Investigation of Techniques for Enhancement of Efficiency of a Hybrid Photovoltaic and Solar Thermal System: Literature Review on Applications and its Advancement

Abstract

Over the most recent couple of decades, tremendous consideration is drawn towards photovoltaic–thermal systems because of their advantages over the solar thermal and PV applications. This paper intends to show different electrical and thermal aspects of photovoltaic–thermal systems and the researches in absorber design modification, development, and applications. From the previous review articles, it has been concluded that the heat energy exhausted from the PV module can be further utilized in different ways and helps in achieving better efficiency. Furthermore, the types of photovoltaic–thermal systems such as air collector, water collector, and combi system, coupling with heat pump and their application to buildings are also stated. This paper also discussed certain design aspects like modifications in the flow channel by adding fins, thin metallic sheets, roll-bond absorber, and porous media and the effect of these modifications on the hybrid system’s efficiency. Further- more, the use of the latest technologies such as nano fluids, thermoelectric generators, and phase-change materials improves the overall system performance. The role of soft-computing techniques is forecasting the impact of various parameters on the photovoltaic–thermal system is also discussed.

Introduction

I. INTRODUCTION

The industrial reformation in the eighteenth century has tremendously hiked energy demand globally. The devel- oped countries around the globe shift their focus towards sustainable power sources, especially solar and wind, to meet the increasing energy demand [1]. Amongst all the available sustainable energy sources, the solar PV has the highest capital cost, but due to its lower operational cost and maintenance [2], this technology is acknowledged around the world.

Other advantages of solar PV are increased efficiency and pollution-free energy [3]. The installed capacity of solar PV is increasing day by day worldwide due to its above-mentioned point of interest as shown in Fig. 1.

 Banker and Pearce [4] discussed the development of PV technology over the last 2 decades. The PV technology gained popularity due to the decline in the price of a photovoltaic module. This reduction in cost is mainly due to competition among the manufacturers. Different governments in various parts of the world also show interest in emerging PV technology.

Incentives had also been provided to consumers in many parts of the world. Liou [5] discussed different silicon- and non-silicon-based technologies utilized for photovoltaic applications, as depicted in Fig. 2. The crystalline silicon technology is widely accepted as compared to other solar cell technologies because of lower cost and higher performance. In the most recent research, the effi- ciency of multi-crystalline silicon technology up to 23% is mentioned in the literature [6]. Tiwari et al. [7] reviewed the latest PV generation technologies and their applications. Debberma [8] reviewed the latest research in the area of PV generation and its application buildings. Apart from these traditional PV technologies, a few latest cell technologies are also discussed in the literature.Gallium arsenide (GaAs): GaAs is a composite semi- conductor formed by the combination of gallium and arsenide elements. The efficiency of GaAs can be increased by alloying it with other elements like alu- minum, phosphorous, and antimony. This technology is not so popular because of its high fabrication cost [8].

1. Dye-sensitized solar cell (DSSc): This technology is discovered by Michael Gretel and Brian Oregano in   the year 1991. DSSc is developed from the semiconductor formed by the combination of a photosensitized anode and an electrolyte. This latest technology gained attention due to its lower cost of fabrication, higher efficiency, and its ability to respond at low radiation levels. To enhance the power conversion efficiency (PCE) and stability for commercial applications, some dye-sensitized materials are also identified, such as porphyrin- based dyes and dyes containing polythiophene [9].
2. Perovskite solar cells (PSCs): PSCs are developed to achieve higher efficiency and low-cost solar cell. The fabrication of PSCs can be achieved using two different methods: (1) Mesoporous architecture and (2) thin-film architecture. Although the PSCs are prepared using simple chemical approach, it offers very high power conversion efficiency. The highest power conversion efficiency reported from the PSCs was 22.1% [10].
3. Organic solar cell: This latest technology is in trend because of its low cost and conversion efficiency of about 9%, but further enhancement in the efficiency is required if it is to be used for commercial applications. Its fabrication involves electron donor and acceptor materials instead of a semiconductor p–n junction [8]. The solar cell market mainly depends upon the crystalline silicon technology, but nowadays, amorphous or thin-film technology is widely accepted commercially for solar PV applications, because its efficiency does not vary much with the change in temperature, which happens with mono-crystalline and poly-crystalline  silicon-based PV cells. However, it offers certain disadvantages such as shorter life and less efficiency as compared to crystal- line silicon. However, the cost of generation of electricity by PV technology is much higher than the generation of heat energy. Therefore, generating thermal energy from the photovoltaic application creates much interest among the researchers. The current photovoltaic technology has the drawback of net absorbing radiation from the entire spec- trum. Therefore, electrical efficiency (ηele) is low, since a major portion of incident sunlight is wasted as heat. The temperature of the cell increases because of this heat, which results in reduction of ηele of the solar PV system. Therefore, the removal of heat energy associated with the PV cell is important.
4. Photovoltaic–thermal (PV/T) is the combination of PV technology and solar thermal technology, which converts the incident radiation into electricity and heat simultaneously, gains popularity. By cooling the PV surface with the help of air/water as a flowing fluid, ηele of the system is significantly improved [11]:

A PV/T system requires a PV module, a channel, coolant (air/water), DC fan, and collector [12]. The classification of PV/T technology is depicted in Fig. 3. The coolant in the PV/T system is further used for drying of crops, room heating, and water heating [13]. Ibrahim et al. [14] classified the PV/T system based on fluid circulation below the PV such as natural or forced flow. The simplest and economical  method used for cooling is the circulation of air by natural means, but at the same time, this method is less efficient in geographical regions where ambient tempera- ture is greater than 20 °C [15].

The performance of hybrid PV/T system is measured in terms of thermal, electrical, and exergy efficiencies of the system. The ηele of the system mainly depends upon the cell temperature, since the material used for the manufacturing of PV cells is sensitive to change in temperature.

The ηth of PV/T system changes with the change in air mass flow rate, type of solar collector, modifications in the absorber such as adding fins and TMS in the coolant chan- nel, sheet and tube absorber, roll-bond absorber, and tem- perature at the inlet and on the basis of fluid flow (single channel/double channel).

In previous studies, most of the researchers discussed the flat-plate collector because of its simple design and control operations [16]. A concentrating collector requires a large number of reflectors and lenses and complex mechanism for sunlight tracking makes the overall system complex and costly [17], but this type of PV collector helps in extracting higher energy as compared to flat-plate PV collector [18].

Therefore, it is preferred in industrial applications.

Another important aspect that makes PV/T a potential application is integrated with buildings to utilize thermal energy and electricity. These systems are known as building- integrated photovoltaic (BIPV) solar systems and building- integrated photovoltaic–thermal (BIPV/T) systems [19].

When the PV/T system is incorporated into the building, it generates heat, light, and electrical energy simultaneously for building use [20]. With the evolution of soft-computing techniques, optimization of parameters becomes quite easier which helps the researchers to understand the dynamics of the system. Since the current technology is in developing phase with the recent research going on, it offers several limitations: (1) higher installation cost as compared to PV and solar thermal system, (2) engineers working in this domain face various technical problems in design, (3) the market potential of PV/T is still very low compared to solar PV systems, and (4) researchers often get confused with the contradictory statements given in earlier reviews. To understand these factors, a review of the current research status of PV/T is needed. Although several reviews on the PV/T technology already exist in the literature, in the present article, the authors have carried out a comprehensive review on PV/T air collector, PV/T water collector, recent advancement in PV/T air and water collector and building-integrated PV/T. However, due to recently emerged soft-computing techniques, the performance prediction of PV/T becomes quite easy. Hence, it has become necessary to discuss the role of soft-computing techniques in PV/T. Furthermore, the present article also includes the role of thermoelectric generator in enhancing the performance of PV/T, solar dryer for rural areas, effect of nano fluids and PCM on the performance of PV/T, recent advancement in thermal absorber design, i.e., roll-bond absorber and PV laminations on roll-bond absorber, PV/T with SAHP and application of PV, and PV/T in buildings.

II. PHOTOVOLTAIC–THERMAL (PV/T) AIR COLLECTOR

The theory of PV/T was stated by Kern and Russel [21]. The concept of PV/T evolves from the fact that more than half of the sunlight incident on the solar cell is converted into heat. This heat may cause structural damage to the cell if it remains on the PV cell surface for a longer period. The heat recovered from the module can be for numerous applications such as crop drying, floor heating, hairdryer, etc. The layered diagram of PV/T module is shown in Fig. 4.

The PV/T air-collector design varies from each other based on the channel position. The overall efficiency (ηT) of the PV/T system is the sum of its thermal and electrical efficiencies [22–24]:

Various parameters that affect the performance of PV-TEG such as the method of integration of TEG, location, and properties of TEG and its thermal resistance have been discussed in detail.

