Chapter 1

NCER—An Overview

Energy is the capacity of a physical system to perform work. It exists in several forms such as heat, mechanical (potential and kinetic), light, electrical, or other forms of energy. According to the law of conservation of energy, the total energy of a system remains constant. However, energy may transform from one form into another form. The SI unit of energy is the joule (J) or Newton-meter (N × m). Joule is also the SI unit of work.

Energy is now well recognized as an essential parameter of socio-techno-economic development of any system and it is presently used as the measure of the standard of living, quality of life, civilization, and culture of a country. Both the Industrial Revolution in the 19th century, specifically after World War II, and the awareness of energy importance have revolutionized the fuller utilization of all the known and unknown energy reservoirs. As a result of this process, energy conversion, management, resource recovery, and storage have attracted the attention of the scientists, engineers, and technologists, which made them accept the challenges of rising demand of energy requirements.

Energy consumption dictates social inequalities and disparities between one country and the other. Conventional energy sources such as fossil fuels (coal, natural gas, and oil) and nuclear fuels (uranium and thorium) have been a resource of world energy needs since the Industrial Revolution. However, the fast depleting rate of conventional energy resources, climate change and environmental problems, and 1973 oil crisis forced the countries to redefine their energy development objective to use clean, affordable, and secure sources of energy to continue eco-friendly technological progress. Non-conventional energy resources from the sun (such as solar light, heat, and wind), the earth (such as geothermal, micro-hydroelectric, and bio-mass and bio gas), and the sea (such as tides, waves, and ocean thermal) are just some examples of energy sources that meet such objectives, and these energy resources have risen to the challenge of meeting the increasing energy demands of the present and future generations.

Oil shales are perhaps the oldest energy resource used in the ancient days for producing shale oil very much like petroleum and diesel. This important energy resource is available in abundance in many countries but high cost of shale oil production and associated environmental problem have restricted their development.

This chapter outlines the various aspects related with all the possible conventional and non-conventional resources, principles of conversion, pros and cons, applications, and storage of energy resources.

1.1 HISTORY OF HUMAN CIVILIZATION

Human civilization has taken a long way to reach the present technology made society. This movement is based on consuming or providing energy for social obligations. The following five indicators of social development (such as quality of life, lifestyle, and standard of living) have always been considered as bare minimum. Techno-economic development maintained pace with social development:

1. Food (Roti)
2. Cloth (Kapada)
3. Shelter (Makan)
4. Health (Swasthya)
5. Education (Siksha)

It may be difficult to find out exactly how people’s senses of values have changed through history. However, to some extent, it can calculate how their material wealth has changed, and how much energy has been used for that purpose (see Figs. 1.1 and 1.2). For not only can it be worked out how much energy has been consumed as food, but also know that as material wealth increases, increasing amounts of energy will be needed to create that wealth.

Figure 1.1 Bar chart for daily energy used by a man through human history

Figure 1.2 World population and daily per capita energy consumption through human history

1.1.1 Primitive Man

About two million years ago, there appeared a primitive man—an ape man who could walk on two legs and uses his hands and had the intelligence to make simple tools. His energy consumption was no more than was needed for basic biological survival and is believed to have been around 3,000 kilocalories a day (see Figs. 1.1 and 1.2). Therefore, his energy needs were no more than those of any other animal, and nothing could have been further from modern materialistic society than this totally natural existence of our early forerunner.

Human civilization is considered with no fire and no hunting. Only requirement was food. The earliest humans probably lived primarily on scavenging, not actual hunting. Early humans in the Lower Paleolithic lived in mixed habitats that allowed them to collect seafood, eggs, nuts, and fruits besides scavenging. Rather than killing large animals for meat, they used carcasses of large animals killed by other predators or carcasses from animals that died by natural causes.

1.1.2 Hunting Man

A hunter–gatherer or forager society is one in which most or all food is obtained from wild plants and animals in contrast to agricultural societies that rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of homo, and all modern humans were hunter–gatherers until around 10,000 years ago. Hunter–gatherer societies tend to be relatively mobile, given their reliance upon the ability of a given natural environment to provide sufficient resources in order to sustain their population and the variable availability of these resources owing to local climatic and seasonal conditions. Individual band societies tend to be small in number (10–30 individuals), but these may gather together seasonally to temporarily from a large group (100 or more) when resources are abundant. In a few places where the environment is especially productive, such as that of the Pacific Northwest coast or Jomon-era Japan, hunter–gatherers are able to settle permanently.

In the early periods, a single tool is usually made from the core of the flint, resulting in an instrument that can be used in a fairly rough manner for either cutting or scraping. Hundreds of thousands of years later, craftsmen have become skilled at forming the flakes themselves into implements of various kinds, producing specialist tools for cutting, scraping, gouging, or boring, as well as sharp points for arrow and spear heads. These sophisticated stone tools, in their turn, make it possible to carve materials such as antler or bone to create even sharper points or more complex shapes (such as hooks or needles).

The predominant use of stone as the material for tools has caused this period to be known as the Stone Age. The specialization of work also involved creating specialized tools such as fishing nets and hooks and bone harpoons.

1.1.3 Early Agricultural Man

Following the development of agriculture, hunters–gatherers have been displaced by farming or pastoralist groups in most parts of the world. Only a few contemporary societies are classified as hunters–gatherers, and many supplements, sometimes extensively, their foraging activity with farming and/or keeping animals. The transition into the subsequent Neolithic period is chiefly defined by the unprecedented development of nascent agricultural practices. Agriculture originated and spread in several different areas including the Middle East, Asia, Mesoamerica, and the Andes beginning as early as 10,000 years ago. Forest gardening was also being used as a food production system in various parts of the world over this period. Forest gardens originated in prehistoric times along jungle-clad river banks and in the wet foothills of monsoon regions.

1.1.4 Advanced Agricultural Man

Following these revolutionary changes in life and culture in places such as Mesopotamia and parts of Africa, world population rose again to 30 million; daily per capita energy consumption reached 12,000 kilocalories. Therefore, the transition from hunting man to early agricultural man, as we might call this next stage, was relatively rapid when compared with the previous pace of change. Even so, it still took around 20,000 years. They are considered as using advanced agricultural activities together with tools and domestic animals. In the gradual process of families improving their immediate environment, useful trees, and vine species were identified, protected, and improved, whilst undesirable species were eliminated. Eventually, superior foreign species were selected and incorporated into the gardens. Many groups continued their hunter-gatherer ways of life, although their numbers have perpetually declined partly as a result of pressure from growing agricultural and pastoral communities. Many of them reside in arid regions and tropical forests in the developing world. Areas that were formerly available to hunters–gatherers were—and continue to be—encroached upon by the settlements of agriculturalists. In the resulting competition for land use, hunter-gatherer societies either adopted these practices or moved to other areas. In addition, Jared Diamond has blamed a decline in the availability of wild foods, particularly animal resources. In North and South America, for example, most large mammal species had gone extinct by the end of the Pleistocene, according to Diamond, because of overexploitation by humans although the overkill hypothesis he advocates is strongly contested. As the number and size of agricultural societies increased, they expanded into lands traditionally used by hunters–gatherers. This process of agriculture-driven expansion led to the development of the first forms of government in agricultural centres such as the Fertile Crescent, Ancient India, Ancient China, Olmec, Sub-Saharan Africa, and Norte Chico.

As a result of the now near-universal human reliance upon agriculture, the few contemporary hunter-gatherer cultures usually live in areas unsuitable for agricultural use. As agricultural production increased, technology and culture progressed; villages became towns, and towns became cities. As organizational structures to unite these groups of settlers were developed, city-states, or small states based on the city as a unit, came into being. The Babylonian dynasty, which had started out from one of these city-states, is believed to have united all of the city-states of Mesopotamia into one nation under its control in 2169 BC. This was yet another step toward political sophistication by the time of the birth of Jesus Christ; constant improvements in agriculture and other skills had contributed to an increase in the world’s human population to 250 million. This doubled to 500 million by about 1650, when daily per capita energy consumption had raised again to 26,000 kilocalories. It had taken 5,000 years for early agricultural man to change into ‘advanced agricultural man’, the state of human civilization on the threshold of the industrial revolution.

1.1.5 Industrial Man

In the late 18th century in England, coal was first used to provide the energy to make steam, which in its turn was used to drive engines. These early engines drove spinning machines for cotton, which meant that what had always been manual work was suddenly transformed into work that could be done by a machine. The industrial revolution really did revolutionize industry. Large factories, capable of producing large quantities, sprang up. Society, which for so long had been based on agriculture, invested vast amounts in German Professor J. Liebig’s discovery of how to enhance agricultural yield by using artificial fertilizer that can be produced artificially in a factory. Once this came into use in agriculture, the food production increased with an increased population. Further, even greater numbers could work in the factories. The industrial production of fertilizers and the subsequent rapid rise in agricultural productivity made the first stage of the industrial revolution was complete.

1.1.6 Technological Man

As industrial activity expanded, society became more and more complex and more and more materialistic. However, while mankind had previously always existed in a kind of harmony with the natural environment, the danger arose that those natural bounds might be overstepped. World population soared: one billion (i.e., a thousand million, or a one followed by nine zeroes) in 1850; one and a half billion in 1900. As a result, energy consumption also soared to 77,000 kilocalories per person per day. ‘industrial man’ had taken only a few thousand years to replace agricultural man. Expanding populations and growing materialism have led to clashes among nations, including the two World Wars of the 20th century. These wars themselves have spawned yet more advances in science and technology based on yet more inventions and discoveries. Greater and greater amounts of energy from coal, oil, and nuclear power have been consumed. Thus, mankind armed with so much technical knowledge, numbered 2 billion in 1930, or half a billion more than just 30 years before that. In 1981, there were 4.6 billion of us, or more than double the number 50 years ago. At 2,30,000 kilocalories, a modern person’s daily consumption of energy had reached 100 times that of our primitive forebears. Industrial man had been replaced by ‘technological man’. By calculating the difference between the energy required for biological survival and the total consumed by the technological man and then by comparing that amount with that consumed by primitive man and the difference is almost infinite. Further, remember that it took only hundred years or more for the technological man to change from industrial man.

1.1.7 Eco-friendly Technological Man

There are now about 6 billion of us, each requiring incomparably more energy than any other animal. When we multiply the daily per capita consumption by the total population, we have an incredibly huge amount, which is bound to rise yet further as we become more materialistic, and as the population continues to increase. The world is no longer big enough for us. The demands of individuals and nations are straining spaceship. Earth needs yet another new kind of human being to support this all-consuming society, to find and guarantee new resources, and to use them effectively. This new type of person must be not only a technocrat, but must also have a determination to restore harmony with the natural environment. Such human population may be considered as eco-friendly technological man.

1.2 WORLD POPULATION AND ENERGY CONSUMPTION PATTERN PROJECTION

From the study of human history the worldwide population and per capita energy consumption projection is shown in Figures 1.1–1.3. From the general trend to a more detailed analysis of the actual study of yearly changes, it can be seen that the growth was, in fact, irregular. There have been periods (World War I and II) when the general pattern has been reversed. There has been notable decreasing energy consumption. The annual percentage rates of change show slight fluctuation from year to year, but if these short-term perturbations are overlooked, one can pick up three main tendencies in energy consumption.

Figure 1.3 World population and per capita energy consumption projection through history

1. Fast almost exponential growth from 1850: beginning of World War I with average annual average rate of growth = 3.6% and annual average rate of per capital growth = 4.3%.
2. Slow growth during World War I up to World War II (1910–1950) with average annual percentage rate of aggregated consumption = 1.5% and annual per capita consumption growth = 1%.
3. Greatly accelerated, almost exponential growth from World War II till date. With average annual average rate of growth = 4.9% and annual average rate of per capital growth = 2.9%.

Although an increase in energy consumption was noted throughout the world, there was a big difference in the level of energy requirements and rate of growth in different countries. Table 1.1 shows the per capita energy consumption of different countries that indicates the level of technosocioeconomics status of one nation as compared to others. In order to give an idea about how India compares with other economies in energy consumption, we can say that India used 510 kg of energy when compared to U.S.A, which consumes 7,778 kg of energy per capita. The world average of energy consumption is close to 1,818 kg, as shown in Tables 1.1 and 1.2.

