International Journal of Energy Science (IJES) Volume 4 Issue 6, December 2014 doi: 10.14355/ijes.2014.0406.01
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Investigational Analysis of Two Specially Designed Heat Exchangers used in Hybrid Solar Water System V. N. Palaskar*1, S. P. Deshmukh2 *1
Department of Mechanical Engineering, 2Department of General Engineering
*1
Veermata Jijabai Technological Institute Mumbai India, 2Institute of Chemical Technology Mumbai India
*1
E‐mail: vnpalskar@vjti.org.in; 2E‐mail:sp.deshmukh@ictmumbai.edu.in
Abstract Hybrid photovoltaic /thermal (PV/T) solar water system is a combined solar photovoltaic module and solar thermal collector, forming a device that generates electrical and thermal energy from a single integrated unit. The overall performance of any hybrid system depends on selection of heat exchanger configurations i.e. shape, size; and its materials. This paper offers design and performance analysis of two specially designed configurations namely oscillatory and spiral flow heat exchangers used in hybrid solar water system. The investigational results like performance efficiencies of photovoltaic, thermal, and combined PV/T system for both heat exchangers over a range of operating conditions are discussed and assessed for latitude of Mumbai. The final results showed that, for same water flow rate; copper spiral flow heat exchanger generated 68.20% combined PV/T efficiency and aluminium oscillatory flow heat exchanger produced 65.30% combined PV/T efficiency. At peak PV power point condition; the PV power and efficiency produced by both heat exchangers were found equal. Keywords Solar Photovoltaic Module; Solar Thermal Collector; Single Integrated Unit; Heat Exchanger Configurations; Oscillatory and Spiral Flow Heat Exchangers
Introduction Solar photovoltaic (SPV) module absorbs solar radiation to generate electricity. Solar radiations absorbed by module also increase its operating temperature. The cooling of PV module improves generation of electrical power and its efficiency reasonably. Generally; PV module is cooled by circulating cold water through the heat exchanger fixed at the bottom of the module. Such heat exchanger is known as PV absorber surface. In a hybrid photovoltaic/thermal (PV/T) solar water system, simple PV module and thermal units are mounted
together to enable simultaneous conversion of solar energy to electrical and thermal energy. The hybrid PV/T solar system generates higher energy output per square meter of its surface; and could prove cost effective than conventional PV modules if the cost of thermal component is low. Jin‐Hee Kim and Jun‐Tae Kim (2012) studied two hybrid PV/T water collectors with different heat exchanger surfaces namely; sheet & tube and fully wetted type PV absorbers. Experimental work and calculations confirmed that combined PV/T efficiency of the system rose to 65% and 60.6% respectively using different heat exchangers in hybrid system. Comparison of the performance of both absorber surfaces using unglazed and glazed PV module designs revealed that; an unglazed PV module produced more electrical energy and glazed PV module generated more thermal energy. Investigational study was performed on oscillatory flow heat exchanger used in hybrid PV/T water system to predict its performance for latitude of Mumbai (Palaskar and Deshmukh, 2013‐a). The performance efficiencies of photovoltaic, thermal, and combined PV/T hybrid water system over range of operating conditions were discussed and analyzed during the studies. The final results of this system at solar radiation of 918 W/m2 and cooling water mass flow rate of 0.035 kg/sec showed considerable improvements in the performance of the system with combined PV/T efficiency of 53.7 % and PV efficiency of 11.7 %. During the experimental process, operating temperature of cooled module was found decreased by 27% as compared to un‐cooled module. Seven types of heat exchangers, namely, direct flow, oscillatory flow, serpentine flow, web flow, spiral flow, parallel‐serpentine flow, and modified serpentine‐
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parallel flow, were designed and their performances were studied using simulation techniques (Othman et al., 2008). Simulation results of these systems showed that, the heat exchanger with spiral flow arrangement produced highest thermal efficiency of 50.12% with PV module efficiency of 12.8%.
