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Cooling performance enhancement of PV systems: Review
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Any heat harvesting system experiences high heat loss to the ambient. Hence, using matured insulation such as vacuum insulation to control any thermal heat leakage is highly required. In the current research investigation, a novel hybrid new fusion-edge sealed vacuum concentrated so-called VCPV/T system. The new design of a vacuum insulated layer is employed to reduce the thermal losses and improve the overall electrical, thermal, and exergy performance of a concentrated photovoltaic solar thermal collector (CPV/T). A comprehensive 3D conjugate heat transfer model is developed, validated with mesh independent tests for both CPV/T and VCPV/T at Re of 75 to achieve the higher precision of results in numerical simulations. The results show in the new VCPV/T the percentage rise in the maximum cell temperature between both systems achieved to be 1.0%, 1.7%, and 2.16% at three different concentration ratios (CR) of 1, 2, and 3, respectively. The results of VCPV/T implicate a sensible enhancement in the overall performance compared to the conventional CPV/. For, CR = 3, the maximum thermal, electrical, and total exergy predicted to be 144.5 W, 33 W, and 177.6 W all around 13:00 h for new VCPV/T systems, respectively. At CR = 3, about 14% and 10.7% enhancement in thermal and total exergy, respectively.
Photovoltaic/thermal (PV/T) are high-tech devices to transform solar radiation into electrical and thermal energies. Nano-coolants are recently considered to enhance the efficiency of PV/T systems. There is no accurate model to predict/optimize the PV/T systems’ electrical efficiency cooled by nano-coolants. Therefore, this research employs machine-learning approaches to simulate PV/T system electrical performance cooled by water-based nanofluids. The best topology of artificial neural networks, least-squares support vector regression, and adaptive neuro-fuzzy inference systems (ANFIS) are found by trial-and-error and statistical analyses. The ANFIS is found as the best method for simulation of the electrical performance of the considered solar system. This approach predicted 200 experimental datasets with the absolute average relative deviation (AARD) of 13.6%, mean squared error (MSE) of 2.548, and R2=0.9534. Furthermore, the ANFIS model predicts a new external database containing 63 samples with the AARD=15.21%. The optimization stage confirms that 30 lit/hr of water-silica nano-coolant (3wt%, 12.5 nm) at radiation intensity of 788.285 W/m² is the condition that maximizes electrical efficiency. In this optimum condition, the enhancement in the PV/T electrical efficiency is 27.7%. Finally, the fabricated ANFIS model has been utilized for generating several pure simulation predictions that have never been published before.
This paper dealt with a series of numerical investigations on a new porous cooling channel applied to PV/T systems in order to improve the insufficient heat transfer in the conventional channel. The proposed porous cooling channel based on field synergy theory had a higher overall heat transfer coefficient, which enhanced the total efficiency of the PV/T system. The numerical model was validated with experimental data. The results showed that holes distributed non-uniformly near the outlet of the cooling water led to a better cooling effect, and a hole diameter of 0.005 m led to an optimal performance. The total efficiency of the PV module with the new cooling channel was 4.17% higher than the conventional one at a solar irradiance of 1000 W/m² and an inlet mass flow rate of 0.006 kg/s. In addition, as the solar irradiance increased from 300 to 1200 W/m², the total efficiency of the new PV/T system dropped by 5.07%, which included reductions in both the electrical and thermal efficiency. The total efficiency was improved by 18.04% as the inlet mass flow rate of cooling water increased from 0.002 to 0.02 kg/s.
Integration of a dual-fluid heat exchanger with a photovoltaic/thermal (PV/T) system has become increasingly important because it not only significantly reduces the photovoltaic (PV) solar cells’ temperature but also produces additional thermal energy. In this study, energy, exergy, and economic analyses of a dual-fluid (water/air) PV/T system are performed in comparison with a reference PV module and single-fluid PV/T systems for the climate of Cheonan, South Korea. Daily and yearly performance evaluations of all of the aforementioned PV/T systems were carried out through experimentation. Based on the experimental findings, the economic feasibility of the dual-fluid PV/T system is assessed in the context of its financial benefits over both a shorter and longer period of time. Results show that the energy and exergy efficiencies of the dual-fluid PV/T system are significantly higher than those of single-fluid PV/T systems, by 20% and 11%, respectively. In addition, relevant to local domestic electricity price, the cost of energy is reduced by 80%, 60%, and 45% with the dual-fluid PV/T system and water and air type PV/T systems, respectively. Furthermore, using the dual-fluid PV/T system, extra revenue is generated through carbon credit by mitigating CO2 emissions into the atmosphere.
