FLAT-PLATE COLLECTORS

Solar Energy IPhysics 471

2004-1Instructor : Prof. Dr. AHMET ECEVİT

Presented by: YASİN GÜNERİ

TABLE OF CONTENT TABLE OF CONTENT

PAGESPAGES

1)INTRODUCTION 1)INTRODUCTION 3 3

2)FLAT-PLATE COLLECTORS 2)FLAT-PLATE COLLECTORS 55

A.A. ABSORBER PLATE & FLOW PASSAGES ABSORBER PLATE & FLOW PASSAGES 99 B.COVER PLATES B.COVER PLATES 1212 C.ENCLOSURE / INSULATION C.ENCLOSURE / INSULATION 15153)3) PROPER OR PROPER ORIIENTATENTATIIONON AND AND ANGLE ANGLE of of SOLAR COLLECTOR SOLAR COLLECTOR 17 17 A.A. FLAT-PLATR COLLECTORS FACING SOUTH AT FIXED TILT FLAT-PLATR COLLECTORS FACING SOUTH AT FIXED TILT 18 18 B. ONE-AXİS TRACKING FLAT-PLATE COLLECTORS WHIT AXIS ORIENTEB. ONE-AXİS TRACKING FLAT-PLATE COLLECTORS WHIT AXIS ORIENTED D 1919 NORTH-SOUTHNORTH-SOUTH C.C. TWO-AXIS TRACKING FLAT-PLATE COLLECTORS TWO-AXIS TRACKING FLAT-PLATE COLLECTORS 20204) 4) COLLECTOR PERFORMANCE COLLECTOR PERFORMANCE

2121 A. ABSORBED RADIATION A. ABSORBED RADIATION 25 25 B. COLLECTOR HEAT REMOVAL FACTOR B. COLLECTOR HEAT REMOVAL FACTOR 26 26 C. OVERALL HEAT LOSS COEFFICIENT C. OVERALL HEAT LOSS COEFFICIENT 27 275) COLLECTOR EFFICIENCY 5) COLLECTOR EFFICIENCY

29296) APPLICATIONS 6) APPLICATIONS

3232 A.A. DOMESTIC APPLICATIONS DOMESTIC APPLICATIONS 3333

B.B. COMMERCIAL APPLICATTIONSCOMMERCIAL APPLICATTIONS

35 35

7) CONCLUSION 7) CONCLUSION 3737

REFERENCES 38REFERENCES 38

1. INTRODUCTION1. INTRODUCTION

Solar collectors are heat exchangers that use Solar collectors are heat exchangers that use solar radiation to heat a working fluid, usually solar radiation to heat a working fluid, usually liquid or air. They can be classified in three liquid or air. They can be classified in three groups:groups:

- Flat-plate collectors, - Flat-plate collectors, - Evacuated-tube collectors- Evacuated-tube collectors - Focusing collectors.- Focusing collectors.

In flat-plate collectors there is no optical In flat-plate collectors there is no optical concentration of sunlight and they are generally concentration of sunlight and they are generally stationary . In addition to this their outlet temperature stationary . In addition to this their outlet temperature capability is below 100 capability is below 100 °°CC

However to reach higher temparatures evacuated-tube However to reach higher temparatures evacuated-tube collectors and focusing collectors are used. collectors and focusing collectors are used. In In evacuated-tube collectors they use vacuun to reduce evacuated-tube collectors they use vacuun to reduce heat lost and to protect the absorber coating from heat lost and to protect the absorber coating from deteration.By this way they can reach temperatures deteration.By this way they can reach temperatures up to 140 up to 140 °°C and they can collect both direct and C and they can collect both direct and diffuse solar radiationdiffuse solar radiation

And focusing collectors, they are not stable and they And focusing collectors, they are not stable and they follow the sun to get direct radiation; theycan not follow the sun to get direct radiation; theycan not utilize diffuse radiation. And they are also capable of utilize diffuse radiation. And they are also capable of producing high temperatures [1].producing high temperatures [1].

