study on solar panels

7/29/2019 Study On Solar Panels

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1. INTRODUCTIONNowadays, most of the worlds energy (80%) is produced from fossil fuels.

Massive exploitation is leading to the exhaustion of these resources and imposes a

real threat to the environment, apparent mainly through global warming and

acidification of the water cycle. The distribution of fossil fuels around the world is

equally uneven. The present system as it is cannot be maintained for more than two

generations [5]. The world faces a big problem of depletion of conventional

sources of energy which have to be replaced by new ones. Renewable energy is

one of the most promising alternatives to the above problems. Photovoltaic panels

in particular can provide a good source of producing clean electricity. Solar

irradiance is a key driving force of the Earth. It is also ultimately the source of all

energy supplies except for nuclear energy. Photo voltaic (PV) arrays convert solar

irradiance directly into electrical energy through a solid-state system[8].

The efficiency of the solar panel decreases with increase in cell temperature

[TC] since the efficiency is inversely proportional to the panel temperature. The

cell temperature of PV module is increased because a large part of the solarradiation is not converted into electrical energy but is absorbed by the panel as

heat[5,8]. Irreversible damage of PV cells also occurs due to increase in cell

temperature [TC]. Hence cooling is essential for obtaining higher PV panel

efficiency as well as to prevent irreversible damage of PV panel. The cooling of

photovoltaic (PV) cells is a problem of great practical significance. However, the

high cost of solar cells is an obstacle to expansion of their use. The technique used

for cooling of PV panel should be simple, reliable, minimal in power consumption

and relatively inexpensive.


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PV cooling has the potential to reduce the cost of solar energy in three ways.

First, the electrical efficiency of PV cells decreases with temperature increase.

Cooling can improve the electrical production of standard flat panel PV modules.

Second, cooling makes possible the use of concentrating PV systems. Cooling

keeps the PV cells from reaching temperatures at which irreversible damage

occurs, even under the irradiance of multiple suns. This makes it possible to

replace PV cells with potentially less expensive concentrators. Finally, the heat

removed by the PV cooling system can be used for building heating or cooling, or

in industrial applications. The main focus of this paper is on temperature

distribution and its effect on efficiency of the PV module with and without cooling.

1.1. SOLAR IRRADIANCEProducing an enormous amount of energy by fusion, the Sun radiates 3.9

1026 W. Sun is considered as a black body due to its high surface temperature.

Most of the radiation emitted is in the visible spectrum. The Earth, also acting as a

black body, absorbs a fraction of this incident shortwave radiation. The

atmosphere, and snow and ice cover on the ground reflect about 30% of this

incident radiation back to space [8].

There is a distinction between direct and diffuse radiation. When it comes

directly from the sun it is known as direct radiation. When the radiation is scattered

by the atmosphere back to Earth it is called diffuse radiation. On an annual basis,

about half of the radiation is direct and the other half is diffuse. On a clear sunny

day, the power density of is approximately 1kW/m2[8]. This number is lower on

overcast days and in the winter. As expected, annual solar irradiance is greatest in

the Equatorial region and in high sunny deserts.


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The solar energy received by Earth is more than 10,000 times the current use

of fossil fuels and nuclear energy combined [2]. This means that harnessing such a

large potential energy source has the potential to replace a significant amount of

carbon based fuels thus reducing the amount of carbon dioxide emitted

anthropogenically.

1.2. PV PANELThe photovoltaic effect was first discovered by the physicist Edmund

Becquerel in 1839 [8]. He noticed an increased in voltage from his wet-cell battery

when its silver plates were exposed to sunlight despite that, this technology is

considered to be a very recent one. The first PV cell was constructed by Fritts in

1941 with an efficiency of 1%. In 1954, semiconductors were first introduced to

PV cells, increasing their efficiency to 6% and later to 11%[8]. Solar PV panels

have been used almost exclusively on all satellites since 1958 and on several other

space projects. PV panels are used as the Primary electricity source in space

missions and satellites. The cost of producing electricity for house applications has

dropped dramatically and PV panels are becoming more and more economic

viable.

The conversion of solar energy to electrical and thermal energy has been

practiced for many years. In order to convert the solar energy to electrical, PV

panels are used. A basic solar PV panel consists of connected PV cells, which

contain a semiconductor material covered by protective glass connected to a load.

Photovoltaic panels use the photoelectric effect in order to convert solar energy

directly into electrical energy [5]. When sunlight hits the semiconductor, electrons

become excited. These excited electrons are separated by an internal field inherent

in the semiconductor and collected into an external circuit generating electricity.


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Photovoltaic panels convert solar radiation to electricity with efficiencies in

the range of 6% to11% [8], depending on the type of the cell. Polycrystalline

silicon solar cells offer the highest range of possibilities for applications. This is a

consequence of their modest price relative to the mono-crystalline silicon cells, and

their considerable stability and efficiency (about 15%). Furthermore, these cells are

sold in the form of panels having dark blue appearance which is aesthetically

pleasant.

When the temperature of a photovoltaic module is increased, the efficiency

drops. This can typically result in an efficiency drop off of 0.5% per C increase in

the cell temperature [5, 8]. The operating temperature is increased because a large

part of the solar radiation is not converted to electricity but is absorbed by the

panel as heat [4]. Natural circulation of air is the easiest and cheapest way to

remove this heat from the panel and consequently increase the efficiency.

2. LITERATURE REVIEWMelanie D. Zauscher [2006] explained the necessity of PV module cooling

[8] in his work Solar Photo Voltaic Panel from a heat transfer perspective. The

efficiency of PV panel is inversely related to temperature of PV panel. Electrical

efficiency (electrical) was calculated analytically from ambient temperature and solar

irradiance through suitable analytical modeling . The temperature of PV panel is

reduced by adopting active cooling technique. In this technique a duct containing

fins are attached at the rear surface of PV panel. Water is circulated inside the duct

using a pumping process, hence it is a type of active cooling system. The thermal

efficiency was found to be decrease with increase in inlet water temperature. The

temperature of PV panel is reduced by forced convection.


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Bryce Cruey , Jordan King and Bob Tingleff [2006] developed methods for

cooling the PV panel by using ducts attached to theback-plate Experiments was

done with ducts having with and without fins[4]. The experiment was repeated by

varying process parameters such as cooling fluid velocity, fin thickness, fin

spacing and fin length. The resultant decrease in cell temperature and efficiency

increase was noted. It was found that induced turbulent flow in the cooling duct

causes greater heat transfer from the panel, which increases the panels electrical

output and efficiency. Changing the fin conductivity has little impact on panel

output.

