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AUTOMATIC SYSTEM FOR COOLING OF PHOTOVOLTAIC PANEL

Buletinul AGIR nr. 4/2012 ● octombrie-decembrie 1

AUTOMATIC SYSTEM FOAUTOMATIC SYSTEM FOAUTOMATIC SYSTEM FOAUTOMATIC SYSTEM FOR COOLING OF PHOTOVOR COOLING OF PHOTOVOR COOLING OF PHOTOVOR COOLING OF PHOTOVOLTAIC LTAIC LTAIC LTAIC PANELPANELPANELPANEL

As.Eng. Ionel-Laurentiu ALBOTEANU PhD1, Prof. Eng. Gheorghe MANOLEA PhD

1,

Eng. Alexandru NOVAC PhD2, Eng.Constantin ŞULEA

1University of Craiova, Faculty of Electrical Engineering

2S.C. PROMAT S.A.

RRRREZUMAT. EZUMAT. EZUMAT. EZUMAT. lucrarea prezintălucrarea prezintălucrarea prezintălucrarea prezintă o soluţie cu privire la creşterea eficienţei panourilor fotovoltaice prin reducerea pierderilor o soluţie cu privire la creşterea eficienţei panourilor fotovoltaice prin reducerea pierderilor o soluţie cu privire la creşterea eficienţei panourilor fotovoltaice prin reducerea pierderilor 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 rădatorat incălzirii celulelor fotovoltaice. Soluţia constă în aplicarea pe spatele panourilor fotovoltaice a unui sistem de rădatorat incălzirii celulelor fotovoltaice. Soluţia constă în aplicarea pe spatele panourilor fotovoltaice a unui sistem de rădatorat incălzirii celulelor fotovoltaice. Soluţia constă în aplicarea pe spatele panourilor fotovoltaice a unui sistem de răcire cire cire cire cu acu acu acu apăpăpăpă.... FuncţioFuncţioFuncţioFuncţionarea automată narea automată narea automată narea automată sistemsistemsistemsistemuluiuluiuluiului de răcire va conduce lde răcire va conduce lde răcire va conduce lde răcire va conduce la creştere eficienţei panourilora creştere eficienţei panourilora creştere eficienţei panourilora creştere eficienţei panourilor fotovoltaicfotovoltaicfotovoltaicfotovoltaiceeee şi reducerea şi reducerea şi reducerea şi reducerea consumului de energieconsumului de energieconsumului de energieconsumului de energie.... Cuvinte cheie:Cuvinte cheie:Cuvinte cheie:Cuvinte cheie: sistem de răcire, automatizare, panou fotovoltaic, microcontroler, senzor de temperatură ABSTRACABSTRACABSTRACABSTRACT.T.T.T. The paper presents a solution focused on increasing efficiency The paper presents a solution focused on increasing efficiency The paper presents a solution focused on increasing efficiency The paper presents a solution focused on increasing efficiency of photovoltaic panelof photovoltaic panelof photovoltaic panelof photovoltaic panel by reducing losses due to by reducing losses due to by reducing losses due to by reducing losses due to

warming photovoltaic cells. The solution consists in a water cooling system applied to the back of photovoltaicwarming photovoltaic cells. The solution consists in a water cooling system applied to the back of photovoltaicwarming photovoltaic cells. The solution consists in a water cooling system applied to the back of photovoltaicwarming photovoltaic cells. The solution consists in a water cooling system applied to the back of photovoltaic panelspanelspanelspanels.... Automatic operation ofAutomatic operation ofAutomatic operation ofAutomatic operation of the cooling system will lead to increased efficiency of solar panels and reduce energy consumptionthe cooling system will lead to increased efficiency of solar panels and reduce energy consumptionthe cooling system will lead to increased efficiency of solar panels and reduce energy consumptionthe cooling system will lead to increased efficiency of solar panels and reduce energy consumption Keywords:Keywords:Keywords: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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NATIONAL CONFERENCE OF ELECTRICAL DRIVES – CNAE 2012


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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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).

3333.1. SLAVE MODULE.1. SLAVE MODULE.1. SLAVE MODULE.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.

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.

3.2. MASTER3.2. MASTER3.2. MASTER3.2. MASTER MODULEMODULEMODULEMODULE

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.

Fig. 5. Cabling of master module - the part with components

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

2 3

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3.3. RS 485 3.3. RS 485 3.3. RS 485 3.3. RS 485 ---- RS 232 ADAPTOR MODULERS 232 ADAPTOR MODULERS 232 ADAPTOR MODULERS 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.

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.

3.3.3.3.4444. TEMPERATURE SENSOR. TEMPERATURE SENSOR. TEMPERATURE SENSOR. TEMPERATURE SENSOR

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.

Fig. 8. Temperature sensor: a) overall view; b) pins configuration

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. 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;

3

4

2 1

3

2

1

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Fig. 10. Location of sensors on the PV panel

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.

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.

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. 12. Evolution of Power of pump

From the graph we can see that the average power

absorbed by the circulation pump in the cooling system

is insignificant, about 16W.

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), co-

financed by the European Social Fund, within the

Sectorial Operational Programme Human Resources

Development 2007-2013.

T1 T2 T3

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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

series, issue 3/ 2011, ISSN 1842-4856, pp. 15-25, "Academica

Brancusi" Publisher.

[2] Alboteanu, L., Monitoring temperature of photovoltaic

modules, Annals of the "Constantin Brancusi" University

of Targu Jiu, Engineering series, issue 3/ 2010, ISSN

1842-4856, pp. 15-24, "Academica Brancusi" Publisher.

[3] Alboteanu, L, Ocoleanu, F., Novac, Al., Manolea, Gh., Remote monitoring system of the temperature of detachable

contacts from electric cells în revista Analele Universităţii din

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

Report 2009 MVK160 Heat and Mass Transport May 11, 2009,

Lund, Sweden

[5] Huang B. J., Lin T. H., Hung W. C., Sun S., Performance

evaluation of solar photovoltaic/thermal systems, Solar Energy

Vol. 70, No. 5, pp. 443–448, 2001.

[6] Lates, R., Optimisation of the solar collectors’ design for

implementation in the built environment in Romania, Doctorat

Thesis, "Transilvania" University of Brasov, 2010, Brasov,

Romania.

[7] Lates, M., Lates, R., Hansen, P., U., Hybrid Systems

Implementation for Domestic Users, Proceedings of The 2nd

Conference of Sustainable Energy, 3-5th of July, Brasov,

Romania, ISBN 978-973-598-316-1. pp.457-462.

[8] Manolea, Gh., Nedelcut, C., Novac, Al., Ravigan, F.,

Alboteanu, L., The automation and supervision of the

cultivation environment for horticulture products, Annals of

the University of Craiova, seria holticultura, vol. XI, Ed.

Universitaria, 2006, ISSN 1334-1274, pp. 131-133.

[9] Novac, Al., Ravigan, F., Alboteanu, L., Nedelcut, C.,

Humidity measurement in the saturated steam sterilization

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International Conference On Electromechanical

And Power Systems, October 3-6, 2007 - Chişinău,

Rep.Moldova.

[10] *** - Atmega8 User datasheet.

[11] *** - Atmega 128 User datasheet.

[12] *** - Dallas 18B20 Temperature sensor. Datasheet.

About the authors

As. PhD. Eng. Ionel-Laurenţiu ALBOTEANU University of Craiova

email:[email protected]

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


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


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


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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