Dimri [54] worked upon the PVT-TEC model using three different PV modules, viz., opaque, semitrans- parent, and aluminum-based. The performance of the sys- tem with the thermal-based model is then compared with ANN model. From the outcomes, it has been concluded that there is a good agreement in the result between the two models. In another study, Dimri [55] developed the mathematical equations for semitransparent PVT-TEC collector, and compared the performance with PV-TEC and semitransparent PV collector. The outcomes of the analysis show that the ηele of the semitransparent PVT- TEC is significantly higher than PV-TEC and PV collector.

Vorobiev et al. [56] developed a hybrid PVT-TEC model in which a thermoelectric generator is integrated with a PV module. Based on theoretical calculations, 30% of ηT were achieved from the hybrid system.

 In rural areas, there is a need for drying the grains to remove the moisture content. If the moisture is not prop- erly removed, then it will affect the productivity of farm- ers. Tiwari [57] performed an experimental analysis on PV/T air-collector integrated drying system which is useful in preserving the crops, as shown in Fig. 14. From the experimental analysis, it has been observed that for the crops with high moisture content, the performance is better under forced convection mode, while natural convection mode is better for the drying of crops with low moisture content. Singh et al. [58] discussed the benefits of green- house solar dryers in terms of energy savings. The mathematical modeling is presented and the performance evaluation has been discussed based on characteristic plots.

Aymen [59] investigated the working of a solar drying system connected with FPC under forced convection mode. The experiments were conducted to extract the moisture from red paper and sultana grapes. It has been observed from the analysis that 7 h had taken to dry red paper, while 17 h had taken to dry sultana grapes. The payback period of the solar drying system was found

III. PV/T WATER COLLECTOR

Water is considered as the most vital segment for the presence of living beings on the earth. PV/T water collector satisfies the need of electricity along with hot water. PV/T water collector has almost the similar structure as the PV/T air collector except for the air channel. In the PV/T water collector, water is forced to flow through the tubes beneath the PV module to cool down the PV module which in turn increases the ηele of PV/T water collector. Zondag. discussed various configurations of PV/T water collector based on water-flow patterns below the PV module, as shown in Fig. 15. Chow [60] studied the outcomes of additional glass cover on PV/T water collector. From the experimental analysis, it has been concluded that the thermal energy output is higher for glazed design, while the unglazed module is suit- able if energy at the output is of interest. Kiran and Devadiga [61] presented the comparative analysis of PV/T water collector with standalone PV and solar water heater. From the experimental analysis, the ηele and ηth of the PV/T system

were found to be 8.26% and 57.90%, respectively, which is significantly higher than individual PV and solar water heater. Daghigh [62] per- formed simulation using TRANSYS software to analyze the overall performance of the PV/T water collector in Malay- sian climatic conditions. Rajput  [63] discussed the concept of cylindrical pin finned heat sink to cool the panel to improve its ηele. It has been revealed from the outcomes that the temperature of the rear surface reduces to 58.45 °C from 88.81 °C with the proposed modification.

The demand for clean water is increasing day by day, along with the demand for electrical and thermal energy. Solar distillation is the most economical and commonly used method to convert contaminated water into fresh- water. Integrated PV/T solar still satisfies the demand for clean water along with thermal and electricity [64]. Sotehi et al. [65] investigated the performance of a hybrid PV/T module coupled with solar still to achieve the possibility

of net-zero energy building. It was reported that solar still coupled with PV/T system earned lots of profit by selling the electricity along with distilled water.

The additional advantage offered by the PV/T water- based system is that the water used as flowing fluid can be further reused in buildings, homes, etc. as hot water. Tripanagnostopoulos [73] did the experimental work to analyze the effect of glazing and a reflective coating on the performance of PV/T water collector. It has been concluded from the experimental study that the use of glazing helps in increasing the thermal output. Tiwari and Gaur [74] reported that a semitransparent module exhibits better efficiency than an opaque based module

A. PV/T combi technology

The synchronization of PV/T air-based system and PV/T water-based system led to the development of PV/T combi system which helps in achieving a better efficiency, since water and air both were used as a circulating fluid. The schematic diagram of the PV/T combi collector is shown in Fig. 16. The concept of the PV/T combi system was first introduced by Tripanagnostopoulos [75]. By combining two types of heat collector media, the temperature of PV cells is greatly reduced, and cell efficiency is improved as compared to PV/T water or PV/T air collector.

