Wireless Data Acquisition for Photovoltaic
Power System
Makbul Anwari',
Anwari I, Arief
AriefHidayat
Hidayat',I, M. Itnran
Imran Hamid',
HamidI, and Taufik'
Taufik2
'Faculty
IFaculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
Electrical Engineering Department, Cal Poly State University, San Luis Obispo, USA
E-mail:
E-mail : makbul@ieee.org
Abstract This paper presents a wireless system for
monitoring
monitoring the input and output of the array in a photovoltaic
generation plant. The system comprises of sensors, data
data
acquisition system, wireless access point and user computer that
enable the users to access the array parameter wirelessly.
Description and function of set up equipment are presented as
well as the application program that supports the system.
1.
l. INTRODUCTION
Recently, the number of energy in the world is reaching to
concern state. This is caused by the need of energy is growing
very fast. Due to concerns regarding global warming and air
pollution, there has been an international movement in the
renewable energy technologies for electricity
promotion
promotion of renewable
generation, green energy is one among proposed solutions for
these issues [l].
[I].
Solar energy is converted to electricity in a photovoltaic
generation plant that contains photovoltaic array as solar­
electricity conversion equipment, electrical
electrical power converter,
power storage and other supporting equipment. According to
operation mode, photovoltaic generation plants are met in
isolation mode, grid interconnected mode and plant that can
modes.. For all of these modes, there are needs
operate in both modes
to acquire the input and output parameter of the photovoltaic
array as the generation equipment. The acquired parameters
are used for control action information, generation
generation planning,
energy forecasting, and performance observation or
documentation need. Some of the parameters are irradiance,
temperature and array's electrical
electrical output. A satisfied data
acquisition system is required for this need.
Related to acquisition system for photovoltaic performance,
ai. have accomplished a research in which,
Benghanem et aI.
instruments are used to detect, integrate, and record
several instruments
solar energy measurement using both conventional electronics
as well as microprocessor data acquisition system [2]. Further,
Machacek et aI., developed a system for measuring, collecting,
analyzing, and displaying data for 100 W solar energy
converter, data acquisition is formed by NI-6023E plug-in
card and feed the rough data to the control program built in a
MATLAB script [3].
Data from acquisition system module are needed to produce
useful information. The speed of the process is the important
parameter. To accommodate this requirement, during the past
decade, digital control has been widely used. Digital control,
which is determined by application of microprocessors, makes
the sampling and computing process are faster than before.
Implementation of such a system has been done on a dc
voltage monitoring and control system for a wind turbine
inverter [4].
Voltage
lta g e Divider
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l. Simplifieddiagramof
SImplIfied dIagram of the Wireless data acqutsitron
acquIsitIOn for
for photovoltalc
photovoltaic system.
Lapto pUser
p U ser
Regarding with data transmission, Chen,et.al, have studied
carrying the acquired signal from data acquisition module
using internet [1]. Java language is used for designing a
dynamic webpage to graphically display various real time
waveforms of the controlled system for multi-user at the same
time. The system is implemented on a small scale wind power
time.
generation system equipped with an EZDSP 2812 controller.
An FPGA ECIO is implemented as a bidirectional
communication interface for coordinating the asynchronous
data transmission modes.
In this paper, we present a photovoltaic generation
monitoring system for a 5 kWp laboratory scale photovoltaic
generation. Temperature, irradiance, voltage, and current of
the array are acquired, processed and then transmitted such
that can be used for reviewing the performance of the
generation plant. Acquired data is transmitted by wireless
method using Wi-Fi signal (IEEE 802.11
802.11 standard), while
of PIC 16F877A is used to control the
microcontroller of
acquisition system process and a Delphi application program
is built to graphically display the acquired data. Figure 1
show the simplified diagram of
of such system.
II. PV GENERATION
GENERATIONCHARACTERISTIC
CHARACTERISTIC FOR
FOR MONITORING
MONITORING
SYSTEM
SYSTEM
The acquisition system is aimed to detect and collect the
parameters that indicate the electrical characteristic of the
array and the factors influencing them.
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Fig.
Fig. 2. V- I characteristic ofPV
ofPV module, (a) characteristics on various
various
irradiance
at a constant
temperature,, (b) Characteristic on various
irradianceat
constanttemperature
various
temperature at a constant
constantirradiance
irradiance
As shown in Figure 2, photovoltaic array characteristic (V-I
curve) shows the dependency of
of cell current and voltage to
irradiance and temperature. Irradiance contributes to the cell
current, the higher irradiance the higher current draw by array
photovoltaic, while the temperature effects to the cell voltage,
the higher temperature the lower voltage appears on the cell
I- V
terminal. In Figure 2a, it is shown a set of photovoltaic cell 1-V
curve under varying irradiance at a constant temperature,
meanwhile figure 2(b) shows the one at the same irradiance
values, but under varying temperature. Both figures are also
show the point where the multiplication of PV array voltage
and current reaches the maximum value:
value: maximum power
point (MPP), at which condition that the array operates with
maximum efficiency and produces maximum output power.