In a review articles during 2012, 2013‐b Palaskar and Deshmukh have commented on research literature, development, and selection of various PV absorber designs; materials and use of concentrators for higher energy output of hybrid solar systems. The review article commented that the overall system performance of hybrid system could be improved considerably by applying above mentioned techniques. It was concluded that the spiral flow heat exchanger made of copper and fitted with reflectors produced higher combined PV/T efficiency than simple hybrid systems. It was also revealed that such system will have better commercial viability in future.
Kostic et al. (2008) have carried out experimental studies using sheet and tube type of heat exchanger and PV/T water collector system fitted with a pair of flat aluminum concentrators. In these studies, it was observed that the aluminum sheet concentrators mounted at 100 and 560 to the vertical plane of PV module produced 8.6% and 39% more electrical and thermal energy than simple PV module. Aluminum foil concentrators used in the system produced 17.1% more PV energy and 55% more thermal energy than un‐cooled PV module.
In this study; design and performance analysis of aluminum oscillatory and copper spiral flow heat exchangers used in hybrid system are compared on the basis of various technical parameters for latitude of Mumbai. The first hybrid system was developed by fitting oscillatory flow heat exchanger at bottom side of module. This type of heat exchanger was designed and fabricated using aluminium square tubes. Aluminium tubes were used for this study for its good thermal conductivity and ease of fabrication. The second hybrid PV/T system was fabricated using spiral flow heat exchanger. This heat exchanger was designed and fabricated using copper square tubes. Copper tubes were used for this study due to high thermal conductivity of copper and ease of its manufacturing. The investigational results like performance efficiencies of photovoltaic; thermal and combined PV/T system for both heat exchangers over a range of operating conditions are discussed and assessed in this experimental work.
The overall performance of a simple PV module was found improved when it was cooled directly by passing water on its top surface during experiments (Hosseini, et al., 2011). The flowing water film absorbed heat from module and converted it to hot water that was used for low temperature applications. Cooling of module resulted in improving overall efficiency of combined system compared to conventional module. The experimental results showed that electrical performance of the combined system was 33% higher than conventional module when the PV module was cooled using flowing film of cooled water. Three PV/T water collector systems, namely; direct flow; parallel flow and split flow were designed and their thermal performances were compared experimentally for various tilts of hybrid system (Kamaruzzaman, et al., 2011). Experimental Results and analysis of the work found that split flow PV/T system produced 51.4% thermal power which was marginally higher compared to 50.8 % and 50.6% thermal efficiencies of other two systems.
Materials and Methods Commercial PV Module with Experimental Stand Tata Bp India made commercial PV module with rated capacity of 180 watts was used to conduct experiments on un‐cooled and cooled PV module for both heat exchangers. The rectangular module with its length and width of 1.587m and 0.79m respectively was having area of 1.25m2. Open circuit voltage and current at STC of the module were 44.8volts and 5.40 amps respectively. As per technical specifications of the module at STC its efficiency found was 14.52% at standard test conditions. Photovoltaic module with all its parts was mounted on mild steel stand facing South direction on the terrace of the main building of the Institute.
Experiments were performed by Tripanagnostopoulos et al., 2003 on hybrid PV/T systems, with and without glazing, and, with and without reflectors, operating at temperatures of 250C, 350C, and 450C respectively. It was found that PV/T system, with glazing and flat reflectors and operating at 250C system temperature; generated maximum annual electrical energy (167.98 kWh/ m2 y) with electrical efficiency of 10.21% and; maximum annual thermal energy (831.75 kWh/m2 y) with thermal efficiency of 50.57%.
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given in Table 1. Figure 1 shows complete drawing of PV module and heat exchanger assembly with important dimensions and necessary features such as entry for water inlet and outlet of heat exchanger etc. The hydraulic leak test was conducted on heat exchanger using water pump to locate and eliminate minute leakages in joints and passages of water flow; before it was finally assembled to perform experimental work. The actual installation of an oscillatory flow PV absorber surface at bottom side of module is shown in figure 2.
