis
• Web interface
• Real time graphics
• History
• Views
• Temperature
• Supercapacitor Voltage
• Input Voltage
• Charging
• Backup status
Energy Harvesting Workshop
26
27. November 6th, 2013
Energy Harvesting Workshop
Data analysis: examples
Fig. A: Temperature
Fig. B: Input Voltage (VIN)
Fig. C: Supercap charging
Fig. D: Supercap discharge
27
29. November 6th, 2013
Energy Harvesting Workshop
Board specifications
Feature
Description
Sources:
Solar / TEG / Piezoelectric
Input voltage ranges:
Solar: 5 ÷ 18 VDC
TEG: 20 ÷ 500 mVDC
Piezoelectric: max 18 VAC
Temperature Sensor:
0 ÷ 50 °C
Resolution:
0.4 °C
Wireless communication:
2400-2483.5 MHz ISM (GFSK)
Transmission rate:
1 and 2 Mbps support
Current/Power IDLE mode:
9 uA / 30 uW
Current/Power TX mode:
18.9 mA / 62 mW
Maximum TX distance:
100 m
Backup operation:
> 24 h
29
30. November 6th, 2013
Energy Harvesting Workshop
30
References
Energy Harvesting Technologies
Springer
By Shashank Priya and Daniel J. Inman
Covers a very wide range of interesting topics
My Master Thesis
Università degli Studi di Napoli “Federico II”
By Daniele Costarella
Available online: http://danielecostarella.com
31. November 6th, 2013
Energy Harvesting Workshop
Thank you
@dcostarella
http://it.linkedin.com/in/danielecostarella
31