automatic system fo automatic system for cooling of photovo r

AUTOMATIC SYSTEM FOR COOLING OF PHOTOVOLTAIC PANEL
FOR
R COOLING OF PHOTOVOLTAIC
AUTOMATIC SYSTEM FO
PHOTOVOLTAIC
PANEL
As.Eng. Ionel-Laurentiu ALBOTEANU PhD1, Prof. Eng. Gheorghe MANOLEA PhD1,
Eng. Alexandru NOVAC PhD2, Eng.Constantin ŞULEA
1
University of Craiova, Faculty of Electrical Engineering
2
S.C. PROMAT S.A.
REZUMAT. lucrarea prezintă o soluţie cu privire la creşterea eficienţei panourilor fotovoltaice prin reducerea pierderilor
datorat incălzirii celulelor fotovoltaice. Soluţia constă în aplicarea pe spatele panourilor fotovoltaice a unui sistem de răcire
răcire
cu apă
apă.
pă. Funcţionarea
Funcţionarea automată sistemului
sistemului de răcire va conduce la
la creştere eficienţei panourilor fotovoltaice
fotovoltaice şi reducerea
consumului de energie.
energie.
Cuvinte cheie: sistem de răcire, automatizare, panou fotovoltaic, microcontroler, senzor de temperatură
ABSTRACT.
ABSTRACT. The paper presents a solution focused on increasing efficiency of photovoltaic panel by reducing losses due to
warming photovoltaic cells. The solution consists in a water cooling system applied to the back of photovoltaic panels.
Automatic operation of the cooling system will lead to increased efficiency of solar panels and reduce energy consumption
Keywords: cooling system, automation, photovoltaic panel, microcontroller, temperature sensor
1. INTRODUCTION
Crystalline silicon currently offers a yield of 15-16%
and some studies consider that its limits would be
reached approximately 25% under laboratory conditions
[2]. Although other materials such as Ga, offering a
yield of 30%, prohibitive price makes them suitable
only for space applications. Recently, researchers of
U.S. universities have announced that was obtained a
photocell with a yield of 60%. It's a big step towards the
upper limits of efficiency photovoltaic cells [5]. Very
complex technology and materials used do remain only
the state of laboratory. Therefore, in the next decade,
nothing seems to threaten the supremacy of silicon.
Recently more and more companies have been able to
increase the yield offered by solar cells based on
silicon. In March 2003, BP Solar announced an
efficiency of 18.3%, while Sanyo has already put on the
market a cell with an efficiency of 19.5% [4].
Overheating of a PV module decreases performance
of output power by 0.4-0.5% per 1°C over its rated
temperature (which in most cases is 25 degrees C). This
is why the concept of "cooling of PV" has become so
important [1].
To reduce this phenomenon can be applied on the
back to panel a cooling water system, which can
provide hot water for domestic applications [1].
2. COOLING SYSTEM OF PHOTOVOLTAIC
PANEL
The PV panel made in the present study comprises a
commercial PV module and a cooling system (figure 1).
A USP 150 mono, crystalline solar PV module (1600
mm x 800 mm) (rated 150Wp, 42 V peak voltage) was
adopted to be combined with a water cooling system.
The cooling system adheres to the back of the
commercial PV module. Thermal grease was used
between the plate and the PV module. For better
contact. Below the heat collecting plate, a PU thermal
insulation layer is attached using a fixing frame.
Fig. 1. Section of cooling system
The experimental system was built using the PV
module and cooling system combined with a water
storage tank (Figure 2). To enhance the heat transfer of
cooling system, we installed a DC pump to circulate the
water from the tank through the cooling system.
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For a solar water heater, there exists a critical inlet
water temperature that is proportional to the ambient
temperature, the solar radiation intensity, and the
thermal parameters of the cooling system
Ensuring water circulation pump is controlled by a
microcontroller that collects information on the panel
temperature by two temperature sensors mounted on it.
Fig. 2. Structure of PV system
3. AUTOMATON SYSTEM OF
TEMPERATURE CONTROL
The system designed for a monitoring of the
temperature is a module system made by the Center of
Innovation and Technological Transfer C.I.T.T.
Craiova, [3],[8],[9]. The automaton can measure six
values of temperature in different points (fig. no.3).
There are available values of temperature and humidity
inside it, which are almost equal with the values around
it.
Fig. 3. Automaton for monitoring the temperature
There are presented the temperatures T1… T6 from
the electrical cell. T7 and U it represents the
temperature and the humidity from the vicinity of the
equipment (the sensor is placed inside the equipment).
The temperature values are between –50 +125
Celsius. If the information is not correct, then the
message « ---« appears on the screen. The values for
humidity are between 0…100 %.
If the information for humidity is not available then
the message « ---« appears on the screen.
