EEEP 3/2012

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OPTIMAL INTEGRATION OF DISTRIBUTED ENERGY STORAGE AND SMALL GENERATORS INTO AN ISLANDED MICROGRID
WITH RENEWABLE SOURCE

Thang Vu, Xavier Le Pivert, Christian Schaeffer

pdf  (PDF 546k)

Abstract: The purpose is to study how best to integrate distributed energy storage and small thermal generators in a Microgrid mainly powered by renewable sources. Optimal placing and capacity sharing of distributed energy storage helps to reduce Joule losses and voltage drops. Small generators give same advantages at optimal location. Optimal capacity sharing of Distributed energy storage is based on Droop mode control of specific inverter. Storage units are guided to behave homogenously to have the same evolution of State of Charge, so the same life cycle. By minimizing the Joule losses, the decentralization of storage allows to reduce the conductor section or the size of renewable power sources at design phase. For existed grid, it could delay distribution grids upgrade investment. It should be therefore financially interesting.

Keywords: Distributed Energy Storage, Optimal placing, Droop mode

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TRANSFORMATION OF HORIZONTAL GLOBAL SOLAR DATA INTO TILTED IRRADIATION AT HOURLY SCALE: COMPARISON OF VARIOUS METHODOLOGIES

Gilles Notton, Christophe Paoli, Siyana Vasileva, Lilyana Ivanova, Marie Laure Nivet and Ludmil Stoyanov

pdf  (PDF 1778k)

Abstract: Global irradiation on tilted planes is required in all engineering calculations for solar systems. Various methodologies are compared in view to obtain these data from measured horizontal global solar irradiation using empirical or semi-physical models and Artificial Neural Network (ANN).

Keywords: Solar radiation estimation, ANN method, conventional method.

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ON SOLAR ABSORPTION REFRIGERATOR'S PERFORMANCES

Emna Berrich, Ali Fellah, Ammar Ben Brahim, Fethi Aloui, Michel Feidt 

pdf  (PDF 113k)

Abstract: Solar absorption refrigerator's performances are analysed by a conceptual optimization. The simulation is based on hierarchical decomposition, on the principles of the endoreversibility, respectively of the exoreversibility of the solar absorption refrigerators. Optimization is carried out by adopting the method of Lagrange multipliers. This methodology was been applied to absorption cycle composed of a solar concentrator (hot source), a thermal solar converter (thermal engine 1), an intermediate source, a cold source and four main elements: a generator, an absorber, a condenser and an evaporator. The generator and the absorber constitute a thermal engine ET2 and the whole condenser evaporator forms the thermal receptor RT. The parameterization of the installation comprises fluxes and powers and the temperatures that reign in the thermal machine compartments.  This made it possible to get out two equation systems which guarantee the coupling of general optimal performance characteristics of a simple effect solar absorption cycle. The functional and conceptual characteristics are studied. In particular, the effect of the external sources temperatures on the performances is discussed. These results are interesting in absorption machines conception viewpoint. They encourage studies in an irreversible way.

Keywords: Absorption refrigerator, Solar energy, Optimization, Hierarchical decomposition, Endoreversibility, Exoreversibility.

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FEASIBILITY STUDY OF HYBRIDATION OF MINI DIESEL POWER STATIONS WITH PHOTOVOLTAIC ENERGY SYSTEMS

Said Diaf and Gilles Notton
pdf  (PDF 250k)

Abstract:. Nowadays, the majority of diesel power stations located in the southern part of Algeria operate under difficult conditions and their diesel generators don't operate at nominal regime. The hybridation of micro diesel power stations with photovoltaic(PV) energy system permits to reduce the operation time of diesel generators and consequently reduces the fuel consumption. This paper presents a technical economic of hybrid photovoltaicdieselbattery system. The objective of this work consists on developing a decision-making tool that allows the opportunity evaluation for combining micro diesel power stations with PV energy system.
This decision making tool is based on
    establishing of technical and economic models of the systems components
    optimization of system sizing
The simulation results related to this study will be presented and analyzed in this paper.

Keywords: hybrid system, diesel generator, optimum system sizing, loss of power load probability, levelized cost of energy

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EXPERIMENTAL STUDY OF LOSSES IN DOUBLY-FED INDUCTION GENERATOR

Vladimir Lazarov, Zahari Zarkov and Ludmil Stoyanov

pdf  (PDF 1560k)

Abstract: This paper presents an experimental study of the losses doubly-fed induction generator (DFIG) for wind energy conversion system. The experiments were performed on a laboratory test bench. The losses in the components of the system - electronic converters, transformer and induction machine - are determined by measuring the power in different system points and by making the appropriate calculations. Quantitative assessment of the distribution of losses and of the overall system efficiency is also carried out. The results can serve to validate the theoretical models and assumptions. Although the study is designed for a small power machine, it makes it possible to outline certain trends and connections between the losses and the energy flows in systems with DFIG.

