Focus

As we search for solutions to providing energy in a sustainable manner to a growing world population that demands a higher quality of life, it is instructive to understand the distribution of energy available on our planet and how it is used. This chapter provides a description of the energy resources on Earth and the transformations that they undergo in both natural and human-driven processes.

Synopsis

Earth is continuously exposed to large quantities of energy, primarily in the form of solar radiation, a small fraction of which is stored through a series of biochemical and chemical transformations, whereas most of it is dissipated through natural processes. Additionally, huge reservoirs of energy exist on the planet from the time of its creation several billion years ago, mainly as radionuclides and thermal energy embedded in the Earth's crust and interior.

Focus

Controlled nuclear fusion has the potential to provide a clean, safe energy source with an essentially limitless supply of fuel, relatively few proliferation concerns (compared with those mentioned in Chapter 14), and substantially fewer of the waste-management concerns discussed in Chapter 15. Large experimental devices currently under construction are intended to demonstrate net fusion energy production, a key technological milestone on the way toward the commercial production of electricity. The economic practicality of energy from fusion processes, however, will still require other significant advances, including in the development of materials that can survive the harsh fusion environment.

Synopsis

The nuclear fusion of light elements is the energy source of the stars. A fusion-based power plant holds the prospect of a nearly limitless fuel source, without the concerns of greenhouse-gas emissions, nuclear proliferation, or serious waste management. While the release of enormous amounts of energy from this process has long been demonstrated in weapons, controlling and harnessing this energy for electricity production constitutes a technologically much more difficult problem. At present, the fusion community is exploring two major approaches to controlled nuclear fusion: magnetic confinement and inertial confinement. In the magnetic fusion energy (MFE) approach, powerful magnetic fields confine low-density hydrogen plasma as it is heated to very high temperatures. In the inertial fusion energy (IFE) approach, tiny pellets of solid hydrogen are compressed to very high densities and temperatures.

Focus

Improvements in materials have played a primary role in the transition from a bare subsistence economy to current high living standards in the developed world. They will be even more important in meeting the challenges of increasing pollution, changing global climate, growing population, and increasing resource demands that humankind will face in the twenty-first century. However, the marvelous structures created by materials science are only scientific curiosities unless they can compete with (and, ultimately, supplant) existing materials and technologies by being cheaper and more useful. This chapter explores the close connection between materials and economics.

Synopsis

The fierce competition among materials for markets drives innovation in materials, cost reductions, and new designs both in terms of materials and in terms of the products and processes that compose US and world economic activity. The invention and discovery of new materials in the laboratory drive innovation, making possible products and processes that were only engineering dreams in the past. New products and designs require new materials, spurring innovation. Indeed, some materials have the potential to lead to more desirable products and services, decreased energy use, reduced risks to the environment and human health, and reduced consumption of scarce resources.

Focus

This chapter explains and discusses present issues and future prospects of batteries and supercapacitors for electrical energy storage. Materials aspects are the central focus of a consideration of the basic science behind these devices, the principal types of devices, and their major components (electrodes, electrolyte, separator). Both experimental and modeling issues are discussed, in the context of needed advancements in battery and supercapacitor technology.

Synopsis

Electrical energy storage is needed on many scales: from milliwatts for electronic devices to multi-megawatts for large grid based, load-leveling stations today and for the future effective commercialization of renewable resources such as solar and wind energy. Consider the example of hybrid electric vehicles (HEVs) (Chapter 31). In HEVs, batteries and/or capacitors are used to capture the energy evolved in braking, and HEV buses use an all-electric drive, which allows them to get up to traffic speed much faster than regular buses, pollute less while moving, and generate zero pollution when standing. The next generation of electric vehicles will be be plug-in hybrids (PHEVs), which require larger batteries. In addition, an all-electric vehicles (EVs) might find niche markets such as city buses, postal delivery vans, and utility-repair vehicles that stop and start frequently and have limited daily ranges; high-cost hot-rod sports cars; and small commuter cars. In all of these transportation applications, low cost and long life are essential for commercial success. Judging by these criteria, most, if not all, vehicles in a decade could be HEVs. However, while present battery and capacitor storage systems, have increased market penetration of PHEVs and EVs further technical improvements are needed to make them fully cost competitive.

