Double Pass, Hybrid -Type (Pvt)

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International Journal of Energy & Technology 4 (34) (2012) 110

1. INTRODUCTION

Solar energy is one of the most important sources of clean

energy.Solar thermal energy systems convert solar energy

into heat and solar photovoltaic systems convert solar energy

into electrical energy. In solar thermal energy systems

electrical energy is one of the inputs for extracting the useful

energy. A single unit which is obtained by combining the

solar thermal energy system with photovoltaic panels or solar

cells pasted on the absorber plate is known as a hybrid

collector or photovoltaic thermal collector (PV/T). A hybrid

PV/T collector produces both thermal and electrical energy

simultaneously. This conceptincreases the electrical

efficiency of photovoltaic systems by increased cooling rate

and overall efficiency of the hybrid unit. Hybrid PV/T

collector can significantly reduce overall energy use that

might required to supply for circulating working fluid for

thermal collector and electrical energy required to cool the

PV panels to improve their performance and life. A number

of theoretical, numerical and experimental studies have been

reported on the solar Hybrid PV/T air collector using air or

water as the working fluid. Integrated PV/T collector based

energy system produce both thermal energy and electrical

energy, Kern and Russel [1]. Hybrid energy systems (PV/T)

can be integrated to rooftops of any building to produce

electrical energy, for lighting, hot fluid for space heating and

drying purposes, Agarwal and Tiwari, [2]. For different

months and cities, for a 1.2 m2

PV/T, monthly total energy

was varying from 35-60 kWh and monthly total exergy from

716 kWh with air as the working substance for Indianclimates. The monthly variation of exergy has a similarbehavior like monthly thermal energy for all weather

conditions, Joshi and Tiwari [3]. The thermal efficiency

increases with increase in height and number of fins of a

double pass flat plate solar air heater with longitudinal fins,

whereas the entropy generation was inversely proportional to

the height and number of fins, Naphon [4].

The annual maximum heat and electricity were obtained

in the case of continuous withdrawal from hybrid

photovoltaic thermal (PV/T) solar water heating system,

Dubey and Tiwari, [5]. As per the analytical expression,

overall thermal efficiency of integrated PV/T solar system

increases with increase in constant flow rate and decreases

with increase in constant collection temperature, Tiwari et

al.[6]. Integration of a PV/T and Earth Air Heat Exchanger

(EAHE) system, with the green house would save overall

energy consumption of green house Nayak and Tiwari,

[7].The instantaneous energy and exergy efficiency values of

PV/T air heaters varies from 55% to 65% and 12% to13%respectively, Joshi and Tiwari, [8].The collectors fully

covered by PV modules and air flowing below the absorber

plate give better performance in terms of thermal energy,

electrical energy and exergy gain in the analysis of N hybrid

photovoltaic thermal (PV/T) air collectors connected inseries, Dubey et.al.[9]. The largest irreversibility was

occurring at the conventional solar collectors in which

collector efficiency was lowest. The experimental results also

revealed the use of passive techniques such as staggered

sheets and fins. The efficiency of solar collector has been

increased approximately up to 30% in comparison with theconventional solar collector, Ucar and Inalli [10]. The

photovoltaic roof with ventilated air gap was suitable for theapplication in summer, because this integration could leads to

low cooling loads and high photovoltaic conversion

efficiency,Wang et al.[11].Substantial steps need to be taken

MODELING AND SIMULATION OF A DOUBLE PASS, HYBRID -TYPE (PV/T)

SOLAR AIR HEATER WITH SLATS

M. Srinivas and S. Jayaraj

Department of Mechanical Engineering, National Institute of Technology Calicut, Calicut-673601, India

Email [email protected],[email protected]