Variation of
of irradiance and temperature in photovoltaic
module is characterized as short time fluctuation;
fluctuation; follows the
behavior of
of atmospheric condition around plant during time.
The effect of
of this variation is the unpredictable variation of
of
power output, current and voltage of
of the plant. An acquisition
system for this condition should consider the phenomenon.
III. PV GENERATION
GENERATIONMONITORING
MONITORING SYSTEM
SYSTEM
The PV generation and monitoring system shown in Figure
1, is a diagram of
of a laboratory scale system that contains three
units photovoltaic array produces three dc
de voltages of
of 0 - 150
150
range.
range. These de
dc voltages is then fed to three single phase PV
inverter respectively to be inverted to ac power before sending
to the utility. Maximum current for each array are lOA
lOA de.
dc.
Array power input in form of temperature and irradiance and
the de
dc output of
of array are picked up as data acquired for the
monitoring system.
Three ACS754 current sensors with maximum current 50A
and sensitivity of 37.8 mV/A
mVfA are connected to de
dc output of
each solar array, while irradiance and temperature sensor
placed around the array. For voltage acquisition, 1k.o.-1M.o.
lkQ-IMQ
voltage divider was used, which means 10mV for every one
volt de
dc solar panel output. LM35 temperature sensor which
sensitivity of 10mV
10mV/oC
fOC is used for measure the ambient
temperature of solar panel. The irradiance is sensed using
LDR.
Data acquisition diagram is shown in Figure 3. In order to
determine the analog signal from the sensor to be passed to
ADC, which contains eight analog signal from sensors (3 for
dc
de current, 3 for dc
de voltage, one for irradiance and the
remaining for temperature) dual eight-channels analog
multiplexer DG407B are used. The analog multiplexer was
controlled using microcontroller and passing the multiplexing
signal with their own voltage references.
In the ADC block, each analog signal from multiplexer is
digitalized to eight bits digital signal. Eight-bit signal is used
caused by the condition that communication between
microcontroller and serial to Ethernet module uses eight bit
data. Thus, voltage reference Vrej
for ADC is
rej
8
,
Vrej
=
resolution
x
2
where
the
resolution
is equal to
rej
sensitivity of each sensor. ADC operation is also controlled by
the microcontroller.
In this system, the microcontroller is employed to run the
following function: controlling the multiplexer for
determining the analog signal from the sensor to be passed;
controlling the operation of ADC, and as communication
protocol between Ethernet and the acquisition system. To
accommodate these functions,
functions, the low-power consumption
PIC 16F877A microcontroller is used. This unit is built within
eight channels 10 bit ADC and an UART connection for serial
communication.
Microcontroller serial connection is connected to Wiznet
EGSR7150 in order to convert format data from serial to
Ethernet data, conversion process is reversal. Further, the
acquainted data is sent to the access point to be sent in form of
Wi-Fi signal
signal to connected user computer.
To accommodate communication between computer and
acquisition system and to display the result, a computer
application program is required.
There are 5 charts that show the measured and calculated
parameters. Voltage, current,
current, and calculated PV array power
of whole channel is displayed in one chart respectively. Each
PV array power output is obtained by multiplying the voltage
and current of respective array. The array temperature and
irradiance are displayed separately in others charts. Nominal
values of these parameters are also displayed. To start data
acquisition, user must connect the application to acquisition
module by pressing the "Connect to network" button. Timer
setting button is provided to determine measurement interval
of the acquisition data.
Prototype of the photovoltaic acquisition system is shown in
Figure 6. The left side picture shows layer for power supply,
voltage divider and current sensor, this layer is placed in the
bottom of acquisition compartment. The right side pictures
shows layer
layer for the microcontroller, multiplexer, Vref
ref board
and data converter.
Sensor
System
Serial
PIC 16F877A Connection Serial Microcontroller Ethernet
Microcontroller
~~~
Receivequeryfrom
Receive query from PCI
PCI
Vref
No
No
notebook trough
notebook
trough
wlrelessaccesspoint
wlrelessaccess
point ?
Serial to Ethernet
Converter
Fig. 3. Data acquisition system diagram
For this need, an application program, written in Delphi
language is developed. This program is built to allow
allow the user
user
can interact and control the process steps in these two sub­
systems (microcontroller in acquisition system and displaying
process in computer). Communication between computer and
acquisition system is done wirelessly.