Bjornar Sandness and John Rekstad developed photovoltaic/thermal (PV/T)

collector with a polymer absorber plate. Polymer heat absorber plate is attached to

the back plate of PV panel[3]. This heat absorber plate is used for collecting excess

heat energy in the PV panel. Experimental and analytical modeling for PV/T

collector shows the system temperature as close to operation temperature. The

PV/T collector is compared with pure thermal absorber and it was found that the

PV/T collector had reduced thermal efficiency. The reduced thermal efficiencyresults in cooling of PV panel since lower-temperature operation of heat collector ,

consequently efficiency of PV panel is increased.

Efstratios Chaniotakis [2001] analyzed the water cooled PV and the air

cooled PV panels. The former uses water in order to cool the panel while the latter

uses air as the coolant .Water and air is circulated inside the duct attached to back-

plate of PV module. Naturally ventilated panels and water cooled panels canprovide higher efficiencies than conventional ones. The system is analyzed for

both water cooled and air cooled PV systems and compare them in order to reveal

the most promising. Furthermore, by altering various physical parameters of the

heat exchanger in the water PV system, the maximum efficiency is aimed. This


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information can be used in maximizing the efficiency of any collector design.

Various important characteristics that a conventional PV can provide, such as the

power, are calculated and compared to those of water cooled PV. The direct

comparison of both air cooled and water cooled systems was done in order to

reveal advantages and disadvantages. The results showed that the most efficient

and promising system is the water cooled photovoltaic [5]. Such a system proved

to be feasible. Furthermore it was clearly shown that altering various parameters of

the system has as a result different efficiencies-output.

A. Shahsavar, M.Salmanzadeh, M.Ameri and P. Talebizadeh (2011)

developed building integrated photovoltaic-thermal (BIPVT)for using the cooling

potential of ventilation and exhaust air in buildings for cooling the photovoltaics

panels and also by heating the ventilation air by heat rejection of PV panel.

Mathematical modeling was done for this system and the equation for efficiency of

the PV panel is derived [10]. The efficiency thus derived is a function of cell

temperature (Tc). Hence the efficiency of PV panel can be directly calculated from

the cell temperature (Tc). The results showed that, the exhaust and ventilation air in

heating ventilating air conditioning system can be used as the cooling fluid for PV

panels and increases their efficiency.

Anja Royne, Christopher J. Dey & David R. Mills [2006] analysed various

methods that can be used for cooling of PV cells. Different solar concentrators

systems are examined and grouped according to geometry. Theoptimum cooling

solutions differ between single-cell arrangements, linear concentrators and densely

packed photovoltaic cells[1]. Single cells typically only need passive cooling [1],

even for very high solar concentrations. For densely packed cells under high

concentrations (4150 suns), an active cooling system is necessary, with a thermal

resistance of less than10-4 Km2/W. Only impinging jets and micro-channels have


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been reported to achieve such low values. Two-phase forced convection would

also be a viable alternative.

Gur Mittelman,Aiman Alshare, Jane H. Davidson [2009] developed new

approach for temperature regulation, suitable for rooftop integrated PV, involves

fitting an open channel beneath the PVmodule. The panels are cooled by radiation

and free convection as ambient air rises through the channel. A scale analysis and

numericalstudy of PV modules with a back mounted air channel provides heat

transfer rates over a practical range of operating conditions andchannel geometries

[6]. A generalized correlation for the average channel Nusselt number for the

combined convectiveradiative cooling isdeveloped for modified channel Rayleigh

numbers from 102 to 108, channel aspect ratios between 15 and 50 and inclination

anglesbetween 300 and 900. The usefulness of a passive cooling channel to improve

PV efficiency is illustrated by system analyses of typicalPV modules.

Akbarzadeh. A and Wadowski.T [1995] introduced passive method of

cooling through thermosyphoon [2]. The thermosyphoon consists of two heat

exchangers piped together, initially evacuated and filled with refrigerant. The

lower heat exchanger is evaporator, flooded with refrigerant. The upper heat

exchanger contains saturated vapour which acts as condenser. If heat is supplied to

evaporator, part of the liquid evaporates and increases the pressure in whole

circuit. If the upper heat exchanger is externally cooled, refrigerant vapour

condenses and liquid returns by gravity to evaporator. The net result is substantial

heat transfer at faster rate from evaporator to condenser. PV cells are attached to

evaporator of thermosyphoon and condenser is exposed to natural convective heat

transfer. By using thermosyphoon temperature of PV cells are reduced to 46 0C and

efficiency is increased to 10%.


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3. AIM AND OBJECTIVES3. 1. AIM

The first and foremost aim of this work is to study the effect of Temperature

over the efficiency of the PV panel electrical effect, analyse the temperature

distribution over the PV panel and to implement a novel technique for cooling the

PV panel for maintaining an optimum working temperature. The next step is to

increase the efficiency of the PV panel by reducing the operating temperature of

the panel. The irreversible damages caused by the overheating of PV panel is

undesirable, it makes the panel lose its efficiency to a greater extent. Hence the

damage of PV panel should be prevented which could increase the life time of the

panel.

On the whole a complete thermal analysis of Photovoltaic panel is done by

considering all modes of heat transfer and heat generation and suitable cooling

technique is sorted out to maintain the panel in thermal equilibrium. Thus a

sustainable and stable output is achieved with increased efficiency. This stable

mode of operating the panel increases the life cycle of the PV panel. This is

achieved by properly removing the heat generated in the system. The Cooling

system attached to the PV panel removes the heat efficiently. It provides a proper

channel for the flow of heat. The cooling system also helps to maintain a uniform

temperature over the entire panel there by preventing the concentration of heat in a

particular area.


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3.2.OBJECTIVES

The main objective of this work is to get the maximum possible efficiency

from the panel by implementing suitable methods for cooling. The method adopted

should be passive and no energy should be expended in the cooling process as it

makes the cooling process ineffective. Extra energy will be wasted in cooling

process if the process is active and hence passive type of cooling is essential. In

this work Capillarity action is used to circulate the coolant (ie) water in this case.