Photovoltaic Heat Exchanger Designs and Fabrications 1)
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Oscillatory Flow Heat Exchanger
The combined efficiency of PV/T system depends on material and arrangements of heat exchanger mounted at bottom of module. A detailed literature review and simulation based results of circular stainless steel oscillatory flow PV absorber surface (Othman et al., 2008) were studied with experimental work using different materials and shapes of tubes. The aluminium square section tube was used to provide good surface contact and thermal conductivity to absorb heat from the module and cooling it to reasonable temperature. The circular stainless steel tubes were replaced with aluminium square tubes to provide larger surface to surface contact for better heat absorption rate from the bottom of module. TABLE 1 HEAT EXCHANGER CHARACTERISTICS
Size of square Aluminium tube Pitch between two consecutive square tubes Total length of heat exchanger PV module bottom area occupied by heat exchanger
12 x 12 x 1mm 34 mm 36 mts 37 %
FIG. 2 INSTALLATION OF OSCILLATORY FLOW PVABSORBER SURFACE AT BOTTOM SIDE OF PV MODULE
2)
The cogeneration efficiency of photovoltaic/thermal water system depends on material and configurations of PV heat exchanger mounted at bottom side of module. After a detailed literature review and analysis of simulation based results (Othman et al., 2008) of stainless steel square spiral flow PV absorber surface were analyzed with experimental work by using copper tube material. The copper square section tube provides good surface contact and high thermal conductivity compared to stainless steel material to absorb heat from module and cools it at reasonable temperature.
FIG.1 PV MODULE AND HEAT EXCHANGER ASSEMBLY WITH IMPORTANT DIMENSIONS AND NECESSARY FEATURES
To achieve maximum combined efficiency of hybrid system; spiral flow PV absorber arrangement was used with square hollow tubes. The manufacturing and assembly of copper spiral flow PV absorber surface was simple as compared to other types of flows and its materials. The detailed heat exchanger specifications are given in table 2. Figure 3 shows detailed drawing of PV module and heat exchanger assembly with important dimensions and necessary features such as water inlet and outlet of heat exchanger. The
To attain highest combined PV/T efficiency, oscillatory flow PV absorber system was used with hollow tubes of square cross section. The manufacturing and assembly of aluminium oscillatory flow PV absorber surface was simple as compared to other types of heat exchangers. It was light in weight and cost effective compared to other types of configurations and materials. The characteristic details of the heat exchanger are
Spiral Flow Heat Exchanger
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hydraulic leak test conducted on heat exchanger helped to locate and eliminate minute leakages in joints and passages of water flow; before its final assembly. This test helped to ensure proper circulation of water at certain pressure and flow through the heat exchanger sealing the leakages of the heat exchanger. The actual installation of spiral flow PV absorber surface on bottom side of PV module is shown in figure 4.
measure ambient temperature and temperatures on the top and bottom side of PV module during experimental process. A 16 channel temperature data logger was used to scan and record thermocouple temperatures automatically at specified time period. A DC voltmeter and ammeter were used to measure voltage and current at various loading conditions. A DC load bank of 36 Volts and 180 Watt capacity was used to measure voltage and current across load applied to PV module during experimental process. A 500 LPH rota‐meter was used to measure flow rate of water at the inlet of the oscillatory flow PV absorber surface. Dial type temperature gauges were used to measure water temperature at the inlet and outlet of the heat exchanger to calculate thermal power. Electrical water pump was used to circulate water through heat exchanger surface absorbing heat and cooling the PV module during tests. The complete; assembled experimental setup with all components is shown in figure 5 for both heat exchangers.
