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					International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 6, November - December (2013) © IAEME
                             AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)                                                     IJMET
Volume 4, Issue 6, November - December (2013), pp. 91-99
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2013): 5.7731 (Calculated by GISI)                 ©IAEME
www.jifactor.com




  PERFORMANCE ANALYSIS OF AN OSCILATORY FLOW DESIGN HEAT
       EXCHANGER USED IN SOLAR HYBRID WATER SYSTEM

                   V. N. Palaskar1,   S. P. Deshmukh2*, A.B. Pandit3,    S.V. Panse4
        1
            Dept. of Mechanical Engineering, Veermata Jijabai Technological Institute Mumbai.
             2*
                Department of General Engineering, Institute of Chemical Technology Mumbai.
            3
              Department of Chemical Engineering, Institute of Chemical Technology Mumbai.
                    4
                      Department of Physics, Institute of Chemical Technology Mumbai.



ABSTRACT

        Electrical efficiency of commercial PV module drops to 10-35% because of its heating. By
removing this detrimental heat, efficiency of module can be improved considerably. Module with
temperatures at 25°C can produce 10-35% more power. Practically PV modules convert up to 15% of
solar energy into PV energy and remaining 85% energy is lost to surrounding in the form of heat.
Thus in general module generates more heat than PV energy and heat thus generated remains unused.
Hybrid PV/T solar system combines commercial PV module and solar thermal water collector
forming an integrated system that produces simultaneously electricity and thermal energy. An
oscillatory flow PV absorber surface and its effect on performance of hybrid solar system are studied
in this paper. Experimental outcomes like PV, thermal and combined PV/T efficiencies over a range
of operating conditions are discussed and analyzed for Mumbai latitude. The final results showed
combined PV/T efficiency of 53.7 % and PV efficiency of 11.7 % at solar irradiance of 918 W/m2
and mass flow rate of cooling water at 0.035 kg/sec.

Keywords: Commercial PV Module, Solar Thermal Water Collector, Hybrid PV/T Solar Water
Systems, Oscillatory Flow PV Absorber, Combined PV/T Efficiency.

1. INTRODCTION

       An absorbed solar radiation by PV module results in generation of electricity and it’s heating.
The cooling of PV module improves its electrical efficiency at a reasonable level. Generally PV
module cooling is done by circulation of cold water through a heat exchanger called as PV absorber
surface, fixed at bottom side of commercial PV module. In hybrid PV/T solar water system,
commercial PV module and thermal water collector are mounted together and this combined system

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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 6, November - December (2013) © IAEME