Table 1.1 Energy Consumption of a Few Countries (2006)

Table 1.2 Population, Energy Use and Growth During 1999–2008

1.3 ENERGY SYSTEMS MODEL

A system is a big black box having input and output pairs related by parameters that permit to relate an input, an output, and a state. When the black-box view is applied to energy systems’ modelling and planning, an energy activity sector (such aes industrial, transportation, domestic, and agriculture), or a city region or country can be represented as a system shown in Figure 1.4. It is clear from the figure that system is characterized by the following five parameters:

Figure 1.4 Energy system’s model

1. Production and sustenance
2. Inputs
3. Outputs
4. Feedback
5. Dissipation

1.3.1 Production and Sustenance Activities

Every society or system is comprised of two important activities: sustenance and production. Sustenance activities relate with the social development that includes standard of living and lifestyle and to fulfil the indicator of quality of life, such as food, cloth, shelter, education, and health. However, these activities are not self-sustaining. They have to be sustained through continuous inputs either from within the system itself or from the outside or as subsidy from government and other agencies. Production activities relate with techno-economic development of the system. It is an important parameter of a system since it is self-sustaining and creates employment. Competitiveness in global market is a constraint for production activities.

1.3.2 Inputs

Inputs to the system are as follows:

1. Low grade energy: These are available at almost zero cost from agricultural land and forests. Early men could sustain their survival with such a meagre amount of energy. This has also caused deforestation and ecological imbalance. It has now become insufficient for any kind of development.
2. Potential sources of energy: These are any material object available from the earth, the sun, and the sea that contain energy in abundance and transferable to a usable form. Further, it has tremendous impact on the system development as a whole.
3. Subsidy or aid from government or outside agencies: This input may be useful for only in emergency for short duration. Such an input to the system should be avoided to the extent possible.

1.3.3 Outputs

Output includes industrial products and goods produced through rural and cottage industries. Energy comes in the form of money obtained by sales of products and goods in global markets.

1.3.4 Feedback

It comes in the form of money from the sale of output goods. A portion of output is fed back to the system for its development. Care should be taken that feedback be restricted to a portion of output only. Net output should be kept in reserved for emergency and adverse calamities.

1.3.5 Dissipation

Dissipation will always be present in any energy activity system. This is also referred to as degraded energy output of the system. It leaves the system as garbage, low-grade heat, smoke, etc., that damage the environment in terms of pollution. Waste energy recovery system converts waste into wealth. However, dissipation cannot be completely avoided by energy conversion system; further, it can be minimized to a large extent.

Expressing all the material objects of the energy system in same energy unit, the system can be expressed as follows:

(1.1)

From Equation (1.1), it can be analysed that the objective of improving standard of living conditions, lifestyles, and quality of life in any system, energy for sustenance must be raised.

Equation (1.1) also depicts that for techno-socio-economical development of system, input energy (I) to the system should be increased and dissipation (D) should be minimized to the extent possible. Thus, all the enhanced potential sources of energy inputs and waste energy recycling provide energy for sustenance (S) and outputs (O) resulting in overall development of system considered.

1.4 SYSTEM ACCEPTABILITY INDEX (δ)

System acceptability index can also be taken as the measure of gross efficiency of the system and can be expressed as

Degraded energy outputs leave the system as garbage, low grade heat, smoke, etc., which damage the environment in terms of pollution. Therefore, it must be kept as low as possible. The numerical value of index, δ, is a measure of the system’s acceptability. A value of δ = 1 can be approached by properly conducting any energy management program to avoid dissipation in the system.

1.5 CAUSES OF ENERGY SCARCITY

While the whole world is in the grip of energy scarcity, several countries, including India also, are facing various associated difficulties for its techno-socio-economic development because of energy shortages and many more things. However, they have been further complicated by the energy dependence on the other countries. Energy use scenario, as shown in Table 1.3, indicates that how equality (social and economical) can be achieved, when 30% population is utilizing 70% of energy and 70% population is forced to live with the 30% of the remaining energy.

Table 1.3 Energy Use Scenario

Following points may be considered as the principal causes of energy scarcity.

1.5.1 Increasing Population

Undoubtedly, only 40–45% population constitutes child producing groups, worldwide population is increasing at an alarming rate. It is extrapolated that by the turn of 21st century, population will increase manifold (Malthusian population model). These populations are unevenly distributed worldwide. Africa shares the largest population growth rate, followed by South Asia and then by Europe.

1.5.2 Increasing Energy Usage or Consumption

The movement of civilization from early man to the present technological man was totally based on energy usage. Energy is constantly used at home, at work, and for leisure period of enjoyment. Energy maintains techno-socio-economic development. Energy provides the society with heat and electricity daily and motive power to industry, transportation, and modern way of life.

1. In homes, for lighting and cooking, domestic appliances, televisions, computers, etc.
2. In industry to power the manufacture of the products.
3. In transport system to power cars, trucks, ships, and aeroplanes for transporting peoples and goods.

An increase in the world population and consequent increase in energy consumption increases energy demands manifolds. World Energy Council has provided the most reliable prediction as shown in Figure 1.5. This indicates that by 2050, the world population will nearly be doubled from the present level and will rise to about 10 billion. Likewise, energy demand is projected to be at least double than the present level (Energy council).

Figure 1.5 Population and energy consumption (Energy council)

1.5.3 Uneven Distribution of Energy Resources

It is well understood that very few wealthy countries have access to and actually use the largest part of the world’s energy and material resources. The generation of environmental and social instability in several area of globe can be discussed in relation to the existence of disparity. Uneven distribution of energy and resource trade among countries is of paramount importance to environmental and political stability. For example, Middle East countries are full of crude oil reserves, but they are forced to involve in conflicts and wars and their energy reserves are forcefully used by wealthy countries. Geographical distribution is the main consideration for an unevenly distribution of fossil fuels (coal, oil, gas, and nuclear). Renewable energy flows are also spread out unevenly. Cloudiness in equatorial regions reduces solar radiation. Whole stretches of the continent have insufficient wind. There are very few sites with the best potential for geothermal, tides, or ocean thermal. In fact, a few densely populated region or area have no significant locally available energy sources at all.

1.5.4 Lacks of Technical Knowhow

Despite the fact that several countries or regions are having energy in abundance, they are not able to fully utilize them due to the lack of knowledge of conversion, transmission, distribution, and utilization. Because of the lack of technical knowledge, resources are mined and processed in resource enriched countries and then refined and used in developed countries. The price of exported resources is normally inadequate to compensate for the depletion of energy reserves and the environmental burden that is generated by resource extraction and primary processing in energy enriched countries. However, resources drive significant economic and environmental benefits in techno-economically developed countries.

1.6 SOLUTION TO ENERGY CRISIS OR SCARCITY

Owing to the growing importance of energy awareness, efforts should be systematically diverted in the following directions to tackle the gigantic energy crunch problems:

1. Minimizing population growth exploitation and harnessing the large utilization of known and unknown energy reservoirs.
2. Development of energy conversion techniques to convert basic energy available from energy reservoirs (primary energy resources) to usable form of energy (secondary energy resources). Usable energy form should be such that it is easy to generate, control, transport, and utilize. Electrical energy being the one and only usable form of energy to meet all these at present. Hydrogen energy and heat energy are other usable energy forms that are also being projected.
3. Keep the new energy system pollution free as far as possible, thereby environmentally acceptable to human beings.
4. The development of cheap and reliable energy storage systems. Maintaining new energy development program that is independent of foreign impact to the extent is possible.
5. Energy management.

1.7 FACTORS AFFECTING ENERGY RESOURCE DEVELOPMENT

An impartial examination of certain basic principles of energy availability studies reveals the following five factors that make energy resource development more difficult than normally realized.

1.7.1 Energy or Fuel Substitution or Scale of Shift

Today, there is no readily available energy resources that is large enough to substitute for fossil fuels (coal, oil, gas, and nuclear) at requisite scale. Undoubtedly, solar energy is several orders of magnitude larger than any conceivable global energy demand (about 10¹⁷ w). Practical conversion to electricity using photovoltaic or large scale industrial heat are quite negligible.

1.7.2 Energy Density

The amount of energy contained in a unit of material object (energy resource) is termed as energy density. Air-dry crop residue (mostly straw and agricultural waste) contain only 12–15 MJ/kg. For example, the energy density of good quality coal is twice as high (i.e., 25–30 MJ/ kg) as that of crude oil (i.e., 42–45 MJ/kg). In order to obtain an equivalent output, replacement of a unit of fossil fuels with approximately 2 kg of phytomass will be needed to substitute solid biofuel. The ratio would be about 1.5 times when substituting plant-derived ethanol for petrol. These realities would be reflected in the reserve capacity, cost, and operation of the required infrastructure.

1.7.3 Power Density

Power density refers to the rate of energy production per unit of earth’s area and usually expressed in watts per square meters (w/m²). Owing to lengthy period of formation (from biomass to coal and then from coal to hydrocarbons), fossil fuel deposits are an extraordinarily concentrated source of high quality energy. They are commonly produced with power densities of 10² or 10³ w/m² of coal or hydrocarbon field, and hence, only small land areas are required to supply enormous energy flows. In contrast, biomass energy production has densities below 1 w/m², while density of electricity produced by water and wind is below 10 w/m². Only photovoltaic electricity generation can deliver larger than 20 w/m², although the cost and performance are the constraints of mass utilization.

1.7.4 Intermittency

Growing demand for fuels, energy, and electricity fluctuates daily and seasonally in modern civilization. Further, the base load, which is defined as the minimum energy required meeting the demand of the day, has been increasing. Easily storable high-energy density fossil fuels and thermal electricity generating stations that are capable of operating with high load factors (775% for the coal-fired stations, 790% for nuclear plants) meet these needs.

On the other hand, wind and direct solar radiation are intermittent and far from practicable. They can never deliver such high load factors. Photovoltaic electric generation is still so negligible to offer any meaningful averages. The annual load factors of wind generation in countries with relatively large capacities are 20–25%. Unfortunately, we still lack the means for storing wind or solar-generated electricity on a large scale.

1.7.5 Geographical Energy Distribution

As already mentioned, there are uneven distributions of fossil fuels and the non-fossil fuels (solar, wind, etc.). Cloudiness in the equatorial zone reduces direct solar radiation. Whole stretches of continent has insufficient wind. There are very few sites with the best potential for geothermal, tidal, or ocean energy conversions. Based on the abovementioned five basic considerations, energy sources can be considered possible, probable, and practicable as given in Table 1.4.

Table 1.4 Energy Options

1.8 QUALITY OF ENERGY FORM

Nowadays, there seems to be a lot of confusion between energy and technology. Society seems to depend so much on technology with an assumption that it can solve anything. However, energy is part of the fundamental fabric of the universe. As such, it is not dependant on technology.

According to the second law of thermodynamics, energy flows from an organized form to a disorganized form (the concept of entropy) or from a concentrated form to a more dispersed form. Obviously, more work can be done with energy in concentrated form (as it is easier to convert to other usable form, transport, distribute, and utilize). This gives rise to the concept of energy quality.

To illustrate this, let us assume two large containers with each containing 10 units of energy (20 units in total) in the form of compressed air. One container is at a high pressure, and the other at a low pressure. If a valve is installed between the two containers and is opened, energy (in the form of pressured gas) will flow from the container with the high pressure to the one with the low pressure, as the pressures in the two containers will try to equilibrate. Let us consider transfer of one unit of energy from the high-pressure container to the other. If an energy balance is made on the containers, 20 units of energy are still there. However, if transfer of one unit of energy back to the high-pressure container is required, the same will need a compressor to do it. Therefore, even though it is still there, nothing can be done with that unit of energy, as it has lost its quality.

Similarly, heat flows from a hotter to a cooler medium. In fact, all energy flows from a higher quality to a lower one, as the universe is a cold quasi-void and energy tries to fill it and equilibrate itself (have the same quality everywhere). This is why no process is perfectly reversible; there will always be losses to go back to the highest form of energy, like the energy consumption of the compressor in the preceding example. The branch of thermodynamics concerned with the usefulness of a given energy form is called energy. Electricity is the usable energy form with the highest quality (the one that requires the biggest compressor to produce). Heat has a much low quality, but its quality increases with temperature for applications requiring heat. Heat can be produced from electricity at 100% efficiency by passing a current in a resistance; however, if conversion of heat into the electricity is attempted, there will be large losses (>60% losses). Further, low losses occur if the temperature is high. Using higher quality energy for lower quality applications makes no sense in the context of thermodynamics. For example, when designing a heating system, it makes no sense to produce heat at 100ºC, if the system requires heat at 40ºC. Similarly, producing electricity (and suffering the high losses required to do so) and converting it to heat for space heating is a very inefficient use of energy. For example, converting solar radiation to heat with solar collectors will give about 6 times more energy than converting it to electricity using photovoltaic. The electricity route may be convenient for transport, but it is definitely inefficient. Oil is a very high quality form of energy. It is very concentrated and easy to transport. It took about 85 tons of vegetation to produce one barrel of oil. This means that in the last 100 years, we have consumed oil that is equivalent to 13,000 years of plant growth (or photosynthesis) on the planet. Society has become used at depending on high quality forms of energy to accomplish its everyday tasks, as the planet is enriched with a good supply of them. As these are fast depleting and becoming less abundant, there will be need to replace them with more dispersed ones, like concentrating solar energy to a usable form. Converting dispersed energy into a more concentrated form will always be inefficient, that is, a basic law and technology will not allow anyone to bypass it.

