Sharif Digital Repository

Variability and uncertainty of wind and photovoltaic (PV) generations greatly influence technical and financial aspects of power systems. This paper examines the potential impacts of large-scale wind and PV farms on reliability level of composite generation and transmission systems. At first, reliability models of renewable-based units are developed. In these models, both component failure rates and uncertainty nature of renewable resources are taken into account. Using the proposed technique, the multi-state analytical models of a wind farm placed in Manjil and a PV farm placed in Jask both in Iran are extracted. Then, reliability studies of high renewable-energies penetrated power system... 

To attain an ongoing electricity economy, developing novel widespread electricity supply systems based on diverse energy resources are critically important. Several photovoltaic (PV) technologies exist, which cause various pathways to produce electricity from solar energy. This paper evaluates the competition between three influential solar technologies based on photovoltaic technique to find the optimal pathways for satisfying the electricity demand: (1) multicrystalline silicon; (2) copper, indium, gallium, and selenium (CIGS); and (3) multijunction. Besides the technical factors, there are other effective parameters such as cost, operability, feasibility, and capacity that should be... 

This paper describes the designing and evaluation of an alternative energy system which consists of PEMFC, PV, PEM electrolyser, methane reformer and hydrogen tank. In order to find out the minimum capacity of the components, a system sizing model is developed in MATLAB based on meteorological and electrical demand data. Three scenarios are considered based on different combinations of solar energy and fossil fuel energy as energy resources. The heating energy produced by the fuel cell is recovered for supplying domestic hot water while the system would supply electrical energy. Results show that system sizing strongly depends on scenarios and unit cost of electricity decreases through the... 

Variability and uncertainty of wind and photovoltaic (PV) generations greatly influence technical and financial aspects of power systems. This paper examines the potential impacts of large-scale wind and PV farms on reliability level of composite generation and transmission systems. At first, reliability models of renewable-based units are developed. In these models, both component failure rates and uncertainty nature of renewable resources are taken into account. Using the proposed technique, the multi-state analytical models of a wind farm placed in Manjil and a PV farm placed in Jask both in Iran are extracted. Then, reliability studies of high renewable-energies penetrated power system... 

Miscellaneous sorts of renewable energies, despite of their positive impacts on the power system operation cost and environmental concerns, could jeopardize the system reliability due to introducing significant degrees of intermittency and uncertainty. This challenge could be overcome by composing various sources of renewable energies with complimentary natures. This paper devises an explicit mathematical framework to compromise the contribution of wind and solar energies. The optimization problem is to maximize the system reliability subject to a fixed monetary investment associated with both wind and solar. The problem formulation is based on mixed-integer programming (MIP) format in which... 

Nanoparticulated TiO 2 fibers as one-dimensional long structures were introduced into TiO 2 P25 nanoparticle films using coelectrophoretic deposition. This prevented the usual crack formation occurring in wet coatings, and resulted in less porosity and higher roughness factor of the films that provided more favorable conditions for electron transport. The films used as the photoanode of a dye solar cell (DSC) produced 65% higher photovoltaic efficiency. TiO 2 fibers can be excellent binders in single-step, organic-free electrophoretic deposition of TiO 2 for DSC photoanode  

Distributed generation (DG) units are often interfaced to the main grid using power electronic converters including voltage-source converters (VSCs). A VSC offers dc/ac power conversion, high controllability, and fast dynamic response. Because of nonlinearities, uncertainties, and system parameters’ changes involved in the nature of a grid-connected renewable DG system, conventional linear control methods cannot completely and efficiently address all control objectives. In this paper, a nonlinear adaptive control scheme based on adaptive backstepping strategy is presented to control the operation of a grid-connected renewable DG unit. As compared to the popular vector control technique, the... 

Different structures of TiO2 photoelectrodes are fabricated with various arrangement modes of the layers. TiO2 nanoparticles, synthesized by stabilizing agent free non-hydrolytic sol–gel method, are employed as the under layer, whereas carbon-doped TiO2 hollow spheres, prepared by hydrothermally grown carbon template, are used as the scattering layer of solar cells. The nanoparticles (22 nm) have anatase structure, while 300–700 nm hollow spheres show mixtures of anatase and rutile phases. X-ray photoelectron spectroscopy confirms that carbon is doped into TiO2 hollow spheres, resulting in a decrease in band gap energy in the range 2.96–3.13 eV compared with 3.04 eV band gap energy for the... 

Different structures of TiO2 photoelectrodes were fabricated with various arrangement modes of the layers. TiO2 nanoparticles were synthesized by a combination of sol–gel and solvothermal methods and were employed as the active layer of solar cells. Hierarchical TiO2 spheres (HTS) and spherical TiO2 particles (STP) were also prepared by hydrothermal and sol–gel processes, respectively, and used as the scattering layer of solar cells. Field emission scanning electron microscope and X-ray diffraction analyses revealed that all synthesized morphologies showed anatase structure with particle size around 20, 200–400 nm and 1.5–2.0 µm for the... 

Well-crystallized TiO2 and neodymium (Nd)-doped TiO2 nanoparticles with various doping levels were synthesized by hydrothermal method and utilized as the photoanode of nanostructured solar cells. The results indicated that Nd-doping was caused the absorption spectra shift to higher wavelength while the morphology and surface area were unchanged. As a result, by employing 0.4 mol% Nd in the TiO2 photoelectrode, the overall conversion efficiency of the cell reached 9.08% which is 26% higher than pure one. Based on the photo-electrochemical characterizations, the improvement is a consequence of electrons injection increment from dye to TiO2 conduction... 