2. FLAT-PLATE COLLECTORS2. FLAT-PLATE COLLECTORS A flat plate collector is basicly a black surface that is placeA flat plate collector is basicly a black surface that is placed d at at

a convenient path of the sun.And a typical flat plate collector a convenient path of the sun.And a typical flat plate collector is a metal box with a glass or plastic cover (called glazing) on is a metal box with a glass or plastic cover (called glazing) on top and a dark-colored absorber plate on the bottom. The sides top and a dark-colored absorber plate on the bottom. The sides and bottom of the collector are usually insulated to minimize and bottom of the collector are usually insulated to minimize heat lossheat loss.[2].[2]

Figure 2.1 gives examples of flat-plate collectorsFigure 2.1 gives examples of flat-plate collectors

Figure 2.1 Flat-plate collectors[3]Figure 2.1 Flat-plate collectors[3]..

Components of a typical flat plate collector:Components of a typical flat plate collector: Absorber plate:Absorber plate: It is usually made of copper,steel or plastic.The It is usually made of copper,steel or plastic.The

surface is covered with a flat black metarial of high surface is covered with a flat black metarial of high absorptance.If copper or steel is used it is possible to absorptance.If copper or steel is used it is possible to apply a selective coating that maximizes the apply a selective coating that maximizes the absorptance of solar energy and minimizes the absorptance of solar energy and minimizes the radiation emitted by plate.radiation emitted by plate.

Flow passages:Flow passages: The flow passages conduct the working fluid through The flow passages conduct the working fluid through

the collector. If the working fluid is a liquid , the flow the collector. If the working fluid is a liquid , the flow passage is usually a tube that is attached to or is a passage is usually a tube that is attached to or is a part of absorber plate. If the working fluid is air , the part of absorber plate. If the working fluid is air , the flow passage should be below the absorber plate to flow passage should be below the absorber plate to minimize heat lssos.minimize heat lssos.

Cover plate: To reduce convective and radiative heat losses from

the absorber , one or two transparent covers are generally placed above the absorber plate.They usually be made from glass or plastic.

Insulation: These are some metarials such as fiberglass and they

are placed at the back and sides of the collector to rduce heat losses.

Enclosure: A box that the collector is enclosed in holds the

componrnts together, protect them from weather, facilitates installation of the collector on a roof or appropriate frame [1].

Here in figure 2.2 we can see components of flat plate Here in figure 2.2 we can see components of flat plate collectors.collectors.

Figure 2.2 Cross Figure 2.2 Cross ssection of a ection of a bbasic asic fflat-lat-pplate late ssolar olar ccollector [ollector [44].].

A. Absorber plate & Flow passagesA. Absorber plate & Flow passages

Copper,which has high conductivity and is corrosion-resistant, Copper,which has high conductivity and is corrosion-resistant, is the material for absorber plates, but because copper is is the material for absorber plates, but because copper is expensive, steel is also widely used. For a copper plate 0.05 expensive, steel is also widely used. For a copper plate 0.05 cm thick with 1.25-cm tubes spaced 15 cm apart in good cm thick with 1.25-cm tubes spaced 15 cm apart in good thermal contact with the copper, the fin efficiency is better thermal contact with the copper, the fin efficiency is better than 97 percent.than 97 percent.

The surface of the absorber plate determines how much of the The surface of the absorber plate determines how much of the incident solar radiation is absorbed and how much is emitted incident solar radiation is absorbed and how much is emitted at a given temperature. Flat black paint which is widely used at a given temperature. Flat black paint which is widely used as a coating has an aas a coating has an abbsorsorpptance of about 95 percent for tance of about 95 percent for incident shortwave solar radiation. It is durable and easy to incident shortwave solar radiation. It is durable and easy to apply [1]apply [1]..

