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  • Open access
  • 179 Reads
Explicit Expressions for Solar Panel Equivalent Circuit Parameters Based on Analytical Formulation and the Lambert W-Function
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Due to the high dependence of the photovoltaic energy efficiency on environmental conditions (temperature, irradiation...), it is quite important to perform some analysis just focusing on the photovoltaic device characteristics in order to optimize the energy production, even in case of small-scale users. The use of equivalent circuits is the preferred option to analyze solar cells/panels performance. However, the aforementioned small-scale users rarely have the equipment or expertise to perform large testing/calculation campaigns, the only information available for them being the manufacturer datasheet which normally refers to fixed irradiation and temperature levels. The solution to this problem is the development of new and simple methods to define equivalent circuits able to reproduce the behavior of the panel for any working condition, from a very small amount of information. In the present work a direct and completely explicit method to extract solar cell parameters from the manufacturer datasheet is presented and tested. This method is based on analytical formulation which includes the use of the Lambert W-function to turn the series resistance equation explicit. Therefore, the calculations involving this parameter are simplified. The presented explicit method is used to analyze the performance (i.e., the I-V curve) of a commercial solar panel at different levels of irradiation and temperature. The analysis performed is based only on the information included in the manufacturer's datasheet. Results indicate a good correlation level with experimental data.
  • Open access
  • 72 Reads
State of the Art and Future Trends in Grid Codes Applicable to Isolated Electrical Systems
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Electrical power systems are changing their traditional structure, which was based on a little number of large generating power plants placed at great distances from loads by new models that tend to split the big production nodes in many smaller ones. The set of small groups which are located close to consumers and provide safe and quality energy is called distributed generation (DG). The proximity of the sources to the loads reduces losses associated with transportation and increases overall system efficiency. DG also favors the inclusion of renewable energy sources in isolated electrical systems or remote microgrids, because they can be installed where the natural resource is located. In both cases, as weak grids unable to get help from other nearby networks, it is essential to ensure appropriate behavior of DG sources to guarantee power system safety and stability. The grid codes sets out the technical requirements to be fulfilled for the sources connected in these electrical networks. In technical literature it is rather easy to find and compare grid codes for interconnected electrical systems. However, the existing literature is incomplete and sparse regarding isolated electrical systems and this happens due to the difficulties inherent in the pursuit of codes. Some countries have developed their own legislation only for their island territory (as Spain or France), others apply the same set of rules as in mainland, another group of island countries have elaborated a complete grid code for all generating sources and some others lack specific regulation. This paper aims to make a complete review of the state of the art in grid codes applicable to isolated systems, setting the comparison between them and defining the guidelines predictably followed by the upcoming regulations in these particular systems.
  • Open access
  • 103 Reads
Assessment of the Wave Energy Conversion Patterns in Various Coastal Environments
An important next stage in exploiting the ocean energy potential is to install several identical devices within an array, like doing in wind farms, to raise in this way their overall electricity production. The way in which the ocean energy devices will perform, as well as their economic viability, is critically linked to their design and moreover they depend directly on the specific environmental conditions characteristic of a certain area. Thus, due to the specific wave climate, one device can perform better than another in a particular coastal area while in another nearshore area the situation might be completely reversed. From this perspective, the main objective of the present work is to assess the performances of various WEC devices that would operate in different coastal environments. Three different groups of coastal environments were considered. They are: (I) the Iberian continental nearshore covering both Spanish and Portuguese coasts, (II) the Canaries Islands and the Archipelago of Madeira and (III) two enclosed seas (Black and Caspian seas). Various wave energy converters were evaluated covering the full range of the existing devices. Among these, the most representational devices considered are: Wave Dragon, Pelamis, Archimedes Wave Swing, Aqua Boy, Oyster, Langlee and Wave Bob. In order to evaluate the electric power expected in a certain location, the bivariate distributions of occurrences corresponding to the sea states defined by the significant wave height and the energy period were designed in each coastal area. The wave data were provided by hindcast studies covering extended time periods that were performed with numerical wave models based on the spectrum concept. The transformation efficiency of the wave energy in electricity was evaluated via the load factor and also through an index defined as the ratio between the electric power estimated to be produced by each specific WEC and the expected wave power corresponding to the location considered.The present work provides valuable information related to the effectiveness of various technologies for the wave energy extraction that would operate in different coastal environments. Moreover, the results can be easily extrapolated to some other nearshore areas.
