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					Physics 162                                                   Winter 2007



                          The Big Picture

      We use a heck of a lot of energy
        primitive society used < 100 W of power per person

        our modern society burns 10,000 W per person

        surely not in our homes! Where is this energy going?



      Energy availability has enabled us to focus on higher-level
       issues as a society
         art

         Science

         entertainment

         home shopping network

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Physics 162                                                 Winter 2007



                    Once upon a time…
     Long ago, almost all of our energy came from food
      (delivering muscle power), and almost all our energy went
      into securing food for ourselves
     Enter the work animal, supplementing our muscle power and
      enabling larger-scale agriculture
     Later we burned wood to run boilers, trains
     150 years ago, muscular effort and firewood provided most of
      our energy—and today this is less than 1% of the story
     Today, more energy goes into growing/harvesting food than
      comes out of food! (is this bad news for biodiesel??)



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Physics 162                                                                    Winter 2007



                     The Global Energy Scene
      Global energy production is about 400 QBtu/yr
         a QBtu is a quadrillion Btu, or 1015 Btu

         so about 41020 J per year

      U.S. share is about one fourth of this (100 QBtu or 1020 J)

      1020 J/yr = 31012 W (do the calculation!)
         divided by 300 million people (3108) = 104 W 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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                  Physics 162                                                                                                                                  Winter 2007



                                                                      The Great Energy Disparity
                                             30,000
                                                                                           Switzerland
Gross Domestic Product (GDP): $ per capita




                                                                                                                        Sweden
                                                                                                  Japan
                                                                                                             Iceland      Norway
                                             20,000                                                                                                       Canada

                                                                                                                       Germany                      United States
                                                                                          Italy           U.K.
                                                                                                                   Belgium



                                             10,000

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

                                                                                                                                    1989 data; Reproduced from
                                                                                 Poland                                             Fig. 1.3, Ristinen and Kraushaar
                                                                    Cuba
                                                          India
                                                  0               Ecuador
                                                      0                     10              20                   30                40               50                 60
                                                                                  Energy equivalent barrels of oil per capita per year
                                                                                                                                                                             4
  Physics 162                                      Winter 2007



                      Now on a Logarithmic Scale



• More Countries

• Fills in the gaps

• 1971 data




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Physics 162                                                        Winter 2007



              A note on graphs: log vs. linear
      Many graphs in the book are on logarithmic scales
      This condenses wide-ranging information into a compact
       area
      Pay attention, because you could warp your intuition if you
       don’t appreciate the scale
      Log scales work in factors of ten
      A given vertical span represents a constant ratio (e.g., factor
       of ten, factor of two, etc.)
      An exponential increase looks like a straight line on a logarithmic
       scale


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Physics 162                                                                                     Winter 2007



                                   Example Plots




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


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Physics 162                                                                       Winter 2007


     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    $50
     1    $55
     2    $60.50                                 Rule of 70 (or 72):
     3    $66.55
     4    $73.21                Doubling time = 70 years/annual % growth rate
     5    $80.53
     6    $88.58
     7    $97.44
     8    $107.18
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Physics 162                                 Winter 2007



              Evolution of Energy Sources




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Physics 162                                               Winter 2007



                U.S. Consumption in 1996
  Source         Amount          QBtu    Percent   1018 Joules

  Coal           1.00109 tons   20.99   22.3%     22.1

  Natural Gas    21.91012 ft3   22.59   24.1%     23.8

  Petroleum      6.14109 bbl    35.72   38.1%     37.7

  Nuclear        681109 kWh     7.17    7.6%      7.56

  Renewables     695109 kWh     7.39    7.9%      7.80

  Total                          93.81   100.0%    99.0


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    Physics 162                                                                                        Winter 2007



                   The Fall of the Work Animal
     Used to rely completely on animals
      for transportation
     Trains entered the picture in the
      mid-1800s




                                            Average Horsepower/person in the US
     Cars entered the scene in a big way                                                   automotive
      around 1920
     World has never been the same
                                                                                                 Nonautomotive
     Work animal fell off the map around                                                          inanimate

      1940
     Today automotive is over 95% of
      the story

                                                                                         work animal


                                                                                  Year

                                                                                                                 11
Physics 162                                                Winter 2007



                How much does this cost us?
   Presently in the US we use the energy equivalent of ~60
    barrels/year/person

    60 barrels/yr x 42 gallons/barrel x $2.80/gallon = $7056/year
                                                     = $19.30/day
    Total spent in US = $7056/year * 290,000,000 ~ $2T
                                                ~ 20% of US GDP

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


                                                                     12
Physics 162   U.S. Consumption vs. Production Winter 2007




                               policy change




                                                        13
 Physics 162                             Winter 2007


Where is our energy produced, and of what flavor?




