MEV Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 Journal of Mechatronics, Electrical Power, and Vehicular Technology e-ISSN: 2088-6985 p-ISSN: 2087-3379 mev.lipi.go.id doi: https://dx.doi.org/10.14203/j.mev.2021.v12.10-17 2088-6985 / 2087-3379 ©2020 Research Centre for Electrical Power and Mechatronics - Indonesian Institute of Sciences (RCEPM LIPI). This is an open access article under the CC BY-NC-SA license (https://creativecommons.org/licenses/by-nc-sa/4.0/). MEV is Sinta 1 Journal (https://sinta.ristekbrin.go.id/journals/detail?id=814) accredited by Ministry of Research & Technology, Republic Indonesia Experimental and model validation of photovoltaic-thermal (PVT) air collector: exergy analysis Ahmad Fudholi a, b, *, Mariyam Fazleena Musthafa c, Goh Li Jin a, Rudi Darussalam b, Ahmad Rajani b, Andri Setiawan b, Anwar b, Mohammad Hossein Yazdi d, Hazim Moria e,Mohd Yusof Othman a, Mohd Hafidz Ruslan a, Kamaruzzaman Sopian a a Solar Energy Research Institute, Universiti Kebangsaan Malaysia Bangi Selangor, 43600, Malaysia b Research Centre for Electrical Power and Mechatronics, Indonesian Institute of Sciences (LIPI) Komp LIPI Bandung, Jl. Sangkuriang, West Java, 40135, Indonesia c Department of Energy, Ministry of Environment Green Building, Handhuvaree Hingun, Maafannu, Male', 20392, Republic of Maldives d Dept. of Electric Power Generation Stations, Network and Supply Systems, Institute of Engineering and Technology, South Ural State University 76, Lenin Avenue, Chelyabinsk, 454080, Russian Federation e Department of Mechanical Engineering Technology, Yanbu Industrial College Yanbu Al-Sinaiyah City, 41912, Kingdom of Saudi Arabia Received 21 February 2021; Accepted 09 June 2021; Published online 31 July 2021 Abstract Solar energy is a renewable energy that can produce heat via a thermal system and generate electricity via a photovoltaic (PV) module. A photovoltaic-thermal (PVT) collector is a system that has a PV module combined with a thermal collector system. The PVT collector is a popular technology for harvesting solar energy. A PVT collector can generate both electrical and thermal energies simultaneously. The study aims to validate the PV and outlet temperature for various mass flow rates and solar radiation. To develop a predictive model, a steady-state energy analysis of a PVT air collector was performed. An energy balance equation was solved using the matrix inversion method. The theoretical model was developed and validated against the experimental results, which have a similar trend and are consistent with the experimental results. On the other hand, the validated model was used to study the performances of PVT air collectors using exergy analysis for the mass flow rate ranging from 0.007 kg/s to 0.07 kg/s and solar radiation ranging from 385 W/m2 to 820 W/m2. The result from the mathematical model was found to be consistent with the experimental data with an accuracy of about 95 %. The average PVT exergy efficiency was found to be 12.7 % and 12.0 % for the theoretical and experimental studies, respectively. ©2021 Research Centre for Electrical Power and Mechatronics - Indonesian Institute of Sciences. This is an open access article under the CC BY-NC-SA license (https://creativecommons.org/licenses/by-nc-sa/4.0/). Keywords: mathematical model; thermal efficiency; electrical efficiency; second law efficiency. I. Introduction Global crisis on primary energy sources, such as coils and gas, has facilitated the study of renewable energy technologies. Studies have focused on solar energy to address the global crisis on oil and gas prices worldwide. Sustainable energy sources, such as solar energy, are clean energy that contributes a substantial proportion to fulfilling the energy demand by societies. The yielding of solar energy for photovoltaic (PV) systems in energy technology can be broadly classified into two systems. PV energy system changes solar energy into electrical energy, and thermal energy system converts solar energy into thermal energy. The combination of PV and solar thermal collectors in the system can produce heat and electrical energy from solar energy. The use of a cooling system alongside PV system is validated as PVT system or PV with the cooling system. Given the beneficial dual use of PVT compared with a single PV system, efficient use of solar energy may contribute to the demand for heat and electrical energy to be supplied to industries and societies [1][2]. PVT collector systems using air as heat