In this research, a pilot study and analysis of an innovative multi-channel photovoltaic/thermal (MCPV/T) system in a geographic location (35° 44' 35'' N, 50° 57' 25'' E) has been carried out. This system consists of integrating a photovoltaic panel and two PV/T heat-sink converters. The total electrical, exergy and energy efficiencies of the system at air flow rate of 0.005 kg/s and radiation intensity of 926 w/m2 were 9.73%, 10.72%, and 47.24%, respectively. An air flow rate of 0.011 kg/s and the radiation intensity of 927 w/m2 were also achieved to be 9.35%, 10.40% and 65.10%, respectively.
Based on simulation results considering experiments validations, as the air flow rate increases, the overall energy efficiency increases to the maximal amount of 80%. However, the maximum exergy efficiency value has a local optimal point of 13.46% at a fluid flow rate of 0.024 kg/s. Similarly, with increasing channel heights, the total energy efficiency decreased to 70%, and the maximum exergy efficiency has a local optimal point of 13.64% at channel height of 0.011 m. As an overall achievement, the system has higher energy quality (exergy efficiency) in laminar flow regime and has higher energy efficiency under turbulent flow conditions.
Solar photovoltaic (PV) and solar thermal systems are most widely used renewable energy technologies. Theoretical study indicates that the energy conversion efficiency of solar photovoltaic gets reduced about 0.3% when its temperature increases by 1°C. In this regard, solar PV and thermal (PVT) hybrid systems could be a solution to draw extra heat from the solar PV panel to improve its performance by reducing its temperature. Here, we have designed a new type of heat exchanger for solar PV and thermal (PVT) hybrid systems and have studied the performance of the system. The PVT system has been investigated in comparison with an identical solar PV panel at outdoor condition at Dhaka, Bangladesh. The experiments show that the average improvement of open circuit voltage (Voc) is 0.97 V and the highest improvement of Voc is 1.3 V. In addition, the overall improvement of output power of solar PV panel is 2.5 W.
In the present work, the electrical and thermal performances of a newly designed PV/T (photovoltaic/thermal) air collector, which was proposed and fabricated by the author, have been investigated experimentally in the natural weather conditions. The PV/T air collector has a single-pass double-flow air channel. Also, a non-uniform cross-section transverse rib was attached at the back surface of the PV (photovoltaic) module to improve the heat transfer performance between the PV module and flowing air. The experiment was carried out in an outdoor field on a clear day with various air mass flow rates ranges from 0.0198 kg/s to 0.07698 kg/s. In the results, it was found that the average thermal efficiency of the PV/T collector increased from 35.2% to 56.72% as the air mass flow rate increased. The average electrical efficiency also increased from 14.23% to 14.81% with an increase in an air mass flow rate, but the effect of air mass flow rate on the increase in electrical efficiency was inconsiderable. The average overall efficiency, which represents the sum of electrical and thermal efficiencies, was in the range of 49.44% to 71.54% and it increased as the air mass flow rate increased. The maximum value of average overall efficiency during the test period was found to be 71.54% at an air mass flow rate of 0.07698 kg/s. From the results, it was confirmed that the newly designed PV/T air collector provides a significant enhancement in solar energy utilization.
The temperature of a photovoltaic (PV) plate increases with increasing absorbed irradiation, leading to degradation of the electrical efficiency of the PV cells. The heat can be dissipated by air or water to prevent the deterioration of the cells. In this study, a concentrating photovoltaic thermal (PV-T) dual-fluid solar collector is proposed in which two types of concentrators are integrated. The collector’s performance was analysed with air and water as the working fluids. Analytical expressions were derived from the energy balance equations for each component of the collector. The mean temperature values of the PV plate, air inlet/outlet, water inlet/outlet, glaze and collector back wall were experimentally recorded under different fluid mass flow rates and solar irradiations. The readings were then used to compute the thermal and electrical efficiencies of the collector. The results obtained from the numerical and experimental analyses were compared and evaluated by employing the mean absolute percentage error method. The results show that incorporating two fluids increases the thermal and electrical efficiencies. The total thermal and electrical efficiencies achieved are 67.00% and 13.02%, respectively, at air and water mass flow rates of 0.0103 kg/s and 0.0164 kg/s, respectively, and a solar irradiation of 650 Wm−2. The outcomes of this research are expected to help advance the designs of dual-fluid PV-T solar collectors and offering a broader range of thermal applications.
