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    A detailed analysis of a novel auto-controlled solar drying system combined with thermal energy storage concentrated solar air heater (CSAC) and concentrated photovoltaic/thermal (CPV/T)
    (Pergamon-Elsevier Science Ltd, 2023) Benlioglu, Muhammet Mustafa; Karaagac, Mehmet Onur; Ergun, Alper; Ceylan, Lhan; Ali, Ismail Hamad Guma
    In recent years, the use of solar energy, one of the renewable energy sources, has been increasing in many areas due to its practical, environmental, and economic benefits. Besides, the drying industry is an applied area where solar energy can be implemented. Solar drying systems are used in the industry to reduce high drying costs and to obtain better quality products. In this study, a novel solar drying system was designed by combining concen-trated solar air collector (CSAC) and concentrated photovoltaic/thermal system (CPV/T). In addition, the automation system has been integrated for data acquisition from the system and humidity-temperature control of the drying chamber. The SAC's inlet air was preheated by a heat exchanger using thermal energy from the PV/T. The drying system has been designed to be more useful by using phase change material in the collector. Thus, the drying process can be performed on cloudy days and after sunset. In addition, the designed system can generate electricity from the PV module to meet the electricity requirement. The mint which grows in various regions worldwide was chosen as the product to be dried in this study. Mint was dried from the first moisture content of 3.3125 g water/g dry matter to the last moisture content of 0.0625 g water/g water/g dry matter. Besides, the average overall efficiency of the system, PV module electrical efficiency, and drying efficiency were found to be 61%, 10%, and 26%, respectively. Furthermore, the average system exergy efficiency, PV module exergy effi-ciency, and concentrated solar air heater exergy efficiency values were calculated as 20%, 16%, and 21.9%, respectively. In the experiment, the ambient average temperature was 22 degrees C, while the average drying chamber temperature was 30 degrees C. The mint drying quality efficiency was 67% on average at this drying chamber tem-perature. The energy, exergy efficiency, and sustainability index of the system were calculated as 61%, 38.8%, and 1.69, respectively. Moreover, the enviro-economic cost of the system was determined to be 0.39 (SIC)/h.
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    Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system
    (Pergamon-Elsevier Science Ltd, 2022) Karaagac, Mehmet Onur; Ergun, Alper; Gurel, Ali Etem; Ceylan, Ilhan; Yildiz, Gokhan
    Energy consumption has continuously increased depending on the rapidly growing human population, enlarging economies, advancing technologies, and improving living standards. A noteworthy share of the energy consumption has been arising from the buildings all across the world. Refrigeration, heating, and air conditioning systems have accounted for a significant portion of the energy consumption in the buildings. Therefore, it is possible to both reduce energy consumption, and mitigate the carbon footprints by efficiently designing, constructing, and operating these systems. In this framework, the present research has centered on the refrigeration systems, and aimed to develop a novel defrost method for photovoltaic thermal (PV/T) assisted sustainable refrigeration systems. In the conventional refrigeration systems, the frost process occurs when air condenses on the evaporator surface as a result of the evaporator surface temperature being below the freezing point of water or the dew point temperature of the air in the conditioned space. Differently in the present work, PV/T system is used to prevent the frost process in the refrigeration system, unlike the conventional systems. Accordingly, the efficiency loss caused by the temperature increment will be prevented by cooling the PV module, and it is aimed to be more efficient by reducing the daily power consumption as an alternative solution method to the frost that occurred on the evaporator in refrigeration systems. On this purpose, a novel evaporator design is developed, and used for defrosting in this study. Accordingly, this novel design includes a refrigerant line inside the evaporator and a hot water line from the PV/T in this design. In the results, it is noticed that the system designed for winter conditions could be used for defrosting. While an average of 605 W for heat energy was used for each defrost process, the average defrost duration was recorded to be approximately 4 min. While the average electrical efficiency of the PV module was found to be 13.6%, the average total efficiency was found to be 38%. Besides, Average PV module surface temperature was determined as 36.4 degrees C, average water storage tank temperature was determined as 26.4 degrees C. In addition, the coefficient of performance (COP) of the refrigeration system is calculated to be 4.18. COP increased by an average of 9% during defrosting. Furthermore, the environmental economic cost was calculated to be 14.6 $/h. In the conclusion, it is proven that the novel defrost method proposed in the present work can be used for refrigeration systems, and contribute to both the reduction of energy consumption and mitigation of carbon emissions arising from the buildings.
