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online
atatwww.sciencedirect.com
Energy
Procedia
00
(2018) 000–000
Energy Procedia 00 (2018) 000–000
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Energy
Procedia
152
Energy
Procedia
00(2018)
(2017)1015–1020
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www.elsevier.com/locate/procedia
Applied
Energy Symposium
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Forum 2018:
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and
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Low
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CUE2018,
5–7 June
2018,
Shanghai,
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urban energy
systems,
5–7 June
Shanghai,
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5–7 June
2018,2018,
Shanghai,
ChinaChina
FeasibilityThe
study
of embedded
piezoelectric
generator
system on a
15th International
Symposium
on District Heating
and Cooling
Feasibility study
of embedded
piezoelectric
generator
system on a
highway for street lights electrification
for street
lightsthe
electrification
Assessinghighway
the feasibility
of using
heat demand-outdoor
Lumbumba Taty-Etienne Nyamayoka*, Lijun Zhang, Xiaohua Xia
temperature
function
for a Nyamayoka*,
long-term district
heatXiaohua
demand
Lumbumba
Taty-Etienne
Lijun Zhang,
Xia forecast
Department of Electrical, Electronic and Computer Engineering, University of Pretoria, Pretoria 0002, South Africa
a and ComputeraEngineering, University
b of Pretoria, Pretoria c0002, South Africa
Departmenta,b,c
of Electrical, Electronic
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc
a
Abstract
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
b
Abstract
Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France
c
Energy harvesting
technology
fromÉnergétiques
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of vehicles is- IMT
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Département
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Atlantique,approach
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harvesting
technology
the movement
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paper
presents
a feasibility
on theof
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to obtain
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thatembedded
can be usedintothe
power
street
lights.
paper presents
a feasibility
study
generating
electric
power
from piezoelectric
materials
asphalt
layer
on aThis
highway.
The Pumulani
Plaza
study
ofstation
generating
from
materials
in the asphalt
a highway.
The
Pumulaniresults
Plaza
tollgate
alongelectric
the N1power
highway
in piezoelectric
Pretoria is selected
for embedded
this study because
it has layer
a highontraffic
volume.
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Abstract
tollgate
station The
along
the N1energy
highway
in Pretoria
is selected
for this study
because
it has
highcan
traffic
Numerical
are
presented.
average
output
is estimated
at 1.576587613
kWh
per day
anda that
be volume.
enough to
supply 6 results
Highare
presented.
The
average
is estimated at 1.576587613 kWh per day and that can be enough to supply 6 Highpressure
sodium
(HPS)
streetenergy
lights output
of 250 W.
District sodium
heating(HPS)
networks
commonly
addressed in the literature as one of the most effective solutions for decreasing the
pressure
streetare
lights
of 250 W.
greenhouse
fromAll
therights
building
sector. These systems require high investments which are returned through the heat
Copyright
© gas
2018emissions
Elsevier Ltd.
reserved.
Copyright
©
Ltd.
All
rights
reserved.
sales. Due
to
theElsevier
changed
climate
conditions
building committee
renovationofpolicies,
demand
in the and
future
could
decrease,
Copyright
© 2018
2018
Elsevier
Ltd.
All
rights
reserved.
Selection
and
peer-review
under
responsibility
of and
the scientific
Appliedheat
Energy
Symposium
Forum
2018:
Low
Selection and peer-review under responsibility of the scientific committee of the CUE2018-Applied Energy Symposium and
prolonging
investment
return
period.CUE2018.
Selection
andthe
peer-review
under
responsibility
of the scientific committee of Applied Energy Symposium and Forum 2018: Low
carbon
cities
and
urban
energy
systems,
Forum 2018: Low carbon cities and urban energy systems.
The main
scope
of thisenergy
paper is
to assess
the feasibility of using the heat demand – outdoor temperature function for heat demand
carbon
cities
and urban
systems,
CUE2018.
forecast. piezoelectric
The districtgenerator;
of Alvalade,
in piezoelectric
Lisbon (Portugal),
used asroad;
a case
study.source.
The district is consisted of 665
Keywords:
energy located
harvesting;
materials;was
piezoelectric
renewable
Keywords:
generator;
energy harvesting;
materials;
piezoelectric
road; renewable
buildingspiezoelectric
that vary in
both construction
periodpiezoelectric
and typology.
Three
weather scenarios
(low,source.
medium, high) and three district
renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were
with results from a dynamic heat demand model, previously developed and validated by the authors.
1.compared
Introduction
results showed that when only weather change is considered, the margin of error could be acceptable for some applications
1.The
Introduction
(the
error in
annual demand
was lower
than 20% for
all weather
scenarios
afterthe
introducing
renovation
Energy
harvesting
is a method
of generating
electrical
energy
usingconsidered).
the energy However,
surrounding
environment
such
scenarios,
the
error
value
increased
up
to
59.5%
(depending
on
the
weather
and
renovation
scenarios
combination
considered).
harvesting
is a method
generating
electrical
energy using
the energy
such
as Energy
the wind,
solar, energy
of theof gas,
temperature
gradients,
vibration,
liquid surrounding
flows, etc. the
[1].environment
Thermo-electric,
The
of slope
coefficient
average within
the rangevibration,
of 3.8% upliquid
to 8%flows,
per decade, [1].
that Thermo-electric,
corresponds to the
as
thevalue
wind,
solar,
energy ofincreased
thepiezoelectric
gas,ontemperature
gradients,
electromagnetic,
photovoltaic
and
technologies
are the four energy
extractionetc.
technologies
that attract
decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and
electromagnetic,
photovoltaic
andconversion
piezoelectric
technologies
are the four
energy
extraction
technologies
that
attract
the
most
attention
among
energy
technologies.
However,
energy
formed
from
various
objects
in motion,
renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending
on the
the most attention
among
energy
conversion
technologies.
However,
energy
formed Therefore,
from various
objects
in
motion,
vibration
machines
or
any
other
source
of
mechanical
energy
is
not
being
captured.
this
source
of
energy
coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and
vibration
machines
any
of mechanical
notloss,
being
captured. Therefore,
thisused
source
of energy
is
dispersed
and
thusorof
wasted.
As source
anestimations.
effective
method toenergy
utilize isthis
piezoelectric
materials are
to absorb
the
improve
the
accuracy
heatother
demand
is dispersed and thus wasted. As an effective method to utilize this loss, piezoelectric materials are used to absorb the
© 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and
* Corresponding author. Tel.: +27732046035; fax: +27123625000.
Cooling.
* Corresponding
Tel.: +27732046035; fax: +27123625000.
E-mail address:author.
tatynyamayoka@gmail.com.
E-mail address:
tatynyamayoka@gmail.com.
Keywords:
Heat demand;
Forecast; Climate change
1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved.
1876-6102
Copyright
© 2018
Elsevier
Ltd. All of
rights
reserved. committee of the Applied Energy Symposium and Forum 2018: Low carbon cities
Selection and
peer-review
under
responsibility
the scientific
Selection
peer-review
responsibility of the scientific committee of the Applied Energy Symposium and Forum 2018: Low carbon cities
and urbanand
energy
systems, under
CUE2018.
and urban energy systems, CUE2018.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the CUE2018-Applied Energy Symposium and Forum
2018: Low carbon cities and urban energy systems.
10.1016/j.egypro.2018.09.110
1016
2
Lumbumba Taty-Etienne Nyamayoka et al. / Energy Procedia 152 (2018) 1015–1020
L.T-E. Nyamayoka et al./ Energy Procedia 00 (2018) 000–000
wasted mechanical energy and convert it to electrical energy [2]. The piezoelectric materials play an essential role
because the amount of pressure applied is directly proportional to the electrical energy generated. The practical
implementation of the piezoelectricity concept can have a potentially significant impact by reducing the cost of
electricity consumption of a given structure [4,5]. The use of piezoelectric materials to harvest energy from the
movement of the vehicles on the highway is an area of great interest. As the movement of the vehicles is everywhere,
the ability to capture this energy at the lowest cost would be a significant step towards greater efficiency and cleaner
energy generation [3]. Embedding the piezoelectric materials on the highway leads to a piezo-smart-road where the
generating power can supply street lights and the excess power can be fed into the grid.
Literature has recently shown a significant increase in the number of articles which describe the use of piezoelectric
