Chapter 1

Introduction to Energy Systems

The history of humankind, in many ways, is a story of its quest to enhance its standard of living [1]. Notwithstanding the inequities across nations, regions, and societies, this has been overall a success story, with a nearly continual increase in the global mean standard of living since the beginning of time. This increase has been exponential over the last two centuries, and amazingly has continued despite the explosive growth in the global population. The key to this success has been the human ingenuity in harnessing natural resources, none more important than energy. Energy is indeed the master natural resource; it is essential for securing other resources, and with sufficient availability, enables creation of all other resources [2]. The primary energy sources exploited by humankind to satisfy its energy needs depend upon several factors, including resource availability and limitations, technology readiness, impact of utilization, and economics. The interplay of these factors ensures that energy resources, utilization, and distribution patterns remain in a constant state of evolution [3].

A key question regarding humankind’s energy future is whether the society can transition to a “100% renewables” future and do so without an adverse impact on the standard of living [1, 4]. In order to answer this question, it is necessary to understand the magnitude of the challenge, as well as the architecture of the energy systems and the drivers for a change in these systems, particularly with respect to the primary energy source. These concepts are introduced in this chapter, followed by a discussion of renewable energy sources, which provides the context for the subsequent chapters.

1.1 Energy and Society

Energy is ubiquitously regarded as the primary driver for economic growth of societies and nations [5, 6]. The per capita gross domestic product (GDP) of nations unfailingly shows a strong correlation with the per capita total energy usage [1], as shown in Figure 1.1.

A graph represents the functional relationship between GDP and energy consumption across several countries.

Figure 1.1 Per capita gross domestic product as a function of energy consumption.

Source: Newman, J., C. A. Bonino, and J. A. Trainham, “The Energy Future,” The Annual Review of Chemical and Biochemical Engineering, vol. 9, 2018, pp. 153–74.

As seen in Figure 1.1, the parameters (per capita GDP and energy consumption) of advanced economies, such as the United States and other OECD (Organisation for Economic Co-operation and Development) countries, are several orders of magnitude higher than those of developing economies in Asia, Africa, and the Americas. This correlation serves to underline the linkage between energy consumption and development of human capital/human well-being [7]. Developing countries account for roughly one-third of the global energy consumption at the present time [7], while having roughly 60% of the world population [8]. As these countries, with their growing populations, aspire to improve their quality of life and seek to replicate the standard of living of the developed countries, global energy demand can be expected to increase unabatedly in the near future.

Estimates of the global energy consumption are available from several sources including governmental and nongovernmental organizations (e.g., U.S. Department of Energy and the International Energy Agency [IEA], respectively), as well as industries (e.g., BP), which typically publish their energy consumption data annually. The Energy Information Administration (EIA)1 estimates the world energy consumption to be 600 quad (quadrillion Btu)2 in 2018, projecting it to rise to 739 quad by 2040 [9]. The non-OECD countries are anticipated to account for 64% of the energy consumption in 2040, a near-total reversal of the current consumption pattern.

1. The Energy Information Administration (www.eia.gov) is a statistical entity within the U.S. Department of Energy (www.energy.gov) that is engaged in collection, analysis, and dissemination of energy information to help policymakers and improve the energy understanding of the public.

2. A quad (1015 Btu) is a common unit of energy used in the discussion of energy consumption of societies. Other units frequently used in such discussions are exajoules (EJ) and million or billion tons of oil equivalent (Mtoe or Gtoe); 1 quad = 1.055 EJ ≈ 25.2 Mtoe.

It should be noted that, while the level of energy consumption can be correlated to the state of a society’s economy, the precise nature of the causal relationship between energy consumption and economic growth (GDP) is dependent on many factors that are specific to the society [10, 11]. For many societies, the “growth hypothesis” may describe the relationship implying a unidirectional dependence of economic growth on energy consumption. Increasing energy consumption spurs economic growth in such societies. Conversely, for some societies the unidirectional dependence is reversed, with energy consumption increasing with economic growth. However, conserving energy consumption has no impact on economic growth, a situation described as the “conservation hypothesis.” The other two alternative hypotheses that may describe the relationship between the two are the “neutrality hypothesis,” which presumes no causal relationship, and the “feedback hypothesis,” where economic growth and energy consumption both depend on each other [12]. The energy economics literature is replete with studies that seek to examine the relationship between the two for different countries and regions [11]. The overarching inference drawn from these studies is that the relationship is highly complex and no universal relationship is applicable across different economies. However, there appears to be a high likelihood of electricity consumption as the measure of economic growth, suggesting that limiting electricity consumption will put limits on the economic growth of a society [12]. Electricity, however, is not a primary energy source but is an energy carrier, and it is necessary to understand the energy system architecture that serves the energy demands of the society.