TABLE 2 HEAT EXCHANGER CHARACTERISTICS
Size of square Copper tube Pitch between two consecutive square tubes Total length of heat exchanger PV module bottom side area occupied by heat exchanger
12x12x1.25 mm 37 mm 31.5 mts. 32 %
FIG. 5 HYBRID SOLAR WATER SYSTEM WITH MEASURING INSTRUMENTS
FIG.3 PV MODULE AND HEAT EXCHANGER ASSEMBLY WITH IMPORTANT DIMENSIONS AND NECESSARY FEATURES
Experimental Observations In this experimental work, overall performances of two specially designed heat exchangers used in hybrid solar system were compared and analysed for latitude of Mumbai. Experiments were performed during months of March to May 2014. The experiments were performed using same slopes with different water flow rates for 7 hours per day to study required electrical and thermal energy output and efficiencies of the combined PV/T solar system. To determine the performances of both heat exchangers of hybrid systems over a day at actual test conditions, experiments were conducted daily between 9.30 AM and 4.30 PM. In general, performance of hybrid system depends on two key factors namely; intensity of solar radiation and rise in module temperature. The intensity of solar radiation was fluctuating during the day. The rise in module
FIG. 4 INSTALLATION OF SPIRAL FLOW PV ABSORBER SURFACE AT BOTTOM SIDE OF PV MODULE
Measuring Instruments A Dynalab Pyranometer was used to measure global and diffuse radiations on horizontal surface during experiments. K‐type thermocouples were used to
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temperature was directly proportional to solar radiation. To determine the effect of these factors on performance of hybrid systems practically, different readings such as global and diffuse radiations, voltage and current at corresponding loading conditions were recorded at a 30 minutes interval. K‐type temperature sensors with data logger were used to scan and record the ambient temperature and the temperatures at top and bottom of the module at an interval of 1 minute during experimental process.
IT = It x APV (3) It= Ig x rg (4) Where: Ig is global radiation measured by pyranometer on horizontal surface (W/m2) and APV is the area of PV module (m2). Tilt factor (rg) for global radiation and elevation angle (α) as calculated follows: rg = sin (α + β)/sinα (5) α = 90‐Φ+ δ (6)
Experiments on both heat exchangers used in hybrid system were performed maintaining same module slopes of hybrid system for all experimental days. The experiments were conducted for different water flow rate through heat exchanger for each day to determine the exact performance of hybrid systems in terms of electrical; thermal; combined etc; for both heat exchangers at peak PV power point. For different water flow rates required data was collected as per procedure described in the above paragraph. The water temperatures at the inlet and outlet of the hybrid system, recorded at a 30 minute interval, were used to calculate the thermal power, combined PV/T efficiency and performance ratio for both heat exchangers.
Where: Φ and δ are the latitude of location (0) and declination angle (0) respectively. Electrical efficiency ( PV) and thermal efficiency ( T) of hybrid system (%) are found by following equations: = PPV / IT (7)
PV
= PT / IT (8)
T
Combined photovoltaic and thermal (PV/T) efficiency and performance ratio (%) of hybrid solar system are calculated as under: =
PV/T
+
PV
(9)
T
PR= PPV/PSTC (10) Where: PSTC is the electrical power produced by module (W) at standard test condition.
Equations used to Calculate Technical Parameters Different equations from books such as Sukhatme and Nayak (2008); Solanki (2011) and Duffie and Beckman were used to calculate different technical parameters such as photovoltaic power, thermal power, input solar power, performance ratio, photovoltaic, thermal and combined PV/T efficiency for latitude of Mumbai are explained in detail as under.
Results and Discussion Performance Analysis of Oscillatory and Spiral Flow Heat Exchangers used in Hybrid Solar System The cooling of module with oscillatory flow heat exchanger resulted in the rise of open circuit voltage (40.60 Volts) and voltage (32.40 Volts) at peak PV power point of the module at 1 PM as compared to un‐ cooled module. Due to cooling effect; enhancement in electrical power (146.12 W); performance ratio (81.20%) and efficiency (13.30 %) were observed as shown in figures 6 and 7 respectively. By utilizing waste heat energy of module from bottom side; hybrid solar system generated 572 W of thermal power at cooling water flow rate of 0.042 Kg/sec. This PV/T system worked with combined efficiency of 65.3 % as shown in figure 10.
Electrical power (PPV) and thermal power (PT) produced by hybrid system at ATC conditions (W) are given by: PPV = V x I (1) PT = x CP x (Twe‐Twi) (2) Where: V and I are voltage (V) and current (Amp) produced by module of hybrid system. and CP are mass flow rate (kg/sec) and specific heat of water (J/kg 0K). Twe and Twi are water inlet and outlet temperature of heat exchanger (0K).