materials embedded on the asphalt layer on the highways to harvest energy from the movement of the vehicles
[4,5,6,7,8,9]. The biggest challenge in this regard is to generate useful electrical energy and increase the conversion
efficiency of the technology. Gupta et al. [6] have tried to show that the energy generated by the movement of vehicles
on the road can be converted into electrical energy by the piezoelectric effect. The aim of their research was to make
power generation more sustainable, economic and ecological by utilizing the advancement in the technology. Aqsa
Abbasi [7] has described and reviewed a method to generate pollution free electricity through some techniques such
as the piezoelectric effect on piezoelectric crystal and using them in piezoelectric roads, as congestion on the roads is
becoming inevitable with the fancy of the masses towards personal transportation systems for their growing mobility.
Accordingly, it is an object of the present invention to provide a method of electrical power generation that does not
negatively impact the environment. Xiong [8] at Virginia Tech experimented a piezoelectric harvesting system
consisting of multiple cylindrical piezoelectric materials that are compressed by the action of traffic tires. Under a
traffic volume of 4000 vehicles per day (167 vehicles/hour), this system generated a voltage ranging from 400 V to
700 V and electric currents ranging from 0.2 to 0.35 mA. The corresponding power output was obtained by multiplying
voltage by current, yielding a power range between 0.08 and 2.1 Watts per system. Zhang et al. [9] conducted a
comprehensive numerical modeling on harvesting energy using piezoelectric materials in asphalt pavement roadways.
The results reported more energy output on roadways that are built over soft subgrade foundation. In addition, they
remarked that key variables such as depth of embedded disks, position of the wheel with respect to energy harvester,
and vehicle speed influenced the output power.
According to these previous studies, many researchers have demonstrated the utilisation of piezoelectric technology
as a source of electrical energy. For this purpose, this paper shows a feasibility study of an embedded piezoelectric
generator system used to harness energy from the movement of the vehicles on a highway for street lights
electrification. The paper is organized as follows: apart from the introduction, section 2 presents the basic concept of
piezoelectricity, while in section 3; the working principle of embedded piezoelectric generator is given. Section 4
presents the potential and estimation of electrical energy generated from the piezoelectric generator embedded on the
highway. Conclusions are drawn at last.
2. Basic concept of piezoelectricity
2.1. Piezoelectric effect and mode configuration
By definition, piezoelectric effect is the electrical load that builds up in certain solid materials under the action of
mechanical stress. Applying a constraint on a piezoelectric material causes the occurrence of a voltage between the
electrodes. Piezoelectric materials can be configured so that the mechanical stress is perpendicular or parallel to the
electrodes. As a result of compression and tension forces, opposite polarity voltages proportionate to the applied force
can be produced, which can be in mode 33 or mode 31 as shown in Fig.1 [10].
Lumbumba
al. / Energy
152 (2018) 1015–1020
L.T-E.Taty-Etienne
NyamayokaNyamayoka
et al./ EnergyetProcedia
00 Procedia
(2018) 000–000
10173
Fig.1. Piezoelectric conversion coupling mode: (a) mode 33 and (b) mode 31
2.2. Piezoelectric generator mathematic model
The piezoelectric effect converts mechanical strain into an electrical voltage. In general, two effects manifest
piezoelectricity; namely, the direct as well as the converse piezoelectric effect. In the direct piezoelectric effect, the
materials have the ability to convert mechanical strain into electrical charge while in the converse piezoelectric effect;
the materials have the ability to convert an applied electrical potential charge into mechanical strain energy [11]. The
direct and converse piezoelectric effects can be expressed mathematically by two linearized equations. These
mathematical models have four variables (two mechanical and two electrical variables), which can be converted by a
set of nine equations which are called the piezoelectric constitutive law. The IEEE standard on piezoelectricity gives
various series of constants used in conjunction with the axes notation [12]. According to this standard, (1) gives the
electric displacement D and strain S.

