A review on analyzing and evaluating the energy utilization efficiency of countries

Abstract

In recent years, there has been an increasing interest in applying energy and exergy analysis modeling techniques for energy-utilization assessments in order to attain energy saving. In this regard, various approaches have been used to perform the exergy analyses of countries. The main objective of the present study is to evaluate and analyze the energy utilization efficiencies of countries by reviewing the studies conducted on various countries or societies, to which different approaches have been applied. Thermodynamic relations used to perform energy and exergy analyses of countries are given first. The classification of studies conducted and the approaches applied are then investigated in terms of subsectors, such as utility, industrial, residential–commercial, and transportation sectors. Next, the countries considered are evaluated in terms of energy and exergy utilization efficiencies. Finally, the results obtained are discussed. It is expected that the review presented here will provide the investigators with knowledge about how much effective and efficient a country uses its natural resources. This knowledge is also needed for identifying energy efficiency and/or energy conservation opportunities as well as for dictating the energy strategies of a country or a society.

Introduction

After the second half of the twentieth century, the industrial revolution increased the utilization of the new technological products in our daily live. This caused more consumption of the energy and made it an inseparable part of the life. Moreover, the rate of energy consumption per capita has become a criterion of success in the development for countries. Providing the growing society with the energy ceaselessly, safely and sufficiently needs to have an increasing amount of productivity and activity in this area.

Fossil fuels reserves, which provide the most part of the energy sources of the whole world, are limited and gradually decreasing. Noticing this by the large amounts of people obliged the countries to go over again their energy policy and to stop wasting it. The energy policy agenda has also changed significantly since the days of the 1973 and 1979 oil crises. Currently, it is possible to identify three policy themes related to the energy sector. These are as follows [1]: (a) the traditional energy policy agenda relating to security of energy supply, (b) concern about the environmental impact of energy, its production, transformation and use, and (c) the trend towards liberalization and the enhancement of competition in energy markets, notably in the electricity and gas sectors. This situation led the scientists to develop the cycling ways of the energy and to get more efficiency from the energy, which we own. New methods are about energy and exergy analysis.

The energy balance is a basic method of any process investigation. It makes the energy analysis possible, points at the needs to improve the process, is the key to optimization and is the basis to developing the exergy balance. Analysis of the energy balance results would disclose the efficiency of energy utilization in particular parts of the process and allow comparing the efficiency and the process parameters with the currently achievable values in the most modern installations. They will establish also the priority of the processes requiring consideration, either because of their excessive energy consumption or because of their particularly low efficiency.

For these reasons, the modern approach to process analysis uses the exergy analysis, which provides a more realistic view of the process. The exergy analysis is the modern thermodynamic method used as an advanced and useful tool for engineering process evaluation [2], [3]. Whereas the energy analysis is based on the First Law of Thermodynamics, the exergy analysis is based on both the First and Second Laws of Thermodynamics. Both analyses utilize also the material balance for the systems considered.

The exergy of an energy form or a substance is a measure of its usefulness or quality or potential to cause change [4]. Exergy is defined as the maximum work, which can be produced by a system or a flow of matter or energy at it comes to equilibrium with a specified reference environment. Unlike energy, exergy is conserved only during ideal processes and destroyed due to irreversibilities in real processes [5].

According to Szargut et al. [2], the main purpose of exergy analysis is to discover the causes and to estimate quantitatively the magnitude of the imperfection of a thermal or chemical process. Exergy analysis leads to a better understanding of the influence of thermodynamic phenomena on the process effectiveness, comparison of the importance of different thermodynamic factors, and the determination of the most effective ways of improving the process under consideration Dincer [6] reported the linkages between energy and exergy, exergy and the environment, energy and sustainable development, and energy policy making and exergy in detail. He provided the following key points to highlight the importance of the exergy and its essential utilization in numerous ways.

• It is a primary tool in best addressing the impact of energy resource utilization on the environment.

• It is an effective method using the conservation of mass and conservation of energy principles together with the second law of thermodynamics for the design and analysis of energy systems.

• It is a suitable technique for furthering the goal of more efficient energy-resource use, for it enables the locations, types, and true magnitudes of wastes and losses to be determined.

• It is an efficient technique revealing whether or not and by how much it is possible to design more efficient energy systems by reducing the inefficiencies in existing systems. It is a key component in obtaining sustainable development.

• It has a crucial role in energy policy-making activities.

Wall and Gong [7] summarized the historical development of the concept ‘exergy’, while Cengel [8] also described the meaning of exergy in daily life. He writes: “Exergy can be viewed as the opportunities that we have and the exergy destruction as the opportunities wasted. The exergy of a person in daily life can be viewed as the best job that person can do under specific conditions. The difference between the exergy of a person and the actual performance under those conditions can be viewed as the irreversibility or the exergy destruction.” A true understanding of exergy and the insights it can provide into the efficiency, environmental impact and sustainability of energy systems, are required for the engineer or scientist working in the area of energy systems and the environment [9].

The method of exergy analysis has been applied to a wide variety of thermal and thermo chemical systems. A particular thermo dynamical system is the society, for example, of a country or a region [10]. Recently, there has been an increasing interest in applying energy and exergy analysis modeling techniques for energy-utilization assessments in order to attain energy saving.

The main objective of the present study is to evaluate and analyze the energy utilization efficiencies of countries by reviewing the studies conducted on various countries or societies, to which different approaches have been applied. In this regard, thermodynamic relations used to perform energy and exergy analyses of countries are given first. The classification of studies conducted and the approaches applied are then investigated in terms of subsectors, such as utility, industrial, residential–commercial, and transportation sectors. Finally, the results obtained are discussed.