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    Design and Performance of a Photovoltaic Thermal Assisted Solar Desalination Unit for Saline Water Treatment
    (Gazi Univ, 2026) Bishena, Nuredden Saleh; Karaagac, Mehmet Onur; Ergun, Alper; Acar, Bahadir
    The escalating global population, industrialization, and climate change have intensified the demand for clean water, rendering conventional water sources increasingly inadequate. This scarcity has necessitated the development of alternative and sustainable freshwater production methods. In this context, environmentally friendly water treatment technologies powered by renewable energy sources, such as solar energy, present significant potential for energy efficiency. Photovoltaic-thermal (PVT) systems, which concurrently generate electricity and thermal energy, offer dual benefits in applications such as desalination. This study experimentally analyzes the performance of a specially designed solar-powered PVT-assisted desalination system for saline water treatment. Experiments were conducted under environmental conditions using prevailing solar radiation data. The system utilizes waste heat from the PVT unit to produce purified water through evaporation and condensation processes. Experimental results show that the system's total average daily electrical energy output was 344.1 Wh/day. The average electrical power generated during the testing period was 42.8 W. The PV system exhibited an average efficiency of 64.6% between 10:00 AM and 6:00 PM. Regarding freshwater production performance, the average water production rate on June 1 was approximately 4.5 ml/min. Consequently, the total average daily freshwater yield recorded at the end of the day was 2234 ml. While the Gain Output Ratio (GOR) value of the desalination system is 1.9 on average, the overall efficiency value is around 44%. These findings demonstrate that the PVT-integrated system provides an eco-friendly and efficient dual-purpose solution for electricity generation and water purification.
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    Enhancing the performance of parabolic trough solar collectors: Cost-effective innovative designs for sustainable energy harvesting
    (Pergamon-Elsevier Science Ltd, 2024) Karaagac, Mehmet Onur; Akinci, Burak; Ergun, Alper
    This study aims to improve the performance and stability of parabolic trough solar collectors (PTSC), especially those with heat storage capacity. Three different receiver tube designs have been meticulously developed to achieve this goal. As a result of the research, the Black surface (BS) -PTSC and PTSC- Paraffin wax (PW) systems achieved 26.5% and 56.8% more thermal energy flow, respectively, compared to the conventional PTSC. In addition, while the average thermal efficiencies of the PTSC, BS-PTSC, and PTSC-PW systems were found to be 11.2%, 14.1%, and 16.9%, respectively, the average exergy efficiencies of the PTSC, BS-PTSC, and PTSC-PW were 1.4%, 1.9%, and 2.3%. Painting the black copper pipe and filling the receiver tube with paraffin wax PCM increased thermal and exergy efficiency. Besides, comparing the temperature differences based on the PTSC system, it was found that BS-PTSC and PTSC-PW systems have 12.3% and 16.4% higher tank temperatures, respectively. The findings of this research have demonstrated the potential of parabolic trough solar collectors equipped with heat storage. It has also increased the sustainability index in terms of sustainability and reduced CO2 emissions into the atmosphere. Furthermore, it has been shown that these simple and inexpensive designs, without significant modifications to the system, can achieve high thermal performance without unnecessary expensive components.