D dT   T E
(1)

S s ET  dE
Where: D is the electric displacement, S is the strain; d is the piezoelectric charge constant; T is the stress;  T is
the dielectric constant at the constant T condition; sE is the compliance at the constant E condition and E is the external
electric field.
The direct piezoelectric effect is considered where the external electric field (E) is zero when the piezoelectric
material is used for energy harvesting application. If the piezoelectric materials are embedded over the asphalt layer
in the highway subject to traffic loading, the polarization in the axial direction (P3) appears on the vertical surface of
piezoelectric materials. Thus, from equation (1), the piezoelectric polarization in the 3rd axial direction according to
the axes notation in Fig.1 can be written according to the electric displacement (D):
P3  d33T
(2)
Where: P3 is the piezoelectric polarization in the 3rd axial direction according to the axes notation in Fig.1; d33 is
the piezoelectric charge constant of the piezoelectric material and T is the stress.
The vehicle wheel loading at the 3rd axial direction according to the axes notation in Fig.1 causes the stress which
generates an open circuit voltage (V) on the piezoelectric material and it is shown in (3).

V3
E dt  g Tdt

3
p
33
p
(3)
Where: V3 is the electric potential in the 3rd axial direction according to the axes in Fig.1; E3 is the internal electric
field in the PZT; tp is the thickness of piezoelectric material; g3i is the piezoelectric voltage constant of piezoelectric
material.
Therefore, the output electrical energy of the piezoelectric material for energy harvesting can be calculated using
(4).
T
1
1 2  33
1
r 0 A

P3 E3 At p
V
CV 2
(4)
2
2
2
tp
Where: UE is the output electrical energy; C is the capacitance and A is the surface area of piezoelectric material;
εT33r is the relative dielectric constant of piezoelectric material in the 3rd axial direction;  0 is the dielectric constant

UE
of vacuum.
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Lumbumba Taty-Etienne Nyamayoka et al. / Energy Procedia 152 (2018) 1015–1020
L.T-E. Nyamayoka et al./ Energy Procedia 00 (2018) 000–000
2.3. Different type of piezoelectric materials
There are many kinds of piezoelectric materials that can be used to harvest energy from the movement of the
vehicles on the highways. The main classes are made of crystals that have a natural piezoelectric effect such as
piezoceramics (lead zirconate titanate [PZT]), polymer (polyvinylidene fluoride [PVDF]), macro fiber composite
[MFC], piezoelectric semiconductors [ZnO2] and glass ceramics [Ba2TiSiO6, Li2Si2O5]. However, each piezoelectric
material has different mechanical and piezoelectric properties. The most commonly used are piezoceramics and
polymer. The piezoceramics are rigid, while the polymers are flexible and soft. The polymers generate less energy
than the piezoceramics and this is due to the different piezoelectric and dielectric properties.
3. Working principle of embedded piezoelectric generator
The piezoelectric generator is composed of one or more piezoelectric materials. The piezoelectric materials are
incorporated into the asphalt layer to harvest the energy generated by the movement of the vehicles as shown in Fig.2
below. As the vehicles move, the wheels exert pressure over the asphalt layer, which causes deformation of the
piezoelectric materials. This deformation absorbs the pressure and generates electrical power.
Fig. 2. Embedded piezoelectric generator.
4. Potential and estimation of electrical energy generated from piezoelectric generator
Several researchers and organizations have tested and calculated the electrical power outputs from the piezoelectric
generator embedded in highways using different approaches. In this section, a case study is discussed to estimate the
potential of an embedded piezoelectric generator by calculating the average amount of daily electrical energy
generation.
4.1. Potential electrical energy generation from a piezoelectric generator embedded in N1 Highway Pretoria
The N1 highway is a national route in South Africa that stretches 1 937 kilometers from Cape Town through cities
including Bloemfontein, Johannesburg, Pretoria and Polokwane all the way to the Beit Bridge border post, on the
Limpopo River between South Africa and Zimbabwe [13]. It forms the first section of the famed Cape to Cairo Road.
In the process of traffic data collection, it appears that the N1 presents a far heavier traffic profile than other highways
in South Africa. The section where the N1 heads towards Pretoria along the Ben Schoeman Highway carries about
300,000 vehicles per day and is purported to be the busiest stretch of road in South Africa [14]. From this, the
piezoelectric generator is proposed to be installed at the Pumulani Plaza tollgate station because of the high traffic
volume and its convenience for the system installation because the N1 at the Pumulani Plaza tollgate station has six
dual-lane carriageways. The piezoelectric generator is located exactly at the area before and after each lane
carriageways entrance along the wheel path of the vehicles.
Lumbumba Taty-Etienne Nyamayoka et al. / Energy Procedia 152 (2018) 1015–1020
L.T-E. Nyamayoka et al./ Energy Procedia 00 (2018) 000–000
1019
5
4.2. Average power output of the piezoelectric generator embedded in N1 Highway Pretoria
In order to predict the average power output from the piezoelectric generator embedded on the N1 highway at the
Pumulani Plaza tollgate station, specific parameters and assumptions are adopted using the information derived from
[15]. The vehicle mass and axle loading are important variables in predicting the power output. The data traffic
collected give the average traffic volume of 300,000 vehicles per day where the speeds of the velocity are strictly
60km/h. The rolling resistance force ( Fr ) of the wheels to the piezoelectric generator is calculated by:
Fr  N f  Cr  m  g  Cr
(5)
Where: N f is the normal force and Cr is the coefficient of rolling friction ( Cr varies between 0.03 – 0.15).
Consider that the average mass of the vehicles is 1650 kg, then:
Fr =1650  9.8  0.05=485.1N
The power required to compensate the rolling resistance is found by:
P
Fr  v
(6)
r
v
Where: is the speed of the vehicle. Here the speed of the vehicle is 25 km/h because of the location of the
piezoelectric generator embedded along the wheel path of the vehicles at the Pumulani Plaza tollgate station.
Pr  = 485.1  25  1000/3600=3368.75W.
The loading time t is the duration of the cycle when the wheel approaches to the piezoelectric generator embedded
and then passes over the full length. The square-shaped of the piezoelectric generator is 0.50  0.50. The loading time
can be calculated according to the length of the piezoelectric generator l p and the speed of the vehicles v .