The experimental setup of the PV/T combi was installed and tested at the solar energy laboratory, Malaysia by Oth- man et al. [76]. The ηth of the PV/T combi collector was calculated according to the relation given by Duffie and Beckman [77]:

The PV/T combi system increases the surface area for heat exchange which helps in achieving high ηth and ηele. Nasim [78] use a decision tree approach and statistical correlation method to improve the performance of the PV/T combi collector. Thin metallic sheets of various shapes like sinusoidal, triangular, and rectangular were used in the air channel underneath the water tubes to enhance the air heat extraction through the duct. Although PV/T combi system overcomes the disadvantages offered by PV/T air collector and PV/T water collector, the researchers could not appreci- ate PV/T combi system due to complications in design, high cost, and several maintenance issues.

B. Recent Research in PV/T water collector

Recently, the researchers around the globe took an interest in the use of various nanomaterials along with cooling fluid to improve the thermal conductivity and stability of the fluid. When water is used as a cooling fluid in the channel, it absorbs only 13% of incident solar radiation. Therefore, the focus of research shifts towards the use of nanofluids with direct solar absorption collector [79]. The concept of using nanoparticles for cooling was given by Maxwell [80] in the late nineteenth century, but manufacturing techniques were very limited at that time. Therefore, this technique did not gain much attention. However, with the advancement in manufacturing techniques, nanofluid with direct absorption solar collector received much attention because of its capability to harness the thermal energy more efficiently as com- pared to the conventional solar thermal collectors. Thermal and optical properties are significantly improved when direct absorption solar collectors are incorporated with nanofluids. It has been observed from the facts that the thermal proper- ties of nanoparticles are further enhanced when mixed with little concentration of metals and metal oxides. Tyagi et al.

[81] analyzed the performance of flat-plate PV/T collector and direct absorption solar collector with nanofluid in the channel. It has been observed that nanoparticle increases the absorption of solar radiation as compared to pure water and helps in achieving a better efficiency. The absorption of radiation increases using nano-fluid and it helps in achieving better ηth [82]. Yazdanifard [83] discussed the effect of the size of nanoparticles, concentration of nanoparticles, and types of nanoparticles on the overall performance of the PV/T system. It has been reported that the performance of Al2O3 nanoparticles with water as a base fluid is better than TiO2 nanoparticles. Said [84] investigated experimentally the effect of Al2O3 nanofluid on the energetic perfor- mance of flat-plate PV/T collector. From the investigations, it has been reported that the energetic performance of the system improved significantly by mixing nanofluid with water. Bianco [85] investigated the effect of Al2O3 nanofluid on PV/T water collector. From the experiments, it is noticed that the temperature of the front surface and backside of the PV panel reduced by the mixing of nano- fluid with water as a base fluid. This helps in achieving a better PV conversion efficiency of the system. Barode [86] discussed the proficiency of carbon-based nanofluids in improving the ηth of four different types of solar collectors. The authors highlighted the impact of the concentration of nanofluid, temperature, and flow rate on the solar collector’s performance. The outcome of the experiment shows that at a concentration of 0.3 vol% of carbon nanofluid, the ηth of hybrid PV/T, parabolic trough, flat plate, and evacuated-tube solar collectors have been improved up to 97.3%, 74.7%, 95.12%, and 93.43%, respectively. At a very low concentration of 0.01 vol% of carbon nanofluid in the base fluid, an improvement up to 122.7% has been observed in the ηth of direct absorption solar collector. It is also worthy to note that carbon nano fluids also work as excellent anti-corrosion additives for the solar collector. Various authors reported increased electrical and thermal efficiency of PV/T collector using different nanoparticles in the channel with water as a base fluid as depicted in Table 1

Recently, phase-change materials (PCM) are used with PV/T module to minimize the temperature of the solar cell. A PCM material swing between its solid and liquid phases when a change in temperature is observed. When the ambient temperature is higher than that of the PCM, heat transfer is observed from the atmosphere to the PCM material, which changes its state from solid to liquid. When the ambient temperature is lower than that of the PCM, heat transfers from the PCM to the surroundings, creating a warming impact and PCM again changes its state to solid [92]. A perfect PCM material must be non-corrosive and it must offer characteristics like high Lf and λ. An experimental analysis has been carried out by Preet [93] on the PV/T-PCM system with different mass flow rates to observe the impact of PCM on its performance. The PV/T set up with PCM is shown in Fig. 17.