transfer medium are known as PVT air collector systems. The * Corresponding Author. Tel: +62-812-7519-3956 E-mail address: a.fudholi@gmail.com https://dx.doi.org/10.14203/j.mev.2021.v12.10-17 http://u.lipi.go.id/1436264155 http://u.lipi.go.id/1434164106 https://mev.lipi.go.id/mev/index https://dx.doi.org/10.14203/j.mev.2021.v12.10-17 https://dx.doi.org/10.14203/j.mev.2021.v12.10-17 https://creativecommons.org/licenses/by-nc-sa/4.0/ https://sinta.ristekbrin.go.id/journals/detail?id=814 https://crossmark.crossref.org/dialog/?doi=10.14203/j.mev.2021.v12.10-17&domain=pdf https://creativecommons.org/licenses/by-nc-sa/4.0/ A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 11 air circulation in the system is air circulating through the path between the back of the PV module surface with the system or path insulation on both sides of the PV module. Air is streamed directly through natural convection or forcefully. The hot air that comes out of this system is useful for drying and heating purposes. This system is widely applied in two designs namely the PV system that is integrated with the solar thermal collector system and PV system that is integrated into the building ventilation system. The energy analysis of the PVT air collector has been carried out by researchers. The efficiency of energy analysis is usually determined regardless of the power loss factor for the system. Therefore, over the past few years, most systems are analyzed and designed by taking into consideration the cost, the economy, the environment, and efficiency [3]. PVT collectors can attain net (electrical plus thermal) efficiencies of 70 % or more, depending on the conditions, with electrical efficiencies of 15 – 20 % and thermal efficiencies of more than 50 %. [4]. PVT technologies offer the ability to reduce the number of materials used, the time it takes to install, and the amount of space needed [5]. PVTs are useful for household applications since they can generate both electricity and thermal energy at the same time. Commercial PVT systems, despite their enormous potential, are still not as popular as stand-alone, individually installed PV and thermal systems [6][7]. Exergy analysis is a measure of consistency in determining the value of the economy as mentioned by many researchers. Through exergy analysis, the real efficiency value can be determined by determining the value of system power loss. Consequently, if the energy efficiency value and the efficiency of the exertion are different, the energy efficiency is higher than the efficiency of the previously mentioned factor. Exergy analysis is a very clever step in the design and process of the industry. This is because optimum energy consumption is an important issue. Information from exogenous value is also very important in operating costs, energy recovery, diversity of fuels, and pollutants. Now, exergy analysis is widely used in solar energy assessment such as solar drying systems, solar collectors, and PVT systems [8]. Jadallah et al. [9] designed, fabricate, and modeled for double-pass PVT collectors for drying applications. In the diverse weather conditions, Zoukit et al. [10] constructed and forecasted an indirect form of solar dryer that functions in both forced and natural convection modes. Tiwari et al. [11] constructed and built a hybrid PVT air collection with a dryer, then assessed the system's thermal model. The dryer chamber performed better for crops in forced convection mode than in natural convection mode [11]. The indirect dryer was shown to be more efficient than an open solar dryer [12]. For drying pear, Hajar et al. [13] designed an indirect solar drier method. The higher output temperature reached 57 °C when solar radiation was 900 W/m2, and the drying room's thermal efficiency was 11.11 % [13]. The loss of PV module efficiency is one of the most serious issues with a building-integrated photovoltaic (BIPV) system. As the temperature of a PV panel rises by 1 °C from 25 °C, its efficiency drops by roughly 0.4 – 0.5 %. [14]. Theoretical study and experimental validation of energetic performances of PVT air collectors were studied by Touafek et al. [15]. The simulation results were compared to those obtained through experimentation from outdoor testing. Their comparison reveals a high level of agreement. In the case of the intake and output fluid temperatures, this agreement is more pronounced. This study will derive the output temperature and the PV temperature from the mathematical model