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    Experimental analysis of CPV/T solar dryer with nano-enhanced PCM and prediction of drying parameters using ANN and SVM algorithms
    (Pergamon-Elsevier Science Ltd, 2021) Karaagac, Mehmet Onur; Ergun, Alper; Agbulut, Umit; Gurel, Ali Etem; Ceylan, Ilhan
    In this paper, a concentrated photovoltaic-thermal solar dryer (CPV/TSD) using nano-enhanced PCM (Al2O3Paraffin wax) is experimentally studied. A comprehensive thermodynamic analysis of the system according to the first and second laws is discussed. Besides, the drying parameters (moisture content and moisture ratio) are predicted using the two machine learning algorithms (ANN and SVM) and compared the prediction success with four evaluation metrics (R2, rRMSE, MBE, and rMAE). The overall thermal energy efficiency and exergy efficiency of the CPV/TSD system are found to be 20% and 8%, respectively. Although solar radiation to the environment has decreased a lot, it has been found that the thermal energy transferred to the nano-enhanced PCM prevents the decrease in greenhouse temperature for the first 100 min. In the system, mushrooms are dried from the initial moisture content of 17.45 g water/g dry matter to the final moisture content of 0.0515 g water/g dry matter. Then the drying rate value for CPV/TSD system is calculated to be 0.436 g matter/g dry matter.min. On the other hand, even if both ANN and SVM algorithms have exhibited very satisfying results, ANN is coming to the fore in the prediction of the drying parameters considering all evaluation metrics together.
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    Experimental investigation of a novel PCM-enhanced underfloor heating system for energy-efficient sustainable buildings
    (Pergamon-Elsevier Science Ltd, 2025) Karaagac, Mehmet Onur
    Building energy efficiency can be enhanced by reducing heating and cooling demands, a crucial factor for sustainable development. This study experimentally investigates a novel underfloor heating system enhanced with thermal energy storage using an organic phase change material (PCM) encapsulated in paraffin wax. The PCM was positioned between heating pipes, and experiments were conducted in a temperature-controlled room. The thermal performance of the PCM-integrated system was compared to that of a conventional system without PCM. Results show that the PCM-integrated system increased room heating durations by 27-33 % and cooling durations by 35-43 %. During the 7-h experimental period, the conventional system consumed thermal energy at a rate of 114.88 kW, whereas the PCM-integrated system consumed only 111.01 kW, corresponding to a 3.4 % reduction. Additionally, surface temperature fluctuations were reduced by 52.6 %, improving thermal comfort. These results demonstrate that the inclusion of PCM significantly extends heating and cooling cycles, enhances thermal comfort by minimizing temperature fluctuations, and improves overall energy efficiency by reducing heat transfer to the floor mortar. This innovative approach not only advances energy-efficient heating technologies but also contributes to reducing environmental impacts.
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    Experimental performance investigation of high reflective and diffuse reflective concentrating photovoltaic/ thermal (CPVT) systems using non-imaging concentrators from energy, exergy, and economic viewpoint
    (Pergamon-Elsevier Science Ltd, 2025) Ustaoglu, Abid; Buyukpatpat, Hakan; Kaya, Huseyin; Kursuncu, Bilal; Karaagac, Mehmet Onur; Okajima, Junnosuke
    A diffuse reflective (DR) surface in a concentrating photovoltaic thermal system (CPVT) system can provide uniform solar energy dispersion, minimizing hot spots, uneven lighting, and efficiency loss compared to costlier, highly reflective (HR) surfaces. This study uniquely compares the performance of HR-CPVT and DR-CPVT systems, highlighting the significant thermal and electrical efficiency of HR-CPVT while demonstrating the cost-effectiveness of DR-CPVT. The direct comparison of these systems under varying conditions provides novel insights into the trade-offs between high performance and economic feasibility. The performances of CPVTs were examined under various seasonal and weather conditions. The advantage of HR-CPVT was less pronounced in autumn due to seasonal effects. In the summer season, the cooling effect of water becomes more prominent, and the HR-CPVT outperformed the DR-CPVT by 6.1 to 8.5 %, depending on the mass flow rate in terms of overall efficiency. This advancement majorly arises from thermal efficiency. HR-CPVT achieved about a 5.6-7.9 % larger thermal efficiency. However, the electrical efficiency difference was minimal (similar to 0.5 %) and diminished to 0.1 % in the afternoon due to practical PV power generation limits. Despite its high reflectivity, HR-CPVT showed only marginal exergetic benefits over DR-CPVT. The simple payback period was calculated to be 3.65 years for HRCPVT, while it was only 3.19 years for DR-CPVT due to its lower installment cost. RSM analysis accurately predicts the experimental results.