Liang [94] proposed a model in which the graphite layer is used underneath the water channel as shown in Fig. 18 and compared the performance with the conventional PV. The average ηele reported for the proposed PV/T model and conventional PV system was 6.46% and 5.15%, respectively. Ong [95] worked upon an experimental model in which a solar water heater is integrated with the TE module, which is used for the generation of electrical energy with hot water. The performance of the combined system was evaluated at a different fluid flow rate. From the observations, it has been observed that 0.16% of ηele is also achieved along with hot water.

The thermal absorber is the major component in the PV/T system that greatly influences its overall performance. Over the last few years, various changes in design, material, connection methodology, and manufacturing techniques of thermal absorber have been observed. Sheet and tube design is the typical thermal absorber configuration used in PV/T system. The other configurations are roll-bond absorber and fully wetted type absorber. In the roll-bond absorber, channels are embedded between two rolled aluminum sheets, while in conventional sheet and tube design, the channels are welded under the plate. The performance of the flat-plate PV/T collector with roll-bond absorber was investigated by Haurant [96]. The modified system is used for hot water production. The performance of PV/T water collector has been compared based on different roll-bond absorber configurations, i.e., serpentine pipe and harp pipe [97].

The major technological drawback of the PV/T system lies in the connection technology used to combine PV cells with the thermal absorber. The conventional connection methods include fixing of PV cell with thermal absorber with glue (gluing) and package lamination. In the gluing method, air bubbles are trapped between the thermal absorber with PV cell which causes an increase in thermal resistance between the PV cell and absorber along with irregular distribution of cell temperature.

In packing lamination, upper glass, PV cells, and thermal absorber             are laminate together in one step to decrease the thermal resistance between the connections. The performance of PV/T system has been compared based on above two con- nection techniques by Dupeyrat [98], and it has been concluded that a significant improvement in thermal and electrical performance of PV/T system has been observed using lamination method as compared to gluing method.

Ying [99] investigated the performance of PV/T water collector with roll-bond absorber, as shown in Fig. 19. The low-cost thermo-laminating method is used for PV-absorber connection which makes the system suit- able for the application in rural areas. The test setup was installed at Sichuan Basin, China. The ηele and ηth reported for the installed system were 15% and 85% which ensure the heat transfer capability of the roll-bond absorber plate.

Aste [100] analyzed the performance of covered and uncovered PV/T water collectors coupled with two aluminum roll-bond absorbers. The channel configurations used in covered and uncovered PV/T water collector are shown in Fig. 20. The simulation study carried out based on mathematical modeling and it has been observed that the ηT of uncovered PV/T water collector is higher than the covered PV/T water collector.

Wu [101] presented a critical review of the ther- mal absorber connection method with PV/T module. EVA lamination method is the best suited for the connection of thermal absorber of PV/T module as compared to another conventional method. The authors further discussed the advantages of the roll-bond absorber, heat pipe array, extruded heat exchanger, and cotton wick design over the conventional thermal absorbers, such as sheet and tube design, rectangular tunnel absorber, fins, and groove absorb- ers. Song et al. [102] discussed the challenges faced by the PV manufacturing industry during lamination. Based on finite-element modeling, it is found that the back surface of the PV cell suffers from more stress during the lamination. Over the last few decades, coupling of heat pump with PV/T gained a significant attention because of high-energy output and lower power consumption. Ji et al. [103] com- pared the performance of PV/T-SAHP with the conventional PV/T system. The outcome shows that the ηele of PV/T-SAHP system improved by 13.4% because of the good heat-absorbing capacity of refrigerant as compared to the conventional PV/T system. A significant improvement in ηele of PV/T-SAHP system as compared to PV/T

system was reported by Fang [104]. In another study, Ji [105] presented the mathematical modeling of PV/T-SAHP system. Based on numerical simulation, the performance of the combined system is estimated and the ηele of the PV/T-SAHP was 13.4%. Using direct expansion evaporator, further enhancement in electrical and thermal performance of PV/T-SAHP system was observed [106]. Zhou et al. [107] developed a roll-bond PV/T heat pump system to investigate the tri-generation (cooling/heating/ electricity) operation of the system. The five major parts of the combined system are depicted

The outcomes of the experimental investigation showed that the RB-PV/T heat pump system is capable of supplying the electricity demand of a building with high efficiency along with space heating and cooling. An experimental investigation was performed by Kong et al. [108] to investigate the effect of charge quantity of refrigerant on the COP and efficiency of the direct expansion-solar- assisted heat pump (DX-SAHP) system.