Here a table about matteHere a table about matterrs that absorber plate may be made s that absorber plate may be made fromfrom

Table 2.1 Characteristics of absorptive coatings [1].Table 2.1 Characteristics of absorptive coatings [1].

Material Material Absorptance Absorptance

((αα))

EmittanceEmittance

((εε) )

Break down Break down temparature temparature

((°°C)C)

CommentsComments

Black siliconBlack silicon

paint paint 0.86-0.94 0.86-0.94 0.83-0.89 0.83-0.89 350 350 Slicone Slicone

binder binder

Black siliconBlack silicon

paintpaint 0.9 0.9 0.50.5 Stable at Stable at

highhigh

temperaturetemperature

Black copper Black copper

over copperover copper 0.85-0.90.85-0.9 0.08-0.120.08-0.12 450450 Patinates Patinates

with moisturewith moisture

Black Black chorome chorome over nickelover nickel

0.92-0.940.92-0.94 0.07-0.120.07-0.12 450450 Stable at high Stable at high

temperaturestemperatures

Here in figure 2.3 we can see absorber plate and flow Here in figure 2.3 we can see absorber plate and flow passagespassages

Figure 2.3 Cross Figure 2.3 Cross ssection of a ection of a absorber plate&flow passagesabsorber plate&flow passages ofof a a fflatlat

pplate late ccollectorollector [4]. [4].

B. Cover platesB. Cover plates

A cover plate for a collector should have a high transmittance A cover plate for a collector should have a high transmittance for solar radiation and should not detoriate with time. The for solar radiation and should not detoriate with time. The material most commonly used is glass. A 0.32-cm thick sheet material most commonly used is glass. A 0.32-cm thick sheet of window glass ( iron content, 0.12 percent ) transmits 85 of window glass ( iron content, 0.12 percent ) transmits 85 percent of solar energy at normal incidence. And all glass is percent of solar energy at normal incidence. And all glass is practically opaque to long-wavelength radiation emitted by the practically opaque to long-wavelength radiation emitted by the absorber plate.absorber plate.

Some plastic materials can be used for collector glazing.They Some plastic materials can be used for collector glazing.They are cheaper and lighter than glass and, because they can be are cheaper and lighter than glass and, because they can be used in very thin sheets, they often have higher transmittance. used in very thin sheets, they often have higher transmittance. However, they are not as durable as glass and they often However, they are not as durable as glass and they often degrade with exposure to ultraviolet radiation or high degrade with exposure to ultraviolet radiation or high temperatures [1].temperatures [1].

Here a table about matters that Here a table about matters that covercover plate may be made from plate may be made from

Table 2.2 Charactericts of cover plate materials [1].Table 2.2 Charactericts of cover plate materials [1].

TestTest PolyvinlyPolyvinly

floridefloride PolyethylenePolyethylene

terephthatalet terephthatalet or polysteror polyster

PolycarbonatePolycarbonate Fiberglass Fiberglass rein forced rein forced plasticsplastics

Solar Solar Transmission, %Transmission, %

92-9492-94 8585 82-8982-89 77-9077-90

Maximu Maximu operating operating temperature temperature °° C C

110110 100100 120-135120-135 9595

Thermal Thermal Expansion Expansion CoefficientCoefficient

4343 2727 6868 32-4032-40

Thickness, Thickness, mmmm

0.10.1 0.0250.025 3.23.2 1.01.0

Length of Length of

life, yearslife, years In 5 years 95% In 5 years 95% retainsretains

44 7-207-20

Here in figure 2.4 we can see cover part.Here in figure 2.4 we can see cover part.

Figure 2.4 Cross Figure 2.4 Cross ssection of a ection of a covercover ppart of a art of a fflat-lat-pplate late ccollectorollector [4]. [4].