  • Open access
  • 114 Reads
Biofuel Similar to Bodiesel Obtained by Using a Lipase from Rhizopus Oryzae, Optimized by Response Surface Methodology
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A new biofuel like biodiesel applicable to diesel engines is obtained by the enzymatic ethanolysis reaction of sunflower oil with ethanol, in free solvent media, by using BIOLIPASE-R®, a low cost powdered enzyme preparation containing obtained  lipases from a strain of Rhizopus oryzae. This is a multipurpose additive from Biocon®-Spain, used in food industry. This biofuel integrates glycerol as monoglyceride (MG) together to two fatty acid ethyl esters (FAEE) molecules by the application of the 1,3-selective lipases. Thus, this process minimizes waste generation and maximizes efficiency of the process because no residual glycerol is produced. Response surface methodology (RSM) is employed to evaluate the main reaction parameters (reaction temperature, oil/ethanol ratio and pH) on the conversion of sunflower oil. Water content and amount of lipase were also investigated. Regarding the results, we found that operates optimally with a water content of the reaction medium of 0.15 %, 0.05 - 0.1 % lipase by weight relative to the weight of oil used, 20 °C, volume ratio (ml/ml) oil/ethanol 12/3.5 and pH 12 (by addition of 75 µl of 10 N NaOH dissolution). These achieved results have proven a very good efficiency of the biocatalyst in the studied selective process.
  • Open access
  • 70 Reads
Solar Air Colectors for Space Heating and Ventilation Applications – Performance and Case Studies in Romania Climatic Conditions
Solar air collectors have various applications: on one side, they can be used for air heating in cold seasons; on the other side they can be used in summer to evacuate the warm and polluted air from residential, offices, industrial and commercial buildings. The paper presents experimental results of a solar collector air, in climatic conditions from South Eastern Europe. The relationships between the direct solar irradiation, the heat flow resulted, the air velocity at the outlet, the air flow rate, the time of input in nominal regime of the collector and efficiency of conversion of solar energy into thermal energy are highlighted. Thus, it was shown that after maximum 50 minutes, solar air collectors, with baffles and double pass of air can reach 50 % efficiency for solar irradiation of 900-1000 W/m. 2The article also presents a mathematical model and the results of a computational program that allows sizing solar collectors for the transfer of the air, for their purpose to improve the natural ventilation of buildings. The article is completed with a case study, sizing the area to be covered with solar collectors to ensure ventilation of a house with two floors or for an office building. Also, the ACH coefficient was calculated and compared.
  • Open access
  • 101 Reads
Fuel Cell Power Systems for Autonomous Underwater Vehicles: State of the Art
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Autonomous Underwater Vehicles (AUV's) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time they are usually powered by lithium-ion secondary batteries, which have insufficient specific energy. In order for this technology to achieve a mature state increased endurance is required. Fuel cell power systems have been identified as an effective means to achieve this endurance but no implementation in a commercial device has yet been realized. This paper summarizes the current state of development of the technology in this field of research. First, the most adequate type of fuel cell for this application is discussed. The prototypes and design concepts of AUV's powered by fuel cells which have been developed in the last few years are described. Possible commercial and experimental fuel cell stack options are analyzed, examining solutions adopted in the analogous aerial vehicle and automotive applications as well as the underwater ones, to see if integration in an AUV is feasible. Current solutions in oxygen and hydrogen storage systems are overviewed and specific energy is objectively compared between battery power systems and fuel cell power systems for AUV's. A couple of system configuration solutions are described including the necessary lithium-ion battery hybrid system. Finally, some closing remarks on the future of this technology are given.
  • Open access
  • 50 Reads
Operational Characteristics of Liquid-piston Heat Engines
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Liquid piston Stirling engines (sometimes termed "fluidyne" engines) have been studied, proposed, applied in a variety of energy conversion applications including water pumping and electricity generation from solar energy. They are attractive for low capital costs and simplicity of construction. In addition, their operation as external combustion engines allows for flexibility in primary energy sources which is a distinct advantage when a low-cost or free source of heat can be paired with their minimal construction costs. Disadvantages of these devices include relatively low efficiency and low power density.      This paper describes test results from a solar-powered fluidyne engine utilizing a Fresnel lens for concentrating solar energy, and from a combustion powered engine equipped with an orifice-style dynamometer for controlled loading of the engine.     Temperature, pressure, and volume phasing along with indicated work and brake work are presented and discussed. The Fresnel lens provided ample power for sustained operation of the engine, and engine cycles and operational characteristics of the solar powered engine are discussed. Operating without load, the pressure and volume phase difference was 72 degrees and the dynamic mechanical response showed no delay from the thermodynamic expansion due to temperature changes of the working fluid. The function and capacity of the orifice-style dynamometers are evaluated for testing various configurations of liquid-piston engines under load. Engine cycles and operating characteristics of the loaded engines are presented and discussed. Relative sizes of indicated work and brake work are explored as functions of engine configuration.
