physics 162 winter 2007 1 the big picture we use a heck of a lot of energy we use a heck of a lot of...

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Physics 162 Winter 2007

The Big PictureThe Big Picture

We use We use a heck of a lota heck of a lot of energy of energy primitive society used < 100 W of power per personprimitive society used < 100 W of power per person our modern society burns 10,000 W per personour modern society burns 10,000 W per person surely not in our homes! Where is this energy surely not in our homes! Where is this energy

going?going?

Energy availability has enabled us to focus on higher-Energy availability has enabled us to focus on higher-level issues as a societylevel issues as a society artart ScienceScience entertainmententertainment home shopping networkhome shopping network

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Once upon a time…Once upon a time…

Long ago, almost all of our energy came Long ago, almost all of our energy came from from foodfood (delivering muscle power), and almost all (delivering muscle power), and almost all our energy went into our energy went into securing foodsecuring food for ourselves for ourselves

Enter the work animal, supplementing our Enter the work animal, supplementing our muscle power and enabling larger-scale muscle power and enabling larger-scale agricultureagriculture

Later we burned wood to run boilers, trainsLater we burned wood to run boilers, trains 150 years ago, muscular effort and firewood 150 years ago, muscular effort and firewood

provided provided mostmost of our energy of our energy—and today this is —and today this is less than 1% of the storyless than 1% of the story

Today, more energy Today, more energy goes intogoes into growing/harvesting food than growing/harvesting food than comes out ofcomes out of food! food! (is this bad news for biodiesel??) (is this bad news for biodiesel??)

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The Global Energy SceneThe Global Energy Scene

Global energy production is about 400 QBtu/yrGlobal energy production is about 400 QBtu/yr a QBtu is a quadrillion Btu, or 10a QBtu is a quadrillion Btu, or 101515 Btu Btu so about 4so about 410102020 J per year J per year

U.S. share is about one fourth of this (100 QBtu U.S. share is about one fourth of this (100 QBtu or 10or 102020 J) J)

10102020 J/yr = 3 J/yr = 310101212 W (do the calculation!) W (do the calculation!) divided by 300 million people (3divided by 300 million people (3101088) = 10) = 1044 W W

per person (10 kW, as stated above)per person (10 kW, as stated above)

We’ll talk about units next week. 1 Btu is the energy required to raise 1 pound of water by 1oF. There are about 1000 Joules (J) in a Btu. A Watt (W) is a measure of power, or energy per unit time, and 1 W = 1 J/s. A 100 W light bulb uses 100 J of energy each second.

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The Great Energy DisparityThe Great Energy Disparity30,000

20,000

10,000

010 20 30 40 50 600

Energy equivalent barrels of oil per capita per year

Gro

ss D

omes

tic

Pro

duct

(G

DP

): $

per

cap

ita

PolandCuba

EcuadorIndia

Italy U.K.

Japan

Switzerland

Sweden

NorwayIceland

Germany

Belgium

Canada

United States

Many countries in the world lie in this quarter-circle!!

1989 data; Reproduced from Fig. 1.3, Ristinen and Kraushaar

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• More Countries

• Fills in the gaps

• 1971 data

Now on a Logarithmic Scale

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A note on graphs: log vs. A note on graphs: log vs. linearlinear

Many graphs in the book are on logarithmic Many graphs in the book are on logarithmic scalesscales

This condenses wide-ranging information into This condenses wide-ranging information into a compact areaa compact area

Pay attention, because you could warp your Pay attention, because you could warp your intuition if you don’t appreciate the scaleintuition if you don’t appreciate the scale

Log scales work in Log scales work in factors of tenfactors of ten A given vertical span represents a constant A given vertical span represents a constant

ratio (e.g., factor of ten, factor of two, etc.)ratio (e.g., factor of ten, factor of two, etc.) An An exponential increaseexponential increase looks like a looks like a straight straight

lineline on a logarithmic scale on a logarithmic scale

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Example PlotsExample Plots

Exponential plot is curved on linear scale, and straight on a logarithmic scale

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Aside: Exponential Growth and the Rule of 70 (or 72)If some quantity, the price of oil say, increases by 10% per year,

how many years does it take for the price to double?

10 years x 10%/year = 100% = doubled price: correct???

No, because the increase compounds (as in your savings account or, maybe more appropriately for today’s college student, on your credit card)

Say the price of oil is $50/barrel this year and it increases by 10%/year. Prices in following years:

0 $501 $552 $60.503 $66.554 $73.215 $80.536 $88.587 $97.448 $107.18

Rule of 70 (or 72):

Doubling time = 70 years/annual % growth rate

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Evolution of Energy SourcesEvolution of Energy Sources

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U.S. Consumption in 1996U.S. Consumption in 1996