and validate them against an experiment from indoor testing. The study aims to validate the PV and outlet temperature for a mass flow rate of air ranging between 0.007 kg/s and 0.07 kg/s and solar radiation of 385 W/m2 and 820 W/m2. The validated data would then be used to analyze the exergy of PVT air collector and compare it with the exergy of the PVT used in the experiment. Exergy analysis identifies the causes, locations, and magnitude of the inefficiencies of the system and provides an accurate measure of how a system approaches the ideal. II. Materials and Methods A. Mathematical modeling The cross-sectional view of the PVT air collector is shown in Figure 1. Various heat transfer coefficients are shown in the Figure 1. The energy balance equation for PVT air collectors is based on the following assumptions: all convection heat transfer coefficients in the channels and flowing air are equal and constant; the usable heat gain to by air is uniform along the length of the collector; and the ohmic losses in the solar cell are insignificant [16]. Figure 1 shows temperatures such as Tp is PV temperature, Ti is inlet temperature, Tb is bottom temperature, Tf is fluid (air) temperature, and To is outlet temperature. Ut and Ub are top and bottom loss coefficients. S is solar radiation, α, τ coefficients are absorption and transmission coefficient, respectively. Heat transfer coefficient of radiation from PV to ambient (hrpa), heat transfer coefficient of radiation from PV to bottom (hrpb), and heat transfer coefficient of convection from PV to fluid (hcpf). The steady-state energy balance equations for PVT air collectors are given as follows: For PV, Figure 1. Schematic diagram of heat transfer coefficients in a PVT air collector A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 12 𝜏𝜏𝜏 = 𝑈𝑡�𝑇𝑝 − 𝑇𝑎� + ℎ𝑐𝑝𝑐�𝑇𝑝 − 𝑇𝑐� + ℎ𝑟𝑝𝑟�𝑇𝑝 − 𝑇𝑟� + 𝜂𝑃𝑃𝜏 (1) For the airflow channel, ( ) ( ) ( )o i cpf g f cbf b fmC T T h T T h T T− = − + − (2) For the backplate, ( ) ( ) ( )rpb p b cbf b f b b ah T T h T T U T T− = − + − (3) where t b t k U l = (4) 1 1 t w rpa U h h −   =   +  (5) ℎ𝑟𝑝𝑟 = 𝜎�𝑇𝑝+𝑇𝑏��𝑇𝑝2+𝑇𝑏 2� � 1 𝜀𝑝 + 1 𝜀𝑏 −1� (6) ( )( )2 2rpa p p sky p skyh T T T Tε s= + − (7) 1.50.0522sky aT T= (8) Where pε , s , aT , skyT , bT and pT are the emissivity of PV, Stefan– Boltzmann constant, ambient temperature, sky temperature, backplate temperature, and PV temperature, respectively. The convective heat transfer coefficients [16] are given as in equations (9) to (15). h k h Nu D = (9) in which 𝐷ℎ = 4𝑊𝑊 2(𝑊+𝑊) (10) where W , d , and hD are the width, depth, and equivalence diameter of the channel, respectively; k is the air thermal conductivity, and; Nu is the Nusselt number [16]. Nusselt numbers are given as follows [16]: For Re<2300 (laminar flow region), 𝑁𝑁 = 5.4 + 0.00190�RePr� 𝐷ℎ 𝐿 �� 1.71 1+0.00563�RePr� 𝐷ℎ 𝐿 �� 1.17 (11) For 23006000 (turbulent flow region), 0.8 0.40.018 Re PrNu = (13) where Re and Pr stand for Reynolds and Prandtl numbers, given as [16] Re h ch mD A µ = (14) Pr C k µ = (15) For a short collector of less than 10 m, the theoretical model assumes that the mean air temperature is equal to the arithmetic mean [16], where ( ) 2 i o f T T T + = (16) The physical properties of air are density, specific heat, thermal conductivity, and viscosity as published. The major design parameters are given as W = 0.53 m, L = 1.2 m, Ta = Ti = 27 oC, εp = 0.7, τ = 0.92, εb = 0.9, α = 0.9, and V = 1 m/s [16]. For simplicity, equations (1) to (3) can be presented in a 3 × 3 matrix form: [ ][ ] [ ]A T B= (17) 1 2 3 4 5 6 cpf rpb p cpf cbf f rpb cbf b Z h h T Z h Z h T Z h h Z T Z  − −          =                (18) where 1 t cpf rpbZ U h h= + + (19) 2 t a pZ S U T Sat η= + − (20) ( )3 2cpf cbfZ h h mC= − + + (21) 4 2 iZ mCT= − (22) ( )5 cbf rpb bZ h h U= − + + (23) 6 b aZ U T= − . (24) The temperature vector can be calculated using the matrix inversion form, as shown in equation (17) [ ] [ ] [ ]1T A B−= . (25) The first and second laws of thermodynamics are used to conduct exergy analysis, which includes taking into account total exergy intake, exergy outflow, and exergy destructed from the system. The general exergy balance is expressed as [16][17]: if the effects related to kinetic and potential energy changes are ignored: i o dEx Ex Ex− =∑ ∑ ∑ (26) or ( )i th PV dEx Ex Ex Ex− + =∑ ∑ ∑ , (27) in which 4 4 1 1 3 3 a a i s s T T Ex ANS T T       = − +        (28) ( ) 273 1 273 a th o i o T Ex mC T T T  + = − −  +  (29) A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 