فهرست مطالب amirhossein shiravi

In recent years, generation of electricity through photovoltaic power plants has developed rapidly. The availability of sunlight and the appropriate return on investment are two important factors in the impressive growth of photovoltaic (PV) power plants. Unfortunately, increase in PV cell temperature is one the main defects of them and it has a significant negative effect on the electrical efficiency of PV panels. In this paper, using paraffin as phase change material (PCM) on the performance of photovoltaic cells has been investigated experimentally. The material has melting point of about 58˚C. Also, the effect of airflow at two different velocities of 2 and 4 km/h in presence of paraffin have been tested, too. To have a better management on performing the tests, a solar simulator was used, so that the solar irradiation and wind stream were supplied by means of a projector and an industrial blower, respectively. Results showed 13-16˚C decrease in PV temperature for the three modified cases, in comparison with the conventional one. Moreover, the effect of mentioned temperature reduction on both electrical efficiency and output power were also studied. Finally, the environmental effects of commissioning a 10-kW PV power plant were checked by using RETScreen software. Accordingly, the annual reduction of carbon dioxide (CO2) emission is estimated for all considered cases.

Nowadays, the environmental crisis, due to the combustion of fossil fuels in thermal power plants has become a global issue. Application of renewable energies is the best strategy to overcome the crisis. The photovoltaic power plants are the most popular alternative for governments. As temperature rises in PV cells, a significant drop in their produced power is observed. Therefore, it is important to lower the cell temperature with an appropriate cooling method. In this paper, three types of cooling fluids; pure water, pure Ethylene-Glycol (EG) and mixture of water/EG with the same ratio, are experimentally investigated. Based on the results, application of pure water in the PVT system, shows better performance than other two fluids. While the conventional PV module has shown the surface temperature of higher than 70 ˚C, the proposed PV modules integrated with pure water, pure EG and water + EG have shown surface temperatures of 32.7 ˚C, 36.6 ˚C and 33.7 ˚C, respectively. The maximum temperature reduction of 37.3 ˚C compared to conventional PV module, increased the output power up to 51%. Accordingly, if conventional PV modules are used for commissioning a nominal 20 kW PV power plant, only 11.7 kW is attained, whereas, water cooled PV modules can improve the output power up to 17.7 kW.

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.

The heat transfer coefficient of a fluid is one of the most important effective factors on the performance of a fluid in the heat transfer process. Due to the higher conductive heat transfer coefficient of metals than liquids, metal particles can be used to increase the heat transfer rate of liquids. Nano fluid is one of the novel and developing methods to improve heat transfer rate in heat exchangers. In this paper, the main effective parameters on increasing the convective heat transfer coefficient of carbon nano fluid compared to water as based fluid, including: flow rate and concentration, in the range of 7100 to 16700 for Reynolds which is known as turbulent flow, are investigated. The results illustrate that increasing in Re number leads to increase the Nusselt number and convective heat transfer coefficient, and moreover decrease the friction factor. It is also showed that in a constant Re, carbon nano fluid has been able to create up to 10.17% more convective heat transfer coefficient, compared with pure water as base fluid. It was found that adding Carbon nano-particles to water, initially leads to increase in the convective heat transfer coefficient of the nanofluid. This increase continues to a concentration of about 0.2 wt% of the nano-carbon, and then has a descending trend. In addition, the pressure drop due to changes in Re, was investigated too, and showed that the behavior of this curve is in agreement with Moody’s diagram.

Energy is an important parameters for sustainable development of each country. Renewable energies are one of the main ways to reach this aim. Photovoltaic (PV) power plants is one of the most popular renewable power generation methods that is available in most parts of the world. Rising the PV cell temperature is one of the proved weak points which negatively affects their electricity production. Different ways have been proposed in order to degradation of temperature effects on PV cells. One of them, is using phase change materials (PCMs) to prevent the rapid rise of the temperature of PV modules. PCMs absorb parts of temperature of cells, which is leads to decrease the PV temperature. Several methods were presented in PV/T field based on PCMs. The main purpose of this paper is to introduce the major coolant ways of PV modules and provides a review of different methods of cooling PV modules by using PCMs. For each section, some suggestions for developing purposes have been presented.

