experimental validation of glazed hybrid micro-channel solar cell thermal tile

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Solar Energy 85 (2011) 3046–3056

Experimental validation of glazed hybrid micro-channel solarcell thermal tile

Sanjay Agrawal a,⇑, Arvind Tiwari b

a Centre for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, Indiab Bag Energy Research Society (BERS), Mahamana Nagar, Karaundi, Varanasi, India

Received 29 March 2011; received in revised form 19 July 2011; accepted 3 September 2011Available online 28 September 2011

Communicated by: Associate Editor S.C. Bhattacharya

Abstract

In this communication, an attempt has been made to evaluate the theoretical performance of a glazed hybrid micro-channel solar cellthermal (MCSCT) tile. Experiment has been performed in indoor condition and it has been observed that there is good agreementbetween theoretical and experimental values with correlation coefficient and root mean square percentage deviation in range of0.995–0.998 and 3.21–4.50 respectively. Effect of design parameters on different combination (series and parallel) of glazed hybridMCSCT tile for Srinagar climatic condition, India has also been evaluated. The theoretical results of glazed hybrid micro-channel pho-tovoltaic thermal (MCPVT) module for 75 Wp have been compared with the result of single channel photovoltaic thermal (SCPVT) mod-ule. The average value of electrical and thermal efficiency of glazed hybrid MCPVT module are 14.7% and 10.8% respectively which issignificantly higher than SCPVT module. The overall annual exergy efficiency based on second law of thermodynamics has also beenevaluated at different mass flow rate for glazed hybrid MCPVT module for Srinagar climatic condition. It has been observed that max-imum overall exergy efficiency is 20.28% at 0.000108 kg/s mass flow rate.� 2011 Elsevier Ltd. All rights reserved.

Keywords: Glazed solar cell; Photovoltaic module; Micro-channel; Electrical efficiency; Thermal modeling

1. Introduction

Classification of photovoltaic thermal system has beenshown in Fig. 1a. Theoretical and experimental studies of(PVT) have been conducted as early as in mid 1970s. Wolf(1976), Florschuetz (1975, 1979), Kern and Russell (1978)and Hendrie (1979) on different occasions have presentedthe key concept and the data with the use of either wateror air as the coolant. The research works that carried outmainly on flat-plate collectors have been presented by Rag-huraman (1981), Cox and Raghuraman (1985), Braunsteinand Kornfeld (1986) and Lalovic (1986). The works ofO’leary and Clements (1980), Mbewe et al. (1985), Al-Baali(1985) and Hamdy et al. (1988) have included the perfor-

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doi:10.1016/j.solener.2011.09.003

⇑ Corresponding author. Tel.: +91 9911428863.E-mail address: [email protected] (S. Agrawal).

mance analysis of concentrating PVT systems. Hayakashiet al. (1989) have also presented a system in which a roofhas covered by 48 m2 of PV-modules, which were con-nected to transparent tubes and filled with a black fluid.The electrical and thermal energy have been stored in bat-teries and two water tanks of 1 m3 each respectively.

Bhargava et al. (1991) have investigated the effect of airmass flow rate, air channel depth, length and fraction ofabsorber plate area covered by solar cells (packing factor,PF) on single pass air collector. Nishikawa et al. (1993)have presented a system in which the PVT functionsdirectly as the evaporator of a heat pump. The modelingof a channel type PVT collector for the cases of both air(100–300 kg/h) and water (40–120 kg/h) has been carriedout by Prakash (1994). He has observed that decreasingthe duct depth increases the thermal performance of airand water heater. Fujisawa and Tani (1997) have compared