SourceSource AmountAmount QBtuQBtu PercentPercent 10101818 JoulesJoules

CoalCoal 1.001.00101099 tons tons 20.9920.99 22.3%22.3% 22.122.1

Natural GasNatural Gas 21.921.910101212 ft ft33 22.5922.59 24.1%24.1% 23.823.8

PetroleumPetroleum 6.146.14101099 bbl bbl 35.7235.72 38.1%38.1% 37.737.7

NuclearNuclear 681681101099 kWh kWh 7.177.17 7.6%7.6% 7.567.56

RenewablesRenewables 695695101099 kWh kWh 7.397.39 7.9%7.9% 7.807.80

TotalTotal 93.8193.81 100.0%100.0% 99.099.0

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The Fall of the Work AnimalThe Fall of the Work Animal

Used to rely completely on Used to rely completely on animals for transportationanimals for transportation

Trains entered the picture Trains entered the picture in the mid-1800sin the mid-1800s

Cars entered the scene in a Cars entered the scene in a big way around 1920big way around 1920

World has never been the World has never been the samesame

Work animal fell off the Work animal fell off the map around 1940map around 1940

Today automotive is over Today automotive is over 95% of the story95% of the story

Ave

rag

e H

ors

ep

ow

er/

pers

on

in

th

e U

S

Year

automotive

work animal

Nonautomotive

inanimate

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How much does this cost us?How much does this cost us?

Presently in the US we use the energy equivalent of Presently in the US we use the energy equivalent of ~60 barrels/year/person~60 barrels/year/person

60 barrels/yr x 42 gallons/barrel x $2.80/gallon = 60 barrels/yr x 42 gallons/barrel x $2.80/gallon = $7056/year$7056/year

= $19.30/day= $19.30/day Total spent in US = $7056/year * 290,000,000 ~ Total spent in US = $7056/year * 290,000,000 ~

$2T$2T

~ 20% of US GDP~ 20% of US GDP

This does not include the economic and social costs This does not include the economic and social costs of ongoing instability in oil-producing regions of the of ongoing instability in oil-producing regions of the world . . .world . . .

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Physics 162 Winter 2007U.S. Consumption vs. ProductionU.S. Consumption vs. Production

policy change

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Where is our energy produced, and of Where is our energy produced, and of what flavor?what flavor?

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LessonsLessons Our energy use is completely dominated by fossil fuels, Our energy use is completely dominated by fossil fuels,

with only about 15% coming from nuclear and with only about 15% coming from nuclear and hydroelectrichydroelectric hydroelectric is the only truly renewable resource of hydroelectric is the only truly renewable resource of

the twothe two Part of our enormous appetite is due to the expanse of Part of our enormous appetite is due to the expanse of

our country: transportation is importantour country: transportation is important Space heating is also an issue in a country where Space heating is also an issue in a country where

detached houses are the ruledetached houses are the rule Any industrial society (at our current scale) is going to Any industrial society (at our current scale) is going to

have a large demand for energyhave a large demand for energy Our use of energy is more efficient than it could be! Our use of energy is more efficient than it could be!

Conservation measures since the 1970’s have allowed Conservation measures since the 1970’s have allowed energy usage to increase more slowly than the growth energy usage to increase more slowly than the growth of the GDP.of the GDP.

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Thanks to a lifestyle invented by your Thanks to a lifestyle invented by your grandparents and perfected by your grandparents and perfected by your

parents generation, we live in a special parents generation, we live in a special time and place…time and place…

We use almost 100 times the average amount used by We use almost 100 times the average amount used by the world ( per person)the world ( per person)

This phase has only lasted for the last century or soThis phase has only lasted for the last century or so Most of our resources come from fossil fuels presently, Most of our resources come from fossil fuels presently,

and this has a short, finite lifetime and using it comes and this has a short, finite lifetime and using it comes with potentially serious environmental consequences.with potentially serious environmental consequences.

2000 2500 3000 3500 4000150010005000year

Fos

sil f

uel u

sage

Reproduced from Fig. 1.2, Ristinen and Kraushaar

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Global Energy: Where Does it Come Global Energy: Where Does it Come From?From?

7.27.228.728.7Hydroelectric*Hydroelectric*

then radiated awaythen radiated away2,000,0002,000,000Sun Abs. by Earth*Sun Abs. by Earth*

0.0080.0080.030.03Solar Direct*Solar Direct*

0.030.030.130.13Wind*Wind*

0.130.130.50.5GeothermalGeothermal

0.40.41.61.6Biomass (burning)*Biomass (burning)*

6.66.62626Nuclear EnergyNuclear Energy

22.522.58989Natural Gas*Natural Gas*

23.223.29292Coal*Coal*

40.040.0158158Petroleum*Petroleum*

Percent of TotalPercent of Total10101818 Joules/yr Joules/yrSourceSource

* Ultimately derived from our sun Courtesy David Bodansky (UW)

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Gas costs less than Gas costs less than Perrier Perrier ! ! What’s going on here?What’s going on here?

