Energy is considered a prime agent in the generation of wealth and a significant factor in economic development. The importance of energy in economic development is recognized universally and historical data verify that there is a strong relationship between the availability of energy and economic activity. Although in the early 1970s, after the oil crisis, the concern was on the cost of energy, during the past two decades the risk and reality of environmental degradation have become more apparent. The growing evidence of environmental problems is due to a combination of several factors since the environmental impact of human activities has grown dramatically. This is due to the increase of the world population, energy consumption, and industrial activity. Achieving solutions to the environmental problems that humanity faces today requires long-term potential actions for sustainable development. In this respect, renewable energy resources appear to be one of the most efficient and effective solutions.
A few years ago, most environmental analysis and legal control instruments concentrated on conventional pollutants such as sulfur dioxide (SO2), nitrogen oxides (NOx), particulates, and carbon monoxide (CO). Recently, however, environmental concern has extended to the control of hazardous air pollutants, which are usually toxic chemical substances harmful even in small doses, as well as to other globally significant pollutants such as carbon dioxide (CO2). Additionally, developments in industrial processes and structures have led to new environmental problems. Carbon dioxide as a greenhouse gas plays a vital role in global warming. Studies show that it is responsible for about two thirds of the enhanced greenhouse effect. A significant contribution to the CO2 emitted to the atmosphere is attributed to fossil fuel combustion (EPA, 2007).
The United Nations Conference on Environment and Development (UNCED), held in Rio de Janeiro, Brazil, in June 1992, addressed the challenges of achieving worldwide sustainable development. The goal of sustainable development cannot be realized without major changes in the world's energy system. Accordingly, Agenda 21, which was adopted by UNCED, called for "new policies or programs, as appropriate, to increase the contribution of environmentally safe and sound and cost-effective energy systems, particularly new and renewable ones, through less polluting and more efficient energy production, transmission, distribution, and use."
The division for sustainable development of the United Nations Department of Economics and Social Affairs defined sustainable development as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs." Agenda 21, the Rio declaration on environment and development, was adopted by 178 governments. This is a comprehensive plan of action to be taken globally, nationally, and locally by organizations of the United Nations system, governments, and major groups in every area in which there are human impacts on the environment (United Nations, 1992). Many factors can help to achieve sustainable development. Today, one of the main factors that must be considered is energy and one of the most important issues is the requirement for a supply of energy that is fully sustainable (Ronsen, 1996; Dincer and Ronsen, 1998). A secure supply of energy is generally agreed to be a necessary but not a sufficient requirement for development within a society. Furthermore, for a sustainable development within a society, it is required that a sustainable supply of energy and effective and efficient utilization of energy resources are secure. Such a supply in the long term should be readily available at reasonable cost, sustainable, and able to be utilized for all the required tasks without causing negative societal impacts. This is the reason why there is a close connection between renewable sources of energy and sustainable development.
Sustainable development is a serious policy concept. In addition to the definition just given, it can be considered as development that must not carry the seeds of destruction, because such development is unsustainable. The concept of sustainability has its origin in fisheries and forest management in which prevailing management practices, such as overfishing or single-species cultivation, work for limited time, then yield diminishing results and eventually endanger the resource. Therefore, sustainable management practices should not aim for maximum yield in the short run but smaller yields that can be sustained over time.
Pollution depends on energy consumption. Today, the world daily oil consumption is 80 million barrels. Despite the well-known consequences of fossil fuel combustion on the environment, this is expected to increase to 123 million barrels per day by the year 2025 (Worldwatch, 2007). A large number of factors are significant in the determination of the future level of energy consumption and production. Such factors include population growth, economic performance, consumer tastes, and technological developments. Furthermore, government policies concerning energy and developments in the world energy markets certainly play a key role in the future level and pattern of energy production and consumption (Dincer, 1999).
In 1984, 25% of the world population consumed 70% of the total energy supply, while the remaining 75% of the population was left with 30%. If the total population were to have the same consumption per inhabitant as the Organization for Economic Cooperation and Development (OECD) member countries have on average, it would result in an increase in the 1984 world energy demand from 10 TW (tera, T = 1012) to approximately 30 TW. An expected increase in the population from 4.7 billion in 1984 to 8.2 billion in 2020 would even raise the figure to 50 TW.
The total primary energy demand in the world increased from 5,536 GTOE3 in 1971 to 10,345 GTOE in 2002, representing an average annual increase of 2%. It is important, however, to note that the average worldwide growth from 2001 to 2004 was 3.7%, with the increase from 2003 to 2004 being 4.3%. The rate of growth is rising mainly due to the very rapid growth in Pacific Asia, which recorded an average increase from 2001 to 2004 of 8.6%.
The major sectors using primary energy sources include electrical power, transportation, heating, and industry. The International Energy Agency (IEA) data shows that the electricity demand almost tripled from 1971 to 2002. This is because electricity is a very convenient form of energy to transport and use. Although primary energy use in all sectors has increased, their relative shares have decreased, except for transportation and electricity. The relative share of primary energy for electricity production in the world increased from about 20% in 1971 to about 30% in 2002 as electricity became the preferred form of energy for all applications.
Fueled by high increases in China and India, worldwide energy consumption may continue to increase at rates between 3% and 5% for at least a few more years. However, such high rates of increase cannot continue for too long. Even at a 2% increase per year, the primary energy demand of 2002 would double by 2037 and triple by 2057. With such high energy demand expected 50 years from now, it is important to look at all the available strategies to fulfill the future demand, especially for electricity and transportation.
At present, 95% of all energy for transportation comes from oil. Therefore, the available oil resources and their production rates and prices greatly influence the future changes in transportation. An obvious replacement for oil would be biofuels such as ethanol, methanol, biodiesel, and biogases. It is believed that hydrogen is another alternative because, if it could be produced economically from renewable energy sources, it could provide a clean transportation alternative for the future.
Natural gas will be used at rapidly increasing rates to make up for the shortfall in oil production; however, it may not last much longer than oil itself at higher rates of consumption. Coal is the largest fossil resource available and the most problematic due to environmental concerns. All indications show that coal use will continue to grow for power production around the world because of expected increases in China, India, Australia, and other countries. This, however, would be unsustainable, from the environmental point of view, unless advanced clean coal technologies with carbon sequestration are deployed.
Another parameter to be considered is the world population. This is expected to double by the middle of this century and as economic development will certainly continue to grow, the global demand for energy is expected
3 TOE = Tons of oil equivalent = 41.868 GJ (giga, G = 109).
to increase. For example, the most populous country, China, increased its primary energy consumption by 15% from 2003 to 2004. Today, much evidence exists to suggest that the future of our planet and the generations to come will be negatively affected if humans keep degrading the environment. Currently, three environmental problems are internationally known: acid precipitation, the stratospheric ozone depletion, and global climate change. These issues are analyzed in more detail in the following subsections.
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