Focus

Gas hydrates are typically formed when water and gas (e.g., light hydrocarbons) come into contact at high pressure and low temperature. Current estimates of the amount of energy trapped in naturally occurring gas hydrate deposits, which are found in ocean sediments along the continental margins and in sediments under the permafrost, range from twice to orders of magnitude larger than conventional gas reserves. This has led to gas hydrates being considered as a potential future unconventional energy source.

Synopsis

Gas hydrates (or clathrate hydrates) are icelike crystalline solids imprisoning gas molecules (e.g., methane, carbon dioxide, hydrogen) within icy cages. These fascinating solids present an attractive medium for storing energy: naturally in the deep oceans and permafrost regions, which hold vast quantities of energy waiting to be unlocked and used as an alternative energy supply; and artificially by manipulating synthetic clathrate materials to store clean fuel (natural gas or hydrogen). Conversely, the formation of these solids in oil and gas flowlines (the pipes through which oil and gas are transported, for example, from a well to a processing facility) can lead to blockage of the flowlines and disastrous consequences if not carefully controlled. This chapter on gas hydrates begins with an overview of the discovery and evolving scientific interest in gas hydrates, followed by a basic description of the structural and physical properties of gas hydrates and the different energy applications of gas hydrates. The main focus of this chapter is on surveying the potential prospect of producing energy in the form of clean gas from naturally occurring gas hydrates, which present a potential alternative energy resource and could be a significant component of the alternative energy portfolio. The paradigm shift from exploration to production of energy from gas hydrates is clearly illustrated by the production tests that have either been performed or are planned in the Mackenzie Delta in Canada, on the North Slope of Alaska, and off the coast of Japan.

Focus

Sunlight has two fundamental characteristics that make its use as a cost-effective large-scale source of electricity challenging: its low power density and its broad spectrum. The first characteristic means that sunlight has to be collected over large areas to gather significant amounts of power, and the second characteristic means that conventional solar cells are inherently limited in converting this power to electricity. The “concentrator photovoltaics” (CPV) approach using multijunction solar cells addresses these two challenges head-on.

Synopsis

Sunlight shines with a power of about 1 kW m−2, on average, onto the Earth's surface. Although this might feel considerable to a beachgoer on a hot sunny day, for electrical power generation, this power density is actually inconveniently small. For perspective, consider that a typical electrical power plant generates 1 GW, enough to supply the needs of a rather small city and about 0.1% of the total electricity generation capacity in the USA. The very best conventional solar cells are of efficiency about 20%, so to make a 1-GW solar photovoltaic power plant would require at least 5 km2 of solar cells. To gather sunlight over such large areas and convert it to electricity economically is a fundamental challenge of photovoltaics. One approach, discussed in other chapters, is to reduce the cost of the solar cells. In contrast, this chapter describes an alternative approach that reduces the amount of cells needed: CPV.

Focus

Photoelectrochemistry studies photo-driven electrochemical processes (light-driven processes which interconvert electrical and chemical energy). As with photovoltaics, photoelectrochemical processes can directly convert sunlight into electricity, but have the additional capabilities of being able to store energy, as in solar batteries, or to directly convert solar energy to chemical energy, as in the production of hydrogen fuel or disinfectants. The challenges involved, which have impeded the development of photoelectrochemical devices, can include corrosion, lower solar-energy-conversion efficiency, and packaging vulnerabilities of liquid systems. (i) Dye-sensitized solar cells, (ii) STEP energetic chemical generation and (iii) photoelectrochemical waste treatment are technologies that address many of these challenges.