1.9 ENERGY RESOURCES AND CLASSIFICATION

The following sections deals with the classification of promising energy resources of immediate interests.

1.9.1 Primary and Secondary Energy Resources

1. Primary energy resources are derived directly from natural reserve. Examples are chemical fuels, solar, wind, geothermal, nuclear hydropower, etc. They are used either in basic raw energy form or by converting them to usable form (secondary energy).
2. Secondary energy resources are usable forms of energy generated by means of suitable plants to convert the primary energy. Examples are electrical energy, steam power, hot water power, hydrogen energy, etc.

Usable form of energy is cost effective, highly efficient with improved performance, environmentally acceptable and system acceptability index approaching to unity is achievable during conversion, transportation, distribution, and end use. From the abovementioned viewpoints, electrical energy will continue to be dominant and will also be a usable form of energy till the turn of the century.

Primary energy resources may be further sub-classified as follows:

1. Conventional and non-conventional energy resources: (a) Conventional energy resources and their technical knowledge are known to mankind to a great extent. They are the energy stored within the earth and the sea. They include both fossil fuels (coal, oil, and gas) and nuclear energy (uranium and thorium) and required human intervention to release the energy from them. These sources have formed over hundreds of millions of years ago and when they are used, there will be no more for future generations. They are also known as finite energy resources. (b) Non-conventional energy resources are also known as infinite energy resources. Their technical knowledge is little known and they need full exploitation and improved technical understanding. However, it may be mentioned that owing to the cost factor and overall performance, one may think of utilizing all these energy resources only when all the conventional energy resources have been fully exploited and utilized. They are obtained from the energy flowing through the natural environment. It is necessary to note that the energy is passing through the environment as a current or as a flow and whether there is an artificial device there to intercept and harness the power or not. Further, it is important to know the rate at which useful energy can be obtained from these sources.
2. Renewable and non-renewable energy resources: (a) Renewable energy resources are continuously restored by nature. Examples are solar, water, wind, etc. (b) Non-renewable energy resources are the reserve that is once accumulated in nature has practically ceased to form under new geological conditions. They are also known as expendable energy. Examples are coal, oil, gas, nuclear, etc. Therefore, energy resources may be represented as shown in Table 1.5.

Table 1.5 Classification of Energy Resources

1.9.2 Oil

Oil companies estimate that the world’s proven oil reserves are about 1,050 thousand million barrels (BP 2002). This is equivalent to about 6.4 × 1,021 J or 6,400 exajoules. Estimates of reserves are always subject to uncertainty and change. There is a very uneven distribution of oil reserves across the world, with some 71% of proven oil reserves being in the Middle East. The ultimately recoverable and unconventional reserves are very much more difficult to specify. The estimates of additional reserves that will be found and the growth to existing fields will vary widely. However, there is general agreement that crude oil is a finite resource that will run short and may sometime become very expensive in the first half of this century.

1.9.3 Natural Gas

The proven reserves of natural gas are presently some 152 trillion cubic meters (about 5.9 × 1,021 Joules or 5,900 exajoules). This is about the same as the reserves of oil. However, because gas is more difficult to transport and trade, there has not been as much effort is put into finding gas when compared with that of finding oil. There are some prospective regions of the world that have not been fully explored. Technologies for extracting gas constantly improve, thus making it difficult to estimate the sizes of the gas fields. The 2001 world gas consumption rate of 2.5 trillion cubic meters per annum (The World Fact book) has doubled over the last 30 years, while oil consumption has only increased some 30%.

1.9.4 Coal

In 1999, the proved recoverable reserves of coal is around one million tonnes [The World Energy Council estimates]. There is much more coal than any other fossil fuel. This is equivalent to about 3 × 10²² J or 30,000 exajoules; this is enough to sustain present production for more than 200 years. The world’s consumption of coal is still rising (at less than 1% a year), but most industrial countries over recent decades have decreased their dependence on coal. The use of coal is limited more by environmental considerations than by the size of the resource. Modern techniques for burning coal using liquefaction and gasification processes can greatly reduce some of the pollutants from coal. However, coal always produces a great deal of carbon dioxide (greenhouse gas). There had been no cost-effective way developed for capturing and sequestering this carbon dioxide, but extensive research programs are underway.

1.9.5 Uranium

The economically accessible reserves of natural uranium were estimated by the World Energy Council in 1999 at three million tonnes. In the 1970s, this was expected to last no more than a few decades, but due to the slower grown than the expected growth in the nuclear industry and increased availability of uranium and the decommissioning of nuclear weapons, this time frame has been extended. There are public reservations about the cost and the safety of nuclear power plants, but they produce almost no CO₂ and the technology is mature.

1.9.6 Hydroelectric Power

At present, hydroelectricity provides the second biggest renewable energy contribution to world energy supply, with an annual output of 2,600 TWh. Information received from energy sources indicates that the world’s total technically feasible hydro potential is about 14,400 TWh/yr, out of which just over 8,000 TWh/yr is currently considered to be economically feasible for development.

Hydropower is dependent on rainfall, and climate change could affect this potential. There is also considerable opposition to the building of large dams for social and environmental reasons.

1.10 ENERGY TRANSFER FRAMES

Most of the world’s energy resources are from the conversion of the sun’s rays to other energy forms after being incident upon the planet. Some of that energy has been preserved as fossil energy; some is directly or indirectly usable; for example, via wind, hydro- or wave power.

In order to have better understanding of the energy conversion storage and related aspects of immediate importance, it is essential to know the promising energy resources and their nature and characteristics in detail, which will lead to the development of economical and feasible energy storage and conversion techniques. Discussions of all these energy resources are beyond the scope of this chapter. However, these resources and the techniques for conversion to usable electrical energy form and intermediary product forms, which are capable of being stored, can be well understood from Figure 1.6. It represents the transformation of basic energy resource to usable form and intermediary products. Following Figure 1.6, a suitable energy conversion and storage schemes can be selected and designed to meet the requirements.

Figure 1.6 Energy transfer frame

1.11 ENERGY CONVERSION

In whatever form the basic energy may be available from various conventional and non-conventional energy reservoirs, the development of techniques and systems for their conversion to usable form, and transportation from one place to any other distances be fully established. Only the techniques and equipment for obtaining the energy in electrical form and related technology is established up to a large extent, and hence, it is believable that electricity may remain a primary usable form of energy during the next few decades. Certain known important techniques for basic resource conversion into electrical energy are as follows.

1.11.1 Indirect Energy Conversion

The systems that employ the energy conversion chain:

Converters utilizing such processes of conversion are called as electro-mechanical energy converters. They convert chemical and nuclear fuels. For example, solar thermal, wind, ocean tides, and waves.

1.11.1.1 Thermal-lectromechanical Energy Converters

Thermal prime movers are the most common prime movers used to generate electricity. These include steam turbines, gas turbines, gasoline engines, and diesel engines. In all cases, the prime mover is a rotating device that rotates electrical conductors through a magnetic field to produce electricity. The steam necessary to drive steam turbine is obtained when coal or gas is burnt in boilers. For nuclear power plants, heat resulting from nuclear fission is used to produce the steam. Steam at maximum possible pressure and temperature is used to ensure maximum efficiency of operation of the turbine. Turbine units with a rating of 500 MW and above are common, as large turbine sizes result in lower capital costs per MW of capacity.

1.11.1.2 Binary Cycle

Such a conversion system is very common and promising for low thermal heat of solar and geothermal resources. It is presently thought as one of the most important energy conversion system that may continue for centuries to come. Besides the conventional energy system, all the non-conventional systems in the world (in particular, India), such as solar and geothermal resources, suffer from the low temperature and low pressure characteristics and hence require one or more types of binary cycle capable of assisting in the conversion of these energy resources into usable electrical energy form. A schematic arrangement of a binary cycle used for the purpose may be understood from Figure 1.7.

Figure 1.7 Binary cycle

It consists of the following parts:

1. Hot water tank or well: It either stores solar heat with the help of concentrating collectors or geothermal fluid or similar basic energy resources.
2. Heat exchanger: This is normally required to transfer the collected heat in the tank to the working fluid.
3. Power unit: The heated working fluid is then used to drive turbine to produce mechanical energy through coupled generators’ air engine; the heat exchanger and power unit are combined in one, but a closed vapour cycle system needs a condenser and a feed pump in addition to all the abovementioned components. Further, in binary cycle, hot water is transferred to another. Each of these components may consist of one or more parts. For example, in hot liquid, isobutene or pentene or Freon gas is used. This secondary fluid vaporizes at an adequate pressure for turbine drive and could be condensed by surface water, which a tower could then cool. Heat transfers from hot water to secondary fluid occur without phase change, thus eliminate problems from evaporation-caused deposits.

1.11.1.3 Cogeneration

Cogeneration is a term used for representing the coincident generation of steam and electricity by an industrial complex with or without the involvement of a utility or by the utility itself. Hence, a cogeneration plant may

1. Be owned and operated by the individual industry or the central supply systems.
2. Serve one or more individual users or can have isolated operation.
3. Be an integral part of the local supply grid.

However, each cogeneration schemes and their use should be carefully analysed in the context of individual industrial process, social, economical, and environmental interferences. Cogneration schemes, if implemented, may result in as high a thermal efficiency of 80% as compared to fossil-fuel fired integrated stations operating at the maximum thermal efficiency of 30–40%. The two attractive thermal cycle used in cogeneration schemes is the topping cycle and bottoming cycle that refer to the points in the thermal cycles at which electrical or mechanical energy are produced.

In topping cycle, fuel is burnt to produce electrical or mechanical power; the waste heat from the power production plant serve as process heat, which may be reutilized for electrical or mechanical power. In bottoming cycle, the excess process heat is then converted into electrical or mechanical power. With such an efficient conversion of thermal heat into kilowatt hour, cogeneration appears to be a solution of conserving energy.

1.11.2 Hydroelectromechanical Energy Converters

Hydroelectric power plants and tidal power plants both use hydraulic turbines as prime movers, which convert the potential energy of an elevated body of water to rotating kinetic energy. There are two basic types of hydroelectric power plants: run-of-the-river plants and reservoir plants. As its name implies, run-of-the-river plants are built so that the turbine blades are simply turned by the water as it flows in the river. However, most hydro plants are reservoir-type plants, which means there must be a dam to regulate the water flow and to stored add the height to the stored the water. The powerhouse contains the hydraulic-mechanical works consisting of turbines, the upstream waterways (penstock) carrying water from the reservoir to the turbine, and the downstream discharge, water into channels. It also contains the electric generators. The height the water falls through the penstock is called the head.

Let g is the acceleration due to gravity, 9.81m/s², H is the head of the water in meters, Q is the flow rate of water through the turbine in cubic meters per second, and V is the velocity of water in m/s through the penstock.

The power available at the turbine is,

(1.2)

Since a dam converts potential energy into kinetic energy, we get

(1.3)

From which,

(1.4)

The velocity of the water through the penstock can be converted to flow rate in cubic meters per second through

(1.5)

The power produced is proportional to the head and the flow rate. Dams are roughly classified into low head (6 to 30 m), medium head (30 to 200 m), and high head (above 220 m). To transfer water downstream, low-head plants utilize dams and high-head plants use penstocks.

There are three types of hydraulic turbines available

1. Kaplan turbines are used for heads up to 60 m.
2. Francis turbines are used for heads from 30 to 300 m and of ratings exceeding 500 MW have been built.
3. Pelton wheels, for heads larger than 90 m and of ratings of 40 MW are in use.

Maximum efficiencies of hydraulic turbines are between 85 and 95%. Hydraulic turbines can be started almost instantaneously from rest, and they have the obvious advantage that no losses are incurred when at a standstill. Thus, working in parallel with thermal power stations, hydroelectric plants can meet peak loads at minimum operating cost.

1.11.3 Direct Energy Conversion

Several conversion processes in which the heat-to-mechanical energy transformation link is not essential. In this, systems employ the energy conversion chain:

In such processes, the source energy is converted directly to electricity. Hence, the definition of direct energy conversion is a process of conversion of one form of energy (such as sunlight) to another (such as electricity) without going through an intermediate stage (such as steam to spin generator turbines).