can simultaneously convert solar energy to electricity and thermal energy. This system will generate
higher combined energy output per square meter than commercial PV modules and could be cost
effective in future if additional cost of thermal unit is low.
        Seven new designs for heat exchangers namely Direct flow, Oscillatory flow, Serpentine flow,
Web flow, Spiral flow, Parallel-Serpentine flow and Modified Serpentine-Parallel flow type of hybrid
PV/T collectors were designed, investigated and their performance were compared by simulation
techniques [1]. From simulation results it was concluded that spiral flow design produced highest
thermal efficiency of 50.12% with cell efficiency of 14.98%.
         Different experiments had been performed on sheet and tube heat exchanger PV/T water
collector systems attaching flat concentrators to sides of PV module [2]. Two flat Aluminum
concentrators were mounted to sides of PV module at an angle 100 and 560 to the vertical plane of
PV/T water collector. These aluminum sheet concentrators were found more effective as compared to
conventional PV module in producing PV electric and thermal energy in the range of 8.6% and 39 %
respectively. Aluminum foil concentrators produce 17.1% PV energy and 55% thermal energy more
than.
         Experimental studies were conducted on hybrid PV/T water collector system by using two
heat exchanger surfaces i.e. Sheet and tube type absorber and fully wetted absorber [3]. During the
experiments it was observed that, the wetted collector surface and sheet-and-tube surface produced
combined PV/T efficiency of 65% and 60.6% respectively. The performances of above two absorber
surface were also compared by considering unglazed and glazed designs. The final result showed that
unglazed system produces more electrical energy than conventional PV module due to the PV
module cooling effect because of heat exchanger. It was also found that the glazed system generated
more thermal energy compared to unglazed system due to solar radiation reflection and increase in
the PV module temperature introduced by the glass cover.
        Investigational study was performed on PV/T water collector system using a stainless steel
spiral flow absorber collector as a heat transfer or heat exchanger surface [4]. In this study the
performance of photovoltaic, thermal and combined photovoltaic-thermal water collector system
over range of operating conditions were discussed and analyzed. At solar irradiance of 1321 W/m2
and mass flow rate of 0.041 kg/s of cooling water, hybrid PV/T system produced combined PV/T
efficiency of 65 % with electrical efficiency of 12%.
        Experimental study was performed on conventional PV module by running thin film of water
over top surface to cool it to increase its overall performance [5]. The above result showed that
working temperature of PV module for combined system was lower as compared to conventional PV
module. Since heat removed from PV module by water film was utilized for low temperature
applications, overall efficiency of combined system was higher than conventional module.
Experimental results of this study showed that electrical performance of the combined system was 33%
higher than un cooled module.
        Three PV/T water collector systems i.e. direct flow, Parallel flow and Split flow were
designed and their thermal performances were compared experimentally at various tilt of hybrid
PV/T system [6]. During these experiments, it was found that the split flow PV/T system was able to
produce 51.4 % thermal power as compared to other two PV/T systems.
        In this study, performance analysis of commercial PV module and hybrid PV/T solar system
are compared on the basis of various technical parameters at ATC conditions for Mumbai latitude.
Commercial PV module is converted to hybrid PV/T system by fixing an oscillatory flow design PV
absorber heat exchanger at backside of PV module. This heat exchanger had been designed and
fabricated by using Aluminum square tubes. Aluminum tubes are used for this study for its high
thermal conductivity and light weight. Hollow square tube shaped pipes were used to fabricate heat
exchanger to enhance surface contact between back side of PV module and top side of heat
exchanger. Increase in PV power, thermal power, Photovoltaic, thermal and combined PV/T

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efficiency and decrease in top and bottom module temperatures at different flow rates for highest
electrical power point condition are discussed and analyzed. Performance ratio of the commercial PV
module and hybrid PV/T system has been calculated and compared.

2. EXPERIMENTAL

2.1 Commercial PV module with stand
        A commercial PV module made by Tata Bp India, of 180 watts of capacity was selected to
predict effect of water cooling on its performance for latitude of Mumbai. Electrical specifications of
the module are given in Table-1 at standard test conditions (STC). The manual tracking was used to
track PV module to South direction at different slopes during experimental process. Commercial PV
module fixed on stand is placed on roof of institute’s main building at I.C.T. Mumbai.

                              Table 1 Electrical data of the PV module
   Module      Power    ISC   VOC       IMP     VMP     FF    η mod    Module     Module       PV
                                                                                             module
               (W)     (A)     (V)      (A)     (V)            (%)      L (m)     W (m)     area (m2)

 Tata Bp        180    5.4    44.8     4.99     36.6   0.75    14.5      1.58      0.79       1.25
 Mono
 Crystalline



2.2 PV absorber or heat exchanger surface
        The combined efficiency of PV/T system depends on materials used and design configuration
of PV absorber surfaces or heat exchangers mounted at back side of      PV module. To ensure good
experimental results, aluminum square tubes were used as it has high thermal conductivity and it is
light in weight. Various configurations of PV absorber surfaces were designed and tested by
simulation to predict highest combined hybrid PV/T efficiency under certain range of weather
conditions [2].
        The hybrid system to be generated maximum combined PV/T efficiency, oscillatory flow PV
absorber was fabricated using aluminum hollow tubes of square cross section. The selected size of
hollow square aluminum tube was 12 x 12 mm with 1 mm thickness. The pitch of 34 mm was
maintained between two consecutive tubes respectively for forming complete heat exchanger. The
said heat exchanger was fabricated using argon welding technique in house. The actual installation of
an oscillatory flow PV absorber surface at rear side of PV module is shown in fig.1. Total pathway
followed by cold water as inlet to hot water outlet was designed 36 meters length. Total PV module
surface area occupied by heat exchanger surface was 37%. This heat exchanger area absorbs heat
from bottom side of PV module and cools it at satisfactory temperature level. The hydraulic test was
conducted on heat exchanger by pump to locate and eliminate minute leakages in joints and passages
of water flow, before it was finally assembled in experimental setup.




