A Critical Review on Enhancement in System Performance of Flat Plate Hybrid PV/T Solar Collector Sys

International Journal of Energy Science (IJES) Volume 3 Issue 6, December 2013 doi: 10.14355/ijes.2013.0306.03

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A Critical Review on Enhancement in System Performance of Flat Plate Hybrid PV/T Solar Collector System V. N. Palaskar1, S. P. Deshmukh2 Department of Mechanical Engineering,Veermata Jijabai Technological Institute, Mumbai, India Department of General Engineering, Institute of Chemical Technology (Deemed University), Mumbai, India

1 2

Abstract The combined efficiency i.e. electrical and thermal of a simple flat plate solar hybrid PV/T water/air collector system is low. Therefore above systems are commercially not viable till date. To make these systems commercially viable, development in the system configurations can be done by modifying PV absorber shape, size & materials, and also by attaching various types of diffuse reflectors or flat concentrators to the sides of commercial PV module. PV absorber surface design with various configurations such as simple open air channel, single pass with rectangular tunnel, spiral flow absorber collector, thin metallic sheet suspended at the middle of air channel, fins at the back wall of an air duct etc., are used in a simple flat plate solar hybrid PV/T water/air collector systems to enhance its system performance at one sun concentration and above.

This article reviews a simple flat plate hybrid PV/T water/air collector systems with and without PV absorber surface design with various configurations as discussed above.

Finally effect of attaching a flat concentrators or diffuse reflectors with unglazed and glazed surface on performance of these systems is also discussed and analyzed.

Keywords Hybrid Solar System; Photovoltaic/ Thermal Collector; Flat Concentrators; Diffuses Reflectors

Introduction An absorbed solar radiation by PV module results in generation of electricity and it’s heating. Cooling of PV modules improves its electrical efficiency at a reasonable level. The natural or forced air circulation is a simple and low cost method to remove waste heat from back side of commercial PV module. But this method is less effective if ambient air temperature is over 20 0C. The water heat extraction is more expensive than air heat extraction, but it is used for the above application, as the water temperature from mains is normally under 20 0C throughout the year.

The usual mode of PV cooling is by circulation of water through a heat exchanger or PV absorber

surface attatch in thermal contact with PV module on rear surface. In a simple flat plate solar hybrid PV/T water/air collector systems, the PV panels and thermal units are mounted together and the systems can simultaneously convert solar radiation in to electricity and thermal energy. The hybrid PV/T systems provide a higher energy output than standard PV panels and could be the cost effective in near future if the additional cost of the thermal component is low.

An extension of the Hottel‐Whiller model had been used for the analysis of hybrid PV/T collector systems for both thermal and electrical performance of a combined collector systems as a function of collector design parameters (Florschuetz LW 1979). A hybrid PV/T collector system consists of a PV panel which was placed on a thermal collector with a gap between them had been used to achieve an effective PV cooling with increament in electrical efficiency (T. Takashima et al. 1994). A hybrid PV/T collector system with low, medium or high concentration reflectors was attached with the above modified system (Al‐Baali 1986).

Because of this modification, the electrical and thermal output of a hybrid PV/T collector system was found increased significantly.

The effect of plane booster reflector had been studied for solar air heaters with solar cells were used for solar drying applications (H.P. Garg 1991). A new type of PV/T collector system with dual heat extraction operation either water or air circulation was studied (Y. Tripanagnostopoulos et al. 2001). The above dual PV/T collector system had been combined with booster diffuse reflectors, achieving a significant increase in output of electrical and thermal energy.

The different experiments had been performed on hybrid PV/T water collector system by attaching flat Aluminum concentrators with commercial PV module (Lj. Kostic et al. 2009). The final results showed that electrical and thermal energy generated by hybrid

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Three PV/T water collector systems had been designed and their thermal performances had been compared such as direct flow PV/T, Parallel flow PV/T and Split flow PV/T systems (Kamaruzzaman Sopian et al.). Out of these three PV/T systems, the split flow PV/T design had showed better thermal performance compared to other two PV/T systems such as direct flow and parallel flow.

PV/T water collector system with Aluminum sheet concentrators were 8.6% and 39% higher than without flat concentrator. Also final results had showed that electrical and thermal energy generated by hybrid PV/T water collector system with Aluminum foil concentrators were 17.1% and 55% higher than that without concentrator.

