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Chapt12lecture 1227038145573080-8
- 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 12 Lecture Outline
- 2. Learning Outcomes After studying this chapter, you should be able to answer the following questions: • What are our dominant sources of energy? • What is peak oil production? Why is it hard to evaluate future oil production? • How important is coal in domestic energy production? • What are the environmental effects of coal burning? Is clean coal possible? • How do nuclear reactors work? What are some of their advantages and disadvantages? • What are our main renewable forms of energy? • Could solar, wind, hydropower, and other renewables eliminate the need for fossil fuels? • What are photovoltaic cells, and how do they work? • What are biofuels? What are arguments for and against their use? 12-2
- 3. We are not only responsible for what we do, but also for what we do not do. –Moliere 12-3
- 4. 12.1 Energy Resources and Uses • Throughout Denmark, the state has subsidized wind power research, so that now Danes are world leaders in this fast-growing industry. 12-4
- 5. How do we measure energy? 12-5
- 6. Fossil fuels supply most of our energy • Fossil fuels (petroleum, natural gas, and coal) now provide about 87 percent of all commercial energy in the world. • Renewable sources— solar, wind, geothermal, and hydroelectricity—make up about 7 percent of our commercial power (but hydro accounts for almost all of that). 12-6
- 7. 12.2 Fossil Fuels • Fossil fuels are organic (carbon-based) compounds derived from decomposed plants, algae, and other organisms buried in rock layers for hundreds of millions of years. • Oil supplies over 40 percent of U.S. energy demands and over 99 percent of fuel for cars and trucks, according to the U.S. Department of Energy (fig. 12.4). • Coal-fired power plants supply most of our electrical energy. 12-7
- 8. Coal resources are vast • World coal deposits are vast, ten times greater than conventional oil and gas resources combined, and one- quarter of global coal deposits are in the United States (fig. 12.5). • But coal mining is a dirty, dangerous activity . 12-8
- 9. New plants can be clean 12-9
- 10. Have we passed peak oil? • We have already used more than 0.5 trillion bbl—almost half of proven oil reserves. • Competition has already raised oil prices, from around $15 per barrel in 1993 to more than $150 per barrel in 2008. 12-10
- 11. 12.3 Nuclear Power • In 1953 President Dwight Eisenhower presented his “Atoms for Peace” speech to the United Nations. • He announced that the United States would build nuclear-powered electrical generators to provide clean, abundant energy. • Nuclear power now amounts to about 8 percent of U.S. energy supply (1 percent more than the world average). • Half of the U.S. plants (52) are more than 30 years old and are thus approaching the end of their expected operational life. 12-11
- 12. How do nuclear reactors work? • Radioactive uranium atoms are unstable— that is, when struck by a high-energy subatomic particle called a neutron, they undergo nuclear fission (splitting), releasing energy and more neutrons. 12-12
- 13. We lack safe storage for radioactive waste • One of the most difficult problems associated with nuclear power is the disposal of wastes produced during mining, fuel production, and reactor operation. • How these wastes are managed may ultimately be the overriding obstacle to nuclear power. 12-13
- 14. 12.4 Energy Conservation • Much of the energy we consume is wasted. • U.S. automobile gas mileage averages more than doubled from 13 mpg in 1975 to 28.8 mpg in 1988. • Unfortunately, the oil glut and falling fuel prices of the 1990s discouraged further conservation. • By 2004 the average slipped to only 20.4 mpg. 12-14
- 15. What Can You Do? Steps to Save Energy and Money 1. Live close to work and school, or near transit routes, so you can minimize driving. 2. Ride a bicycle, walk, and use stairs instead of elevators. 3. Keep your thermostat low in winter and high in summer. Fans are cheaper to run than air conditioners. 4. Buy fewer disposable items: producing and shipping them costs energy. 5. Turn off lights, televisions, computers, and other appliances when not needed. 6. Line-dry your laundry. 7. Recycle. 8. Cut back on meat consumption: if every American ate 20 percent less meat, we would save as much energy as if everyone used a hybrid car. 9. Buy some of your food locally, to reduce energy in shipping. 12-15
- 16. Green building can cut energy costs by half 12-16