ABSTRACT

A solar hybrid energy system having photovoltaic and thermal (PV/T) devices, which produces both thermal and electrical

energies simultaneously is considered for analysis. A double pass hybrid solar air (PV/T) heater with slats is modeled and

fabricated to study its thermal and electrical performance. Air as a heat removing fluid is made to flow through upper andlower channels of the collector. The collector is modeled in such way that the absorber plate is partially covered by PV

modules. The raise in temperature of the solar cell is expected to decrease its electrical performance. Thin metallic strips

called slats are attached longitudinally at the bottom side of the absorber plate to improve the system performance byincreasing the cooling rate of the absorber plate. Thermal and electrical performances of the whole system at varying cooling

conditions are presented. The proposed model can be successfully used for evaluating the effect of different operatingparameters under different ambient conditions for predicting the overall performance of the system. The overall thermal

efficiency at mass flow rate 0.0123 [kgs-1] by experiments and analytically is 36.9 % and 37.4% respectively.

Keywords: Double pass, Photovoltaic, Solar air heater, Slats, Thermal

International Journal of

Energy & Technology

www.journal-enertech.eu

ISSN 2035-911X
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Srin ivas and Jayaraj / I nternational Jour nal of Energy & Technology 4 (34) (2012) 110 2

towards reducing the cost to make PV/T collectors

morecompetitive, Charalambous et al.[12]. The thermal

efficiency of a PV/T dual fluid collector with metal absorber

obtained was nearly 80%, and electrical performance of the

system was satisfactory, and still scope for further

improvement of cooling the photovoltaic panels was noted,

Assoa et al.[13]. The presence of porous media had improved

the thermal efficiency (theoretical and experimental) of thedouble pass solar air heater, Sopian et al.[14]. The

photovoltaic panel temperature decreases with increase in air

gap between panels and roof of building. Gan [15]. The

systematic evolution of photovoltaic technologies for energy

production, namely first, second, third generation PV and

their recent developments are discussed. The efficiency of the

current photovoltaic technology could be improved by usingthin films and higher concentrations of photosensitive

materials. Solar cells produced by nano structured materials

shows reduced weight than conventional solar cells, M V

Biagini et al. [16]. The effect of solid volume fraction on

buoyancy flow inside a solar collector with flat-plate cover

and undulating absorber is analysed numerically. The CuOnano particles with the highest solid volume fraction proved

to be most effective in enhancing performance of heat

transfer rate than base fluid. Average heat transfer is found to

be higher for convection than radiation. Nasrin and Alim.

[17]. It is observed that the present researchers tried to

improve the efficiency of box type collector .Very few works

were attempted to extract accumulated heat in the absorber

plate (PV panel) with fins, and concluded that there is still

scope for performance improvement by heat extraction.

Almost 90% of above reported works were on single pass

PV/T collectors.

In the present work, a new design of double pass hybrid

(PV/T) solar air heater with slats (DPHSAH) was studiedanalytically and experimentally. This design is a beautiful

blend of solar thermal energy system (double pass solar air

heater with slats) and solar photovoltaic system. To the best

of authors knowledge no work had been reported with slats

attached to absorber plate. Monocrystalline silicon solar cells

were used in the device. A computer code (C- language) was

made in computing analytical results.

2.MATHEMATICAL MODEL

A steady state one dimensional analysis is done on the

system. The governing equations are obtained which involvesthe energy balance equations at various parts of the collector.The heat transfer model is as shown in the Fig.1.

To simplify the analysis following assumptions were made.

i. The system is in quasi - steady stateii. One dimensional heat conduction is good

approximation for the present study

iii. Temperature of the glass cover, PV panels(absorber plate) and back plate vary only in the

air flow direction

iv. The glass cover, PV panels (absorber plate) andback plate are at uniform temperature

v. Good contact between the PV panels andabsorber plate, slats and the back plate is

achieved

vi. The ohmic losses in the solar cell are negligible2.1 Energy balance

The energy balance equations are written for various

segments of the PV/T hybrid air heater with slats as given

below.