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Nomenclature

Ac area of solar cell (m2)

b width of the micro-channel (m)Cf specific heat of air (J/kg K)d depth of the micro-channel (m)De characteristic dimension or equivalent diameter

of micro-channel (m)dx elemental length (m)dt elemental time (s)fc coefficient of frictionh heat transfer coefficient (W/m2 K)hbi heat transfer coefficient from back of tedlar to

ambient (W/m2 K)hto heat transfer coefficient from top glass cover to

ambient (W/m2 K)hT heat transfer coefficient from back of tedlar to

flowing air (W/m2 K)hb,in heat transfer coefficient from back of insulation

to ambient (W/m2 K)I(t) incident solar intensity (W/m2)K thermal conductivity (W/m K)L length (m)_mf air mass flow rate in micro-channel (kg/s)N number of glazed micro-channel solar cell ther-

mal (MCSCT) tileNu Nusselt number_Qu useful heat (W)Re Reynolds numberT temperature (K)U overall heat transfer coefficient (W/m2 K)

Utca an overall heat transfer coefficient from solarcell to ambient through glass cover (W/m2 K)

Utcf an overall heat transfer coefficient from solarcell to flowing air through tedlar (W/m2 K)

Ub an overall back loss heat transfer coefficientfrom flowing air to ambient (W/m2 K)

V velocity of fluid (air) flowing inside of channel(m/s)

v velocity of air (m/s)b0 temperature coefficient of efficiency (1/K)go efficiency at standard test condition

(I(t) = 1000 W/m2 and Ta = 25 �C)

Greek letters

a absorptivityb packing factors transmittivityg efficiencyq density (kg/m3)

Subscripts

a ambientc solar celleff effectivef fluid (air)fi inlet fluidfo outgoing fluidin insulationT tedlar

S. Agrawal, A. Tiwari / Solar Energy 85 (2011) 3046–3056 3047

the annual performance of a flat-plate water collector, a PVmodule and a single glazed and unglazed PVT collectorwith mono-crystalline silicon solar cells. The evaluationof the measured data have shown that the single glazedPVT collector was the best, followed by flat-plate watercollector, unglazed PVT and PV module in terms of overallenergy gain. In terms of exergy analysis, the best perfor-mance was given by unglazed PVT, followed by PV mod-ule, single glazed PVT and flat-plate water collector.

Hegazy (2000) and Sopian et al. (2000) have studied theglazed photovoltaic thermal air system for a single and adouble pass air heater for space heating and the drying.Kalogirou (2001) has investigated monthly performanceof an unglazed hybrid PVT system under forced mode ofoperation for climatic condition of the Cyprus. He hasfound an increase of the mean annual efficiency of thePV solar system from 2.8% to 7.7% with thermal efficiencyof 49%. A detailed sensitivity analysis has been conductedto determine the influence of the uncertainties in the mea-sured parameters on the uncertainty level that can beassigned to coefficients of the efficiency curve for solar col-lectors (Braccio et al., 2002). Lee et al. (2001) and Chow

(2003) have presented interesting modeling results on aircooled PV modules. Ji et al. (2003) have investigated afacade integrated 40 m2 PVT collectors for use in residen-tial buildings in Hong Kong, comparing thin film and crys-talline silicon. For water heating, the annual thermalefficiencies have been found to be 48% for the thin film caseand 43% for the crystalline silicon case. The movement of aphotovoltaic module has been controlled by programmablelogic-controller (PLC) unit to follow the Sun’s radiation.They have found that the daily output power of the PVwas increased by more than 20% in comparison with thatof a fixed module. Vorobiev et al. (2005) have investigatedthe option to make a cell work at relatively high tempera-ture (around 100–200 �C) and use the excessive heat in ahybrid system of some kind to increase the total efficiencyof solar energy utilization.

Kalogirou and Tripanagnostopoulos (2005) have calcu-lated the yield of a 4 m2 PVT thermosyphon system for dif-ferent climates. For their crystalline silicon PVT module,they found a useful thermal gain of 5.7 GJ for Nicosia,5.0 GJ for Athens and 3.8 GJ for Madison, while the elec-trical performance ranged from 532 to 499 kWh. Design of

PVT Green house

PVT air collectors

connected in series

Duct below PV

Single pass

Double Pass

PVT water collectors connected in parallel

PVT water collectors connected

in series

Duct above PV

PVT module based air collectors

PVT module based water collectors

SAPV

Opaque

Photovoltaic thermal system

Micro-channel Solar cell thermal tile

Photovoltaic thermal module

Unglazed micro-channel Solar cell thermal tile

(channel between solar cell and tedlar)

Glazed micro-channel Solar cell thermal tile

(channel between tedlar and insulation)

Unglazed micro-channel photovoltaic thermal

module

Glazed micro-channel photovoltaic

thermal module

Semitransparent

PVT air collector

PVT water

collector

PVT Drying

SAPV

BIPVT

Day-lighting

Fig. 1a. Classification of photovoltaic thermal systems.