Synopsis

Society's electrical needs are largely continuous. However, clouds and darkness dictate that photovoltaic (PV) solar cells have an intermittent output. A photoelectrochemical solar cell (PEC) can generate not only electrical but also electrochemical energy, thereby providing the basis for a system with an energy-storage component. Sufficiently energetic insolation incident on semiconductors can drive electrochemical oxidation/reduction and generate chemical, electrical, or electrochemical energy. Aspects include efficient dye-sensitized or direct solar-to-electrical energy conversion, solar electrochemical synthesis (electrolysis), including the splitting of water to form hydrogen, the generation of solar fuels, environmental cleanup, and solar-energy-storage cells. The PEC utilizes light to carry out an electrochemical reaction, converting light to both chemical and electrical energy. This fundamental difference between the PV solar cell's solid/solid interface and the PEC's solid/liquid interface has several ramifications in cell function and application. Energetic constraints imposed by single-bandgap semiconductors have limited the demonstrated values of photoelectrochemical solar-to-electrical energy-conversion efficiency for and using multiple-bandgap tandem cells can lead to significantly higher conversion efficiencies. Photoelectrochemical systems not only may facilitate solar-to-electrical energy conversion, but also have led to investigations into the solar photoelectrochemical production of fuels, photoelectrochemical detoxification of pollutants, and efficient solar thermal electrochemical production (STEP) of metals, fuels, and bleach, and carbon capture.

Focus

The global energy landscape encompasses the distribution of energy resources, as well as the related aspects of energy production, storage, transmission, use, and efficiency. In addition, energy use has been correlated with economic development. Together, these attributes define the context within which countries strive to satisfy their energy demands, in terms of both economic productivity and quality of life. With the current rapid increase in demand for energy, the question of how countries will provide their populations with access to a clean and affordable energy supply in an environmentally sustainable manner has emerged as a grand challenge for today's society.

Synopsis

This chapter summarizes the global energy resources and their availability, economic viability, and environmental consequences. Although these topics are discussed with respect to individual fuels and technologies in greater detail in other chapters of this book, they are examined here in a broader sense relating to the overall global energy landscape.

Focus

The conversion of solar energy to alternative fuels is becoming a vital need in view of the current oil prices, the possible ecological damage associated with oil drills, especially off-shore, and the global distribution of oil reserves. There are several routes by which to convert solar energy to fuels, such as electrochemical, photochemical, photobiological, and the thermochemical route, the last of which is the focus of this chapter. This route involves using solar heat at high temperatures to operate endothermic thermochemical processes. It offers some intriguing thermodynamic advantages, with direct economic implications. It is also an attractive method of storage for solar energy in chemical form. An important vector of this route is the production of hydrogen, a potentially clean alternative to fossil fuels, especially for use in the transportation sector.

Synopsis

There is a pressing need to develop advanced energy technologies to address the global challenges of clean energy, climate change, and sustainable development. The conversion of solar energy to fuels can basically be done through three routes, separately or in combination: the electrochemical route, which uses solar electricity; the photochemical/photobiological route, which makes direct use of solar photons; and the thermochemical route, which utilizes solar heat, usually at high temperatures, for endothermic processes.

Focus

During the last 30 years, wind energy technology has emerged as the leading renewable alternative to electrical power production from fossil fuels. Commercial development and deployment, driven by lower capital costs, technical innovations, and international standards, continue to facilitate installed capacity growth at a rate of 30%–40% per year worldwide [1]. Utility-class machines exceed 2 MW, with robust designs providing 95%–98% availability. Future technology advances will focus on lowering the cost of land-based systems and evolving next-generation technology for ocean deployments in both shallow and deep water.

Synopsis

Wind energy technology is poised to play a major role in delivering carbon-free electrical power worldwide. Advanced technology and manufacturing innovations have helped the cost of wind energy drop from $0.45 per kW·h 30 years ago to $0.05–$0.06 per kW·h, thus positioning wind energy to be directly competitive with fossil-fuel power generation. In 2009, wind technology accounted for 39% of all new electrical generation in the USA [2]. Worldwide, wind deployment continues to penetrate new markets, with power-plant installations spanning months instead of years. In the European Union, cumulative wind power capacity increased by an average of 32% per year between 1995 and 2005, reaching 74,767 MW by the end of 2009 [3]. The USA leads the world in total installed capacity, while India and China are emerging as major potential markets. Wind energy can no longer be considered European-centric and has become an international alternative to fossil-fuel power generation.

Focus

Photovoltaic (PV) conversion of solar energy could be much more effective than it is currently, using basic p–n junctions. The approaches required to reach theoretical conversion limits (~90%) are very challenging. Some have already been demonstrated, such as multijunction devices. Others, with considerable improvements in the description of excited states in condensed matter and in nanoscience, might be on the verge of a breakthrough. Given current knowledge about solar energy conversion and materials science, is it possible to achieve the ultimate solar cell?