  • Open access
  • 66 Reads
Review on the Existing and Developing Underground Coal Gasification Techniques in Abandoned Coal Seam Gas Blocks: Australia and Global Context
Coal is the major energy source and provides about 40 percent of the total electricity production of the world .For Australia it is nearly 80%. Meeting up global demand for less emission of GHS, Australia is seeking alternative ecofriendly renewable energy sources. In Australia, there is huge range of fossil fuel resources (especially deep seated coal deposits, which are difficult to extract with conventional mining) and the policy makers are seeking "clean coal" technology for further usages of the resources. CSG (coal seam gas) and UCG (underground coal gasification) are identified technology for exploiting those coal deposits. The UCG is much more effective process for energy exploitation (theoretically greater than 15-20 times) compared to CSG process. Demonstration of UCG projects and development of these technology received momentum as one of the successful project at Chinchilla, Queensland, Australia is operating successfully from 1997 to 2013 for power generation. Last few years there was a debate for choosing priority policy for CSG or UGC. Australian local entrepreneur and global IOCs sought for massive scale CSG extraction and presently this industry is in booming stage. Apparently it is seen from the industry trend for UCG operation is behind the race compared to CSG activity. But the future prospect of UCG is bright, as we can say for adopting policy "First CSG later on UGC; can't be CSG after UCG operation, as there left nothing exploitable in the coal body". The ideal conditions of the coal body are deviated while CSG operation is being done. Very minor amount of hydro-carbon (in-situ natural gas) are extracted but major share of the coal deposit are left over at deep geological formation. Even there is a provision for simultaneous operation of the both in the same block. Review on the existing and developing sophisticated technology for next phase of abandoned CSG fields is a potential area for further R&D. The success of this effort can enlightened the black coal towards "Cleanest and Greenest" source of energy for next generation Hydrogen fuel.
  • Open access
  • 74 Reads
Hydrogen Storage in Boron Nitride and Carbon Nanomaterials
Thermogravimetry/differential thermogravimetric analysis of boron nitride (BN) nanomaterials showed possibility of hydrogen storage of 1–3 wt%. Possibility of hydrogen gas storage in BN and carbon (C) clusters was investigated by molecular orbital calculations. Chemisorption calculation of hydrogen for BN clusters showed that hydrogen bondings with nitrogenatoms and tetragonal rings were the most stable. Conditions of H2 gas storage in B36N36 cluster, which was considered as a cap structure of B99N99 nanotube, were predicted by first principle single point energy calculations. H2 molecules would beintroduced from hexagonal rings of the cage structure. Stability of H2 molecules inside BN and C clusters was alsoinvestigated by molecular orbital calculations. C and BN clusters showed possibility of hydrogen storage of 6.5 and 4.9wt%, respectively. Chemisorption calculation was also carried out for B24N24 with changing endohedral elements in BNcluster to compare the bonding energy at nitrogen and boron, which showed that Li is a suitable element for hydrogenationto B24N24. BN fullerene materials would store H2 molecule easier than carbon fullerene materials, and its stability for hightemperature would be good.
  • Open access
  • 109 Reads
Analysis and Design of Multicarrier PWM Based Multilevel Z-Source Inverter Fed Induction Motor Drives with DTC
This paper presents the simulation as well as prototype model for design and analysis of 5-level neutral point clamped (NPC) inverter fed medium voltage induction motor drive. The development of prototype model shows the flexibility of the multilevel z-source inverter to establish an ideal AC voltage from more than a few levels of DC voltages with lesser harmonic content. The Z-source network is placed to unite the input DC source and the inverter to accomplish the buck-boost capability. Three different multi-carrier PWM techniques are analyzed and several fascinating characteristics are revealed. The Direct Torque Control (DTC) is the most well-liked approach to control performance of induction motor drive is also presented in this paper. The effect of this paper illustrate that, this developed prototype model will bridges the existing research gap between theoretical and practical execution of multilevel       z-source inverters for medium voltage industrial applications. Satisfactory and improved performance of multilevel            z-source inverters is demonstrated through test results under various operating circumstances and the effort has been made to validate the effectiveness the simulation and hardware implementation of the proposed inverter topology.
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