3048 S. Agrawal, A. Tiwari / Solar Energy 85 (2011) 3046–3056

PV integrated solar-collector for natural circulation ofwater has been presented by He et al. (2006).

Naveed et al. (2006) have examined a PVT air systemconsists of PV module integrated with an unglazed tran-spired collector and found that the electrical performancehas been improved with temperature reduction of 3–9 �Cwith reduction in PV area from 25 to 23 m2. For the devel-opment, market introduction, increase general understand-ing, contribute to internationally accepted standards onperformance, testing, monitoring and commercial charac-teristics of PVT solar system in building sector a three yearresearch work have been initiated by Hansen and Sorensen(2006) as a part of International Energy Agency (IEA)Solar Heating and Cooling (SHC) Programme.

Tripanagnostopoulos (2007) has proposed a new type ofPVT collector with dual heat extraction operation whichimproves the performance of hybrid PVT systems. Assoaet al. (2007) have studied the effect of cooling fluid (i.e.,

water) circulating between the glazing and the moduleand it was stored in a storage tank. For this, two collectorsconnected in parallel are used and it was found that thedaily 2.8 kWh thermal energy can be stored as pre-heatedwater. Fraisse et al. (2007) have presented energy perfor-mance of water hybrid PVT collectors applied to combisys-tems of direct solar floor type by using poly-crystallinephotovoltaic modules for Macon area in France. Theyhave studied four different cases of PV and PVT. They haveobserved that annual photovoltaic cell efficiency was 6.8%less than the conventional PV module due to increase intemperature. Hansen et al. (2007) have presented the mar-ket, modeling, testing and demonstration of PVT systemsunder the framework of IEA. They have conducted exper-iments on different types of PVT systems and concludedthat the market survey interviews with architects and solardealers are the most important factor for profitability ofthe system and building integration. An outdoor test

Fig. 1b. Schematic view at A of Fig. 2a of glazed hybrid micro-channelsolar cell thermal (MCSCT) tile.


method to determine the thermal behavior of solar domes-tic water heating systems has been developed by Garcıa-Valladares et al. (2008), which would be useful for solarequipment manufacturers in order to design and optimizedtheir products and also for the consumers to select the mostsuitable system. The analytical expression for electrical effi-ciency of hybrid PVT air collector (semi transparent andopaque PV module with and without duct) has beenderived by Dubey et al. (2009) and they found that the semitransparent PV module with duct gives higher electrical aswell as thermal efficiency.

Energy and exergy analysis of photovoltaic thermal col-lector with and without glass cover have been studied byChow et al. (2009) and concluded that the increase of on-site solar radiation or ambient temperature has been afavorable factors for selecting a glazed PVT system. Nayakand Tiwari (2008) have made energy and exergy analysis ofPVT integrated with solar green house and they observedthat the exergy efficiency of PVT solar green house is 4%.Exergy analysis of integrated photovoltaic thermal solar(IPVTS) water heater under constant flow rate and con-stant collection temperature modes has been done byTiwari et al. (2009) and they observed that the daily overallthermal efficiency of IPVTS system increases with increaseconstant flow rate and decrease with increase of constantcollection temperature. Performance analysis of a hybridphotovoltaic-thermal integrated system has also been doneby Radziemska (2009). He presented the concept of exergyanalysis for evaluation of the PVT systems which is veryuseful tools for the improvement and cost-effectiveness ofthe system. The performance in terms of overall annualthermal, exergy gain and exergy efficiency of proposedmicro-channel photovoltaic thermal module have beenevaluated by Agrawal and Tiwari (2011). They concludedthat proposed hybrid micro-channel photovoltaic thermalmodule gives better results than single channel photovol-taic thermal module of Tiwari and Sodha (2006) andDubey et al. (2009).