Water is made to circulate over the back plate by attaching Wicks along the surface

of the back plate. These wicks are placed in the form of grid over the surface. One

end of the wick is immersed inside the water reservoir and the other end is free.

Continuous supply of water should be there for sustained cooling effect. The water

flowing along the wicks gets evaporated due to increase in temperature thereby

producing the required cooling effect. The method used for cooling should be cost

effective and should be cheap. Temperature is recorded over the day for every half

an hour using Thermocouples attached to the surface. Hourly irradiance data and

ambient temperature should be recorded for analysis. A mathematical thermalmodel has to be developed for theoretical analysis. Single degree equation in terms

of cell temperature should be developed. Hourly cell temperature is obtained from

solving the equations. Experimental values should be compared with the

theoretical values for verification. Effect of Temperature over the efficiency should

be obtained from study of the temperature of the photovoltaic panel.

4. DESIGN CONSIDERATION FOR PV COOLING:Only a fraction of the incoming sunlight striking the cell is converted into

electrical energy The remainder of the absorbed energy will be converted into

thermal energy in the cell and may cause the junction temperature to rise unless the


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heat is efficiently dissipated to the environment. The major design considerations

for cooling of photovoltaic cells are listed below:

4. 1. CELL TEMPERATURE

The photovoltaic cell efficiency decreases with increasing temperature. The

cells will also exhibit long-term degradation if the temperature exceeds a certain

limit. The cell manufacturer will generally specify a given temperature degradation

coefficient and a maximum operating temperature for the cell.

4. 2. UNIFORMITY OF TEMPERATUREThe cell efficiency is known to decrease due to non-uniform temperatures

across the cell. In a photovoltaic module, a number of cells are electrically

connected in series, and several of these series connections can be connected in

parallel. Series connections increase the output voltage and decrease the current at

a given power output, thereby reducing the ohmic losses. However, when cells are

connected in series, the cell that gives the smallest output will limit the current.

This is known as the current matching problem. Because the cell efficiency

decreases with increasing temperature, the cell at the highest temperature will limit

the efficiency of the whole string. This problem can be avoided through the use of

bypass diodes(which bypass cells when they reach a certain temperaturein this

arrangement you lose the output from this cell, but the output from other cells is

not limited) or by keeping a uniform temperature across each series connection.

4. 3. RELIABILITY AND SIMPLICITYTo keep operational costs to a minimum, a simple and low maintenance

solution should be sought. This also includes minimising the use of toxic materials

due to health and environmental concerns. Reliability is another important aspect

because a failure of the cooling system could lead to the destruction of the PV

cells. The cooling system should be designed to deal with worst case scenarios

such as power outages, tracking anomalies and electrical faults within modules.


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5. HEAT TRANSFER IN SOLAR PV PANELSPhotovoltaic panels absorb energy and convert it to electricity .Not all this

energy is converted to electricity since the panels are not 100% efficient. Most of

this energy is converted to heat. They passively absorb about 80% of the incoming

solar irradiance as heat. This would not be such a problem if not for a 0.5%

efficiency loss of the solar PV panels associated with a1o C increase of the cell

temperature. Therefore, heat transfer plays an important role in the actual output of

PV arrays .The three modes of heat transfer are involved with the solar PV array.

The main energy input is solar irradiance in the form of shortwave radiation. The

solar panel undergoes heat removal by convection, radiation, and conduction. The

heat removed from the panel is in the form of longwave radiation due to the much

colder temperature of the panel compared to the Sun. A schematic of this heat

transfer mechanism is shown in fig 5.1.

Fig 5.1. Heat Transfer In Solar Pv Panel


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5. 1. CONDUCTIONConduction is the transfer of heat from one part of a substance to another

part of the same substance, or form one substance to another in physical contact

with it. In the case of the PV panel, energy is absorbed by the silicon cell and heat

is conducted to the back and front of the panel via the intervening layers. However,

the heat conducted is negligible because of the small contact area between the solar

array and its structural framework

5. 2. CONVECTIONConvection is the transfer of heat within a fluid by mixing of one portion of

the fluid with another. The movement of the fluid may be caused by differences in

density resulting from the temperature differences as in natural convection (or free

convection), or the motion can be produced by mechanical means as in forced

convection. Heat transfer due to convection in PV panel [6] is given by the

following equation

Qconv= (Tc-T0)/Rconv (1)

Where Qconvheat transfer due to convection,

Tc -cell temperature ,

T0 - ambient temperature,

Rconv -thermal resistance for convection

5. 3. RADIATIONRadiation is the means of heat transfer between distant surfaces. Energy is

carried byelectromagnetic waves. Heat transfer due to radiation in PV panel [6] is

given by the following equation

Qrad = 4T03(Tc-T0) (2)

where Qrad - heat transfer due to radiation,

Tc -cell temperature ,


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T0 - ambient temperature,

-surface emissivity,

- Stephan-Boltzmann constant

6. THERMAL MODEL FOR PV PANEL6.1. THERMAL CIRCUIT FOR PV PANEL

Fig 6.1.1 Thermal Circuit for PV Panel Without Cooling

The temperature of each individual PV cell is a function of its materials,

configuration,time of day, rotation of the Earth and environmental factors such as

wind, temperature,cloud cover and humidity. To determine the temperature of the

solar PV panel a comprehensive heat transfer analysis must be performed.To

examine the best cooling system for a given concentrator requires the development

of a thermal model that will predict the heating and electrical output ofcells. In this

project, a one-dimensional model is used because this is consistent with aclosely

packed set of cells where heat flow is primarily directed in the normaldirection.The

thermal circuit for PV panel without cooling is shown in Fig 6.1. 1.Where I is the


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incoming solar irradiance, Qrad is the heat lost due to radiation Qconv is the heat lost

due to convection, Qair is the heat removed by air. T0 and TC represents ambient

temperature and cell temperature respectively.

The heat removed by air Qair is given by the following equation

Qair= h(Tc- T0) (3)

Where his the heat transfer coefficient for air = 25 W/m2K

Fig.6. 1. 2 Thermal Circuit for PV Panel With Cooling

Water is used for cooling the PV panel through wicks and the heat removed

by water is denoted by Qcool. The thermal circuit for PV panel with cooling is

shown in fig 6. 1.2. The heat removed by water is given by the following equation

Qcool= h(Tc- T) (4)


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where Qcool - is heat removed by water.

