Christopher J. Koroneos

Exergy analysis of renewable energy sources

Oil crises in the past years made more obvious the dependency of economies on fossil fuels. As a consequence, the need for new energy sources became more urgent. Renewable energy sources could provide a solution to the problem, as they are inexhaustible and have less adverse impacts on the environment than fossil fuels. Yet, renewable energy sources technology has not reached a high standard at which it can be considered competitive to fossil fuels. The present study deals with the exergy analysis of solar energy, wind power and geothermal energy. That is, the actual use of energy from the existing available energy is discussed. In addition, renewable energy sources are compared with the non-renewable energy sources on the basis of efficiency.

Exergy analysis of cement production

In the present paper, cement production in Greece has been examined using the exergy analysis methodology. The major goal of the modern cement and concrete production industry is the minimisation of energy costs and environmental effects. The rational management of raw materials and energy requires analytical decision making tools that will provide the necessary information for the identification of possible improvements in the life cycle of a product. The second law of Thermodynamics allows for the evaluation of the irreversibility and the exergetic performance of a process. The analysis involves assessment of energy and exergy input at each stage of the cement production process. The chemical exergy of the reaction is also calculated and taken into consideration. It is found that 50% of the exergy is being lost even though a big amount of waste heat is being recovered.

A laboratory study of cotton gin waste pyrolysis

The disposal of wastes associated with the processing of cotton is posing great problems in some ginning sites in Greece. Traditional disposal methods, such as open-air incineration and landfilling are no longer adequate due to increasing environmental concerns. This paper evaluates cotton gin wastes as an energy resource by studying the effect of temperature on the product yields in their pyrolysis. Experiments were carried out in a captive sample batch reactor at 1 bar in a helium atmosphere. The heating rate was 80–100°C s−1 and the temperature range studied was 350–850°C. The pyrolysis yielded char and gaseous products. Liquids and tar were produced in very small quantities. The gaseous products yield increased with temperature in contrast to the yield of char. The peak temperature at which the percentage of gaseous products was equal to the percentage of char was 550°C; above this temperature the percentage of gaseous products was higher than that of the char. Gases contained a high percentage of CO and H2 increased with temperature. Experimental data combined with a first-order kinetic model was used to estimate the kinetic parameters of total weight loss and the yield of CO, CH4 and H2.

The Optimal use of Renewable Energy Sources—The Case of Lemnos Island

The efficient use of renewable energy sources (RES) is one of the major issues in the modern energy sector. The objective of this work was to examine the potential of wind energy, solar energy (e.g., photovoltaics), and biomass energy sources to meet the current energy use in the island of Lemnos in Greece. An optimization methodology was applied to the energy system of the island, where various RES are abundant and could be exploited to satisfy part of the islands energy needs. An optimization model has been developed having as an objective the satisfaction of Lemnos Island energy needs from RES taking into consideration a multiplicity of criteria such as environmental impacts, energy demand, energy cost, and resources availability. A series of solutions have resulted, based on deterministic model runs, providing decision makers the flexibility to choose the appropriate solution based on the given situation.

Exergy analysis of geothermal electricity using the Kalina cycle

The geothermal energy that is stored in the earth is so vast that could supply all the energy needed by humanity. The difficulty in tapping this energy lies in its diffusivity. The geothermal energy in regions near volcanoes is close to the surface and easy to use economically. In this paper a vapour dominated system will be examined. The electricity that is produced from such a system is economically and environmentally in a better position than the electricity produced from coal or diesel. The Kalina cycle will be used in this system and an exergy analysis is performed. The Kalina cycle is a new concept in power generation and uses a mixture of 70% ammonia and 30% water as the working fluid with the potential to increase the exergy efficiency over the Rankine cycle. The exergy analysis will provide a qualitative and quantitative picture of the process.

Exergetic life cycle assessment of a grid-connected, polycrystalline silicon photovoltaic system

