Search

Since the solar irradiation is accessible in many parts of our planet, it is a viable replacement for fossil fuels, so commissioning photovoltaic (PV) power plants are increased, rapidly. One of the main problems that this technology faces is the increase in the temperature of solar cells. In this paper, streaming water layer over the upper side of PV modules is considered as a cooling method. This technique not only lowers the surface temperature, but also keeps the surface clean. Four different water flow rates of 0.5, 1, 2, and 4 lit/min were used so that two different flow patterns, water streaks and water film, were formed. In addition, the negative effect of the residual water layer over the surface of the PV panel on the absorbed radiation was evaluated experimentally. As results, temperature drops of 20.6 °C and 29.7 °C were measured for flow rates of 0.5 and 2 lit/min, respectively. Also, for the case of 4 lit/min, the efficiency is increased by 6.7% compared to the conventional case. Moreover, it was observed that after the formation of a water layer, the water flow rate no longer has a significant effect on cooling. Finally, a comparison between the electrical efficiency enhancements of this study with those of similar researches was performed. [ABSTRACT FROM AUTHOR]

Solar water heaters represent a crucial component of sustainable energy systems, offering the potential to reduce energy costs and limit carbon emissions. This study focuses on the investigation of energy and exergy efficiency enhancement in evacuated tube solar water heaters deployed in the hot climate of Dezful, Iran. Specifically, the study evaluates the impact of engine-oil as a circulation fluid within copper U-tubes positioned inside evacuated tubes, with the addition of TiO2 nanoparticles in two concentrations (0.2 mass% and 0.4 mass%). Additionally, the study assesses the effectiveness of a metallic twisted tape insert within the U-tubes to augment the heat transfer rate, with the aim of improving the overall efficiency and performance of the system. In the assessments, the thermal efficiency diagram was divided by three phases and the behavior of each one was elaborated. As results, employing metallic-insert leads to 1.5 °C more water temperature. Moreover, 5.6 °C difference between 0.4 mass% TiO2 + insert and the base case was observed in the evening which results in 24.4% and 25.52% higher thermal efficiency and exergy efficiency, respectively. [ABSTRACT FROM AUTHOR]

Solar water heaters are one of the most popular applications of renewable energy. So, many modifications have been performed on them to boost their performance. The novelty of the current experimental work is to simultaneous employment of porous medium inside water reservoir and oil-based nanofluid as circulating fluid. Accordingly, TiO2 nanoparticles with two concentrations of 0.2 and 0.4 mass% were dispersed in engine oil as-based fluid. As results, when concentration of 0.4 mass% TiO2 in engine oil is integrated with porous medium, the temperature is increased by 6.4 °C. This temperature enhancement leads to boost the thermal efficiency more than 41%. Moreover, thermal efficiency increments of 5.4% and 19% are occurred, for the cases of employing porous media and simultaneous application of 0.4 mass% TiO2/oil with porous media, respectively. The exergy efficiency was assessed by means of the modified approach. Accordingly, utilization of only porous medium creates 19.6% improvement in the exergy efficiency of the system. Furthermore, the entropy generation in the system was calculated, too, and the base case showed 14.7% more entropy generation compared with TiO2/oil integrated with porous medium. Lastly, a comparative study has been done to show the superiority of this work in comparison with the others. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement in thermal systems is one of the most important efforts of researchers. Adding nanoparticles to circulating fluid is an effective way to increase the heat transfer rate, while its effect on pressure drop may be positive or negative in various cases. In this paper, both thermal and hydrodynamic aspects of flowing a TiO2/water nanofluid were considered with concentrations of 0.05, 0.1, 0.2, 0.5, and 1 mass percentages. The nanofluid was streamed through a helical coiled path, under a constant heat flux and different flow rates. The thermal characteristics are followed by calculations of Nusselt number (Nu), convective heat transfer coefficient, and heat transfer enhancement (HTE%). Accordingly, the utmost increase in Nusselt number was found as 29.8 and 36.5% for the concentration of 1 mass%, in laminar and turbulent flows, respectively. The pressure drop was assessed by means of friction factor and drag reduction percentage (DR%), so that in the lowest concentration and the lowest Reynolds number, the maximum DR% occurred as 6.4%. To have a better understanding of the system, the pumping power is reported against HTE% amounts. [ABSTRACT FROM AUTHOR]