1.2 Energy System Architecture

Energy system architecture is frequently visualized as an interconnection of five elements [13, 14]:

  1. Services are the demands of individuals and society; for example, transportation, communication, comfortable environment, and so on.

  2. Service technologies are systems that provide the desired services through various appliances and machines; for example, automobiles, air conditioners, and so on.

  3. Energy currencies (or carriers) are materials or forms of energy that provide the motive forces for operating the service technologies. Electricity, heat, hydrogen, gasoline, methanol, and methane are typically cited as examples of energy currencies [15].

  4. Transformer technologies provide the energy currencies by conversion of energy sources. Thermal power plants and solar photovoltaic devices are two examples of transformer technologies that provide the energy currency, electricity.

  5. Energy sources are natural resources and raw materials used for obtaining energy currencies via transformer technologies. Coal, petroleum, sunlight, wind, and so on are examples of energy sources.

This energy system architecture is shown in Figure 1.2 in the form of a qualitative flow diagram.

A figure presents the architecture model of energy system.

Figure 1.2 Energy system architecture.

The energy sources, currencies, and services are represented by arrows indicating material or energy flows. The transformer and service technologies are represented as blocks indicating a combination of equipment, processes, and operations. The system has a clearly identified input (energy source) and an equally clearly identified output (service). The functions of the transformer technologies and service technologies are also apparent in this architecture. The energy source forms the feed (inlet) stream of the transformer technologies that yield an energy currency as the product (outlet) stream. The energy currency is the feed (inlet) stream to the service technologies, and the outlet of the service technologies is the desired service, which is the final product of the entire energy system.

It can readily be seen that different energy currencies can be used via different service technologies to obtain the same service. For example, the demand for transportation service can be satisfied by using liquid fuels, such as gasoline and diesel, or electricity through different service technologies—an internal combustion engine (ICE) for liquid fuels and a motor (typically an AC motor) driven by electricity. Similarly, the demand for heat for cooking food can be satisfied by using hydrocarbon fuels (natural gas, kerosene, etc.) in a stove, or electricity in a microwave oven or cooking range.

1.3 Evolution of Energy Systems

The choice of the energy currency for a particular service depends on many factors, including availability of both the currency and service technology, convenience and ease of use, safety and environmental/health impacts, and above all, cost. Furthermore, one can expect a continuous evolution in the components of the energy system architecture for a particular service as more effective currencies, service technologies, and transformer technologies become available. As an example, the need for artificial lighting was satisfied through utilization of gas and kerosene in the 19th century; however, the use of these energy currencies has been effectively supplanted by electricity, wherever it is available. The transition away from hydrocarbon sources to electricity can be ascribed to factors such as increased efficiency, lower cost, increased safety through lower risk and hazards, convenience, and flexibility [16]. Similarly, several different energy currencies—firewood and other biomass, liquid hydrocarbons (kerosene), gaseous hydrocarbons (natural gas, liquefied petroleum gas [LPG]), electricity—are used worldwide to satisfy the demand for cooking. A large number of households in developing countries rely heavily upon solid (firewood) and liquid (kerosene) fuels, while those in developed countries typically use gaseous fuels or electricity. This transition to gaseous fuels and electricity is also observed in more affluent segments of societies in developing countries [17].

Electricity is the most versatile of energy currencies and is the one most used by people for cooling, heating, lighting, cooking, and operating a variety of machines, instruments, equipment, and so on. Electrical energy provides the motive power for a large fraction of public transportation systems, particularly in urban areas. Even in personal transportation applications, a field dominated by hydrocarbon-fueled ICE vehicles, newly emerging electric vehicles are beginning to garner a bigger share. It should be noted that electric vehicles dominated the automobile market before rapid developments in ICE technology, which resulted in the disappearance of electric vehicles from the road toward the end of the second decade of the 20th century [18]. Electricity may again be the dominant (if not sole) energy currency in transportation service, not only through the developments in transportation technologies but also aided by mandates such as the decision of the United Kingdom to ban the sale of nonelectric vehicles from 2040 onward [19]. Similar initiatives are being considered by other jurisdictions—California in the United States, for example—which intend to shift the societies toward a nonhydrocarbon transportation future. Regardless of whether this future is realized or not, the importance of electricity as the energy currency is bound to increase.