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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     Figure 1 Installation of an oscillatory flow PV absorber surface at rear side of PV module

2.3 Fiber Glass wool
       Fiber Glass wool insulation with thermal conductivity of 0.04 W/m 0k was inserted on
backside of PV absorber surface. The main purpose of fitting glass wool insulation at back side of
heat exchanger was to insulate heat exchanger by reducing overall temperature loss of the system. A
blanket form of glass wool with 50 mm thick and 24 Kg/ m3 density were used from backside of heat
exchanger. Aluminum sheet cover plate of 16 gauges was attached protecting glass wool and to form
a complete assembly of hybrid PV/T solar system.

2.4 Measuring instruments
        A Dynalab Radiation Pyranometer was used to measure global solar radiations mounted
parallel to PV module surface. An ACD Anemometer was fitted to measure wind velocity of
surrounding air. K-type thermocouples were used to measure ambient temperature and temperatures
at top and bottom of PV module. A Sixteen channel temperature data logger was used to scan and
record thermocouple temperatures of PV module during experiments over a day. A DC voltmeter and
Ammeter were used to measure voltage and current at various loading conditions over a day. A DC
load bank of 36-Volt with 180-watts capacity was used to measure voltage and current across load
applied to PV module during experiments. A 500 LPH Rota meter was used to measure flow rate of
water at inlet of an oscillatory flow PV absorber surface over a day. Dial type temperature gauges
were used to measure inlet and exit water temperatures of heat exchanger. Electrical water pump was
used to circulate cold water through PV absorber or heat exchanger surface to trap heat and cool PV
module. A Complete assembled experimental set up with all components is shown in fig. 2.




              Figure 2 Hybrid (PV/T) solar water system which shows all Measuring
                  Instruments/ apparatus connected each other to form assembly


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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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2.5 Experimental observations
        The main objective of this research work was to analyze the performance of oscillatory flow
PV surface of hybrid PV/T solar system at ATC conditions for Mumbai latitude. All experiments
were conducted during month of May-2013. For this month 50 slopes (Mumbai latitude-150) was
selected with horizontal surface at south direction. Electrical and/or thermal energy generated by
solar equipments were proposed to operate for 5 to 6 hrs per day and 300 days per year for Indian
climate. To predict accurate performance of hybrid PV/T system over a day, daily experiments were
started at morning 9:30 am and were continued till 4:30 pm (7 hrs per day). The electrical energy
produced by PV module over a day was dependent on two main key factors i.e. intensity of solar
radiation falling on module surface and rise in module temperature. Intensity of solar radiation was
found fluctuating over a day and raise of module temperature was found directly proportional to
solar radiation.
        Experiments had been performed on hybrid PV/T solar system at set slope to estimate various
parameters practically. For this different reading such as global radiation; wind velocity of
surrounding air; voltage and current at corresponding loading conditions were recorded at 30 minutes
time interval. K-type thermocouples were attached to data logger to scan and record temperatures of
PV module at various points at top & bottom side and ambient air temperature in 30 second time
interval. Some additional readings such as inlet and exit water temperatures of the system were
recorded to calculate thermal power for every 30 minutes of time interval. This experiment was
conducted on three separate days for different water flow rates such as 0.028, 0.035 and 0.042 kg/sec
respectively. This was done to predict the optimum flow rate of system generating highest PV,
thermal, combined PV/T efficiency and performance ratio. During experiments for different flow
rates, water pump was used to circulate cool water through heat exchanger of PV/T system between
10 am and 3 pm.