A theoretical study was conducted on the performance of photovoltaic cells by forced airflow on the cell base. The study was conducted using numerical simulation software (ANSYS- cfx) to select the best model for its manufacture. The simulation results showed that the air guides model is the best, directing the largest amount of air to the base of the cell and the lowest cost and available in local markets. Air guides shall be installed inside an aluminum channel fixed to the bottom of the cell base and the channel dimensions shall be selected according to the dimensions of the photovoltaic cell to be cooled. A numerical study determine the best number and best location of the air guides inside the duct channel and the tilt angle of air guides and showed that the optimum number of pneumatic guides is (18) in a position (70 mm) from the base of the channel and at a 45-mile angle with the horizon.
The conversion efficiency of photovoltaic (PV) panels is reduced while the PV temperature rises. It is revealed that that every Celsius degree rise in PV temperature can result in as large as a 0.65% drop in the efficiency. This phenomenon attracts substantial scholar attentions in mitigating and controlling the PV temperature. Among those applied techniques, phase change material (PCM) is considered as a potential candidate to hold the PV temperature at a low degree because of its latent heat storage. The integrated system is therefore named PV-PCM system. In this study, the daily performance and viability of this system was evaluated through simulation, illustrating that the temperature of PV can be reduced by 24.9°C through adding PCM, and hence the electricity output increased by up to 11.02%. This study also demonstrates that the latent heat capacity of PCM and natural convection of melted PCM can control PV temperature and enhance the heat dissipation rate from PV to PCM rate by 4 to 5 times.
A limited number of studies have examined the effect of dual-fluid heat exchangers used for the cooling of photovoltaic (PV) cells. The current study suggests an explicit dynamic model for a dual-fluid photovoltaic/thermal (PV/T) system that uses nanofluid and air simultaneously. Mathematical modeling and a CFD simulation were performed using MATLAB® and ANSYS FLUENT® software, respectively. An experimental validation of the numerical models was performed using the results from the published study. Additionally, to identify the optimal nanofluid type for the PV/T collector, metal oxide nanoparticles (CuO, Al2O3, and SiO2) with different concentrations were dispersed in the base fluid (water). The results revealed that the CuO nanofluid showed the highest thermal conductivity and the best thermal stability compared to the other two nanofluids evaluated herein. Furthermore, the influence of CuO nanofluid in combination with air on the heat transfer enhancement is investigated under different flow regions such as laminar, transition, and turbulent. Using a CuO nanofluid plus air and water plus air the total equivalent efficiency was found to be 90.3% and 79.8%, respectively. It is worth noting that the proposed models could efficiently simulate both single and dual-fluid PV/T systems even under periods of fluctuating irradiance.
In this paper a novel technique proposed and implemented practically for photovoltaic cell efficiency enhancements. It is known that Iraq is one of the hottest countries in the world. It has a solar insolation average and energy higher than that of most of other countries. Solar photovoltaic cell has a limited efficiency boundary, which is affected by the amount of absorbed solar heat (energy). It is found that; when the solar array temperature excess 70 C⁰, the photovoltaic solar cell efficiency will be decreased remarkably. This novel technique which include painting the solar cell surface with chlorophyll only one time and painting it's surface with chlorophyll and polymer mixture another time gives a perfect solution to get a wide band of solar temperature array with a remarkable efficiency enhancement. The experimental results show that coating solar cell surface with chlorophyll only increases its efficiency by 5.5 % which is the maximum increase, while coating solar cell surface with chlorophyll and polymer mixture increases its efficiency by 3.1 % only.which is less than increase in the first case but more than that of solar cell without coating. All cells tested at constant solar irradiation (I=1000 W/m^2), and variation of temperature in range (30 °C to 80 °C).
Recently, applying nanofluids in PV/T systems for improving the performance of these systems has been fascinating many researchers. In this kind of research, nanofluids are employed in the PV/T systems as coolant or optical filter. To emphasis the capability of the nanofluids in PV/T systems, the present study aims first, to comprehensively review the features, structures, and the outcomes of PV/T system that applied nanofluids and investigated the effectiveness of nanofluids, and second, to comprehensively analyze the effective parameters on the performance of a nanofluid-based flat plate photovoltaic/thermal system in both laminar and turbulent regime. In this study, with respect to literature, a vast attempt has been done to study the effects of nanofluids parameters including volume fraction (0–4%), size (21 nm and 100 nm) and type of nanoparticles (TiO2 and Al2O3), as well as type of base fluid (water and mixture of ethylene glycol-water). The accuracy of proposed mathematical model was demonstrated through the comparison of predicted results and the available data in the literature. It can be concluded from the results that, to improve the performance of the system, adding nanoparticles is more efficient in laminar regime compared to turbulent one. The results also indicated that using nanoparticles of larger diameter leads to greater total energy and exergy efficiency in the turbulent regime, while contrary behavior is observed in laminar flow. Moreover, it was observed that employing aluminum oxide in nanofluids improves the system performance more than titanium oxide, where water based nanofluids show higher energy and exergy efficiency compared to ethylene glycol-water based nanofluids.
