•19
•Fossil Fuels: Energy and Impacts
•History of energy use
•People have long exploited energy sources.
•Coal, oil, gas, solar, and wind power were all used before 1200 B.C.
•Fire, animal labor, and hot springs were used long before that.
•But only since the industrial revolution have we harnessed energy sources on a grand scale.
•Fossil fuels
•Fossil fuels = highly combustible substances formed from the remains of organisms from past geological ages
•Compressed tissues of plants (and some animals) from 100–500 million years ago store chemical energy from photosynthesis.
•This greatly concentrated energy is released when we burn coal, oil, or gas.
•Fossil fuel use has been rising for years
Growth in coal has slowed, but oil and gas are still rising.
•Fossil fuels:
Formation
•Plants and animals die
•Organic material settles in anaerobic site and is partly decomposed
•Organic material is buried
•Heat and pressure alter chemical bonds
•Coal, gas, oil formed
•Distribution of fossil fuel reserves
•Saudi Arabia has the most oil.
•Russia has the most natural gas.
•The U.S. has the most coal.
•Per capita energy use varies
•Nations differ greatly in amounts of energy used per person.
•Developed nations like the U.S. use by far the most.
•Coal
•Coal: compressed under high pressure to form dense
carbon structures
•First used 3,000 years ago
•Powered the industrial revolution in England, then in other countries
•Today is surpassed by oil, but is still the most abundant fossil fuel
•Provides 1/4 of the world’s commercial energy consumption
•How coal is formed
•Peat is partially decayed organic matter near the surface, a precursor to coal.
•With more time, more heat and pressure, squeezing out more moisture, coal becomes more energy-rich.
• Anthracite is the most compressed and most energy-rich type of coal.
•Coal production and consumption
China produces and consumes the most coal, followed by the United States.
•Coal mining
Coal is mined
•either underground, in subsurface mining,
•or from the surface, in strip mining.
•Electricity generation from coal
Coal is most used to generate electricity. Heat from coal burning boils steam, turning a turbine to power a generator.
•Oil
•Crude oil (petroleum): sludgelike mix of hundreds of types of hydrocarbon molecules; forms at temperatures and pressures found 1.5–3 kilometers below ground
•Oil refineries sort the various hydrocarbons of crude oil, separating those to be used in gasoline with those used for other purposes (tar, asphalt).
•Modern extraction began in the 1850s in Pennsylvania.
•Today oil is the world’s most-used fuel.
•Estimating recoverable reserves
•Technology limits how much oil can be extracted.
•Economics determines how much oil will be extracted.
•Proven recoverable reserve = amount of oil that is technologically and economically feasible to remove
•Once oil deposits are identified, oil companies typically conduct exploratory drilling.
•Oil: Drilling
•Liquid oil exists in pores in rock deep underground.
•We must drill into rock and extract oil by using a pressure differential.
•The more oil is extracted, the harder it is to extract:
•Primary extraction = initial extraction of available oil
•Secondary extraction = forcing oil out by pumping water or gas into rock to displace it
•Oil: Drilling
•Depletion of oil reserves
•We may have already extracted half of the world’s oil reserves (1 trillion barrels).
•To estimate how long this remaining oil will last, analysts calculate the reserves-to-production ratio (R/P ratio)…
•…by dividing the amount of total remaining reserves by the annual rate of production.
•Depletion of oil reserves: “Hubbert’s peak”
•Geologist M. King Hubbert predicted U.S. oil production would peak around 1970 and then decline.
•He was only a few years off.
•Refining crude oil
•Crude oil from the ground is a messy mix of hundreds of hydrocarbons.
•It is put through a refining process to segregate different components.
•Refining crude oil
•Petroleum products
Refined components of crude oil are used to manufacture many of the material goods we use every day.
•Natural gas formation
Natural gas: primarily methane, CH4, is produced in two ways:
•Biogenicgas = formed at shallow depths by anaerobic decomposition of organic matter by bacteria
•Thermogenicgas = formed at deep depths as geothermal heating separates hydrocarbons from organic material
•Natural gas: History
•Seeps known for 2,000+ years
•Used for street lighting in the 1800s
•Became commonly used after WWII once pipeline technology became safer
•Natural gas production and consumption
•Russia produces the most natural gas.