(i) Glass Cover

pgrpgfgcgfwgcgwsgrgsg TThTThTThTThS 11 (1)

(ii) Absorber Plate

0

2211

221

11

z

sl

c

fpcpffpcpfbpprpbpgprpgpvpgpgdZ

dTknAATThTThTThTThSPPS

(2)

(iii) Bottom Plate

abpbfbpcbpfDz

sl

c

bpprpbp TTUTThdz

dTknA

ATTh

22

1

(3)

(iv) Metal slat

LdzTThdz

dTkA

dz

dTkA

Dz

z

fslcslf

Dz

sl

z

sl

0

22

0

)(2

(4)

(v) Air stream between glass cover and collector plate

)()( 111111

.

fpcpffgcgf

ffTThTTh

dx

dT

W

Cm (5)

(vi) Air stream between absorber plate and bottom plate

Dz

z

fpcpf

c

fbpcbpf

fpcpf

ff

dzTTLnhA

TTh

TThdx

dT

W

Cm

0

2222

22

22

.

)(21

)(

)(

(6)

2.2 Analytical solution

The variablesTg, Tp, and Tbp can be eliminated from

Eqs. (5) and (6) by substituting Eqs (1) (4) in to them.The


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following two linear first-order differential equations

areobtained.

322111ATATADT fff (7)

322112BTBTBDT fff (8)

Ddx

d

Where A1, A2, A3, B1, B2 and B3 are the constants

obtained through algebraic manipulations. The Eqs. (7) and

(8) can be solved by using operational method in Closed-form

solutions with the following boundary conditions.

At x = 0, af TT 1 (9)

At x = L, 21 ff TT (10)

Hence, the temperatures of the fluid in both channels as a

function of distance in flow direction (x-direction) can be

obtained.

3

2121

3131

2

2

222211

1

1

11

BABBA

BAABBeBDCeBDC

BT xDxDf

(11)

2121

3131

212

21

ABBA

BAABeCeCT xDxDf

(12)

Where

C1, C2: the constants obtained by applying the boundary

conditions into Eqs. (11) and (12).

D1, D2: the roots obtained from the second-order differential

operator equation.

3. PERFORMANCE PARAMETERS

The instantaneous thermal efficiency for PV/T DPHSAHis expressed as

dtS

dtTTcm ioth

.

(13)

The instantaneous photovoltaic efficiency for PV/T

DPHSAH is expressed as

dtS

dtPE

pvt (14)

Where SPP pvpvgE (15)

Where refpavrefpv TT 0054.01 (16)

Where ref is the reference efficiency of solar cell at Tref =

25C and the mean cell temperature Tpav is obtained by

integrating the function Tp(x) as follows

Lx

x

Lx

x

p

pav

dx

dxxT

T

0

0 (17)

The combined photovoltaic thermal efficiency of the

system is expressed as

pvthE

io

othSdt

dt

P

dtTTcm

)38.0()(

.

(18)

Fig. 1. Physical model of double pass hybrid photovoltaic

thermal (PV/T) air heater with slats.


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4. HYBRID (PV/T) SYSTEM DESIGN

The double pass hybrid photovoltaic thermal (PV/T) solar

air heater (DPHSAH) consisted of aluminum absorber plate

of dimensions 1 m x 2 m (Wx L) and thickness 2 mm. The

height of the upper and lower channels was 5 cm (each). The

sides and bottom of the collector were insulated with a 5 cm

thick layer of thermocol. Nine slats of size 5 cm height, 2 mlong and thickness of 2 mm (each) were fixed longitudinally

at equal distance at the bottom side of the absorber plate. Top

surface of the absorber plate and lower channels were coated

with black paint for increasing the absorptivity of the system.