The equipment, which can be purchased in eight
different sizes, allows the setting of several important
parameters. As a result there can be set:
- XY device address where X, Y ∈ {0, 1, 2,…, 9, A,
B, C, D, E, F};
- start address of the XYZW data where X, Y, Z,
W ∈ {0, 1, 2,…, 9, A, B, C, D, E, F}. It is
recommended not to use an address placed near FFFF
in order to avoid the overstepping of the presentation
format. The data is represented by the succession of
T1, T2, T3, T4, T5, T6, T7, U. The start address of the
data is the address of the T1 temperature;
- the speed of the serial: 4 800, 9 600, 19 200
bits/s ;
- the parity ODD, EVEN or NONE ;
- the highest temperature that activate the signaling
– it belongs to a range between 0…+125 grade C;
- the lowest temperature that deactivate the
signaling – it belongs to a range between 0…+125
grade C.
The interface for the user is assured through an
alphanumeric display and a three button keyboard.
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AUTOMATIC SYSTEM
COOLING OF
PANEL
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AUTOMATIC
SYSTEM FOR
FOR COOLING
OF PHOTOVOLTAIC
PHOTOVOLTAIC PANEL
The interface for the process is made through a four
connectors placed on the low area and another
connector placed on the right area.
The automaton is made up of two modules:
- the slave module that scans the seven temperature
values and one humidity value;
- the master module receives the data from the
slave module, displays them on an alphanumeric
display and carries out a MODBUS communication
with other numeric systems (automate).
3.1. SLAVE MODULE
The SLAVE module has a central element, the
ATMEGA8 microcontroller [10] (fig. no. 4), U3. Its
reset is carried out by the Q1 circuit, type MCP120.
Because the slave microcontroller sends the data to the
master microcontroller through the serial port, we
have chosen to use one external quartz, Y1, instead of
the internal RC oscillator which is much less stable.
3.2. MASTER MODULE
MASTER Module has been developed with
ATMEGA128 microcontroller [11] (fig. 3). An
efficient reset is carried out by the circuit no.2
(MCP120). As the microcontroller is SMD type
(directly glued to the rear plate), for activating the
programming function it is necessary to use the
connector J4. The optocouple 3 assures the data serial
transfer from the slave module to the master module.
Having a code memory of 128 Koctets, a RAM
memory of 4 Koctets, an EEPROM memory of 4
Koctets, two serial ports, 53 signals of input/output, up
to 100 000 re-programmings and a very good work
speed (up to 16 MIPS) carried out by a 16 MHz
quartz, ATMEGA128 microcontroller represents an
excellent solution.
3
2
Fig. 5. Cabling of master module - the part with components
Fig. 4. Board with components for slave module
The scan of the temperature transducer is carried
out with some blocks that contain a diode and two
resistors. Thus, the microcontroller works with two
electrical signals associated to an acquisition channel,
even if the temperature transducer has only one data
bidirectional.
The seven signals are available at the level of the
couple 3. The supply of the slave module is carried out
through two DC sources 2 and 6, with galvanic
separation . The source 6, through the signal ON, can
be activated by the master module. Thus, if the master
module considers the data coming from the slave
module is wrong, then it can command its reset by
canceling the supply for a short period of time.
The slave module also contains, among other things,
the command block of the relay 5 and an optocouple
used of resetting the supply of the slave module.
The interface with the user is carried out through a
three button keyboard and through an alphanumeric
display with two rows with 16 characters each (fig.
no.6).
Fig. 6. Cabling of master module – the part with junctions
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3.3. RS 485 - RS 232 ADAPTOR MODULE
The automaton can function also independently
from a network by connecting it to a computer through
a RS485-RS232 adaptor module. Such a module
contains a TTL-RS232 driver (3), a TTL-RS485 driver
(2) and a monostable circuit (4) (fig. 7).
The presence of data fluxes is highlighted by the LED-s
D3 and D4. The LED D2 shows that the supply is on.
The design structure has galvanic separation and it can
function with a transfer rate up to 115 kbits/s.
1
2
3
4
The description of the pins:
GND - mass
DQ - Input/Output Data
VDD - supply
The sensor resolution can be set to a value between
9 and 12 bits. The temperature conversion at 12 bits is
carried out in a maximum period of time of 750 ms.
The sensor contains two registers of 8 bits each for
stocking the minim and the maxim alarm levels (TH şi
TL) and another register through which the user can
set the temperature conversion in digital format of 9,
10, 11 or 12 bits. This is the fact that sets the
incrementation pace of the measured values: 0.5, 0.25,
0.125 and 0.0625°C.
The implicit resolution is of 12 bits.
4. EXPERIMENTAL RESULTS
In order to test the automatic system for cooling of
photovoltaic panel in real condition, we have made an
experimental PV system.
The general view of the experimental PV system is
shown in fig. no.9.
Fig. 7. RS485-RS232 adaptor module
The supply of the module is made through the USB
port of the computer. The result is a portable small
product.
2
3.4
3.4. TEMPERATURE SENSOR
1
DS18B20 temperature sensor is made by Dallas
Semiconductors company [12] and it needs no other
parts for producing the signal and it can measure
temperatures between -55 °C and +125°C with a
precision of ± 0.5% in a temperature range of -10°C
… + 85°C.