•The U.S. consumes the most natural gas.
•Gas extraction
•Initially, gas comes out on its own from natural pressure.
•Later, it must be pumped out.
•Other fossil fuels
Other fossil fuels could be used in the future:
•Oil or tar sands = dense, hard, oil substances that can be mined from the ground
•Shale oil = sedimentary rock filled with organic matter that was not buried deeply enough to form oil
•Methane hydrates = occur under the seafloor
•Environmental impacts of fossil fuel use
•Using fossil fuels creates a number of environmental impacts.
•Most energy experts would like to see a switch to renewable and less-polluting energy sources.
•Environmental impacts
Compounds and particulate matter resulting from combustion of coal, oil, and gas:
•Cause air pollution
(from power plants, vehicle exhaust, etc.)
•Drive climate change
(from carbon dioxide emissions)
•Throw the carbon cycle out of balance
(transferring carbon stored underground to atmospheric carbon dioxide)
•Environmental impacts
Water pollution also results from fossil fuel use:
•Acid deposition (from sulfur pollutants emitted in power plant combustion)
•Runoff from non-point sources (cars, homes)
•Oil spills (not just large spills from tankers; mostly small spills from nonpoint sources)
•Environmental impacts
Coal mining has impacts:
•Habitat destruction from strip mining
•Erosion from strip mining
•Chemical runoff from strip mining through acid drainage
•Human health risks for workers from subsurface mining
•Political, social, and economic impacts
•The degree of dependence that our modern economies have on fossil fuels is risky.
•This puts all our eggs in one basket.
•Nations that supply oil can call the shots.
•Nations that need oil are dependent on suppliers.
•Oil commerce
A small number of nations export nearly all the world’s oil.
•Alternatives to fossil fuels
•Because fossil fuels are nonrenewable and will not last forever the world’s economies must find alternatives.
•Most alternatives are costly and depend on undeveloped technologies.
•Three alternatives are the most developed and widely used:
•Nuclear power
•Biomass energy
•Hydroelectric power
•Nuclear energy
•Nuclear energy = energy that holds together protons and neutrons within the nucleus of an atom
•We harness this energy by converting it to thermal energy, which can then be used to generate electricity.
•Each conversion process involves transforming isotopes of one element into isotopes of other elements by the addition or loss of neutrons.
•Nuclear energy: Fission
Nuclear fission = energy is released by splitting apart uranium nuclei by bombarding them with neutrons
This is the process used in nuclear reactors and weapons.
•Nuclear energy
•Comes from the radioactive element uranium
•The nuclear fuel cycle enriches forms of uranium to make it into usable fuel.
•Electricity is generated by controlling fission in nuclear reactors.
•Nuclear energy
•Uranium is used for nuclear power because it is radioactive.
•Radioisotopes emit subatomic particles and high-energy radiation as they decay.
•Each radioisotope decays at a rate determined by that isotope’s half-life, the amount of time it takes for one-half of the atoms to give off radiation and decay.
•Nuclear reactor
In a reactor, fission boils steam to turn a turbine and generate electricity
•Nuclear energy: Fusion
Nuclear fusion = nuclei of lightweight elements are forced together
Not efficient for power production, so is not (yet) used.
•Nuclear troubles
•Although nuclear power is clean, lacking the pollutants of fossil fuels, it has drawbacks:
•Its waste is dangerously radioactive.
•Consequences of accidents can be catastrophic.
•439 nuclear plants remain operating today in the world.
•Nuclear accidents
The 1986 Chernobyl explosion caused the world’s most severe nuclear power plant accident.
•Nuclear accidents
Fallout from Chernobyl was deposited across Europe.
•Nuclear waste disposal
Nuclear waste must be disposed where it will not escape.
•Nuclear waste disposal
Nuclear waste is stored at 125 sites in 39 states.
•Nuclear waste disposal
At Yucca Mountain, all nuclear waste in the U.S. would be buried in a network of tunnels deep underground.