A toughened or tempered glass of dimensions 1 m x 2 m (Wx

L) and thickness 2 mm was provided as front cover for

reducing convection heat losses from the collector. The PV

modules (mono-crystalline silicon solar cells) of glass totedlar type each rated at 25Wp having dimensions 545 mm x

445 mm, were fixed over an absorber plate. Each PV module

consisted of 36 solar cells, connected in series. Two rows,

with four panels in each were connected in series and finally

these two arrays are connected in parallel for obtaining rated(200 Wp) nominal peak power as shown in Fig. 2 (b). Series

connection of solar cells or PV modules enhanced voltage

and parallel connection of solar cells or PV modules

enhanced current. The total area covered by solar cells was

1.054 m2. And the packing factor or the fraction of the total

collector area covered by the solar cells is 0.527.

Specifications of DPHSAH aregiven in Table1 and Table

2.The double pass PV/T solar collector is shown

schematically in Fig. 2(a), and schematic representation of

PV modules connections is shown in Fig. 2 (b).

Fig. 2 (a). Double pass hybrid photovoltaic thermal (PV/T)

solar air heater with slats.

Fig. 2 (b). schematic representations of PV module

connections.

Table 1:Specifications of double pass solar air heater with

slats

Element of system Sizes of element

Absorber plate

( Aluminium absorber ) (1 m X 2 m), (thickness 2mm)

Bottom Plate

(Aluminium plate)(1 m X 2.1 m), (thickness 2mm)

Slats

(Aluminium)

(9 per 1 meter width), (length = 2

m each)

Top Glazing

(Toughened glass)(1 m x 2 m), (thickness 2 mm)

Insulation (Thermocol) 5 cm thick

Table 2: Specifications of double pass solar air heater with

slats

Parameter Value

Nominal peak power (Wp) 25 Wp

Maximum power voltage (Vmpp) 16.8 V

Maximum power current (Impp) 1.49 A

Open circuit voltage (Voc) 21.2 V

Short circuit current (Isc) 1.79 A

Solar cell efficiency (c) 13%

Module efficiency (m) 10%

Length of a PV module (l) 545 mm

Width of a PV module (w) 445 mm

5. EXPERIMENTAL SETUP

PV panels made of mono-crystalline silicon solar cells

were pasted on the absorber plate of a box framed solar air

heater to obtain the hybrid (PV/T) solar air heater. An airblower for circulating the air was fitted at the ground end of

the system. Air entered through the upper channel formed by

the glass cover and the photovoltaic panels and was heated

directly by the sun and the channel walls. After that it flows

through the lower channel formed by the back plate with slats

and the absorber plate. The slats fixed at the back of the

absorber plate (photovoltaic panel) increases the heat transfer

rate to the air and by conducting heat to bottom plate thus

enhances the efficiency of the system by introducing

sufficient turbulence in the lower channel. The setup is

situated in open sky avoiding nearby shading effect which

will reduce the solar insolation effect on the system as shown

in Fig. 3 and Fig. 4. The double pass hybrid photovoltaic

thermal (PV/T) solar air heater (DPHSAH) is kept 110

facing

south at the Solar Energy Center located in National Institute

of Technology Calicut.


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Fig. 3. Double pass hybrid photovoltaic thermal (PV/T) solarair heater with slats.

Fig. 4. Instrumentation used for the experimentation.

5.1 Instrumentation

The following parameters were measured during

experimentation:

i. Inlet air temperatureii. Outlet air temperature

iii. Absorber plate temperature (PV panel)iv. Slat temperaturev. Bottom plate temperature

vi. Solar insolationvii. Load current

viii. Load voltage5.2 Experimental procedure

The PV/T collector was tested at nominal operating

conditions in order to study the electrical, thermal and overall

performance of the system. The solar radiation was measured

using a digital pyranometer installed parallel to the collector

plane. Electrical air blower was used to produce air flow in

the collector and it was controlled through an autotransformer

for different mass flow rates. The air mass flow rate was

determined by the orifice meter which was connected at the

outlet pipe of the collector. The flow rate was varied from0.005 to 0.0123 kg/s. The minimum flow rate corresponds to