C. Enclosure / InsulationC. Enclosure / Insulation The collector enclosure is usually made from steel, aliminium The collector enclosure is usually made from steel, aliminium

or fiber glass.or fiber glass.And order to prevent heat from escaping through And order to prevent heat from escaping through the back of the collector,a layer of insulation is placed behind the back of the collector,a layer of insulation is placed behind the absorber platethe absorber plate [1]. [1].

Table 2.3 Characteristics of insulation materials [1].Table 2.3 Characteristics of insulation materials [1].

MaterialMaterial Density Kg/m3Density Kg/m3 Thermal Thermal

conductivity atconductivity at

95 95 °°C (W/mK)C (W/mK)

TemperatureTemperature

limits limits °°CC

Fiber glass with Fiber glass with

organic binderorganic binder 1111 0.0590.059 175175

“ “ 1616 0.0500.050 175175

““ 2424 0.0450.045 175175

““ 4848 0.430.43 175175

Here in figure 2.5 we can see insulation part.Here in figure 2.5 we can see insulation part.

Figure 2.5 Cross Section of an Insulation Part of a Flat-Plate Collector Figure 2.5 Cross Section of an Insulation Part of a Flat-Plate Collector [4].[4].

3. 3. PROPER ORPROPER ORIIENTATENTATIIONON and and ANGLE ANGLE of of SOLAR COLLECTORSOLAR COLLECTOR

Flat plate collectorts are divided in three main Flat plate collectorts are divided in three main

groups according to how they are oriented:groups according to how they are oriented:Flat-plate collectors facing south at fixed tiltFlat-plate collectors facing south at fixed tiltOne-axis tracking flat-plate collectors with axis One-axis tracking flat-plate collectors with axis

oriented north-southoriented north-southTwo-axis tracking flat-plate collectorsTwo-axis tracking flat-plate collectors

A. Flat-plate collectors facing south A. Flat-plate collectors facing south at fixed tilt:at fixed tilt:

To optimize performance in the winter, the collector can be To optimize performance in the winter, the collector can be tilted 15 ° greater than the latitude; to optimize performance in tilted 15 ° greater than the latitude; to optimize performance in the summer, the collector can be tilted 15 ° less than the the summer, the collector can be tilted 15 ° less than the latitudelatitude [5]. [5]. FigureFigure 3.1 show how the collector is tilted.3.1 show how the collector is tilted.

Figure 3.1 Flat-plate collector at fixed tilt [5].Figure 3.1 Flat-plate collector at fixed tilt [5].

B. One-axis tracking flat-plate collectors B. One-axis tracking flat-plate collectors with axis oriented north-south:with axis oriented north-south:

These trackers pivot on their single axis to track the sun, facing These trackers pivot on their single axis to track the sun, facing east in the morning and west in the afternoon east in the morning and west in the afternoon as shown in as shown in figure 3.2.figure 3.2.

Figure 3.2 Flat-plate collector one axis tracking[5].Figure 3.2 Flat-plate collector one axis tracking[5].

C. Two-axis tracking flat-plate C. Two-axis tracking flat-plate collectors:collectors:

Tracking the sun in both azimuth and elevation, these Tracking the sun in both azimuth and elevation, these collectors keep the sun's rays normal to the collector surface as collectors keep the sun's rays normal to the collector surface as shown in figure 3.3. shown in figure 3.3.

Figure 3.3 Flat-plate collector with two axis tracking[5].Figure 3.3 Flat-plate collector with two axis tracking[5].

4.COLLECTOR PERFORMANCE4.COLLECTOR PERFORMANCE

The thermal performance of a collector can be The thermal performance of a collector can be calculated from a first-law energy balance. according calculated from a first-law energy balance. according to the first law of thermodynamics, for a simple flat-to the first law of thermodynamics, for a simple flat-plate collector an instantaneous steady-state energy plate collector an instantaneous steady-state energy balance is[1] : balance is[1] :