IV. BUILDING?INTEGRATED PHOTOVOLTAIC–THERMAL (BIPV/T) APPLICATION

PV/T system must be integrated into a building for room heating, space heating, etc. to improve its electrical and ther- mal performances. The term ‘Building-integration’ refers to the application of PV or PV/T system into the building envelope with or without the orientation to keep track of sunlight [109].

In BIPV/T the exhausted fluid is utilized for crop drying or surface heating purposes in buildings and hospitals. The BIPV/T system provides better efficiency and occupies less space and requires lesser maintenance as com- pared to solar thermal and solar PV systems individually. The possible growth and limitation of BIPV are discussed in the report presented by the International Energy Agency [113]. Baljit et al. [19] discussed various building-integrated photovoltaic (BIPV) and BIPV/T technologies and its con- struction features. One of the configurations was BIPV-Wall/ façade in which the PV panel was installed vertically on the wall of a building with an air gap or installed as a part of the building, as shown in Fig. 23.

A. Effect of parameters on the performance of BIPV and BIPV/T

Experimental investigations have been carried out to deter- mine the optimum air gap between the PV module and the wall of the building [114]. The size of the air gap decides the heat flow rate. As the air gap increases, the heat transfer through the gap decreases. The speed of airflow through the gap also affects heat transfer performance. The speed of

0.6 m/s reduces the PV module temperature by 38 °C, while the speed of 1.2 m/s reduces the temperature by 45.3 °C [115].

Another configuration of this technology is BIPV-roof. This configuration is used where the speed of natural air is higher, i.e., at high rise buildings. The natural flow of air can effectively cool the PV panel, thereby improving efficiency. Several parameters which are taken into consideration, while incorporating PVs into building roof/facades.

Lin et al. [117] discussed the case study of the BIPV/T air-based rooftop system installed on a solar house in Quebec. Al-damook [118] investigated the impact of PAP connected with an unglazed solar air collector for the western Iraq climatic conditions. The experimental and theoretical results show that the use of an unglazed solar air collector is beneficial in terms of economy and thermal performance and PAP helps in achieving lower life cycle costs.

The experimental study shows that the PCM-PVT sys- tem can maintain a better output temperature and hence enhanced the ηth of the system. Elarga et al. [119] worked on PV/T-PCM model and presented the mathematical modeling of the system. PCM layer helps in achieving bet- ter ηth and led to a reduction in average cooling demand by 20–30%. With PCM, the ηele of the system has increased by 5–8%.

Conclusion

In the present article, a comprehensive literature review on PV/T technology has been conducted, which will be very effective and useful for the researcher in this field. The cur- rent technology shows the application of PV/T in air collector, water collector, buildings, solar-assisted heat pump, and solar drying, with a major focus on the thermal portion. Furthermore, utilization of nanoparticles with water as a base fluid in the channel, the use of thermoelectric, and PCM is a boost to this technology, as these trends improve the PV/T system’s performance. Recently, optimization of parameters using various soft-computing techniques helped to achieve better performance. Moreover, the following observation can be drawn from the present study: The energy efficiency of PV/T air collector increases by parameter optimization using soft-computing techniques. The thermal and electrical efficiency of PV/T air collec- tor increases by modification in the channel such as using fins and thin metallic sheets, adding porous media in the air channel. The thermal efficiency of the PV/T water collector increases by adding nanofluid and PCM in the channel. The thermal efficiency and electrical efficiency of the PV/T water-collector increase with the roll-bond absorber. An extensive review on PV/T technology has been con- ducted with certain future scope listed below in the presented research field: The material used for the fabrication of solar cells plays a vital role in the performance of the PV/T system. It has been found from the previous research that, still, there is a wide future scope of research available in other solar cell technologies such as amorphous silicon and gallium arsenide. The application of roll-bond absorber in the PV/T system may also be an interesting research field. It is reported by many researchers that the performance of the PV/T system is improved significantly using a single laminated PVT system, but still there is a wide future scope available PV lamination technology.

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