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Energy

Chapter 12

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Outline:

• Energy Sources and Uses• Coal - Oil - Natural Gas• Nuclear Power• Conservation• Solar Energy

Photovoltaic Cells• Fuel Cells• Energy From Biomass• Energy From Earth’s Forces

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Table 12.01

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ENERGY SOURCES AND USES

• Work - Application of force through a distance. Work= Distance/Time

• Energy - The capacity to do work.• Power - Rate at which work is done.

power (w) = voltage (v) * current (I)

power (watts) = energy transfered (joules)

time (seconds) Calorie - Amount of energy necessary to heat 1

gram of water 1oC. Joule - Amount of work done when a force of 1

Newton is exerted over 1 meter.

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Current Energy Sources

• Fossil Fuels currently provide about 86% of all commercial energy in the world.

Other renewable sources make up 9.5% of commercial power. Nuclear power makes up 6.5% of commercial power.

Worldwide Commercial Energy Production

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Per Capita Consumption

• Richest 20 countries consume nearly 80% of natural gas, 65% of oil, and 50% of coal production annually.

On average, each person in the U.S. and Canada uses more than 300 GJ of energy annually.

- In poorest countries of the world, each person generally consumes less than one GJ annually.

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How Energy is Used• Largest share of energy used in the U.S. is consumed by industry (32.6%).• Residential and Commercial buildings use 37.6% of primary energy consumed in

U.S.• Transportation consumes about 26% of all energy used in the U.S.

Three trillion passenger miles and 600 billion ton miles of freight carried annually by motor vehicles in the U.S.

About half of all energy in primary fuels is lost during conversion to more useful forms while being shipped, or during use.

Nearly two-thirds of energy in coal being burned to generate electricity is lost during thermal conversion in the power plant.

- Another 10% is lost during transmission and stepping down to household voltages.

• Natural gas is most efficient fuel. Only 10% of its energy content is lost during shipping and

processing.- Ordinary gas-burning furnaces are about 75% efficient.- High-economy furnaces can be upwards of 95% efficient.

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Natural Resource Categories

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FOSSIL FUELS• Coal

World coal deposits are vast, ten times greater than conventional oil and gas resources combined.

- Total resource is estimated at 10 trillion metric tons. Proven-in-place reserves should last about 200 yrs.

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Coal

• Mining Dirty and dangerous

- Several thousands have died of respiratory diseases. Black Lung Disease - Inflammation and fibrosis caused by

accumulation of coal dust in the lungs or airways.

• Air Pollution 900 million tons of coal burned in U.S. for electric power generation.

- Multiple pollutants released. Sodium Dioxide (18 million metric tons) Nitrogen Oxides (5 million metric tons) Particulates (4 million metric tons) Hydrocarbons (600,000 metric tons) Carbon Dioxide (1 trillion metric tons)

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Oil• Resources and Reserves

In 2004, proven reserves were roughly 1 trillion barrels.

- Another 800 billion barrels remain to be discovered or are currently not recoverable.

As oil becomes depleted and prices rise, it will likely become more economical to find and bring other deposits to market.

Often contains high sulfur level. Sulfur is highly corrosive, thus the oil is

stripped out before the oil is shipped to market.

• Primarily used for transportation. Provides more than 90% of

transportation energy.

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Oil Cont’d• Oil Shales and Tar Sands

Estimates of total oil supply usually do not reflect large potential from unconventional oil sources such as shale oil and tar sand.

- Could potentially double total reserve.- Severe environmental costs.

Toxic sludge production. Water use

Pitch Lake, Trinidad & Tobago

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Natural Gas

• World’s third largest commercial fuel. 23% of global energy consumption. Produces half as much CO2 as equivalent amount of

coal. Most rapidly growing energy source.

- Difficult to ship long distances, and to store in large quantities.

Resources and Reserves Proven world reserves of natural gas are 5,500

trillion cubic feet.

- Current reserves represent roughly 60 year supply at present usage rates.

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Proven-In-Place Natural Gas Reserves

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NUCLEAR POWER

• President Dwight Eisenhower, 1953, “Atoms for Peace”speech. Nuclear-powered electrical generators

would provide power “too cheap to meter.”- Between 1970-1974, American utilities

ordered 140 new reactors. 100 subsequently canceled.

Electricity from nuclear power plants was about half the price of coal in 1970, but twice as much in 1990.

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How Do Nuclear Reactors Work• Most commonly used fuel is U235, a

naturally occurring radioactive isotope of uranium.

- Occurs naturally at 0.7% of uranium, but must be enriched to about of 3%.

• Formed in cylindrical pellets (1.5 cm long) and stacked in hollow metal rods (4 m long).

About 100 rods and bundled together to make a fuel assembly.

- Thousands of fuel assemblies bundled in reactor core.