3
Fig. 9. Experimental PV system
The description of the components:
1- PV panel;
2- Panel of automation;
3- Electrical equipaments of PV system.
According to figure 10, the three temperature
sensors where installed in this way:
T1 - the sensor placed in the extreme right side of
the PV panel;
T2 - the sensor placed in the center of PV panel;
T3 - the sensor placed in the extreme left side of the
PV panel;
Fig. 8. Temperature sensor: a) overall view; b) pins configuration
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PANEL
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OF PHOTOVOLTAIC
PHOTOVOLTAIC PANEL
T3
T2
T1
To emphasize the power consumption of the pump
that provides cooling PV panel were read every 5
minutes the values of voltmeter and ampermeter
connected in circuit pump, electric power was then
calculated, values resulting graphical form in figure
no.12.
Fig. 10. Location of sensors on the PV panel
Fig. 12. Evolution of Power of pump
The experimental results consisted of monitoring the
temperature values from the three sensors mounted on
absorber plate of the PV panel cooling system.
Experiments were made on 13.06.2012date, between
12.00 and 13.00 time, the results are presented
graphically in figure no.11.
From the graph we can see that the average power
absorbed by the circulation pump in the cooling system
is insignificant, about 16W.
Fig. 11. Evolution of temperatures on the PV panel
Prescribed temperature at the initial moment was
37oC.
Is observed from the graph that the PV panel
temperature oscillates around these values with a
hysteresis of ± 1 °C during the period 0-15min. This
was done automatically by the system developed, which
allowed the pump start and stop according to the
prescribed temperature for PV panel.
The next time 15-60min, prescribed value of
temperature change in value of 37 ° to 38 ° C value.
Is observed in the graphic is also increased by about
1 °C panel temperature.
5. CONCLUSIONS
From the graphs of experimental results it is observed
that:
PV panel temperature values evolve around the
prescribed values;
PV panel is hotter in the center than in the
extremities;
PV panel temperature values are similar to the
extremities;
The power absorbed by pump is insignificant
compared with the advantages of cooling system.
In conclusion, the experimental results emphasize
the good side of a PV system operation and on the other
hand, accuracy and efficiency of the cooling system
designed for photovoltaic panel that can be applied
successfully in domestic solar applications.
Acknowledgment
This work was supported by the strategic grant
POSDRU/89/1.5/S/61968, Project ID 61968 (2009), cofinanced by the European Social Fund, within the
Sectorial Operational Programme Human Resources
Development 2007-2013.
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2012 - 2012
_____________________________________________________________________________________
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ELECTRICE,
ediţia–XVI,
SUCEAVA
BIBLIOGRAPHY
[1] Alboteanu, L., Increase efficiency of stand alone photovoltaic
systems by reducing temperature of cells, Annals of the
"Constantin Brancusi" University of Targu Jiu, Engineering
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Brancusi" Publisher.
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1842-4856, pp. 15-24, "Academica Brancusi" Publisher.
[3] Alboteanu, L, Ocoleanu, F., Novac, Al., Manolea, Gh.,
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Craiova, seria Inginerie Electrică, Nr. 34, 2010, vol. I, ISSN
1842-4805, pp. 184-189. Editura Universitaria.
[4] Gonzalo C., G., Heat transfer in a photovoltaic panel, Project
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About the authors
As. PhD. Eng. Ionel-Laurenţiu ALBOTEANU
University of Craiova
email:lalboteanu@em.ucv.ro
Graduated from the University of Craiova, Faculty of Electromechanical Engineering -2004, graduate master studies in
"Electromechanically Systems Complexes" specialization-2006, PhD engineer since 2009. It is currently a teacher at the
Faculty of Electrical Engineering.
Prof. PhD. Eng. Gheorghe Manolea
University of Craiova
email:ghmanolea@gmail.com
Graduated from the University of Petrosani-1970, PhD engineer since 1981, professor at the University of Craiova, Faculty
of Electromechanical Engineering. Leader in doctoral field "electrical engineering". Director of the Center for Innovation
and Technology Transfer.
Phd. Eng. Alexandru Novac
SC PROMAT SA Craiova
email:alexandru_novac@yahoo.com
2004 University of Craiova, PhD in Electrical Engineering, theme of thesis: "Digital command of electromechanical drive
with asynchronous motors";1996 University of Craiova, Faculty of Electromechanical Engineering, diploma of Master in
"Command of Industrila Robots " specialization; 1995 University of Craiova, Faculty of Electromechanical Engineering,
diploma of Engineer in "Electro mechanics" specialization; It is currently an engineer at SC PROMAT SA Craiova.
Eng . Constantin ŞULEA,
University of Craiova
email:constantin.sulea@gmail.com
Graduated from the University of Craiova, Faculty of Electromechanical Engineering -2007, graduate master studies in
“Engineering and management and environmental quality" specialization. It is currently a PhD student in doctoral field
"electrical engineering"
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