T- is the temperature of the water used for cooling.

h - heat transfer coefficient for water = 30 W/m2

K

6. 2. ELECTRICAL POWER OUTPUTThe cell efficiency varies with both temperature and concentration. There

arevarious models for temperature and concentration dependency found in

literature.Most of the models predict quite similar dependencies in the lower

temperature range; most models assume straight lines. Thedifferent values

predicted arise from the fact that cells have different peak efficiencies. Therefore, a

simple approach is used in this article by assuming a lineardecrease in efficiency

with temperature, and no dependency on concentration. The electrical efficiency

of the PV panel [10] is given by following equation

= a(1-b*Tc) (5)

where is electrical efficiency of the PV panel,where a and b are

parameters describing a particular cell we use the values given in fig 6. 2. 1.The

values of parameters a and b depends cell temperature Tc.

The electrical output Pel is given as

Pel = Tc (6)


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Fig 6.2.1. Comparison of Various Models for Efficiencies with Cell Temperature

6.3ENERGY BALANCE:

If I is the incoming solar irradiance and Qcool is the heat removed by water.

The following equation must be satisfied to achieve thermal equilibrium.

IQrad- Qconv- Pel- Qcool=0 (7)

From equations (1) to (6) it is noted that the values of Q rad, Qconv, Pel and

Qconv are functions of cell temperature (Tc) and ambient temperature (T0) . By

solving the equation (7) the cell temperature (Tc) is obtained from the ambient

temperature (T0). The solar irradiance value (I) is obtained from Indian

meterological department website. The cell temperature thus obtained is theoretical

cell temperature (Tc)theo. The calculation for theoretical cell temperature with and

without cooling is as follows


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6.4.THERMAL MODEL FOR PV PANEL WITHOUT COOLING

Date: 10th March 2012 Time: 10:00AM

T0=280C=301K I=600W/m2

Energy Balance:

I-Qrad-Qconv-Pel-Qcool=0

Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3013(Tc-28) Qrad = 5.288*(Tc-28)

Qrad = 5.288Tc-148.06

Qconv= (Tc-T0)/Rconv Rconv= 0.2*103m2K/W

Qconv=(Tc-28)/ 0.2*103 = .005 (Tc-28)

Qconv = .005Tc-0.14

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2

Qair= h(Tc- T0) h = 25W/m

2k T0=280C

=25(Tc-28)

Qair=25Tc-700

1.02*10-4

*Tc2-30.84Tc+1448.2 = 0

Tc=46.950C


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Time: 10:30AM T0=280C=301K I=698.6W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3013(Tc-28) Qrad = 5.288*(Tc-28)

Qrad = 5.288Tc-148.06


Qconv=(Tc-28)/ 0.2*103 = .005 (Tc-28)

Qconv = .005Tc-0.14

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=280c

=25(Tc-28)

Qair=25Tc-700

1.02*10-4

*Tc2-30.84Tc+1546.8 = 0

Tc=50.160C


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Time: 11:00AM T0=300C=303K I=663.67W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3033(Tc-30) Qrad = 5.394*(Tc-30)

Qrad = 5.394Tc-161.82


Qconv=(Tc-30)/ 0.2*103 = .005 (Tc-30)

Qconv = .005Tc-0.15

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=300C

=25(Tc-30)

Qair=25Tc-750

1.02*10-4

*Tc2-30.95Tc+1575.64 = 0

Tc=50.920C


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Time: 11:30AM T0=320C=305K I=780.1W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3053(Tc-32) Qrad = 5.5*(Tc-32)

Qrad = 5.5Tc-176.04


Qconv=(Tc-32)/ 0.2*103 = .005 (Tc-32)

Qconv = .005Tc-0.16

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=320C

=25(Tc-32)

Qair=25Tc-800

1.02*10-4

*Tc2-30.84Tc+1756.3 = 0

Tc=56.550C


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Time: 12:00 PM T0=320C=305K I=906.52W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3053(Tc-32) Qrad = 5.5*(Tc-32)

Qrad = 5.5Tc-176.04


Qconv=(Tc-32)/ 0.2*103 = .005 (Tc-32)

Qconv = .005Tc-0.16

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=320C

=25(Tc-32)

Qair=25Tc-800

1.02*10-4

*Tc2-31.06Tc+1882.72 = 0

Tc=60.630C


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Time: 12:30PM T0=330C=306K I=923.15W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3063(Tc-33) Qrad = 5.56*(Tc-33)

Qrad = 5.56Tc-183.35


Qconv=(Tc-33)/ 0.2*103 = .005 (Tc-33)

Qconv = .005Tc-0.165

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=330C

=25(Tc-33)

Qair=25Tc-825

1.02*10-4

*Tc2-31.11Tc+1931.7 = 0

Tc=62.100C


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Time: 1:00PM T0=340C=307K I=863.27W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3073(Tc-34) Qrad = 5.61*(Tc-34)

Qrad = 5.61Tc-190.77


Qconv=(Tc-34)/ 0.2*103 = .005 (Tc-34)

Qconv = .005Tc-0.17

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=340C

=25(Tc-34)

Qair=25Tc-850

1.02*10-4

*Tc2-31.17Tc+1904.19 = 0

Tc=61.100C


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Time: 1:30PM T0=350C=308K I=813.37W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3083(Tc-35) Qrad = 5.66*(Tc-35)

Qrad = 5.56Tc-198.3


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.175

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=350C

=25(Tc-35)

Qair=25Tc-875

1.02*10-4

*Tc2-31.22Tc+1935.06 = 0

Tc=61.990C


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Time: 2:00PM T0=350C=308K I=761.81W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3083(Tc-35) Qrad = 5.66*(Tc-35)

Qrad = 5.56Tc-198.3


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.175

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=350C

=25(Tc-35)

Qair=25Tc-875

1.02*10-4

*Tc2-31.22Tc+1835.27 = 0

Tc= 58.790C


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Time: 3:00PM T0=370C=310K I=618.76W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3103(Tc-37) Qrad = 5.77*(Tc-37)

Qrad = 5.77Tc-213.73


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.185

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=370C

=25(Tc-37)

Qair=25Tc-925

1.02*10-4

*Tc2-31.33Tc+1757.67 = 0

Tc= 56.110c


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Time: 3:30PM T0=370C=310K I=510.64W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3103(Tc-37) Qrad = 5.77*(Tc-37)

