Energy Sys

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History of the Energy System

In the Beginning: Pre-IndustrializationThe muscle power of human beings and animals was the first application of energy by humans and the food chain was theenergy system in use. Humans have long "designed" energy systems with the goal of producing the most work possible wthe least amount of humaneffort to generate the energy.

Pre-Industrial society depended primarily on muscle power and biomass for their energy needs. Biomass consisted primarof wood or peat and its energy delivery had a low efficiency. Amory Lovins, an expert on energy, states, "Most of theenergy generated by wood or peat went up in the chimneys rather than into the room or cooking pot of pre-industrialsocieties."

Animal power in the form of horse mills, wind power in the form of windmills, and water power with the use of a water whwere major energy sources harnessed until the 19th century; especially for "industrial uses." Wood and charcoal were thmain fuels for cooking, heating, and other domestic uses, but coal and oil were available as well. "In the Middle East crudoils have been known for millennia from natural seepage and pools, but they were used only rarely as fuels, and morefrequently as protective coatings."1 Coal has its origin in "the lithification of peats produced by accumulations of dead plamatter in wetlands. Difference in original vegetation and, more importantly, in magnitudes of durations of transformingtemperatures and pressures, have produced a large variety of coals."2 As early as the 13th century, coal pits were minedand coal energy was used specifically for the forcing and smelting of metals. In the 1600's, England experienced an energcrisis due to a shortage of wood and began using coal as a substitute fuel source for domestic purposes. Even in the 1700wood was the major fuel source in colonial America.

The Industrial RevolutionThe quest for more powerful energy sources was propelled by the inventions and discoveries of the Industrial Revolution.

sophisticated mechanical inventions were made, a large reliable and seemingly inexhaustible source of energy becamenecessary for industrial uses, and transportation. The need for large quantities of accessible, dependable, and transportabenergy encouraged the exploration of energy sources. The inventions of the Industrial Revolution provided the equipmentfurther mine or drill the already visible deposits of coal and oil.

Steam power was developed in the 1600's in conjunction with coal mining to help pump water out of the mines. It had beknown since ancient times that heat could be used to produce steam, which could then do mechanical work. However, it wonly in the late eighteenth century that commercially successful steam engines were invented. The first commerciallysuccessful steam engine was invented by Thomas Savery (1650-1715), an English military engineer. In 1712, this enginewas refined by Thomas Newcomen (1663-1729), another Englishman. The Newcomen engine was widely used in Britain aEurope throughout the eighteenth century, but had very low energy efficiency.

A greatly improved steam engine was designed and built in 1763 by James Watt who was asked to repair a Newcomenengine. Watt built and then sold or rented his engines to mining companies, charging them for the "power" in the rate of

work the engine produced. Today, the unit for power is called a Watt.

The sun was also studied as an energy source in the 18th century. In 1767, the first solar thermal collector was developeby the Swiss scientist Horace de Saussure. Solar thermal power was used in the American west as an energy source forcooking until oil and natural gas became a more reliable way to generate energy. For simple cooking solar energy wasabsorbed by black cast iron pots. Solar thermal collectors were also used in the form of hot boxes to cook food.

In 1839, Alexandre Becquerel discovered that an electric current could be generated when certain elements were exposedight. The scientific explanation of this phenomenon by Albert Einstein, called photoelectricity (light-induced electricity),came much later in 1905. Photoelectricity is the basis of the photovoltaic cells, now used to convert light into electricity.Despite the century and a half since it discovery, photovoltaic means of generating electricity have not been developed wenough vigor for it to become a major source of electricity. This is because the material technology for photovoltaic paneldeveloped slowly. As coal and other fossil fuels were easier to use, and available in plenty, not much effort has gone intophotovoltaic research.

Until the early 1800's our understanding of the science of energy was not well developed. The theory at that time was thecaloric theory, which said that heat is a substance called "caloric" that flowed from hotter to colder bodies. In the 1840's tEnglish physicist James Prescott Joule did a long series of experiments that showed that heat is a form of energy. Joulefound the relationship between a unit of mechanical energy and a unit of heat. This helped Joule finalize what chemists annatural philosophers had come to believe--that the total energy in the universe is constant, although energy is continuouschanging forms.

1Smil, Vaclav. Energies: An Illustrated Guide to the Biosphere and Civilization. The MIT Press: Cambridge, MA, 1999.

2Nye, David E. Consuming Power: A Social History of American Energies. The MIT Press: Cambridge, MA, 1999.


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The study and invention of the heat engine and steam power established and confirmed the Laws of Thermodynamics. Fro1840-1880, Joule, Lord Kelvin, and James Clark Maxwell in England; Sadi Carnot and Rudolf Clausius in France; and LudwBoltzmann in Austria formulated a theory of heat engines, laying the foundations of Thermodynamics, literally the science"motion from heat." (Thermo=heat and dynamics=motion).

In 1820, the advances in mechanical and materials engineering made the railroad the most efficient and fastest means oftransportation. Coal and wood were used as the primary fuel source for the steam engine. The locomotive also changedsociety's perception of travel and transportation.

Wind energy was developed on a large scale in the United States as an energy source for farms and railroad stations, usintall windmills to pump water from underground wells. There were specific design developments that made these windmillsmore efficient, although they still generated relatively little power. The height of these windmills helped to ensure theycaught the wind and a tailfin generally kept the fan facing the wind.

Another result of the Industrial Revolution was an energy distribution infrastructure built into cities that promoted domestconvenience. As early as 1816, natural gas was piped into cities for domestic uses such as cooking, home illumination, anstreet lighting. The steam engine was used to pump water into homes and sewage away from homes. The city wasundergirded with networks that usually began with water pipes and gas lines and gradually expanded to include sewers,electrical conduits, and telephone lines.3

In 1859, when petroleum was drilled in Titusville, Pennsylvania, an apparently plentiful energy source began to replace coOil was distilled into kerosene (referred to as coal oil) and used as a lamp oil. It replaced dwindling supplies of whale oil ufor lamps. There were many reasons oil became a more desirable fuel source than coal: it was easy to obtain and transpot emitted less particulate pollution than coal; it replaced scarce whale oil as a fuel for lamps; and coal had become anunreliable fuel source because of the labor issues surrounding the mining of coal. Miners were striking for safer work

environments and more money, which affected the amount of coal available to the consumer.

But the most significant use of crude oil was as the liquid fuel for the internal combustion engine, designed in 1861 byNikolaus August Otto. The internal combustion engine became one of the most influential inventions of the IndustrialRevolution. Although this engine is low in efficiency, it could produce enough work to move a large metal vehicle fardistances. The fuel of the internal combustion engine was also easier to use than, for example, shoveling coal into a furnato power a locomotive. This was the beginning of the use of liquid fuel to advance transportation.

In 1879, Thomas Edison invented the incandescent light bulb -- a major step in the human use of storable energy leadingeventually to large-scale electrification. Electricity is similar to a liquid fuel in that it can be transported easily (although nefficiently) from one place to another. One of Edison's goals was to make electricity affordable for all homes. Edison begawith the distribution of electricity through a direct current (DC). This meant that electrons would flow one way through awire to bring electricity to a home; however, a good portion of the energy was lost as the electrons moved through the wiThis loss of energy using direct current to move electricity meant that power plants had to be built close to the homes the

plant serviced and was eventually considered impractical.

Nikola Tesla, an inventor employed by Edison, discovered that electrons would alternate or travel back and forth on a wireand travel longer distances with less energy loss. This was called alternating current (AC) and had an advantage because could be more easily generated. Edison had so much money invested in his DC power plants that he discredited Tesla'salternate current as dangerous -- thus beginning a "war of the currents." Tesla eventually joined forces with GeorgeWestinghouse and began developing power plants using alternating current (AC).

In the late 19th and early 20th centuries the steam turbine, using coal as a fuel, was developed as a cheap power sourcethat generated electricity. In 1882, the first functional steam turbine was designed by Charles Parsons, an English engineHe used the high pressure of steam to hit the blades of a rotor. The principle of the turbine was a major step toward todaproduction of electricity.

In 1893, Westinghouse demonstrated a "universal system" of generation and distribution at a Chicago exposition. The

universal system meant that power or energy could be used in a variety of ways at many different voltages. Westinghoususing Tesla's invention of the transformer and the electric motor, as well as steam turbines, transformed Niagara Falls intone of the first hydroelectric plants in the world

In 1910, Henry Ford opened the 60-acre Highland Park automotive plant with a moving assembly line. This was thebeginning of an eventually enormous use for fossil fuels. Fossil fuels were used not only to propel the automobiles that wmade at the plant, but also to generate electric power for the automotive plant.

