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Energy. Chapter 13. Section 13-1. What is net energy and why is it important?. Basic science: Net energy is the only energy that really counts.
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Energy Chapter 13
Section 13-1 What is net energy and why is it important?
Basic science: Net energy is the only energy that really counts • The usable amount of high-quality energy available from a given quantity of an energy resource is its net energy yield: the total amount of useful energy available from an energy resource minus the energy needed to make it available to consumers. • We can express net energy as the ratio of energy produced to the energy used to produce it. As the ratio increases, the net energy also rises. When the ratio is less than 1, there is a net energy loss.
Net energy ratios for various energy systems over their estimated lifetimes differ widely
Energy resources with low or negative net energy need help to compete in the marketplace • Any energy resource with a low or negative net energy ratio cannot compete in the open marketplace with other energy alternatives with higher net energy ratios unless it receives financial support from the government (taxpayers) or other outside sources of funding. • For example, the low net energy yield for the nuclear power fuel cycle is one reason why many governments throughout the world must heavily support nuclear power financially to make it available to consumers at an affordable price.
Section 13-2 What are the advantages and disadvantages of fossil fuels?
Fossil fuels supply most of our commercial energy • The direct input of solar energy produces several other forms of renewable energy resources: wind, flowing water, and biomass. • Most commercial energy comes from extracting and burning nonrenewable energy resources obtained from the earth’s crust. • 87% from carbon-containing fossil fuels (oil, natural gas, and coal). • 6% from nuclear power. • 8% from renewable energy resources—biomass, hydropower, geothermal, wind, and solar energy.
When crude oil is refined, many of its components are removed at various levels
How long might supplies of conventional crude oil last? • Crude oil is now the single largest source of commercial energy in the world. • Proven oil reserves are identified deposits from which conventional crude oil can be extracted profitably at current prices with current technology. • Geologists project that known and projected global reserves of conventional crude oil will be 80% depleted sometime between 2050 and 2100. The remaining 20% will likely be too costly to remove.
How long might supplies of conventional crude oil last? • Options include: • look for more oil. • use less oil. • waste less oil. • use other energy resources.
OPEC controls most of the world’s crude oil supplies • 13 countries make up the Organization of Petroleum Exporting Countries (OPEC). • In 2010, OPEC holds about 77% of the world’s proven crude oil reserves. • OPEC’s members are Algeria, Angola, Ecuador, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. • The U.S. has only about 2% of the world’s proven oil reserves. China has only 1.1%, India has 0.4%, and Japan has no oil reserves.
OPEC controls most of the world’s crude oil supplies • Currently, the world’s largest producers of oil are, in order, Russia, Saudi Arabia, and the U.S. Energy experts project that by about 2020, Iraq will become the world’s third largest oil producer. • Since 1984, production of conventional crude oil from proven reserves has exceeded new oil discoveries. Since 2005, global crude oil production has generally leveled off. Of the world’s 64 major oil fields, 54 are now in decline.
Using crude oil has advantages and disadvantages • Oil spills cause catastrophic damage. • In 2010, the BP Company’s Deepwater Horizon oil-drilling rig exploded, spilling an estimated 679 million liters (180million gallons) of crude oil into U.S. Gulf Coast waters. • In 1989, the oil tanker Exxon Valdezran aground and spilled 42 million liters (11 million gallons) of oil into Alaskan waters. • More than 2.5 times the estimated amount of crude oil spilled in the 2010 Gulf Coast disaster has been spilled from off the coast of Nigeria with little media attention.
Will heavy oil be a useful resource? • Oil shale is rock that contains a solid combustible mixture of hydrocarbons called kerogen which can be processed to produce shale oil. • Producing shale oil requires large amounts of water and has a low net energy and a very high environmental impact. • Estimated potential global supplies of unconventional shale oil are about 240 times larger than estimated global supplies of conventional crude oil. • Shale has a low net energy yield so would require subsidies to compete on the open market, and shale extraction would have a high environmental impact, causing severe land disruption, high water use, and high CO2 emissions when produced and burned.
Using heavy oil from oil shale and tar sands as energy source has advantages and disadvantages
Natural gas is a useful and clean-burning fossil fuel • Natural gas is a mixture of gases of which 50–90% is methane (CH4). • Has high net energy. • Versatile fuel that can be burned to heat indoor space and water, propel vehicles and produce electricity. • Lies above most reservoirs of crude oil. • When a natural gas field is tapped, propane and butane gases are liquefied and removed as liquefied petroleum gas (LPG). • Cleanest-burning among the fossil fuels, releasing much less CO2 per unit of energy than coal, crude oil, and synthetic crude oil from tar sands and oil shale.
Using conventional natural gas has advantages and disadvantages
Use of fracking to extract natural gas is controversial • Hydraulic fracturing, or fracking, pumps water mixed with sand and some toxic chemicals underground to fracture deep rock and free up natural gas stored there. • The gas flows out, along with a toxic slurry of water, salts, toxic heavy metals, and naturally occurring radioactive materials that is stored in tanks and holding ponds. • Drillers maintain that fracking is necessary for exploiting this reserve at a reasonably low cost, and they argue that no groundwater contamination directly due to fracking has ever been recorded.
Coal is a plentiful but dirty fuel • Coal is a solid fossil fuel formed from the remains of land plants that were buried 300–400 million years ago and exposed to intense heat and pressure over those millions of years. • Coal is burned in power plants to generate about 42% of the world’s electricity, and burned in industrial plants to make steel, cement, and other products. • The three largest coal-burning countries are China, the U.S., and India. • Coal is plentiful and cheap.