- 17. 12.5 Energy from Biomass • Firewood is our original source of fuel. • Biofuels, ethanol and biodiesel, are by far the biggest recent news in biomass energy. • In the United States, both farm policies and energy policies have promoted biofuel crops. • Small amounts of ethanol have been added to gasoline for years, because oxygen-rich ethanol molecules help gasoline burn (oxidize) more completely. 12-17
- 18. 12.6 Wind and Solar Energy 12-18
- 19. Wind energy is our fastest growing renewable • It is estimated that wind could produce about 50 times the total capacity of all nuclear power plants now in operation. • Wind farms are large concentrations of wind generators producing commercial electricity. 12-19
- 20. Solar energy is diffuse but abundant • Passive solar absorption has been updated in modern homes with massive, heat-absorbing floors and walls, or with glass-walled “sun spaces” on the south side of a building. • Active solar systems generally pump a heat- absorbing fluid medium through a relatively small collector, rather than passively collecting heat in a stationary medium, such as masonry. • Photovoltaic cells capture solar energy and convert it directly to electrical current. 12-20
- 21. 12.7 Water Power • The invention of water turbines in the nineteenth century greatly increased the efficiency of hydropower dams (fig. 12.31). • By 1925 falling water generated 40 percent of the world’s electric power. • Fossil fuel use has risen so rapidly that water power is now only one-quarter of total electrical generation. • Ocean tides and waves contain enormous amounts of energy that can be harnessed to do useful work. 12-21
- 22. Geothermal heat, tides, and waves could supply substantial amounts of energy in some places 12-22
- 23. 12.8 Fuel Cells • Fuel cells are devices that use ongoing electrochemical reactions to produce an electrical current. 12-23
- 24. 12.9 What Is Our Energy Future? 12-24
- 25. Practice Quiz 1. Where are Samsø and Ærø islands, and how do they supply their energy needs? 2. Define energy, power, and kilowatt-hour (kWh). 3. What are the major sources of global commercial energy? 4. How does energy consumption in the United States compare to that in other countries? 5. Who is the leading supplier of oil to the United States? 6. What are proven-in-place reserves? 7. How much coal do we have, and how long will it last? 8. Why don’t we want to use all the coal in the ground? 9. Where is most liquid oil located? How long are supplies likely to last? 10. What are tar sands and oil shales? What are the environmental costs of their extraction? 11. Why is natural gas considered to be a superior fuel to either coal or oil? 12. How are nuclear wastes now being stored? 13. Explain active and passive solar energy. 14. How do photovoltaic cells work? 15. What’s a fuel cell, and how does it work? 16. What are biofuels, and how could they contribute to sustainability? 12-25
Editor's Notes
- In this chapter and throughout this book, you will read about many cases in which humans have caused serious environmental problems. You will also read about promising, exciting solutions to many of these problems. Your task as a student of environmental science is to gain an idea of what some of the larger current problems are, what some solutions might be, and how you might use knowledge from a variety of disciplines—from biology and chemistry to economics—to develop tomorrow’s strategies for more sustainable living on our planet.
- Landmark rules in the 2007 United States energy bill, for example, required a quadrupling of ethanol production from biomass by 2020, in just 13 years. In combination with agricultural subsidies, ethanol receives supports of about $7 billion per year, or about $2 per gallon. The same energy bill established the first new standards for vehicle efficiency in over 30 years. This kind of rule may make it possible for you to buy a car that gets 60–70 miles per gallon of gas. That kind of efficiency hadn’t been available in the United States (although it has been available elsewhere) since the 1970s, with the exception of hybrid cars. Thus, national energy policies can influence how much you pay at the pump, as well as national dependence on imported energy. U.S. energy policies give the lion’s share of funding to oil and gas development ($13 billion in tax incentives in 2007), nuclear energy ($25 billion in underwriting), coal, and gas.
- To understand the magnitude of energy use, it is helpful to know the units used to measure it. Work is the application of force over distance, and we measure work in joules (table 12.1). Energy is the capacity to do work. Power is the rate of energy flow or the rate of work done: for example, one watt (W) is one joule per second. If you use a 100-watt light bulb for 10 hours, you have used 1,000 watt-hours, or one kilowatt-hour (kWh). Most American households use about 11,000 kWh per year (table 12.2).