We spend about $19/day, or $7000/yr per person We spend about $19/day, or $7000/yr per person on energy in the U.S.on energy in the U.S. about 20% of GDPabout 20% of GDP saves us much more than 20% of our time saves us much more than 20% of our time

(labor-saving devices, transportation, etc.)(labor-saving devices, transportation, etc.) But we’re running through our fossil fuel resources But we’re running through our fossil fuel resources

at a phenomenal rateat a phenomenal rate let’s see if this lasts even another hundred let’s see if this lasts even another hundred

years!years! The ‘third world’ is increasing its use of energy The ‘third world’ is increasing its use of energy

resources as it tries to adopt your parents lifestyleresources as it tries to adopt your parents lifestyle Our world will see a profound change in the next Our world will see a profound change in the next

century as we adjust to a world without gasolinecentury as we adjust to a world without gasoline

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Still fuzzy on the concept of Still fuzzy on the concept of energy?energy?

Don’t worryDon’t worry—we’ll cover that in great detail in —we’ll cover that in great detail in the coming weeksthe coming weeks

Energy is defined as the Energy is defined as the capacity to do workcapacity to do work But what is But what is workwork??

we’ll get to this shortlywe’ll get to this shortly At some level,At some level, I* I* don’t know what energy is: why don’t know what energy is: why

there is such a thing, why it’s conserved, where it there is such a thing, why it’s conserved, where it all came from, etc. all came from, etc. these are deep and interesting questions that these are deep and interesting questions that

some physicists try to understandsome physicists try to understand

Any questions???

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How about a question to work on right How about a question to work on right now?now?

The Toyota Prius, one of the early and increasingly popular The Toyota Prius, one of the early and increasingly popular hybrid vehicles, has a base list price of about $22,000 in hybrid vehicles, has a base list price of about $22,000 in 2006, about $4000 of which pays for the electric motor, 2006, about $4000 of which pays for the electric motor, batteries, second drive train, etc. The feds say the average batteries, second drive train, etc. The feds say the average mileage is about 47 mpg. An approximately comparable mileage is about 47 mpg. An approximately comparable non-hybrid Toyota called the Matrix averages about 33 non-hybrid Toyota called the Matrix averages about 33 mpg. Assume a Prius with a regular internal combustion mpg. Assume a Prius with a regular internal combustion engine would get the mileage of a Matrix. engine would get the mileage of a Matrix.

With gas costing about $3.00/gallon, how many miles would With gas costing about $3.00/gallon, how many miles would you have to drive before the savings on gasoline make up you have to drive before the savings on gasoline make up for the $4000 you had to pay to buy a hybrid?for the $4000 you had to pay to buy a hybrid?

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My answer . . My answer . .

To drive one mile with the Prius costsTo drive one mile with the Prius costs

$3/gal $3/gal = $0.064/mile= $0.064/mile47 miles/gal47 miles/gal

To drive one mile with the Matrix costsTo drive one mile with the Matrix costs

$3/gal $3/gal = $0.091/mile= $0.091/mile33 miles/gal33 miles/gal

Every mile drive we save $0.091 - $0.064 = $0.027/mile on gas. Every mile drive we save $0.091 - $0.064 = $0.027/mile on gas. To save $4000 we need to driveTo save $4000 we need to drive

$4000/($0.027/mile) ~ $4000/($0.027/mile) ~ 148,000 miles148,000 miles

At 12,000 miles/year, that’s over 12 years. So, each year we At 12,000 miles/year, that’s over 12 years. So, each year we recoup about $300-400 of the initial $4000 investment.recoup about $300-400 of the initial $4000 investment.

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But wait, it’s worse than that . . .But wait, it’s worse than that . . .

The Prius has two drive trains and a battery pack. Maintenance costs will likely be higher than for a conventional engine. There is not very good data on that yet.

The lifetime of the NiH battery pack itself is an issue. Toyota now offers an 8-year warranty on the battery, with a current (dealer) replacement cost of about $3000. This should be included in the maintenance costs, too. At a rate of $300-400/year, that will consume most of the savings from higher gas mileage.

It’s possible that a current model hybrid will never actually pay for itself - that it is impossible to recoup the initial investment plus ongoing maintenance costs. Toyota knows this and is trying to bring the cost of hybrid technology down. Market forces and economy of scale will make this happen (some).

Federal subsidies also change the equation by lessening the burden on individuals by spreading the cost across all taxpayers. Is this a good investment?

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But what about COBut what about CO22 emissions and emissions and Global Warming?Global Warming?

Hybrids make us feel good - very environmentally conscious - since they emit fewer greenhouse gases. But the cost of any modern contrivance is heavily dependent on the cost of energy: our lifestyle is very energy intensive. Since a hybrid costs more, it must take more energy to produce than a regular internal combustion engine. How many miles must one drive before this ‘environmental cost’ is recouped?

I don’t think the data exist to answer this question very accurately: it depends on what fraction of the extra $4000 was spent on energy. If 25% of the added cost were energy, then you need to drive about 40,000 miles before the Prius become really ‘green’.

It’s not really clear what all needs to be included. Should we include some fraction of the energy used by Toyota employees to get to work every day? It’s a tough question.

physics 162 winter 2007 1 the big picture we use a heck of a lot of energy we use a heck of a lot of...

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