Useful energy = energy absorbed – heat loss to Useful energy = energy absorbed – heat loss to

gain (Qu) by the collector surroundings gain (Qu) by the collector surroundings

And,And, Absorbed energy = Absorbed energy = AACC F FRR S S Lost energy = Lost energy = AACC F FRR U ULL (Ti-Ta) (Ti-Ta)

where ;where ;

AACC = Collector area, = Collector area, m2m2

FFRR = Heat removal factor, unitless = Heat removal factor, unitless

S = Absorbed solar radiation, J/S = Absorbed solar radiation, J/m2m2

UULL = Heat transfer loss coefficient, J/ = Heat transfer loss coefficient, J/m2 °m2 °CC

Ti = The mean absorber plate temperature, Ti = The mean absorber plate temperature, °°CC

Ta = The ambient temperature, Ta = The ambient temperature, °°C.C.

So;So;

Equation 4.1 Useful gain enerrgy equation[6].Equation 4.1 Useful gain enerrgy equation[6].

QQUU = A = ACC F FRR S - A S - ACC F FRR U ULL (Ti-Ta) (Ti-Ta)

Equation 4.1 is an extremely useful equation and Equation 4.1 is an extremely useful equation and applies to essentialy all flat-plate collectors.applies to essentialy all flat-plate collectors. And to improve theperformance of solar collector it is And to improve theperformance of solar collector it is necesssary either to reduce the overall energy loss necesssary either to reduce the overall energy loss coefficient or reduce area from which energy is lost.coefficient or reduce area from which energy is lost. That is; the maximum possible useful energy gain (heat That is; the maximum possible useful energy gain (heat transfer) in a solar collector occurs when the whole transfer) in a solar collector occurs when the whole collector is at the inlet fluid temperature; heat losses to collector is at the inlet fluid temperature; heat losses to the surroundings are then at a minimum [1,6].the surroundings are then at a minimum [1,6].

A. Absorbed radiation (S):A. Absorbed radiation (S):

In equation 4.1 S is absorbed radiation and it is equal to:In equation 4.1 S is absorbed radiation and it is equal to:

Equation 4.2 Absorbed solar radiation[6].Equation 4.2 Absorbed solar radiation[6].

In equation 4.2 ; areIn equation 4.2 ; arethe view factors from the collector to the sky and the view factors from the collector to the sky and from the collector to the ground, respectively. from the collector to the ground, respectively. The subscripts b,d, and g represent beam, The subscripts b,d, and g represent beam, diffuse, and ground , respectively.diffuse, and ground , respectively. is is transmittance and absorptance product.Rb is the transmittance and absorptance product.Rb is the ratio of beam radiation on the tilted surface to that on a ratio of beam radiation on the tilted surface to that on a horizantal surface at any time[6].horizantal surface at any time[6].

( ) ( ) ( ) ( )

−++

++=

2

cos1

2

cos1 βταρβτατα gdbgddbbb IIIRIS

)2/cos1(),2/cos1( ββ −+

( )τα

B. Collector heat removal factor (FB. Collector heat removal factor (FRR):):In equation 4.1 FR is collector heat removal factorIn equation 4.1 FR is collector heat removal factor ; ; a quantity that relates the a quantity that relates the actual useful energy gain of a collector to the useful gain if the whole collector actual useful energy gain of a collector to the useful gain if the whole collector surfaces were at the fluid inlet temperature[6]. And it is given by equation 4.3.surfaces were at the fluid inlet temperature[6]. And it is given by equation 4.3.

Equation 4.3 the collector heat removal factor FR [6].Equation 4.3 the collector heat removal factor FR [6].

Where;Where; m’ = Fluid mass flow rate, kg/sm’ = Fluid mass flow rate, kg/s Cp = Fluid specific heat, J/kg Cp = Fluid specific heat, J/kg °°CC

The quantitiy FR is equavialent to the effectiveness of a The quantitiy FR is equavialent to the effectiveness of a conventional heat exchange, which is defined as the ratio of the actual conventional heat exchange, which is defined as the ratio of the actual heat transfer to the maximum possible heat transfer. The maximum heat transfer to the maximum possible heat transfer. The maximum possible useful energy gain (heat transfer) in a solar collector occurs possible useful energy gain (heat transfer) in a solar collector occurs when the all whole collector is at the inlet fluid temperature; heat when the all whole collector is at the inlet fluid temperature; heat losses to the surroudings are than at a minimum [6].losses to the surroudings are than at a minimum [6].