The direct energy conversion devices are known as direct energy converters. They convert solar, thermal, chemical, and nuclear energies into electricity without involving a rotating or reciprocating mechanical prime mover. The following are the various direct energy converters:

1. Fuel cells and batteries
2. Photovoltaic
3. Photoelectric
4. Electrostatic generators
5. Thermionic
6. Thermoelectric
7. Ferroelectric generators
8. Magnetohydrodynamic generators
9. Piezoelectric generators

It is projected that, of all the direct energy converters, only solar photovoltaic and fuel cells will contribute to the production of any significant amount of electrical power in the near future.

1.11.3.1 Photovoltaic Conversions

The photoelectric effect was first noted by a French physicist, Edmund Becquerel, in 1839, who found that certain materials would produce small amounts of electric current when exposed to light. In 1905, Albert Einstein described the nature of light and the photoelectric effect on which photovoltaic technology is based, for which he later won a Nobel Prize in physics. The first photovoltaic module was built by Bell Laboratories in 1954. It was billed as a solar battery and was mostly just a curiosity as it was too expensive to gain widespread use. In the 1960s, the space industry began to make the first serious use of the technology to provide power aboard spacecraft. Through the space programs, the technology advanced; its reliability was established, and the cost began to decline. During the energy crisis in the 1970s, photovoltaic technology gained recognition as a source of power for non-space applications.

Figure 1.8 illustrates the operation of a basic photovoltaic cell. It is also called a solar cell. They are made of some kinds of semiconductor materials, like silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current, that is, electricity. This electricity can then be used to power a load, such as a light or a tool.

Figure 1.8 Operation of a basic photovoltaic cell

Photovoltaic conversion is thus considered a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect.

1.11.3.2 Working of Solar Cells

As already mentioned, solar cell is the other name for photovoltaic. These cells are responsible for producing energy out of sunlight it receives. They are made of special materials that are semiconductors. These semiconductors produce electricity when sunlight falls onto its surface. Solar electric cells are simple cells to use, they do not require anything but sunlight to operate; they are long lasting, reliable, and easy to maintain. Normally, solar panels’ life time is 25 years.

A solar cell (see Fig. 1.9) is essentially a PN junction with a large surface area. The P-type material is thick (about 200–300 μm). The N-type material is kept thin (of the order of 0.2–0.3μm) to allow light to pass through to the PN junction. Light travels in packets of energy called photons. The energy (E) of photon is given by

Figure 1.9 Physical configuration of a typical solar cell

(1.6)

where

h = Planck’s constant, 6.62 × 10⁻²⁷ erg/s

c = velocity of light, 3 × 10⁸ m/s

λ = wavelength of light, μm

From which, we get

(1.7)

When a photon of light is absorbed by one of these atoms in the N-type silicon, it will dislodge an electron, creating a free electron and a hole. The free electron and hole have sufficient energy to jump out of the depletion zone. If a wire is connected from the cathode (N-type silicon) to the anode (P-type silicon), electrons will flow through the wire. The electron is attracted to the positive charge of the P-type material and travels through the external load (meter) creating a flow of electric current.

The hole created by the dislodged electron is attracted to the negative charge of N-type material and is migrated to the back electrical contact layer. As the electron enters the P-type silicon from the back electrical contact, it combines with the hole restoring the electrical neutrality. A number of solar cells electrically connected to each other and mounted in a support structure or frame is called a photovoltaic module. Modules are designed to supply electricity at a certain voltage, such as a common 12-V system. The current produced is directly dependent on how much light strikes the module.

1.11.3.3 Thermionic Conversion

Thermionic Converter or thermionic generator is a device for the direct conversion of thermal energy into electrical energy on the basis of the phenomenon of thermionic emission. It consists of a hot electrode that thermionically emits electrons over a potential energy barrier to a cooler electrode, producing a useful electric power output. Caesium vapour is used to optimize the electrode work functions and provide an ion supply (by surface contact ionization or electron impact ionization in a plasma) to neutralize the electron charge.

The simplest type of thermionic converter consists of two electrodes separated by a vacuum gap (less than 5 mm). A typical simple caesium thermionic converter is shown in Figure 1.10. One electrode is the cathode, or emitter, and the other is the anode, or collector. The electrodes are made of refractory metals, usually molybdenum, rhenium, or tungsten. A heat source supplies enough thermal energy for appreciable thermionic emission to occur from the surface of the metal. After passing through the inter-electrode gap, which is a few tenths of a millimetre in size, the electrons impinge on the surface of the collector, where they create an excess of negative charge and increase the collector’s negative potential. If heat is continuously supplied to the emitter and if the collector, which takes up heat from the electrons that reach it, is correspondingly cooled, then an electric current will be maintained in the external circuit, and work will thus be done. Since a thermionic converter is essentially a heat engine whose working fluid is an ‘electron gas’ (the electrons ‘evaporate’ from the heated emitter and ‘condense’ on the cooled collector), the efficiency of a thermionic converter cannot exceed that of the Carnot cycle. The thermionic converter produces a voltage of 0.5–1 V. This voltage is of the order of the contact potential difference, but differs from it by the value of the voltage drop across the inter-electrode gap and the voltage losses in the switching lines (see Fig. 1.10). The maximum density of the current generated by a thermionic converter is limited by the emission capacity of the emitter and may reach a few tens of amperes from 1 cm² of surface. To obtain optimal values of the work function of the emitter (2.5–2.8 electron volts [eV]) and collector (1.0–1.7 eV) and to compensate for the electron space charge formed near the electrodes, a slightly ionized caesium vapour is usually introduced into the interelectrode gap.

Figure 1.10 Schematic of a thermionic converter

Positive caesium ions are formed when caesium atoms collide with electrons (1) at the hot cathode or (2) in the inter-electrode space. The first case is known as surface ionization. In the second case, a caesium atom may be ionized by a single electron impact or through stepwise ionization, in which the caesium atom is brought into an excited state by an initial collision with an electron and is ionized by subsequent collisions. In this second case, arcing occurs; this mode of operation is the one most widely used. Present-day thermionic converters operate at cathode temperatures of 1,700°–2,000°K and anode temperatures of 800°–1,100°K. At such temperatures, the power density at the cathode surface reaches tens of watts per cm², and the efficiency of the converters may exceed 20%.

According to the nature of the heat source, thermionic converters are classified as follows:

1. Nuclear: The heat for nuclear thermionic converters may come from a nuclear fission reaction (in reactor-powered converters) or the decay of a radioactive isotope (in isotope-powered converters). The first reactor-powered thermionic converter called Topaz in the world was built in the USSR in 1970. It has an electric power output of about 10 kW.
2. Solar: In solar thermionic converters, the emitter is heated by the thermal energy of solar radiation, which is collected with solar concentrators.
3. Flame heated: Flame-heated thermionic converters operate on the heat released in the combustion of organic fuel.

Thermionic converters have several advantages over traditional electromechanical converters:

1. Absence of moving parts
2. Compactness
3. High reliability
4. Possibility of operation without regular servicing.

As of mid-1970s, a continuous operating life of over 40,000 h had been achieved for an individual thermionic converter.

A promising application of thermionic converters is their use as high-temperature units of multistage energy converters—for example, in combination with thermoelectric converters operating at low temperatures.

1.11.3.4 Fuel Cells

A fuel cell is a device that converts the chemical energy of a fuel (hydrogen, natural gas, methanol, gasoline, etc.) and an oxidant (air or oxygen) into electricity. In principle, a fuel cell operates like a battery. However, unlike a battery, a fuel cell does not run down or require recharging. It will produce electricity and heat as long as fuel and an oxidizer are supplied. Fuel cells come in many varieties; however, they all work in the same general manner. They are made up of three segments that are sandwiched together:

1. anode
2. electrolyte
3. cathode

An electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible. Commonly, electrolytes are solutions of acids, bases, or salts. Furthermore, some gases may act as electrolytes under conditions of high temperature or low pressure. Electrolyte solutions can also result from the dissolution of some biological (e.g., DNA, polypeptides) and synthetic polymers (e.g., polystyrene sulfonate), termed polyelectrolytes, which contain charged functional groups.

Electrolyte solutions are normally formed when a salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules in a process called salvation. For example, when Table salt, NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction

(1.8)

It is also possible for substances to react with water producing ions, for example, carbon dioxide gas dissolves in water to produce a solution that contains hydronium, carbonate, and hydrogen carbonate ions. Note that molten salts can be electrolytes as well. For instance, when sodium chloride is in a molten state, the liquid conducts electricity. An electrolyte in a solution may be described as concentrated, if it has a high concentration of ions, or dilute if it has a low concentration. If a high proportion of the solute dissociates to form free ions, the electrolyte is strong; if most of the solute does not dissociate, the electrolyte is weak. The properties of electrolytes may be exploited using electrolysis to extract constituent elements and compounds contained within the solution.

Two chemical reactions occur at the interfaces of the three different segments. The net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is produced, which can be used to power electrical devices, normally referred to as the load (see Fig. 1.11).

Figure 1.11 Block diagram of a fuel cell

At the anode, a catalyst oxidizes the fuel, usually hydrogen, turning the fuel into a positively charged ion and a negatively charged electron. The electrolyte is a substance specifically designed so ions can pass through it, but the electrons cannot. The freed electrons travel through a wire creating the electric current. The ions travel through the electrolyte to the cathode. Once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, usually oxygen, to create water or carbon dioxide. The most important design features in a fuel cell are as follows:

1. The electrolyte substance usually defines the type of fuel cell.
2. The most common fuel is hydrogen.
3. The anode catalyst, which breaks down the fuel into electrons and ions. The anode catalyst is usually made up of very fine platinum powder.
4. The cathode catalyst, which turns the ions into the waste chemicals like water or carbon dioxide. The cathode catalyst is often made up of nickel.

A typical fuel cell produces a voltage from 0.6 V to 0.7 V at full-rated load. Voltage decreases as current increases, due to following factors:

1. Activation loss
2. Ohmic loss (voltage drop due to resistance of the cell components and interconnects)
3. Mass transport loss (depletion of reactants at catalyst sites under high loads, causing rapid loss of voltage).

To deliver the desired amount of energy, the fuel cells can be combined in series and parallel circuits, where the former yields higher voltage and the latter allows a higher current to be supplied. Such a design is called a fuel cell stack. The cell surface area can be increased to allow stronger current from each cell.

1.11.3.5 Thermoelectric Conversions

The Seebeck effect is the conversion of temperature differences directly into electricity and is named after the German physicist Thomas Johann Seebeck, who in 1821 discovered that a compass needle would be deflected by a closed loop formed by two metals joined in two places, with a temperature difference between the junctions. This was because the metals responded differently to the temperature differences, creating a current loop and a magnetic field.

The device diagram of the circuit on which Seebeck discovered the Seebeck effect is shown in Figure 1.12, and there are two different metals used. Seebeck did not recognize there was an electric current involved, so he called the phenomenon the thermomagnetic effect. Danish physicist Hans Christian Ørsted rectified the mistake and coined the term ‘thermoelectricity’. The voltage created by this effect is of the order of several microvolts per Kelvin difference. One such combination, copper–constantan, has a Seebeck coefficient of 41 mV/K at room temperature. Using the principle known as ‘the Seebeck Effect’, electricity can be generated, if there is a temperature differential between the two sides of a thermoelectric module. Because this type of system depends upon a consistent temperature differential to provide electricity, the modules are often combined with a known heat source such as natural gas or propane for remote power generation or waste heat recovery. They are often used in remote locations where power is required but solar energy is unreliable or insufficient, such as offshore engineering, oil pipelines, remote telemetry, and data collection. For power generation and waste heat recovery applications, thermoelectric modules have been optimized for efficient performance.

Figure 1.12 Seebeck effect

The term ‘thermoelectric effect’ encompasses three separately identified effects:

1. Seebeck effect
2. Peltier effect
3. Thomson effect

1.11.3.6 Magnetohydrodynamics

It provides a way of generating electricity directly from a fast moving stream of ionized gases without the need for any moving mechanical parts—no turbines and no rotary generators.

1.11.3.7 Working Principle

The magnetohydrodynamics (MHD) generator can be considered to be a fluid dynamo as shown in Figure 1.13. This is similar to a mechanical dynamo in which the motion of a metal conductor through a magnetic field creates a current in the conductor except that in the MHD generator, the metal conductor is replaced by conducting gas plasma.