Energy technologies developed rapidly during the 20th century. Although the current version for solar thermal collectors wdesigned in 1908, they were not developed well enough for mass distribution. In the 1920's, 30's, and 40's, there wasarge-scale construction and development of hydroelectric plants/dams to support increasing population in the Southwest

3Nye, David E. Consuming Power: A Social History of American Energies. The MIT Press, 1999. (p. 94)


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In 1938, Otto Hahn and Fritz Strassman demonstrated nuclear fission and within four years (1942), Oak Ridge, Tennessewas chosen as the site for the first functional nuclear reactor plant, and for the preparation of uranium and plutonium useto the create the atomic bomb at Los Alamos. The first nuclear chain reactor was demonstrated at the University of Chican December 1942. In July 1945, the testing of the first atomic bomb at Alamogordo, New Mexico, demonstrated thetechnology used to release nuclear energy on a large scale. In 1957, the first commercial nuclear power plant opened inShippingport, Pennsylvania.

The first large scale use of photovoltaic (PV) solar energy in conjunction with satellite technology developed in the 1950'sThe United States Vanguard I was the first PV-powered satellite.

By the early part of the 20th century, crude oil and its products had become an indispensable part of the industrial economJames Young had patented a process in England in 1850 to distill oil from coal and shale. Oil refining is not just aboutgasoline. The distilled chemicals from crude oil have many purposes -- for example, petroleum is used for plasticsmanufacturing. Young's process of fractal distillation forms the basis of the world's oil refining industry.

Figure 4 shows the oil reserves that we know for sure as of 1987.

Figure 4:Proven Oil Reserves as of 1987 (billions of barrels)Source: Energy, National Academy Press, pg 268

While a large amount of oil occurs in many parts of the world, the largest stores are located in the regions governed by thArab countries. The Oil and Petroleum Economic Cartel (OPEC) is the economic coalition of these countries that control thflow of that oil. In the 1970's, OPEC placed an embargo on their oil sales. This "energy crisis" brought energy scarcity to tconsciousness of all nations -- and especially the U.S., with its higher dependence on imported oil. This crisis began togenerate interest in the exploration of renewable energy sources for large-scale generation of electricity and other energyneeds.


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Human Energy Needs

Figure 5:Composite of satellite images showing the extent of outdoor lightingin the continental United States. Courtesy of the Defense Meteorological Satellite Program (DMSP).

Our energy consumption has led us to develop new energy sources and technologies. In a century, liquid fuels and electri

have improved our standard of living and provided us with more mobility than people in any other era. This section reviewour human energy needs, how we currently meet them, and what the future may have to offer.

Energy is essential for all we do as individuals and as societies. Energy production, use, and distribution also cause some the most pressing environmental problems. Figure 6 shows the overall picture of human energy needs, the ways in whichmeet our energy needs, and the impacts.

Figure 6: Flowchart of Energy Needs.

Although industrialized countries use the most energy at present, newly industrialized countries are increasing their rate ouse. Figure 7 graphs the projected energy needs of industrialized countries, developing countries, and Eastern Europe andthe former Soviet Union. Many environmental and economic issues arise from the escalating energy use all over the worldUnderstanding the science and technology driving the energy system enables us to better understand our relationship to environment.


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actual work. The rest is dissipated as heat. The other inherent inefficiency is in the fact that to move one person, we havespend energy moving over a ton of extra material (the automobile itself).

Figure 9: Average Annual Residential Vehicle Fuel Consumption by Region, 1994.Source: Energy Information Agency

Use of crude oil is escalating as developing countries emulate industrialized mobility. Figure 10 shows the use of crude oiltransportation needs. This increase in oil consumption specifically for transportation not only impacts the environment, italso further depletes the limited oil reserves in the Earth's core. Increased consumption of oil for transportation could also

affect a variety of industries (i.e. plastics), which in turn affects the economy.

Figure 10: Use of Crude Oil for Transportation Needs.

A review of the science supporting our current energy systems can be found in the section "Science Notes."

Science Notes: Energy Transformation

The definition of energy as the ability to do work came from the 19th century as steam engines and other work-producingmachines were developed. The first engines converted heat (thermal energy) into motion (dynamics). The science of heatengines developed by Lord Kelvin in England and Joule and Clausius in France founded the science of thermodynamics. Thshowed that two rules always held when energy was used to produce motion or work. These are called the two Laws ofThermodynamics. It was noticed that when engines performed work, heat was always produced in addition to the work, athat this represented wasted energy.

The Two Laws of ThermodynamicsOne of our observations about energy is that the total quantity of mass and energy combined in the universe is always thsame. Energy can change forms and mass and energy may even change into each other, but the total quantity remains thsame. This fact is called the principle of Conservation of Energy, or the First Law of Thermodynamics. For most reactionsthat are studied here the total energy remains constant.


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EXAMPLES OF EFFICIENCY:How efficient is an automobile?In other words, how much of the energy in thegasoline results in kinetic energy or energy of motion of the automobile?

12% if well maintained, 8-10% if not maintainedWhat are the implications of this inefficiency? Of the 20 gallons you of gasoline youput in your car, how much actually moves the car to your destination?

1.6-2.4 gallonsthe rest is transformed to waste heat and noise

How efficient is a coal-fired power plant?transformation by steam turbine: 30-40%

How efficient is a hydroelectric plant?transformation by water driven turbine: 80%(the difference from above is because no conversion to steam is involved)

How efficient is a nuclear power plant?the nuclear reaction is 90% efficient, however the same combustion process(steam turbines) is used to generate electricity as with the coal-fired plant sothe net efficiency: 30-40%.

How efficient is the human body?conversion of the energy in the food to muscular and other kinds of work 20%efficient

Based on the First Law of Thermodynamics, we neither create nor destroy energy. Whenever we say that we are producinenergy, what we really mean is that we are transforming energy from one form to another that is more usable. Energy ths the result of work usually manifests as change in position or as the motion of an object. Energy that is stored is called

potential energy -- energy that has the 'potential' to do work. A second form of energy -- energy of motion -- is calledkinetic (meaning "moving") energy. Both kinetic and potential energy can be transformed into work.

Later in this unit we present the physical basis of energy and work. Without going into the details that will come then, let discuss two transformations of energy: a waterfall and a pendulum. Every gallon of water in the fall has potential energy athe top of the waterfall by virtue of its position. At the bottom of the waterfall, this gallon of water travels faster and hasgained kinetic energy at the expense of potential energy. As a pendulum swings back and forth, the energy changes frompotential energy at the top position to kinetic energy at the lowest position and potential energy again as it goes to the toWe will explain the deeper meanings of potential and kinetic energy later in the unit.

We begin by reviewing some fundamentals of physics and chemistry relevant to understanding the basic principles of enetransformation. In particular, we focus on concepts related to the fundamental aspects of energy: Matter, Force, and Enerand the Fundamental Forces of Nature. Then we describe the physics and chemistry of Measuring Energy, Work, and PowChemical reactions and energy release are then described to understand more clearly how the chemical combustion of fos

fuels produces the carbon dioxide and other products that cause environmental problems.

Science Notes: Measuring Matter, Force, and Energy

Matter, force, and energy are common terms that have scientific meanings close to the common use of the words. Mattethe stuff of which everything is composed, and force is something that is capable of changing the motion of an object.Energy is a property that tells us how much work we can get out of the object that possesses that energy. In keeping withe fact that science is based on measurements and observations, all of these entities are described in terms that we canobserve and measure. Therefore, we first discuss these entities by examining and measuring their effects.

Matter and force are the two fundamental entities of which the universe is composed. All that exists can be classified inthese terms. All environmental phenomena occur because of the interactions between matter and transformations of man space and time. As the arrangements between forces and masses change, the change is manifested in terms of energ

Table 4 gives the abbreviations for the physical qualities and their definition and units.


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Physical Quantity Definition, Unit

mass m quantity of matter, kilogramdistance d linear dimension of space, metertime t dimension of time, second

speed, velocity, v distance per time, m/secacceleration, a velocity change per time, m/sec2

force F mass times acceleration, kg. m/sec2= Newton, nt

Work, energy W, E force times distance, nt.m = Joule, J

Table 4:Summary of physical quantities and units.