The main objective of this paper is to study on singleglazed hybrid solar cell thermal tile having micro-channelbelow the tedlar (Fig. 1b) with air flow below the tedlarunlike unglazed solar cell proposed by Agrawal and Tiwari(2011). The effect of intensity on overall performance of

prototype of glazed hybrid micro-channel solar cell thermaltile in indoor condition has also been carried out becausetill now only large area of channel or duct based photovol-taic thermal system has been found in literature.

2. Experimental setup

The schematic view of glazed hybrid micro-channelsolar cell thermal (MCSCT) tile has been shown inFig. 1b. In glazed hybrid micro-channel solar cell thermaltile, micro-channel has been placed between tedlar andinsulation. The glazed hybrid MCSCT tile consists of a sin-gle solar cell (mono crystalline silicon), rated at 2.2 Wp

having dimensions 0.12 m length and 0.12 m width hasbeen considered and it has been mounted on a rectangularwooden channel. The channel has dimensions0.12 m � 0.12 m � 5000 lm. The wooden channel has beensealed with putty and adhesive tape to avoid air leakage.There is provision for the inlet and outlet air to flowthrough the micro-channel of solar cell under forced mode.If the outlet of one glazed hybrid MCSCT tile is connectedto the inlet of another glazed hybrid MCSCT tile, then it isreferred as series connection. If the inlet and outlet of eachglazed hybrid micro-channel solar cell thermal tile aresame, then it is referred as parallel connection For the per-formance evaluation, the following different configurationsof glazed hybrid MCPVT module have been considered:

Case I: Four columns each having nine hybrid MCSCTtile in series are connected in parallel as shown inFig. 2a.Case II: Nine rows each having four hybrid MCSCT tilein series are connected in parallel as shown in Fig. 2b.Case III: Two columns each having eighteen hybridMCSCT tile in series are connected in parallel as shownin Fig. 2c.Case IV: Three rows each having twelve hybrid MCSCTtile in series are connected in parallel as shown inFig. 2d.

The glazed hybrid MCPVT modules have been analyzedin the terms of an electrical efficiency and thermal effi-ciency. The result has also been compared with result ofphotovoltaic thermal (PVT) module with single duct ofstudied by Tiwari and Sodha (2006) which will be referredas single channel photovoltaic thermal (SCPVT) modulewith similar conditions. The values of various designparameter of glazed hybrid micro-channel solar cell ther-mal (MCSCT) tile have been given in Table 1.

2.1. Solar simulator

A solar simulator with a 3-phase lamp array is employedto imitate the necessary solar irradiation in the testing ofmicro-channel solar cell thermal tile. Photographs of devel-oped solar simulator and hybrid MCSCT tile have beenshown in Fig. 3a. The schematic elevation and plan of

Fig. 2a. Case I: (4 column each having 9 cells in series are connected inparallel).

Fig. 2b. Case II: (9 Rows each having 4 cells in series are connected inparallel).

Fig. 2c. Case III: (2 columns each having 18 cells in series are connected inparallel).

Fig. 2d. Case IV: (3 rows each having 12 cells in series are connected inparallel).


experimental setup has been shown in Fig. 3b. The solarsimulator has 28 tungsten halogen lamps (Philips manufac-tured; Model: 392472) each having 500 W, 9000 lumens.The halogen lamps are arranged in 7 � 4 matrices for uni-form distribution of irradiance on the hybrid MCSCT tile.The available area for testing is 1 � 2 m2 .The height of thesimulator from the floor is 200 cm. Intensity of simulatorcan be varied between 300 W/m2 and 1000 W/m2 by

decreasing the gap by screw and jack mechanism betweenhalogen lamp and mild steel platform of solar simulator.

2.2. Experimental observations and instrumentation

The experiment has been conducted at intensity of 700 W/m2 and the constant mass flow rate of 1.08 � 10�4 kg/s on

Table 1Design parameters of glazed hybrid micro-channelsolar cell thermal tiles.