The ubiquity of electricity for a vast majority of services is, in part, due to its high “quality,” or exergy, which is a measure of the maximum amount of work that can be obtained from an energy source [20, 21]. Electricity’s high exergy, coupled with the ease of utilization with virtually no training requirements on the part of the end user in most applications, contributes to its dominant position in energy systems. However, apart from the end-use considerations (diversity and multitude of service technologies and applications), the other equally significant contributing factor is that it can be obtained relatively easily from practically every primary energy source.3 The primary energy sources typically used for generation of electricity can be classified into fossil sources (coal, natural gas, petroleum, and other hydrocarbons), nuclear, and renewables (solar, wind, hydropower, and biomass). According to EIA, the fossil sources accounted for 59% of ~4200 billion kWh of electricity generated in the United States in 2020, while the nuclear and renewables contributions were 19% and 21%, respectively. Natural gas and coal dominated the fossil generation section, while hydropower and wind dominated the contributions of the renewables sector. Figure 1.3 shows EIA’s reference case scenario (where the United States is a net energy exporter in the near future) for the roles of primary energy sources in electricity generation through 2050 [22].

3. Theoretically, it is possible to convert any form of energy to any other form. However, in some cases, it may require an inordinately complex scheme to accomplish the conversion, unlike the generation of electricity. Notwithstanding the complexity of the transformer technology (conversion process and plant), the path for conversion to electricity from any primary energy source is usually straightforward and well defined.

A graph presents the comparison of four different energy sources' contribution as primary source of electricity generation.

Figure 1.3 Electricity generation from primary energy source: EIA reference case scenario.

Source: U.S. Energy Information Administration, “Annual Energy Outlook 2021 (aeo2021),” https://www.eia.gov/outlooks/aeo/pdf/AEO_Narrative_2021.pdf.

As seen in Figure 1.3, the shares of both nuclear and coal as a primary energy source for electricity are projected to decrease significantly, whereas those of natural gas and renewables are projected to increase. This increase is incremental for natural gas, while it is quite substantial for renewables. It should be noted that electricity generation accounts for ~38% of the primary energy consumption in the United States, with the remaining 62% consumed by transportation, industrial, residential, and commercial sectors.4 Overall, all forms of renewable energy are expected to account for nearly 17% of the total primary energy consumption in 2050, including all sectors of the U.S. economy. The percentage contributions of fossil and nuclear resources will decrease, with the decrease in contribution from coal consumption offsetting an increase in natural gas [22]. Globally, the primary energy consumption is anticipated to exhibit a similar pattern, with renewables accounting for 15%–17% of the total primary energy consumption and fossil sources showing an overall reduction primarily due to the decline in exploitation of coal for electricity generation [9].5 The factors influencing these trends are briefly discussed below.

4. The actual numbers for 2020, according to EIA, were electrical power, 38.3%; transportation, 26.4%; industrial, 24.0%; residential, 6.7%; and commercial, 4.3%.

5. A discrepancy can be seen between the numbers for various sectors and energy sources reported by different forecasting organizations. For instance, IEA World Energy Outlook numbers [23] will be different from those forecast by EIA. Nevertheless, all such forecasts for future energy systems will exhibit a similar trend of a decreasing fossil and increasing renewables portfolio.

1.3.1 Fossil Sources: Resource Limitations and Climate Change

Earth has a finite volume and mass, and in theory, all resources derived from the earth, including fossil energy resources, are limited and subject to exhaustion depending on the utilization rates. Resource limitations, none more so than those of energy resources, have a direct impact on the economics and well-being of societies, and scientists have long attempted to forecast fossil resource utilization and potential exhaustion trends [3]. Sometimes these attempts are spectacularly successful, as exemplified by the predictions of M. King Hubbert, a much celebrated geologist for Shell Oil. Hubbert accurately predicted the peak oil production year for North America, giving rise to the term “Hubbert’s Peak” [23]. Several scientists have attempted to apply Hubbert’s principles to analyze regional and global oil productions, also predicting peak oil production years [24]. Unfortunately, these peak year predictions have failed to match up in real time, and oil production does not seem to show any signs of slowing down, mainly due to the technological advances and human ingenuity in exploiting both the “conventional” and “nonconventional” types of oils [25, 26]. It should be noted that, globally, the oil production and supply situation is influenced by political decisions, as well-known reserves are located in geopolitically unstable regions. The price of oil has exhibited significant fluctuations in recent years, and these fluctuations can have a severe impact on the economies of less-developed, poorer countries [25].