A heat-recovery ventilator (HRV) effectively conducts ventilation by recovering waste heat from indoors to outdoors during heating periods. However, dew condensation associated with the HRV system may arise due to the difference between the indoor temperature and the very low outdoor temperature in winter, and this can decrease the heat exchange efficiency. These problems can be solved by the pre-heating of the incoming air, but additional energy is required when pursuing such a strategy. On the other hand, an air-type photovoltaic thermal (PVT) system produces electricity and thermal energy simultaneously using air as the heat transfer medium. Moreover, the heated air from the air-type PVT system can be connected to the HRV to pre-heat the supply air instead of taking in the cold outdoor air. Thus, the ventilation efficiency can be improved and the problems arising during the heating period can be resolved. Consequentially, the heating energy required in a building can be reduced, with additional electricity acquired as well. In this paper, the performance of an air-type PVT system coupled with an HRV is assessed. To do this, air-type PVT collectors operating at 1 kWp were installed in an experimental house and coupled to an HRV system. Thermal performance and heating energy required during the winter season were analyzed experimentally. Furthermore, the electrical performances of the air-type PVT system with and without ventilation at the back side of the PV during the summer season were analyzed.
The objective of this work is to simulate a water-based flat plate photovoltaic/thermal system with glass cover and without it in laminar and turbulent regime and investigating the effects of solar irradiation, packing factor, Reynolds number, collector length, pipes diameter and number of pipes on the performance of this system. The accuracy of the model has been validated with the available data in the literature, where good agreements between the results have been achieved. The results showed that the energy efficiency in the glazed photovoltaic/thermal system is higher than unglazed one, while its exergy efficiency depends on the packing factor, Reynolds number and collector length. The results also indicated that increasing of solar radiation and packing factor increases total energy and exergy efficiency in both laminar and turbulent regime. Besides, it was found that there are the optimum values for mass flow rate and number of pipes that maximize exergy efficiency. The value of the optimum mass flow rate is larger in the case of unglazed system compared to that of glazed one. Furthermore, in most cases, the total energy efficiency in turbulent regime is higher, whereas the total exergy efficiency in laminar regime is superior.
Photovoltaic-thermal (PV/T) solar collectors convert solar radiation into electrical power and heat. A considerable amount of received solar energy can be lost to the ambient from the top surface of the PV/T module, especially in windy regions. Thus, in this study, a new vacuum-based photovoltaic thermal (VPV/T) collector is designed and comparatively analyzed with the conventional PV/T collector. The new design differs from the conventional PV/T design by including vacuum layer above the silicon wafer. Besides, to enhance the heat dissipation from the silicon wafer in the VPV/T design to the thermal absorber, the thicknesses of ethylene-vinyl acetate and tedlar polyester tedlar layers underneath the silicon wafer are decreased. A comprehensive 3D conjugate thermal model is developed and validated. The comparison is conducted at steady and transient conditions. The effect of Reynolds number (Re), wind speed, glass emissivity, and vacuum pressure are investigated. And finally, the exergy analysis for both designs are compared. The results showed that the new VPV/T collector has accomplished a 26.6% increase in the thermal power without changing the electrical power gain at Re of 50 and solar irradiance of 1000Wm-2. In addition, the vacuum pressure degradation from 0.01 Pa to 10 Pa slightly decreases the gained thermal power of the new VPV/T. A further increase in the vacuum pressure from 10 Pa to 1.013×10 5 Pa significantly decreases the gained thermal power with a slight increase in the electrical power. Furthermore, the total predicted VPV/T and the conventional PV/T exergy efficiency are 40% and 32%, respectively.
The PVT-air solar system simultaneously generates electrical and thermal energy. Therefore, increasing the cost-effectiveness of the system requires an appropriate choice of key parameters such as mass flow rate and air channel depth. In this paper, a PVT-air kit of a single module with a 30° slope was used to measure photovoltaic electricity and air heating power in the city of Sfax, Tunisia. Besides, a computer method was implemented using the ANSYS Fluent 17.0 software and the MATLAB program to analyse the properties of the airflow and to characterise PVT-air yields under different mass flow rates and depths. From the comparison of numerical and experimental data, the numerical method was validated with a good agreement. Indeed, we have found that increasing of the airflow rate improves the thermal efficiency with a slight change on electrical output. However, the reduction in depth shows an improvement on thermal efficiency and a negligible effect on electrical efficiency. Also, we have presented the thermal and electrical performance of PVT-air as a function of the key parameters with the Hottel-Whillier-Bliss formulation.