A thin flat metallic sheet (TFMS) and Fins had been attached in the air duct acting as a heat transfer augmentations in air cooled hybrid PV/T collector systems to improve its overall performance (J.K. Tonui and Y. Tripanagnostopoulos 2007). In these studies, the steady‐state thermal efficiencies of the modified systems were compared with those of typical PV/T air collector system.

System Performance of Flat Plate Hybrid PV/T Solar Air Collector Systems A Single‐pass solar collector with open channel absorber had been converted into a rectangle tunnel absorber modified hybrid PV/T air collector system as shown in Fig 1 and 2 (Gohli Jin et al.). The dimensions of these PV panel were taken 1.20 m x 0. 53 m; produced 80W power. Total 39 tunnels of hollow rectangular tubes were used to fabricate the PV absorber system. The solar PV/T collector system was tested by using 23 simulator halogen lamps. The modified PV/T air collector system was tested with and without rectangular tunnel to compare the final performance results. The solar irradiances from simulation lamps were set at 385.2 W/m2 and 817.4 W/m2 respectively. During experiments the mass flow rates were set from 0.011 kg/s to 0.0754 kg/s.

The various experiments were performed on hybrid PV/T water collector systems with Unglazed and glazed configurations (Y. Tripanagnostopoulos et al.).

The final results had showed that unglazed system produces more electrical energy than thermal energy.

When stationary diffuse reflectors were attached with PV/T water collector system with unglazed and glazed configurations, then PV/T water collector system with glazed and stationary diffuse reflectors had produced more electrical and thermal energy compared to unglazed and stationary diffuse reflectors.

A single‐pass hybrid PV/T air collector system with rectangular tunnel acting as a heat absorber surface had been design and evaluated (Gohli jin et al.). The final results showed that the system performance in terms of electrical and thermal energy had been increased as compared to single‐pass hybrid PV/T system without rectangular tunnel absorber.

FIGURE 1: SOLAR PHOTOVOLTAIC THERMAL AIR COLLECTOR

An experimental study had been performed on PV/T water collector system by using a spiral flow absorber collector used for heat transfer augmentation from back side of module (Adnan Ibrahim et al.). Finally the results of system performance of the photovoltaic, thermal and combined photovoltaic‐thermal water collector system over range of operating conditions were discussed and analyzed.

Where: 1‐Blower, 2‐ Ducting, 3‐PV cell, 4‐Insulator, 5‐ Hot air out from collector.

An experimental study had been performed on PV/T water collector system cooled by a thin film of water running over top surface of commercial PV panel (R. Hosseini et al. 2011). The results showed that the working temperature of the PV panel for combined system was lower compared to the conventional panel.

The final results proved that the electrical performance of the combined system was higher than the conventional one.

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FIGURE 2: SINGLE PASS SOLAR COLLECTOR SYSTEM

The various experiments had been performed on modified PV/T air collector system by varying the solar irradiances and mass flow rates. The final results were showed that the surface temperature of PV panel drops with increasing the mass flow rate of cool air which flows through the rectangular tunnel system (Fig‐3).

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Three geometrical configurations of PV absorber surface design had been considered such as open air channel‐REF model, the modified‐TFMS model (thin flat metallic sheet) and Fin model for hybrid PV/T air collector systems (J.K. Tonui et al. 2007), as shown in fig‐6. Three identical prototype test models were constructed from three Pc‐Si PV modules with aperture area of 0.4m2 and rated power capacity of 46 W.

FIGURE 3: COMPARISON OF PANEL’S TEMPERATURE

The electrical efficiency of hybrid PV/T air collector system had been increased with the mass flow rate as shown in Fig‐4. The hybrid PV/T air collector system with tunnel showed better electrical efficiency compared to collector system without tunnel.

FIGURE 6: CROSS‐SECTIONAL VIEW OF PV/T AIR COLLECTOR MODELS

During the experiments, combinations such as natural and force air flow circulation for REF, TFMS and FIN models had been used at a time. For forced air flow circulation experiments, the air circulation was maintained by using air pump. For natural air flow circulation experiments, the inlet and outlet vents were left open to atmosphere for free‐air flow circulation.

Under forced flow air circulation the results showed that, the Fin system yields high thermal efficiency of 30%; followed by TFMS with 28% and lastly the typical with 25% for REF model respectively. Under natural air flow circulation the final results obtained that the Fin system yields high thermal efficiency of 20%; followed by TFMS with 18% and lastly 16% for REF model respectively at noon day.