Matter is discussed in terms of the quantity of matter. This is called the mass. The unit we will use to measure mass isthe kilogram (gram, milligram) in the MKS system that is globally adopted as the scientific system of units. For mostengineering applications, and for common trade in the United States, the British system is used, in which the unit of massthe pound.

Force is a more complicated concept. We experience or observe force through its action on matter (as a push or pull).When a force acts on matter, it changes the way that quantity of matter is moving (Newton's first law). So we measureforce by its capacity to produce acceleration in a mass. Acceleration is a measure of change of motion, measured by how

much speed (m/sec) changes in a second. So the units for acceleration are meter per second per second, or, m/sec2.(Newton's second law: F = ma). Thus the unit to measure force is a composite of the measure of mass, and of

acceleration. The unit is called a newton (kg.m/sec2), written as NT or N. So a one-newton force can change the

acceleration of a 1 kg mass by 1m/ sec2.

When a force (F) is applied to an object and moved through a distance (d, measured in meters, m) in the direction of theforce, we define the work (W) done as: Work = Force * Distance moved in the direction of the force, or symbolically,

W = F d(Joules, J = NT m)

When F is measured in newtons (NT, or N) and distance in meters, the resulting quantity of work is expressed in Joules. S

a force capable of producing an acceleration of 2.3 m/sec2by acting on a mass of 3 kilograms is a 6.9 NT force. The weigof an object of mass m on Earth is the force due to Earths gravitational pull on that object. The gravitational acceleratio

the Earth is about 9.8 m/sec2. (This means that the gravitational force exerted by the Earth on a 1 kg object is 9.8 nt.).

Thus the weight of a 5-kilogram object on Earth is 5 kg * 9.8 m/sec2, or 49.0 nt.

A 2.5 NT force moving something through a distance of 4 m (meters) in its direction does a work of 2.5 nt * 4 m, or 10Joules. When a 5 kg object falls a distance of 4 m, the work is done by the Earths gravitational force. As the gravitationaforce on 5kg is 49 NT, the work done by the Earth on the 5 kg object in pulling it down by 4 m is 49 nt * 5 kg = 245 n= 245 Joules.

Measuring Energy: Work, Energy, Heat, and PowerAll phenomena involve transformations of energy between potential and kinetic forms. We discuss some transformationsand calculations involving energy in the next section. Before we do that, we need to understand some definitions ofdifferent means of measuring energy.

Due to historical reasons, different measures of energy were developed and used in physics and chemistry. In the earlytimes, physics dealt mainly with motion -- of bodies such as planets and stars, as well as smaller masses. Thus forces amotion were the focal points of early physics4. Physics measured energy by means of the force required to change the stof motion. The units of physics dominated the emerging fields of engines as well, where forces were used to produce

motion. How much energy could be produced every second was the question in designing engines. The amount of energper unit of time is defined as power. Thus power has the units of Joules (energy) per second, also known as a watt. Onwatt is one Joule per second. We also have the Horsepower, which is the unit in the British system. It is understandablethat with the horse as one of the important animal engines, the early engines were compared to the power of a horse tomove things.

Chemistry started as the study of changes in the nature of substances5. Heat was a common method used to changesubstances. Temperature, or the feel of heat, was used to measure the amount of heat in a substance. Thus heat energwas measured by chemists in terms of the energy required to change the temperature of a common substance - water. T

4Physics derives its name from the Greek word "Physis," meaning the nature of things; and the field was given its name by Aristotle.

5Chemistry derives its name from "Cheo," which means "to pour."


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the unit of energy (heat) most used by chemists was the calorie, defined as the amount of heat required to change thetemperature of one gram of water by one degree Celsius. Of course, there are also two different measures of temperaturedepending on whether you follow the British or the Metric system. We will confine ourselves to the Metric system, andhence to degrees celsius (or centigrade). Count Rumford (Benjamin Thompson) and James Joule, scientists in theeighteenth century, were among the earliest to show that mechanical energy and heat could be changed into each other,primarily by noting that when mechanical work is done, the friction produces heat.

Joule in fact determined that 4.18 Joules of mechanical work is equivalent to 1 calorie of heat 6. In practice, a calorie is avery small amount of heat, and so a kilocalorie, also written as Calorie (or kcal) is used. A kilocalorie is therefore 4,180Joules. The units of energy, heat, and power are summarized in Table 5. Because of the different origins of the ways ofmeasuring energy, and the numerous manifestations of energy, there are several units for measuring energy. Units alsovary depending on the practices in different fields, and on the type of energy being measured. This can be confusing attimes. The tables below summarize most of the units and contexts.

UnitsPhysical Quantityand Definition Metric system British system

Energy, work (mechanical) = force x distance nt.m = J ft-lbsEnergy (chemical, heat) = energy to changetemperature

calorie (cal) British thermal unit (BTU)1BTU = 778 ft-lbs

Power = work/energy per unit time J/sec = Watt1000 Watts = 1 KW

horse-power (HP)1 HP = 550 ft.lbs/sec1 HP = 746 watts

Energy = power * time kilowatt x hour =(kwh) kilowatt hour

no equivalent

Table 5:Physical Quantity, Definition and Units.

Work and energy transform into one another. They are measured in the same units. So a "Joule" is also a unit for measurenergy. As described in more detail later, all energy is either stored (potential energy) or is in the process of causing motof an object (kinetic energy). Thus we can represent the energy work relationship in a continuous state of mutualtransformation in a system, including the energy that is "lost" (has become unavailable)

PotentialEnergy Work

KineticEnergy

+ UnavailableEnergy

Depending on the context, the different units above are used in physics or mechanical engineering:

Physics/mechanical: work = force * distance = lb * ft2/ sec2, kg * m2/ sec2(Joule)

electrical energy: kilowatts * hour = kilowatt hour (KWh) hydraulics/fluids: energy head = equivalent distance in feet, or meters chemical process energies: energy head and calorific content = calorie

For physics, mechanics, and engines, the work is typically stated in terms of moving something in a unit of time, e.g.,energy per second, with power (watts) in terms of joules per second. For chemistry, the work is changing the nature ofsubstances, therefore the units are in terms of the amount of heat needed to change the temperature of water (calorie).

Name of Unit Symbol Value in calories Value in Joules Measureskilocalorie kcal or

Cal1000 4184 Scientific work unit for

nutritional requirements andheat

calorie cal 1 4.184 Scientific work

British Thermal Unit BTU 252 1054 Engineering Technology,heating, a/c

Joule J .24 1 Standard unit especially formechanical energy

Kilowatt-hour kwh 8.6 105 3.6 106 Standard Unit for ElectricalEngineering

Quad Used for large quantities ofEnergy

Table 6:Units of Energy and conversion factors.

6There is an anecdote that Joule did this experiment for the first time by noting the temperature difference between the bottom and top

a beautiful waterfall in Switzerland while he was on his honeymoon there!


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Exercises

1. Look at the following appliances to get an idea of the power they generate: a hair dryer,a toaster, a clothes dryer, a light bulb. For frame of reference, we receive about 1,400watts of solar energy for every square meter of the Earth.

2. Each kilogram of water at Niagara Falls falls through a height of 184 ft. (orapproximately 56 m). What is the amount of work done by the force of gravity on the 1kg of water? What happens to this work?

3. You use a force of 19.6 nt to raise a rock (of mass 2 kg) vertically through a distance of

3 m from the ground.

Why vertically? What force are you working against? What is providing the energy for that work? How? How many Joules of work is done?

Now, assume the rock is kept at the level of 3 m above ground. How many Joules of(stored) potential energy does it have? Potential energy will be released if the rock isallowed to fall. For example, suppose the rock falls squarely on the top of a nail headheld vertically on a piece of wood, and the nail has to overcome a force of friction of9.8 nt to be driven into the wood.

How far can the rock theoretically drive the nail in?

What assumptions have you made in answering this?

4. A block is pushed 1 meter along a horizontal surface by a horizontal force of 60 nt. Theopposing force of friction is 10 nt.

How much work is done by the 60 nt force? What is the work of the friction force? Where does the work go? What is the role of gravity in this situation?

5. Power is the energy released (work done) per unit time, or the rate of releasing energy(or, doing work). It is measured in watts (Joules per second).

Thus a coal burning power plant of 1000 megawatts (MW) releases __________ Joulesevery second. Where does the power come from?