13 PV pEx ASη= . (30) PVT air collectors' electrical efficiency can be computed as ( )0 1 0.0045 25p pTη η  = − −  (31) The overall performance of the system is evaluated using the total efficiencies, known as overall efficiency or PVT efficiency (ɳPVT) and can be expressed as PVT th PVEx Ex Ex= + (32) where thEx is the thermal exergy, PVEx is the PV exergy, PVTEx is the PVT exergy, oEx is the output exergy, iEx is the input exergy (radiation exergy), dEx is the exergy destroyed, A is the PV area, N is the PV number, S is the solar radiation, sT is the solar temperature ( sT =5777K), aT is the ambient temperature, ,o iT T , and pT are the outlet, inlet, and PV temperatures, respectively. The PVT exergy efficiency is expressed as , o ex PVT i Ex Ex η = (33) B. Experimental study This PV has been tested by the manufacturer in the industry under the radiation intensity of 1000 W/m2 and room temperature of 25 °C to achieve a maximum power of 80 W. The PVT air collector was evaluated using a specially constructed solar simulator in the laboratory, as shown in Figure 2 and Figure 3. The solar simulator was made using 23 halogen bulbs, each rated at 500 W, as seen in Figures 2 and 3. The solar simulator's brightness and solar radiation were controlled using regulators. The tests were carried out with five different mass flow rates (0.007 kg/s to 0.07 kg/s) and solar radiations of 385 W/m2 and 820 W/m2. The air velocity reading range was 0.2 to 40 m/s, with an accuracy of 1 % of the reading 1 digit and a precision of 0.01 m/s. It was decided to utilize an Eppley pyranometer since it is simple to operate and does not require the usage of a sun tracking equipment. This pyranometer was intended to be able to detect 90 % or more of all solar radiation data on the world. The constants for the Eppley pyranometer used in this study were 11.99 × 10-6 V/Wm-2. The thermocouples temperature range for J-type is 0 °C – 760 °C which was suitable with the multimeter used. Materials used in the experiment were shown in Table 1. Data were recorded to calculate electrical and thermal efficiencies. III. Results and Discussions The efficiencies of PVT air collectors were obtained. The temperature distribution of PVT air Figure 2. Photograph of PVT air collector under solar simulator Figure 3. Schematic of PVT air collector under solar simulator Table 1. Material used in the experiment No. Material Number Function 1 SHARP NE-80E2EA Polycrystaline 80 W PV panel 1 Generate electricity 2 500 W halogen lamp 23 Supply of light and thermal radiation 3 350 W (Yuhchang) fan 1 Cooling the PV 4 Air heater (500 W halogen lamp) 2 Heating the inlet air 5 2000 VA voltage regulator 6 Changing power halogen lights 6 2000 VA voltage regulator Changing wind velocity of the fan 7 500 VA voltage regulator 1 Changing the heating power of the air 8 Insulation Prevent air out 9 Pyranometer 1 To observe solar radiation 10 J-type thermocouples Detect heat to a certain point 11 Switches (such as switch fan) Connection to 10 thermocouples 12 Air duct 1 Connect solar collector with fan 13 DTA 4000 anemometer Detecting the velocity of the wind 14 52 K/J thermometer multimeter 2 Pointing temperature readings from thermocouples 15 72-7740 multimeter (connect to the pyranometer) 1 To detect the radiation intensity A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 14 collectors was determined using the mathematical model's. The result shows that by lowering the temperatures Tp, Tf, and Tb simultaneously, the mass flow rate increases, as shown in Figure 4 and Figure 5. Since can be seen in Figures 4 and 5, raising the mass flow rate simultaneously decreased the temperatures (Tp and To) of the PVT collector for both solar radiations, as more and more air volume is available to remove heat from the channel walls, lowering PV temperature. Because the air velocity in the channel is increased, the outlet air temperature decreases as the air flow rate rises [18]. This is because air has less time inside the channel to reach higher outlet temperatures. For the PVT which received solar radiation of 820 W/m2, output air temperature and PV temperature presents higher values (Figure 5) than the PVT which received solar radiation of 385 W/m2 (Figure 4). The reason for this observation is due to more irradiance intercepted by the PVT collector hence more heat energy is transferred to the PV. This leads the PV to attain a higher temperature and allows more heat energy to be transferred to the airflow