An experimental analysis and a numerical modelling of a newly designed solar air collector was conducted. The honeycomb structure with large surface area was introduced to the collector to form a blackbody-like heat absorbing core. PV panels were used to drive an electric fan that provide mechanical air circulation without additional energy supply. The effect of irradiance and PV panel coverage ratio on the overall thermal efficiency of the collector were investigated. The system was experimentally tested under irradiance of 200 W/m2 to 600 W/m2 with PV coverage ratio of 15%, 30%, 45%, 60%, 75% and 90%. The thermal behaviour of the system was analysed. It was observed that the honeycomb solar air collector integrated with well-designed PV configuration would be able to achieve suitable thermal efficiency. Over the range of experimental conditions, the maximum instantaneous efficiency reached 64% when PV coverage ratio was 45%. A numerical model was developed and verified, further exploring the thermal efficiency dependency on PV coverage ratio and radiation conditions. The investigation confirmed that there is a theoretical optimum PV coverage ratio that can maximize overall efficiency and the numerical model offered a methodology to predict thermal behaviour of the system under practical conditions.
Nanofluids, which are new generation cooling fluids, have been found to improve the heat transfer coefficient and enhance the system performance in recent years. In this observation, TiO2/water nanofluid (with 0.5 wt% and 1 wt% TiO2) is used as a coolant to investigate the photovoltaic thermal (PVT) collector under solar radiation intensities of 500, 700 and 900 W/m² and mass flow rates ranging from 0.012 kg/s to 0.0255 kg/s. At high solar radiation, the thermal energy efficiency is high but is inversely proportional to the electrical energy efficiency due to the increment in PV surface temperature. The energy efficiency of 1 wt% TiO2 nanofluid-based PVT collector is 85%–89% compared with 60%–76% of water-based collector at 0.0255 kg/s. The improvement in exergy efficiency of 1.0 wt% TiO2 is 6.02% compared with that of water-based collector at the mass flow rate of 0.0255 kg/s. In addition, a new theoretical approach model is developed to compare the theoretical and experimental results of the TiO2/water nanofluid-based PVT collector. Considerably close agreement between the new theoretical approaches and experimental is obtained with an accuracy of 97.6%–99.2%.
Solar air collector is the major component of solar energy utilization system which absorbs the incoming solar radiation, converts it into thermal energy and transfers the energy to the fluid flowing through the collector. This paper aims to review the techniques available in the literatures to promote the thermal performance of solar air collector, including: (1) add ribs/fins/meshes on the collector plate or use different shaped surface to reorganize the airflow in the laminar sublayer; (2) employ air impinging jet to favor convection heat transfer between the air and absorber plate by reorganizing the airflow near the absorber plate; (3) replace the single-duct collector by double/multi-pass duct to reorganize the airflow of main stream with the purpose to extend the residence time; (4) introduce baffles to create secondary flow, enhance the convective heat transfer, which can be deemed as reorganize the airflow in the whole collector chamber. The main novelty of this review is to find the deep relationships among these improvement methods, and further, summarize these methods as one unified method-airflow reorganization. This review presents and discusses the studies about these optimization methods and provides a perspective for researchers to understand the internal connections among these methods.
An investigation on the effect of cooling channel position on heat transfer characteristics and thermoelectric performance of air-cooled PV/T systems has been conducted numerically. Two design positions, cooling channels above PV panel (case1) and below PV panel (case2), were considered. It is found that the effect of internal radiation in the cooling channel on the system performance is greater for case1 in comparison to case2, while an opposite behavior is presented for the cooling effect on PV panels. Except for the effect of air inlet temperature, the magnitude and variation trend of the convective Nusselt number on PV panels are almost the same for two case systems. A maximum total exergy efficiency is obtained at the air inlet temperature of 298.15 K for case1 system and 295.65 K for case2 system. From the perspective of the amount of supplied energy, the case1 system is preferred. Detailed analysis focusing on the quality of energy should be carried out to determine the merits of case1 and case2 systems.