The cooling of module with spiral heat exchanger resulted in increase in open circuit voltage (40 Volts) and voltage (31.5 Volts) at peak PV power point of the module at 12.30 PM as compared to simple module. The cooling of module also helped increasing electrical
Total solar radiation (IT) normal to module surface (W) and solar radiation (It) calculated normal to module surface (W/m2) are calculated using following formulas:
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power (143.6W), performance ratio (80 %) and efficiency (12.9%) as shown in figures 6 and 7 respectively. By utilizing waste heat of module, this hybrid solar system generated 616 W of thermal power at water flow rate of 0.042 Kg/sec. The combined PV/T efficiency of 68.2 % was recorded for the hybrid system as shown in Figure 10. Figure 7 shows low PV efficiencies in the morning and late afternoon for both heat exchangers of PV/T systems. These mainly happened as angle of incidence of solar rays decreases from morning to noon and increases to late afternoon. At noon its value is lowest and sun rays strike normal to module surface; generating peak electrical power and efficiencies and less for other periods.
recorded was less as compared to March 2104.The hybrid PV/T system with spiral flow system produced less electrical energy and efficiency; compared to thermal energy and efficiency. Due to high intensity of solar radiation; the module temperature increased; decreasing its electrical power. Since copper spiral flow heat exchanger has good configuration design having high thermal conductivity; which absorbs more heat from module and cools it at reasonable temperature. By considering overall performance; copper spiral flow heat exchanger hybrid system was found best option for generating electrical and thermal energy during these months than aluminium oscillatory flow heat exchanger. Tables 3 and 4 shows the technical data recorded during trials such as solar radiation, ambient temperatures, temperature of module at top side, electrical, and thermal power for both heat exchangers of hybrid system. The observations and results of these tables showed that, module of hybrid system could produce more electrical power at less solar radiation during month of March irrespective of more ambient temperature. During months of April and May, module of hybrid system could produce less electrical power at more solar radiation irrespective of less ambient temperature.
The temperature of water recorded at outlet of both heat exchangers was around 35.500C, which is suitable for low temperature applications. The forced circulation system was used from 10 AM to 3 PM to supply water to both heat exchangers of hybrid system during experimental process. Due to this, enhancement in system performances and reduction in operating temperatures were observed daily during these time periods as shown in figures of 6 to 10 for both heat exchangers. It was also observed that for both heat exchangers, the temperature attended by bottom side sheet attached below heat exchangers was recorded and equal to the ambient temperature during trials. These results showed that, the selected thickness of glass wool insulation was precise for these hybrid system applications.
The results obtained from both heat exchangers of hybrid systems showed that; spiral flow heat exchanger could produce more thermal power as compared to oscillatory type heat exchanger. The experiments performed on both the hybrid system shows that both heat exchangers produced same electrical power and efficiency at same water flow rate and optimum tilts of module during different days of experiments.
Performance Assessment of Oscillatory and Spiral Flow Heat Exchangers used in Hybrid Solar System Experiments were conducted on oscillatory flow heat exchanger of hybrid system during month of March‐ 2014. During this month; the value of solar radiation intensity measured was less and ambient temperature recorded was more than its values in the months of April and May 2104. This helped oscillatory flow system to produce more electrical energy and efficiency; compared to thermal energy and efficiency. The cost of generation of combined energy; using aluminium oscillatory flow heat exchanger in hybrid system was less than copper spiral flow heat exchanger due to its less investment.