•Greenhouse gas emissions
Coal, oil, and natural gas emit far more greenhouse gases than do renewable energy sources and nuclear energy.
•Biomass
Organic substances produced by recent photosynthesis
(unlike fossil fuels, products of ancient photosynthesis)
•Uses of biomass energy
•More than 1 billion people burn fuelwood or charcoal as their principal power source for cooking, heating, etc.
•New uses:
•Burning in power plants to produce biopower
•Converting into biofuels to power automobiles
•Many new biomass resources are the waste products of preexisting industries or processes, e.g., forestry, landfill waste.
•Biomass energy consumption
Energy consumption patterns vary greatly between developing and developed nations.
•Biofuels
•Ethanol = alcohol produced by fermenting corn and other carbohydrate-rich crops:
•Added to gasoline to reduce automotive emissions
•Automakers are producing flexible fuel vehicles that run on 85% ethanol and 15% gasoline.
•Biodiesel = produced from vegetable oil, used cooking grease, or animal fat:
•Used in cars with diesel engines
•Cuts down on emissions compared with petrodiesel
•Biodiesel
Biodiesel has fewer emissions than petroleum-based diesel.
•Hydroelectric power
In hydroelectric power, moving water is used to turn turbines and generate electricity.
The storage technique
stores immense amounts
of water behind dams.
•Hydroelectric power
For nations with large amounts of flowing water (Brazil, Norway, Austria, Canada…), hydropower has been key to their economic development.
98% of U.S. rivers
are dammed.
•Hydroelectric power
Water flowing through a dam spins turbines that turn generators to create electricity.
•Hydroelectric power
•“New renewables”
Commonly referred to as “new” because:
•They are not yet used on a wide scale.
•They are harnessed using technologies that are still in a rapid phase of development.
•It is widely believed that they will play a large role in our energy use in the future.
They provide only 0.5% of our global energy supply.
•“New renewables”
•Solar: from the sun’s rays
•Wind: from the wind
•Geothermal: from heat and heated water beneath the ground
•Ocean sources: from the tides and from waves
•Hydrogen: fuel and fuel cells that store renewable energy in usable form
•Growth of renewable sources
Renewable sources, esp. wind and solar, are growing at an astounding rate.
These figures are percentage growth per year.
•Renewable sources: Outlook
The outlook for renewable sources is good.
•But will governments raise subsidies to the level offered to fossil fuels?
•Will research and development proceed fast enough?
•Will companies have incentives to invest in developing these sources?
•Will consumers choose alternative energy sources?
•Solar energy
•Use of energy from the sun
•Huge potential: Each day Earth receives enough sunlight to power human consumption for 27 years, if we could somehow capture it all.
•Technology not new:
•First thermal solar collector: 1767
•First commercial solar water heaters: 1890
•Solar energy
•Passive solar = designs buildings to maximize capture of sunlight in winter, but keep buildings cool in summer
•through window placement, absorbent materials, and thermal mass materials that absorb, store, and release heat
•Active solar = uses technological devices to focus, move, or store solar energy
•solar panels: dark, heat-absorbing metal plates in glass-covered boxes, often mounted on roofs
•Solar energy: Active solar
Numerous mirrors focus sunlight on a receiver atop a “power tower” in the California desert. This facility was the first to generate much solar power commercially.
•Solar energy: PV cells
•Photovoltaic cells (PV cells) convert solar energy directly into electrical energy by making use of the photoelectric effect:
•When sunlight strikes a charged metal plate, electrons migrate to another plate, and electric current is produced.
•In PV cells, light strikes negatively charged phosphorus, and electrons migrate through silicon to positively charged boron.
•Solar energy: PV cells
Electrons move from the phosphorus side of the silicon plate to the boron side, creating electric current. PV cells are arranged in modules, panels, and arrays.
•Pros and cons of solar power
PROS:
•Renewable as long as sun keeps on shining
•Sun’s energy abundant, if technology can capture it
•Allows for local control over power
•Solar cookers in developing nations lessen workloads.