in the channel increasing the output temperature [19]. Table 2 shows the results of PV and the outlet temperature of the PVT air collector. The average errors in the calculation of the outlet and PV temperature were 6.3 % and 5.1 % for S = 385 W/m2, and 3.8 % and 5.7 % for S = 820 W/m2, respectively. The mathematical model made reasonable forecasts for outlet and PV temperatures, with average errors of 5.0 % and 5.4 %, respectively. The mathematical model's outputs are 95 % and 94.6 % accurate, respectively, when compared to experimental data for outlet and PV temperatures. Figure 6 and Figure 7 show the exergy analysis of PVT air collectors. PVT exergy efficiency is in a similar trend and rises very slowly for both experimental and theoretical studies, which produced PVT exergy efficiencies of 11.5 % to 12.9 %. For solar radiation of 385 W/m2 in the theoretical study, the PVT air collector produced a PVT exergy of 28.6 W to 29.3 W with electrical exergy of 26.8 W to 28 W and thermal exergy of 1.2 W to 1.9 W. For solar radiation of 385 W/m2 in the experimental study, the PVT air collector produced a PVT exergy of 27.8 W to Figure 4. Mathematical model and experimental result of PVT air collectors for solar radiation of 385 W/m2 Figure 5. Mathematical model and experimental result of PVT air collectors for solar radiation of 820 W/m2 25 30 35 40 45 50 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Te m p er at u re ( o C ) Mass flow rate (kg/s) Theoretical PV temperature Experimental PV temperature Theoretical outlet temperature Experimental outlet temperature Theoretical back plate temperature 30 35 40 45 50 55 60 65 70 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Te m p er at u re ( o C ) Mass flow rate (kg/s) Theoretical PV temperature Experimental PV temperature Theoretical outlet temperature Experimental outlet temperature Theoretical back plate temperature Table 2. Comparison of theoretical and experimental studies for outlet and PV temperatures of PVT air collectors m (kg/s) S (W/m2) Outlet temperature (°C) PV temperature (°C) Theoretical Experimental % error Theoretical Experimental % error 0.00696 385 35.9 32.2 11.5 45.3 46.5 2.6 820 45.8 41.4 10.6 64.4 66.0 2.5 0.02492 385 31.8 29.9 6.4 40.6 43.5 6.7 820 37.2 35.9 3.6 55.2 58.5 6.0 0.03861 385 30.4 29.4 3.4 39.8 41.4 3.9 820 34.1 33.4 2.2 53.6 56.1 4.7 0.05387 385 29.7 28.4 4.6 38.4 40.6 5.4 820 32.8 32.3 1.5 50.7 54.7 7.9 0.06958 385 29.3 27.8 5.6 37.3 40.1 7.0 820 31.9 31.6 0.9 48.5 52.2 7.6 Average 5.0 5.4 A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 15 29.1 W with electrical exergy of 26.6 W to 27.6 W and thermal exergy of 0.3 W to 1.7 W. Referring to Figure 7, for solar radiation of 820 W/m2, the PVT air collector produced a PVT exergy of 58.7 W to 62.3 W with a thermal exergy of 5.5 – 8.4 W and an electrical exergy of 51 – 56.1 W for the theoretical study, and a PVT exergy of 55.5 – 58.7 W with thermal exergy of 0.9 – 5.9 W and electrical exergy of 50.4 – 53.7 W for the experimental study. Table 3 shows the errors for exergy efficiencies of PVT air collectors. The variations of PV exergies with mass flow rate are shown in Figure 8 and Figure 9. The PV exergy of PVT air collectors increases with increasing air mass flow rate. A comparison of exergy efficiencies of PVT Figure 8. Electrical exergy versus mass flow rate for 385 W/m2 Figure 9. Electrical exergy versus mass flow rate for 820 W/m2 26.5 27.0 27.5 28.0 28.5 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 E le ct ri ca l e xe rg y (W ) Mass flow rate (kg/s) Theoretical Experimental 50 51 52 53 54 55 56 57 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 E le ct ri ca l e xe rg y (W ) Mass flow rate (kg/s) Theoretical Experimental Figure 6. Variations of exergies and exergy efficiency with mass flow rate for 385 W/m2 Figure 7. Variations of exergies and exergy efficiency with mass flow rate for 820 W/m2 0 5 10 15 20 25 30 35 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 E xe rg y, E ff ic ie n cy ( W , % ) Mass flow rate (kg/s) Electrical exergy theoretical Thermal exergy theoretical PVT exergy theoretical PVT exergy efficiency theoretical 0 10 20 30 40 50 60 70 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 E xe rg y, E ff ic ie n cy ( W , % ) Mass flow rate (kg/s) Electrical exergy theoretical Thermal exergy theoretical PVT exergy theoretical PVT exergy efficiency theoretical PVT exergy efficiency experimental Thermal exergy experimental Table 3. Error for exergy