If the power plant were a hydroelectric plant instead, generating power using theNiagara waterfalls, how much water (in kilograms) will have to fall every second if thewater falls through the 56m to release the same amount of energy?

In the operation of the Niagara power plant, 102,000 cu.ft. of water falls through 56mevery second. If allthis energy could be converted to electricity, how many megawattsof power would be produced?

6. A skier who weighs 700 nt skis down a hill that is 60 m long and 20 m high. If 1000 Jof energy is lost in overcoming friction, what is his kinetic energy at the bottom of thehill?

Science Notes: Energy Accounting and Balance

Once we understand the various transformations of energy that are possible, an energy balance can be used to track enethrough a system, and is a very useful tool for determining resource use and environmental impacts. The idea is to use thFirst and Second laws to determine how much energy is needed at each point in the system and in what form that energyThe accounting system keeps track of energy in, energy out, and non-useful energy versus work done, and transformatiowithin the system. An energy balance diagram is used. Non-useful work is what is often responsible for environmentalproblems.


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Example: We wish to determine how much coal is needed to produce 1 kWh of electricity.Assume the power plant is 33% efficient, with 85% of waste heat to cooling tower, and 15%to stack. Assume you can get 24 kJ of energy from 1 gram of coal. Note that 1 kW ofelectricity is equivalent to 1 KJ/s of electricity. What are the environmental issues?

Figure 11: Coal Fired Power Plant.

1 KJ/s kWh * 3600 s/hr = 3600 KJ per hourIf the power plant is 33% efficient, then need 3600 * 3 = 10,800 KJ10,800 KJ * 1/24 KJ/gram = 450 grams coal = approximately 1 lb = 454 gramsTherefore, we need 450 grams coal for 1 KWh of electricity

How much electrical energy do we use worldwide?

10 EJ (1990), 1 ExaJoules = 1018 Joules, or 27.8 * 1015kWh.

A home in the US may average 500 kWh over a month.

What happens to non-useful energy in this example?0.85*7200 = 6120 KJ to cooling water (note that we use vast amounts of water to coolwaste heat; this cooling water produces thermal pollution of water bodies)

Also, 0.15*7200 = 1080 KJ goes to stack as waste heat, which carries impurities in theform of air pollution.

Environmental issues for this example are nonrenewable natural resource consumption, airpollution, water pollution, and solid waste.

Science Notes: Fundamental Forces of Nature

All forces in nature may be classified into four types. The gravitationalforce holds together the universe at large, plus tatmosphere, water, and us to the planet Earth. The electromagneticforce governs atomic level phenomena, bindingelectrons to atoms, and atoms to one another to form molecules and compounds. The strong nuclearforce holds thenucleus together. The fourth force, the weak nuclearforce, is responsible for certain types of nuclear reactions and hasittle bearing on energy sources today.

Table 7 shows the four forces, the property on which each acts, and examples of each force. Gravitation andelectromagnetism are the two forces with which we will be primarily concerned, as these are the two forces that operate athe macroscopic level of environmental systems. These also currently form the basis of our most prevalent sources forenergy technologies. The strong nuclear force is the strongest of the forces. Nuclear fusion reactions on the surface of thesun are the result of the nuclear strong force.

FORCE RELEVANT PROPERTY EXAMPLES

Gravitational Mass Weight of object near a planet; force that keepsplanets in their orbits around the sun

Electromagnetic Electric charge Force that keeps an electron in its orbit aroundthe atomic nucleus; (i.e., attraction or repulsionbetween a charged plastic comb and a strandof hair)

Strong Nuclear Isotopic spin* Force that keeps protons and neutrons togetherin a nucleus

Weak Nuclear Spin* Force responsible for certain types of nuclearreactions

Table 7:The four fundamental forces (or, interactions) and the properties on which they act.*Spin and isotopic spin are properties of elementary particles that we will not define here.


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Figure 13:First three periods in the Periodic Chart.

Lithium and sodium would tend to "lose" one electron to become more stable (more like the closest inert element). They cdo this, for example, by combining with elements that can gain stability by adding one electron to their shell -- elementssuch as F and Cl. These pairs therefore favor ionic bonds, in which the electron is actually transferred.

When similar atoms such as H or O or N come together they can gain stability by sharing electrons in a covalent bond.

Shared electrons spend time with either of the H atoms in H2for equal amounts of time, for instance. In a case of a coval

bond such as those in H2O, however, the electrons spend more time on the average in the neighborhood of the oxygen.

The water molecule, which has an angle of 105 between the two H-O bonds, is therefore a polarmolecule, being more negative at the oxygen end of the molecule, because the negatively chargedelectrons spend more time near the oxygen atom.

Nitrogen, hydrogen and oxygen atoms go to more stable configurations by forming the diatomic gases,N2, H2, and O2respectively rather than remain in the atomic form: N, H, and O. When hydrogen atomsare produced in any reaction, pairs of these hydrogen atoms form covalent bonds with each other so thateach has the helium (nearest inert gas) configuration at least a fraction of the time. Hydrogen has oneelectron and needs a total of two to be like He. So two hydrogen atoms share a pair of electrons, each

belonging to one of the original atoms, thus forming H2. Schematically, it could be written as HxxH (xrepresenting an electron). This schema is represented by H-H where the single line represents a bondconsisting of two shared electrons.

Again, the same can be said for oxygen and nitrogen. Oxygen has an atomic number of 8, and has four electrons in theoutermost shell. It needs two more to be like Neon (nearest inert gas).

EXERCISE:

Nitrogen has __ electrons in the outer shell, needs __ to be more like _____

Carbon has __ electrons in the outer shell, needs __ to be more like _____

Oxygen has __ electrons in the outer shell, needs __ to be more like _____

Phosphorus has __ electrons in the outer shell, needs __ to be more like _____

Hydrogen has __ electron in the outer shell, needs __ to be more like _____

Following this logic, we can figure out the most frequent bond configurations for carbon, nitrogen, oxygen, phosphorus,hydrogen, with 4, 3, 2, 3 and 1 bonds respectively, as schematically in Figure 14.

Figure 14:Shows the bond configurations forcarbon, nitrogen, oxygen, phosphorus, and hydrogen.


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Energy System

Energy transformations using chemical sources consist of changing the mutual configurations of these compoundsaccompanied by the release of energy, which we can then use for something. Chemical bonds contain energy that mayreleased when the bonds are made.

Representation of BondsEach atom has a number of bonds coming out of it equal to the number of electrons it shares in covalent bonds. So the lin

of a bond represents two electrons in activity, one from each of the two atoms it bonds. Thus for H 2, H-H is really H:H, weach hydrogen atom contributing one electron to the bond.

Let's look at the example of nitrogen (atomic number = 7). Nitrogen, being 3 electrons short of its nearest inert gas (neonatomic no. = 10), tries to bond so as to share 3 of it's electrons with other atoms bonding with it, in order to get a comple

shell of 10 whenever possible. Thus it may share electrons with another N atom (forming N2), or with hydrogen (forming

NH3).

Figure 15:Representations of compound using the bond scheme.

Similarly carbon can bond with four hydrogens to form CH4 (a gas called methane), or with two oxygen atoms to form COas depicted above. Note that we always have four bonds coming out of carbon, one out of hydrogen, and one out of oxygeLook at their position in the periodic table to see why this is so. Atoms in the middle of the Periodic Table and their bondinbecome more complicated, and we will not need to deal with them here.

Carbon is the basis for all our life forms. It is a very versatile atom because of its capability to form four bonds. Dependingon the amount of hydrogen available to bond, and the temperature and pressure conditions, carbon can form a plethora ocompounds with hydrogen alone. One such family is the hydrocarbons, important in our context because they are the basof fossil fuels.

Note how some of these compounds have double and triple bonds between carbons. This happens when carbon andhydrogen combine under circumstances in which there is not enough hydrogen to satisfy all four bonds of each carbon. Fo

example, if there is plenty of hydrogen to combine with carbon, we get CH 4or C2H6(Ethane), with all single bonds. With

ess hydrogen we get C2H4or C2H2(less hydrogen for the same number of C atoms). C2H4has a double bond between th

carbons, and C2H2has a triple bond. Compounds with double and triple bonds are called unsaturated, while single bond

compounds like C2H6are said to be saturated. Unsaturated compounds are more reactive than saturated compoundsbecause not all the C atoms are bonded to four other atoms. Hydrocarbons are not the only compounds that can be

unsaturated. Carbon monoxide is a good example of an unsaturated compound, "looking" for another oxygen atom to forCO2, a more saturated compound. When carbon (in coal or wood, for example) burns in an environment with insufficientoxygen, it forms CO which is deadly when breathed in. This is the reason to ensure plenty of access to fresh air when wehave a fireplace or running car engine.