PurposeNowadays, the intensive use of natural resources in order to satisfy the increasing energy demand suggests a threat to the implementation of the principles of sustainable development. The present study attempts to approach thermodynamically the depletion of natural resources in the methodological framework and the principles of life cycle assessment (LCA).MethodsAn environmental decision support tool is studied, the exergetic life cycle assessment (ELCA). It arises from the convergence of the LCA and exergy analysis (EA) methodologies and attempts to identify the exergetic parameters that are related to the life cycle of the examined system or process. The ELCA methodology, beside the fact that it locates the system parts which involve greater exergy losses, examines the depletion of natural resources (biotic and abiotic) and the sustainable prospective of the examined system or process, under the scope of exergy. In order to obtain concrete results, the ELCA methodology is applied to a large-scale, grid-connected, photovoltaic (PV) system with energy storage that is designed to entirely electrify the Greek island of Nisyros.Results and discussionFour discerned cases were studied that reflect the present state and the future development of the PV technology. The exergy flows and balance for the life cycle of the PV system, as they were formed in the ELCA study, showed that the incoming exergy (solar radiation, energy sources, and materials) is not efficiently utilized. The greater exergy losses appear at the stage of the operation of the PV installation. Due to the fact that contribution of the renewable exergy (solar radiation) to the formation of the total incoming exergy of Life Cycle is significant, it emerges that satisfaction of electric power needs with a PV system appears to be exergetic sustainable. The increase of the Life Cycle exergetic efficiency supported by the future technological scenario in contrast to present scenarios emerges from the increased electricity output of the PV system. Consequently, the increased exergetic efficiency involves decreased irreversibility (exergy losses) of the PV system’s life cycle.ConclusionsThe application of ELCA in electricity production technologies exceeds the proven sustainable prospective of the PV systems; however, it aims to show the essence of the application of ELCA methodology in the environmental decision making process. ELCA can be a useful tool for the support and formation of the environmental decision making that can illustrate in terms of exergetic sustainability the examined energy system or process.

Renewable energy systems : the environmental impact approach

High energy consumption and the world population increase will lead to shrinking reserves of fossil fuels. Concern about carbon dioxide emissions may discourage widespread dependence on fossil fuels and encourage the development and use of renewable energy systems employing a variety of technologies Renewable energy systems have themselves an environmental impact. Land use and material employed are two areas that may have an adverse impact on the positive environmental picture of the renewable energy systems. The objective of this paper is to analyse these impacts with the use of a very powerful tool, the Life Cycle Assessment (LCA).

Exergy analysis for power plant alternative designs, part I

Exergy analysis is being used to investigate different design schemes of a power plant in Crete, Greece in two parts. The following cases are analyzed: 1) installation of a steam turbine unit that will utilize heavy fuel oil as fuel, 2) installation of a gas turbine unit that will utilize diesel oil, 3) installation of a 95 MW diesel power plant that uses heavy fuel oil, and 4) installation of a cogeneration unit that will consist of a 70 MW gas turbine and a 25 MW steam turbine. In particular, the conversion of the 25 MW unit (unit No. 5) of the power plant of Linoperamata to a 95 MW cogeneration unit is studied. In this article (Part I) the analysis of the existing unit is performed. All necessary data are obtained from the existing power plants (steam, gas turbine and diesel fuel) located at Linoperamata. Exergy analysis is used for the evaluation of the proposed solutions.

Integration Potentials of Insular Energy Systems to Smart Energy Regions

Abstract Smart energy regions are defined as regions that offer maximal quality of living to their inhabitants with a minimal consumption of energy by intelligently joining of infrastructure (energy, mobility, transport, communication, etc.) on different hierarchical levels (building, district, city). The development of insular energy systems into smart energy regions, due to their special character, is presented with some challenges. The focus of this article is on presenting the potential of insular energy systems transforming into smart energy regions. Insular energy systems are defined based on data retrieved from Energy Information Administration (EIA) and classified according to their size and the nature of their isolation. In terms of this study, two novel indexes are introduced: the necessity index, which quantifies the need, and the ability index, which represents the capability of an insular energy system to develop into a smart one. These indexes are defined for those insular systems that are considered potentially upgradable. The analysis revealed that the main prerequisites to achieve the development of insular energy systems into smart ones are the reduction of GHG emissions, the introduction of political obligation toward promoting environmentally friendly policies, and the increase of RES utilization for energy production.

Electricity from Geothermal Energy with the Kalina Cycle An Exergy Approach

The geothermal energy that is stored in the earth is so vast that could supply all the energy needed by humanity. The difficulty in tapping this energy lies in its diffusivity. The geothermal energy in regions close to volcanoes is close to the surface and easy to use economically. In this paper a vapor dominated system will be examined. The electricity that is produced from such a system is economically and environmentally in a better position than the electricity produced from coal or diesel. The Kalina cycle will be used in this system and an exergy analysis is performed. The Kalina cycle is a new concept in power generation and uses a mixture of 70% ammonia and 30% water as the working fluid with the potential to increase the exergy efficiency over the Rankine cycle. The exergy analysis will provide a qualitative and quantitative picture of the process.