When struck by neutrons, radioactive uranium atoms undergo nuclear fission, releasing energy and more neutrons.

Triggers nuclear chain reaction.

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Kinds of Reactors

• Seventy percent of nuclear power plants are pressurized water reactors. Water circulated through core to absorb heat from fuel

rods.- Pumped to steam generator where it heats a

secondary loop. Steam from secondary loop drives high-speed

turbine producing electricity. Both reactor vessel and steam generator are

housed in a special containment building preventing radiation from escaping, and providing extra security in case of accidents.

Under normal operating conditions, a PWR releases very little radioactivity.

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How Do Nuclear Reactors Work Cont’d

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Pressurized Water Reactor - PWR

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Nuclear Wastes – Yucca Mt. Nevada• Production of 1,000

tons of uranium fuel typically generates 100,000 tons of tailings and 3.5 million liters of liquid waste.

Now approximately 200 million tons of radioactive waste in piles around mines and processing plants in the U.S.

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Radioactive Waste Management

• About 100,000 tons of low-level waste (clothing) and about 15,000 tons of high-level (spent-fuel) waste in the U.S. For past 20 years, spent fuel assemblies have been

stored in deep water-filled pools at the power plants. (Designed to be temporary)

- Many internal pools are now filled and a number plants are storing nuclear waste in metal dry casks outside.

- U.S. Department of Energy announced plans to build a high-level waste repository near Yucca Mountain, Nevada in 1987.

- Facility may cost between $10 and 35 billion, and will not open until at least 2010.

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ENERGY CONSERVATION

• Utilization Efficiencies Most potential energy in fuel is lost as

waste heat.- In response to 1970’s oil prices, average

U.S. automobile gas-mileage increased from 13 mpg in 1975 to 28.8 mpg in 1988.

Falling fuel prices of the 1980’s discouraged further conservation.

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Energy Conversion Efficiencies

• Energy Efficiency is a measure of energy produced compared to energy consumed. Household energy losses can be reduced

by one-half to three-fourths by using better insulation, glass, protective covers, and general sealing procedures.

- Orient homes to gain advantage of passive solar gain in the winter.

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SOLAR ENERGY

• Average amount of solar energy arriving on top of the atmosphere is 1,330 watts per square meter.

Amount reaching the earth’s surface is 10,000 times more than all commercial energy used annually.

- Until recently, this energy source has been too diffuse and low intensity to capitalize for electricity.

• Passive Solar Heat - Using absorptive structures with no moving parts to gather and hold heat.

Greenhouse Design• Active Solar Heat - Generally pump heat- absorbing medium through a

collector, rather than passively collecting heat in a stationary object. Water heating consumes 15% of U.S. domestic energy budget.

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High-Temperature Solar Energy• Parabolic mirrors are curved reflective surfaces that collect light and

focus it onto a concentrated point. Two techniques: Long curved mirrors focused on a central tube containing a heat-

absorbing fluid. Small mirrors arranged in concentric rings around a tall central tower

track the sun and focus light on a heat absorber on top of the tower where molten salt is heated to drive a steam-turbine electric generator.

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Photovoltaic Solar Energy• Photovoltaic cells capture solar energy and

convert it directly to electrical current by separating electrons from parent atoms and accelerating them across a one-way electrostatic barrier.

Bell Laboratories - 1954- 1958 - $2,000 / watt- 1970 - $100 / watt- 2002 - $5 / watt

During the past 25 years, efficiency of energy capture by photovoltaic cells has increased from less than 1% of incident light to more than 10% in field conditions, and 75% in laboratory conditions.

Invention of amorphous silicon collectors has allowed production of lightweight, cheaper cells.

Photovoltaic Cells

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Storing Electrical Energy

• Electrical energy storage is difficult and expensive. Lead-acid batteries are heavy and have

low energy density.- Typical lead-acid battery sufficient to

store electricity for an average home would cost $5,000 and weigh 3-4 tons.

Pumped-Hydro Storage Flywheels

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Promoting Renewable Energy

• Distributional Surcharges Small charge levied on all utility customers

to help finance research and development.• Renewable Portfolio

Mandate minimum percentage of energy from renewable sources.

• Green Pricing Allow utilities to profit from conservation

programs and charge premium prices for energy from renewable sources.

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FUEL CELLS• Fuel Cells - Use ongoing electrochemical reactions to produce

electric current. Positive electrode (cathode) and negative electrode (anode)

separated by electrolyte which allows charged atoms to pass, but is impermeable to electrons.

- Electrons pass through external circuit, and generate electrical current.

• Fuel cells - provide direct-current electricity as long as supplied with hydrogen and oxygen.

Hydrogen can be supplied as pure gas, or a reformer can be used to strip hydrogen from other fuels.

Fuel cells run on pure oxygen and hydrogen produce no waste products except drinkable water and radiant heat.

- Reformer releases some pollutants, but far below conventional fuel levels.