Note that many representations are two-dimensional, and that in actuality, the electrons

forming the bonds are distributed in three dimensions. In a compound like CH 4, the carbonis in the middle of a tetrahedron with the 4 H atoms at the vectors.


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Energy System

Figure 16:Linear hydrocarbons.

Similarly there can also be C3H8(propane), C4H10(butane), C5H12(pentane) and so on. When a formula is written as CH4just showing the proportion of atoms, it is called an empirical formula. When the bonds are shown as in Figure 15, it iscalled a structural formula. A single empirical formula may represent different compounds because the structures may bedifferent for the same number of atoms combining.

Try drawing propane, butane, and pentane. Note that there are always four bonds comingfrom carbon. The linear structures are called aliphatic hydrocarbons. In addition to the linearhydrocarbon molecules, hydrocarbons may also be formed into ring structures. The ring

structure possesses the property that enables us to smell these compounds! So they arecalled aromatic hydrocarbons. The simplest aromatic hydrocarbon is C6H6, benzene. Thestructure of benzene was long a puzzle in chemistry, with chemists wondering what the

structural formula for C6H6could be. They knew the empirical formula was C6H6. It is saidthat the great organic chemist Kekul, who had been wondering about this, dreamed onenight of a snake swallowing its tail and was inspired to draw the ring structure! Note thealternating single and double bonds, a clever way of ensuring four bonds from each carbonshell.

The versatility of carbon in forming bonds, ring structures and various configurations is the basis of life on our planet. Thechemistry of carbon compounds is therefore called organic chemistry. More complicated carbons compounds are describedthe Ecological System and Materials System. For now let us look at some additional aromatic and aliphatic compounds, annote some aspects that are relevant to energy storage and release.

Aliphatic hydrocarbons are the basis of fossil fuels. All saturated hydrocarbons react with oxygen at high temperatures toform carbon dioxide and water, and give off energy. This oxidation reaction is the basis of the internal combustion engine

Gasoline normally contains hydrocarbons from C6to C18, a mixture of over 100 compounds! An example reaction of thecombustion of a hydrocarbon is:

C7H16+ 11O2 7CO2+ 8H2O + energy

"Burning" (or a combustion reaction) consists of combining with oxygen at high temperatures. The combustion reaction of

acetylene (C2H2) with oxygen gives off such a large amount of energy that it is used as a welder's torch.

Ring compounds do not play as large a role in energy production butoften occur as byproducts or waste products. These polyaromatichydrocarbons (PAH's) pose a serious pollution problem.

Ring compounds, based on the benzene ring, are so common in

biochemistry that we just draw to represent C6H6. Adding one more

carbon and two hydrogens to the benzene ring gives us C7H8which ismethyl benzene or toluene:

Ring compounds can get very complicated. Several organiccompounds playing an important role in our physiology are shown inthe unit on Ecological Systems.


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Energy System

Chemical Energy Release and Bond EnergiesThe amount of energy released when a bond is formed between atoms is called the bond energy. Bond energies represenstate of potential chemical energy. We can get energy from a system as it moves from a state of higher potential energy one of lower potential energy (e.g. water falling). Chemical reactions in which the compounds formed after a reaction (calproducts) have lower total bond energy than the reactants can release chemical energy. Such reactions in which energy isgiven off are called exothermic (or more correctly, exoergic) reactions. Conversely, reactions that absorb energy are said be endothermic.

Table 8 gives the energies for bonds we will commonly encounter. The table defines these energies in units of kcal/mole. mole is an abbreviation for "gram-molecular weight" of a substance.

BOND Energy(kcal/mole) BOND Energy(kcal/mole)H-H 104 H-F 135C-H 99 H-Cl 103

C-C 83 H-Br 87C=C 146 H-I 71C C 200 N-N 39O-O 35 N N 225

O=O 119 N-H 93O-H 111 CL-CL 58C-O 86 Br-Br 46C=O 177 I-I 35

Table 8: Bond Energies.(the bond energy is expressed in kcal/mole.)

Let us see what the energy values in Table 8 mean. The bond energy of H-H is 104 kcal/mole. This means that when

hydrogen atoms combine to form molecular hydrogen H2, represented by the reaction H + H H2, for every mole (2g) o

H2formed, 104 kcal of energy are released. Conversely it takes 104 kcal to break apart a mole (6 x 1023) of hydrogen

molecules. From this we can draw a simple chemical energy level diagram for the above reactions, analogous to Figure 12gravitational potential energy.

Figure 17:Energy Level Diagram of H2.

One mole of an H2(2g) molecule has 104 kcal total potential energy less than 2 g of H atoms. This is why when H atoms

formed in a reaction, and these atoms are the only atoms available, they combine to form H 2(roll down the potential ene

"hill" towards a more stable state). In forming the H-H bond, 104 kcal of energy are released for every 2 g (6.02 x 10 23

molecules) of hydrogen gas (H2) formed. Similarly oxygen, and nitrogen exist as O2and N2rather than in the atomic form

as O and N. So whenever we say hydrogen, oxygen, or nitrogen gas, we mean H2, O2, N2. For H, O, N we specifically sayatomic hydrogen, atomic oxygen, and atomic nitrogen.

Science Notes: Chemical Formations

Formation of Ammonia (NH3) as Example

Let us look at a more complicated example of the formation of a molecule. Just as the energy released by water falling cabe captured, we can find ways to capture chemical energy. Let us look at a more complicated reaction: the formation of

ammonia. Nitrogen gas (N2) and hydrogen gas (H2) can be made to combine to form NH3, or ammonia gas. As we proceeook for the answers to these questions: Is the reaction exothermic? How many kilograms of hydrogen are needed toproduce one kilogram of ammonia?

The reaction is N2+ 3H22NH3


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Energy System

This equation says that one mole of N2requires three moles of H2for a complete reaction, and this would then yield two

moles of NH3. Note that we can also say that one molecule of N2reacts with three molecules of H2to yield two molecules

ammonia (NH3). But the table gives energies in units of kcal/mole, which is why it is easier to work with moles. The energnvolved in the reaction involving just one or two molecules of ammonia is too small.

The following table contains the variety of ways in which you can write the reaction that forms ammonia. All the descriptiobelow are equivalent. The atomic masses are rounded off values from the Periodic Table.

Nitrogen + Hydrogen Ammonia

N2 + 3H2 2NH3

N N + 3 H-H 2NH3

1 mole of N2 + 3 moles of H2 2 moles of ammonia

28 g of N + 6 g of H 34 g ammonia

What are the energies of the reactions? In order to get the molecular structure of ammonia, we have to break one N Nbond and 3 H - H bonds. This requires that we supply energy to break the bonds. From Table 8, we get the bond energie

N N 225 kcal/moleH - H 104 kcal/moleN - H 94 kcal/mole

To form each molecule of NH3, we break one bond of N2and three of H2, and then 3 N - H bonds form to make NH3. To

calculate energy released (or absorbed) in the reaction, we have to calculate the energy needed to break the bonds of N2and H2, and the energy released when the atoms rearrange to form NH3.

Energy required to break

the bonds of N2, 3H2

Energy released formingthe bond 2NH3

N2 : 1 mole x 225 kcal/mole = 225 : 2 moles x (3 x 93 kcal/mole) =

3H2 : 3 moles x 104 kcal/mole = 3122NH3

: 2 moles x 279 kcal/mole = 558

total energy absorbed = 537 kcal total energy released = 558 kcal

558 kcal - 537 kcal = 21 net kcal released for 2 moles of NH2formed, so the net energy released is 10.5kcal/mole of ammonia formed.

More energy is released than absorbed in the formation of ammonia, so this reaction is exothermic. We can also say that

10.5 kcal are released when 17g of ammonia are formed. The energy level diagram here is more complex than that for thH + H = H2reaction because of the steps involved.

Figure 18:Energy Level Diagram for the formation of Ammonia (NH3).

For this reaction, we had to put in some energy to "activate" the reaction, which was the energy required to break the N 2and H2bonds. N2and H2brought together with no addition of energy would not spontaneously react. This is analogous toour striking a match to start the burning of coal. The energy required to start the reaction is called activation energy. Theft to themselves, the N and H form bonds to release 568 calories.