In these experimental works, trials were conducted on single photovoltaic commercial module by changing heat exchangers during selected experimental days. The first hybrid system was created by locating oscillatory heat exchanger at bottom of module during month of March‐2014. During months of April‐May 2014; oscillatory heat exchanger was replaced and second hybrid system using spiral flow heat exchanger was used to perform experiments to compare its performance with oscillatory flow heat exchanger. As experiments were conducted on different days and months; both heat exchangers showed different overall performances over a day. These experiments were conducted on both heat exchangers by keeping same tilts; flow rates; days of experiments for latitude
Experiments performed on spiral flow heat exchanger of hybrid system during month of April and May‐2014. During these months, the intensity of solar radiation measured was more and ambient temperature
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TABLE 4 TECHNICAL DATA RECORDED AND CALCULATED FOR SPIRALL
of Mumbai. After analysing the results of two hybrid systems; the overall performance of copper spiral flow heat exchanger was observed better than aluminium oscillatory heat exchanger. This mainly happened due to the selection of high thermal conductivity material for heat exchanger and best water flow configuration design of heat exchanger. In this configuration; water flows from inlet to centre of heat exchanger and from centre to the exit of heat exchanger. Due to this pattern of water flow; heat exchanger absorbs more heat from bottom of module and cools at satisfactory temperature; enhancing its electrical as well thermal power and efficiency compared to other type of heat exchangers.
FLOW HEAT EXCHNAGRER OF HYBRID SYSTEM
Sr no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Use of thermal grease compound at top side of heat exchangers and bottom side of module may lead to the reduction of air gap between these surfaces improving the rate of heat transfer. This leads in reduction of the operating temperature of module; improving photovoltaic; thermal and combined power and efficiencies of both heat exchangers. The performance of these hybrid systems will be improved by fitting reflectors to the sides of the module to enhance its concentration ratio, and electrical as well thermal power output. The operating temperature of cooled module for both heat exchangers may further be reduced by lowering inlet water temperature; enhancing photovoltaic; thermal and combined PV/T power and efficiencies of system. Sufficient water head maintained in storage tank of cooling water can use thermo siphoned hybrid PV/T system. This will be the ideal solution for electrical power generation and hot water production. By using this concept; an autonomous hybrid system may be developed for its use in rural areas.
Time 09:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30
Ig 572 688 739 801 870 875 892 881 876 865 802 786 636 551 449
Ta 33.7 36.0 37.4 37.5 36.7 36.0 35.4 34.6 34.1 33.6 33.8 34.9 35.7 36.3 35.5
Tmod 48.4 49.3 48.0 50.3 52.2 53.1 52.5 51.1 50.1 48.8 46.2 46.0 45.6 45.5 42.4
Ppv 48.7 78.5 94.9 115.0 137.1 139.0 143.6 140.1 137.4 134.7 115.8 108.1 59.6 39.3 22.8
Pt 0.0 0.0 483.9 571.9 571.9 571.9 615.9 615.9 615.9 571.9 571.9 483.9 0.0 0.0 0.0
FIG. 6 PV POWER PRODUCED BY AL_OSCILLATORY AND CU_SPIRAL FLOW HEAT EXCHNAGERS USED IN HYBRID SYSTEM
TABLE 3 TECHNICAL DATA RECORDED AND CALCULATED FOR OSCILATORY FLOW HEAT EXCHNAGRER OF HYBRID SYSTEM
Sr no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Time 09:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30
Ig 431 510 638 678 715 784 841 851 844 808 769 696 624 531 431
Ta 34.4 37.6 39.9 40.3 40.2 38.3 36.6 35.8 35.0 34.1 34.0 35.4 36.3 36.8 36.8
Tmod 42.1 46.5 41.8 43.7 46.2 47.5 47.5 48.7 46.8 45.1 45.4 44.3 44.8 43.4 40.7
Ppv 33.08 47.88 82.40 97.28 105.47 136.17 142.46 146.12 143.10 131.67 115.37 87.89 64.13 41.33 24.91
Pt 0.0 0.0 440.0 440.0 483.9 483.9 527.9 571.9 483.9 440.0 440.0 440.0 0.0 0.0 0.0
FIG. 7 PHOTOVOLTAIC EFFICIENCY PRODUCED BY AL_OSCILLATORY AND CU_SPIRAL FLOW HEAT EXCHNAGERS USED IN HYBRID SYSTEM
Illustration of Cost Effectiveness The Sample cost analysis for aluminum oscillatory and copper spiral flow heat exchanger used in hybrid solar water systems is shown in tables 5 and 6 respectively for peak PV power point water flow rate.