A novel methodology to control the temperature of the indoor photovoltaic system is presented. This work introduces an Indoor Photovoltaic System (IPVS) consisting of an Indoor Lighting System (ILS), Temperature Controller (TC) and the Maximum Power Point Tracker (MPPT). In IPVS, sunlight is brought inside the room using ILS which consists of Fresnel lenses mounted on the solar tracker to properly orient the lenses toward the sun. Infrared and ultraviolet radiations of the solar spectrum are filtered out and only visible part is converged at a specific point, guided indoor through optical fibers. Further, a novel optical temperature controller is introduced that maintains the temperature of the solar panel to the standard test conditions. Temperature controller ensures the optimum temperature of the solar panel. To ensure the cell to operate at its maximum power point, a variable step sized Incremental Conductance maximum power point tracking algorithm is implemented. Degradation of the output power of the solar panel is always because of the variation in temperature and solar irradiance that has been compensated by the temperature controller and the MPPT respectively. The graphs of the output power verify the validity of the proposed IPVS. The results presented here verified that the temperature controller accurately controls the temperature of the solar panel and the MPPT tracks the maximum power point without steady-state oscillations smoothing the output power of the indoor solar photovoltaic panel.
Steady-state energy analysis was performed on a photovoltaic thermal (PVT) collector with ∇-groove. Energy balance equation was obtained using the analytical and the matrix inversion methods. Theoretical results were consistent with the experiments results. Theoretical and experimental studies were conducted under solar radiations of 385 and 820 W/m² and mass flow rates between 0.007 and 0.07 kg/s. Exergy analysis was performed to determine the effect of various solar radiations (300–1200 W/m²). On the other hand, exergy analysis was performed to obtain loss exergy, PVT exergy efficiency, and improvement potential under solar radiations of 385 and 820 W/m² and mass flow rates between 0.007 and 0.07 kg/s.
Cooling of photovoltaic (PV) panels was investigated experimentally outdoors using two nanofluids and water as a cooling medium for volume flow rate ranging from 500 to 5000 mL/min at concentrations (0.01 wt.%, 0.05 wt. %, and 0.1 wt.%) under different radiation intensity. Two types of nanofluids were used, namely Al 2 O 3 in water-polyethylene glycol mixture at pH 5.7, and TiO 2 in water-cetyltrimethylammonium bromide mixture at pH 9.7, respectively. The cooling of PV panel required incorporating a heat exchanger of aluminium rectangular cross section at its back surface to accommodate different volume flow rate of the cooling medium aforementioned. The system was tested under climate conditions of Jerash-Jordan. Determination of flow characteristics; friction factor, f and product of friction factor Reynolds number, of TiO 2 , Al 2 O 3 nanofluids and water as a cooling medium were investigated. Also, a f Re comparison of the temperature between the cooled PV cell and without cooling for volume flow rate ranging from 500 to 5000 mL/min was presented. Results showed that the na-nofluid cooled PV cell in both types caused higher decrease in the average PV cell temperature compared with the cooled cell with water and without cooling. In addition, Al 2 O 3 nanofluid showed better performance than TiO 2 nanofluid. Furthermore, experimental results showed that higher concentration of nanofluid produces a better cooling effect of the PV cell for all the studied range of volume flow rate. Also, electrical analysis of power and efficiency showed that TiO 2 nanofluid gives better performance for the studied range of volume flow rate and concentrations compared with water cooling and without cooling.
This study presents an improved photovoltaic-thermal (PV-T) solar collector system that integrates a PV panel with a serpentine-flow stainless steel tube as the water-heating component and a double-pass air channel as the air-heating component. A Fresnel lens is used as the glazing and primary concentrator, and compound parabolic concentrators (CPCs) are used as the secondary concentrator. The system can simultaneously generate hot air and hot water in addition to electricity, and the total energy generated per unit area is higher than that of a single-fluid system. This triple-function PV-T solar collector is well suited for a wide range of thermal applications and offers options for hot and/or cold air and water use depending on the application and energy needs. This paper establishes, develops, and validates a conceptual design for a concentrating PV-T dual-fluid solar collector with 1D steady-state energy-balance equations for the dual-fluid (air and water) configuration. Next, this model is used to predict the performance of the dual-fluid solar collector with varying air and water mass flow rates. Then, the simulation results of the single- and dual-fluid operational modes are compared. The simulated results have shown that the total equivalent efficiencies for single fluid condition have ranged from approximately 30 to 60%, and increased to a maximum efficiency of near to 90% for the case of the dual fluids. The dual fluids operation mode has reduced the solar cells temperature and hence increased the electrical output.
The performance of the hybrid photovoltaic (PV) module depends on its operating conditions (especially temperature). Only a small percentage of incoming solar radiation is converted into electricity, and the rest is converted into heat. This overheats the PV module and reduces its performance. This work presents the performance of photovoltaic-thermal (PV/T) solar collector with dual channels for different fluids. The PV/T solar collector's electrical and thermal characteristics like temperatures of the solar cell and outlet fluids, electric power generation efficiency and thermal power efficiency are analyzed through comparison of four PV/T collectors with different fluids. It is found that water-water cooled PV/T collector is the most efficient in both electrical and thermal performance. Water-water cooled PV/T collector can provide the most amount hot water. The temperature of water in air-water case is the highest. Air-air cooled PV/T collector may provide the most amount hot air which its temperature is the highest. It is also found that an increase in mass flow rate of water and the height between the upper pipe and the lower pipe leads to better overall efficiency in water-water cooled PV/T collector.