C. Overall heat loss coefficient (UC. Overall heat loss coefficient (ULL):):

In equation 4.1 UIn equation 4.1 ULL is the collector overall loss is the collector overall loss

coefficient and it is equal to the sum of the top, coefficient and it is equal to the sum of the top,

bottom,and edge loss coefficients [6]: bottom,and edge loss coefficients [6]:

Equation 4.4 Overall loss coefficientEquation 4.4 Overall loss coefficient U ULL [6]. [6].

UULL=Utop+Ubottom+Uedge,W/m=Utop+Ubottom+Uedge,W/m²²KK

EEnergy diagram of typical flat flate collectornergy diagram of typical flat flate collector is is shown in figure 5.1. % 92 of the total sunshine shown in figure 5.1. % 92 of the total sunshine reaches to the copper absorber.% 8 of the total reaches to the copper absorber.% 8 of the total sunshine is reflected from glass.% 5 of the sunshine is sunshine is reflected from glass.% 5 of the sunshine is emitted from the panel, %12 is lost through emitted from the panel, %12 is lost through convection and conduction.convection and conduction.

Figure 5.1 Energy diagram for typical flat plate collector [3]Figure 5.1 Energy diagram for typical flat plate collector [3]

5. COLLECTOR EFFICIENCY5. COLLECTOR EFFICIENCY

The basic method of measuring collector The basic method of measuring collector performance is to expose the operating collector to performance is to expose the operating collector to solar radiation and measure the fluid inlet and outlet solar radiation and measure the fluid inlet and outlet temperatures and the fluid flow rate.The useful gain is temperatures and the fluid flow rate.The useful gain is [6];[6];

EqEquation 5.1 Energy gained by liquid[6].uation 5.1 Energy gained by liquid[6].

Where;Where;

m’ = Fluid mass flow rate, kg/sm’ = Fluid mass flow rate, kg/s

Cp = Fluid specific heat, J/kgCp = Fluid specific heat, J/kg°°CC

)( 0 iPU TTCmQ −′=

The equation 5.1 which describes the thermal The equation 5.1 which describes the thermal performance of a collector operating under steady performance of a collector operating under steady conditions, can be rewritten [6];conditions, can be rewritten [6];

Equation 5.2 Useful gain enerrgy equation[6].Equation 5.2 Useful gain enerrgy equation[6].

Where is a transmittance-absorptance product Where is a transmittance-absorptance product that is weighted according to the proportions of beam, that is weighted according to the proportions of beam, diffuse, and ground reflected radiation on the diffuse, and ground reflected radiation on the collector collector [6][6]..

( ) ( )[ ]aiLTRcu TTUGFAQ −−= τα

( )τα

And finally; instantaneous efficiency And finally; instantaneous efficiency can be defined as [6]:can be defined as [6]:

That is;That is;

( ) ( )T

aiLRR

Tc

ui G

TTUFF

GA

Qn

−−== τα

( )Tc

ipi GA

TTCmn

−= 0'

6) APPLICATIONS6) APPLICATIONS

Flat plate collectors are used for both;Flat plate collectors are used for both;