1 cm head and maximum flow rate corresponds to 6cm head

of water column in U tube differential manometer of orifice

meter. Calibrated Chromel Alumel (K type) thermocouples

with digital temperature indicator are used to measure

temperatures at several locations of the system. Ambient air

temperature and collector outlet air temperatures are

measured by digital thermometers provided at suitable

locations. Load was connected to the PV cells through a 50

, 5A rheostat for measuring the load voltage and load

current multimeters were used separately. The PV/T solar

collector was operated at a fixed mass flow rate from sunrise

to sunset under clear blue sky. All the measurable parameters

are recorded at every 1 hour time interval. Data collected was

used to determine the thermal, electrical and overall

efficiency of the system. The system was operated for

different mass flow rates to study the performance variation

of the PV/T solar collector.

6. PERFORMANCE ANALYSIS

The performance of a photovoltaic thermal (PV/T) solar

collector can be described by a combination of efficiencyterms.

100

c

thSA

Tcm (19)

100cell

LLel

SA

VI

(20)

)38.0/()( 0 elthth (21)

Overall thermal efficiency (Eq.3) from a PV/T system is

given by the combination of thermal efficiency from the

PV/T system and electrical efficiency from the PV/T systemdivided by electrical power generation efficiency (0.38) of a

conventional power plant. Huang et al.[18]. Since thermal

energy is low grade energy and electrical energy is high grade

energy, electrical power generation efficiency is used to

express electrical energy in terms of low grade energy.

6.1 Uncertainty analysis

Determination Uncertainty in the measured results of

experimentation is important.

Root Sum Square method can be used to determine

the combined effect of random measurement errors.


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According Root sum Square method to the result R is a given

function of independent variables x1, x2, x3 xn.

Thus R= R (x1, x2, x3 xn) (22)

Let wRbe the uncertainty in the result and w1, w2, w3 .wnbe the uncertainties in the independent variables. If the

uncertainties in the independent variables are all given withthe same odds, then the uncertainty in the result having these

odds is given as ( Holman[19]).

22

3

3

2

2

2

2

1

1

.......

nn

R wx

Rw

x

Rw

x

Rw

x

Rw

(23)

Uncertainties associated with the individual elements of

the DPHSAH are given in Table 3.The uncertainity in theresults of calculations of thermal efficiency was obtained as

4.2%. Similarly, the uncertainty in the calculation ofelectrical efficiency is 0.2% and the uncertainty in the

calculation of overall thermal efficiency is 5.6%.

Table 3:Uncertainties associated with the individual elements

of the DPHSAH

Equipment Measurement Error

Thermocouples PV/Tairtemperature 1 C

Pyranometer Irradiance 5%

Multimeter PV current 1%

Multimeter PV voltage 1.4%

7. RESULTS AND DISCUSSION

The maximum temperature rise of the fluid at different air

mass flow rates is shown in Fig. 5. It has been observed that

with increase in air flow rates, for a fixed solar insolation (S =

625 [Wm-2

]) ambient temperature (Ta = 301 [K]), analytical

maximum temperature rise is showing a decreasing trend.

This may be due to the extraction of system accumulated

thermal energy at higher mass flow rates. Experimental

results are also found to follow the trend shown by the

analytical results; the variation in the experimental results

obtained can be due to the variation in outdoor ambient

conditions.

Fig. 5. Variation of air temperature with air mass flow rate.

Analytically, air temperature rise is showing an increasing

trend with solar insolation, thismay be due to the increase in

the available thermal energy owing to the increase in

insolation on the collector. However, higher the mass flow

rate of the air to the system, for the same insolation and

ambient air temperature (Ta = 301 [K]) lower the rise in air

temperature due to heat capacity of air as shown in the Fig. 6.

It is also observed that experimental results are following thetrend of the analytical results, with little variation due touncontrollable outdoor conditions.

Fig. 6. Variation of air temperature against solar insolation at

different air mass flow rates.