Qrad = 5.77Tc-213.73


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.185

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=370C

=25(Tc-37)

Qair=25Tc-925

1.02*10-4

*Tc2-31.33Tc+1649.55 = 0

Tc= 52.660C


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Time: 4:00PM T0=370C=310K I=397.53W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3103(Tc-37) Qrad = 5.77*(Tc-37)

Qrad = 5.77Tc-213.73


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.185

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T0=370C

=25(Tc-37)

Qair=25Tc-925

1.02*10-4

*Tc2-31.33Tc+1536 = 0

Tc= 49.050C


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6.5.THERMAL MODEL FOR PV PANEL SYSTEM WITH COOLING

Date: 11th March 2012 Time: 10:00AM

T0=290C=302K I=705.2 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3023(Tc-29) Qrad = 5.34*(Tc-29)

Qrad = 5.34Tc-154.88


Qconv=(Tc-29)/ 0.2*103 = .005 (Tc-29)

Qconv = .005Tc-0.145

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2

Qcool= h(Tc- T) h = 30W/m

2k T=25 0C

=30(Tc-25)

Qcool=30Tc-750

1.02*10-4

*Tc2-35.9Tc+1610.22 = 0

Tc=44.860C


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Time: 10:30AM T0=300C=303K I=695.27 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3033(Tc-30) Qrad = 5.388*(Tc-30)

Qrad = 5.388Tc-161.65


Qconv=(Tc-30)/ 0.2*103 = .005 (Tc-30)

Qconv = .005Tc-0.15

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.5546(1-(1.84*10-4*Tc)

Pel=0.5546Tc-1.02*10-4

Tc2


2k T=26 0C

=30(Tc-26)

Qcool=30Tc-780

1.02*10-4

*Tc2-35.95Tc+1637.07 = 0

Tc=45.540C


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Time: 11:00AM T0=310C=304K I=835 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3043(Tc-31) Qrad = 5.447*(Tc-31)

Qrad = 5.447Tc-168.87


Qconv=(Tc-31)/ 0.2*103 = .005 (Tc-31)

Qconv = .005Tc-0.155

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=27 0C

=30(Tc-27)

Qcool=30Tc-810

1.02*10-4

*Tc2-36.01Tc+1814.02 = 0

Tc=50.380C


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Time: 11:30AM T0=320C=305K I=928.14 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3053(Tc-32) Qrad = 5.447*(Tc-32)

Qrad = 5.5Tc-176.04


Qconv=(Tc-32)/ 0.2*103 = .005 (Tc-32)

Qconv = .005Tc-0.16

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=28 0C

=30(Tc-28)

Qcool=30Tc-840

1.02*10-4

*Tc2-36.06Tc+1944.34 = 0

Tc=53.930C


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Time: 12:00PM T0=330C=306K I=964.73 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3063(Tc-33) Qrad = 5.55*(Tc-33)

Qrad = 5.55Tc-183.39


Qconv=(Tc-33)/ 0.2*103 = .005 (Tc-33)

Qconv = .005Tc-0.165

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=29 0C

=30(Tc-29)

Qcool=30Tc-870

1.02*10-4

*Tc2-36.11Tc+2018.28 = 0

Tc=55.90C


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Time: 12:30PM T0=340C=307K I=943.11 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3073(Tc-34) Qrad = 5.61*(Tc-34)

Qrad = 5.61Tc-190.75


Qconv=(Tc-33)/ 0.2*103 = .005 (Tc-34)

Qconv = .005Tc-0.17

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=30 0C

=30(Tc-29)

Qcool=30Tc-900

1.02*10-4

*Tc2-36.17Tc+2034.03 = 0

Tc=56.240C


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Time: 1:00PM T0=340C=307K I=828.34 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3073(Tc-34) Qrad = 5.447*(Tc-34)

Qrad = 5.61Tc-190.75


Qconv=(Tc-31)/ 0.2*103 = .005 (Tc-31)

Qconv = .005Tc-0.17

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=30 0C

=30(Tc-27)

Qcool=30Tc-900

1.02*10-4

*Tc2-36.17Tc+1919.26 = 0

Tc=53.070C


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Time: 1:30PM T0=350C=308K I=861.6 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3083(Tc-35) Qrad = 5.66*(Tc-35)

Qrad = 5.66Tc-198.29


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.175

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=31 0C

=30(Tc-31)

Qcool=30Tc-930

1.02*10-4

*Tc2-36.22Tc+1990.06 = 0

Tc=54.950C


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Time: 2:00PM T0=350C=308K I=806.7W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3083(Tc-35) Qrad = 5.66*(Tc-35)

Qrad = 5.66Tc-198.29


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.175

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4

*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=31 0C

=30(Tc-31)

Qcool=30Tc-930

1.02*10-4

*Tc2-36.22Tc+1935.16 = 0

Tc=53.440C


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Time: 2:30PM T0=350C=308K I=545.57 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 @=5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3083(Tc-35) Qrad = 5.66*(Tc-35)

Qrad = 5.66Tc-198.29


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.175

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=31 0C

=30(Tc-31)

Qcool=30Tc-930

1.02*10-4

*Tc2-36.22Tc+1674.03 = 0

Tc=46.220C


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Time: 3:30PM T0=350C=308K I=217.89 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3083(Tc-35) Qrad = 5.66*(Tc-35)

Qrad = 5.66Tc-198.29


Qconv=(Tc-35)/ 0.2*103 = .005 (Tc-35)

Qconv = .005Tc-0.175

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=31 0C

=30(Tc-31)

Qcool=30Tc-930

1.02*10-4

*Tc2-36.22Tc+1346.35 = 0

Tc=37.170C


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Time: 4:00PM T0=340C=307K I=355.95 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3073(Tc-34) Qrad = 5.61*(Tc-34)

Qrad = 5.66Tc-190.75


Qconv=(Tc-34)/ 0.2*103 = .005 (Tc-34)

Qconv = .005Tc-0.17

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=30 0C

=30(Tc-30)

Qcool=30Tc-900

1.02*10-4

*Tc2-36.22Tc+1990.06 = 0

Tc=39.950C


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Time: 4:30PM T0=330C=306K I=224.55 W/m2

Energy Balance:


Qrad = 4T03(Tc-T0) =0.855 =5.67*10

-8W/m2K4

= 4*0.855*5.67*10-8*3063(Tc-33) Qrad = 5.55*(Tc-33)

Qrad = 5.55Tc-183.39


Qconv=(Tc-33)/ 0.2*103 = .005 (Tc-33)

Qconv = .005Tc-0.165

Pel = Tc = a(1-b*Tc) a=0.5546 b=1.84*10-4K-1

Pel = 0.555(1-(1.84*10-4*Tc)

Pel=0.555Tc-1.02*10-4

Tc2


2k T=29 0C

=30(Tc-29)

Qcool=30Tc-870

1.02*10-4

*Tc2-36.22Tc+1990.06 = 0

Tc=35.40C


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7. EXPERIMENTAL METHODThe aim of this project is to decrease the cell temperature of the PV panel.