Similar resource limitation concerns have been often expressed with regard to coal6 and natural gas; like petroleum, there seems to be no end in sight for either of these two resources. EIA predictions for natural gas do not show any signs of production slowing down over the next three decades [22].

6. Concerns about Britain running out of coal were expressed as early as in 1865 (Jevons, William Stanley, The Coal Question: An Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of Our Coal-Mines, Macmillan, London, 1865). Jevons warned that coal shortages were imminent, and continued growth and prosperity of the country was impossible.

The production of coal is indeed expected to decline, as seen in Figure 1.3. However, this decline is not in any way related to resource scarcity but is due to the role of fossil fuels in climate change in general. The use of coal is particularly fraught with adverse consequences on the environment. A large percentage of coal deposits around the world is of low quality, with sulfur being the predominant impurity. Using this “dirty” coal without appropriate “clean coal technologies” results in the emissions of SOx and NOx, which return to the ground in the form of acid rain [27]. It should be noted that coal contains several other impurities including heavy metals, such as lead, cadmium, mercury, tin, nickel, antimony, arsenic, and so on, in addition to sulfur and nitrogen; treatment/abatement steps are needed to prevent them from harming human health and the environment. The need to incorporate processing steps to prevent or minimize the adverse effect on the environment imposes economic costs on coal use, reducing its competitiveness as a primary energy source. Similarly, the quality of crude oil and petroleum fractions is also progressively getting low, with higher sulfur and other impurities imposing processing requirements similar to coal [28].

However, the most significant driver for reduction in the use of fossil fuel resources, whether clean or dirty, is the concern for climate change due to the emission of greenhouse gases (GHGs), such as carbon dioxide, nitrous oxide, and methane, as a result of the combustion and handling of fossil fuels [29]. Carbon dioxide is considered to be the controlling factor in global warming caused by the GHGs; increase in atmospheric carbon dioxide concentration from a long-time stable value of 300 ppm to current levels of ~414 ppm is attributable to the anthropogenic carbon emissions from the burning of fossil fuels since the beginning of the industrial revolution in the late 18th century [29, 30]. These emissions may cause the mean surface temperature of the earth to rise by anywhere between 2°C and 6°C above the preindustrial levels [29]. In 2018, IPCC, the Intergovernmental Panel on Climate Change, issued a special report outlining the impact of a temperature rise of 1.5°C on human beings and ecosystems [31]. Among the most severe impacts possible due to this temperature rise are as follows:

  • Rising sea levels making much of the coastal land uninhabitable, displacing millions of human beings

  • Increase in the frequency and intensity of climate extremes and weather events (rainfalls, droughts, hurricanes, etc.)

  • Loss of biodiversity through species loss and extinction on land

  • Reduced productivity of fisheries and aquaculture, as well as reduced yields from crops

  • Increased morbidity and mortality

Limiting the damage to the earth’s climate requires addressing the presumed cause contributing to this damage. Future energy systems are hence expected to lessen their dependence on fossil fuel resources.

1.3.2 Nuclear Energy: Economics, Safety, and Waste Management

Developments in nuclear physics in the latter half of the 19th century to early 20th century led to harnessing of the energy of nuclear fission, first for destructive purposes in the Second World War, and second for civilian nuclear power after the war [32]. Today, 448 nuclear reactors worldwide provide ~400 GW of electricity, with nearly 100 more reactors under various stages of planning and construction. The United States has 98 operating reactors that supply electricity to satisfy ~18% of consumer demand [33]. Although the United States accounts for nearly 25% of the nuclear electricity generated worldwide at the present time, it has only four new reactors in the planning or construction stages, and several reactors in its aging fleet (few new reactors were brought online in the last 30 years) are facing closure [34]. This situation is dramatically different from the optimistic scenarios visualized in the mid-1970s, where 15-GW-capacity nuclear reactors of the future were going to produce electricity too cheap to be metered [35].