Figure 7 shows that temperature dependent electrical

efficiency of the (PV/T) system increases with increase in air

mass flow rates for fixed ambient conditions (Ta = 301 [K]).It is also observed that, increase in solar insolation increases

the absorber (PV panel) temperature, which reduces the

electrical performance of the system, as shown in the Fig. 7.

Fig. 8 shows that unlike electrical performance of the system

the thermal performance increases for fixed ambient

temperature and air flow rate to the system. This is due to

the absorber plate (PV panel) being subjected to higher

temperatures at higher solar insolation owing to lower

specific heat property of aluminium.

Fig. 7. Variation of electrical efficiency against mass flow

rate at different solar insolations (analytical).


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Fig. 8. Variation of thermal efficiency against mass flow rate

at different solar insolations (analytical).

Fig. 9. Variation of electrical efficiency against different air

mass flow rates.

Electrical efficiency (both analytical and experimental)

increases with mass flow rate of air as shown in Fig.9. It is

observed that the higher mass flow rates are able to extractthe accumulated thermal energy from the absorber plate (PV

panels), and thus improving the electrical performance of the

system. The analytical results are found to follow the trend of

the experimental results.

Thermal efficiency (both analytical and experimental)increases with mass flow rate of air as represented in Fig. 10.

It is observed that the higher mass flow rates are able to

extract the accumulated thermal energy from the absorber

plate (PV panels), and thus improving the thermal

performance of the system. The analytical results are found to

follow the trend of the experimental results.

Fig. 10. Variation of thermal efficiency against different airmass flow rates.

Figure 11 shows that overall thermal efficiency (both

analytical and experimental) increases with mass flow rate of

air. It is observed that higher air flow rates improve the

thermal, electrical and overall performance of the system.

Overall performance is obtained by converting high grade

energy (electrical energy) in to equivalent low grade energy

(heat). It is also observed that, most of the time there is a

chance for fluctuations in outdoor conditions with respect tosolar insolation and ambient air temperature, which causesthe intermediate drop and rise of the thermal, electrical and

overall performance of the system. This uneven heating and

cooling causes regular expansions and contractions within the

layers of structure of PV panels (a glass to tedlar

monocrystalline silicon solar cells are covered both sides by

EVA with top cover as ARC), which is the main reason forthe limited life period of PV panels (25 years for mono-

crystalline silicon solar cells). If the system is operated at

higher air mass flow rates this draw back on life and electrical

performance of the PV panel can be reduced, thus the overall

performance of the system can be increased by operating at

higher air mass flow rates. It is also revealed that whenelectrical performance is lower due to higher absorber plate

temperature (PV panel), thermal performance is higher, and

thus loss in electrical performance is compensated in thermal

performance of the system. At times when thermal

performance is lower due to lower ambient temperature,

electrical performance is higher due to smaller PV panel

temperature. However, electrical performance is always

controlled by the solar insolation.

Fig. 11. Variation of overall efficiency against different air mass

flow rates.

8. CONCLUSIONS

Hybrid photovoltaic-thermal solar collector with slats was

analytically and experimentally studied with respect to itsoperating characteristics. Solar cells generate more electricity

when it is exposed to higher solar insolation, its efficiency

drops when temperature of the solar cells increases. Results

show that electricity production in a PV/T hybrid module

decreases with increasing panel temperature. At times when

electrical performance of the PV panel is lower due to higher

absorber plate temperature, corresponding thermal

performance is higher. Thus loss in electrical energy output is

compensated by thermal gain of the system, which makes

hybrid system highly relevant for energy conversion. It isimportant to use slats as an integral part of the absorber

surface in order to achieve better efficiencies. In this case,

both thermal and electrical output of the hybrid PV/T solar


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collector is expected to improve sufficiently. At a mass flow

rate of 0.0123 [kgs-1

] the electrical, thermal efficiencies by

experiments and analytically equals to 6.05%, 21% and 9.3%,

12% respectively.