- Renewable sources— solar, wind, geothermal, and hydroelectricity—make up about 7 percent of our commercial power (but hydro accounts for almost all of that). Excluded from these figures are energy sources not traded commercially. Wood biomass provides the primary energy source for at least a billion people in developing countries. This is an important energy source for poor people but can be a serious cause of forest destruction (chapter 6). Residential solar water heating and cogeneration (producing electricity from waste heat) are also important, and under-used, sources. Nuclear power is roughly equal to hydroelectricity worldwide (about 6 percent of all commercial energy), but it makes up about 20 percent of all electric power in more-developed countries, such as Canada and the United States. We have enough nuclear fuel to produce power for a long time, and it has the benefit of not contributing to global warming (chapter 9), but as we discuss later in this chapter, safety concerns make this option unacceptable to most people.
- Most of the richest deposits date to about 286 million to 360 million years ago (the Mississippian, Pennsylvanian, and Permian periods: see fig. 11.6), when the earth’s climate was much warmer and wetter than it is now. Impurities in coal, especially sulfur and mercury, are also our most important source of air pollution. Natural gas is a cleaner energy source, and 90 percent of new power plants in the next 20 years will probably burn natural gas.
- Coal seams can be 100 m thick and can extend across tens of thousands of square kilometers that were vast, swampy forests in prehistoric times. The total resource is estimated to be 10 trillion metric tons. If all this coal could be extracted, and if coal consumption continued at present levels, this would amount to several thousand years’ supply. At present rates of consumption, these proven-in-place reserves—those explored and mapped but not necessarily economic at today’s prices—will last about 200 years. Proven reserves are generally a small fraction of a total resource (fig. 12.6). Do we really want to use all of the coal? Coal mining is a dirty, dangerous activity. Underground mines are notorious for cave-ins, explosions, and lung diseases, such as black-lung suffered by miners. Surface mines (called strip mines, where large machines strip off overlying sediment to expose coal seams) are cheaper and generally safer for workers than tunneling, but leave huge holes where coal has been removed and vast piles of discarded rock and soil (fig. 12.7).
- Because coal causes so much air pollution, a great deal of effort has been invested in developing clean coal plants. While the initial cost of these plants is higher than older technology, they can pay for themselves over time. One of these systems is integrated gasification combined cycle (IGCC), a technology that could produce zero-emissions electricity from coal. Power plants using this system could generate electricity while capturing and permanently storing carbon dioxide and other pollutants. An IGCC plant has been operating successfully for the past decade just outside of Tampa, Florida. Every day, the Polk power plant converts 2,400 tons of coal into 250 megawatts (MW) of electricity, or enough power for about 100,000 homes. Unlike conventional coal-fired power plants, an IGCC doesn’t actually burn the coal. It converts the coal into gas and then burns the gas in a turbine (fig. 12.8 ). To do this, the coal is first ground into a fine powder and mixed with water to create a slurry. The slurry is pumped at high pressure into a gasification chamber, where it mixes with 96 percent pure oxygen, and is heated to 1,370°C (2,500°F). The coal doesn’t burn; instead it reacts with the oxygen and breaks down into a variety of gases, mostly hydrogen and carbon dioxide. The gases are cooled, separated, and converted into easily managed forms. After purification, the synthetic hydrogen gas (or syngas) is pumped to the combustion turbine, which spins a huge magnet to produce electricity. Superheated gases from the turbine are fed into a steam generator that drives another turbine to produce more electrical current. Combining these two turbines makes an IGCC about 15 percent more efficient than a normal coal-fired power plant. Perhaps even better is that the hydrogen gas could power fuel cells if they become commercially feasible. Contaminants, such as sulfur dioxide (SO 2 ), ash, and mercury, that often go up the smokestack in a normal coal-burning plant, are captured and sold to make the IGCC cleaner and more economical. Sulfur is marketed as fertilizer; ash and slag are sold to cement companies. Mercury removal is an important public health benefit. All the slurry water is recycled to the gasifier; there is no waste water and very little solid waste. Because of these efficiencies, the Polk plant produces the cheapest electricity in the whole Tampa system. It doesn’t now capture carbon dioxide, because it isn’t required to, but it could easily do so. If we had CO 2 emission limits, IGCC plants could either pump it into deep wells for storage, or use it to enhance oil and natural gas recovery.