Communication process involves two application programs,
one is in the computer side and the other
other is in microcontroller
side. Flowchart of communication between these two
application programs is shown in Figure 4, which shows two
main
main blocks, indicates the process flow in each side.
when they are
First of all, the programs will self-initialize when
activated. User can decide whether to acquire
acquire data or not. If
acquisition data
data will be done, program will send a query
command to the acquisition program on microcontroller
contains which data to be acquired. Microcontroller in
orders the
acquisition system -based on the command query- orders
signal from the
multiplexer to by-pass the intended analog signal
sensors and digitalized them.
signal from the sensors
sensors contains high noise, which
Analog signal
avoid this, analog
can degrade the measurement accuracy. To avoid
signal is picked up and converted three times; their average is
data
computed and become data to be sent back as acquisition data
to user computer. In user computer, acquisition data is
received by Ethernet port. Application program then processes
the data to be displayed and to be saved in the virtual memory.
shown in Figure 5.
The displaying application program is shown
> - - - -......
Receivequery?
Receive query? :
>---No-......
No
Fig. 4. PC and microcontroller software
software flowchart
flowchart
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V.ACKNOWLEDGMENT
.ACKNOWLEDGMENT
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The authors thank the Malaysian Government, Ministry of
Science, Technology and Innovation (MOST!) for the Science
Fund Grant, Project No. 01-0 1-06-SF0205.
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VI. REFERENCES
REFERENCES
[I]
'
1
~\.
-
-••
[2]
~l
1 • 6'
lOlll.\616;ll21:!l2li2IJ1I1l31J6ll1lO11"II5~50SlSl$
5 1015 JI 25 11 lS III IS 50 55
Tw
T~
o:Ior.!Inlof,S1ll'2llIlr...
O»Y.~.S1JllOOl l... :I~:22:54
:I~:Z2:S.
Tw
T~
[3]
[3]
'adteIs:I92.l68.l,1I0.llI<a'r«tei
J'.... :lt2.16l1.110"~
Fig.5. Application program appearance
[4]
[4]
[5]
[5]
[6]
[6]
[7]
[7]
[8]
[8]
[9]
[9]
Fig. 6. Prototype of
of the photovoltaic acquisition system, (a) upper layer, (b)
lower layer
IV. CONCLUSION
CONCLUSION
A wireless data acquisition system for photovoltaic
generation system that uses PICI6F877A microcontroller as
the main control has been presented. Implementation of the
EGSR7150 Ethernet to serial module and the access point as
Wi-Fi communication tool between acquisition equipments
and user computer for graphically displaying the acquired
parameter has work properly as intended. Implementation of
such a system on a laboratory scale photovoltaic generation
shows the practical simplicity, efficient and low cost.
Po-Yen Chen; Se-Kang Ho; Wei-Jen Lee; Chia-ehi
Chia-Chi Chu; Ching-Tsa
Pan, "An Internet Based Embedded Network Monitoring System for
Renewable Energy Systems", Proc.
Proc. The 7th IntenuJtional
International Conference on
Power Electronics, pp.225-228,
pp.225-228 , October 22-26,2007.
M.Benghanem; A. Maafi, "Data Acquisition System for Photovoltaic
Systems Performance Monitoring", IEEE Trans.
Trans. on Instrumentation and
and
Measurement, Vo1.47, No.1, pp.30-33, February 2008.
J. Machacek; z.
z. Prochazka; 1. Drapela, "System for Measuring and
Collecting Data from Solar-cell Systems", Proc.9th International
Conference Electrical Power Quality and
and Utilization, Barcelona, 9-11
October 2007.
Z. Wang; L. Chang, "A DC voltage Monitoring and Control Method for
Trans. On
Three Phase Grid-Connected Wind Turbine Inverters", IEEE Trans.
Power Electronics, Vol.
Vol. 23, No.3, pp.
pp. 1118-1125, May 2008.
T. Yuki; H. Yoshikiro; K.
K. Kosuke, "Temperature and Irradiance
T.
Dependence of
of the I-V Curves of
of Various Kinds of
of Solar Cells"
International Photovoltaic Science & Engineering Conference,
Shanghai, China 2005
A. Moein, M.
M. Pouladian, "WIH-Based IEEE 802.11
802.1 1 ECG Monitoring
Implementation", Proceedings of
of the 29th Annual International
Conference of
of the IEEE EMBS Cite Internationale, Lyon, France August
23-26, 2007.
23-26,2007.
H. Zhao, X.
X. Chen, K.H.
K.H. Chon, "A Portable, Low-cost, Battery-powered
Wireless Monitoring System for Obtaining Varying Physiologic
Parameters from Multiple Subjects" , Proceedings of the 28th IEEE
30EMBS Annual International Conference, New York City, USA, Aug 30­
Sept3,2006
Sept
3, 2006
A. Perujo; R.
R. Kaiser; D.U Sauer; H. Wenzl; I.
I. Baring-Gould; NWilmot;
N.Wilmot;
F. Mattera; S. Tselepis; F
H. Zhiqiang; Z. Wenxian; L. Jianke, "Research on High-Speed Data
Acquisition and Processing Technique", The Eighth International
ICEMI'2007
Conference on Electronic Measurement and Instruments, ICEMI'2007