Synopsis

Photovoltaic solar cells are now commonplace, and their development has taken advantage of the progress that has been made in electronics. Yet, they are still expensive and far from the performances that could, in principle, be achieved. This chapter first describes the limitations of PV devices as currently designed, before considering the various options being investigated to overcome these limitations. This description is put in perspective with achievable efficiencies according to thermodynamics. Then, we describe various options to experimentally approach the limits set on conversion efficiency of solar energy. While multijunctions are essentially presented in Chapter 20, here the emphasis is on other physical mechanisms than the ones currently operating in p–n diodes. These, first, include purely photonic conversion processes such as up and down conversion combined with a regular PV device, which provides additional power with relatively benign technology changes: an additional functional layer disconnected from the electrical circuit. The focus here is mainly on the optical properties of the additional materials. A second approach relies on the possibility of the absorber being able to harvest more energy from the solar spectrum than what semiconductors and molecules provide today: process of multi-generation of electron–hole pairs with a single photon or, conversely, processes by which several small-energy photons can contribute to the formation of an electron–hole pair. This not only requires new functional materials but also will change the device technology. Finally, we also look at approaches trying to tap into the heat produced upon absorption of photons to generate additional power. These devices are not isothermal, and, on top of optical and electronic properties, one needs to consider heat transfer between sub-parts of the system, and therefore take into consideration their thermal properties.

Focus

Electricity generation is the main source of energy-related greenhouse-gas emissions, and lighting uses one-fifth of its output. Solid-state lighting (SSL) using light-emitting diodes (LEDs) is poised to reduce this value by at least 50%, so that lighting will then use less than one-tenth of all electricity generated. The use of LEDs for lighting will provide reductions of at least 10% in fuel consumption and carbon dioxide emissions from power stations within the next 5–10 years. Even greater reductions are likely on a 10–20-year time scale.

Synopsis

Artificial lighting is one of the factors contributing significantly to the quality of human life. Modern light sources, such as incandescent light bulbs (a heated tungsten wire in a bulb that is evacuated or filled with inert gas) and compact fluorescent lamps (a phosphor-coated gas discharge tube), use electricity to generate light. Worldwide, grid-based electric lighting consumed about 2650 TW·h of electricity in 2005, some 19% of total global electricity consumption [1]. Using an average cost of $2.8 per megalumen-hour (Mlm·h), the International Energy Agency estimated that the energy bill for electric lighting cost end-users $234 billion and accounted for two-thirds of the total cost of electric-lighting services ($356 billion), which includes lighting equipment and labor costs as well as energy. The annual cost of grid-based electric lighting is about 1% of global gross domestic product.

Focus

During the last decade the direct conversion of solar energy to electricity by photovoltaic cells has emerged from a pilot technology to one that produced 11 GWp of electricity generating capacity in 2009. With production growing at 50%–70% a year (at least until 2009) photovoltaics (PV) is becoming an important contributor to the next generation of renewable green power production. The question is that of how we can move to the terawatt ( TW ) scale [1].

Synopsis

The rapid evolution of PV as an alternative means of energy generation is bringing it closer to the point where it can make a significant contribution to challenges posed by the rapid growth of worldwide energy demand and the associated environmental issues. Together with the main existing technology, which is based on silicon (Si), the growth of the field is intertwined with the development of new materials and fabrication approaches. The PV industry, which was, until recently, based primarily on crystalline, polycrystalline, and amorphous Si, grew at an average annual rate of 50% during 2000–2010. This rate was increasing, at least until the 2008 economic crisis, with production of ~11 gigawatts (GWp) per year in 2009 [2]. While this may seem a very large number, PV installations in total are still supplying only <0.03% of all the world's power needs (~14–15 TW) [2]. As production increases, increasing individual cell efficiency and translating that to modules, as well as reducing manufacturing expenses and increasing system lifetimes, are all critical to achieving grid parity, the point at which the cost of PV power is equal to the price of grid electricity.