- In the 1940s Dr. M. King Hubbert, a Shell Oil geophysicist, predicted that oil production in the United States would peak in the 1970s, based on estimates of U.S. reserves at the time. Hubbert’s predicted peak was correct, and subsequent calculations have estimated a similar peak in global oil production in about 2005–2010 (fig. 12.9). While global production has not yet slowed, many oil experts expect that we will pass this peak in the next few years. About half of the world’s original 4 trillion bbl (600 billion metric tons) of liquid oil are thought to be ultimately recoverable. (The rest is too diffuse, too tightly bound in rock formations, or too deep to be extracted.) Of the 2 trillion recoverable barrels, roughly 1.15 trillion bbl are in proven reserves (defined in fig. 12.6). We have already used more than 0.5 trillion bbl—almost half of proven reserves—and the remainder is expected to last 40 years at current consumption rates of 28.5 billion bbl per year. Middle Eastern countries have more than half of world supplies (fig. 12.10). More technological innovation is also supported by high prices. At the same time, high prices encourage conservation. The cost of insulating your house is easier to justify when heating and cooling costs are high. Companies can afford to experiment with new designs for light bulbs, cars, and consumer electronics when they are confident consumers want them.
- In 1953 President Dwight Eisenhower presented his “Atoms for Peace” speech to the United Nations. He announced that the United States would build nuclear-powered electrical generators to provide clean, abundant energy. He predicted that nuclear energy would fill the deficit caused by predicted shortages of oil and natural gas. It would provide power “too cheap to meter” for continued industrial expansion of both the developed and the developing world. Today there are about 440 reactors in use worldwide, 104 of these in the United States. Half of the U.S. plants (52) are more than 30 years old and are thus approaching the end of their expected operational life. Cracking pipes, leaking valves, and other parts increasingly require repair or replacement as a plant ages. Rapidly increasing construction costs, safety concerns, and the difficulty of finding permanent storage sites for radioactive waste have made nuclear energy less attractive than promoters expected in the 1950s.
- The most commonly used fuel in nuclear power plants is U235, a naturally occurring radioactive isotope of uranium. Uranium ore must be purified to a concentration of about 3 percent U235, enough to sustain a chain reaction in most reactors. The uranium is then formed into cylindrical pellets slightly thicker than a pencil and about 1.5 cm long. Although small, these pellets pack an amazing amount of energy. Each 8.5 g pellet is equivalent to a ton of coal or 4 bbl of crude oil. The pellets are stacked in hollow metal rods approximately 4 m long. About 100 of these rods are bundled together to make a fuel assembly. Thousands of fuel assemblies containing about 100 tons of uranium are bundled in a heavy steel vessel called the reactor core. Radioactive uranium atoms are unstable—that is, when struck by a high-energy subatomic particle called a neutron, they undergo nuclear fission (splitting), releasing energy and more neutrons. When uranium is packed tightly in the reactor core, the neutrons released by one atom will trigger the fission of another uranium atom and the release of still more neutrons (fig. 12.15). Thus, a self-sustaining chain reaction is set in motion, and vast amounts of energy are released. The chain reaction is moderated (slowed) in a power plant by a neutron-absorbing cooling solution that circulates between the fuel rods. In addition, control rods of neutron-absorbing material, such as cadmium or boron, are inserted into spaces between fuel assemblies to shut down the fission reaction or are withdrawn to allow it to proceed. Water or some other coolant is circulated between the fuel rods to remove excess heat. The greatest danger in one of these complex machines is a cooling system failure. If the pumps fail or pipes break during operation, the nuclear fuel quickly overheats, and a “meltdown” can result that releases deadly radioactive material. Although nuclear power plants cannot explode like a nuclear bomb, the radioactive releases from a worst case disaster, such as the meltdown of the Chernobyl reactor in the Soviet Ukraine in 1986, are just as devastating as a bomb. (See related story on Chernobyl at www.mhhe.com/cunningham5e.)
- One of the best ways to avoid energy shortages and to relieve environmental and health effects of our current energy technologies is simply to use less (see What Can You Do? on the next slide). Much more could be done. High-efficiency automobiles are already available. Low-emission, hybrid gas-electric vehicles get up to 30.3 km/liter (72 mpg) on the highway (see related story on hybrid engines at www.mhhe.com/cunningham5e). Amory B. Lovins of the Rocky Mountain Institute in Colorado estimates that raising the average fuel efficiency of the U.S. car and light-truck fleet by 1 mpg would cut oil consumption about 295,000 bbl per day. In one year, this would equal the total amount the U.S. Department of the Interior hopes to extract from the Arctic National Wildlife Refuge in Alaska.