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Physics 162                                                  Winter 2007



                              Lessons
     Our energy use is completely dominated by fossil fuels, with
      only about 15% coming from nuclear and hydroelectric
        hydroelectric is the only truly renewable resource of the two

     Part of our enormous appetite is due to the expanse of our
      country: transportation is important
     Space heating is also an issue in a country where detached
      houses are the rule
     Any industrial society (at our current scale) is going to have a
      large demand for energy
     Our use of energy is more efficient than it could be!
      Conservation measures since the 1970’s have allowed energy
      usage to increase more slowly than the growth of the GDP.

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Physics 162                                                                                        Winter 2007

Thanks to a lifestyle invented by your grandparents and
  perfected by your parents generation, we live in a
                special time and place…
                     We use almost 100 times the average amount used by the world ( per
                      person)
                     This phase has only lasted for the last century or so
                     Most of our resources come from fossil fuels presently, and this has a short,
                      finite lifetime and using it comes with potentially serious environmental
                      consequences.
  Fossil fuel usage




                                                                       Reproduced from Fig. 1.2,
                                                                       Ristinen and Kraushaar



                        0      500    1000    1500    2000     2500   3000       3500         4000
                                                        year
                                                                                                             16
Physics 162                                                            Winter 2007

   Global Energy: Where Does it Come From?
              Source                 1018 Joules/yr      Percent of Total
  Petroleum*                              158                   40.0
  Coal*                                   92                    23.2
  Natural Gas*                            89                    22.5
  Hydroelectric*                         28.7                   7.2
  Nuclear Energy                          26                    6.6
  Biomass (burning)*                      1.6                   0.4
  Geothermal                              0.5                   0.13
  Wind*                                  0.13                   0.03
  Solar Direct*                          0.03                  0.008
  Sun Abs. by Earth*                   2,000,000       then radiated away

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

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Physics 162                                                     Winter 2007


       Gas costs less than Perrier ! What’s going
                        on here?
      We spend about $19/day, or $7000/yr per person on energy
       in the U.S.
         about 20% of GDP

         saves us much more than 20% of our time (labor-saving
           devices, transportation, etc.)
      But we’re running through our fossil fuel resources at a
       phenomenal rate
         let’s see if this lasts even another hundred years!

      The ‘third world’ is increasing its use of energy resources as it
       tries to adopt your parents lifestyle
      Our world will see a profound change in the next century as
       we adjust to a world without gasoline
                                                                           18
Physics 162                                                    Winter 2007


              Still fuzzy on the concept of energy?
     Don’t worry—we’ll cover that in great detail in the coming
      weeks
     Energy is defined as the capacity to do work
     But what is work?
        we’ll get to this shortly

     At some level, I* don’t know what energy is: why there is
      such a thing, why it’s conserved, where it all came from, etc.
        these are deep and interesting questions that some
         physicists try to understand

                     Any questions???


                                                                         19
Physics 162                                                            Winter 2007


              How about a question to work on right now?

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

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




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 Physics 162                                                           Winter 2007

                                 My answer . .
To drive one mile with the Prius costs

                   $3/gal = $0.064/mile
                  47 miles/gal

To drive one mile with the Matrix costs

                   $3/gal = $0.091/mile
                  33 miles/gal

Every mile drive we save $0.091 - $0.064 = $0.027/mile on gas. To save $4000 we
   need to drive
                  $4000/($0.027/mile) ~ 148,000 miles

At 12,000 miles/year, that’s over 12 years. So, each year we recoup about $300-400
   of the initial $4000 investment.
                                                                                 21
 Physics 162                                                                   Winter 2007


                       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?

                                                                                         22
 Physics 162                                                              Winter 2007


       But what about CO2 emissions and 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.

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