Wireless Environmental Sensor Node using Energy
Harvesting Technology
Kazuhiro Yamamoto,1 Kenichi Okada,1 Masaki Nakayama,2
Taku Taguchi,3 Kenta Kaneeda,3 Hiroyuki Hayashi,3 and Hiroyuki Kito4
A dye-sensitized solar cell (DSC) is a photovoltaic cell with excellent power generation
performance even under low light or diffused light conditions as well as under high light
conditions. Because DSCs can be used under low light conditions like in the shade, near
windows, inside a room, they are attracting attention as an optimal power generation device in
energy harvesting. Wireless environmental sensor systems powered by DSCs have advantages
such as easy installation and low maintenance costs because the systems do not require battery
change and wiring. In this study, we have developed a wireless environmental sensor node using
energy harvesting technology.
1. Introduction
In recent years, attention has been given to wireless
sensor networks (WSNs) that are built of sensor nodes
and placed in different places to monitor environmental conditions (temperature, humidity, atmospheric
pressure). WSNs are being installed in many fields, for
example energy management (HEMS, BEMS), health
care, security, agriculture, and infrastructure management. This is because the system obtains necessary
information by sensors selected for each location without wiring costs that are reguired of conventional
cable networks. Conventional sensor nodes, however,
are powered by primary batteries and thus involves
the issue of battery exchange costs. Therefore, there
has been a growing demand for wireless sensor nodes
powered by an energy harvester without the need to
change batteries 1). This paper describes our newly developed wireless environment sensor system powered
by a DSC which operates with excellent power generation efficiency under low-light conditions 2) 3).
2. A wireless environmental sensor system powered by energy harvester
2.1. Components of system
The components of a wireless sensor node using energy harvesting technology are shown in Fig. 1. This
node consists of a power supply part and a sensing/
radio transmitting part. Wireless sensor nodes are
needed a aesthetic design. The components of a wireless sensor system that uses above-mentioned energy
1 Photovoltaics Development Section of Environment and Energy Laboratory
2 Network Engineering & Service Dept. of Transmission & Distribution System
Engineering Div.
3 P roducts & Process Development Department of Plant & Production
Engineering Center
4 New Business Creation Sales Department
Fujikura Technical Review, 2015
harvesting technology are shown in Fig. 2. The sensor
station receives sensed data from several sensor nodes
and uploads the data to the cloud server through the
router. The stored data is processed to meet users’
needs and used for many purposes. Balancing charge
and discharge of energy is important for the system to
continuously operate and the key technology will be
detailed later.
2.2. Power supply part
Almost every living space, for example, housing, offices, and stores has lighting fixtures. Our modified
DSC with excellent power generation efficiency under
low-light conditions is a promising energy harvester
Sensing/radio
transmitting part
Power supply part
Generation
device
Micro procesor
Power circuit
Power storage device
Sensor
RF
Fig. 1. Components of a wireless sensor node using energy
harvesting technology.
Cloud
server
920MHz band
Wi - Fi
Sensor node
(indoor type)
FSN - 2001N
(HTTP)
Router
Sensor station
FSN - 2000S
Internet
Data Viewer
Fig. 2. Architecture of a wireless sensor system.
5
Panel 1. Abbreviations, Acronyms, and Terms.
DSC–Dye-Sensitized Solar Cell
EH–Energy Harvesting
HEMS–Home Energy Management System
BEMS–Building Energy Management System
LIC–Lithium Ion Capacitor
EDLC–Electric Double-layer Capacitor
since the device can be used at various places. Typical
illumination levels of typical indoor conditions are
shown in Fig. 3. The illumination levels vary from 50 lx
to 5000 lx depending on each location. If a DSC capable of generating power with light levels over 10 lx is
used, the device generates power efficiently under
these light conditions. DSCs have a high degree of
flexibility in design and can be designed in module
(size, number of cells connected in series) to suit the
Near a window 5000 lx
Desk 200∼600 lx
conditions of installation because of simple manufacturing process by screen printing and low-vacuum process. External views of various DSC modules are
shown in Fig. 4 and specifications of various DSC modules are shown in Table 1. We use FDSC-FSC4 as a
power generation device of sensor nodes since the
product can be made and has an advantage of a large
effective generation area.