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    First- and second-law thermodynamic analyses of a combined natural gas cycle power plant: Sankey and Grossman diagrams
    (Tubitak Scientific & Technological Research Council Turkey, 2019) Karaagac, Mehmet Onur; Kabul, Ahmet; Ogul, Hasan
    The natural gas combined cycle power plant is one of the best options for generating electricity due to its use of low carbon fuels, high efficiency, and operational flexibility. These plants consist of a combination of Brayton and Rankine cycles, and investigation of these cycles is performed in this paper. Here the parameters of pressure and temperature used in the calculations are taken from a combined cycle power plant. The net power output of the system at 25 degrees C ambient temperature and 101.325 kPa pressure was calculated as 45 and 12 MW for Brayton and Rankine cycles, respectively. In addition, Brayton, Rankine, and combined cycle efficiencies were calculated as 37.5%, 27%, and 47.5%, while the exergy efficiencies were determined as 36%, 44%, and 46%, respectively. In the system elements, the most energy was lost in the combustion chamber and the highest exergy efficiency was achieved in the compressor at 95% level. Impacts of an increase in ambient temperature, compressor pressure ratio, and change on turbine inlet temperature were further investigated. Energy (Sankey) and exergy (Grossman) flow diagrams were further drawn based on the analyses obtained from the combined cycle power plants.
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    Investigation of Non-Imaging CPVT systems designed based on axial tilt acceptance angle: experimental study and response surface methodology
    (Pergamon-Elsevier Science Ltd, 2025) Ustaoglu, Abid; Karaagac, Mehmet Onur; Kursuncu, Bilal; Buyukpatpat, Hakan; Kaltakkiran, Suheda; Okajima, Junnosuke
    This study presents a novel approach by designing and evaluating non-imaging concentrators, including Vtrough, compound parabolic (CPC), and compound hyperbolic (CHC) concentrators optimized with the Earth's axial tilt acceptance angle to enhance solar energy utilization. Thermal and electrical performances and exergybased performance evaluations were experimentally analyzed to calculate useful energy production. Annual performance metrics and payback periods were assessed. Additionally, optimization analyses using response surface methods were conducted to examine interactions among operating parameters. The CPC system achieved the highest thermal and electrical performance, with an overall efficiency of 77.69 % and annual energy production of 103.23 kWh at a 300 ml/min flow rate. However, its higher initial cost extended the payback period to 7.31 years. In contrast, the V-trough system excelled in electricity generation, producing 77.72 kWh annually and demonstrating the minimum return on investment in 5.82 years. The CHC system showed significant efficiency improvements with increased flow rates, with an annual energy production of 81.94 kWh and a payback period of 6.77 years, while it was less effective under low solar radiation conditions. Results highlight the CPC's superior thermal performance, particularly under low radiation, while the V-trough demonstrated stability and economic viability. The findings highlight the importance of temperature management and flow rate optimization in enhancing CPVT system efficiency and longevity.
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    Multilayer radiation shielding assessment of the Korean SMART small modular reactor
    (Pergamon-Elsevier Science Ltd, 2026) Ogul, Hasan; Bastug, Elif Ahsen; Torun, Tunahan Recep; Karaagac, Mehmet Onur
    Small Modular Reactors (SMRs) are recognized as a sustainable and versatile nuclear energy solution due to their enhanced safety features, scalability, and adaptability. In this context, this study evaluates the radiation shielding performance and thermodynamic efficiency of the Korean SMART SMR. A multilayer shielding system, comprising SS316L, water, lead, and tungsten, was proposed and assessed using SERPENT, FLUKA, and GEANT4 simulations. Primary neutrons of 6.81 x 1010 (4.5 MeV), 5.90 x 1011 (500 keV), and 2.88 x 1011 (0.025 eV) were effectively attenuated, while secondary gamma-rays and neutrons were reduced to near zero at the outer layers. Energy and exergy efficiencies were 30.41 % and 60 %, respectively, indicating minimal performance compromise due to shielding. These results demonstrate a robust shielding design that ensures safe operation of compact SMRs and supports their deployment in diverse environments, including electricity generation and modular energy systems. The study also highlights the integration of advanced computational tools for comprehensive assessment of SMR performance and radiation safety, providing a foundation for optimizing shielding materials in next-generation nuclear energy applications.