•No direct greenhouse gas emissions
CONS:
•Not everywhere is sunny enough
•Up-front investment cost is high; takes years to pay for itself
•Solar power
•Wind power
•Takes kinetic energy of wind and converts it to electrical energy
•Fastest growing power source today
•Technology = wind turbines, machines with turning blades that convert energy of motion into electrical energy by spinning a generator
•Windmills have been used for centuries.
•First wind turbine for electricity: late 1800s
•Wind power: Wind turbines
Wind spins the blades, which turn the gearbox, which turns the generator to produce electricity.
•Wind power
Wind speeds vary tremendously from place to place.
Windiest in the U.S. are mountainous areas and parts of the Great Plains.
•Pros and cons of wind power
PROS:
•Renewable as long as wind blows
•No emissions after equipment made, installed
•Can allow local decentralized control over power, and local profit from electricity sales
• Costs low after initial investment; costs dropping
CONS:
•Not everywhere is windy enough.
•Windy sites can be far from population centers.
•Some people object to aesthetics.
•Blades kill birds, bats.
•High start-up costs
•Geothermal energy
•Radioactive decay of elements deep in Earth’s core creates heat that rises toward the surface.
•This heats magma of volcanoes, and also underground water.
•Sometimes water spurts through to the surface in geysers.
•Geothermal power plants use the energy of naturally heated water to generate electricity.
•Geothermal energy
Underground heat warms water, and steam turns turbines and generators.
Condensed steam is reinjected into the aquifer to keep up pressure.
•Geothermal energy
•Iceland uses geothermal energy to heat water for 86% of its homes.
•Heat pumps using surface heat can also be very efficient.
•Geothermal energy is growing 9% annually.
•Pros and cons of geothermal power
PROS:
•Renewable as long as water is heated naturally
•Much lower greenhouse gas emissions than fossil fuels
•Can be inexpensive in areas where geothermal heating naturally occurs
CONS:
•Heated water may give out after a while—hotspot moves or aquifer pressure drops
•Salts in water can corrode equipment, shorten lifespan
•Limited to geographic areas where geothermal heating naturally occurs
•Ocean energy sources
Three sources from oceans:
•Tidal power: The twice-daily flow of tides (rising and falling of seas due to the moon’s gravitational pull) creates energy of motion that can be converted to electricity.
•Wave power: Motion of waves at ocean shores creates energy of motion that can be converted to electricity.
•Thermal power: Exploits differences in warm and cold water. Not yet commercially developed.
•Tidal energy
Bulb turbines spin as tidal flow passes through them.
•Wave energy
There are several designs for wave energy stations.
In this one, air is compressed in a chamber with each incoming wave, driving a turbine to spin a generator.
•Ocean thermal energy
•Warm surface water is piped into facilities where it evaporates volatile substances (e.g., ammonia) to turn turbines.
•Cold, deeper water is then used to condense the substances and start the cycle again.
•Ocean Thermal Energy Conversion (OTEC) project research has been run in Hawaii and elsewhere, but there are no commercial operations yet.
•Pros and cons of ocean power sources
PROS:
•Renewable as long as oceans behave as they always have
•No greenhouse gas emissions
CONS:
•Development could take up large portions of coastline valuable for other uses
•Could interfere with ecology of estuaries and intertidal shorelines
•OTEC not yet commercially feasible
•Hydrogen
•Hydrogen = simplest and most abundant element in universe
•Could potentially serve as basis for clean, safe, efficient energy system
•How it would work:
•Electricity generated from intermittent renewable sources like wind or solar can be used to produce hydrogen.
•Fuel cells can then use hydrogen to produce electrical energy for power.
•Production of hydrogen fuel
•Hydrogen gas (H2) does not exist freely on Earth.
•We need to make it.
•Electrolysis is the cleanest way:
Split water into hydrogen and oxygen:
2 H2O 2 H2 + O2
•This can potentially be very clean, releasing no greenhouse gas emissions.
•Fuel cells
•Production of hydrogen fuel
However, cleanliness of hydrogen production depends…
•If the source of electricity needed for electrolysis is
not clean (e.g., from coal), then greenhouse emissions will still occur.