- Typical fuel cell efficiency is 40-45%.- Current is proportional to the size of the electrodes, while voltage

is limited to about 1.23 volts/cell. - Fuel cells can be stacked together until the desired power level is

achieved.

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Fuel Cells

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FUEL CELLS CONT’D

• Fuel cells provide direct-current electricity as long as supplied with hydrogen and oxygen. Hydrogen can be supplied as pure gas, or a reformer can

be used to strip hydrogen from other fuels. Fuel cells run on pure oxygen and hydrogen produce no

waste products except drinkable water and radiant heat.- Reformer releases some pollutants, but far below

conventional fuel levels. - Typical fuel cell efficiency is 40-45%.- Current is proportional to the size of the electrodes,

while voltage is limited to about 1.23 volts/cell. - Fuel cells can be stacked together until the desired

power level is achieved.

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BIOMASS• Wood provides less than 1% of U.S. energy, but provides up to 95% in

poorer countries. 1,500 million cubic meters of fuelwood collected in the world

annually.- Inefficient burning of wood produces smoke laden with fine ash

and soot and hazardous amounts of carbon monoxide (CO) and hydrocarbons.

Produces few sulfur gases, and burns at lower temperature than coal.

Anaerobic Fermentation

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Fuelwood Crisis

• About 40% of world population depends on firewood and charcoal as their primary energy source. Of these, three-quarters do not have an

adequate supply.- Problem intensifies as less-developed

countries continue to grow. For urban dwellers, the opportunity to

scavenge wood is generally nonexistent.

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Figure 12.26

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Fuelwood Crisis Cont’d

• Currently, about half of worldwide annual wood harvest is used as fuel. 85% of fuelwood harvested and consumed

in developed countries.- By 2025, worldwide demand for

fuelwood is expected to be twice current harvest rates while supplies will have remained relatively static.

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Dung

• Where other fuel is in short supply, people often dry and burn animal dung. Not returning animal dung to land as

fertilizer reduces crop production and food supplies.

- When burned in open fires, 90% of potential heat and most of the nutrients are lost.

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Figure 12.28

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Methane

• Methane is main component of natural gas. Produced by anaerobic decomposition.

- Burning methane produced from manure provides more heat than burning dung itself, and left-over sludge from bacterial digestion is a nutrient-rich fertilizer.

Methane is clean, efficient fuel. Municipal landfills contribute as

much as 20% of annual output of methane to the atmosphere.

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Alcohol from Biomass

• Gasohol - Mixture of gasoline and ethanol. Ethanol raises octane ratings, and helps

reduce carbon monoxide emissions in automobile exhaust.

Could be solution to grain surpluses and bring higher price for grain crops.

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ENERGY FROM EARTH’S FORCES

• Hydropower By 1925, falling water generated 40% of

world’s electric power.- Hydroelectric production capacity has

grown 15-fold. Fossil fuel use has risen so rapidly

that currently, hydroelectric only supplies one-quarter of electrical generation.

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Hydropower

• Total world hydropower potential estimated about 3 million MW. Currently use about 10% of potential supply.

- Energy derived from hydropower in 1994 was equivalent to 500 million tons of oil.

- Much of recent hydropower development has been in very large dams.

- In the U.S., hydropower is produced for an average of $7 per megawatt-hour (MWh) or about one-third the cost of using fossil or nuclear fuels and less than one-sixth the cost of using natural gas

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Dam Drawbacks

• Human Displacement• Ecosystem Destruction• Wildlife Losses• Large-Scale Flooding Due to Dam Failures• Sedimentation• Herbicide Contamination• Evaporative Losses• Nutrient Flow Retardation

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Wind Energy

• Estimated 20 million MW of wind power could be commercially tapped worldwide.

Fifty times current nuclear generation.- Typically operate at 35% efficiency under field conditions.

Under normal conditions, (15 km/hr) electric prices typically run 5 cents per kilowatt hour.

- Standard modern turbine uses only two or three blades in order to operate better at high wind speeds.

• Wind Farms - Large concentrations of wind generators producing commercial electricity.

Negative Impacts:- Interrupt view in remote places- Destroy sense of isolation- Potential bird kills

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Geothermal Energy

• High-pressure, high-temperature steam fields exist below the earth’s surface. Recently, geothermal energy has been

used in electric power production, industrial processing, space heating, agriculture, and aquaculture.

- Have long life span, no mining needs, and little waste disposal.

Potential danger of noxious gases and noise problems from steam valves.

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Tidal and Wave Energy• Ocean tides and waves contain enormous amounts of energy that can

be harnessed. Tidal Station - Tide flows through turbines, creating electricity.

- Requires a high tide / low-tide differential of several meters. Main worries are saltwater flooding behind the dam and

heavy siltation. Stormy coasts with strongest waves are often far from

major population centers.