What is a corresponding example with the gravitational force?


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Energy System

Formation of Water (H2O) as ExampleHydrogen and oxygen combine to form water. Which is more stable -- hydrogen and oxygen gas separately, or incombination as water?

Write equation and balance:

2H2+ O22H2O

amounts element element compound

molecules 2 molecule

hydrogen

+ 1 molecule oxygen yields 2 molecules of

watermoles 2 moles

hydrogen+ 1 mole oxygen yields 2 moles of water

grams 4 g hydrogen + 32 g oxygen yields 36g of waterkilograms 4kg H2 + 32 kg O2 yields 36 kg of water

1. Is the energy release - exothermic or endothermic?

2. Which is more stable, hydrogen gas and oxygen gas separately or combinedchemically as water? Explain.

Structural formula:

2 H-H + O=O 2 H-O-H

(drawn as linear although molecule is not)

Bonds: break old (spend energy), recombines to form new bonds (release energy)

Break 2 H-H, break O=O and in recombination, 4 H-O bonds are made and release energy. Using the bond energies of H-104 kcal/mole, O-O 119 kcal/mole, and H-O 111kcal/mole from Table 8, we can see how much energy is released whenbonds are broken and formed.

BONDS BROKEN BONDS FORMED

Bonds# ofbonds

EnergyRequired

Bonds# ofbonds

EnergyReleased

H-H 2 208 kcal

O=O 1 119 kcalH-O 4 444 kcal

Total: 327 kcalrequired

Total: 444 kcalreleased

Figure 19:Energy level diagram for formation of water.

Energy released is greater than energy required to break bonds so there is a net energy release. The reaction is exothermThe amount of energy released is 444 kcal minus 327 kcal which equals 117 kcal per mole of oxygen burnt or:

444 kcal - 327 kcal = 117 kcal per mole of oxygen burnt 58.5 kcal/mole of hydrogen burnt or 58.5 kcal/mole water formed. 117 kcal for 36g of oxygen; OR 58.5 kcal per 2 g hydrogen; OR 58.5 kcal released when 18 g water formed


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Energy System

C - C + O=O O=C=O

Energy required to break bond:83 kcal/mole + 119 kcal/mole = 202 kcal/moleEnergy Released = 2 x 177 kcal/mole = 354 kcal/mole

net release = 152 kcal/mole of carbonThus 12 g of carbon yields 152 kcal of energy providedsufficient oxygen is available for complete combustion.

1 kg of carbon therefore gives approximately 11,000 kcal152 kcal

12gx 1000 g = 12666 kcal

As coal contains other ingredients, it works out that the

active yield of 1 kg of coal is about 700 kcal.

Byproducts from Coal Combustion

As seen in the equation, CO2is the main byproduct of coal combustion -- 44g of CO2is produced for every 23g of C burnt

The contribution of CO2to global climate change is one of the fundamental problems of our fossil fuel economy. Other

products of coal burning originate from the sulfur and nitrogen present in coal. The nitrogen is usually released as N 2or N

gas. The sulfur forms SO2, which is one of the gases that causes acid rain (discussed in detail in the Atmospheric System)

Insufficient oxygen supply during combustion -- as for example, burning coal (or wood) in a closed environment such as aroom without adequate ventilation or a fireplace without a proper chimney -- produces carbon monoxide. As the oxygen is

depleted, the reaction C + CO22CO becomes possible. Carbon monoxide is a colorless, odorless, and very poisonous g

When breathing in CO, the CO takes the place of O2in the hemoglobin molecules in the blood supply in the lungs, causingasphyxiation.

Energy Use, Efficiency, and the Future

Garrett Hardin who originated the idea of the Tragedy of the Commons, summarizes the two laws of Thermodynamics interms of human significance as:

"You can't win, you are sure to lose;and - you can't get out of the game."7

Whether we can get more "out of the game" is the central question of energy production. The examples above show whatsmall fraction of the input potential energy is actually used as output work. Designing for energy efficiency means in ordeget a higher ratio of output, the input needs to become a central concern of intelligence design and practice.

Most of the energy planning is done by looking at the supply side. We examine how we can increase the supply of the

resource in question, rather than by asking how the demand side (all our uses of energy) can be managed. Energyavailability and use are good indicators of the standard of living in our technological world. In the U.S. the "averageconsumption per capita" is 55 barrels of oil. In the poorer countries, the consumption is 6 barrels per year. Figure 20 shothe projections of world energy supplies from 1970-2020. The increased coal supply is based on mining coal that is harde(and hence more costly) to extract.

Figure 20: World Energy Consumption by Fuel Type, 1970-2020.Sources: History: Energy Information Administration (EIA), Office of Energy Markets and End Use, International Statistics

Database and International Energy Annual 1997, DOE/EIA-0219 (97) (Washington, DC, April 1999). Projections:EIA, World Energy Projection System (2000).

7Hardin, Garret. Filters Against Folly: How to Survive Despite Economists, Ecologists, and the Merely Eloquent. Viking Press, 1985.


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Energy System

Demand-side management instead of or in addition to supply side management would mean a focus on increasing efficienof use and considerations of how to reduce the demand. The CAFE (Corporate Average Fuel Economy) standards legislaten the U.S. in 1980's required a certain level of fuel efficiency of U.S. automobiles. By demanding that the corporationsfigure out an overall fuel rating for all their fleets, the decisions on design and distribution of big and small cars in the totafleet were left to the industry, as long as the total corporate fuel economy goals were met.

There are also some efforts to recapture some of the "waste energy" from the processes of energy generation. Co-generation described in Figure 21 is an example of industries working together to see how exchanges of energy andmaterials could minimize waste.

Figure 21:Co-generation.

An Example of "Waste Power" UseAn unusual example of such a partnership network in Denmark is show in Figure 22. It is the result of 10 years of planni

and involves exchange of water, steam, gas, and gypsum.

Figure 22:Industrial Ecosystem.from Allenby and Graedel, "Defining the Environmentally Responsible Facility."

Measures of Environmental Performance and Ecosystem Condition. National Academy Press: Washington, D.C.


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Energy System

Four companies (a power plant, a refinery, a gypsum facility for producing wall board, and a pharmaceutical plant) effect exchange shown in Figure 22. The "waste" products from the power station (including heat in the form of warm water) arused to warm the greenhouse and other facilities. Such a co-generation system provides an industrial ecosystem with amuch higher efficiency for overall energy use than if any of the organizations had organized independently for their materand energy needs. The ten years of planning required shows that such processes take time to explore the possibilities,develop the relationships, then plan and execute.

Energy Sources, Technologies, and Impacts

Historical, geographical, and political contexts have led to the adoption of different fuels and related technologies to produ

energy. As described in the history section, we have progressed from using above ground, easily accessible sources ofenergy, such as wood and direct solar energy, to fuels such as coal and oil that require large infrastructures and energy tomine and process before extracting energy from them. Table 9 at the end of this section outlines different energy sourcesand the information relevant to the environmental impact of these sources.

As described before, over 95% of the world's energy requirement is currently met by fossil fuels -- coal, oil, and natural gIn various technologies, they release energy by the process of combustion. Major byproducts are carbon dioxide and varioresiduals such as fly ash. The environmental problems relating to fossil fuel use are described in detail in the AtmosphericSystem. Environmental pollution, especially air, global climate change, and resource depletion are the greatest drawbacksheavy fossil fuel use. Another problem (particularly for the U.S.) is dependence on foreign resources. Development of oil ithe Atlantic has been a response to the U.S. need for fuel independence. Alaskan oil exploration involves destruction ofpristine land and unique natural habitats.

Coal burning, while a simple technology, has numerous side effects in addition to carbon dioxide emission noted above. C

occurs in combination with sulfur in many places. High sulfur coal, when burned, produces sulfur dioxide, which is the souof acid rain. Countries like the U.S. regulate the amount of sulfur that can be in coal used for power production; thereforehigh sulfur coal must be cleaned before it can be burned. Coal burning also produces large amounts of particulates in theform of fly or bottom ash, which must be disposed of or recycled.

Currently, coal power plants with the encouragement of government and to the liking of environmental groups, aredeveloping ways to burn coal and reduce the large amount of coal byproducts. Coal-gasification is one such technology. Cs pulverized, mixed with water and then combined with gases such as nitrogen and oxygen. The gaseous mixture is thenheated and a synthetic gas is produced as the particulates or ash falls to the bottom of the burner. As the gas cools, sulfuparticulates are separated and used to make sulfuric acid. This is an example of getting more than one product from a fuesource. The gas is then used to produce steam that spins turbines and generates electricity.