FIGURE 4: ELECTRICAL EFFICIENCY OF BOTH COLLECTORS

The thermal efficiency of hybrid PV/T air collector system without tunnel had reached steady stage when the mass flow rate was 0.04 kg/s (Fig‐5). For collector system with tunnel, thermal efficiency was reached steady stage after mass flow rate of 0.07 kg/s. The photovoltaic, thermal and combined photovoltaic/ thermal efficiency of 10.02 %, 54.70 %, and 64.72 % had been observed respectively after modification of single‐pass open air channel absorber into a rectangle air tunnel absorber surface.

System Performance of Flat Plate Hybrid PV/T Solar Water Collector Systems A special Spiral flow absorber collector had been designed and tested (Adnan Ibrahim et al.), as shown in Fig.7. The rectangular hollow tubes of Spiral flow absorber were made up from stainless steel. The absorber collector as shown in Fig.7, consisting of a single unilateral channel for the water to flow in it which was fitted underneath the standard PV panel of 80 W rating with size of 1 m height, 0.65m length.

The spiral flow absorber tube was fabricated with one inlet and outlet to allow water to enter and exit from tube respectively. The inlet and outlet of spiral tube had been arranged opposite to each other so that

FIGURE 5: THERMAL EFFICIENCY OF BOTH COLLECTORS

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water to flow in reversed direction and covered the entire PV panel surface area from underneath.

The hybrid PV/T water collector systems had been constructed from two Pc‐Si PV modules in combination with water heat extraction device. The two hybrid PV/T water collector systems were used i.e.

PVT/Unglazed and PVT/Glazed. The two modified hybrid PV/T water collector systems had developed by attaching diffuse reflectors i.e. PVT/Unglazed +Ref and PVT/Glazed+Ref. During experiments with diffuse reflectors, the PV/T water collector systems were tested for different values of solar radiations to get data for different angles between systems and sun.

FIGURE 7: THE DESIGN OF SPIRAL FLOW ABSORBER COLLECTOR

The thermal and electrical efficiencies of these systems had been used to calculate monthly and annual energy output by using experimental calculation. These results were compared with the electrical performance of the PV/T water collector systems and that of standard PV modules of the same type in a typical installation and with diffuse reflectors.

The combined PV/T water collector system performance as 65 % had been obtained with electrical efficiency of 12 % at mass flow rate of 0.041 kg/s.

Two fundamental hybrid PV/T water collector systems had been considered (Y. Tripanagnostopoulos et al.), as shown in fig. 8.

TABLE‐1 ANNUAL SYSTEM ENERGY OUTPUT IN kWh/m2 Y

FIGURE 8: CROSS SECTION OF THE PV/T EXPERIMENTAL MODELS.

The stationary flat diffuse reflectors were attached from the higher part of the modules of one row to the lower part of the modules of next row is shown in Fig. 9. The above configuration increases the solar input radiation on PV modules throughout the year, results increase in electrical and thermal energy of the hybrid PV/T water collector systems.

SYSTEM

Annul Electrical Energy KWh/m2 y

% Of nput energy

Annul Thermal Energy KWh/m2 y

% Of input energy

PV MOUDLES

182.84

11.12

‐‐‐

‐‐‐

PV+REF MOUDLES

217.53

13.23

‐‐‐

‐‐‐

PVT/UNGL 25 0C

178.43

10.85

537.87

32.70

PVT/UNGL 35 0C

166.17

10.10

217.13

13.20

PVT/UNGL 45 0C

161.19

9.80

35.79

2.18

PVT/UNGL +REF 25 0C

198.62

12.08

619.77

37.68

PVT/UNGL +REF 35 0C

186.02

11.31

275.53

16.75

PVT/UNGL +REF 45 0C

143.57

8.73

263.96

16.05

PVT/GL 25 0C

149.33

9.08

776.30

47.20

PVT/GL 35 0C

137.55

8.36

467.98

28.45

PVT/GL 45 0C

125.25

7.62

220.39

13.40

PVT/GL +REF 25 0C

167.98

10.21

831.75

50.57

PVT/GL +REF 35 0C

155.77

9.47

519.15

31.56

PVT/GL + REF 45 0C

143.57

8.73

263.96

16.05

Table‐I shows final values of annual energy output for all systems of the annual solar input on the PV plane.