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    Performance analysis of a stationary parabolic trough solar collector with a flat metallic receiver incorporating paraffin wax PCM
    (Pergamon-Elsevier Science Ltd, 2026) Alturki, Tamim Mohamed M.; Karaagac, Mehmet Onur; Ergun, Alper
    This study evaluates the performance of a parabolic trough solar collector (PTSC) equipped with a novel flat metallic receiver designed to enhance heat transfer and storage under stationary non-tracking conditions in Sinop, T & uuml;rkiye. Two receiver configurations were fabricated and experimentally tested: one with paraffin wax (PW) integrated as a phase change material (PCM) and one without PW. The experimental study was conducted in two stages. In the first stage, the influence of mass flow rate on system performance was examined under high (HF), medium (MF), and low (LF) flow conditions. The average thermal efficiencies of the receiver with PW were 37.85%, 35.27%, and 27.55% for HF, MF, and LF, respectively, while the receiver without PW achieved 38.97%, 29.82%, and 19.36%. Increasing the mass flow rate enhanced thermal efficiency in both configurations; however, this effect was considerably more pronounced for the receiver without PW, where the HF efficiency exceeded the MF and LF cases by 30.7% and 101.1%, respectively. For the PW-integrated receiver, the corresponding improvements were limited to 7.3% and 37.3%, indicating a stabilizing effect of latent heat storage. Based on these findings, the HF condition was identified as the optimum operating regime and selected for the second experimental stage. In this stage, the thermal storage performance of the two receivers was directly compared at the same HF rate. The results showed that the PW-integrated receiver achieved 16.6% higher thermal efficiency and 47% higher exergy efficiency than the receiver without PW. Moreover, the latent heat release provided by PW significantly improved temperature stability and system performance during periods of declining solar radiation. Overall, the proposed paraffin-wax-integrated design represents an effective approach for enhancing PTSC performance under stationary operating conditions without requiring complex system modifications. Although long-term cycling tests were not performed, paraffin wax was selected due to its well-documented thermal reliability in previous studies. The reported results are based on a comparative experimental evaluation conducted under real outdoor operating conditions and are intended to highlight the relative performance differences between the two receiver configurations; long-term PCM stability, detailed economic analysis, and optical optimization are beyond the scope of the present study.
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    Performance Analysis of Natural Gas Combined Cycle Power Plant
    (Gazi Univ, 2019) Karaagac, Mehmet Onur; Kabul, Ahmet; Yigit, Fatih
    In this study, the first law analysis of the thermodynamics was applied using the data of a real gas-fired combined cycle power plant. The net power outputs of the system are calculated for the Brayton cycle and Rankine cycle as 48 MW and 12 MW respectively and the effect of changing environmental conditions on the system was examined. It is calculated that the gas turbine has an average efficiency of 38% and the combined cycle has 48% efficiency. With an increase in ambient temperature of 45 degrees C, the system has 22% reduction in net power, while the power required for compression in the compressor section has also increased. As the ambient temperature increased, there was a 20% reduction in specific fuel consumption in the direction of the decrease in air flow entering to the compressor. It has also been revealed that, the environmental temperature has a direct effect on the combined cycle power plant.