APPENDIX

Heat transfer coefficients

The different heat transfer coefficients for each surface in

the solar air heater system can be evaluated as follows:

(i) Wind convection coefficient

The convection heat transfer coefficient from the top

cover due to wind is correlated by Watmuff et al.,

wa Vh 3.38.2

Correlation suggested by (Ammari [20]) proposed by

(Watmuff et al.[21])

Vw = average wind velocity [m s-1

]

(ii) Convection coefficient for the channel flow

For laminar flow region (Re < 2300) (Heaton et al.[22])

correlation, suggested by (Ammari[19])

17.1

71.1

PrRe00563.01

PrRe00190.0

4.5

LD

L

D

Nu

h

h

For turbulent region or for Re > 2300, the following

(Kays and Craw ford [23]) correlation can be used

8.0Re0158.0Nu

hDRe

Pr = Prandtl number

Re = Reynolds numberDh = hydraulic diameter = 2d[m]

d= plate spacing [m]

(iii) Inner surface heat transfer coefficients in ducts

For turbulent flows inside tubes (for Re > 2300)

(Petukhov[24]) correlation

11.0

32

1Pr8

7.1207.1

PrRe8

wf

f

Nu

Here

264.1Reln79.0 f

f is friction factor

is viscosity of air at its temperature[Nsm-2

]

w is viscosity of air at wall temperature [Nsm

-2

]

perimeterwetted

areaflowDh 4

The radiation heat transfer coefficients between theparallel plates can be computed using following equations.

ag

sgsgsgg

rgsTT

TTTTTTh

22

111

22

bpp

bppbpp

rpbp

TTTTh

111

22

gp

pgpg

rpg

TTTTh

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NOMENCLATURE

A slat cross section area [m2]

Ac area of absorber plate [m2]

A cells solar cells area [m2]

C specific heat [kJkg-1

K-1

]

D depth of the slat [m]

Dh hydraulicdiameter [m]

H heat transfer coefficient [WK-1

m-2

]

IL current [ampere]

k thermal conductivity [Wm-1K-1]

L collector length [m]

mass flow rate of air [kgs-1

]

n number of slats

P solar cell packing factor

PE electrical energy [W]

S solar insolation [W m-2

]

T Temperature [K]

Ub bottom heat loss coefficient [W K-1

m-2

]

VL voltage [volt]

W width of the collector [m]

X distances alongues the collector in flow direction [m]

Z vertical distance along the slatdepth [m]

Greek letters

absorptivity

emissivity

el electrical efficiency

th thermal efficiency

(th)o overall thermal efficiency of the system

Stefan Boltzman constant (5.67 x 10-8

[Wm-2

K-4

])

transmissivity

Subscripts

a ambient

av average

bp bottom plate

c convective

f1 working fluid in the upper channel

f2 working fluid at the lower channel

g glass plate

I inlet

o outlet

p absorber plater radiative

s sky

sl slat


10/10

Srin ivas and Jayaraj / I nternati onal Jour nal of Energy & Technology 4 (34) (2012) 110 10

w wind

Abbreviations

ARC anti reflective coating

CPC compound parabolic concentrator

DPHSAH double pass hybrid solar air heater

EAHE earth air heat exchanger

EPBT energy payback time

EVA ethylene vinyl acetate

IMD Indian Metrological Department

PV/T photovoltaic thermal

THE MATERIAL WITHIN THIS PAPER, AT THE AUTHORS RESPONSIBILITY, HAS NOT BEEN PUBLISHED

ELSEWHERE IN THIS SUBSTANTIAL FORM NOR SUBMITTED ELSEWHERE FOR PUBLICATION. NO

COPYRIGHTED MATERIAL NOR ANY MATERIAL DAMAGING THIRD PARTIES INTERESTS HAS BEEN USED IN

THIS PAPER, AT THE AUTHORS RESPONSIBILITY, WITHOUT HAVING OBTAINED A WRITTEN PERMISSION.

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Double Pass, Hybrid -Type (Pvt)