A DSC needs a DC-DC boost-buck converter for
stable power charge, just as other photovoltaic cells 4).
If an input voltage is as low as that of FDSC-FSC4, the
boost efficiency decreases. We thus developed an
original circuit, that uses an IC with high conversion
efficiency under a low input voltage or an ultralow
power consumption IC, to minimize power consumption and losses.
The power storage device we used was a lithium
ion capacitor (LIC) having a low self-discharge rate 5).
We think that an LIC is an optimal power storage device because it is resistant to deterioration from repeated charge and discharge. Figure 5 shows the com-
Wall (office) 50∼300 lx
(store) 500∼700 lx
Shelf (office) 50∼300 lx
(store) 1000∼3000 lx
120
Voltage retention (%)
Fig. 3. Typical illumination levels of indoor conditions.
FDSC - FSC4
FDSC - FSC1
LIC
100
EDLC①
80
60
40
EDLC②
20
0
FDSC - FDC3FG
1000
500
Time (hr)
0
1500
Fig. 5. Self-discharge characteristics amounts of various
capacitors.
Fig. 4. External views of various DSC modules.
Table 1. Specifications of various DSC modules.
6
XX
Unit
FDSC-FSC1
FDSC-FDC3FG
FDSC-FSC4
Maximum power (Pmax)
μW
140 (min), 170 (Typ)
305 (min), 450 (Typ)
180 (min), 250 (Typ)
Operating current (IOPE)
μA
90 (min), 120 (Typ)
100 (min), 130 (Typ)
465 (min), 630 (Typ)
Operating voltage (VOPE)
V
1.5
3.0
0.38
Open circuit voltage (VOC)
V
1.8-2.6
3.5-5.2
0.45-0.65
Cell number
–
4
8
1
External dimension
mm
56 ¥ 91
84 ¥ 130
56 ¥ 112
parison of self-discharge rates between the LIC and an
EDLC, a typical power strage device used in the EH
fields. The results show that the LIC having a low selfdischarge rate is not subject to marked reductions in
voltage for a long time.
The external view of a power module using the FDSC-FSC1 as an energy harvester is shown in Fig. 6.
and the specifications of power module are shown in
Table 2. This module was prototyped to regulate an
output voltage from an LIC and turn a conventional device to a self-powered device just by replacing the primary battery with the module. Charging characteristics of the power module at an illumination of 200 lx
are shown in Fig. 7. The result was good because the
gap between the measurement and calculated values
was very small, equivalent to about a 2.8 μA quiescent
current.
2.3. Sensing/radio transmitting part
Two or more sensors are often required depending
on the fields and applications. We installed in the system five sensors such as temperature, humidity, illuminance, atmospheric pressure, and human detecting
sensors for general purpose use. In addition, radio
transmitting is required for sending data over a long
distance reliably, so we selected a specified low-power
radio with a bandwidth of 920 MHz, which has relatively wide maximum available bandwidth and few
problems of interference. Because these sensors and
wireless modules are required for low energy consumption, they are designed to save the time for sensing and radio transmitting and otherwise go into sleep
mode 6).
3. System properties and applications
The external views of a sensor station and a sensor
node are shown in Fig. 8, and the specifications of
wireless sensor node is shown in Table 3. We think
Fig. 6. An external view of a power module using FDSC-FSC1
as an energy harvester.
Table 2. Specifications of power module.
Rated power
storage
170 μW (Typ) @White LED 200 lx
Maximum
power
DC 3 ± 0.2 V/100 mA
Rush current £ 185 mA (Application time 10 μs)
Power storage
amount
27 mWh (100 J)
External
dimension
W58 ¥ H125 ¥ D15 (mm)
※Without projection
Fig. 8. External views of a sensor station and a sensor node.