efficiencies of PVT air collectors based on Figures 6 and 7 m (kg/s) S (W/m2) PVT exergy efficiency (%) PV exergy efficiency (%) Theoretical Experimental % error Theoretical Experimental % error 0.00696 385 12.56 12.18 3.0 10.96 10.88 0.7 820 12.10 11.46 5.2 9.77 9.67 1.0 0.02492 385 12.91 12.33 4.5 11.25 11.07 1.6 820 12.84 12.11 5.7 10.34 10.14 2.0 0.03861 385 12.79 12.76 0.2 11.30 11.20 0.9 820 12.53 11.44 8.7 10.44 10.29 1.5 0.05387 385 12.80 12.53 2.1 11.38 11.25 1.2 820 12.64 11.46 9.3 10.62 10.37 2.3 0.06958 385 12.84 12.26 4.5 11.45 11.28 1.5 820 12.69 11.51 9.3 10.76 10.53 2.1 Average 5.3 1.5 A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 16 air collectors is presented in Table 4. Figures 8 and 9 show the results for electrical exergy or exergy of PV, 𝐸𝑥𝑃𝑃 obtained from the mathematical model (theoretical) and experimental results. Figure 8 shows the variation of electrical exergy for PVT air collectors at a solar intensity of 385 W/m2. Figure 9 shows the variation of electrical exergy for PVT air collectors at a solar intensity of 820 W/m2. For solar radiation of 385 W/m2, the PVT air collector produced electrical exergy of 26.8 W to 28 W in the theoretical study and 26.6 W to 27.6 W in the experimental study. For the case of solar radiation of 820 W/m2, the PVT air collector produced electrical exergy of 51 W to 56.1 W in the theoretical study and 50.4 W to 53.7 W in the experimental study. From Figures 8 and 9, the results indicate that by increasing the mass flow rate there is a clear increase in the electrical exergy (𝐸𝑥𝑃𝑃) of the PVT collector for both the solar radiations. The likely reason for this observation is due to the decline in the PV temperature when mass flow air of the air increased. This decrease in the PV temperature increased the PV efficiency, mainly because a lower cell temperature increases the voltage significantly (even though it decreases current by a very small amount). For this reason, since the PV efficiency increases, the total useful electrical gain also increased. The results also show that the total electrical exergy (𝐸𝑥𝑃𝑃) of the PVT collector for the PVT which received solar radiation of 820 W/m2 presents higher values (Figure 9) than the PVT which received solar radiation of 385 W/m2 (Figure 8). The greater number of photons associated with higher solar irradiation creates more electron– hole pairs and thus more current in the PV cell, which is the most likely explanation for this result. The PV packing factor, or the percentage of absorber area occupied by PV cells, has a big impact on electrical production. The electrical output per unit collector area increases as the packing factor rises. IV. Conclusion Exergy analysis was used to analyze the performance of PVT air collectors in both theoretical and experimental study. The mathematical model matches the experimental data with an accuracy of around 95 %. The average PVT exergy efficiency in the theoretical and experimental studies is 12.7 % and 12.0 %, respectively. For the theoretical and experimental study, the average PVT exergy is 45.1 W and 42.3 W, respectively, with PV exergies of 40.9 W and 40.2 W and thermal exergies of 4.2 W and 2.1 W. Acknowledgement The authors would like to thank the Ministry of Higher Education Malaysia for funding (FRGS/1/2014/ST02/UKM/03/1), as well as the Solar Energy Research Institute (SERI), UKM for providing laboratory facilities and technical support. Declarations Author contribution All authors contributed equally as the main contributor to this study. Funding statement This research did not receive any specific grant from funding agencies in the public, commercial, or not-for- profit sectors. Conflict of interest The authors declare no known conflict of financial interest or personal relationships that could have appeared to influence the work reported in this paper. Additional information Reprints and permission information is available at https://mev.lipi.go.id/. Publisher’s Note: Research Centre for Electrical Power and Mechatronics - Indonesian Institute of Sciences remains neutral with regard to jurisdictional claims and institutional affiliations. References [1] S. Abdul-Ganiyu, D.A. Quansah, E.W. Ramde, R. Seidu, and M.Y. Adaramola,, "Investigation of solar photovoltaic-thermal (PVT) and solar photovoltaic (PV) performance: a case study in Ghana,". Energies, vol. 13, pp. 1-17, 2020. [2] N. Boulfaf, J. Chaoufi, A. Ghafiri, and A. Elorf, "Thermal study of hybrid photovoltaic thermal(PV-T) solar