FIGURE 9: A PV/T SYSTEMS WITH DIFFUSE REFLECTORS

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These results had given an idea about the limitations of practical use of PV/T systems, as the operation of these systems in moderate (350C) or high (450C) temperatures results to a considerable reduction in electrical and thermal energy respectively.

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Also the solar radiation intensity had augmented up to 65.6% by attaching Aluminum foil concentrators with PV/T collector system, in relation to without concentrators. Because of this increment in solar radiation intensity, the thermal and electrical energy produce by PV/T water collector system had been improved by 55% and 17.10% respectively.

The different experiments had been performed on PV/T water collector system with and without flat plate concentrators attached to this system (Lj. Kostic et al. 2009). To conduct these experiments, a prototype of PV/T water collector system having dimensions of 1.37 x 0.72 m2 made of electrolytic alloy colored anodized aluminum box had been developed.

Experimental set up had been developed for two similar but separate PV panels with each area of 0.44 m2 as shown in fig. 11(R. Hosseini et al. 2011). The maximum output voltage and current were respectively 23V, 2.61A, with power output of 60W. The first panel was used as a combined PV/T system with a film of water running over its top surface without front glass and an additional fabricated system i.e heat exchanger was attached with combined system to utilize the heat generated by the panel. The second panel was a conventional PV as a reference panel. Both panels were facing south with an angle of inclination of 29°.

The power output of solar mono crystalline silicon module was 110 W. The flat concentrators were made of Aluminum sheet and foil with dimensions 1.37x 0.72 m2 as shown in fig. 10. The hybrid PV/T water collector system was positioned at an angle of 450 in relation to the horizontal plane and due south oriented.

Two flat Aluminum concentrators had been attached at sides of PV module of PV/T water collector system, with changeable position in relation to this hybrid system.

The solar radiation was measured by a Kimo SL100 solar meter installed on the corner of one of the panel.

The patch type thermocouples (k type) had been installed on the back surface of the two panels. Two standard thermocouples (k type) were used to measure the temperature of the water before running over the panel and at the lower end of the panel. The temperature of the water coming out of the heat exchanger was also measured by installing a standard thermocouple (k type) at the end of the finned tube type heat exchanger. The different measurements had been executed simultaneously over 14 days during September, 2010 in Tehran and recorded for every 10 minutes.

Heating of tap water in hot water storage tank was monitored for period of 8.00 to 17.00 hours during day.

Generated electrical energy was stored in battery. The current and voltage in PV/T water collector were recorded in every 10 min and registered in the form of tables and graphics by PC. The measurements of solar radiation intensity had been collected during an hour of solar cell in the middle of PV/T water collector system by using MINI‐KLA device as shown in Fig. 10.

FIGURE‐10, MEASUREMENTS OF CONCENTRATED SOLAR RADIATION BY MINI‐KLA DEVICE.

The solar radiation intensity had been increased up to 43.6 % by attaching Aluminum sheet concentrators with PV/T collector system, in relation to without concentrators. Because of this increment in solar radiation intensity, the thermal and electrical energy produce by PV/T water collector system had augmented by 39 % and 8.60 % respectively.

FIGURE 11: SOLAR PV PANEL EQUIPPED WITH WATER FILM PRODUCER

A film of water had been produced over the panel by a tube with a slit along the top end of the PV panel (Fig. 11). A water pump was used to fed water to the tube,

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leaves the slit and flows over the panel as a thin film flow. The water had been collected at the lower end of the panel passing through a finned tube type heat exchanger and consumed the heat gained by the water.

Due to tap water flow and additional cooling by water evaporation, the combined PV/T system’s operating temperature was measured much lower up to 18.7 C0 as compared to the conventional panel (Fig.12). This temperature reduction had caused a noticeable improvement in electrical efficiency up to 33%.

FIGURE 14: DIRECT PV/T WATER COLLECTOR SYSTEM

FIGURE 12: COMPARISON OF CONVENTIONAL PV PANEL TEMPERATURE WITH THE TEMPERATURE OF THE PANEL IN THE COMBINED PV/T SYSTEM.

There was a perceptible enhancement took place in overall efficiency of the combined PV/T system as comparison to the conventional system (Fig.13), because combined PV/T system had produced both electrical and thermal energy at a time.