Increasing heat and carbon content Increasing moisture content Peat (not a coal) Lignite (brown coal) Bituminous (soft coal) Anthracite (hard coal) Heat Heat Heat Pressure Pressure Pressure Partially decayed plant matter in swamps and bogs; low heat content Low heat content; low sulfur content; limited supplies in most areas Extensively used as a fuel because of its high heat content and large supplies; normally has a high sulfur content Highly desirable fuel because of its high heat content and low sulfur content; supplies are limited in most areas Fig. 13-12, p. 310
Coal is a plentiful but dirty fuel • Mining and burning coal have severe impacts on the earth’s air, water, land, climate, and human health. • Coal-burning power and industrial plants are among the largest emitters of the greenhouse gas, CO2. • Coal burning emits trace amounts of toxic and radioactive materials. • Burning coal produces a highly toxic ash that must be safely stored, essentially forever. • China uses three times as much coal as the U.S. and it has become the world’s leading emitter of CO2 and of sulfur dioxide.
This power plant burns pulverized coal to boil water and produce steam that spins a turbine to produce electricity.
Waste heat Cooling tower transfers waste heat to atmosphere Coal bunker Turbine Generator Cooling loop Stack Pulverizing mill Condenser Filter Boiler Toxic ash disposal Fig. 13-13, p. 310
Coal-fired electricity 286% Synthetic oil and gas produced from coal 150% Coal 100% Tar sand 92% Oil 86% Natural gas 58% Nuclear power fuel cycle 17% Geothermal 10% Stepped Art Fig. 13-15, p. 311
Section 13-3 What are the advantages and disadvantages of nuclear energy?
How does a nuclear fission reactor work? • Nuclear power plant is a highly complex and costly system designed to perform a relatively simple task: to boil water to produce steam that spins a turbine and generates electricity. • A controlled nuclear fission reaction is used to provide the heat. • The fission reaction takes place in a reactor. • Light-water reactors (LWRs) produce 85% of the world’s nuclear-generated electricity (100% in the U.S.). • The fuel for a reactor is made from uranium ore mined from the earth’s crust, then enriched and processed into pellets of uranium dioxide.
Small solar-cell power plants Bioenergy power plants Wind farms Fuel cells Solar-cell rooftop systems Rooftop solar- cell arrays Smart electrical distribution system Commercial Small wind turbine Residential Microturbines Industrial Fig. 13-47, p. 342
Small amounts of radioactive gases Uranium fuel input (reactor core) Control rods Containment shell Waste heat Heat exchanger Steam Turbine Generator Hot coolant Useful electrical energy about 25% Hot water output Pump Pump Coolant Pump Pump Waste heat Cool water input Moderator Shielding Pressure vessel Coolant passage Water Condenser Periodic removal and storage of radioactive wastes and spent fuel assemblies Periodic removal and storage of radioactive liquid wastes Water source (river, lake, ocean) Fig. 13-17a, p. 314
What is the nuclear fuel cycle? • In addition to a nuclear power plant, the nuclear fuel cycle includes: • mining uranium. • processing and enriching the uranium to make fuel. • using it in the reactor. • safely storing the resulting highly radioactive wastes for thousands of years until their radioactivity falls to safe levels. • retiring the highly radioactive plant by taking it apart. • storing its high- and moderate-level radioactive material safely for thousands of years.
Nuclear power cycle to produce energy has advantages and disadvantages
Can nuclear power lessen dependence on imported oil and help reduce projected global warming? • Nuclear power advocates contend it will: • Reduce oil dependency. • Reduce or eliminate CO2 emissions and reduce the threat of projected climate change. • Dissenters claim that • While nuclear power plants do not produce greenhouse gasses, the nuclear fuel cycle does. • Increased use of nuclear power in the U.S. will make the country dependent on imports of uranium. • While nuclear emissions are much lower than those from coal-burning power plants, they still contribute to projected atmospheric warming and climate change.
Nuclear Power Is Not Expanding Very Rapidly • 1950s prediction was that by the year 2000 at least 1,800 nuclear power plants would supply most of the world’s electricity. • Some 441 commercial nuclear reactors in 31 countries produce only 6% of the world’s commercial energy and 14% of its electricity. • Nuclear power is now the world’s slowest-growing form of commercial energy.
Experts Disagree about the Future of Nuclear Power • Opposition to Nuclear Power. • Nuclear power industry could not exist without support from governments and taxpayers. • In the U.S., the government provides huge subsidies, tax breaks, and loan guarantees to the nuclear industry, and accident insurance guarantees, because insurance companies have refused to fully insure any nuclear reactor. • Public concerns about the safety of nuclear reactors.
Some critics of nuclear power say any new generation of nuclear power plants should beat all of these criteria; so far, none do
Support for Nuclear Power • Develop nuclear fusion • A nuclear change at the atomic level in which the nuclei of two isotopes of a light element such as hydrogen are forced together at extremely high temperatures until they fuse to form a heavier nucleus, releasing energy in the process • No risk of a meltdown or of a release of large amounts of radioactive materials, and little risk of the additional spread of nuclear weapons. In addition to generating electricity, fusion power could be used to destroy hazardous wastes, and it could have many other uses.
Section 13-4 Why is energy efficiency an important energy resource?
We waste huge amounts of energy • Energy efficiency is the measure of how much work we can get from each unit of energy we use. • Roughly 84% of all commercial energy used in the U.S. is wasted. • About 41% of this energy is unavoidably lost because of the degradation of energy quality imposed by the second law of thermodynamics. • The other 43% is wasted unnecessarily, mostly due to the inefficiency of incandescent light bulbs, industrial motors, most motor vehicles, coal and nuclear power plants, and numerous other energy-consuming devices. • Poor insulation and building design also contribute.