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TABLE 5 COST EFFECTIVENESS OF OSCILLATORY FLOW HEAT EXCHANGER HYBRID PV/T SYSTEM
1
2
3 4 5 6
FIG. 8 THERMAL POWER PRODUCED BY AL_OSCILLATORY AND CU_SPIRAL HEAT EXCHNAGERS USED IN HYBRID SYSTEM
540
1280
90 1220 120 4.6
TABLE 6 COST EFFECTIVENESS OF SPIRAL FLOW HEAT EXCHANGER HYBRID PV/T SYSTEM
1
2
3
4
5 6
Total cost incurred for purchasing and fabrication of hybrid system (%) Total PV/T energy generated by hybrid system with area of 1.25 m2 in KWh per annum at 150 LPH. (Assuming hybrid system runs for 6 hrs per day and 300 days per year ) Power consumed by pump in KWh per annum. (Assuming pump runs for 5 hrs per day and 300 days per year) Net PV/T energy generated by hybrid system with area of 1.25m2 in KWh per annum Net PV/T income from hybrid system in $ per annum.(Assuming $0.1 per KWh for electrical and thermal energy ) Payback period of hybrid system (years)
606
1367
90
1277
125 4.8
Conclusions
The performance of both heat exchangers has been studied, analysed and compared during experimental process for peak PV power condition at same slopes. An oscillatory flow heat exchanger at water mass flow rate of 0.042kg/sec produced 65.30% combined PV/T efficiency with 13.30% PV efficiency and performance ratio of 81%. At the equivalent flow rate; the spiral flow heat exchanger generated power with 68.20% combined PV/T efficiency with 12.90% PV efficiency and performance ratio of 80%. This study showed that; copper spiral flow heat exchanger could generate more combined PV/T efficiency than aluminium oscillatory flow heat exchanger at same flow rate. This enhancement in combined PV/T efficiency was observed due to high thermal conductivity and choice of configuration of copper spiral flow heat exchanger design. Cost of generation of energy using aluminium oscillatory flow heat exchanger hybrid system is less and it is the best option generating thermal energy suitable for different applications. By considering
FIG. 9 THERMAL EFFICIENCY PRODUCED BY AL_OSCILLATORY AND CU_SPIRAL FLOW HEAT EXCHNAGERS USED IN HYBRID SYSTEM
FIG. 10 PV/T EFFICIENCY PRODUCED BY CU_OSCILLATORY & CU_SPIRAL FLOW HEAT EXCHNAGERS USED IN HYBRID SYSTEM
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Total cost incurred for purchasing and fabrication of hybrid system ($) Total PV/T energy generated by hybrid system with area of 1.25 m2 in KWh per annum at 150 LPH. (Assuming hybrid system runs for 6 hrs per day and 300 days per year ) Power consumed by pump in KWh per annum. (Assuming pump runs for 5 hrs per day and 300 days per year) Net PV/T energy generated by hybrid system with area of 1.25m2 in KWh per annum Net PV/T income from hybrid system in $ per annum.(Assuming $0.1 per KWh for electrical and thermal energy ) Payback period of hybrid system (years)
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overall performance; copper spiral flow heat exchanger hybrid system was found best option for generating maximum combined energy. Illustration of cost effectiveness showed that the payback period of hybrid PV/T solar water system using both heat exchangers was same. These experiments proved that hybrid solar water system is a potential alternative for electrical power generation and hot water production.
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solar collector (PVTS) designs. Selected Papers from: Communications & Information Technology; Circuits, Systems and Signals; Applied Mathematics, Simulation and Modeling 2008, Marathon Beach, Attica, Greece. Palaskar V N, Deshmukh S P , Pandit A B, Panse S V. Performance analysis of an Oscillatory flow design heat exchanger used in solar hybrid water system. International Journal of Mechanical Engineering and
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