The wicks are used to circulate water throughout the back-plate of PV panel along

the wicks by capillary action. One end of wicks is placed inside a water reservoir

and it is taken along the back-plate by touching the surface. The other end is left

free. By capillary action water is transferred to dry surface from wet surface which

enables the required cooling action.

7. 1. COMPONENTS

Fig 7.1. 1 Solar PV Panel

The system consists of a PV panel , a digital multi-meter ( to measure the

panel output such as current and voltage), a 1000 Carbon resistor, a six channel


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thermocouple with indicator ( to measure the temperature of PV panel ) , wicks

and water reservoir.

The PV panel used in this project is shown in the Fig. 7. 1. The dimension of

PV panel is 35 X 27.3 cm. The PV panel is made up of single crystalline silicon

cells which are connected in series. The rated voltage and power of PV panel are

6V and 5W respectively.

Fig 7. 1. 2. K-type thermocouple attached to PV panel

K-type thermocouple is used for temperature measurement. K- type

thermocouple probe and six channel digital temperature indicator is used for

measuring temperature at 6 various points on the bottom surface of the panel. The

K-type thermocouple measures temperature between 00C to 12000C effectively.

Hence K-type thermocouple is used for this system. The K- type thermocouple

attached to the back-plate of PV panel is shown in Fig 7. 1. 2.


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The fig 7.1. 3.shows six channel digital temperature indicator used for

temperature measurement. The K-Type thermocouple probes are connected to

indicator. Small change cell temperature is shown in digital display of temperature

indicator

Fig 7. 1.3. Six Channel Temperature Indicator.

24 37 58 37

Fig. 7. 1. 4. Configuration of WicksGrid Structure

3

0

0

228

Wicks

(Grid

structure)

Back plate


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The wicks are attached to the back plate of PV panel by using plastic strips

and tape. The width of the wicks is 2.1 cm. The wicks are placed in the form of

grid. The fig 7.1.4 shows the configuration of wicks placed below the PV panel.

7. 2. METHODOLOGY:

The full experimental setup for cooling of PV pannel is shown in fig 7. 2. 1

The wicks are placed below the PV panel in grid like structure as explained earlier.

The K-type thermocouple is also attached to back plate of PV panel for the

meadurement of cell temperature .

Fig 7. 2. 1. PV Panel withCooling by Wicks

The temperature of PV panel is noted for every hour in a day from the digital

temperature display. The average value of this temperature is taken as cell

temperature (TC) with cooling. The cell temperature thus calculated is the actual

cell temperature.


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The same procedure explained above is repeated for the temperature

measurement of PV panel without cooling by removing wicks from the PV panel.

The average value of the temperatures gives the cell temperature (Tc) without

cooling.

The PV panel output leads are connected to digital multimeter through a

1000 carbon reisistor for voltage measurement.

The thermal efficiency of PV panel [10] is calculated from the equation

given below as

= 0.125 (1- 0.006 (TC-298)) (9)

Where - efficiency of PV panel,

TC- cell temperature of PV panel in K.

From these observations the temperature distribution of PV panel with and

without cooling is studied as follows.

8. RESULTS AND DISCUSSION:This study involves the monitoring of temperature over a day time on hourly

basis, along with temperature other parameters like Current, Voltage and Power.

The ambient temperature and Irradiance values were also recorded hourly from the

Indian Metrological Department Website. The Effect of temperature over the

output of the efficiency is also noted. The efficiency of the PV panel is also

observed. The Observations were made and results were presented in the form of

table. The table 8.1 makes a comparison between actual and theoretical values ofcell temperature.


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Table8. 1. Comparison of Actual And Theoretical Values of Cell Temperature

(Without Cooling)

Date: 10th March 2012(without cooling) Resistance:1000

S.NO TIME AMBIENT

TEMPERATURE

IRRADIANCE CELL TEMPERATURE

TC(C)

T0(C) I(W/m

2) ACTUAL THEORITICA

1 10:00A.M 28 600

42.8

46.95

2 10:30A.M 28 698.641.4

50.16

3 11:00A.M 30 663.6742.2

50.92

4 11:30A.M 32 780.149.4

56.55

5 12:00P.M 32 906.5247.6

60.63

6 12:30P.M 33 923.1548

62.1

7 1:00P.M 34 863.27 47.8 61.1

8 1:30P.M 35 813.3748

62

9 2:00P.M 35 761.8145.2

58.79

10 3:00P.M 37 618.7643.6

56.11

11 3:30P.M 37 510.6241.4

52.66

12 4:00P.M 37 397.53

43.4

49.05


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Table 8. 2. Comparison of Actual and Theoretical Values of Cell Temperature

(With Cooling)

The temperature values were noted from the readings shown by the display

connected with the K-type thermocouple. The current and voltage values were

recorded from the Multi-meter connected across the resistive load. Temperature

based efficiency relations give the output efficiency for each temperature recorded.