3. EQUATIONS USED TO CALCULATE VARIOUS PARAMETERS

       Table 2 shows different equations had been used to calculate photovoltaic power, thermal
power, input solar power, performance ratio, photovoltaic, thermal and combined PV/T efficiency at
ATC conditions for Mumbai latitude [7].

                       Table 2 Equations used to calculate various parameters
                          PPV = V * I                                  (1)

                          PT =         * Cp * (Twe –Twi )              (2)

                          IG = IGn * APV                               (3)

                          PR= PPV/PSTC                                (4)

                            PV   = (V * I)/ IG                         (5)

                            T   = PT / IG                              (6)

                            PV/T   =    PV   +   T                     (7)




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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4. NOMENCLATURE AND GREEK SYMBOLS

       V                        :     PV module voltage at ATC conditions for Mumbai latitude (V)
       I                        :     PV module current at ATC conditions for Mumbai (A)
       APV                      :     Area of PV module (m2)
       PPV                      :     Electrical power produced by PV module (W) at ATC conditions
       PSTC                     :     Electrical power produced by PV module (W) at STC conditions
       PR                       :     Performance ratio of PV module (%)
       ηPV                      :     Electrical Efficiency of PV module (%)
       IGn                      :     Total or Global Solar radiation measured by Pyranometer
                                      (installed at parallel to PV module surface) (W/m2)
                                :     Mass flow rate of water (kg/sec)
       Cp                       :     Specific heat of water (J/kg 0K)
       Twi                      :     Water inlet temperature (0K)
       Twe                      :     Water exit temperature (0K)
       PT                       :      Thermal power produced by hybrid (PV/T) solar water system (W)
         T                      :     Thermal efficiency hybrid (PV/T) solar water system (%)
         PV/T                   :     Combined PV/T efficiency (%)

5. RESULTS AND DISCUSSION

5.1 Performance of hybrid PV/T solar water system
        During the experimental work it was found that the open circuit voltage and voltage at
highest electrical PV power point of module increased to 39.80 V and 30.3 V at 1 pm respectively
with PV module cooling. At the same time period, hybrid system was able to produced highest
current of 4.43 Amps. It was observed that PV output power and efficiency were increased
significantly as a result of cooling effect and it was able to reduce the working temperature of the PV
module. The highest PV power of 134.2 W and efficiency of 11.7 % respectively were observed
during experimental work are shown in figure 3 and 4. A bonus thermal power of 482 W was
obtained from hybrid PV/T solar water system at mass flow rate of 0.035 Kg/sec as shown in figure
5. The maximum temperature of exit water from heat exchanger was measured to 38 0C. This hot
water is suitable for low temperature applications such as domestic, swimming, and preheating etc.
Performance ratio of the combined system was found increased to 75 % as result of cooling effect.
        The combined PV/T efficiency of 53.7 % was obtained from hybrid system at mass flow rate
of 0.035 Kg/sec at highest PV power point condition as shown in figure 5. By attaching heat
exchanger to PV module and utilizing its waste heat energy, module working temperature had been
decreased to 46.7 0C as shown in figure 6.       The Photovoltaic, thermal and combined efficiency for
hybrid PV/T water system for various mass flow rates at highest electrical power point condition are
shown in figure 7.
                               180
                               160
                               140
         Photovoltaic output




                               120
            Power (W)




                               100
                                80
                                60
                                40
                                20
                                 0
                                    09:0009:3010:0010:3011:0011:3012:0012:3013:0013:3014:0014:3015:0015:3016:0016:3017:00
                                                                      Time (Hrs)
                                Figure 3 Photovoltaic power produced by cooled PV module over a day
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                                   16
                                   14