Parameters Values

Cf (J/kg K) 1012To (�C) 25ac 0.9b0 (1/K) 0.0045g0 0.15sg 0.95v (m/s) 1.5V (m/s) 0.9_mf (kg/s) 0.000108Kg (W/m K) 1.1Lg (m) 0.003hT (W/m2 K) 4.3hto (W/m2 K) 11.4hb,in (W/m2 K) 7.3Utca (W/m2 K) 11.1Utcf (W/m2 K) 4.03Ub (W/m2 K) 6.89Ufa (W/m2 K) 2.94UL (W/m2 K) 9.83Ac (m2) 0.0144

Fig. 3a. Photograph of solar simulator with glazed hybrid micro-channelsolar cell thermal (MCSCT) tile.


single glazed hybrid MCSCT tile. The air has been flown withthe help of small DC fan through the micro-channel of tilesto withdraw the heat associated with base of solar cell. Theexperiments have been conducted in order to validate thetheoretical and experimental results. The following parame-ters have been measured at an interval of 15 min to get moreprecise results during the experimentation:

1. Inlet air, outlet, room air and solar cell temperatures.2. Air velocity at outlet.3. Intensity on solar cell.4. Open circuit (Voc) and load voltage (VL).5. Short circuit (Isc) and Load current (IL).

The instruments (used in experiment) and their descrip-tion have been shown in Table 2.

Fig. 3b. Schematic elevation and

3. Thermal modeling

The energy balance equation of glazed hybrid MCSCTtile (Fig. 1b) can be written by following the same assump-tions considered by Agrawal and Tiwari (2011), as follows

(i) For solar cell

½acsgIðtÞbdx� ¼ ½UtcaðT c � T aÞbdxþ U tcf ðT c � T f Þbdx�þ sggcIðtÞbdx ð1Þ

½Rate of solar energy available on glazed solar cell�¼ Rate of heat loss from top surface of solar½� cell to ambient through glass cover�þ Rate of heat transfer from solar cell to flowing½� fluid through tedlar i:e: air�

þ Rate of electrical energy produced½ �

From Eq. (1), the expression for cell temperature can bewritten as

T c ¼aeff IðtÞ þ UtcaT a þ Utcf T f

U tca þ Utcfð2Þ

plan of experimental set up.

Table 2Instrumentation.

S.No. Instrument Operating range Least count Particular

1 Copper-constantanthermocouple

�200–+350 �C 0.1 �C Calibrated against Zeal thermometer in temperaturecontrolled bath circulator

2 Solarimeter 0–1000 W/m2 20 W/m2 Calibrated against pyranometer3 Infrared thermometer �20–+450 �C 0.1 �C Emmissivity setting = 0.954 Clamp meter (1-1000) V DC/AC (1-1000) A

DC/AC0.001 V0.1 A

Calibrated using measurement standard traceable to ERTL(North)

5 Anemometer 0.4–30 m/s 0.1 m/s Low friction ball-bearing vane


where aeff ¼ sgðac � gcÞ

For sg = 1 and micro-channel just below the solar cell,glazed hybrid MCSCT tile becomes unglazed hybridMCSCT tile and then

aeff ¼ ðac � gcÞ;U tca ¼ ho and U tcf ¼ hi

(ii) For air flowing through micro-channelEnergy balance for air flowing in the glazed hybrid

micro-channel of solar cell thermal tile for elemental areabdx is given by

Utcf ðT c � T f Þbdx ¼ m:

fCf

dT f

dxdxþ UbðT f � T aÞbdx ð3Þ

½Rate of heat transfer from solar cell to flowing fluid

through tedlar i:e: air�¼ ½The rate of heat gain by flowing fluid i:e: air in channel�þ½Rate of heat transfer from flowing fluid to ambient�

Here it is important to mention that the expression forUb is different than the value of hb.

