Introduction

Our civilization and the ever-increasing high standard of living that we have been enjoying in recent times are the direct outcome of our ability to harness all forms of energy usefully so as to achieve the physical comfort and economic benefits that we expect and demand� The quality of life and the survival of all living creatures on earth can be closely identified with the conservation of our earth’s resources while aiming to maintain a cleaner environment� We recognized that the whole fields of energy and the environment are interrelated in a complex manner with numerous influencing factors and issues� These need integration so that we can approach the problems to be faced more knowledgably and effectively� For example, the topic of “energy” cannot be considered without considering the contributions of factors that can be described not only in terms of thermodynamics, physics, and chemistry, but also in terms of other fields, including economics, sociology, ecology, and politics�

Over the millennia of human existence, the main sources of energy for the production of heat or work became increasingly dependent and have been derived from fuels either in the form of fossilized resources of various types or the more recent origin derived primarily from living matter of plant, animal, or marine origin� The bulk of the controllable energy available to us at present is obtained through the combustion of fossil fuels� These fuels can be considered as non-renewable sources of ancient stored solar energy that took many millions of years to be formed� By virtue of their chemical structure they can release readily and rapidly, under the appropriate conditions, sufficient energy in the form of heat that can be converted to mechanical or electrical work in suitable work-producing devices commonly described as engines� Under exceptional circumstances their chemical energy ideally can be converted fully to electrical/mechanical work such as in the ideal fuel cell�

It is important to note throughout that the main issue confronting our civilization at present and in the years to come is the adequate and economic provision of energy, while continuing to improve the quality of life and ensuring at the same time a cleaner environment�

The following is a brief review of the most common forms of energy encountered in engineering systems and their processes:

Internal energy is the sum of microscopic forms of energy of a system, which is related to the molecular structure and the degree of molecular activity� It is a function of the sum of the kinetic and potential energies of the molecules�

Sensible energy refers to the kinetic energy of the molecules of the system and is a strong function of temperature�

Latent energy is the internal energy associated with phase changes of the system, for example, from liquid to vapor�

Formation energy refers to the chemical bonding energy of the system� Nuclear energy is associated with bonding within the nucleus of the

atom, which is partly released during nuclear reactions�

The bulk of the energy resources available to us can be viewed to be solar in origin� These may be either of the direct type, arising from the present incidence of solar energy on earth, or the energy available in the form of fossil fuels, which can be considered as an indirect, ancient, and nonrenewable form of stored solar energy that may have taken millions of years to be processed into the form of common fossil fuels� As shown in Figure 1�1, the combustion of fossil fuels at the present time can be viewed to be merely a process that releases some of the solar energy and carbon dioxide used during the ancient photosynthesis process and stored millions of years ago but with many orders of magnitude at different time periods�

Other forms of indirect solar heating are also responsible for producing the following forms of energy:

1� Energy derived from bio-sources such as plants, wood, and animal waste

2� Wind energy associated with air movement from breezes to hurricanes

3� Energy derived from waves, sea currents, and hydropower

Other forms of non-solar in origin energy mainly include the following:

1� Nuclear energy that is derived mainly from nuclear fission processes 2� Nuclear fusion energy that may become at some time in the far

distant future potentially available for implementation as a usable energy resource

3� Geothermal energy derived from hot sources within the earth’s crust

4� Other sources of energy of lesser practical importance that may become available in limited and specific applications such as through the oxidation of certain metallic or non-metallic materials

An estimate of the average solar power received by earth is 173 PW (173 × 1015 W)� Approximately only 47% of this energy is converted directly into heat while around 30% is reflected back into space� Around 23% of the energy received is used in the evaporation of water� These figures are absolutely huge in comparison to merely around 6 TW (6�0 × 1012) estimated to be the average power consumed in recent years for human activities�

1.4.1 Hydropower

Electricity generated by hydropower was dominant for many decades as an economic energy resource� Dams were built all over the world to provide vast supplies of electricity at a relatively low cost� Industrialized nations have exploited most of their likely sources for hydroelectric power� Only a limited potential for further development may be still available mainly with less developed nations� The exploitation of this source of energy is subject also to the growing concerns about the negative environmental and social impacts of the development of such large scale projects�

1.4.2 Ocean/Wave Energy

Harnessing the energy of the seas, such as through the tides, ocean currents, and waves, is under continued research and development, but it still requires much further effort, time, and expenditure of resources to make it sufficiently successful even in relatively small scale units� It is through the change in the potential and kinetic energy of water elevation and motion that it can be captured to produce electricity� This is done through a variety of measures that would include paddles or oscillating water columns� A major limitation associated with these systems is their tendency to disturb seriously the ecology of their surroundings such as of tidal basins due to changes to the tidal flow and silting�

1.4.3 Wind Energy

Wind energy utilization represents a very small fraction of the current energy demand of virtually all countries� This fraction has been increasing, albeit slowly over the years� A wide variety of radically different designs and sizes of wind turbines are involved� Often their location is not optimum and they are far away from where there is much demand for their electrical output�

Wind as a source of energy is variable, oscillatory, and unpredictable� It depends on the location, time, elevation, and direction� The rated output of a wind turbine is seldom achieved for long� The power that can be obtained ideally is proportional to the cube of the prevailing wind speed, which increases significantly with the height above the ground� Hence, wind turbines are usually mounted on very tall supporting towers� The efficiency of wind turbines at any location and for any set of equipment depends on the strength and direction of the prevailing wind� Additional losses are incurred to get the electrical output linked into the grid� Also, the transmission and

integration of the electrical output from various units is costly because it involves a number of isolated individual units�

The output voltage and frequency of the electricity generated are not constant and not optimum for transfer via the grid system� Relatively complex control and rectifying equipment and procedures are needed, with often huge-capacity batteries provided for electrical storage� These all contribute to additional losses, increased costs, and lowering of the conversion efficiency� At present, the cost of electricity produced, which is high and variable with time and seasons, is highly dependent on taxation and government subsidies� The price charged for the electricity can be artificially inflated by supportive consumers�

Wind turbines are expensive, very bulky, difficult to construct and install especially in offshore sites, and maintenance is expensive and unwieldy� Very large sizes are required for acceptable load and efficiency� A typical example is a horizontal axis turbine rated at 200 kW of three blades with around 15 m blades on a 25 m tower� The efficiency of electrical power generation drops significantly at part load requiring a threshold of wind speed for activation� Also, safeguards are needed to protect against excessive wind speeds such as in storms and gales�

Wind turbines tend to be considered by some to be ecologically unsightly and noisy with negative consequences to cattle, animals, birds, and farming activities� The real estate cost of a wind farm can be substantial and those installed at sea remain largely insufficiently developed� Nevertheless, harnessing the energy of the wind has grown significantly in sophistication, capacity, and distribution all over the world in recent years, since it represents in principle a relatively green form and cheap renewable source of energy� However, time is needed before wind-derived energy will be contributing a sufficiently substantial fraction of total energy requirements worldwide� A main challenge associated with the exploitation of wind energy is its variable and intermittent nature, which requires the maintenance of costly reserves of alternative power capacity to supply the energy needed during periods of low speed winds� Sufficiently extensive infrastructure is also required for the control and distribution of the generated power to points of its consumption� Mainly with the aid of measures such as government tax incentives and surcharges to consumers, wind power is being made an increasingly attractive and a viable renewable option to supplement the energy produced through the combustion of fossil fuels, particularly for electric power generation�

1.4.4 Solar Energy

Solar energy’s contributions to our world are many and include the making of fossil fuels, hydropower, biofuels, wind, ocean currents, rain, thermal sea gradients, and so on� The energy available is intermittent and dependent on time of the day, time of the year, location, elevation, season, angle of incidence,

and whether cloudy or clear� On the whole, there have been relatively limited deliberate solar energy applications for direct power production or heating� High-intensity solar energy tends to be located largely in sparsely populated areas of the globe and requires for its exploitation large areas of land�

Solar energy in principle is renewable, free, clean, and abundant� Its increased exploitation should contribute towards reducing the consumption of fossil fuels and associated harmful exhaust emissions including the greenhouse gases� The likelihood of such increased exploitation of solar energy is seriously governed by the cost and availability of fossil fuels� Also, tax incentives for its use with partial capital support for solar devices can be very influential in increasing its usage�

Thermal energy as received on earth is of multi-wavelengths and its exploitation for the production of work is subject to Carnot cycle limitations� The energy on average is very dilute with approximately only 1 kW/m2 (or 1 mW/mm2) received� Some solar energy is absorbed as it travels into the atmosphere due to the presence of CO2, H2O, and O3, and only relatively low temperatures are achieved unless special measures are devised to have it concentrated� Solar energy may be used for air conditioning and cooling but quite less effectively than through the expenditure of electrical work� However, there are good prospects for its limited usage for desalination of sea water�

Green vegetation utilizes solar energy at extremely low efficiency (e�g�, <1�0%)� Additionally, much land is used and energy expenditure is required for planting, fertilizers, harvesting, collection, transport, and processing� Also, additionally, emissions are produced with high costs involved� Solar applications are well suited for low temperature domestic water heating use� Mainly a variety of flat plate collectors of different designs, size, and construction are employed such as that shown schematically in Figure 1�2� These tend to be simple and made of sheets of flat glass placed at an angle over shallow black bases� These solar collectors are viable only for producing

warm water and its temperature remains lower than 100°C� Such collectors may be driven either entirely via natural convection, as shown in Figure 1�3, or electrically driven pumps can be incorporated� To provide all the heat required by a typical house a prohibitively large mass of water is required� Some special fluids occasionally may be utilized to exploit their latent heat of fusion such as through melting�

Solar water heaters tend to be bulky, requiring pure water� Their effectiveness may deteriorate with time� They are unsightly and for better effectiveness they need to be oriented to the moving sun� Collectors receive solar heat and emit some of it� Accordingly, the temperature reached in a solar heating application will depend on a balance between the rate of heat received and that lost to the surroundings�

Solar cells produce electricity from incident sunlight on the surfaces of special materials such as silicon by emitting electrons from the photons of the sunlight� Photovoltaic energy conversion units are semiconductors where solar energy incidence produces free electrons� They tend to be of rather low efficiency, expensive, and of very small outputs and unit sizes� Their output can deteriorate with age, elements, and accumulating dust and scratches on their receiving surfaces� Hence, the electricity produced from solar energy can be much more expensive than electrical energy produced from fossil fuel fired central power stations�

Parabolic mirrors may concentrate light into high-temperature energy but over much smaller areas� They are limited in their application, inefficient, unreliable, and with safety concerns� There are some very limited applications in metallurgy and metal oxide refining while supplementing with the use of natural gas to produce pure metals and synthesis gas (i�e�, CO and H2)�

There are some very long-term speculative proposals to produce electricity from solar energy in outer space and beam it to earth via micro-wave power� This proposal remains unrealistic with great expense and associated with very serious safety hazards�

The technology of the exploitation of solar power is being developed increasingly globally in recent years; but it remains at the present time generally insufficiently cost competitive with large-scale electricity production from sources based on using fossil fuels, hydropower, or nuclear energy� Solar energy appears increasingly attractive for smaller, stand-alone, remote, and specialized applications and for providing a low-temperature energy source for heating and drying purposes, especially for domestic applications� Simple solar collector installations manufactured locally are being increasingly used in many parts of the world to provide hot water domestically in small units, often without the need for the supply of electric energy (Figure 1�4)�

Research into developing new materials for photovoltaic electric generation continues to contribute toward reducing costs and improving durability and the conversion efficiency of solar energy into electricity� However, so far solar energy has not made sufficiently substantial contributions to the global electric energy supplies�

1.4.5 Geothermal Energy

Geothermal energy may be competitive as a source of thermal energy for district heating and as a base electrical power provider in areas where geothermal energy sources of the right quality and capacity are available� Iceland is an example where relatively accessible naturally occurring underground heat sources for the production of steam of the right quality for power generation and hot water for domestic heating are available in some locations� However, the exploitation of geothermal energy in general so far appears to have its serious limitations such as those of environmental, social, economic, geographical, or variable quality nature�

1.4.6 Nuclear Energy

Nuclear power so far represents a relatively small fraction of the total global energy mix and less than 20% of global electrical energy production� Certain countries such as France tend to produce and use very much more than this average� However, there are lingering serious limiting concerns associated with the building and operation of nuclear energy facilities in general and in particular in locations prone to the occurrence of earthquakes such as in Japan� These concerns include additionally high operational and capital costs, serious potential safety concerns, severe sitting constraints, limitations on nuclear fuels processing and supplies, disposal of spent fuels, and security issues� These have been considered to be sufficiently serious more recently to have prompted some countries to be reluctant to build new nuclear plants and even phase out existing ones earlier than originally planned�

A listing of the estimates of the relative size of energy and power of a wide range of common processes and sources are listed in Table 1�1�

It is important to keep in mind that there are too many sources of potential losses and wastage in the path of the generation, processing, transport, and distribution of energy to the point of its end use� These losses vary very widely and can amount to a very large fraction of the energy initially available to start with� For example, as shown in Table 1�2, the electrical energy available to be used at a domestic electric light switch can be only a small fraction of the electric energy generated and supplied eventually to the consumer� It is yet even a smaller fraction of the chemical energy of the fossil fuel that was burned to raise steam and generate the electricity� It is also yet a very minute fraction of the initial ancient solar energy that fell on earth millions of years ago, which was responsible for producing in the first place the stored energy in the fossil fuel employed� Obviously, it is imperative in any analysis of the environmental impact and effectiveness of energy-consuming devices and their processes to identify and pursue the entire energy path from its initial production stage to its ultimate consumption� This needs to be performed while considering all the possible potential losses along the way and the associated cumulative emissions and their consequent impact on the environment� Unfortunately, to date this remains an uncommon practice rarely followed in virtually all of our operations (Figure 1�5)�

As an example, it is highly misleading to talk of a “zero emission electric car” or that hydrogen needs to be considered as a clean renewable fuel associated with producing no undesirable emissions� Often, there is an excessive amount of energy input and associated emissions with the production of the electric power or the manufacture of hydrogen, albeit at a different location from where the consumption takes place�

Table 1�2 shows an example of a possible accounting of the relative effectiveness and associated degradation and losses in ancient solar energy that could have been responsible in the first instance for the formation of a coal used in electric power generation to its ultimate fraction as an electric energy at its point of usage�

This would show that only a few percent of the energy of the coal in place is usefully available eventually as electricity (i�e�, for the example shown, 0�60 × 0�80 × 0�90 × 0�70 × 0�35 × 0�60 × 0�60 = 0�038), which is around 380 parts per million of the original solar energy that could have gone to produce the coal in the first place�

Another important consideration is disparity in the effectiveness of the recovery and processing of fuel resources and hence the cost of energy derived from a fossil fuel from one location to another worldwide� For example, the economic and environmental costs associated with the mining, processing, and producing petroleum from Canadian oilsands can be more than an order of magnitude greater than those from conventional land-based rich oil reservoirs in a region such as that of Southern Iraq, which is believed to have still significant amounts of untapped oil and gas reserves that can be conventionally extracted and shipped economically�

Virtually every energy source available is being increasingly harnessed and exploited� Obviously, the efficiency of the utilization of these energy resources available is very important in reducing costs and the overall current and future demand for primary energy resources and mitigating the associated environmental challenges� The conversion links in the complex energy chain from the

primary energy resources to eventual energy services must be fully optimized� The average overall energy utilization efficiency worldwide at present may be as low as 10%, while more recently in some developed countries it may be higher than 30%� This would indicate that there is much potential for improvement in the effective utilization of energy globally in the coming years� But, there are overwhelming influencing factors yet to be brought into effective control� These include the fact that the average energy consumption per capita worldwide in recent years tended to increase� This trend may be expected to continue increasing in the coming years� This is further compounded by the continuing increases in the average standard of living, life expectancy, and the population of the world� An example of poor management and wastage of oil resources is the early days of oil exploitation (Figure 1�6)� Another more recent example is the continuing practice in some locations of flaring huge quantities of fuel gas associated with liquid petroleum production�

Our civilization has been sustained for millennia by the exploitation of fossil fuel resources mainly through combustion to produce the needed energy, which is solar in origin� The consumption rates of these resources tend to exceed their rates of replenishment� Other forms of energy of the non-fossil type are available but contribute only a small fraction of our energy needs at present or in the near future� The effectiveness of the utilization of fuel energy usefully has been generally low� This is being continually improved in recent years while the negative contribution to the quality of the environment is being minimized� It is imperative in any analysis of the environmental impact and the effectiveness of energy-consuming devices and their processes to identify and pursue the entire energy path from its initial production stage to its ultimate utilization