Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
In this paper, the effect of material parameters on the efficiency of Ge and InGaAs\np-n junction solar cells which are most commonly used as the sub-cell of multi-junction solar\ncells are investigated and the results due to these two cells are compared. The efficiency of Ge\n(EG=0.67 eV) solar cell which is easy to manufacture and inexpensive in cost, is compared\nwith the efficiency of InGaAs (EG=0.74 eV) solar cell which is coming with drawback of high\nproduction difficulties and cost. The theoretical efficiency limit of Ge and InGaAs solar cells\nwith optimum thickness were determined by using detailed balance model under one sun\nAM1.5 illumination. Since the band gap values of two cells are close to each other,\napproximate detailed balance efficiency limits of 16% for InGaAs and 14% for Ge are\nobtained. When drift- diffusion model is used and the thicknesses and doping concentrations\nare optimized, the maximum efficiency values are calculated as 13% for InGaAs and 9% for\nGe solar cell. For each solar cell external quantum efficiency curves due to wavelength are also\nsketched and compared....
Solar energy is certainly an energy source worth exploring and utilizing because of the\nenvironmental protection it offers. However, the conversion efficiency of solar energy is still low.\nIf the photovoltaic panel perpendicularly tracks the sun, the solar energy conversion efficiency will\nbe improved. In this article, we propose an innovative method to track the sun using an image sensor.\nIn our method, it is logical to assume the points of the brightest region in the sky image representing\nthe location of the sun. Then, the center of the brightest region is assumed to be the solar-center,\nand is mathematically calculated using an embedded processor (Raspberry Pi). Finally, the location\ninformation on the sun center is sent to the embedded processor to control two servo motors that are\ncapable of moving both horizontally and vertically to track the sun. In comparison with the existing\nsun tracking methods using image sensors, such as the Hough transform method, our method based\non the brightest region in the sky image remains accurate under conditions such as a sunny day\nand building shelter. The practical sun tracking system using our method was implemented and\ntested. The results reveal that the system successfully captured the real sun center in most weather\nconditions, and the servo motor system was able to direct the photovoltaic panel perpendicularly\nto the sun center. In addition, our system can be easily and practically integrated, and can operate\nin real-time....
The solar chimney power plant is a relatively new electricity generation concept,\nbased on renewable energy, combining the greenhouse effect with the chimney suction.\nThe solar chimney powerplant consists of three parts, the solar collector, the\nchimney and the turbine generator unit, of which the study was focused on the later\npart. To evaluate the turbine performance inside the solar chimney powerplant, experimental\nsystem was constructed in Aswan, Egypt that has a metrological site\n(23Ã?Å¡58'N and 32Ã?Å¡47'E) occurs. The system was constructed to evaluate the performance\nof the solar chimney turbine and power generation characteristic in the hottest\nsite where Aswan is located at the nearest of the Tropic of Cancer at the summer\nseason. Velocity, electric power generation and the turbine efficiency are studying in\nthis work. The numerical analyses were performed by using a commercial code CFX,\nANSYS 16.1 to simulate the flow through the turbine and overall system. The study\nshows that the range of power generated (1.2 W - 4.4 W). It can be estimated, according\nto the results, the variation trend in pressure drops with the turbine rotation\nspeed increase with small differences when the turbine rotation speed surpasses 1800\nrpm with average efficiency of 57%. It is concluded that the theoretical model is basically\nvalid for the system under study, and the CFD simulation can be used conveniently\nto predict the performance of the system, the comparison between them and\nexperimental result shows a good agreement....
This paper reports an experimental investigation of the dust particle deposition process on\nsolar photovoltaic (PV) modules with different surface temperatures by a heating plate to illustrate\nthe effect of the temperature difference (thermophoresis) between the module surface and the\nsurrounding air on the dust accumulation process under different operating temperatures. In general,\nif the temperature of PV modules is increased, the energy conversion efficiency of the modules is\ndecreased. However, in this study, it is firstly found that higher PV module surface temperature\ndifferences result in a higher energy output compared with those modules with lower temperature\ndifferences because of a reduced accumulation of dust particles. The measured deposition densities\nof dust particles were found to range from 0.54 g/m2 to 0.85 g/m2 under the range of experimental\nconditions and the output power ratios were found to increase from 0.861 to 0.965 with the increase\nin the temperature difference from 0 to 50 ââ??¦C. The PV module with a higher temperature difference\nexperiences a lower dust density because of the effect of the thermophoresis force arising from\nthe temperature gradient between the module surface and its surrounding air. In addition, dust\nparticles have a significant impact on the short circuit current, as well as the output power. However,\nthe influence of particles on open circuit voltage can be negligible....
A new type of solar tower was developed through laboratory experiments and numerical\nanalyses. The solar tower mainly consists of three components. The transparent collector area is an\naboveground glass roof, with increasing height toward the center. Attached to the center of the inside\nof the collector is a vertical tower within which a wind turbine is mounted at the lower entry to the\ntower. When solar radiation heats the ground through the glass roof, ascending warm air is guided\nto the center and into the tower. A solar tower that can generate electricity using a simple structure\nthat enables easy and less costly maintenance has considerable advantages. However, conversion\nefficiency from sunshine energy to mechanical turbine energy is very low. Aiming to improve this\nefficiency, the research project developed a diffuser-type tower instead of a cylindrical tower, and\ninvestigated a suitable diffuser shape for practical use. After changing the tower height and diffuser\nopen angle, with a temperature difference between the ambient air aloft and within the collector,\nvarious diffuser tower shapes were tested by laboratory experiments and numerical analyses. As a\nresult, it was found that a diffuser tower with a semi-open angle of 4ââ??¦ is an optimal shape, producing\nthe fastest updraft at each temperature difference in both the laboratory experiments and numerical\nanalyses. The relationships between thermal updraft speed and temperature difference and/or tower\nheight were confirmed. It was found that the thermal updraft velocity is proportional to the square\nroot of the tower height and/or temperature difference....
A new graphene-based flexible solar cell with a power conversion efficiency >10% has been\ndesigned. The environmental stability and the low complexity of the fabrication process are the two\nmain advantages of the proposed device with respect to other flexible solar cells. The designed solar\ncell is a graphene/silicon Schottky junction whose performance has been enhanced by a graphene\noxide layer deposited on the graphene sheet. The effect of the graphene oxide is to dope the graphene\nand to act as anti-reflection coating. A silicon dioxide ultrathin layer interposed between the n-Si\nand the graphene increases the open-circuit voltage of the cell. The solar cell optimization has been\nachieved through a mathematical model, which has been validated by using experimental data\nreported in literature. The new flexible photovoltaic device can be integrated in a wide range of\nmicrosystems powered by solar energy....
Loading....