PV/Thermal flat transpired plate is a kind of air-based hybrid Photovoltaic/Thermal (PV/T) system concurrently producing both thermal and electrical energy. In order to develop a predictive model, validate, and investigate the PV/Thermal flat transpired plate capabilities, a prototype was fabricated and tested under outdoor conditions at Shahid Bahonar University of Kerman in Kerman, Iran. In order to develop a mathematical model, correlations for Nusselt numbers for PV panel and transpired plate were derived using CFD technique. Good agreement was obtained between measured and simulated values, with the maximum relative root mean square percent deviation (RMSE) being 9.13% and minimum correlation coefficient (R-squared) 0.92. Based on the critical radiation level defined in terms of the actual exergy gain, it was found that with proper fan and MPPT devices, there is no concern about the critical radiation level. To provide a guideline for designers, using equivalent thermal efficiency as an appropriate tool, optimum values for suction velocity and PV coverage percent under different conditions were obtained.
This paper discusses theoretical and indoor experimental studies of a bi-fluid type photovoltaic/thermal PV/T solar collector. 2D steady-state analysis was developed and computer simulation was performed using MATLAB. Experiments were conducted for steady-state analysis under the solar simulator at Solar Energy Research Lab UiTM Perlis, Malaysia. The test includes all three modes of fluid operation under the same PV/T system, namely: the air mode, the water mode, and the simultaneous mode of water and air. The simulation results were validated against the experimental results using three methods of error analysis: root mean square percentage deviation (RMSPD), mean absolute percentage error (MAPE), and coefficient of determination (R2). On average, the MAPE, RMSPD, and R2 computed for the fluid output temperature are approximately 0.92%, 1.19%, and 0.98, respectively. Thus, we concluded that the simulation and experimental results are in good agreement. The PV/T collector designed in this study has a variety of applications as it can be operated in three different modes of fluid operation, and the theoretical model is useful in modelling all three modes without further modification.
Research on PV/T (photovoltaic/thermal) solar collectors has been conducted for years because the collector can provide electric power and thermal energy simultaneously. A tri-functional PV/T collector is presented and studied in this paper. The collector can work in PV/water-heating mode or PV/air-heating mode for different energy demands. For two working modes, steady-state model and dynamic model of the collector are developed and validated with experimental results. Based on the validated models, the performance of collector is investigated under different flow rates, wind speeds, inlet air temperatures, and initial water temperatures. For PV/air-heating mode, the effects of wind speed and flow rate are investigated. A flow rate of 0.02 kg/(m2·s) is recommenced to balance the temperature increase and thermal efficiency. For PV/water-heating mode, the decrease of thermal efficiency with wind speed increase is observed but it slows down when wind speed is over 5 m/s. The curve of daily thermal efficiency is plotted with different initial water temperature in tank. With annual analysis under different climates, the tri-functional PV/T collector is proved to have better annual performance than separated PV/T water collector and PV/T air collector which could be left unused in some seasons.
In the present study the series combination of N PVT water collectors, partially covered with photovoltaic module, in two different configurations namely case A: Photovoltaic module at lower portion; case B: Photovoltaic module at upper portion, have been analyzed. Analytical expressions for instantaneous thermal efficiency and temperature dependent electrical efficiency have been derived. The performances of both configurations have been compared on thermal efficiency basis and temperature dependent electrical efficiency basis. It has been concluded that at moderate mass flow rate, for large number of PVT water collectors connected in series both cases give nearly same results.
This paper presents an improved design of a photovoltaic/thermal (PV/T) solar collector integrating a PV panel with a serpentine-shaped copper tube as the water heating component and a single pass air channel as the air heating component. In addition to the electricity generated, this type of collector enables the production of both hot air and water, increasing the total efficiency per unit area compared to the conventional PV/T solar collector. The use of both fluids (bi-fluid) also creates a greater range of thermal applications and offers options in which hot and/or cold air and/or water can be utilized depending on the energy needs and applications. In this paper, the design concept of the bi-fluid PV/T solar collector is emphasized with 2D steady state energy balance equations for the bi-fluid configuration are developed, validated and used to predict the performance of the bi-fluid solar collector for a range of mass flow rates of air and water. The performance of the collector is then compared when the fluids are operated independently and simultaneously. The simulations indicate that when both fluids are operated independently the overall thermal and electrical performance of the solar collector is considered as satisfactory and when operated simultaneously the overall performance is higher. The bi-fluid PV/T solar collector discussed in this paper will add insights to the new knowledge of optimizing the utilization of solar energy by a PV/T solar collector and has potential applications in various fields.