air collector using finite element method," International Journal of Renewable Energy Research, vol. 6, no. 1, pp. 171-182, 2016. [3] S.S.S. Baljit, H. Y. Chan, and K. Sopian, "Review of building integrated applications of photovoltaic and solar thermal systems,". Journal Cleaner Production,. vol. 137, pp. 677–689, 2016. [4] I. Guarracino, C.N. Markides, A. Mellor, and N.J. Ekins-Daukes, "Dynamic coupled thermal and electrical modelling of sheet and tube hybrid photovoltaic/thermal (PVT) collectors,". Applied Thermal Engineering, vol. 101, pp. 778–795, 2016. [5] C. Good, "Environmental impact assessment of hybrid photovoltaic-thermal (PV/T) systems, a review," Renewewable and Sustainable Energy Reviews, vol. 55, pp. 234–239, 2016. [6] M. Fuentes, M. Vivar, J. de la Casa, and J. Aguilera," An experimental comparison between commercial hybrid PV-T and simple PV systems intended for BIPV," Renewewable and Sustainable Energy Reviews, vol. 93, pp. 110–120, 2018. [7] I. Guarracino, J. Freeman, A. Ramos, S.A. Kalogirou, N.J. Ekins- Daukes, and C.N. Markides, "Systematic testing of hybrid PV- thermal (PVT) solar collectors in steady state and dynamic Table 4. Comparison of the exergy efficiencies of PVT air collectors Results PVT exergy efficiency (%) Reference Theoretical Experimental Theo.: ηPV=10 %, ηth=17.2 % 10.75 11.5 [20] Theo.: ηPV=14-15 % 12-15 10.6 [21] N.A. 13.5 6.4 [22] Theo.: ηPV=9.77-11.45 % Exp.: ηPV=9.67-11.28 % 12.10-12.91 11.44-12.84 Present study https://mev.lipi.go.id/ https://doi.org/10.3390/en13112701 https://doi.org/10.3390/en13112701 https://doi.org/10.3390/en13112701 https://doi.org/10.3390/en13112701 https://www.ijrer.org/ijrer/index.php/ijrer/article/view/3294/pdf_1 https://www.ijrer.org/ijrer/index.php/ijrer/article/view/3294/pdf_1 https://www.ijrer.org/ijrer/index.php/ijrer/article/view/3294/pdf_1 https://www.ijrer.org/ijrer/index.php/ijrer/article/view/3294/pdf_1 https://doi.org/10.1016/j.jclepro.2016.07.150 https://doi.org/10.1016/j.jclepro.2016.07.150 https://doi.org/10.1016/j.jclepro.2016.07.150 https://doi.org/10.1016/j.jclepro.2016.07.150 https://doi.org/10.1016/j.applthermaleng.2016.02.056 https://doi.org/10.1016/j.applthermaleng.2016.02.056 https://doi.org/10.1016/j.applthermaleng.2016.02.056 https://doi.org/10.1016/j.applthermaleng.2016.02.056 https://doi.org/10.1016/j.rser.2015.10.156 https://doi.org/10.1016/j.rser.2015.10.156 https://doi.org/10.1016/j.rser.2015.10.156 https://doi.org/10.1016/j.rser.2018.05.021 https://doi.org/10.1016/j.rser.2018.05.021 https://doi.org/10.1016/j.rser.2018.05.021 https://doi.org/10.1016/j.rser.2018.05.021 https://doi.org/10.1016/j.apenergy.2018.12.049 https://doi.org/10.1016/j.apenergy.2018.12.049 https://doi.org/10.1016/j.apenergy.2018.12.049 A. Fudholi et al. / Journal of Mechatronics, Electrical Power, and Vehicular Technology 12 (2021) 10-17 17 outdoor conditions," Applied Energy, vol. 240, pp. 1014–1030, 2019. [8] A. Fudholi, M. Zohri, N.S.B. Rukman, N.S. Nazri, M. Mustapha, C.H. Yen, M. Mohammad, and K. Sopian, "Exergy and sustainability index of photovoltaic thermal (PVT) air collector: a theoretical and experimental study," Renewable and Sustainable Energy Reviews, vol. 100, pp. 44-51, 2019. [9] A.A. Jadallah, M.K. Alsaadi, S.A. Hussein. The hybrid photovoltaic-thermal double-pass solar system for drying applications. IOP Conf. Series: Materials Science and Engineering vol. 765 No. 012024, 2020. [10] A. Zoukit, Hicham El Ferouali, Issam Salhi, Said Doubabi, and Naji Abdenouri, "Takagi Sugeno fuzzy modeling applied to an indirect solar dryer operated in both natural and forced convection," Renewable Energy, vol. 133, pp 849-860, 2019. [11] S. Tiwari, Sanjay Agrawal, and G.N. Tiwari, "PVT air collector integrated greenhouse dryers," Renewable and Sustainable Energy Reviews, vol. 90, pp. 142–159, 2018. [12] C.K.K. Sekyere, F.K. Forson, and F.W. Adam, "Experimental investigation of the drying characteristics of a mixed-mode natural convection solar crop dryer with back up heater," Renewable Energy, vol. 92, pp. 532-542, 2016. [13] E. Hajar, T. Rachid, and B.M. Najib," Conception of a solar air collector for an indirect solar dryer. Pear drying test," Energy Procedia, vol. 141, pp. 29–33, 2017. [14] Jin-Hee Kim, Sang-Myung Kim, and Jun-Tae Kim, "Experimental performance of an advanced air-type photovoltaic/thermal (PVT) collector with direct expansion air handling unit (AHU)," Sustainability, vol. 13 No. 888, pp. 1-10, 2021. [15] K. Touafek, A. Khelifa, L. Boutina, I. Tabel, and