Focus

The chemical industry is intimately linked with the realities of transformation of fossil fuels to useful compounds and materials, energy consumption, and environmental sustainability. The questions that concern us are the following: how can one minimize energy consumption in the chemical industry and reduce waste formation in chemical reactions, and can we transform this industry from one based primarily on petroleum to one that utilizes renewable feedstocks? In this chapter we will see how this “greening” of this major industrial and energy sector will require the use of catalysis and development of new catalysts.

Synopsis

Thomas Jefferson stated that “the earth belongs in usufruct to the living.” This premise is the basis of present recognition that, if the natural capacity of planet Earth to deal with pollution and waste is exceeded, then our lifestyle will become unsustainable. In this context, it is difficult to imagine life in the twenty-first century without accounting for the role the chemical industry plays in our modern society. For example, in the transportation sector, the most obvious aspect is the production of efficient fuels from petroleum, but one also should consider catalytic converters that reduce toxic emissions, and engineering polymers and plastics that reduce vehicle weight and therefore reduce fuel consumption. In daily consumer life we use chemicals in products such as paints, DVDs, synthetic carpets, refrigerants, packaging, inks and toners, liquid-crystal displays, and synthetic fibers. Pesticides and fertilizers are needed in order to increase agricultural productivity and pharmaceuticals to keep us healthy. In this chapter we will try to understand the aspects involved in the sustainability of the chemical industry. We will describe how to measure and control environmental performance and then define what we mean by green processing in the chemical industry, specifying green process metrics, introducing key concepts such as atom economy, E-factors, and effective mass yields. With these concepts together with the evaluation raw material costs, waste treatment, and unit processes needed for production of a chemical one can appreciate the “greenness” of a chemical process. The second part of this chapter will describe the role catalysis has in chemical transformations and how catalysis is used to reduce energy consumption and waste formation, together leading to increased sustainability. Examples will be given for a spectrum of applications ranging over oil refining, ammonia production, manufacture of important chemical intermediates and materials, and use of catalysis for the production of commodity chemicals. Finally, we will discuss the role catalysis may play in the replacement of fossil-fuel feedstocks with renewable ones, and how catalysis may contribute to our search for solar fuels.

Focus

The resurgence of nuclear power as an economical source of energy, plus as a strategy for reducing greenhouse-gas (GHG) emissions, has revived interest in the environmental impact of the nuclear fuel cycle. Just as GHG emissions are the main environmental impact of fossil-fuel combustion, the fate of nuclear waste determines whether nuclear power is viewed as an environmentally friendly source of energy. Not only must nuclear materials be designed that can operate under the extreme conditions within a reactor, but also new materials must be developed that can contain radionuclides for hundreds of thousands of years and prevent their release to the biosphere.

Synopsis

A variety of nuclear fuel cycles exists, each with its own types and volumes of nuclear waste [1]. An open nuclear fuel cycle envisions the direct geological disposal of the used nuclear fuel, mainly UO2. A closed fuel cycle uses chemical processing of the used fuel to reclaim fissile material, namely 235U and 239Pu, which is then fabricated into a new, mixed-oxide (MOX) fuel that provides additional power in a second cycle of irradiation and fission in a nuclear reactor. Only a limited number of cycles of reprocessing can be applied, because of changes in the nuclide composition of the used fuel; thus, MOX fuel eventually requires geological disposal as well. In addition, the chemical processing itself creates waste streams that consist mainly of fission-product elements that are highly radioactive (e.g., 137Cs) or have very long half-lives (e.g., 135Cs), as well as transuranium elements (e.g., 237Np) that form in the fuel as a result of neutron-capture and decay reactions. For all of these radionuclides, robust and extended isolation from the environment is required. More advanced “symbiotic” reprocessing technologies envision the separation of those radionuclides that can be transmuted in specially designed fast reactors (e.g., ones that utilize higher-energy neutrons to fission minor actinides, such as Np, Am, and Cm). Regardless of the type of fuel cycle envisioned, materials must be designed that can incorporate and isolate all residual radionuclides from the environment until they have decayed to safe levels of radioactivity. Nuclear-waste forms must be able to incorporate complex mixtures or individual radionuclides, survive the effects of radiation and self-heating caused by radioactive decay, and resist alteration and corrosion in a variety of geological environments over very long periods. The challenge for materials scientists is to design materials compatible with remote fabrication in high radiation fields. The response of these materials to radiation fields and to the geochemical and hydrological conditions in a geological repository must be well enough understood to project their performance over hundreds of thousands of years [2].