         PV module efficiency
                                   12
                                   10
                                    8
               (%)                  6
                                    4
                                    2
                                    0
                                       09:0009:3010:0010:3011:0011:3012:0012:3013:0013:3014:0014:3015:0015:3016:0016:3017:00
                                                                               Time (Hrs)
                                         Figure 4 Photovoltaic efficiency of cooled PV module over a day

                                  70
                                  60
                                  50
            PV/T Efficiency (%)




                                  40
                                  30
                                  20
                                  10
                                   0
                                   09:0009:3010:00 10:3011:00 11:30 12:0012:30 13:0013:30 14:00 14:3015:00 15:3016:0016:30 17:00
                                                                              Time (Hrs)
  Figure 5 Photovoltaic efficiency of combined PV/T efficiency of cooled PV module over a day


                                         70
                                         60
                Top side PV Module




                                         50
                 temperature (0C)




                                         40
                                         30
                                         20
                                         10
                                          0
                                                09:0009:3010:0010:3011:0011:3012:0012:3013:0013:3014:0014:3015:0015:3016:0016:3017:00
                                                                               Time (Hrs)
        Figure 6 Top side temperature (TTPV) attended by cooled PV module over a day

                                                      60
                                                      55
                                                                  ηPV
                                                      50
                                                      45          ηT
                                                      40          ηPVT
                                         Efficiency




                                                      35
                                                      30
                                                      25
                                                      20
                                                      15
                                                      10
                                                       5
                                                       0
                                                           0     0.01         0.02         0.03          0.04         0.05
                                                                         Water mass flow rate (Kg/sec)

  Figure 7 Maximum Photovoltaic, Thermal and combined efficiency for various mass flow rates

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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5.2 Performance comparison of commercial PV and hybrid PV/T solar system
         The Performance comparison of un cooled PV module and cooled PV module or hybrid PV/T
system under actual test condition at highest PV power point condition is shown in table 3. Effect of
cooling showed drastic increase in working voltage, current, PV power, and PV efficiency
respectively. This hybrid system was able to generate thermal power of 482 W and efficiency of 42%
with mass flow rate of 0.035 Kg/sec.
         By partial removal of waste heat from the PV module it was possible to generate maximum
photovoltaic efficiency of 11.7 %, thermal efficiency of 42% and combined PV/T efficiency of
53.7 % respectively. The above results showed that 53.7% solar power was converted into useful
work and remaining 46.3 % waste heat increased the temperature of module and its surrounding air.
With use of thermal grease between bottom side of module and top side of heat exchanger, electrical,
thermal and combined efficiency may be enhanced significantly and working temperature of module
can be maintained at reasonable level. So life span of commercial modules can be increased
drastically and it can be used in desert area.
         Flat reflectors attached to module sides of hybrid system, may increase performance of this
system drastically in terms of generation of current. Current produced by module is linearly
propositional to intensity of solar radiation. Intensity of solar radiation falling on module is
dependent on concentration ratio. By adding reflector overall performance of above system could be
improved with marginal increase in cost of equipment and system can be used for low to medium
temperature applications in future. Replacing aluminum oscillatory flow design with square copper
spiral flow design PV absorber may enhance overall performance of hybrid system appreciably. This
may happen due to high thermal conductivity of copper material and its flat top surface.

          Table 3 Performance comparison of simple PV module and hybrid PV/T system
                      at highest PV power point condition at ATC conditions
              Sr.          Technical parameters          Commercial       Hybrid
              No                                         PV module         PV/T
                                                                          system
               1 Voltage (V)                                  27.5         30.30
               2 Current (A)                                   4.2          4.43
               3 PV power (W)                                115.2         134.2
               4 PV efficiency (%)                            10.2          11.7
               5 Thermal power (W)                            ----          482
               6 Thermal efficiency (%)                       ----           42
               7 Combined PV/T efficiency (%)                 ----          53.7
               8 Top side module temperature (0C)              64           46.7
               9 Performance ratio                             64            75