A)A) Domestic applications Domestic applications

B)B) Commercial applications Commercial applications

Flate plate collectors mainly used in residential buildings where Flate plate collectors mainly used in residential buildings where the demand for hot water has a large impact on energy bills. This the demand for hot water has a large impact on energy bills. This generally means a situation with a large family, or a situation in generally means a situation with a large family, or a situation in which the hot water demand is excessive due to frequent laundry which the hot water demand is excessive due to frequent laundry washing [2].washing [2]. For instance, a family of 4 members consumes on an average For instance, a family of 4 members consumes on an average 100 litre of hot water a day at 60 100 litre of hot water a day at 60 ˚C˚C. Hot water of 100 litre . Hot water of 100 litre capacity at 60 capacity at 60 ˚C˚C approximate can be delivered by a single approximate can be delivered by a single collector system of 2 mcollector system of 2 m²² area. The solar water heating systems area. The solar water heating systems

are are generally provided with auxiliary backup in the insulated hot generally provided with auxiliary backup in the insulated hot storage tank for the rainy and heavily overcast cloudy days [7].storage tank for the rainy and heavily overcast cloudy days [7].

A) A) Domestic applicationsDomestic applications

Here we can see solar flat-plate collectors used for Here we can see solar flat-plate collectors used for heating buildings.heating buildings.

Figure 6.1 Flat plate collectors used for heating buildings [8].Figure 6.1 Flat plate collectors used for heating buildings [8].

B) Commercial applicationsB) Commercial applications

Commercial applications include laundromats, car washes, Commercial applications include laundromats, car washes, military laundry facilities and eating establishments. Solar water military laundry facilities and eating establishments. Solar water heating systems are most likely to be cost effective for facilities heating systems are most likely to be cost effective for facilities with water heating systems that are expensive to operate, or with with water heating systems that are expensive to operate, or with operations such as laundries or kitchens that require large operations such as laundries or kitchens that require large quantities of hot water. quantities of hot water. And unglazed liquid collectors are commonly used to heatAnd unglazed liquid collectors are commonly used to heatwater for swimming pools. Because these collectors need not water for swimming pools. Because these collectors need not withstand high temperatures, they can use lessexpensive withstand high temperatures, they can use lessexpensive materials such as plastic or rubber. They also do not require materials such as plastic or rubber. They also do not require freeze-proofing because swimming pools are generally used onlyfreeze-proofing because swimming pools are generally used onlyin warm weather or can be drained easily during cold weather in warm weather or can be drained easily during cold weather [2]. [2].

Here we can see solar flat-plate collectors used for Here we can see solar flat-plate collectors used for heating swimming pools.heating swimming pools.

Figure 6.2 Flat-plate collectors used for heating swimming pools [9].Figure 6.2 Flat-plate collectors used for heating swimming pools [9].

7) CONCLUSION7) CONCLUSION

Flat-plate collectors which are used for water heating,

are long lasting, and also in long term they are cheaper

than other water heating systems.However,they requires

large areas if high energy output is a requirement.

Than solar energy is free if we do not include the initial

cost for installation and the maintenance.

Finally; bessides these we should remember by using

solar energy we can protect nature.

REFERENCESREFERENCES[1] Jan F. Kreider, Charles J. Hoogendoorn, [1] Jan F. Kreider, Charles J. Hoogendoorn, Frank Kreith “ Solar Design “ Hemisphere Frank Kreith “ Solar Design “ Hemisphere Publishing Corporation, (1989), pp. 44-55.Publishing Corporation, (1989), pp. 44-55.[2] [2] http://www.flasolar.comhttp://www.flasolar.com[3] [3] http://www.solarnetrix.comhttp://www.solarnetrix.com[4] [4] http://www.solstice.crest.orghttp://www.solstice.crest.org[5] [5] http://www.rredc.nrel.govhttp://www.rredc.nrel.gov[6] [6] Duffie, J. A. and Beckman, W. A. , 1991. Solar Engineering of Thermal Processes , John Wiley and Sons Inc., New York, pp.250-290 .[7] [7] http://www.iredaltd.comhttp://www.iredaltd.com[8] [8] http://www.ips-solar.comhttp://www.ips-solar.com[9] [9] http://www.northeastpoolstore.comhttp://www.northeastpoolstore.com