The energy in the bonds within the nucleus may be released through nuclear fission or nuclear fusion reactions. Thetechnology used to produce nuclear power is based on nuclear fission. The fuel for fission reactions are heavy nuclei,

particularly uranium, thorium, and plutonium (a material that no longer occurs in nature, but of which the U.S. and statesthe former Soviet Union have enormous supplies because of the bomb programs). The U.S. led the world in nuclear poweproduction, producing about 728 billion kilowatt-hours. France ranked second, with 375 billion kilowatt-hours, and Japanwas third, at about 309 billion kilowatt-hours produced.8 In 1999, the nuclear share of total electricity generation for Frawas 75%, for Japan was 33%, and for the U.S. was 20%.9Nuclear energy is often considered the desirable alternative tocoal, because it does not release carbon dioxide. The materials involved in nuclear power are, however, heavily radioactivvarying from uranium, the starting material, to the various byproducts during all phases of the energy production cycle, athe last byproduct, generally termed "radioactive waste." These byproducts are "radioactive," that is, they emit particles oradiation and high-energy electromagnetic radiation, such as gamma rays. This quality makes the materials dangerous.People and other parts of nature exposed to this radiation can suffer serious long-term damage. Many of the radioactivematerials are also very long-lived, continuing to emit radiation for hundreds of years or more. Nuclear fission powertechnologies have been designed with numerous safeguards and extreme caution as to be "safe." However, if the globaleconomy were to depend predominantly on nuclear power, radioactive material transport over air, land, and water couldpose a very large exposure risk. Radioactive waste disposal is also a challenging problem, as it has to be kept isolated for

thousands to millions of years!

Nuclear fusion is the reaction responsible for the production of energy in the sun. Hydrogen is the main fuel for energysource. In fact, the sun is a huge nuclear fusion reactor. But the extreme high temperature and pressure needed for fusioto take place has been a formidable obstacle to designing fusion systems on any usable scale. Nuclear fusion would notproduce many radioactive wastes like fission but will produce radioactive tritium (an isotope of hydrogen) for which wewould have to design safeguards.

8Source: Energy Information Administration, International Energy Annual 1999, DOE/EIA-0219(99) (Washington, DC, January 2001.)

9Source: Energy Information Administration, International Energy Outlook 2001, DOE/EIA-0484(2001) (Washington, DC, March 2001.)


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Energy System

Hydropower, wind, direct solar radiation, and geothermal power are all renewable resources. Of these, hydropower is thebest developed. Starting with water wheels that converted the kinetic energy of running water into various kinds of motioto vast projects like the Hoover Dam, the technology for conversion of hydropower to electricity has long been explored.While it produces no byproducts, hydroelectric power requires waterfalls or dams with a large volume of flow. In the case dams built for hydropower, the devastation of land and distinctive ecological niches can be large. The conflict betweendevelopment of cheap hydroelectricity, preservation of habitat, and economic interests are encapsulated in the example othe endangerment of salmon in the Pacific Northwest, due to extensive dam building on the Columbia River. Hydropower also come from hot water springs, where the kinetic energy of water comes from the heat at the Earth's core.

The Sun and EnergyExcept for nuclear energy, geothermal energy from the Earth's hot core, and energy from running water accelerated by thEarth's gravitation naturally (waterfalls) or artificially (dams), all other energy on the Earth comes from the sun. The sun'energy also plays a principal role in hydropower by driving the water cycle. The nature of solar radiation -- electromagnetenergy from the sun -- is described in detail in the Atmospheric System.

YOU ARE HEREOn average, one square meter on the side of the Earth facing the sun receives 1400 W (Joules per second). In a 24-hourperiod the total amount of energy reaching the upper atmosphere is 14.4 million calories. One-third of it is reflected backnto space by cloud cover, and the rest, traveling through the atmosphere, powers the wind and water cycle, and drives tEarth's climate. The total sunshine entering our atmosphere every year is equivalent to 500,000 billion barrels of oil or800,000 billion metric tons of coal! On a bright sunny day in the northern latitudes, when the sun is at the highest point,

about 1000 Watts/ m2reaches the ground. On cloudy days, it can be as low as 200 Watts/m2.

The main problem with solar energy for high levels of use comes from the fact that it is so diffuse and spread out, and ha

to be collected over large areas. In effect, this is what the foliage of plants does, storing some of the energy throughphotosynthesis. It is important to note that only a small fraction of the solar spectrum -- in the violet and some in the redregion -- is used for photosynthesis. Sunlight has a large quantity of energy in the green and yellow regions, most of whics reflected by the leaves. However, it is the capture of energy through photosynthesis, combined with elements like carbooxygen, and hydrogen from the Earth and its atmosphere, which results in biomass immediately. This biomass eventuallresults in a favorite fuel of today (coal) after millions of years of "processing" by the Earth. Oil and natural gas are similarproduced from organisms buried for millions of years under rock foundations. Ancient humans used the gentle, spread ousolar energy and biomass for drying, cooking, and heating. Today's needs demand much larger quantities concentrated inspace and time. This tendency promotes rapid depletion of the solar "capital" invested into coal formation over millions ofyears.

One of the less thoughtful energy uses in our convenience-dominated society is the use of "high-quality" and concentrateenergy even when "low-quality" spread-out energy would suffice. A good example is our use of fossil fuel energy drivenclothes dryers, even in the summer when clothes could just dry on a clothesline from direct solar energy. In the ideal use

energy, we would distinguish between the needs requiring high or low "quality" energy. Using energy at the appropriateevel and from renewable resources is what is referred to by Amory Lovins as a "soft energy path." One soft technologyphilosophy argues that we adapt our life styles to suit the energy available to us.

Figure 23 is derived from the proceedings of UNERG, the United Nations Conference on New and Renewable Sources ofEnergy held in Nairobi, Kenya, in 1981. The figure shows the different grades of energy derived from direct solar energy.Passive collectors are static and collect heat energy that falls on them. Active collection involves mechanisms for storingand/or following the direction of the sun's rays to receive the maximum energy. Many ancient civilizations, including theEgyptians, Pueblo and Anastasi Indians, and Greeks, built their houses to take maximum advantage of the sun's apparentmovement in the sky. However, as more technological energy systems developed, building with the sun's position in mindbecame a lost art, especially in industrialized countries.


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Energy System

Figure 23:Sun-trapping options.Source: UNERG, but slightly modified.

Photon collection refers to collecting the energy through natural or artificial chemicals -- in the form of biomass (firewood,animal dung, and waste materials) or in water or chemicals such as certain salts, which hold the heat.

To convert solar radiation into electricity, we use photovoltaic cells. Photovoltaic cells are based on the phenomenon ofphotoelectricity -- that light can release electrons from certain materials. Using these materials, light can be converteddirectly into electricity. This phenomenon was discovered in the late 1800's by George May in Ireland. Rudolf Hertz inGermany produced the first photoelectric cell soon thereafter using the element selenium and Albert Einstein explained thphysics of photoelectricity in 1905. However, the first practical solar cells were only developed in the 1950's by the BellTelephone Company. The early version of the cell cost thousands of dollars per watt of electricity yielded. The first largescale testing occurred in space on the NASA satellite Vanguard in 1958.

The conversion efficiency (amount of electrical energy output per input of light energy) of the largest photoelectric cells isstill below 20%. This means we have to collect sunlight over a large area for any useful application. For example, if theconversion efficiency is 15%, we need a 6.5 square feet of photovoltaic material to power a 100-watt light bulb.

Solar technologies have made the largest inroads in space applications. Collection of solar energy by satellites for Earth'sapplications have been long considered. The basic idea is that if the collection were in a geosynchronous orbit around theEarth (35,890 km or about 22,500 miles above the equator), we could capture the energy before so much of it wasabsorbed by clouds and the atmosphere. Various technical difficulties have essentially halted this SPS (Solar Power Satellproject.

If we followed a philosophy of ecologically friendly design, the best use of solar would be in the passive or active collectionrather than the conversion to electricity. However, as a society, we have chosen to use electricity as the form of energy foalmost all applications and a large source of our environmental problems -- pollution, resource depletion, habitat loss -- lin this societal choice.