6. CONCLUSIONS

        During this research, the performance of cooled module or hybrid PV/T water system with
square Aluminum oscillatory flow PV absorber surface at ATC conditions for latitude of Mumbai
was studied. Commercial PV module converted to hybrid PV/T system, improved PV electrical
power and efficiency of water cooled module by 16.5 % and 13.6 % respectively at 1 pm. This is
mainly because of maximum solar radiation was observed during this time for the day. Water cooling
of module by using heat exchanger decreased its temperature by 37 % at water flow rate of 0.035
kg/sec improving overall performance of the system. It was also observed that because of cooling
effect, the performance ratio of PV module of hybrid PV/T system was increased by 11%. Hybrid

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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PV/T system produced thermal power and efficiency of       482 W and 42% respectively achieving
combined efficiency of 53.7 %. The combined efficiency of PV/T system may increase if inlet water
temperature is kept as low as possible. With this hybrid PV/T solar system, actual combined
efficiency of system was found to be 53.7 % as compared 54.85% efficiency found by simulation [2].
Above studies showed that actual experimental results were close to the simulation work carried out
on the similar setup.
        The hybrid PV/T solar water system harnessed solar energy to 53.7% of total solar radiation
falling on earth surface and converted 42 % heat energy to hot water utilizing the free heat energy,
cooling PV module. On yearly basis hybrid system can produce combined PV/T energy of 1110
KWh with PV electrical energy of 345 KWh for PV module area of 1.25 m2. With this study it can be
concluded that the hybrid PV/T solar water system has a potential as an alternative method used for
power generation. Use of thermal compound between bottom side of module and top side of heat
exchanger, may enhance electrical, thermal and combined efficiency significantly and working
temperature of module can be reduced drastically increasing its life span. This will make the use of
system suitable in desert area also.

REFERENCES

Journal Papers

  [1] Adnan Ibrahim, Kamaruzzaman Sopian, Mohd Yusof Othman, M. A. AlGhoul, Azami
      Zaharim: Simulation of different configuration of hybrid Photovoltaic Thermal Solar
      Collector (PVTS) Designs, Selected Papers from: Communications & Information
      Technology 2008, Circuits, Systems and Signals 2008, Applied Mathematics, Simulation,
      Modeling 2008, Marathon Beach, Attica, Greece, June 1-3, 2008.
 [2] Lj. Kostic, T. Pavlovic and Z. Pavlovic- Influence of Physical Characteristics of Flat
      Aluminum Concentrators on Energy Efficiency of PV/Thermal Collector, Proceedings of the
      Tenth Annual Conference of the Materials Research Society of Serbia, September -2008, 115
      (2009), No. 4.
 [3] Jin-Hee Kim1 and Jun-Tae Kim, The Experimental Performance of an Unglazed PVT
      Collector with         Two Different Absorber Types, Hindawi Publishing Corporation
      International Journal of Photo energy Volume 2012, Article ID 312168, 6 pages
      doi:10.1155/2012/312168.
 [4] Adnan Ibrahim, Mohd. Yusof Othman, Mohd Hafidz Ruslan, Sohif Mat, Azami Zaharim and
      Kamaruzaman Sopian: Experimental Studies on Water based PV/T Collector, Solar Energy
      Research Institute, University Kebangsaan Malaysia.
 [5] R. Hosseini , N. Hosseini, H. Khorasanizadeh : An experimental study of combining a
      photovoltaic system with a heating system, World Renewable Energy Congress 2011-Sweden,
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 [6] Kamaruzzaman Sopian, Goh Li Jin, Mohd. Yusof Othman, Saleem H. Zaidi, Mohd Hafidz
      Ruslan: Advanced Absorber Design for Photovoltaic Thermal (PV/T) Collectors, Recent
      Researches in Energy, Environment and Landscape Architecture, ISBN: 978-1-61804-052-7.

 Book

 [7]    C.S. Solanki, Solar Photovoltaic (Fundamentals, Technologies and Applications), Second
        Edition, PHI Learning Pvt. LTD. New Delhi, 2011.



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