This paper presents a comparative study between compound parabolic concentrated (CPC) and conventional flat hybrid double-pass photovoltaic–thermal (PVT) systems. A mathematical thermal–electrical model is developed and verified with published experimental data. The use of detailed five-parameter electrical modeling in the analysis made it possible to estimate the electrical parameters of PV cells, such as voltage and current. A parametric study is conducted to investigate the effect of different design and operation variables such as length, packing factor, duct depth and flow rate on thermal and electrical performance. Furthermore, the study investigated the performance of proposed systems with fins attachment and the effect of their material and type on performance. The model is applied to simulate and analyze thermal and electrical performance of finned (F) and un-finned (UF) flat and CPC photovoltaic systems for a selected case at Dhahran, Saudi Arabia. The results show that annual thermal gain is 1% higher for flat-PVT (F) compared to flat-PVT (UF). On the other hand, the annual electrical gain for flat-PVT (F) is 3% higher than flat-PVT (UF). The CPC-PVT (F) is estimated to have more than 3% thermal and 8% electrical gain compared to CPC-PVT (UF). Among studied four configurations, CPC-PVT (F) system will have the best performance.
This study investigated experimentally the performance due to automatic cooling and surface cleaning of Photovoltaic (PV) module installed on the roof of a building in hot arid area as compared with that of a module without cooling and cleaning. The module cooling is controlled automatically according to the rear side temperature via rejection of none-converted solar-energy to the ambient to keep the PV module surface temperature always close to the ambient temperature. In addition, this system controls the cleaning period of the module front surface. The results showed a decrease of about 45.5% and 39% in module temperature at front and rear faces, respectively. Consequently, the cooled and surface cleaned module has an efficiency of 11.7% against 9% for the module without cooling and cleaning. Moreover, the maximum output power produced by cooled and cleaned module is 89.4 W against 68.4 W for non-cooled and non-cleaned module.
Using concentrating photovoltaic (CPV) cells is an effective method for the low-cost photovoltaic conversion. However, higher temperature and non-uniform surface temperature distribution will result in the electrical output decline of CPV cells and shorten their life time. To obtain higher net output power of CPV cells and prolong their life time, we designed a novel multi-layer manifold microchannel cooling system to effectively lower the cell surface temperature and improve the uniformity of surface temperature distribution. Thermal image analysis indicated that the surface temperature difference of the CPV cells was below 6.3 °C. The multi-layer manifold microchannel had a heat transfer coefficient of 8235.84 W/m2 K and its pressure drop was lower than 3 kPa. The results show that the hybrid CPV cells have a satisfactory net output power due to their lower pumping power and the higher electrical output of CPV cells.
A new way of improving the heat dissipating ability and PV efficiency of the solar cells by enhancing the ther- mal conductivity of the rear EVA layer was reported. The thermal conductivity, electrical resistivity, degree of curing of the EVA encapsulating composites and the PV efficiency of the solar cells are investigated. Filling with the thermal conductive fillers enhances the thermal conductivity of the composites effectively. The thermal conductivity of the filler influences sig- nificantly the thermal conductivity of the composite at high filler loading (greater than 20 vol%). Thermal conductivities of the composites filled with SiC, ZnO or BN reach respectively 2.85, 2.26 and 2.08 W/m·K at filler content of 60 vol%. The composites filled with ZnO or BN exhibit superior electrical insulation to those filled with SiC or Al2O3. ZnO can promote the cross-linking reaction of the EVA matrix. The test results indicated that the EVA composite encapsulating rear films filled with thermal conductive fillers are able to improve the PV efficiency and the heat dissipating ability of the solar cell effectively.
The book focuses on solar radiation characteristics, solar radiation
available for practical applications, heat transfer, radiation
characteristics of opaque materials, theory of flat-plate collectors,
and concentrating collectors. Also discussed are solar process
economics, solar water heating, solar heating system design, solar
cooling, conversion to mechanical energy, evaporative processes, and
selfgradient ponds.
Efficiency Improvement of a Photovoltaic Thermal. Energy
- Lee Joo Hee
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Soteris_A._Kalogirou_Auth.-Solar_Energy_Engineering._Processes_and_Systems-Academic_Press-2014-with-Cover-Page-v2
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