Figure 1.13 Principle of MHD generator

When a conductor moves through a magnetic field, it creates an electrical field perpendicular to the magnetic field and the direction of the movement of the conductor. This is the principle, discovered by Michael Faraday, behind the conventional rotary electricity generator. Dutch physicist Antoon Lorentz provided the mathematical theory to quantify its effects.

The flow (motion) of the conducting plasma through a magnetic field causes a voltage to be generated (and an associated current to flow) across the plasma, perpendicular to both the plasma flow and the magnetic field according to Fleming’s right-hand rule. Lorentz Law describing the effects of a charged particle moving in a constant magnetic field can be stated as follows

(1.9)

where

The calculation of open circuit voltage is straightforward. In a properly functioning MHD generator, open circuit voltage is given by

(1.10)

where

The relatively low ceiling of conversion efficiency of conventional generators prompted the scientists and engineers to look for new ways of converting heat energy directly into electrical energy. In the process, MHD shows promise as a way of generating electricity on a large scale.

MHD can be looked upon as a combination of fluid mechanics and electromagnetism; or in other words, behaviour of electrically conducting fluids in the presence of magnetic and electric fields. Operating principle of MHD is based on the fact that when as ionized (conductive) gas flows across a magnetic field an emf is induced in it, and if electrodes are placed in appropriate positions, this emf can deliver a current to an external load. However, MHD power generation is associated with many varying problems. Some important problems are as follows:

1. Production of very high temperature required for the plasma gases.
2. Increasing the working time of the plant by suitable design of plants.

Undoubtedly, the solution of all these associated problems will lead to the development of large MHD power plants. Several MHD projects were initiated in the 1960s, but overcoming the technical challenges of making a practical system proved very expensive. Interest consequently waned in favour of nuclear power which since that time has seemed a more attractive option. MHD power generation has also been studied as a method for extracting electrical power from nuclear reactors and also from more conventional fuel combustion systems.

1.12 RENEWABLE ENERGY

Renewable energy is the energy that comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally replenished). The availability of the renewable energy resources is discussed in the following sections.

1.12.1 Worldwide Renewable Energy Availability

About 16% of global final energy consumption comes from renewable as shown in Figure 1.14, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity.

Figure 1.14 Worldwide renewable power capacity excluding hydro

New renewable energy (small hydro, modern biomass, wind, solar, geothermal, and biofuel) accounted for another 3% and were growing very rapidly. The share of renewable energy in electricity generation is around 19%, with 16% of global electricity coming from hydroelectricity, and 3% from new renewable energy.

Potential for renewable energy is given in Table 1.6.

Table 1.6 Potential for Worldwide Renewable Energy

More than half of the energy has been consumed in the last two decades since the industrial revolution, despite advances in efficiency and sustainability. According to IEA world statistics in four years (2004–2008), the world population increased 5%, annual CO₂ emissions increased 10%, and gross energy production increased 10%.

1.12.2 Renewable Energy in India

It is a sector that is still in its infancy. As of December 2011, India had an installed capacity of about 22.4 GW of renewable technology-based electricity, about 12% of its total. For context, the total installed capacity for electricity in Switzerland was about 18 GW in 2009. Table 1.7 provides the capacity breakdown by various technologies. As of August 2011, India had deployed renewable energy to provide electricity in 8,846 remote villages, installed 4.4 million family biogas plants, 1,800 micro-hydel units, and 4.7 million square meters of solar water heating capacity. India anticipates adding another 3.6 GW of renewable energy installed capacity by December 2012. India plans to add about 30 GW of installed electricity generation capacity by 2017 based on renewable energy program conducted by the central government’s Ministry of New and Renewable Energy.

Table 1.7 India Installed Capacity of Renewable Energy Till August 2011

1.12.3 Solar Energy

The annual amount of energy reaching the surface of the earth as solar radiation is about a billion kWh. An appropriate combination of solar thermal panels and photovoltaic cells could convert this to any desired combination of heat and electricity at an estimated efficiency of about 10%. Thus, the potential amount of energy that could be produced annually is 10⁸ kWh; this would mean covering the entire surface of the globe with solar thermal panels and photovoltaic cells.

Solar heating and photovoltaic are potentially a very large source of energy in the forms, and the technology to use them already exists. Still, it has to be worked out how to integrate them with other technologies, and they need storage to be used effectively. Therefore, the contribution from this source must remain substantial, but uncertain at this stage.

The solar thermal power industry is growing rapidly with 1.2 GW under construction as of April 2009 and another 13.9 GW announced globally through 2014. Spain is the epicentre of solar thermal power development with 22 projects for 1,037 MW under construction, all of which are projected to come online by the end of 2010. In the United States, 5,600 MW of solar thermal power projects have been announced. In developing countries, three World Bank projects for integrated solar thermal or combined cycle gas turbine power plants in Egypt, Mexico, and Morocco have been approved.

Solar photovoltaic cells convert sunlight into electricity and photovoltaic production has been increasing by an average of more than 20% each year since 2002, making it a fast-growing energy technology. At the end of 2010, cumulative global photovoltaic (PV) installations surpassed 40 GW and PV power stations are popular in Germany and Spain.

Many solar photovoltaic power stations have been built, mainly in Europe.^[9] As of December 2011, the largest photovoltaic (PV) power plants in the world are the Golmud Solar Park (China, 200 MW), Sarnia Photovoltaic Power Plant (Canada, 97 MW), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW), Finsterwalde Solar Park (Germany, 80.7 MW), and Okhotnykovo Solar Park (Ukraine, 80 MW).

1.12.4 Wind Power

Wind energy is the kinetic energy of air in motion. Wind turbines extract the kinetic energy present in the wind, and convert it to rotary shaft motion. The shaft motion transmits power to generators by gearboxes, belts and pulleys, roller chains, or by hydraulic transmissions. The power in the wind is proportional to the cube of the wind velocity. Let us assume

V is the wind speed (m/sec); ρ is the air density (approximately1.2 kg/m² at sea level); S is the cross-sectional area of air flow m²; m is the mass of the wind passing per unit time through rotor area; t is the time period of wind flow (s).

Therefore, SVt is the volume of air passing through S (which is considered perpendicular to the direction of the wind) and

(1.11)

Total wind energy flowing through an imaginary area A during the time t is

(1.12)

Power is the energy per unit time, and therefore, the wind power incident on A (e.g., equal to the rotor area of a wind turbine) is

(1.13)

Wind power in an open air stream is thus proportional to the third power of the wind speed; the available power increases eightfold when the wind speed doubles. Therefore, wind turbines for grid electricity need to be especially efficient at greater wind speeds. Thus, the general formula for available wind power is:

(1.14)

where P = power available in the wind in W. The available power of wind (P) is theoretically achievable; however, in practice, power extracted from the wind will theoretically be maximum and is given as

(1.15)

where C_p is the performance coefficient of a wind machine. It is the ratio of the power extracted by the rotor to the power available in the wind stream. The maximum theoretical value of coefficient of performance is

It is also known as Betz limit. Depending upon wind rotor design and wind speed, coefficient of performance (efficiency) of 30–50% can be achieved. It is established theoretically and experimentally as well. In all the cases, the power coefficient passes through a maximum at a particular value of tip speed ratio. Except the propeller type, the rise and fall of the power coefficient around the maximum value is quite rapid. The highest value of C_p is obtained with the propeller-type rotor.

Observations

1. From problem 1, it can be observed that there is very little power available in low winds.
2. The only way to increase the available power in low winds is by sweeping a large area with the blades.
3. The first key concept that this formula show is that when the wind speed doubles, the power available increases by a factor of 8
4. The second key concept from this formula is that the power available increases by a factor of 4 when the diameter of the blades doubles.

Total wind power capacity for top ten countries are given in Table 1.8.

Table 1.8 Total Wind Power Capacity for Top 10 Countries

Estimating the total energy carried by all the world’s winds is possible, but not very useful. It does not seem sensible to include winds at one kilometre above the surface of the earth, in the middle of the larger oceans, or in the remote regions of the Arctic and Antarctic regions. Considering only sites on land or in coastal waters, the estimated total potential energy that can be provided is 20,000 TWh per year—about twice the 1987 global electricity consumption.

Electricity (25 TWh) was generated from wind in 1999. This is less than one hundredth of the electricity generated by hydro, but about 10 times that was generated by the wind in 1990. Wind generation capacity is growing very quickly, but because winds do not always blow when we need the electricity, there will be a limit to the use of this resource until there is some economical way to store the energy. Eighty-three countries around the world are using wind power on a commercial basis.

1. Cambay Graben in Gujarat
2. Manikaran in Himachal Pradesh
3. Surajkund in Jharkhand
4. Chumathang in Jammu & Kashmir

1.12.5 Tidal Power

Tidal plants will probably be worthwhile only in places where the tidal range is particularly large, which means that estimating a ‘world total’ involves not a general assessment but careful site by site investigation. Using this approach, the potential output of the most promising sites is considered to be about 386 per year or around 10% of the world’s total stations generating around 670 GHz (equal to 0.67) of electricity per year.

Tidal power is essentially a specific form of hydropower, and therefore, uses basically the same equipment as a regular tidal station. The difference is in the available power to extract from the tide. A reversible hydraulic turbine is used so the inflow and outflow of the tide can generate electricity.

The following is the diagram of a simple barrage: tidal barrages work like a hydro-electric scheme. However, the dam is much bigger. A huge dam or a barrage is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam.

As the tide comes in, the dam allows the seawater to pass through into a holding basin. As soon as the tide is about to go down, the dam is closed. The water held back in this way will be used to feed the turbines at low tide. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. Large lock gates, like the ones used on canals, allow ships to pass.

There would be a number of benefits, including protecting a large stretch of coastline against damage from high storm tides, and providing a ready-made road bridge. However, the drastic changes to the currents in the estuary could have huge effects on the ecosystem, and huge numbers of birds that feed on the mud flats in the estuary when the tide goes out would have nowhere to feed.

Figure 1.15 Tidal barrage

A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out—in other words, only for 10 h each day. However, tides are totally predictable, so we can plan to have other power stations generating at those times when the tidal station is out of action.

There are different types of turbines that are available for use in a tidal barrage. A bulb turbine is one in which water flows around the turbine. If maintenance is needed, then the water must be stopped. This is a time consuming process resulting in loss of generation. When rim turbines are used, the generator is mounted at right angles to the turbine blades.

A rough estimate of power output from a tidal barrage can be obtained from a simple energy balance method by considering the average change of potential energy during the draining process.

Let ρ is the density of water 1,025 kg/m³ (seawater varies between 1,021 and 1,030 kg/m³), g is the acceleration due to gravity (9.81 m/s²), A is the horizontal area of the tidal pool (m²), h is the vertical range of the tide (m), m is the total mass of water in the tidal basin above the low water level, T is the time interval between tides, i.e., the tidal period, 1/2 (factor half) is due to the fact that as the basin flows empty through the turbines, the hydraulic head over the dam reduces. The maximum head is only available at the moment of low water, assuming the water level is still present in the basin.

Therefore, (1.16)

The height of the centre of gravity = h/2

Therefore, work done in raising the water

(1.17)

Average power for a tidal period is calculated by dividing the extracted energy by the tidal period (T).

Hence, the average power output, (1.18)

1.12.5.1 Calculation of Tidal Power Generation

1.12.5.2 Advantages of Tidal Power Generations

Although the initial costs of tidal power generations are extremely high as compared to conventional hydroelectric power plants, they are associated with large number of the following advantages.

1. A firm output is guaranteed and the output can be predicted well in advance.
2. Tidal power is unaffected by the vagaries of nature like draught.
3. The impact of tidal power plants on ecology is minimum since no unhealthy waste such as exhaust gas, ash, atomic refuse, or atmospheric radiation are involved
4. Unlike hydroelectric power plant and atomic power plants, the tidal plant do not make demands on large areas of valuable lands.
5. Tidal power plants can also add to recreational facilities.
6. Tidal basins created can also increase the possibility of fish farming.

1.12.5.3 Development of Tidal Power Scheme in India

Nevertheless, the possibility of developing tidal power scheme in India may be examined in view of the following all aspects:

1. Economic aspects of tidal power schemes when compared to the conventional schemes.
2. Problems associated with the construction and operation of plant.
3. Problems related to the hydraulic balance of the system in order to minimize the fluctuation in the power output.

1.12.6 Wave Energy

Sea wave energy is now the vanguard in averting a world energy crisis not only on technical grounds but also from economic, environmental, and political considerations. Solar and wind energy fickle and widely diffused over the earth surface. However, nature has evolved a very elegant system of gathering solar energy by the windward shores, thus solving at a stroke the problems of collection storage and transmission of energy.