S. Haddad "Theoretical study and experimental validation of energetic performances of photovoltaic/thermal air collector," International Journal of Photoenergy, pp. 1-10, 2018. [16] A. Fudholi, M. Zohri, G. L. Jin, A. Ibrahim, C. H. Yen, M. Y. Othman, M. H. Ruslan, and K. Sopian, "Energy and exergy analyses of photovoltaic thermal collector with ∇-groove," Solar Energy, vol. 159, pp. 742-750, 2018. [17] A. Fudholi, K. Sopian, M. H. Yazdi, M. H. Ruslan, A. Ibrahim, and H. A. Kazem, "Performance analysis of photovoltaic thermal (PVT) water collectors, Energy Conversion and Management, vol. 78, pp. 641–651, 2014. [18] J.K. Tonui, and Y. Tripanagnostopoulos, "Air-cooled PV/T solar collectors with low cost performance improvements," Solar Energy, vol. 81, no. 4, pp. 498–511, 2007. [19] J.K. Tonui, and Y. Tripanagnostopoulos, "Performance improvement of PV/T solar collectors with natural air flow operation," Solar Energy, vol. 82, no. 1, pp. 1–12, 2008. [20] F. Sarhaddi, S. Farahat, H. Ajam, and A. Behzadmehr, "Exergetic performance assessment of a solar photovoltaic thermal (PV/T) air collector, "Energy and Buildings, vol. 42, no. 11, pp. 2184– 2199, 2010. [21] A. S. Joshi and A. Tiwari, "Energy and exergy efficiencies of a hybrid photovoltaic-thermal (PV/T) air collector," Renewable Energy," vol. 32, no. 13pp. 2223–2241, 2007. [22] M. Bosanac, B. Sørensen, I. Katic, H. Sørensen, B. Nielsen, and J. Badran, "Photovoltaic/ thermal solar collectors and their potential in Denmark", Denmark, 2003. https://doi.org/10.1016/j.apenergy.2018.12.049 https://doi.org/10.1016/j.apenergy.2018.12.049 https://doi.org/10.1016/j.rser.2018.10.019 https://doi.org/10.1016/j.rser.2018.10.019 https://doi.org/10.1016/j.rser.2018.10.019 https://doi.org/10.1016/j.rser.2018.10.019 https://doi.org/10.1016/j.rser.2018.10.019 https://doi.org/10.1088/1757-899X/765/1/012024 https://doi.org/10.1088/1757-899X/765/1/012024 https://doi.org/10.1088/1757-899X/765/1/012024 https://doi.org/10.1088/1757-899X/765/1/012024 https://doi.org/10.1016/j.renene.2018.10.082 https://doi.org/10.1016/j.renene.2018.10.082 https://doi.org/10.1016/j.renene.2018.10.082 https://doi.org/10.1016/j.renene.2018.10.082 https://doi.org/10.1016/j.rser.2018.03.043 https://doi.org/10.1016/j.rser.2018.03.043 https://doi.org/10.1016/j.rser.2018.03.043 https://doi.org/10.1016/j.renene.2016.02.020 https://doi.org/10.1016/j.renene.2016.02.020 https://doi.org/10.1016/j.renene.2016.02.020 https://doi.org/10.1016/j.renene.2016.02.020 https://doi.org/10.1016/j.egypro.2017.11.114 https://doi.org/10.1016/j.egypro.2017.11.114 https://doi.org/10.1016/j.egypro.2017.11.114 https://doi.org/10.3390/su13020888 https://doi.org/10.3390/su13020888 https://doi.org/10.3390/su13020888 https://doi.org/10.3390/su13020888 https://doi.org/10.3390/su13020888 https://doi.org/10.1155/2018/2794068 https://doi.org/10.1155/2018/2794068 https://doi.org/10.1155/2018/2794068 https://doi.org/10.1155/2018/2794068 https://doi.org/10.1016/j.solener.2017.11.056 https://doi.org/10.1016/j.solener.2017.11.056 https://doi.org/10.1016/j.solener.2017.11.056 https://doi.org/10.1016/j.solener.2017.11.056 https://doi.org/10.1016/j.enconman.2013.11.017 https://doi.org/10.1016/j.enconman.2013.11.017 https://doi.org/10.1016/j.enconman.2013.11.017 https://doi.org/10.1016/j.enconman.2013.11.017 https://doi.org/10.1016/j.solener.2006.08.002 https://doi.org/10.1016/j.solener.2006.08.002 https://doi.org/10.1016/j.solener.2006.08.002 https://doi.org/10.1016/j.solener.2007.06.004 https://doi.org/10.1016/j.solener.2007.06.004 https://doi.org/10.1016/j.solener.2007.06.004 https://doi.org/10.1016/j.enbuild.2010.07.011 https://doi.org/10.1016/j.enbuild.2010.07.011 https://doi.org/10.1016/j.enbuild.2010.07.011 https://doi.org/10.1016/j.enbuild.2010.07.011 https://doi.org/10.1016/j.renene.2006.11.013 https://doi.org/10.1016/j.renene.2006.11.013 https://doi.org/10.1016/j.renene.2006.11.013 https://www.yumpu.com/en/document/read/4467325/photovoltaic-thermal-solar-collectors-and-their-potential-in-denmark https://www.yumpu.com/en/document/read/4467325/photovoltaic-thermal-solar-collectors-and-their-potential-in-denmark https://www.yumpu.com/en/document/read/4467325/photovoltaic-thermal-solar-collectors-and-their-potential-in-denmark Introduction II. Materials and Methods A. Mathematical modeling B. Experimental study III. Results and Discussions Conclusion Acknowledgement Declarations Author contribution Funding statement Conflict of interest Additional information References