DATE: 11th March 2012(with cooling) Resistance:1000

S.NO TIME AMBIENT

TEMPERATURE

IRRADIANCE CELL TEMPERATURE

TC(C)

T0(C) I(W/m

2) ACTUAL THEORITICAL

1 10:00A.M 29 705.2 43.6 48.07

2 10:30A.M 30 695.2751.4

48.55

3 11:00A.M 31 835 45.8 54.17

4 11:30A.M 32 928.14 58.4 58.10

5 12:00P.M 33 964.73 51.4 60.23

6 12:30P.M 34 943.11 58.2 60.40

7 1:00P.M 34 828.34 61.2 55.8

8 1:30P.M 35 861.6 55.6 58.79

9 2:00P.M 35 806.7 47.4 57.03

10 2:30P.M 35 545.57 48 48.66

11 3:30P.M 35 217.89 45.4 38.16

12 4:00P.M 35 355.95 44.4 42.60

13 4:30P.M 33 224.55 37.2 36.43


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Table 8. 3. Hourly Temperature Variation over PV Panel (Without Cooling)

Date: 10th

March 2012 Resistance:1000

S.NO TIME TEMPERATURE OF PV

PANEL

(c)

AMBIENT

TEMPERATURE

(c)

OUTPUT

VOLTAGE

OUTPUT

CURRENT

OUTPUT

POWER

EFFICIENCY

T1 T2 T3 T4 T5 Tavg V AMPS W %

1 10:00A.M52 53 58 44 55 52.4 28 8.9 8.9 0.07569 11.912

2 10:30A.M55 55 58 47 61 55.2 28 8.76 8.76 0.063362 10.235

3 11:00A.M54 54 56 47 60 54.2 30 7.84 7.84 0.057456 10.31

4 11:30A.M56 55 59 44 56 54 32 9.02 9.02 0.076038 10.325

5 12:00P.M51 53 55 55 67 56.2 32 7.47 7.47 0.06989 10.16

6 12:30P.M 56 55 61 59 73 60.8 33 8.54 8.54 0.073788 9.8157 1:00P.M

58 60 64 57 69 61.6 34 8.5 8.5 0.0785 9.755

8 1:30P.M60 62 66 53 62 60.6 35 8.56 8.56 0.069389 10.325

9 2:00P.M57 58 61 49 60 57 35 8.8 8.8 0.072761 10.1

10 3:00P.M47 45 51 47 54 48.8 37 8.4 8.4 0.065934 10.715

11 3:30P.M52 53 50 45 53 50.6 37 8.45 8.45 0.056852 10.58

12 4:00P.M50 50 44 38 47 45.8 37 6.6 6.6 0.062568 10.94


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Table 8. 4. Hourly Temperature Variation over PV Panel (With Cooling)

DATE: 11th

March 2012 (With Cooling) Resistance: 1000

S.NO TIME TEMPERATURE OF PV

PANEL

(c)

AMBIENT

TEMPERATURE

(c)

OUTPUT

VOLTAGE

OUTPUT

CURRENT

OUTPUT

POWER

EFFICIENCY

T1 T2 T3 T4 T5 Tavg V AMPS W %

1 10:00A.M46 47 52 44 55 48.8 29 8.9 8.9 0.0792 10.715

2 10.30A.M52 52 57 47 61 53.8 30 8.76 8.76 0.0767 10.34

3 11:00A.M53 53 56 47 60 53.8 31 7.84 7.84 0.0615 10.34

4 11:30A.M48 49 53 44 56 50 32 9.02 9.02 0.0814 10.625

5 12:00P.M57 57 63 55 67 59.8 33 7.47 7.47 0.0558 9.89

6 12:30P.M59 61 68 59 73 64 34 8.54 8.54 0.0729 11.435

7 1:00P.M58 60 63 57 69 61.4 34 8.5 8.5 0.0723 9.77

8 1:30P.M 52 52 57 53 62 55.2 35 8.56 8.56 0.0733 10.235

9 2:00P.M49 50 56 49 60 52.8 35 8.8 8.8 0.0774 10.415

10 2:30P.M50 47 51 47 54 49.8 35 8.4 8.4 0.0706 10.64

11 3:30P.M46 45 50 45 53 47.8 35 8.45 8.45 0.0714 10.79

12 4:00P.M41 40 44 38 47 42 35 6.6 6.6 0.0436 11.225

13 4:30P.M37 38 41 38 42 39.2 33 7.07 7.07 0.0500 11.435


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The observation was carried out for two days. On the first day no wicks were

used for cooling. Temperature was recorded without cooling (Table 3). On the next

day wicks were attached to the back-plate surface and water is allowed to flow

through the wicks and the required cooling action was achieved. Temperature was

recorded as the previous day (Table 4). The temperature obtained on these two

days was compared and considerable cooling was noted.

The output power can be calculated from the current and the voltage

measured during the experiment. The conversion efficiency of the PV panel[10] is

calculated from the following relation.

=0.125(1-0.006(Tc-298))

Where TC is the Cell temperature in K

The efficiency is calculated hourly for every temperature recorded over the

complete day. This efficiency calculation is done for two consecutive days without

cooling and with cooling of PV panel. The efficiency calculated on both days was

compared and the increase in efficiency was noted. The Maximum rise in

efficiency was found to be 1.62%. The maximum temperature decrease was noted

to be around 3.2C. So it is clear that this system is capable of increasing the

efficiency by 2% for every decrease in 4C.

Graphs were plotted between various parameters for comparison and

validation of results. Two graphs were drawn between Temperature distribution in

PV panel and Time. A graph representing the variation of efficiency with the time,

variation of power with time were drawn. Graphs were drawn to compare the

efficiency variation with and without cooling, to compare the obtained values with

theoretical values. A considerable increase in efficiency was noted for this


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configuration of cooling. This increase in efficiency could be further increased by

using improved cooling system. A liquid having higher coefficient of convection

could be used for increasing the efficiency.

Fig8. 1.HourlyTemperature Variation Across The Panel

The graph in fig 8. 1. shows the hourly variation of temperature across the

Photovoltaic panel. The dotted line shows the average temperature of the back

plate. The Variation of the ambient temperature for every hour is also indicated inthe graph. It is seen that the temperature rises to maximum at the midday and falls

down. These observations were made without the cooling effect (i.e.) without

wicks

0

10

20

30

40

50

60

70

80

Temperature(C)

Time

10th March 2012(Without cooling)

T1

T2

T3

T4

T5

Tavg

To


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Fig 8. 2. HourlyTemperature Variation Across The Panel (With Cooling)

The graph in fig 8. 2. depicts the temperature variation across the PV Panel

with the cooling (i.e.) with the wicks attached to the back plate. The graph shows

the variation of ambient temperature with time. It is evident from the graph that the

temperature is almost uniform. Cooling reduces large variations in temperature. It

is also noted that there is considerable decrease in temperature due to cooling.