Technical system for the utilization of wave energy must always be developed with a view to one single or a few possible applications for the generated secondary energy. This approach promises maximum utilization of the generated secondary energy. Because of the technical problem in foresight, it may be assumed that wave energy converters will, in the beginning, attain only regional energy supplies.

1.12.6.1 Power Calculation for Ocean Waves

Typical sea wave propagation is shown in Figure 1.16.

Figure 1.16 Sea wave propagation

The distance between two consecutive troughs defines wavelength λ. Wave height H (crest to trough) is proportional to wind intensity and its duration. The wave period T (crest to crest) is the time in seconds needed for the wave to travel with the wavelength λ and is proportional to sea depth. The frequency f = 1/T indicates the number of waves that appears in a given position. Consequently, the wave speed is v = λ/T = λ/f. The ratio λ/2H is called the wave declivity and when this value is greater than 1/7, it can be proved that the wave becomes unstable and vanishes. Longer period waves have relatively longer wavelengths and move faster. Generally, large waves are more powerful. Ocean waves transport mechanical energy.

The power associated with a wave of wavelength λ, height H, and a front b is given by

(1.19)

where

Then, power across each meter of wave front associated to uniform wave is given by

(1.20)

For irregular waves of height H (in meter) and period T (in second), an expression for power per unit wave front can be derived as

(1.21)

1.12.7 Ocean Thermal Energy

The oceans cover a little more than 70% of the earth’s surface. This makes it the world’s largest solar energy collector and energy storage system. On an average day, 60 million km² of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil. If less than one tenth of 1% of this stored solar energy could be converted into electric power, it would supply more than 20 times the total amount of electricity consumed in the United State (263 million inhabitants) on one day.

Within territorial boundaries, India receives large amount of solar energy incident upon it. The temperature difference that thus exists between the surface and the depths provides the source and sink needed to operate a heat engine and generate electrical power 24 h a day. Typically, this surface layer has a uniform temperatures of 25 °C at a depth of 45.7 m (150 feet) while 5 °C water lies at a depth of 91 m (3,000 feet). Thus, the work potential obtainable by lowering the temperature of 1 g of water from 25 °C to 5 °C is given by

(1.22)

This 2.87 J/g is just the work obtained per gram of flux by an ideal hydroelectric power plant with a 292.5 m (960 feet) head. Thus, the top isothermal layers of the tropical oceans have an effective head of 292.5 m. Further, there is an ample prospects for tapping this vast reservoir of work potential. Such tapping of energy is called ocean thermal energy conversion (OTEC).

1.12.7.1 Principles of Ocean Thermal Energy Conversion

The idea behind OTEC is the use of all natural collectors, the sea, instead of artificial collector. As shown in Figure 1.17, warm water is collected on the surface of the tropical ocean and pumped by a warm water pump.

Figure 1.17 Principles of ocean thermal energy conversion

The water is pumped through the boiler, where some of the water is used to heat the working fluid, usually propane or some similar material. If it is a cooler, you can use a material with a low boiling point like ammonia. The propane vapour expands through a turbine that is coupled to a generator generating electric power. Cold water from the bottom is pumped through the condensers, where the vapour returns to the liquid state. The fluid is pumped back into the boiler. Some small fraction of the power from the turbine is used to pump the water through the system and to power other internal operations, but most of it is available as net power.

Like other solar energy conversion system, the basic OTEC plant will be very attractive ecologically when compared to fossil fuel or nuclear power plant and will be virtually non-polluting. The production of ammonia at a tropical OTEC plant may prove attractive socially and economically. If interested to capitalize on the vast tropical ocean energy resource, hydrogen is likely to be the primary long term OTEC produced either directly or by the indirect route of using ammonia as a hydrogen carrier, which is then decomposed into N₂ and H₂ and fed in to H₂– O₂ fuel cells to produce electricity.

1.12.8 Biomass Energy

Plant matter created by the process of photosynthesis is called biomass. In plants, algae and certain types of bacteria, the photosynthetic process results in the release of molecular oxygen and the removal of carbon dioxide from the atmosphere that is used to synthesize carbohydrates (oxygenic photosynthesis). Other types of bacteria use light energy to create organic compounds but do not produce oxygen (non-oxygenic photosynthesis). Photosynthesis provides the energy and reduced carbon required for the survival of virtually all living organisms on our planet, as well as the molecular oxygen necessary for the survival of oxygen-consuming organisms. In addition, the fossil fuels currently being burned to provide energy for human activity were produced by ancient photosynthetic organisms.

1.12.8.1 Photosynthesis in Plants

It is the process by which plants, some bacteria, and some protists use the energy from chlorophyll. Most of the time, the photosynthesis process uses water and releases the oxygen for human survival. Further, there will always be need for the food and energy.

In plants (see Fig. 1.18), photosynthesis occurs mainly within the leaves. Since photosynthesis requires carbon dioxide, water, and sunlight, all of these substances must be obtained by or transported to the leaves. Carbon dioxide is obtained through tiny pores in plant leaves called stomata. Oxygen is also released through the stomata. Water is obtained by the plant through the roots and delivered to the leaves through vascular plant tissue systems. Sunlight is absorbed by chlorophyll, a green pigment located in plant cell structures called chloroplasts. Chloroplasts are the sites of photosynthesis. Chloroplasts contain several structures, each having specific functions.

Figure 1.18 A typical plant

1.12.8.1.1 Oxygenic Photosynthesis The photosynthetic process in all plants and algae as well as in certain types of photosynthetic bacteria involves the reduction of CO₂ to carbohydrate and removal of electrons from H₂O, which results in the release of O₂. This process is known as oxygenic photosynthesis.

Some photosynthetic bacteria can use light energy to extract electrons from molecules other than water. These organisms are of ancient origin, presumed to have evolved before oxygenic photosynthetic organisms.

1.12.8.1.2 Anoxygenic Photosynthesis These organisms occur in the domain bacteria and have representatives in four phyla—Purple Bacteria, Green Sulphur Bacteria, Green Gliding Bacteria, and Gram Positive Bacteria. By the middle of the 19th century, the key features of plant photosynthesis were known. Further, plants could use light energy to make carbohydrates from CO₂ and water.

In photosynthesis, solar energy is converted to chemical energy. The chemical energy is stored in the form of glucose (sugar). Carbon dioxide, water, and sunlight are used to produce glucose, oxygen, and water. The chemical equation for this process is

(1.23)

where [CH₂O] represents a carbohydrate (i.e., glucose, which is a six-carbon sugar). The synthesis of carbohydrate from carbon and water requires a large input of light energy. The standard free energy for the reduction of one mole of CO₂ to the level of glucose is +478 kJ/mol. Because glucose, a six-carbon sugar, is often an intermediate product of photosynthesis, the net equation of photosynthesis is frequently written as

(1.24)

The standard free energy for the synthesis of glucose is +2,870 kJ/mol. Most of the people do not understand chemically, so the abovementioned chemical equation is translated as

A combination of six molecules of water and six molecules of carbon dioxide produce one molecule of sugar and six molecules of oxygen.

Approximately 114 kilocalories of free energy are stored in plant biomass for every mole of CO₂ fixed during photosynthesis. Solar radiation striking the earth on an annual basis is equivalent to 1,78,000 TW, i.e. 15,000, times that of current global energy consumption. Although photosynthetic energy capture is estimated to be 10 times that of global annual energy consumption, only a small part of this solar radiation is used for photosynthesis. Approximately, two thirds of the net global photosynthetic productivity worldwide is of terrestrial origin, while the remainder is produced mainly by phytoplankton (microalgae) in the oceans that cover approximately 70% of the total surface area of the earth. Since biomass originates from plant and algal photosynthesis, both terrestrial plants and microalgae are appropriate targets for scientific studies relevant to biomass energy production.

Any analysis of biomass energy production must consider the potential efficiency of the processes involved. Although photosynthesis is fundamental to the conversion of solar radiation into stored biomass energy, its theoretically achievable efficiency is limited both by the limited wavelength range applicable to photosynthesis, and the quantum requirements of the photosynthetic process. Only light within the wavelength range of 4–7 μm is used by plants. This visible light wavelength range is known as photosynthetically active radiation (PAR).

For a 4-carbon sugar (C₄) plants, such as maize, sorghum, and sugarcane, which is the first product of photosynthesis? The photosynthetically active compounds captures photon energy of PAR is 80%. Photon energy of PAR lost (by absorption, reflection, and transportation) is 20%.

A minimum of eight photon energy of PAR are required to produce one mole of glucose and water each. Thus, energy of PAR conversion to glucose is 50%. Energy stored in the produced glucose from photon energy is 28%. Dark respiration is the reverse process of photosynthesis to sustain plants metabolic process. Photon energy consumed in this process from the stored energy of glucose is 40%.

Considering all the abovementioned facts, a maximum photosynthesis efficiency

For a 3-carbons sugar (C₃) plants such as wheat, rice, soya bean, and tree account for 95% of global biomass. The photosynthetically active compounds captures photon energy of PAR is 74%. Photon energy of PAR lost (by absorption, reflection, and transportation) is 26%. A minimum of eight photon energy of PAR are required to produce one mole of glucose and water each.

Thus, energy of PAR conversion to glucose is 50%. Energy stored in the produced glucose from photon energy is 28%. Dark respiration is the reverse process of photosynthesis to sustain plants metabolic process. Photon energy consumed in this process from the stored energy of glucose is 70%.

Considering all the abovementioned facts, a maximum photosynthesis efficiency

Thus, the efficiency of biomass production of C₃ plants is lower than C₄ plants.

Biomass includes solid biomass (organic, non-fossil material of biological origins), biogas (principally methane and carbon dioxide produced by anaerobic digestion of biomass and combusted to produce heat and/or power), and liquid biofuel (bio-based liquid fuel from bio-mass transformation, mainly used in transportation applications), and municipal waste (wastes produced by the residential, commercial, and public services sectors and incinerated in specific installations to produce heat and/or power). The most successful forms of biomass are sugar cane bagasse in agriculture, pulp and paper residues in forestry, and manure in livestock residues. It is argued that biomass can directly substitute fossil fuels, as more effective in decreasing atmospheric CO₂ than carbon sequestration in trees. The Kyoto protocol encourages further use of biomass energy. Biomass may be used in a number of ways to produce energy. The most common methods are combustion, gasification, fermentation, and anaerobic digestion.

1.12.8.2 Biomass Energy in India

India is very rich in biomass. It has a potential of 19,500 MW (3,500 MW from Bagasse-based cogeneration and 16,000 MW from surplus biomass). Currently, India has 537 MW commissioned and 536 MW under construction. The facts reinforce the idea of a commitment by India to develop these resources of power production.

Table 1.9 is a list of some states with most potential for biomass production:

Table 1.9 Potential for Biomass Production in India

The potential available and the installed capacities for biomass and Bagasse are as follows:

The major part of waste obtainable after the energy utilisation are non-organic, having diversified nature and characteristics, and thus, their identification and separation from the main waste stream by improved techniques are an essential parameter of any energy recovery scheme. On site processing of waste for the reduction of in-home compactors and industrial shredders through improved technology should be employed that may be environmentally acceptable. Collection and transportation components of the waste energy conversion scheme are the most expensive components owing to the many varying social, technical, and other reasons. A careful cost analysis and implementation of this vital component will minimize the running cost of the scheme. The storage of waste for resource recovery and final disposal after suitable treatment is another component of scheme and selection of storage station and other associated problems invite careful attention. Normally, two types of energy recovery systems are used.

Separation of metals, paper, and glass from the rest through the process such as size reduction, screening, vibrating sorting, and electronic scanning; however, a truly homogeneous, inexpensive separation scheme will provide competitive input to waste energy utilization. The conversion of the remaining waste product to usable energy includes:

1. Generation of methane gas (biogas conversion) or other fuels (biological conversion).
2. Generation of electricity either from (step 1) or through thermo-mechanical process.
3. Compositing for fertilizers.

Treatment is meant for those processes designed to reduce waste to innocuous forms without or after energy recovery. The most familiar techniques are the burning of waste at high temperature in the presence of oxygen (known as incineration) and the breaking down of the complex compounds using heat in the absence of oxygen (known as pyrolysis). However, treatment techniques should be selected so as to be accepted socially, environmentally, and economically. The cheapest method for final disposal of waste before or after energy recovery is a systematic burial in ground.