- Innovations in “green” building have been stirring interest in both commercial and household construction. Much of the innovation has occurred in large commercial structures, which have larger budgets—and more to save through efficiency—than most homeowners have. Elements of green building are evolving rapidly, but they include extra insulation in walls and roofs, coated windows to keep summer heat out and winter heat in, and recycled materials, which save energy in production. Orienting windows toward the sun, or providing roof overhangs for shade, are important for comfort as well as for saving money. New houses can also be built with extra-thick, superinsulated walls and roofs. Windows can be oriented to let in sunlight, and eaves can be used to provide shade. Double-glazed windows that have internal reflective coatings and that are filled with an inert gas (argon or xenon) have an insulation factor of R11, the same as a standard 4-inch-thick insulated wall, or ten times as efficient as a single-pane window (fig 12.19). Superinsulated houses now being built in Sweden require 90 percent less energy for heating and cooling than the average American home.
- As recently as 1850, wood supplied 90 percent of the fuel used in the United States. For more than a billion people in developing countries, burning biomass remains the principal energy source for heating and cooking. In urban areas of developing countries, wood is often sold in the form of charcoal (fig. 12.20). Wood gathering and charcoal burning are important causes of forest depletion. Globally, production of ethanol and biodiesel is booming, from Brazil (which uses sugarcane) to Southeast Asia (oil palm fruit) to the United States and Europe (corn, soybeans, rape seed). Ethanol helps reduce carbon monoxide (CO), an important pollutant, by converting it to carbon dioxide (CO2). Most vehicles can burn up to 10 percent ethanol without damaging engines; newer “flexible fuel” vehicles, however, can burn up to 100 percent ethanol. Ethanol, the same alcohol used in beverages, is made by adding yeast to a liquid mix of water and ground grain, then fermenting it to produce alcohol. Biodiesel, derived from organic oils, can be burned in normal diesel engines, and it can be much cheaper to produce than ethanol because it requires no fermentation. Just about anything organic, from turkey entrails and cow dung to soybeans, can be used as a source. Will biofuels eliminate the need for other fuels? No. If all farmland in the United States were converted to corn-ethanol production, we would produce just a portion of the gasoline we use in a year.
- In Denmark’s efforts to reduce dependence on oil imports (opening case study), wind power has been the principal focus, followed by solar thermal (heat) systems. Relative to other alternative sources, wind is cheap and available almost everywhere. Although wind turbines are highly visible, they have a small footprint, so they don’t displace farming and other land uses. How people feel about the visibility of a wind farm depends on whether they are enthusiastic about energy alternatives, whether it earns money for their community, and which particular view is obstructed by the turbines. Solar energy can be converted to heat (thermal energy), as well as electricity. The sun is an almost inconceivably rich source of energy. The average amount that reaches the earth’s surface is some 10,000 times greater than all commercially sold energy used each year. However, this energy is diffuse and low in intensity. Innovations in recent years have produced new strategies for concentrating solar energy, to make it useful for more purposes.
- Although Denmark remains the world leader in wind energy, the United States and other countries are catching up rapidly. Wind generation capacity in the United States grew by 20 percent in 2006 and by another 45 percent in 2007. Those increases brought the level of installed resources to 17 million MW, enough for almost 5 million homes. Wind power emerged as more than 1 percent of total U.S. energy demand in 2007. Texas is the leader in U.S. wind power, with just over one-third of installed capacity, followed by California, Minnesota, Iowa, and Washington.
- The sun is a giant nuclear furnace in space, constantly bathing our planet with a free energy supply. Solar heat drives winds and the hydrologic cycle. All biomass, as well as fossil fuels and our food (both of which are derived from biomass), results from conversion of light energy (photons) into chemical bond energy by photosynthetic bacteria, algae, and plants.