Nowadays, using of renewable sources are popular methods to generating energy. Photovoltaic (PV) technology is one of the most popular ways to producing power. In hot days of year, which the maximum irradiation of sun is available, because of the temperature value is high, the efficiency of PV cells is falls down. In this paper, in order to decrease the temperature of PV cells, using Polyethylene-Glycol 600 (PEG-600) as phase change material (PCM), for cooling the PV panel was studied. The results show the positive effect of fins on controlling the temperature of photovoltaic cells. Moreover, in order to increasing the rate of melting the PCM, integrating some fins was investigated too. The panel with PCM included, in about 80 mins of the end of test, had a same temperature with the conventional panel, as well as panel with both PCM and fins, at the end of experiment, had a temperature difference of about 9°C compared with conventional panel. Furthermore, the maximum efficiency difference between the panel with PCM and panel with PCM + fins, were about 2.4 % and 4.6 %, respectively. This means that fins, due to the increased amount of heat exchange between the panel and PCM, has been able to play an important role to increasing the efficiency and controlling the temperature of the panel. Finally, for economic and industrial feasibility of the proposed prototypes, the economical estimation is also presented.

The nanofluids have been able to occupy an important place in engineering, in spite of being a young science. While nanoparticles are very effective in increasing heat transfer of base fluids, they cause a significant pressure drop in the flow. In this paper, the effect of different concentrations, 0.1 to 0.4 wt.%, of carbon nanofluid in water have been investigated on the pressure drop of fluid flow over the Reynolds range from 14,000 to 28,000. The variation of pumping power was measured and the corresponding results illustrated increasing in the friction factor of the nanofluid at concentration 0.4  up to 70%, leading to a 68% increase in the pumping power.

Nowadays, environmental protection and efforts to reduce pollution, caused by industrial activities, on one hand, and research on finding new and improved energy supply options on the other, have become one of the major concerns of governments around the world. In recent years, photovoltaic (PV) systems, due to their proved potential are rapidly developed in most parts of the earth. The objective of this study, is to estimate the amount of CO2 emission reduction by implementing a 7 MW PV power plant. The location of this power plant is in the north of Hamedan province, Iran. Moreover, the amount of not consumed fossil fuel were measured. Finally, it is found that the total reduction of 134050 t CO2 will be achieved when PV power plant is used compared to a natural gas one, during 25 years. Moreover, in this paper, the energy payback time (EPBT) and the Energy Yield Ratio (EYR) are calculated. The results show that EPBT is about 5.5 years and EYR of mentioned PV power plant is more than 4.2.

The electricity generation from renewable sources is growing rapidly. The use of photovoltaic panels is one of the most popular renewable power generation methods that is available in most parts of the world. One of the problems facing to this industry is increasing the temperature of the panels during the hot days of the year; which reduces their output power. The use of phase change materials (PCMs) is a way to prevent the rapid rise of the temperature of the panels. In this paper, polyethylene glycol 600 (PEG 600) is used behind the panel as a PCM. This material, absorbs a portion of the panel's heat and causes to lower the temperature of the panel. In order to enhance the heat absorbed by the PEG600, a number of fins are also mounted on the back of the panel, and the results are compared with the non-fin state. The results show that at the beginning 150 minutes from the start of the experiment, the temperature difference between panel with both PCM and fin compared with conventional panel, is between 18 C and 34.1 C. Furthermore the maximum efficiency difference between the panel with both PCM and fin, with conventional panel is 4.65% and for the panel with PCM and non-fin, with conventional panel is 2.45%. Finally, the comparison of both experimental measurement and analytical calculation were performed.