1.12.8.3 Biological Hydrogen Production

Biological hydrogen production appears to be another promising conversion technique for Indian environment as compared to other hydrogen producing schemes because of the following points:

1. The only energy input is solar energy and a hydrogen donor (probably seawater).
2. Biological hydrogen schemes can be operated at relatively low temperature (20°–50° C).
3. Scheme is free from pollution.
4. The fuel produced, hydrogen gas, is a clear burning fuel (yielding water).
5. It can be used for multi-utility scheme, such as production of food for human and animal consumption, fuel as methane or alcohol, and commercially usable chemical products.

1.12.8.4 Biogas Conversion

Organic wastes, which, on natural anaerobic digestion produce methane gas is an essential byproduct of civilization, often offensive in its raw state are available in plenty in both urban as well as rural areas. Anaerobic digestion not only provides valuable fuels and enhances the fertilizer value of the waste, but also provides a convenient, safe, aesthetic, and economical waste disposal method.

Anaerobic digestion is a complex biological conversion process during which organic matter is decomposed by anaerobic bacteria organism into stabilized minerals and gas. The organic substrate need not be pure. The entire substrate—carbohydrates, fats, and proteins—with the possible exception of a small amount of fibre is broken during the digestion process yielding methane and carbon dioxide.

Bio-energy conversion seems to be the most promising energy conversion techniques

(specifically for India) in near future probably because of the following points:

1. The absence or the difficulties related to the installation of centralized power supply systems.
2. Increasing energy demand for energy even in remote rural areas or isolated parts of the country.
3. Basic need for large amounts of protein for food and feeding purpose, and inexpensive methods available for collecting and storing of energy.

Energy schemes utilizing plant (biomass) as source of liquid fuel (such as ethanol or methanol) are, therefore, worth attempting in addition to electrical power generation. The production of usable energy through algal and similar crops includes the following three important conversion steps.

1. Production of organic matters and photosynthesis.
2. Collection and processing of plant material.
3. Fermentation of organic matter to produce liquid and gaseous fuels and their storage.

Sugar crops, trees, grains, and grasses are various aquatic fuel sources and have relative potentials on each other and utilized in any biomass production schemes. Sugar crops and algal crops seem to be the most promising crops of importance suitable for the bio-energy conversion in India.

1.12.9 Decentralized and Dispersed Generation

Decentralized energy is the opposite of centralized energy. It is also referred to as distributed energy, distributed generation, or onsite power generation. It generates the power and energy that a residential, commercial, or industrial customer needs onsite. Examples of decentralized energy production are solar energy systems and solar refrigerator energy systems.

Decentralized generation is the production of electricity at or near the point of use, irrespective of size, fuel, or technology. Decentralized electric generation will reduce capital investment, lower the cost of electricity, reduce pollution, reduce production of greenhouse gas, and decrease vulnerability of the electric system to extreme weather conditions and terrorist attacks. Decentralized generation can be distributed or dispersed and can be powered by a wide variety of fossil fuels.

Distributed power generation is any small-scale power generation technology that provides electric power at a site closer to customers than central station generation. Dispersed generation is similar to decentralized energy, which is the opposite of centralized energy. It is defined as the efficient deployment of clean, efficient, and renewable power, located very near a load centre, that can be anywhere in size from 1 MW to 100 MW.

Distributed generation is used mainly for onsite power generation. Dispersed generation is strategically located on the transmission grid to overcome bottlenecks in the transmission and distribution system and to improve the stability of the system.

1.12.9.1 Features of Dispersed Generation

Dispersed generation reduces both power transfers between regions of the power system and power imbalance in each region. Dispersed generation also allows for a uniform distribution of the overall system by responding fast to demand variation. Dispersed generation offers more flexibility and can be dispatched in incremental blocks of power as needed. It provides reliability and stability to the system. Total failure can be avoided when the load centres are supported by dispersed generation. A major outage such as the one experienced in August 2003 could have been avoided with the help of dispersed generation powered by reciprocating engines and bringing power back online within 10 min.

1.12.9.2 Types of Distributed Energy Resources

Distributed energy resource (DER) systems are small-scale power generation technologies (typically in the range of 3 kW to 10,000 kW) used to provide an alternative to or an enhancement of the traditional electric power system. The usual problem with distributed generators is their high costs. Following may be considered as distributed energy resources:

1. One popular source is solar panels on the roofs of buildings. Unlike coal and nuclear, there are no fuel costs, pollution, mining safety, or operating safety issues. Solar power has a low capacity factor, producing peak power at local noon each day. Average capacity factor is typically 20%.
2. Another source is small wind turbines. These have low maintenance and low pollution. Construction costs are higher per watt than large power plants, except in very windy areas. Wind towers and generators have substantial insurable liabilities caused by high winds, but good operating safety.
3. Solid oxide fuel cells using natural gas, like the bloom energy server, have recently become a distributed energy resource.
4. Distributed cogeneration sources use natural gas-fired microturbines or reciprocating engines to turn generators. The hot exhaust is then used for space or water heating or to drive an absorptive chiller for air conditioning.

The clean fuel has only low pollution. Designs currently have uneven reliability, with some makes having excellent maintenance costs and others being unacceptable.

1.12.9.3 Advantages for Dispersed Generation

1. Low cost of electricity: The fact that the consumer is benefited with low cost of electricity could well be the key driver for dispersed generation.
2. Geographical factors: Existence of transmission congestion and high price in major metropolitan areas provide ample potential for dispersed generation.
3. Saving on outage cost: The rising demand for premium power may force many industrial and commercial consumers to switch to dispersed generation to protect against the risk of power outages.
4. Increasing demand in intermediate sector: Flexibility to meet intermediate load accelerates the demand for dispersed generation.
5. Low payback period: As utility providers are worried about investing for long-term, dispersed generation calls for lesser investment and lower payback period.

1.12.9.4 Technological Options

Dispersed generation options can be classified either on the basis of the prime movers used or engines, turbines, fuel cells, or on the basis of fuel resources used (renewable and non-renewable).

Figure 1.19 illustrates the technology options for distributed generation. In India, many renewable energy technologies are being employed in a number of distributed generation projects. The technologies include biomass gasifier, solar thermal and photovoltaic systems, small wind turbines (aero-generators), and small hydro-power plants.

Figure 1.19 Technology options for distributed power generation

1.12.9.5 Relevance of Distributed Generation in India

In India, distributed generation has found three distinct markets:

1. Back-up small power generation systems including diesel generators that are being used in the domestic and small commercial sectors.
2. Stand-alone off-grid systems or mini grids for electrification of rural and remote areas.
3. Large captive power plants such as those installed by power intensive industries.

1.12.10 Geothermal Energy

There is a constant flow of heat from the hot interior of the earth, and a corresponding rise of temperature as one go deep underground. In most places, this is too little to be useful with present technology. However, some parts of the world are particularly favoured with very hot water or steam with only a few hundred meters below the surface, where the hot fluid breaks through naturally. Further, hot springs or geysers are found, and these have been used as heat source for hundreds of years.

As the resource varies so much from place to place, a ‘world total’ is obtained by detailed investigation of possible sites. The world total capacity for electricity production from geothermal resources is about 8,000 MW. The World Energy Council estimates that in 1999, about 68 TWh of energy came from geothermal sources, including both direct heat and electricity.

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating and opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming, if widely deployed in place of fossil fuels.

The International Geothermal Association (IGA) has reported that 10,715 MW of geothermal power in 24 countries is online, which is expected to generate 67,246 GWh of electricity in 2010. This represents a 20% increase in geothermal power online capacity since 2005. The growth of IGA projects is predicted to be 18,500 MW by 2015, due to the large number of projects presently under consideration, often in areas previously assumed to have little exploiTable resource.

In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants. The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California. The Philippines follows the US as the second highest producer of geothermal power in the world, with 1,904 MW of capacity online; geothermal power makes up approximately 18% of the country’s electricity generation.

According to the December 2011 report, India identified six most promising geothermal sites for the development of geothermal energy. These are in decreasing order of potential:

1. Tattapani in Chhattisgarh
2. Puga Valley in Jammu&Kashmir—first geothermal power plant, with 2–5 MW capacity at Puga in Jammu&Kashmir is proposed.

1.13 OIL SHALE

The rapid depletion rates of global reserves of conventional fossil fuel (oil) have led to an increased focus on unconventional oil sources, many of which are associated with shale. Oil shale is a fine-grained sedimentary rock that contains solid bituminous materials (called kerogen, which is an organic matter) that release petroleum-like liquids (shale oil or gas) when the rock is heated from which oil or gas can be extracted. All types of kerogen consist mainly of hydrocarbons, smaller amounts of sulphur, oxygen, and nitrogen, and a variety of minerals.

They were formed millions of years ago by deposition of silt and organic debris on lake beds and sea bottoms. Heat and pressure then transformed the materials into oil shale in a process similar to that forms oil over long periods of time. Similar to traditional petroleum, natural gas, and coal, oil shale and kerogen are also fossil fuels. Fossil fuels are developed from the remains of algae, spores, plants, pollen, and a variety of other organisms that lived millions of years ago in ancient lakes, seas, and wetlands.

Dr Chudamani Ratnam, former chief of Oil India Ltd, from 1990 onwards, repeatedly claimed that India had a big treasure of shale oil in Arunachal Pradesh and other parts of the northeast. He said these deposits could produce 140 million tonnes per year for 100 years, making India a net oil exporter. However, the deposits looked uneconomic, so he was not taken seriously.

Shale formations are best known for shale oil—a type of unconventional oil. Deposits of oil shale are found in many areas around the world and large areas of the United States, Russia, Argentina, Libya, Israel, and China are known to have shale oil and gas reserves. In the United States, it is claimed that the Green River formation is an underground oil shale formation that contains as much as 1.8 trillion barrels of shale oil. Despite the fact that not all of this can be extracted, it is claimed that shale oil reserve in United States will be more than three times the proven petroleum reserves of Saudi Arabia.

Oil shale generally contains enough oil that it will burn without any additional processing, and it is known as the rock that burns.

There are several different types of shale found throughout the world including oil shale and bituminous shale. These two types are important sources of various grades of unconventional oil. Shale oil was considered a more secure source of oil during the World War II but commercial development started only in 1960s. However, difficulty of extracting and producing oil from shale and environmental damage made it a less attractive resource compared to oil from conventional wells.

Most processes of shale oil production use significant amount of water and the chemicals used may harm humans and animals. The process is energy intensive and can require the burning of more fossil fuels in order to provide the necessary power supply.

1.13.1 Extraction of Shale Oil

Oil shale is underground rock formations that contain trapped petroleum. The petroleum trapped within the rocks is known as tight oil and is difficult to extract.

Oil shale can be mined and processed to generate oil similar to oil pumped from conventional oil wells. However, extracting oil from oil shale is more complex than conventional oil recovery and currently it is more expensive.

The important extraction processes of shale oil are as follows:

1. Ex situ retorting: Since the oil substances in oil shale are solid and cannot be pumped directly out of the ground, the following steps must be involved:
   1. The oil shale must be mined and brought to ground surface.
   2. The mined oil shale is then heated at a high temperature (a process called retorting). It involves heating kerogen in a process called pyrolysis. Pyrolysis is a form of heating without oxygen. At about 60°C–160°C, kerogen reaches its natural ‘oil window’, and at 120°C–225°C, kerogen reaches its natural ‘gas window’.
   3. The resultant liquid must then be separated and collected.
2. In situ retorting: An alternative method of extracting shale oil under experimental investigation is referred to as in situ retorting. During the in situ process, oil shale is not mined or crushed. Instead, the rock is heated to its oil window while it is still underground.

   It involves the following steps:

   1. Heating the oil shale while it is still underground
   2. Pumping the resulting liquid to the surface

   However, improvements in drilling technology, such as the emergence of directional drilling, has made extraction of oil from shale less cost prohibitive. Production companies use a variety of methods to extract oil from shale.

3. Hydraulic fracturing (fracking): It involves injecting pressured water and chemicals into a well in order to break into underground reservoirs. Steam can be injected underground in order to heat up oils in the surrounding shale formation, which then seep into the well. Acids can also be injected in order to increase the permeability of rock surrounding the well.
4. Volumetric heating: In this process, the rock is heated directly with an electric current. The heating element is injected either directly in a horizontal well or into a fractured area of the rock, until the oil shale begins producing shale oil. The oil could then be pumped directly from underground.
5. Combined technologies: Some methods are designed for both in situ and ex situ extraction. The internal combustion process uses a combination of gas, steam, and spent shale produced by ex situ processing. These compounds are burned for pyrolysis. The hot gas is continually cycled through die oil shale, pyrolyzing the rock and releasing oil.