t
l p 0.50  3600

 0.072sec
v
25 1000
(7)
The mechanical energy generated from each vehicle's impact is calculated using the integral of power over time.

U in
t
Pr dt

0
0.072

dt 242.55J
 3368.75
(8)
0
The efficiency of mechanical to electrical energy conversion is an essential factor to compare energy harvesters of
different piezoelectric materials. Due to the cyclic loading effect of traffic of the vehicle on the asphalt layer, the
coefficient  of the energy transmission can be at work at different conditions, as shown in (9). The coefficient  is
0.078 according to [16] for the efficiency energy conversion.

UE
U in
(9)
The output electrical energy of the piezoelectric generator generated according to the efficiency conversion of the
energy transmission from mechanical to electrical is:
U E  0.078  242.55=18.9189J
(10)
With: 1J =2.7778×10-7 kWh, the energy generated is UE = 52.55292042 x 10-7 kWh per vehicle.
With the average daily traffic volume of the vehicles on the N1 highway, the total average energy generated from
the piezoelectric generator embedded is 1.576587613 kWh.
One high-pressure sodium (HPS) street light of 250 W can consume 0.25 kWh over an hour. The total number of
street lights that can be lit with this total energy generated are 6. The numerical results from this potential feasibility
study is quite encouraging and interesting.
4.3. Electrical energy storage system
Since the street lights only work at night, the energy generated during the day needs to be stored. The choice of the
energy storage device depends on the power generated and its application. Generally, two kinds of energy storage
devices are used to accumulate the electrical energy generated by the piezoelectric generator embedded on the
highway, namely; supercapacitors and rechargeable batteries. However, with the development of a supercapacitor,
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Lumbumba Taty-Etienne Nyamayoka et al. / Energy Procedia 152 (2018) 1015–1020
L.T-E. Nyamayoka et al./ Energy Procedia 00 (2018) 000–000
several studies have confirmed that the supercapacitors tend to be a more suitable storage system than rechargeable
batteries in the piezoelectric technology [16,17]. The advantages of supercapacitors for such applications are threefold. Firstly, differing from traditional batteries, where the charging and discharging damages the electrode, the
number of charge and discharge cycles of supercapacitors is nearly unlimited with minimal change in performance
from 100% to 80% after 10 years. Secondly, the charging time of the supercapacitors is very short. Thirdly, the
supercapacitors are less influenced by the temperature of the environment. In an unfortunate environment, such as
where there is critically high or low temperature, its ability to resist bad environmental temperature is much better
than traditional batteries.
Conclusion
Energy harvesting from the embedded piezoelectric generator is an attractive technology that can harness the excess
energy wasted on the highway caused by moving vehicles. From the information collected on the N1 highway at the
Pumulani Plaza tollgate station in Pretoria, the potential electrical energy generation was demonstrated and the
numerical results were presented. The energy output of the embedded piezoelectric generator was 1.576587613 kWh
per day, which is quite enough to light 6 high-pressure sodium (HPS) street lights of 250 W. The result of this paper
is a useful guideline for future simulation and for the physical implementation of the system.
Acknowledgements
This paper was sponsored by the National Hub for Energy Efficiency and Demand Side Management at the Centre
of New Energy Systems, Department of Electrical, Electronic and Computer Engineering, University of Pretoria,
South Africa.
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