Solving the Eqs. ()()()(1)–(3), the outlet air temperature(TfoN), instantaneous thermal (gth) and electrical efficiency(g) at Nth number of glazed hybrid micro-channel solar cellthermal tiles connected in series are given by

T foN ¼hpaeff

ULIðtÞ þ T a

� �1� exp

�NbU LL_mf Cf

� �� þ T fi

� exp�NbU LL

_mf Cf

� �ð4Þ

gth¼_mf Cf

U LNAc1� exp

�NbU LLm:

fCf

0@

1A

24

35 hpaeff �U L

ðT fi�T aÞIðtÞ

� �

ð5Þ

g ¼ go 1� boaeff IðtÞ

U tca þ U tcf� ðT o � T aÞ þ

U tcf hpaeff IðtÞU LðUtca þ U tcf Þ

��

� 1�1� exp �NbU LL

_mf Cf

� �NbULL_mf Cf

8<:

9=;þ U tcf

ðUtca þ U tcf Þ

�1� exp �NbULL

_mf Cf

� �NbULL_mf Cf

8<:

9=;ðT a � T fiÞ

9=;35 ð6Þ

Here also for sg = 1 and micro-channel just below thesolar cell, the expressions of glazed hybrid MCSCT tilesconnected in series reduces to expressions of unglazedhybrid MCSCT tiles.

3.1. Overall exergy efficiency of glazed hybrid MCSCT tile

The overall exergy efficiency of glazed hybrid MCSCTtile is defined by Hepbasli (2008) as follows:

gEX ¼_Exout

_Exin

� �� 100 ð7Þ

3.2. Electrical efficiency of glazed hybrid MCSCT tile

Electrical efficiency of glazed hybrid MCSCT tile can becalculated as by Tiwari (2008)

gexp ¼FF � V oc � Isc � IL � V L

Ac � IðtÞ ð8Þ

where fill factor (FF) is measure of sharpness of the I–V

curve. It indicates how well a junction was made in the celland how low is the series resistance. It can be lowered bythe presence of series resistance and tends to be higherwhenever the open circuit voltage is high.

3.3. Statistical analysis

To compare the theoretical and experimental results, thecorrelation coefficient (r) and root mean square percentdeviation (e) have been evaluated by using the followingexpression:

r ¼ nðP

X i � Y iÞ � ðP

X iÞðP

Y iÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffinP

X 2i � ð

PX iÞ2

q ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffinP

Y 2i � ð

PY iÞ2

q ð9Þ

and e ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiPðeiÞ2

n

sð10Þ

where ei ¼X i � Y i

X i

� �� 100

4. Methodology

The “Matlab 7” has been used to compute the electricaland thermal efficiency of glazed hybrid MCSCT tile and

Fig. 4a. Variation of solar cell temperature of glazed hybrid micro-channel solar cell thermal tile at solar radiation 700 W/m2.

Fig. 4b. Variation of outlet air temperature of glazed hybrid micro-channel solar cell thermal tile at solar radiation 700 W/m2.

02468

10121416

10:00 10:15 10:30 10:45 11:00 11:15 11:30 11:45Time

Elec

tric

al e

ffici

ency

, %

TheorticalExperimental

e=4.50 r=0.995

Fig. 4c. Variation of electrical efficiency of glazed hybrid micro-channelsolar cell thermal tile at solar radiation 700 W/m2.


glazed hybrid MCPVT module for all combination i.e. forCase (I–IV), at constant mass flow rate. Overall exergy effi-ciency of glazed hybrid micro-channel photovoltaic ther-mal module (Case II) has also been computed.

The following methodology has been adopted:

4.1. Glazed hybrid micro-channel solar cell thermal(MCSCT) tile (N=1)

a. The solar cell temperature (Tc) of glazed hybridMCSCT tile has been computed from Eq. (2).

b. The outlet air temperature (Tfo) of glazed hybridmicro-channel solar cell thermal has been calculatedwith the help of Eq. (4) considering the design and cli-matic parameter of Srinagar city, India.

c. Thermal efficiency of hybrid micro-channel solar cellthermal has been calculated with help of Eq. (5).

d. The electrical efficiency of glazed hybrid MCSCT tilehas been computed with help of Eq. (6).