1.13.2 Classification of Oil Shales

They are often classified as follows:

1. Depositional history: A sedimentary rock depositional history is the history of the type of environment in which the rock developed. The depositional history of an oil shale includes the organisms and sediments that were deposited, as well as how those deposits interacted with pressure and heat. The Van Krevelen Diagram is a method of classifying oil shales based on their depositional history. The diagram divides oil shales according to where they were deposited:
   1. In lakes (lacustrine): Oil shales from lacustrine environments are formed mostly from algae living in freshwater, saltwater, or brackish water. Lamosite and torbanite are the types of oil shales associated with lacustrine environments. Lamosite deposits make up some of the largest oil shale formations in the world. Torbanite deposits are found mainly in Scotland, Australia, Canada, and South Africa.
   2. In the ocean (marine): Oil shales from marine environments are formed mostly from deposits of algae and plankton. Kukersite, tasmanite, and marinite are the types of marine shales. Kukersite is found in the Baltic Oil Shale Basin in Estonia and Russia. Tasmanite is named after the region in which it was discovered, the island of Tasmania, Australia. Marinite, the most abundant of all oil shales, is found in environments that once held wide, shallow seas. Although marinite is abundant, it is often a thin layer and not economically practical to extract. The largest marinite deposits in the world are in the United States, stretching from the states of Indiana and Ohio through Kentucky and Tennessee.
   3. On land (terrestrial): Oil shales from terrestrial environments are formed in shallow bogs and swamps with low amounts of oxygen. The deposits were mostly the waxy or corky sterns of hardy plants. Cannel shale, also called cannel coal or ‘candle coal’, is probably the most familiar type of terrestrial oil shale. Cannel coal was used primarily as fuel for streetlights and other illumination in the 19th century.
2. By their mineral content: Oil shales are classified into three main types based on their mineral content:
   1. Carbonate-rich shale: The deposits have high amounts of carbonate minerals. Carbonate minerals are made of various forms of the carbonate ion (a unique compound of carbon and oxygen). Calcite, for instance, is a carbonate mineral common in carbonate-rich shales. Calcite is a primary component of many marine organisms. Calcite helps form the shells and hard exteriors of oysters, sea stars, and sand dollars. Plankton, red algae, and sponges are also important sources of calcite.
   2. Siliceous shale: It is rich in the mineral silica or silicon dioxide. Siliceous shales are formed from organisms such as algae, sponges, and microorganisms called radiolarians. Algae have a cell wall made of silica, whereas sponges and radiolarians have skeletons or spicules made of silica. Siliceous oil shale is sometimes not as hard as carbonate-rich shale and can more easily be mined.
   3. Cannel shale: It has terrestrial origins and is often classified as coal. It is formed from the remains of resin, spores, and corky materials from woody plants. It can contain the minerals inertinite and vitrinite. Cannel shale is rich in hydrogen and burns easily.

1.13.3 Use of Shale Oil (Tight Oil)

Shale oil has been used for more than thousands of years by mankind for meeting their energy requirements for road construction, caulking ship, and pipes leakage, and developing burning arrows (Agni band) for use during battle and decorative mosaic. It is only after World War II that shale oil got the newest attention.

1. Shale oil was used for a variety of products including paraffin wax.
2. R&D efforts proved that it can be used immediately as a fuel or upgraded as a refinery feedstock specification by adding hydrogen and removing sulphur and nitrogen impurities similar to crude oil.
3. It is burned to generate electricity.
4. Shale oil is similar to petroleum and can be refined into many different substances including diesel fuel, gasoline, and liquid petroleum gas (LPG).
5. Companies can also refine shale oil to produce other commercial products such as ammonia and sulphur. The spent rock can be used in cement production.

1.13.4 Problems Associated with Shale Oil Production

1. High processing costs: The high costs of heating and drilling wells made commercial oil shale production unprofitable, especially when the cheaper crude oil is available.
2. Environmental concerns: Mining for oil shale can have damaging effects on the environment, such as the following:
   1. When shale oil is combusted (heated), it releases carbon dioxide into the atmosphere. Carbon dioxide is a greenhouse gas.
   2. Substances in the oil shale, such as sulphides, react with water to form toxic compounds that are harmful to the environment and to human beings. Sulphides can cause effects from eye irritation to suffocation.
   3. Water containing toxic substances is unusable and expensive to decontaminate.
   4. The ash by-product can pollute ground, air, and water sources.
   5. Another environmental disadvantage is that extraction of shale oil requires enormous amounts of freshwater. Water is necessary for drilling, mining, refining, and generating power.
   6. It causes land and underground water degradation.

1.14 ENERGY STORAGE

Rapid fluctuations in the demand of electrical energy vary with the seasons, the days of the week, and even the hours of each day. However, the energy supply industry must be capable of generation, transmission, and distribution to meet the peak demand capacity. This results in the under-loaded or lowers the base load operation of the obtained energy. If this energy is stored and used during on-peak operation, there will be definite reduction in the capital cost of the generating systems and cause full use of transmission facilities in transmitting the stored energy to the appropriate locations without running the risk of environmental pollutions.

Further, the exploitation of new unconventional energy resources have indicated that all these resources suffer from the drawback of fluctuations in the energy output owing to many varying reasons. This necessitates the use of some form of energy storage techniques and is thus an essential parameter in the new unconventional energy resource development programme practicable at large scale.

Several energy storage techniques are available to handle large scale energy. Pumped hydro-power, compressed air, thermal oil, thermal steam, and lead acid batteries had their own importance up to 1985, which were superseded by advanced batteries and hydrogen storage up to 2000 AD. Later, super-conducting magnetic energy storage may be the promising scheme for the future. All these energy storage schemes are briefly outlined in following subsections.

1.14.1 Hydro Pump Storage

Energy available during off-peak period is used for pumping water from a lower to a higher elevation where it is stored. The energy may then be recovered during on-peak periods by allowing the water down through a water turbine coupled to an electric generator. Natural bodies of water, existing hydro plants’ reservoirs, especially constructed surface reservoirs or underground cavern or any possible combination of all are used as storage reservoirs. Pumping and generation may be obtained simultaneously by a reversible pump turbine connected to a motor generator.

1.14.2 Compressed Air Storage

Compressed air can be stored in a constant volume and variable pressure reservoirs or in a hydrostatically compensated and constant pressure reservoir, which may be either in natural cavern or a man-made cavity. A modified combustion turbine is used for energy recovery. Compressors and turbines are uncoupled so that they can be operated at different times. During power generation, the function of the combustion turbine compressor is replaced by air from storage.

1.14.3 Thermal Storage

Energy may be stored as sensible heat in fluids or as latent heat in materials that undergo a phase change that may assist in maintaining the steam supply constant while the electrical output of the plant is varied.

1.14.4 Electrochemical Storage or Battery Storage

Except all hydrogen storage, (which is treated as chemical storage), it includes both the conventional battery storage and the hybrid system suitable for the storage of the chemical reactants external to the electrochemical converters. Such a storage system is simple, reliable, and fairly compact system.

1.14.5 Inertial Storage

Energy during the off-peak period is stored in the rotating mass of a flywheel, which can be recovered during the on-peak period. dc Motor and converter, variable frequency field machine and similar equipment are used in such system.

Complete flywheel energy storage system needs a careful study of social, fatal, and other problems during its failure. However, a single motor–generator may be coupled to a number of flywheels.

1.14.6 Hydrogen Storage

Hydrogen storage seems to be the only well-defined, achievable, energy storage system that is sufficiently developed and is likely to outclass the other types of energy storage in the near future. Hydrogen storage may incorporate the well-established technology of gas storage in high pressure tanks or certain kind of metal hybrid storage. Hydrogen thus obtained during off-peak periods and stored can be used during on-peak period either directly or as electricity through fuel cells, etc.

1.14.7 Superconducting Magnetic Energy Storage

In this system, electrical energy is stored in a magnetic field produced by a circulating current in the winding of a magnet. Although this system seems to be very promising during the next century, a thorough study of energy loss during storage period, size etc., are required to be economically acceptable.

1.15 CONCLUSIONS

There is no doubt that various aspects of energy conversion and storage, which have been discussed in the previous sections, have individual and collective importance, but it is essential that attention must be diverted towards the development of reliable and cheap energy conversion and storage schemes capable of being well-appreciated by common people.

It may be mentioned that energy from the sun, biogas, and agricultural waste and their conversion through thermo-mechanical, photovoltaic, biological processes, and storage of energy as hydrogen energy seem to have much potential. While the need for the conservation of energy is recognized, it is too early for India to apply brakes on growing use of energy in various spheres of life, as India is still in a developing stage. However, necessary step must be taken to avoid excessive energy use for non-essential utility.

SUMMARY

• It may be difficult to find out exactly how people’s senses of values have changed through history. Energy consumption pattern can be approximated as exponentially rising till today because of growing population except during the period between World War I and II.
• Energy system model is characterized by production and sustenance, inputs, outputs, feedback, and dissipation.
• System acceptability index (δ) can be taken as the measure of gross efficiency of the system. The numerical value of δ is a measure of the system’s acceptability. A value of δ = 1 can be approached by properly conducting any energy management program to avoid dissipation in the system.
• Energy is a key measure of techno-socio-economic development of a nation.
• Energy consumption and energy scarcity are the main cause of social inequalities between peoples and disparities between developed, developing, and underdeveloped nations.
• Energy resource is defined as any material objects that can be quantified (available in huge quantity) and transferrable (easily converted to useful form).
• Secondary energy resources are usable forms of energy generated by means of suitable plants to convert the primary energy. They are electrical energy, steam power, hot water power, hydrogen energy, and so on.
• The electrical energy is expected to remain as dominant usable form of energy (secondary energy) during centuries as its generation, transmission, distribution, and utilization methods are well established.
• Oil shale is a fine-grained sedimentary rock that contains solid bituminous materials (called kerogen, which is an organic matter) that release petroleum-like liquids (shale oil or gas) when the rock is heated from which oil or gas can be extracted.
• Difficulty of extracting and producing oil from shale and environmental damage caused made it a less attractive resource compared to oil from conventional wells.
• It is essential that attention must be diverted towards the development of reliable and cheap energy conversion and storage schemes that are capable of being well-appreciated by common people.

REVIEW QUESTIONS

1. Define the term energy. Explain its significance in context of techno-socio-economic development.
2. Draw and explain energy system model of any energy activity. Further, explain its parameters and significance.
3. Discuss causes of energy scarcity. Further, mention factors to be considered for solving energy crunch problems.
4. Define system acceptability index and explain its importance.
5. What is an energy system? Explain in brief.
6. Define and explain the term ‘energy resources’. Discuss different ways of their classifications. Mention at least two energy resources in each category.
7. What are the conventional and unconventional energy sources? Describe briefly.
8. List various non-conventional energy resources. Give their availability, relative merits and demerits, and their classification.
9. Discuss the main features of non-conventional energy resources.
10. Briefly explain economic criteria for comparing non-conventional energy resources.
11. What are the conventional and unconventional energy sources? Describe briefly.
12. What are primary and secondary energy sources?
13. What are the advantages and limitations of renewable energy sources?
14. Explain why direct energy conversion processes are becoming more important as compared to conventional generation.
15. What is the various primary energy resources utilized in direct-energy conversion?
16. What are the practical difficulties in exploiting non-conventional energy resources?
17. Discuss the future prospects of solar energy use.
18. Explain the basic principle of Ocean Thermal Energy Conversion (OTEC).
19. How does biomass conversion take place?
20. What are the limitations of solar cells?
21. What is the meaning of biomass? Further, discuss its multipurpose utilization
22. Justify the statement ‘the future fuel of the world will be hydrogen obtained by electrolysis of water with the energy’.
23. Describe the principle of solar photovoltaic energy conversion.
24. What are the different sources of geothermal energy?
25. Discuss the availability of geothermal energy.
26. Explain the basic reasoning that most of the direct energy conversion devices can be classified into ‘cells’ and ‘heat’ systems.
27. Explain and distinguish between tidal, wave, and ocean thermal energy.
28. Explain the basic principle of MHD generator. Further, discuss the practical problems associated with MHD power generation.
29. Discuss the principle and working of MHD power plant.
30. Discuss the performance and limitations of various fuel cells available.
31. Explain the theory of momentum with respect to wind power.
32. Discuss the theory and working principle of ocean thermal energy conversion systems.
33. Discuss the principle and working of sea wave and tidal energy conversion system.
34. Discuss the principle of a solar collector. How collector coating can be used to improve the performance of collector?
35. Discuss the principle of MHD generation.
36. Explain the meaning of decentralized power generation.
37. Describe dispersed generation and mention its applications.
38. State and explain different methods of energy storage.