This study attempts to investigate a new way for cooling PV cell using natural vapor as coolant. The performance of solar cell was examined on simulated sunlight. The natural vapor encountered backside of PV cell vertically in various distribution and different mass flow rates. Also, the effect of natural vapor temperature in cooling performance was analyzed. Results indicated that the temperature of PV cell drops significantly with increasing natural vapor mass flow rate. In detail, the PV cell temperature decreased about 7 to 16°C when flow rate reaches 1.6 to 5grmin-1. It causes increasing electrical efficiency about 12.12% to 22.9%. The best performance of PV cell can be achieved at high... 

The structural, electrical, optical, and photovoltaic properties of aggregated submicron nitrogen-doped TiO2 particles (NTiO2) and the influence of utilizing them, in comparison with undoped ones, as the light-scattering layer of dye-sensitized solar cells were investigated. Field emission scanning electron microscope, X-ray diffraction, and diffuse reflectance spectra showed that both type samples have similar morphology, crystal phase, and scattering feature. Moreover, photoluminescence, Mott–Schottkey, and photovoltaic characteristics such as IMPS/IMVS and charge extraction analysis indicated that the NTiO2 layer is an efficient scatterer in two aspects: enhancement of light-harvesting... 

A comparative study has been made of hybrid solar cells based on poly(3-hexylthiophene) (P3HT) and different nano-structures of TiO2. Electrospinning, which is a low cost production method for large area nanofibrous films, was employed to fabricate TiO2 nanofibers and spin coating method was employed to fabricate organic-inorganic hybrid solar cells based on P3HT and TiO2 nanostructures. The performance of the hybrid solar cells was analyzed for four density levels of the TiO2 nanostructure. It was found that higher densities of TiO2 leads to more interface area and generates excitons, so that the power conversion efficiency increases to... 

Colloidal quantum dot solar cells have recently attracted significant attention due to their low-processing cost and surging photovoltaic performance. In this paper, a novel, reproducible, and simple solution-based process based on supercritical fluid toluene is presented for in situ growth and deposition PbS nanocrystals with oleic-acid passivation. A lead precursor containing sulfur was mixed with oleic acid in toluene and processed in a supercritical fluid condition at different temperatures of 140, 270 and 330 °C for 20 min. The quantum dots were deposited on a fluorine-doped tin oxide glass substrate inside the supercritical reactor. Transmission electron microscopy, X-ray diffraction,... 

Recently, hybrid graphene–quantum dot systems have attracted increasing attention for the next-generation optoelectronic devices such as ultrafast photo-detectors and solar energy harvesting. In this paper, a novel, one-step, reproducible, and solution-processed method is introduced to prepare hybrid graphene–PbS colloids by employing supercritical ethanol. In the hybrid nanocomposite, PbS quantum dots (~3 nm) are decorated on the reduced graphene oxide (rGO) nanosheets (~1 nm thickness and less than 1 micron lengths). By employing X-ray photoelectron and Raman and infrared spectroscopy techniques, it is shown that the rGO nanosheets are bonded to PbS nanocrystals through carboxylic bonds.... 

In this paper the creation of multiple energy hubs that make up a complex energy network are modeled and optimized for a selection of six scenarios to examine both their financial viability and potential reduction of greenhouse gas emissions. As a proposed case study scenario for the model, three energy hubs are considered: a 'residential complex (RC)', a 'commercial shopping plaza (CS)', and a 'school (S)'. The use of combined heat and power systems, solar photovoltaic, solar collectors and network interaction are also examined for their impact on efficiency and cost. The modeling is undertaken and carried out by General Algebraic Modeling System (GAMS). It is shown that cost can be reduced... 

Today, regarding the limitation and environmental side effects of fossil fuel resources, solar hydrogen production is one of the main interests in the energy research area. The development of visible light sensitized semiconductors based on non-toxic components, low cost and available bio-species is an ongoing approach for H2 generation based on water splitting reactions. Here, two different morphologies of TiO2 photoanodes, nanoparticulated and nanotubular, have been modified with simply extracted bacteriorhodopsin (bR) without any linker. Achieving a significant enhancement in photoconversion efficiency of TiO2 photoanodes, η% was increased from 2.9 to 16.5 by bR addition to the TiO2... 

Solar energy exists extensively in all parts of the world. However the intermittency of solar energy presents critical challenges to PV system. The intermittency can be covered by storing solar energy in chemical bonds such as hydrogen. This process can be performed by photovoltaic powered electrolysis of water. The energy transfer efficiency between PV and electrolyzer is subject to the distance between maximum power points (MPP) of PV module and operating points. The operating points can be adjusted by optimizing the design parameters of the electrolyzer but the maximum power points are function of PV module characteristics, solar radiation and ambient temperature. Therefore the weather... 

In this paper, special focus is paid to the long-term adoption of renewable electricity technologies and their implications for emissions reductions in Iran. MESSAGE, as a bottom-up energy supply optimization model, is used to assess the lowest-cost technology options. The potential impacts of transitioning to a renewable electricity supply are quantified, and the investment requirement to achieve a low-carbon generation mix is estimated. Alternative scenarios are defined to evaluate the impact of fossil fuel prices, the carbon tax and government incentives on the utilization of renewable resources, national renewable targets, and emissions reductions. The prioritization of non-hydro... 

Abstract We design a thermo-photovoltaic Tandem cell which produces high open circuit voltage (Voc) that causes to increase efficiency (η). The currently used materials (AlAsSb-InGaSb/InAsSb) have thermo-photovoltaic (TPV) property which can be a p-n junction of a solar cell, but they have low bandgap energy which is the reason for lower open circuit voltage. In this paper, in the bottom cell of the Tandem, there is 30 quantum wells which increase absorption coefficients and quantum efficiency (QE) that causes to increase current. By increasing the current of the bottom cell, the top cell thickness must be increased because the top cell and the bottom cell should have the same current. In...