FIGURE 15: PARALLEL FLOW PV/T COLLECTOR SYSTEM

FIGURE 13: COMPARISON OF CONVENTIONAL PV PANEL OVERALL EFFICIENCY WITH THE OVERALL EFFICIENCY OF THE COMBINED PV/T SYSTEM

Three PV/T water collector systems had been designed, tested and their thermal performances had been compared (Kamaruzzaman Sopian et al.), shown in Fig. 14 to 16.

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FIGURE 16: SPLIT FLOW PV/T WATER COLLECTOR SYSTEM.

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The output fluid temperature from PV/T collector systems for various module numbers under solar irradiance of 500 W/m2 and ambient temperature of 25 0 C had been shown in Fig. 18. After studying the performance characteristic parameters of PV/T system from Fig. 17 and 18, the Split flow design of PV/T water collector system gave better thermal performance compared to Direct flow and Parallel flow and lastly 16% for REF model respectively.

Fig. 14 shows that the parameter diagram of Direct PV/T water Collector system which was the most common, conventional and simple design use in solar water collector and photovoltaic thermal collector. Fig. 15 shows that the parameter diagram of Parallel flow PV/T collector system whcih was used in most product of current solar water collector without PV panel. Fig. 16 shows that the new design parameter diagram which was called as split flow PV/T water collector system. This new design was tested and compared to other collectors design in this simulation.

Conclusions After applying above system configurations techniques to simple flat plate hybrid PV/T water/air collector systems, an improvement in combined system performance took place. So single pass with rectangular tunnel collector, spiral flow absorber collector, thin metallic sheet suspended at the middle of air channel, fins at the back wall of an air duct etc has been used to cool under side of PV module to maintain constant open circuit voltage (VOC) of the PV module. Attaching flat concentrators or diffuse reflectors to PV module, the short circuit current (ISC) of the PV modules has been augmented. So the combined effects of above configurations have enhanced electrical performance of the hybrid PV/T water/air collector system compared to simple flat plate hybrid PV/T water/air systems. When the above system configurations techniques have been applied to these systems, enhancement in thermal performance took place too. Hence the combined system performance i.e. electrical and thermal performance of these systems took place.

FIGURE 17: THERMAL EFFICIENCY OF PV/T SYSTEMS WHEN WATER INPUT TEMPERATURE 26 0C AND AMBIENT TEMPERATURE 25 0C.

The thermal efficiency of these three PV/T systems, when water input temperature was at 260C and ambient temperature 25 0C under different solar irradiance is shown in Fig. 17. Fig. 18, shows thermal efficiency of these three PV/T systems, when water input temperature was at 31 0C and ambient temperature 25 0C under various solar irradiance. The above results showed that at lower temperature of input water, higher thermal efficiency of PV/T collector systems had been obtained.

To make these systems commercially viable in near future in terms of efficiency, performance, life, payback period, cost etc, along with the improvement in system configuration techniques, research and development on optimization of material selections and its application giving higher efficiency of the solar hybrid system may be considered in future development.

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V. N. Palaskar is pursuing Ph.D. (Mechanical Engineering), Department of General Engineering, Institute of Chemical Technology Mumbai, India since 2011‐12. He has completed M.E. (Mechanical Engineering) with first division in 2000 from Veermata Jijabai Technology Institute (Mumbai University) Mumbai, India. He has done B.E. (Mechanical Engineering) with first division in 1994 from Amravati University, Amravati, India. He has got more than 15 years of teaching and 2 1/2 years of research experience. Mr. V. N. Palaskar is working as faculty in Mechanical Engineering Department, Veermata Jijabai Technology Institute, Mumbai, India.

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S. P. Deshmukh is Ph.D. (Tech) from Institute of Chemical Technology (Deemed University), Mumbai in 2009. He has completed M.E. (Production Engineering) with first class in 1991 from Victoria Jubilee Technical Institute Matunga (University of Mumbai) Mumbai, India. He has done B.E. (Production Engineering) with first class in 1986 from Victoria Jubilee Technical Institute (University of Mumbai) Mumbai, India. He has got more than 26 years of teaching and research experience in engineering Institute. Dr. S. P. Deshmukh is working as Associate Professor in Department of General Engineering, Institute of Chemical Technology Mumbai, India.

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Prof. Dr S. P. Deshmukh is a Member of Indian Institute of Industrial Engineering (IIIE), India.

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E‐mail address: sp.deshmukh@ictmumbai.edu.in

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