As mentioned earlier, EIA visualizes a decreasing contribution of nuclear power to U.S. electricity over the next few decades. There are three major drivers for this trend:

  1. Economics: Electricity markets are highly complex entities, with a price structure that fluctuates with demand. Nuclear plants, best suited for base-load power generation, are finding it difficult to compete with low-cost natural gas–fired plants that have superior load-following characteristics and tax-advantaged renewables [36, 37].

  2. Safety: The three major accidents in the history of civilian nuclear power—Three Mile Island (TMI) in 1979, Chernobyl in 1986, and Fukushima in 2011—have raised significant concerns regarding the safety of the nuclear plants [38], and these concerns have impeded the growth of nuclear power.

  3. Nuclear Waste Disposal: Nuclear fission results in the generation of waste streams that retain toxic characteristics for a long time. These waste streams need to be managed responsibly in a manner that is acceptable to the general public [39].

The safety concerns have played such a major role in arresting the growth of nuclear power that it is worthwhile to take a closer look at the three nuclear accidents:

Three Mile Island (TMI): Commercial nuclear reactors in the United States belong to the category of light water reactors (LWRs) utilizing ordinary (light) water to moderate the fission reaction and function as the coolant to transfer the resulting thermal energy to the power conversion system. The nuclear reactor at the TMI power station near Harrisburg, Pennsylvania, was a pressurized water reactor (PWR) wherein no boiling occurs in the primary coolant circuit operating at high (~15 MPa) pressure. Instead, steam generation takes place in a number (typically four) of steam generators where the primary coolant transfers the heat released in the nuclear fission to a secondary stream of light water. The resulting steam drives the turbines in the power conversion system before returning to the steam generators as condensate. A key component of the entire circuit is the pressurizer, which is a vessel containing steam in the upper section and water in the lower section. The pressurizer also has provisions for heating the water as well as spraying cool water into the upper section. The pressurizer functions to maintain the necessary pressure in the reactor and prevents vaporization of the primary coolant in the reactor [40]. The piping circuit connected to the vapor space of the pressurizer includes a pressure relief valve designed to prevent pressure buildup by venting the excess steam into a pool of water in a pressurized relief tank.

The incident at TMI on March 28, 1979, started with a minor malfunction in the secondary circuit that caused the temperature to increase in the primary circuit. The control system reacted to shut down the reactor, and the relief valve opened as designed to relieve the excess pressure in the primary circuit. The valve was programmed to close after a few seconds; however, it remained stuck in the open position, continuing to vent the primary coolant into the relief tank. Unaware of the open position of the relief valve, the operators stopped injection of water into the pressurizer believing the water level to be adequate in the pressurizer and the fuel in the reactor core to be covered in water. This mistake was noticed only after about 2 hours, at which point the core had boiled dry due to the decay heat and partially melted. A substantial amount of hydrogen was produced, mainly due to the reaction between water and the zircaloy cladding of the fuel, and released through the open valve. This led to a hydrogen deflagration resulting in a pressure spike.

Nuclear power stations are designed with multiple layers of containment, and the TMI plant was no exception. The large dry containment—the reactor building—enclosing the nuclear components of the power station (the reactor, steam generator, pressurizer, and relief system) performed as designed, containing the deflagration and preventing any release. Steps taken to close the valve and to force coolant injection into the coolant circuit after discovering the faulty open position of the relief valve prevented complete meltdown of the core, and the molten portion of the core was contained in the reactor vessel. Substantial amounts of radioactive and volatile fission products—cesium, iodine, barium, strontium, and so on—were generated, all of which were contained within the reactor building. The only minor releases were those of biologically inert noble gases having a short half-life [41]. The average dose received by the population in the area is estimated to be equivalent to one-tenth of what a person would receive in a return flight between the United States and Europe.