For a long time, electricity is supplied by means of firing the fossil fuels in thermal power plants. Now, it is well-known that the activity has many environmental and health issues, which are sharply menace the future of earth and humanity. Photovoltaic (PV) system is one of the popular renewable types of energy generation, which is available in most parts of the earth. Unfortunately, temperature rise in a PV module, leads to a significant reduction in its electrical efficiency. In this paper, two methods of wind blowing and mounting fins are considered separately and simultaneously, to overcome the mentioned weak-point. The wind velocity is set to 2 km/h. So, four cases are assessed, experimentally. As results, it was revealed that wind blowing of 2 km/h is more effective than fins in cooling PV module, so that, it can create more than 15 °C lower temperature than mounting fins. The mentioned temperature reduction leads to enhance the electrical efficiency and output power by 2.4% and 21.7%, respectively. In order to show the accuracy of results, all experimental outcomes in electrical efficiency were compared with the analytical formula. Moreover, the environmental evaluation of commissioning a 10 kW PV power plant with the proposed cases are reported, too. [ABSTRACT FROM AUTHOR]

The world is inconceivable without an everlasting demand for energy. Nowadays, various kinds of renewable energies, such as solar energy, are developing rapidly, since they have the least negative environmental impacts. Irradiation intensity is one the most important parameters in photovoltaic (PV) technology, and so integration of mirrors with a PV module can improve its performance. Mounting mirrors increases the radiation intensity but, at the same time, raises the surface temperature, which in turn reduces the electrical efficiency. The novelty of this study is keeping the cell temperature low despite receiving more radiation by installing 10 aluminum fins on the back of the panel. All tests were experimentally performed in the hot climate of Dezful, Iran. As a result, the best tilt angle of the mirror was found at 30°, where the output power was enhanced by 3.3% and electrical efficiency was reduced by 0.5% compared with the conventional case. When aluminum fins were added as heat sinks, both output power and electrical efficiency were enhanced by 11.4% and 13.1%, respectively. Moreover, comprehensive discussions on both energy and exergy are provided. The entropy generation was also calculated and accordingly, the case of PV 30 + fin generates 1.6% less entropy than the base one. [ABSTRACT FROM AUTHOR]

Population and economic growth, industrial activities, development of technology, and depletion of fossil fuels have all led to increasing energy demand. As a result, there is an increasing ambition towards implementation of sustainable energy sources. In this study, first, a review of the literature is conducted to learn about various methods and objectives for optimization of photovoltaic and thermal (PV/T) systems. Then, a case study is considered, and the seasonal and hourly solar radiation are studied. Further, two methods of multiobjective evolutionary algorithm based on decomposition (MOEA/D) and multiobjective particle swarm optimization (MOPSO) are compared. On this basis, the energy and exergy efficiencies are analyzed for a proposed PV/T system. The outcomes are validated by taking into account the previous studies, and a sufficient agreement is found indicating the validity and accuracy of the results. It is also found that the efficiency rates for both energy and exergy soar with a rise in the ambient temperature. Additionally, a growth in the warm water flow rate from 0.4 to 1 kg/s increases the exergy efficiency by 0.6%. It is concluded that the MOEA/D method outperforms the MOPSO in terms of the optimization of the proposed PV/T system. [ABSTRACT FROM AUTHOR]

To provide the progressive global demand for energy, the use of renewable energies is being rapidly developed. Since solar radiation is available in most parts of the earth, the photovoltaic (PV) power plant is one of the worthwhile solutions. As a deficiency, temperature rise in photovoltaic cells leads to a drop in their electrical output power. In this experimental study, the circulation of carbon black nanofluid was investigated as a coolant of PV modules. Both water and ethylene glycol (EG) were used as the base fluids. It is found that all modified cases generate more output power than the conventional one. For instance, water + carbon nanofluid yields 54% more output power compared with the conventional one. To make a real assessment of using nanofluid as a coolant, the electrical consumption by pump and fan must be counted. Therefore, in this study, the net output power is calculated. In the cases of EG and EG + carbon, the net output powers get lower than the conventional module. So, they are not justifiable. In this paper, a modified formula is proposed to calculate the exergy efficiency, in order to achieve more accurate results. Accordingly, from an exergy viewpoint, 16.3% and 4.5% in electrical and thermal exergy efficiencies are achieved, when water + carbon nanofluid was used. Moreover, the values of entropy generation and lost exergy were reported for all considered cases. [ABSTRACT FROM AUTHOR]