Focus

Nuclear power has been a reliable source of electricity in many countries for decades, and it will be an essential component of the mix of energy sources required to meet environmental goals by reducing greenhouse-gas emissions, reducing the dependence on fossil fuels, and enabling global access to energy. Materials science will play a key role in developing options in nuclear power, including new reactors with improved safety (especially in the light of the Fukushima Daiichi nuclear accident), reliability, and efficiency; technology to help minimize proliferation (discussed in Chapter 14); and viable, safe, long-term options for waste management (discussed in Chapter 15). Such efforts will provide opportunities to address broader challenges associated with nuclear energy, including public opinion and the investment risks associated with building new nuclear power plants.

Synopsis

The energy density (i.e., the quantity of useful energy stored per unit volume) of uranium fuel used today in light-water reactors (the most prevalent type of nuclear reactor) is already orders of magnitude larger than that of other energy sources. For example, one reactor fuel pellet produces approximately as much heat energy as 150 gal of fuel oil or 1 ton of high-grade coal. Moreover, the utilization of the energy density is being increased further through improvements in fuel technology and by developments in reactor design. This chapter focuses on the materials science challenges that exist in a fission reactor, that is, those related to the nuclear fuel, the cladding, and the structural materials, which are exposed to extremely high temperatures, moderate pressures, and an intense radiation field. Technical issues that extend beyond the workings of reactors, namely nuclear non-proliferation and nuclear waste, are addressed in Chapters 14 and 15, respectively.

Focus

Shipping delivers huge numbers and amounts of goods to consumers worldwide, whether that be through container ships full of automobiles, tankers full of oil, or trawlers full of fish. Despite being such a central component of the global economy, shipping is not regulated by the Kyoto Protocol, and recent studies project that shipping will produce between 400 Mt and 1.12 Gt of CO2 by 2020, which would be more than aviation and up to 4.5% of global CO2 (http://www.guardian.co.uk/environment/2008/feb/13/climatechange.pollution). This chapter focuses on the need for shipping to change in a carbon-sensitive world and possible changes that would allow shipping to reduce its environmental impact while still delivering increasing amounts of goods efficiently worldwide.

Synopsis

Since oceans cover approximately 70% of the Earth's surface, the development of shipping was inevitable. In addition to allowing human communities on different land masses to engage in the crucial activity of trading commodities such as spices and gold, shipping nucleated the cross-fertilization of groups by transporting people as well. These activities have grown over time to the point that shipping now transports over 90% of the total goods worldwide. In fact, this amount is still growing as international trade continues to expand [1].

Focus

Petroleum and natural gas have been the mainstay of energy production in developed countries. Global energy demand will continue to increase with “globalization.” Oil and natural gas will continue to supply a majority of our energy in the near future and production will be from natural sources of petroleum, coal, and natural gas. For example, Energy Independence has reported that the USA has an estimated 260 billion tons of recoverable coal, equivalent to three or four times as much energy in coal as Saudi Arabia has in oil [1]. The needed increase requires the exploitation of conventional and unconventional reservoirs of oil and gas in an “environmentally friendly” manner. This necessitates advances in materials in the form of better catalysts to produce clean fuels and advanced materials for high-pressure, high-temperature, and high-stress processes.

Synopsis

The National Petroleum Council (NPC) in the USA recently published a report entitled Facing the Hard Truths about Energy that evaluates oil and gas supply and demand in the early part of the twenty-first century [2]. The report concluded that the total global demand for energy will grow by 50%–60% by 2030 due to the increase in world population and higher average standards of living in some developing countries. Clearly, for the next few decades, oil, gas, and coal will continue to be the primary energy sources. The energy industry will have to continue increasing the supply of hydrocarbon fuels to meet the global energy demand. There are ample hydrocarbon resources to meet the demand well into the twenty-first century. The volumes of oil and natural gas located in unconventional reservoirs are much larger than the conventional reservoirs currently used for what has been produced thus far.