4.2. Glazed hybrid micro-channel photovoltaic thermal

(MCPVT) module (N > 1)

a. The outlet air temperature of glazed hybrid MCPVTmodules has been computed using Eq. (4) takingN = 9 for Case I, N = 4 for Case II, N = 18 for CaseIII and N = 12 for Case IV.

b. The thermal efficiency of glazed hybrid MCPVTmodules have been computed using Eq. (5) takingN = 9 for Case I, N = 4 for Case II, N = 18 for CaseIII and N = 12 for Case IV.

c. The electrical efficiency of glazed hybrid MCPVTmodules have been computed with help of Eq. (6)taking N = 9 for Case I, N = 4 for Case II, N = 18for Case III and N = 12 for Case IV.

4.3. Overall exergy efficiency for glazed hybrid MCPVTmodule

An overall Exergy efficiency has been calculated byfollowing Agrawal and Tiwari (2011).

5. Results and discussions

5.1. Experimental validation

Experiment has been performed for validation of glazedhybrid micro-channel solar cell thermal tile. Theoreticalvalues of solar cell, outlet air temperatures and electricalefficiency of single glazed hybrid MCSCT tile have beencomputed from Eqs. (2), (4), and (6) with help of MAT-LAB 7.0 at constant intensity (700 W/m2) and mass flowrate (1.08 � 10�4 kg/s). The variation of solar cell, outletair temperatures and electrical efficiency of single glazedhybrid MCSCT tile with respect to time for theoretical

and experimental results have been shown in Figs. 4a–4c). One can observed that there is good agreementbetween theoretical and experimental values with correla-tion coefficient in range of 0.995–0.998 and root meansquare percentage deviation in range of 3.21–4.50. Due tolimitation of experimental setup, validation was not conve-nient for glazed micro-channel photovoltaic thermalmodule.

5.2. Numerical results

Average hourly global radiation (W/m2) on horizontalsurface, number of days fall under different weather condi-tions and the average ambient temperature (�C) for

10

11

12

13

14

15

16

17

8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00Time (Hours)

Elec

tric

al e

ffici

ency

, %SCPVT module MCPVT module

Fig. 6a. Hourly variation of electrical efficiency of glazed hybrid micro-


Srinagar, India have been taken from Indian meteorologi-cal department (IMD), Pune and same data had beenadopted by Agrawal and Tiwari (2011). The hourly varia-tion of thermal and electrical efficiency of glazed hybridMCPVT module for different Cases (I–IV) as mentionedin system description has been computed with help ofEqs. (5) and (6) and the results have been shown inFigs. 5a and 5b). It has been observed that thermal effi-ciency of glazed hybrid micro-channel photovoltaic module(Case II) is higher than other Cases (I, III and IV). It isbecause outlet air temperature in Case II is more than othercases. One can also see that there is marginal effect ofdifferent series and parallel combination of glazed hybridmicro-channel solar cell thermal (MCSCT) tiles on electri-cal efficiency. It is due to fact that the there are small var-iation in solar cell temperature in all cases. On the basis ofthis it has been concluded that Case II gives better perfor-mance. In all cases since the whole area of the PV module iscovered by solar cells i.e. packing factor (b) is 1 hence theachieved thermal efficiency is low and electrical efficiency iscomparatively high in comparison to conventional PVTmodule.

0

2

4

6

8

10

12

08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00Time (Hours)

Ther

mal

effi

cien

cy, %

Case-ICase-II

Case-IIICase-IV

Fig. 5a. Hourly variation of thermal efficiency of glazed hybrid micro-channel photovoltaic thermal module for four cases for the month ofJanuary of Srinagar.

13.0

14.0

15.0

16.0

17.0

08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00Time (Hours)

Elec

tric

al e

ffici

ency

, %

Case-ICase-II

Case-IIICase-IV

Fig. 5b. Hourly variation of electrical efficiency of glazed hybrid micro-channel photovoltaic thermal module for four cases for the month ofJanuary of Srinagar.