The decrease in output power of a photovoltaic (PV) power plant with increase in temperature is one of the main issues which can be controlled by cooling the PV modules. In this experimental study, various numbers of 10, 20, 30 and 40 aluminum fins in two different geometries of straight and zigzag were mounted at the back side of PV modules. In order to conform the ambient conditions, experiments were done by a solar simulator, under constant irradiation of 630 W m−2. The main objective of the study is to measure the effect of mounted fins at the back surface of PV panels, on electricity generation by lowering the panel surface temperature. PV panels with zigzag fin geometry are found to perform better than those with straight fins and also the module without fins. The results show that in case of 10 fins, temperature drops of 9 °C and 15 °C and increase in output power of 8% and 14% are achieved for straight and zigzag geometries, respectively. The entropy generation as an important thermodynamic parameter is also evaluated and a reduction of 1.5% to 2.5% is found in different experiments. Follow-up potential research areas are also identified. [ABSTRACT FROM AUTHOR]

Nowadays, researches on different kinds of renewable energies including photovoltaic technology are developing rapidly. It is proved that the output power of a PV cell is reduced by increasing the temperature. In this paper, mounting aluminum fins at the back surface of the PV module is proposed as a simple and low-cost method to decrease the PV cell temperature. It was found that using aluminum fins caused more than 7°C reduction in the cell temperature. Besides, it was shown that the entropy generation of the PV module with fin, was 3.5% lower than the conventional one. Also, the positive environmental impacts of using fins at the back surface of the PV module were estimated by RETScreen software, so that, it leads to enhance the performance of the PV power plant by more than 25 %, from an environmental viewpoint. [ABSTRACT FROM AUTHOR]

The convective heat transfer coefficient (CHTC) of a fluid is one of the most effective factors on the performance of a fluid in heat transfer equipment. Due to the higher conductivity of metals than that of liquids, solid metal particles can be mixed in a fluid to improve the CHTC of it. According to recent advances in nanotechnology, using nanofluids is one of the popular methods to increase heat transfer in heat exchangers. In this paper, the main influence factors on increasing the CHTC of the nanofluid, including flow rate and nanofluid concentration, were investigated. For this study, all tests were carried out in the Reynolds range of 10,000 to 31,500 which are definitely in turbulent regime. Furthermore, in order to reduce the number of tests, Design–Expert software using central composite method has been employed. The results indicate that increasing the Reynolds leads to an increase in the CHTC and a decrease in the friction factor. In addition, it was shown that at a constant Reynolds, carbon nanofluid with concentration of 0.21 mass% has about 40.7% higher CHTC than pure water. The variation of friction factor was investigated too and was found that this parameter is increased by increasing the nanofluid concentration and decreasing the Reynolds number. The entropy generation due to heat transfer and friction factor was assessed and finally showed that in 0.21 mass% where the maximum Nusselt is available, the entropy generation is the lowest. By calculating the Bejan number, the portions of heat and friction factors in generating entropy were determined. [ABSTRACT FROM AUTHOR]

Increasing the temperature of photovoltaic (PV) cells decreases their electricity generation. The use of phase change materials (PCMs) is one of the most common methods for controlling the rate of increasing the temperature of PV cells. This research focuses on thermodynamic analysis of PV/PCM systems with and without fins in maximum operating temperature of PV modules (85 °C). Polyethylene glycol 600 (PEG-600) and paraffin, with different melting points, have been studied experimentally as PCM in an indoor condition. Moreover, the effect of using fins was investigated. For this critical temperature, the results showed that using paraffin could be better for controlling the temperature of PV cells, due to its closer melting point with the module temperature. In the case of fins included, the temperature differences of 28.0 °C and 8.8 °C between the case of paraffin + fin and the case of PEG 600 + fin in comparison with the conventional PV module were measured, respectively. At this critical temperature condition, the output power of a PV module cannot exceed the half of its nominal power. The exergy efficiency of the paraffin + fin case was measured to 4.2% more than the conventional one. Also, entropy generation was calculated and reduction up to 5% was shown for paraffin + fin in comparison with the conventional one. Moreover, variations of the Rayleigh number for proposed cases are calculated too. [ABSTRACT FROM AUTHOR]