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    Performance evaluation of nano-enhanced phase change materials for thermal energy storage: An experimental study
    (Elsevier, 2024) Karaagac, Mehmet Onur
    In rapidly developing economies, the increasing energy demand and fossil fuel consumption have made the need for renewable energy sources and efficient thermal energy storage (TES) solutions more urgent than ever. This study focuses on enhancing the thermal energy storage capabilities of paraffin-based phase change materials (PCMs) by incorporating Al2O3, MgO, and CuO nanoparticles. The evaluation of nano-enhanced PCMs focused on their melting temperatures, thermal storage capacities, thermal conductivities, and charge/discharge times. The experimental results revealed significant changes in the thermal properties of the nano-enhanced PCMs compared to pure paraffin. The melting temperature was raised by 2 degrees C due to Al2O3 nanoparticles, whereas CuO and MgO nanoparticles decreased it by 1.7 degrees C and 1.8 degrees C, respectively. Compared to pure paraffin, Al2O3-PW, MgO-PW, and CuO-PW exhibited improvements of 13 %, 39 %, and 48 % in thermal conductivities, respectively. CuO-doped paraffin showed an 11.8 % decrease in discharge time, suggesting its suitability for rapid heat transfer applications like defrosting systems or thermal management in electronics. On the other hand, paraffin doped with MgO showed a minimal 2.24 % reduction in discharge time, indicating its effectiveness in applications requiring heat retention, particularly for improved thermal insulation in building materials. The results highlighted the potential of nano-enhanced PCMs in energy storage and construction is underlined, offering a sustainable approach to improving energy efficiency in various sectors.
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    Public attitudes toward nuclear power plants in Turkey
    (Pamukkale Univ, 2019) Ogul, Hasan; Karaagac, Mehmet Onur
    Due to the increasing energy need, countries are required to optimize their usage of energy sources for sustaining developments. One of the options to meet the sustainable energy is the use of nuclear power plants (NPPs). However, building and using NPPs represent a great challenge to policy makers of the countries: acceptance of this technology by the citizens. Turkey is one of the countries decided to establish NPPs and adjust their policy in this regard. The country's first NPP is already under construction in Mersin, and the second will be established in Sinop. A survey to evaluate public acceptance of NPPs was given to 838 individuals from different cities of Turkey. The participants were interviewed face-to-face between January and March 2018. The endorsement and opposition rates were determined as 42.3% and 31.1%, respectively. The margin of error at 95% CL was found to be +/- 3.3%. Measuring the participants' knowledge of NPPs was also aimed. It has been asked to respondents express if they have basic knowledge of NPPs. 72% of the participants stated that they know the basics of NPPs. To extract the actual rate, three simple questions regarding NPPs have been asked, and only 24.9% of all participants answered 2 or 3 questions correctly. The results were further compared with previous surveys for Turkey and other countries.
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    Thermodynamic analyses of a novel hybrid photovoltaic-thermal (PV/T) module assisted vapor compression refrigeration system
    (Elsevier, 2023) Yildiz, Gokhan; Gurel, Ali Etem; Ceylan, Ilhan; Ergun, Alper; Karaagac, Mehmet Onur; Agbulut, Umit
    Buildings have a respectable share of global energy consumption and it is well-known that refrigeration, heating and air conditioning systems have crucially contributed to this share. Therefore, even a small improvement in these systems has a noteworthy potential in globally saving energy. Accordingly, the performance of Photovoltaic-Thermal module-assisted vapor compression refrigeration system (PV/T-VCRS) has been handled in the present research. PV/TVCRS has been integrated with PV module, refrigeration system, and their hybrid. Additionally, different from the conventional superheating methods, superheating has been performed with a PV/T module in this work. In order to discuss the system performance, and observe the differences between conventional and modified hybrid systems, energy and exergy analyzes have been applied. In the results, the average PV module surface temperature in PV module and PV/T-VCRS is recorded to be 56.16 degrees C and 40.93 degrees C, respectively. This case leads to a direct increment in PV module electrical efficiency. Electrical efficiency, average electrical efficiency in PV module, and PV/T-VCRS are calculated to be 13.49% and 14.69%, respectively. The average COP values are found to be 5.23 for VCRS, and 5.68 for PV/T-VCRS. Total exergy destruction in VCRS and PV/TVCRS has been calculated to be 175.85 W and 443 W. On the other hand, the exergy efficiency is found to be 50.79% in VCRS and 60.73% in PV/T-VCRS. In the conclusion, it is well-noticed that hybrid PV/T-VCRS presented promising results in terms of electrical efficiency, COP, energy, and exergy analyses as compared to those of the conventional system.