0

10

20

30

40

50

60

70

80

TemperatureofPVPanel(

C)

Time

11th March 2012(with cooling)

T1

T2

T3

T4

T5

Tavg

To


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Fig 8. 3.Comparision of cell temperature with and without cooling

The graph in fig 8. 3shows Comparision of cell temperature with and

without cooling. This clearly shows the decrease in temperature after cooling.

40

42

44

46

48

50

52

54

56

58

60

Temperature(C)

Time

Temperature comparision

without cooling

with cooling


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Fig8. 4.Comparison of Efficiency With And Without Cooling

The graph in fig 8. 4.shows the variation of efficiency with and without

cooling and the efficiency was compared in both cases. The increase in efficiency

is evident from the graph. This graph was developed from the temperature graph

and the inverse relation is clear from the graph. The efficiency graph is the inverse

of temperature graph. It confirms the inverse relationship of cell temperature (TC)

and efficiency ()

9.5

9.7

9.9

10.1

10.3

10.5

10.7

10.9

EFFICIENCY(%)

TIME

Efficiency Comparsion

with cooling

Without cooling


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Fig8. 5.HourlyVariation of Power With And Without Cooling

The variation in power with and without cooling is shown in the graph in the

fig 8. 5. This graph shows the electrical characteristics of the PV Panel. The power

output is obtained from the current and voltage values. The power reaches

maximum at the mid-day and decreases as time goes on. The power is constant

along the day time.

0.05

0.055

0.06

0.065

0.07

0.075

0.08

POWER(W)

Time

Power comparision

With cooling

Without cooling


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Fig 8. 6.Comparison of Actual And Theoretical Temperatures Without Cooling

The above graph shows the concurrence of the actual and theoretical values

of temperature, thereby validating the results obtained. The values obtained from

the experiment go well with the theoretical values obtained from thermal model.

This graph was drawn without adopting cooling technique.

0

10

20

30

40

50

60

70

Te

mperature(C)

Time

ACTUAL VS THEORITICAL

10th March 2012

Theoritical

Actual


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Fig 8. 7. Comparison of Actual And Theoretical Values of Temperature With

Cooling

The above graph shows the concurrence of the actual and theoretical values

of temperature, thereby validating the results obtained. The values obtained from

the experiment go well with the theoretical values obtained from thermal model.

This graph was drawn by adopting cooling technique.

0

10

20

30

40

50

60

70

Temperature(C)

Time

ACTUAL VS THEORITICAL

11th March 2012

Theoritical

Actual


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9. CONCLUSIONThe temperature distribution of PV panel with and without cooling is

studied. The actual cell temperature of PV panel is compared with theoretical cell

temperature calculated from thermal modeling. The cooling of PV panel is

achieved by using wicks through capillary action. The efficiencies of PV panel

with and without cooling were compared. Significant cooling of PV panel is

observed, since the temperature of PV panel is decreased by using the cooling

system. The increase in efficiency of PV panel with cooling makes the system

feasible.

The system used for cooling removes the excess heat generated in the PV

panel through natural convection using water. The cooling system is passive, since

no power is consumed for circulating water through wicks. This system is simple

and reliable in nature. The cost of the cooling system is very low when compared

to other active cooling systems. Further research is required in order to decrease

the cell temperature and to increase the efficiency of PV panel. This study can be

further extended by using liquids higher coefficient of convection. Applications of

Nano fluids in could be the best alternative for cooling of Photovoltaic panels.

Nano fluids are efficient in removing heat through convection, applications of

Nano fluids takes this technique a step ahead of time. Further a proper structured

arrangement wicks and liquid flow aids better cooling.


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10.REFERENCES1. Anja Royne, Christopher J. Dey , David R. Mills (2004), Cooling Of

Photovoltaic Cells Under Concentrated Illumination: A Critical Review,

School of Physics , University of Sydney, Sydney, Australia, pp.452- 481

2. A.Akbarzadeh and T.Wadowski (1995) , Heat Pipe Based Cooling SystemFor Photovoltaic Cells Under Concentrated Solar Radiation, Energy

conservation and renewable energy group, Department of Mechanical

Engineering, Royal Melbourne Institute of Technology, Victoria, Australia,

pp.84-86

3. Bjornar Sandness and John Rekhstad (2006) A Photovoltaic/Thermal(Pv/T) Collector With A Polymer Absorber Plate; Experimental Study And

Analytical Model, Department of Physics, University of Osla, Norway,

pp.2-8.

4. Bryce Cruey ,Jordan King, Bob Tingleff (2006), Cooling of PhotovoltaicCells pp.2-32.

5. Efstratios Chaniotakis (2001) ,Modelling and Analysis of Water CooledPhotovoltaics, Energy Systems and the Environment, pp.1-54.

6. Gur Mittelman, Aiman Alshare, Jane H. Davidson (2009), A model andheat transfer correlation for rooftop integrated photovoltaics with a passive

air cooling channel, Department of Mechanical Engineering, University of

Minnesota, , Minneapolis ,USA, pp.- 1150-1154

7. J. M. Olchowik, S. Gulkowski, K. J. Cielak, J. Bana, I. Jwik, D.Szymczuk, K. Zabielski, J. Mucha, M. Zdrojewska, J. Adamczyk, R.

Tomaszewski (2006) , Influence of temperature on the efficiency of mono-

crystalline silicon solar cells in the South-eastern Poland conditions ,

Material sciencePoland, vol.24, No.4, pp.2-6


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8. Melanie D. Zauscher(2006),Solar Photovoltaic Panels From aHeatTransfer Perspective, Department of Mechanical and Aerospace

Engineering, University of California, San Diego, pp.1-6.

9. Hughes, Ng Ping Sze Cherisa, and Osman Beg (2011) Computational Studyof Improving the Efficiency of Photovoltaic Panels in the UAE, World

Academy of Science, Engineering and Technology, pp. 278-282.

10.A. Shahsavar, M. Salmanzadeh, M.Ameri, P.Talebizadeh(2011) , Energysaving in buildings by using the exhaust and ventilation air for cooling of

photovoltaic panels, Department of Mechanical Engineering, Shahid

Bahonar University of Kerman, Iran, pp. 2219-2223.

11.H.A.Zondag, W.G.J. van Helden, M.J.Elswijk, M.Baker (2004), PV Thermal Collector development - an overview of the lesson learnt, 19th

European PV solar Energy Conference and Exhibition, June 2004, Paris ,

France, pp.2-4

study on solar panels

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