Wind is derived from solar energy moving large masses of air. The two basic phenomena that are responsible for windpatterns are a large global circulation and local effects. Cool polar air is drawn towards the tropics to replace lighter, warmair that rises and moves towards the poles. This creates areas of high and low pressure and circulation patterns are set udifferently in the northern and southern hemispheres because of the Earth's rotation. This sets up the global patterns, sucas the trade winds. Locally, the circulation depends upon whether the air is over land or water. Air over oceans and largebodies of water is cooler than that over land, and cooler air is drawn toward the land as the warmed air rises. Togetherthese two patterns produce movements of enormous complexity.

The wind represents kinetic energy of air arising from the thermal energy of sunlight. A large part of this energy is lost invarious functional forces, and only a small portion can be captured by windmills. High tech windmill designs have beendeveloped by various aircraft companies, because of their expertise in wind dynamics.


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Energy System

In summary, the sun it still our most valuable source, powering most of our energy sources. Our survival may depend upoa wise and judicious use of the numerous, versatile sources the sun provides.

Life Cycle of Electricity GenerationElectricity is a form of energy that has become the core of our industrial societies. The ease with which it can betransported, stored, controlled, and used has changed the fabric of society. This section looks at the generation of electricfrom various common fuel sources.

Electrical energy is the combined potential and kinetic energy of electrons in materials. Materials that have electrons thatare mobile, rather than being confined to orbits around the atomic nucleus, can conduct electricity. Metals are primeexamples of conductors. A discovery by Michael Faraday of England in 1831 is the cornerstone of our large-scale electricitgeneration. Faraday discovered that when a conductor moves in a magnetic field, an electric current is produced in theconductor. This Faraday's Law, and the fact that we can make large magnets is the basis of an electric generator. If we cause an energy source to move a conducting coil of wire that is placed in a magnetic field, the current produced in the wirecan then be transported to deliver electric energy. Figures 24.A-D demonstrate the sequence of electric power productionand distribution from four sources: running water, coal, nuclear fission, and wind.


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Figure 24.A-D:Electricity Generation Methods

A power plant consists essentially of a huge generator -- a gigantic coil of wire capable of rotating in the space between thpoles of an enormous horseshoe magnet. The motion of the coil is caused by a shaft connecting it to a turbine, whoserotation spins the coil. In all power plants then, the energy obtained from the sources has to cause the turbines to turn,which then rotates the coil. This energy is delivered directly to the turbines by the falling water in a hydroelectric powerplant, and by the wind in a wind farm. In the case of coal and nuclear fission, the primary energy is used to transform wanto steam or high-pressure water, which then drives the turbines. Figures 24.A-D illustrate the steps prior to this, and shthe similarity of the final steps of electricity distribution for all sources.

The current from the coil is then carried to the final place of use through transmission and distribution lines. Some of theenergy is lost along the wires. To minimize this loss, the electricity is transmitted at very high voltages (thousands of voltalong transmission lines and the voltage "stepped down" near the location of use using transformers. Electricity is then

carried over smaller distribution lines to homes and businesses for use. The huge steel towers typical of transmission lineare a familiar sight, as are the distribution lines -- the smaller wires near buildings attached to "telephone poles."Transformers are the ceramic structures on local distribution line poles.

Impacts of Energy Production and UseEnergy production and use produce some of the most lasting and significant environmental effects. Some of these arediscussed in detail in the Atmospheric System. Each source of energy brings with it some impacts. Here we summarize thoverall nature of the impacts.

Fossil fuels cause some of the largest impacts. In order for a typical 500-Megawatt plant to produce about 158 Terawatt-

hours (tera = 1012) of electricity per year, it takes 1.5 million tons of coal and 0.15 million tons of limestone. It producesemissions to the air of 1 million tons of carbon as carbon dioxide, plus 10000 tons of ash and 193000 tons of scrubbersludge -- both of which contain large quantities of sulfur. (check numbers)Global climate change, resulting from

atmosphere increases in CO2, is described in detail in the Atmospheric System. Even seemingly slight temperature change

can cause changes in weather patterns, climate, melting of polar ice caps, and sea-level rise.


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Figure 25:Industry Emissions, in thousands of short tons.

Source: Energy Information Agency (http://www.eia.doe.gov/neic/brochure/elecinfocard.html)

Gasoline combustion releases pollutants that, under certain conditions, give rise to photochemical smog and high levels oatmospheric ozone. Impacts from oil drilling include destruction of ecosystems. The many impacts of extensive fossil fueuse is discussed in detail in the Atmospheric System.

From the mining and processing of the fuels to the production stage, nuclear power requires the handling of radioactivematerial. The potential for accidental release of these materials and exposure to people, and the problem of long-termdisposal of radioactive wastes, are the main environmental concerns of nuclear power.

Hydroelectric power causes disturbances in ecosystems from dams and large land use. A striking example of the loss ofbiodiversity is the rapidly declining populations in the remaining species of salmon in the Pacific Northwest. The ThreeGorges Dam project currently underway in China requires the displacement of one million people, in addition to thedevastation of land and ecosystems. But the People's Republic of China has made rapid industrialization a national priorit

and this requires an enormous development of power production systems.

Alternative energy sources, such a wind and solar energy, also have large land use implications.


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EnergySource

Force ofOrigin

Energy production Usage Environmental Impact

Oil,Petroleum

Electromagneticforces in atomicbonds

Non renewable

38% of world's consumption in 2000 Easily transported Large portion in transportation

industry

Refining and consuming produce air,water, and solid waste pollutants

NaturalGas


Non renewable 20% of world's consumption in 2000 Flexiblefor use in industries,

transportation, power generation

Produces fewer pollutants than oil and

coal, and less CO2

CoalElectromagneticforces in atomicbonds

Non renewable Primary resource for electricityProduces CO2and other air, water andsolid waste pollutants

Biomass:Wood andorganicwasteincludingsocietalwaste


Renewable In terms of timber, it is

easily harvested andabundant in certain areas;but it takes a long time togrow a tree.

Low energy potential relative to otherresources

Burning emits CO2and other pollutants Possible toxic byproducts from societal

waste Loss of habitat when trees harvested,

unless sustainable tree farms

Hydro-electric

Gravitationalforce of water

Renewable Clean resource with high

efficiency Influenced by climate and

geography

Low economic cost, though high start upcosts

Destruction of farmlands, dislocation ofpeople, loss of habitat, alteration ofstream flows

SolarPower

(photo-voltaics)

Electromagnetic

energy fromthe sun

Renewable High economic cost

particularly in terms of start-up

Dependent on climate and

geographical location Need a storage system for

the energy to ensurereliability

Not advanced enough forglobal use

Technology is already in use forremote applications and non-centralized uses where it is

economically competitive withalternatives Unlimited resource that is clean,

efficient, safe, and renewable

SolarPower -(solarthermal)

Electromagneticenergy fromthe sun

Renewable Central-thermal systems to

convert solar energy directlyto heat

More competitiveeconomically thanphotovoltaics

Dependent on climate andgeographical location

Solar energy technology not advancedenough for global use

Many industrial plants use solar

Geo-thermal

Gravitationalpressure and

nuclearreactions in theEarth's core

Extracts heat fromunderground masses of hotrock.

Technology is stillundeveloped.

Can be geographicallydependent

Consumption is localized Efficient Disrupts natural geyser activity

WindPower

Gravitational &electromagneticenergy fromthe sun

Renewable Unlimited resource that is a

very clean process, nopollutants

Economic cost comparable to currenttechnologies

System must be designed to operatereliably at variable rotor speeds

Technology not advanced enough forglobal societal us

Aesthetic issues, needs lots of land, andpossible bird impacts

NuclearFission

Strong nuclearforces innuclear bonds

Non renewable resource U-235 (uranium)

Highly technologicalinfrastructure necessary forsafe operation

Production of nuclear energyhas a high cost due in part

to regulations High water usage for cooling

Currently accounts for 10-12% of theworlds electricity

Byproduct is highly radioactive andhighly toxic

Produces radioactive wastes that have along lifetime

Disposal solution complex technicallyand politically

Safety issues in terms of operating afacility with the potential to release

radiation to the atmosphere Public perception problem in terms of

radiation, etc.

NuclearFusion

Weak nuclear

Technology is not yet viableand requires researchinvestment

Technology still notdeveloped enough to makethis a viable source

Possibility high for water pollution becauseof radioactive tritium

Table 9: Energy Sources and related information.

Energy Sys

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