Keywords: DFIG, losses, wind generator

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ON THE WAY TO IMPROVE BIO-ETHANOL PRODUCTION FROM WOODEN BIOMASS AS APPROPRIATE ALTERNATIVE FUEL FOR SPARK IGNITION ENGINES

Laurentiu Fara, Alexandru-Cristian Racovitză and Gheorghe Niculae

pdf   (PDF 239k)

Abstract: Bio-ethanol has been proved to be a better alternative fuel to SI Engines for reasons concerning classic fuel economy, lower emissions levels and promising industrial obtaining methods by using chemical and biological means. Bio-ethanol is the main product to be achieved through the fermentation of the sugar-compounds that are themselves obtained from wooden biomass. The primary biomass source comes from a special poplar clones harvested from three different zones of Romania in order to offer a comparison basis in terms of biomass production efficiency. Among all the known industrial fermentation methods of the sweet compounds extracted from biomass, this paper reveals a new and more efficient process given by the enzymatic fermentation.

Keywords: Bio-ethanol, wooden biomass, enzymatic fermentation, efficiency, low emissions.

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THE CONTRIBUTION OF SECOND GENERATION BIOETHANOL TO SUSTAINABLE ENERGY INDEPENDENCE

Kantcho Lahtchev

pdf  (PDF 495k)

Abstract. In this review the basic approaches for development and improvement of bioethanol industry, its perspectives and problems encounter are summarized.  Bioethanol produced from plant biomass by biochemical method (second generation bioethanol) is object of special attention. The perspectives and quality of this biofuel are compared with those of bioethanol produced from starch feedstock (first generation bioethanol). The advantages as well as problems concerning manufacturing and commercialization of second generation bioethanol are discussed also. It is pointed on the necessity of global approach to develop and stimulate such industry. The initial steps of commercialization of second generation bioethanol as well as future impacts of such industry on sustainability and environmental are presented also.
Key words: bioethanol, commercialization, sustainability, environment

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BRIEF REVIEW OF GASIFICATION BIOMASS TECHNOLOGIES, THEIR APPLICATION AND POTENTIAL RISK REGARDING
THE SAFETY AND ENVIRONMENT

Petar Kaleychev, Kostadin Belev, Ivan Ivanov

pdf  (PDF 79k)

Abstract: Biomass gasification as technology for energy production has recently significant development and perspectives for further increasingly application. A number of institutes in the EU work towards establishing a unified approach to the risk assessment of technology for gasification of biomass. The report takes a variant of how this approach can be applied to research of concrete installations. Covers all possible aspects and serves as an addition to the existing information. The report presents initial results up by research into installations for the gasification of biomass, which are intended to show their position on the safety and impact on the environment. They are a basis for future research focused on the formation of recommendations and proposals on specific aspects of the operation of these facilities.

Keywords: gasification, biomass, risk assessment, safety, environment

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NEARLY-ZERO-ENERGY BUILDING: STUDY CASE ON A BLOCK OF FLATS

Emilia-Cerna Mladin, Alexandru Dobrovicescu, Tudor Prisecaru

pdf  (PDF 179k)

Abstract: The study is focused on a multi-family building block of flats type and includes an energy analysis on its construction and installations elements. Results conclude with energy performance indicators and recommendations for additional energy efficiency measures. Different packages of measures were analyzed for economical efficiency and appropriate conclusions are drawn. It is thus shown how a building can approach conditions compatible with nearly zero energy consumption from classical sources, with reasonable costs for owners.  
Keywords: nearly-zero energy, energy efficiency, energy performance, energy efficient buildings 
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INFLUENCE OF THE COATINGS ON THE THERMAL PERFORMANCE OF INSULATING GLASS UNITS

Nina Penkova

pdf  (PDF 304k)

Abstract: A mathematical model of 3D conjugated heat transfer at insulating glass units (IGU) is composed and applied for numerical calculations by computational fluid dynamic technique with ANSYS. Temperature field in glass panes and temperature, pressure and velocity fields in gas space are calculated for several variants of flat double glazed IGU: uncoated glass panes; low emissivity coating on inner pane and uncoated outer glass pane, and solar control coating on outer pane and uncoated inner glass pane. The numerical calculations are made for winter and spring conditions in order to validate the models and to analyze the coatings influence on thermal behaviour of IGU.
Keywords: IGU, coatings, CFD calculations, heat transfer, free convection

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COMPUTATION OF PERFORMANCE AND EFFICIENCY OF THE WATER OXYGENATION PROCESS IN NON-STATIONARY CONDITIONS

Nicolae Băran, Alexandru Sorin Pătulea and Ionela Mihaela Căluşaru

pdf  (PDF 342k)

Abstract: The paper presents a method for computing the performance and efficiency of the water oxygenation process. The method can be used when the concentration of dissolved oxygen increases in function of the duration of the process of introducing in the water. The theoretical results are verified by experimental researches.
Keywords: oxygen dissolved in water, oxygenation efficiency.

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