- Much of the hydropower development since the 1930s has focused on enormous dams. There is a certain efficiency of scale in giant dams, and they bring pride and prestige to the countries that build them, but they can have unwanted social and environmental effects that spark protests in many countries. China’s Three Gorges Dam on the Yangtze River, for instance, spans 2.0 km (1.2 mi) and is 185 m (600 ft) tall. The reservoir it creates is 644 km (400 mi) long and has displaced more than 1 million people (see related story “Three Gorges Dam” at www.mhhe.com/cunningham5e). Ocean tides and waves contain enormous amounts of energy that can be harnessed to do useful work. A tidal station works like a hydropower dam, with its turbines spinning as the tide flows through them. A high-tide/low-tide differential of several meters is required to spin the turbines. Unfortunately, variable tidal periods often cause problems in integrating this energy source into the electric utility grid. Nevertheless, demand has kept some plants running for many decades. Ocean wave energy can easily be seen and felt on any seashore. The energy that waves expend as millions of tons of water are picked up and hurled against the land, over and over, day after day, can far exceed the combined energy budget for both insolation (solar energy) and wind power in localized areas. Captured and turned into useful forms, that energy could make a substantial contribution to meeting local energy needs.
- They are very similar to batteries except that, rather than recharging them with an electrical current, you add more fuel for the chemical reaction. Depending on the environmental costs of input fuels, fuel cells can be a clean energy source for office buildings, hospitals, or even homes. All fuel cells consist of a positive electrode (the cathode) and a negative electrode (the anode) separated by an electrolyte, a material that allows the passage of charged atoms, called ions, but is impermeable to electrons (fig. 12.34). In the most common systems, hydrogen or a hydrogen-containing fuel is passed over the anode, while oxygen is passed over the cathode. At the anode, a reactive catalyst, such as platinum, strips an electron from each hydrogen atom, creating a positively charged hydrogen ion (a proton). The hydrogen ion can migrate through the electrolyte to the cathode, but the electron is excluded. Electrons flow through an external circuit, and the electrical current generated by their passage can be used to do useful work. At the cathode, the electrons and protons are reunited and combined with oxygen to make water. Fuel cells provide direct-current electricity as long as they are supplied with hydrogen and oxygen. For most uses, oxygen is provided by ambient air. Hydrogen can be supplied as a pure gas, but storing hydrogen gas is difficult and dangerous because of its explosive nature. Liquid hydrogen takes far less space than the gas but must be kept below –250°C (–400°F), not a trivial task for most mobile applications. The alternative is a device called a reformer or converter that strips hydrogen from fuels such as natural gas, methanol, ammonia, gasoline, ethanol, or even vegetable oil. Many of these fuels can be derived from biofuels, such as ethanol. Even methane effluents from landfills and wastewater treatment plants can be used as a fuel source. Where a fuel cell can be hooked permanently to a gas line, hydrogen can be provided by solar, wind, or geothermal facilities that use electricity to hydrolyze water.
- Global energy demand continues to rise, as cars, appliances, and factories become more abundant in both rich countries and developing countries. Growing use in China and India, the world’s two most populous countries, is especially important in our energy future. Per capita use in wealthy countries, however, remains far above that in developing areas, and our rate of growth will also dictate the shape of our energy future. This growing demand is raising energy costs. High prices are also pushing innovation in alternative sources and better efficiency. None of the renewable energy sources discussed in this chapter will replace fossil fuels and nuclear power in the near future, because most of our energy infrastructure uses conventional energy sources and because our investments in alternatives has mostly been relatively small. Renewable alternatives can contribute substantially to sustainability, though. Since we import 35 million barrels of oil per day, a one percent savings through better efficiency or sustainable biofuels would represent a lot of oil. The United States, the world’s largest energy consumer, has emphasized oil, coal, and nuclear power in energy policies. President George W. Bush and his father, President George H.W. Bush, both have close family ties to oil producers in the United States and Saudi Arabia, and Vice President Dick Cheney (CEO of an oil services corporation) oversaw energy policies that did little to encourage conservation or alternative energy sources. These strategies helped to maintain U.S. control of critical energy resources. They also maintained our dependence on imported energy and allowed other countries to establish leadership in alternative strategies, such as automobile efficiency, better building practices, and wind power, that will drive much of our energy future. The decisions of future presidents, congresses, voters, and consumers will determine which strategies the United States will take in the future. Your choices, in where you live and what you drive, eat, and buy, will influence these energy futures (fig. 12.36).