Chernobyl: The nuclear reactor at Chernobyl in Ukraine near its border with Belarus was also an LWR, a graphite-moderated boiling water reactor (BWR) of Russian design designated as a reaktor bolshoy moshchnosty kanalny (RBMK) reactor. It is a channel-type reactor, as can be inferred from the name of the reactor, with each channel containing a fuel element cooled by water flowing upward through the channel. A key difference between the BWRs in the United States and the RBMK reactors of Russian design is the positive void reactivity coefficient of the RBMK reactors. This positive void reactivity coefficient results in increasing reactivity (power) with increasing void fraction in the reactor, that is, more coolant being vaporized. The RBMK reactors are also characterized by a high complexity control system, as the channels operate independently of one another. The accident at Chernobyl occurred while conducting some tests during a planned shutdown in April 1986. The accident was initiated in the early morning of April 26, when the operators inserted all the control rods in the reactor for its shutdown. Unfortunately, the reactor design also has a positive “scram” effect that resulted in a power surge, contrary to the operator intent. The power surge damaged fuel elements and ruptured channels, resulting in the formation of a large amount of water vapor in the reactor core. This fed into the positive void reactivity coefficient, leading to an enormous explosion within 6–7 seconds of the initial action of the operators [42]. The initial explosion lifted and overturned the 1000-ton lid of the containment, and combined with subsequent explosions, resulted in massive destruction of the reactor, evaporation of fuel, and spewing of fuel fragments and all kind of debris into the environment. The remaining graphite from the reactor continued to burn over the next 10 days, further emitting all kinds of radioactive contamination. The scale of the explosion resulted in the releases reaching high altitudes, which in turn caused their dispersal over a very large area, effectively all over Europe. Immediate fatalities attributable to the accident are estimated to be 30, while the long-term radiological exposure has resulted in 6500 cases of cancer with about 15 fatalities.

Fukushima: Unlike TMI and Chernobyl, the trigger for the events at Fukushima Daiichi Nuclear Power Station, located 250 miles from Tokyo on the east coast of Japan, lay outside the plant boundary. The epicenter of a magnitude-9.0 earthquake on March 11, 2011, was 200 km away; however, the power of the earthquake set in motion a tsunami that inundated the power station completely within an hour, with wave heights reaching 14 meters, more than twice the height the plants were designed to withstand. Three of the six BWRs at the site were operational, while the other three were under annual maintenance. The operating units were tripped successfully upon detection of the seismic waves, and the control system switched on automatically the on-site emergency diesel generators to drive the coolant circuit upon the loss of grid power [42]. The tsunami flooded these diesel generators resulting in the loss of power to all systems, including controls and instrumentation. The net effect was what is termed a loss of coolant accident (LOCA) with the consequent loss of ability to remove the decay heat from the reactor cores. The cores overheated and melted; release of fission products and subsequent reactions resulted in overpressure compromising the integrity of the containment vessels.

Unlike Chernobyl, the reactor cores did not explode, and the radioactive contaminants released were mostly gaseous and volatile fission products. In comparison, the composition of contaminants in Chernobyl corresponded to that existing in the reactor core. Compared to Chernobyl, there were no cases of acute radiation exposure, and the overall affected area is approximately an order of magnitude lower. The radiation dose received by the population in the surrounding area is not expected to result in statistically significant increase in incidences of cancer [41].

The event at TMI was relatively minor in terms of direct impact on human health or the environment; however, it did manage to create an adverse impact on the general public regarding nuclear energy. The net effect was an abandonment of plans for new nuclear plants, both within the United States and internationally, effectively putting brakes on the anticipated expansion of nuclear power [43]. The accident at Chernobyl resulted from a combination of faulty reactor design and operator error, and had immediate catastrophic consequences, as well as continuing effects at the present time [44, 45]. The accident at Fukushima was a consequence of a natural event—a magnitude-9 earthquake triggering a massive tsunami that overwhelmed the safety systems at the plant. The accident was severely disruptive on individuals and society—resulting in displacement of population within a 20-km exclusion zone around the plant—and devastating in its economic consequences. It should be noted that while the severity of the accident can be equated to the Chernobyl disaster, it was similar to the TMI event in terms of immediate acute effects and casualties. Nevertheless, the Fukushima accident resulted in a significant change in public opinion on nuclear energy, and globally people have become less accepting of nuclear power [46].

The nuclear industry has responded to these events by undertaking development of advanced reactors (the so-called Gen IV reactor systems; for more details, visit: https://www.gen-4.org/gif/jcms/c_59461/generation-iv-systems) that have enhanced and passive safety features, as well as implementing steps to make conventional nuclear plants safer. The nuclear industry is also confident of its ability to have a scientifically and technologically sound solution for effective long-term stewardship of nuclear waste; however, it has, so far, been unable to convince the general public about the viability of the proposed waste disposal/management options [39].

It is possible that the nuclear industry can overcome the concerns regarding plant safety and spent fuel/radioactive waste management, and may well commercialize the advanced reactors sometime in the future. However, such developments are not expected to occur within the next two to three decades. The diminishing role of fossil fuels and nuclear energy as primary energy sources presents an opportunity for renewables to play an ever-increasing role in the energy system.