Table 3. Specifications of wireless sensor node.
Power storage amount (J)
120
100
Data
transmission period
Over one minute interval
· Modifiable interval with an internal switch
· Continues operating condition
300 lx for over 12 hours per day for 5 days
at 5 minutes intervals
Wireless
Specified low-power radio of 920MHz band
IEEE802.15.4g/e
Sensor
Temperature
80
60
Humidity
40
Measured value
20
0
Atmospheric
pressure
Calculated value
0
50
100
Time (hr)
150
200
Fig. 7. An external view of a power module using FDSC-FSC1
as an energy harvester.
Fujikura Technical Review, 2015
External
dimension
-10~50 ˚C
20~95 % RH
300~1 100 hPa
Illuminance
10~65 000 lx
Human detecting
5m
Operating condition
Temperature : -10~50˚C,
Humidity : 20~95 %RH
W120 ¥ H85 ¥ D20 (mm) ※Without projection
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Smart grid
Current
40
2000
35
Power storaeg amount
1500
30
25
20
1000
15
Illumination
intensity
10
5
0
0
1
2
4
3
5
6
7
9
0
Fig. 9. Performance of a wireless sensor system
under a 300 lx illumination condition.
Power monitoring
Current
Agriculture
Temp･humidity･CO2
HEMS
Temp･humidity
Security
RFID･human detection
Parking monitoring
Vehicle detection
1 mWs
(3 µW)
ing
Se
cu
rit
y
ult
ur
e
ric
Ag
se
ns
or
Hu
m
an
se de
ns te
or ct
2
CO
O
de pe
te n-a
cy n
ion dse clos
ns e
Th
or
er
Se
semocu
ns hy
rit
or dro
y
Illu
m
se ina
ns nc
or e
pr Di
es ffe
HE
su re
re nti
M
S
se al
ns
or
FE
M
S
Fig. 10. Example applications of the wireless sensor system.
0.01 mWs
(0.03 µW)
8
Time (day)
Structure monitoring
Vibration
100 mWs
(300 µW)
Fig. 11. Examples of power consumption of various sensor devices.
8
500
Illumination intensity (Ix)
Power storage amount (J)
that the system can be in harmony with any places and
thus widely used. The performance of a wireless sensor system under a 300 lx illumination condition is
shown in Fig. 9. The sensor node was placed under a
condition of 300 lx for 12 hours per day for five days
and a dark (0 lx) condition for two days. These conditions simulate those of offices. The temperature, humidity, illumination and atmospheric pressure were
measured at five minutes intervals. After a cycle of a
week, the power strage value increased in comparison
with the initial value. The result indicate that the system operates continuously as long as the same cycle
goes on.
Example applications of the wireless sensor system
are shown in Fig. 10. and examples of power consumption of various sensor devices are shown in Fig. 11.
Our wireless environmental sensor nodes can be used
at indoor locations such as a smart house. In addition,
these nodes can also be used at fields in the shade
such as IT services for agriculture and structural
health monitoring. Energy consumption of new CO2
sensors is being decreased while these sensors consumed a high level of power and thus were difficult to
use for energy harvesting in the past 7). We, therefore,
expect wireless sensor nodes will spread through various places in the future.
4. Conclusion
We have developed wireless enviornmental senser
nodes by minimizing the charge losses and energy
consumption for sensing and radio transmitting.
These nodes use power generated by DSCs and continuously operate switching from sensing to radio
transmitting at centain intervals. These nodes can be
used in various places because they have no need of
battery replacement and are ready to use just by placing them. We will develop an even lower energy consumption node and put it to practical use in the future.
Acknowledgment
Part of this work was accomplished under contract
to New Energy and Industrial Technology Development Organization (NEDO).
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Fujikura Technical Review, 2015
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