The results of the glazed MCPVT module (Case II) havebeen compared with the results of single channel photovol-taic thermal (SCPVT) module for same climatic conditionand mass flow rate. The hourly variation of electrical andthermal efficiency of glazed hybrid micro-channel andsingle channel photovoltaic thermal module has beenshown in Figs. 6a and 6b). It has been noted that glazed

channel photovoltaic thermal and single channel photovoltaic thermalmodule (Case II) for the month of January of Srinagar.

0

2

4

6

8

10

12

8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00Time (Hours)

Ther

mal

effi

cien

cy, %

SCPVT module MCPVT module

Fig. 6b. Hourly variation of thermall efficiency of glazed hyrid micro-channel photovoltaic thermal and single channel photovoltaic thermalmodule (Case II) for the month of January of Srinagar.

15

16

17

18

19

20

21

0.000036 0.000072 0.000108 0.000144 0.000180 0.000216

Mass flow rate, kg/s

Ove

rall

exer

gy e

ffici

ency

, %

Fig. 7. Effect of mass flow rate on overall exergy efficiency of glazedhybrid micro-channel photovoltaic thermal module for the month ofJanuary of Srinagar.


hybrid MCPVT module gives more electrical as well asthermal efficiency than SCPVT module. This may be dueto air flow pattern of flowing air unlike conventional pho-tovoltaic module. Overall exergy efficiency with respect todifferent mass flow rate has been computed as carried outby Agrawal and Tiwari (2011) and the result has beenshown in Fig. 7. It has been found that at mass flow rateof 0.000108 kg/s an overall exergy efficiency is maximum(20.28%). So that it can be concluded that 0.000108 kg/sis the most optimized mass flow rate for glazed hybridmicro-channel photovoltaic thermal module.

6. Conclusions

The following conclusions have been drawn:

� The glazed hybrid MCPVT module gives higher electri-cal efficiency in comparison with SCPVT module by26.7%.� An overall exergy efficiency i.e. 20.28% has been

obtained at 0.000108 kg/s mass flow rate.� There is good agreement between theoretical and exper-

imental results for glazed hybrid MCSCT tile.

Acknowledgments

The authors are thankful to Prof. G.N. Tiwari and Dr.H.D. Pandey for his idea of analyzing glazed hybrid micro-channel solar cell thermal tile. The authors are also thank-ful to the Central Electronics Ltd (CEL), Sahibabad, Indiafor providing the necessary help to design the glazed hybridmicro-channel solar cell thermal tile.

Appendix A

The following correlation for air with one side heatedand other side insulated given by Kays (1966):

Nu ¼ hT De

K¼ 0:0158ðReÞ0:8

or hT ¼KDe

0:0158ðReÞ0:8

The characteristic dimension or equivalent diameter(De) of micro-channel is given by:

De ¼2LdðLþ dÞ

The Reynolds number (Re) is calculated by

Re ¼ qVDe

l¼ q

l_mf

ðLdqÞ2LdðLþ dÞ ¼

_2mf

lðLþ dÞTo calculate the pressure drop in the micro-channel the

following correlation by Jiang et al. (2001) for friction fac-tor in rectangular micro-channel is used. The pressure dropin micro-channel is calculated with following equation:

DP ¼ fcLV 2q2De

Then coefficient of friction fc can be correlated with Reas follows:

fc ¼ 1639Re�1:48 Re < 600Þ;fc ¼ 5:45Re�0:55ð600 < Re < 2800Þ

In modeling equations, we used following relations fordefining the design parameters, which are shown inTable 1

Glazed micro-channel solar cell thermal (MCSCT) tile:

aeff ¼ sgðac � gcÞ_mf ¼ qLdV

hto ¼ 5:7þ 3:8� v

hb;in ¼ 2:8þ 3� v

Utca ¼Lg

Kgþ 1

hto

� ��1

Utcf ¼LT

KTþ 1

hT

� ��1

Ub ¼Lin

Kinþ 1

hb;in

� ��1

hp ¼U tcf

U tca þ U tcf

� �

Ufa ¼1

Utcfþ 1

U tca

� ��1

UL ¼ Ub þ U fa

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experimental validation of glazed hybrid micro-channel solar cell thermal tile

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