1.4 Future Energy Systems: Growth of Renewables

Population growth and economic development, coupled with technological progress, will continue to drive ever-increasing energy needs around the world [47]. The EIA anticipates the global energy consumption to increase by ~25% over the next two decades, with an ever increasing number of nations and societies engaging in an endeavor to find cheap sources of energy to fuel their needs for wealth and quality of life [9, 48]. At the same time, there is a growing realization of the serious environmental impacts of energy use, including climate change, that have severe consequences for the world [48].

Energy systems across the world are evolving in response to economic and environmental pressures. With reference to the energy system architecture described earlier in this chapter, there is an increasing penetration of electricity as the energy currency or carrier in most services, including transportation service. Examination of forces affecting the primary energy sources reveals that, on the one hand, climate change concerns (and to some extent resource availability) are impelling societies toward lessening their dependence on fossil fuels, coal, and petroleum in particular, whereas, on the other hand, market economics and public perceptions regarding safety and radioactive materials are restricting the role of nuclear energy. These forces have created an ideal situation for the renewable sources of energy to play an increasing role in future energy systems.

As seen in Figure 1.2, the role of renewable energy sources in electricity generation in the United States is expected to increase by ~70% in 2050 over its value in 2018 [22]. Liquid fuels derived from renewable biomass sources are also primed to compete with and replace some fraction of the fossil-based fuels in the transportation sector. In addition to having renewable sources, these biofuels typically have less emission of toxic compounds into the atmosphere upon combustion and can reduce net carbon emissions to minimize climate change impact [49].

Transitioning to renewable energy sources—solar energy and its derivative forms (wind, hydropower, biomass, etc.)—is effectively reverting back to utilizing the energy sources used in preindustrial revolution times, albeit with significantly improved technology with considerations of sustainability and environmental impact. Societies of the future that will rely upon renewable resources are sometimes euphemistically termed Second Solar Civilizations to distinguish them from the preindustrial revolution First Solar Civilizations [50]. The challenge for the Second Solar Civilization is of effective and efficient conversion of solar energy and its derivatives into energy currencies that the modern industrial societies have to come rely upon, namely, electricity and liquid hydrocarbon fuels used for transportation and other uses. The transformer technologies that affect the conversion are based on various physical and chemical processes that are dependent upon the nature of the primary energy source and the desired energy currency. A fundamental treatment of these processes is presented in the successive chapters of this book.

1.5 Summary

Global energy demand is expected to continue unabated in the future, driven by growing populations and their quest to enhance their quality of life. While societies seek access to ever-increasing amounts of energy, they do so with a growing understanding of environmental impacts of energy utilization and resource limitations. Climate change considerations and the need to have a safe source of primary energy have created a need for renewable sources of energy. Harnessing these renewable sources effectively requires a fundamental understanding of processes that form the basis of the technologies converting the primary energy forms into secondary energy forms used in modern societies.

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Problems

1.1 Energy generation and consumption forecasts vary considerably based on the assumptions made to construct the future scenarios. Conduct a comparison of different energy future scenarios specifically with respect to primary energy sources and energy consumption forecast by various entities (EIA, BP, IEA, International Renewable Energy Agency [IRENA], etc.). What are the commonalities in these scenarios? What are the major differences?

1.2 Consider the energy system architecture presented in Section 1.2. Construct the architecture for as many activities as you can think of every day. Include at least one public and one private transportation service architecture.

1.3 As mentioned in Section 1.3.1, concerns regarding limitations of fossil resources have been voiced right from the beginning of their discoveries. Conduct a literature search to obtain the latest estimates of period to exhaustion of petroleum, coal, and natural gas. Suggested search engines for searching scientific and technical literatures include Web of Science, ScienceDirect, SciFinder, Academic Search Premier, or other databases that may be available through the library in your institution.

1.4 IPCC constructs different scenarios for global warming and reports on the probability of various consequences for a particular value of rise in mean earth temperature. How does the severity of impacts change from a temperature rise of 1°C to 2°C? Or to 6°C?

1.5 Both Chernobyl and Fukushima disasters resulted in mass evacuation of populations from the vicinity of the nuclear plants. How have the ecosystems responded since that time with the removal of human beings from the area?

1.6 Referring to question 1.2, how would the energy system architecture change if the primary energy source was one of the renewables? How many services can be easily satisfied by the renewables-driven architecture? Which ones would face the most difficulty?

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