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					Renewable Energy Sources II:
    Alternatives Part II
               Lecture #11
               HNRT 228
               Energy and the Environment




                                        1
                  Chapter 5 Summary
•   Hydroelectric Power
•   Wind Power
•   Ocean Thermal Energy Conversion
•   Biomass as Energy
•   Geothermal Energy
•   Tidal Energy
•   Wave Energy
•   Today’s Focus
    –   Biomass
    –   Others

                                      2
         Recall Renewable Resources
•   Renewable means anything that won’t be
    destroyed by using it
     – sunlight (the sun will rise again tomorrow)

     – biomass (grows again)

     – hydrological cycle (will rain again)

     – wind (sunlight on earth makes more)

     – ocean currents (driven by sun)

     – tidal motion (moon keeps on producing it)

     – geothermal (heat sources inside earth not

       used up fast)
                                                     3
          Renewable Energy Consumption

   Energy        QBtu    Percent    QBtu    Percent
   Source       (1994)   (1994)    (2003)   (2003)
Hydroelectric   3.037     3.43     2.779     2.83

Geothermal      0.357     0.40     0.314     0.32

Biomass         2.852     3.22     2.884     2.94

Solar Energy    0.069    0.077     0.063     0.06

Wind            0.036    0.040     0.108     0.11

Total           6.351     7.18     6.15      6.3



                                                      4
     Another look at available energy flow

•   The flow of radiation (solar and thermal) was
    covered previously
     – earth is in an energy balance: energy in =

       energy out
     – 30% reflected, 70% thermally re-radiated

•   Some of the incident energy is absorbed, but
    what exactly does this do?
     – much goes into heating the air/land

     – much goes into driving weather (rain, wind)

     – some goes into ocean currents

     – some goes into photosynthesis
                                                     5
The Renewable Budget




                       6
        Outstanding Points from Fig. 5.1

•   Incident radiation is 1741015 W
     – this is 1370 W/m times area facing sun (R )
                          2                       2

•   30% directly reflected back to space
     – off clouds, air, land

•   47% goes into heating air, land, water
•   23% goes into evaporating water, precipitation,
    etc. (part of weather)
•   Adds to 100%, so we’re done
     – but wait! there’s more…




                                                      7
               Energy Flow, continued
•   0.21% goes into wind, waves, convection, currents
     – note this is 100 times less than driving the water
       cycle
     – but this is the “other” aspect of weather

•   0.023% is stored as chemical energy in plants via
    photosynthesis
     – total is 4010
                      12 W; half in ocean (plankton)

     – humans are 6 billion times 100 W = 0.610
                                                   12 W

     – this is 1.5% of bio-energy; 0.00034% of incident
       power
•   All of this (bio-activity, wind, weather, etc.) ends up
    creating heat and re-radiating to space
     – except some small amount of storage in fossil fuels


                                                              8
                iClicker Question

•   With respects to energy, hydroelectric power
    represents
     – A    remnant electric power from storms
     – B    remnant water energy from chemical
            bonds
     – C    remnant energy of chemical bonding
     – D    remnant gravitational potential energy
            of precipitation
     – E    a form of fictitious energy


                                                     9
                iClicker Question

•   With respects to energy, hydroelectric power
    represents
     – A    remnant electric power from storms
     – B    remnant water energy from chemical
            bonds
     – C    remnant energy of chemical bonding
     – D    remnant gravitational potential energy
            of precipitation
     – E    a form of fictitious energy


                                                     10
                  iClicker Question
•   What is true about hydroelectric power
    generation since 1950?
     – A     It has always increased in MW produced
     – B     It has always decreased in MW produced
     – C     It has increased and decreased in total
             MW produced, but is now at a peak
     – D     It has both increased and decreased in
             total MW produced
     – E     The percentage of electric power
             produced by hydroelectric plants has
             generally increased over time

                                                       11
                  iClicker Question
•   What is true about hydroelectric power
    generation since 1950?
     – A     It has always increased in MW produced
     – B     It has always decreased in MW produced
     – C     It has increased and decreased in total
             MW produced, but is now at a peak
     – D     It has both increased and decreased in
             total MW produced
     – E     The percentage of electric power
             produced by hydroelectric plants has
             generally increased over time

                                                       12
              iClicker Question

•   What is about the maximum efficiency of
    energy generation using the wind?
     – A   20%
     – B   40%
     – C   60%
     – D   80%
     – E   100%



                                              13
              iClicker Question

•   What is about the maximum efficiency of
    energy generation using the wind?
     – A   20%
     – B   40%
     – C   60%
     – D   80%
     – E   100%



                                              14
               iClicker Question

•   Which state generates the most amount
    of electricity derived from wind power?
     – A    Virginia
     – B    Alaska
     – C    Montana
     – D    California
     – E    Texas



                                              15
               iClicker Question

•   Which state generates the most amount
    of electricity derived from wind power?
     – A    Virginia
     – B    Alaska
     – C    Montana
     – D    California
     – E    Texas



                                              16
                     Biomass
•   Biomass is any living organism, plant, animal, etc.
•   401012 W out of the 174,0001012 W incident
    on the earth from the sun goes into
    photosynthesis
     – 0.023%

     – this is the fuel for virtually all biological
       activity
     – half occurs in oceans

•   Compare this to global human power generation
    of 131012 W, or to 0.61012 W of human
    biological activity
•   Fossil fuels represent stored biomass energy
                                                          17
                      Photosynthesis
•   Typical carbohydrate (sugar) has molecular structure like: [CH2O]x,
    where x is some integer
     – refer to this as “unit block”: C6H12O6 (glucose) has x=6
•   Photosynthetic reaction:
          xCO2 + xH2O + light  [CH2O]x + xO2
         1.47 g 0.6 g 16 kJ         1g        1.07 g
•   Carbohydrate reaction (food consumption) is photosynthesis run
    backwards
     – 16 kJ per gram is about 4 Calories per gram
•   Basically a “battery” for storing solar energy
     – usage just runs reaction backward (but energy instead of light)




                                                                          18
          Photosynthetic efficiency
•   Only 25% of the solar spectrum is useful to the
    photosynthetic process
     – uses both red and blue light (reflects green),
       doesn’t use IR or UV
•   70% of this light is actually absorbed by leaf
•   Only 35% of the absorbed light energy (in the
    useful wavelength bands) is stored as chemical
    energy
     – the rest is heat

     – akin to photovoltaic incomplete usage of
       photon energy
•   Net result is about 6%
                                                        19
       Realistic photosynthetic efficiency
Location               Plant Production       Solar Energy
                        (g/m2 per day)    Conversion Efficiency
Potential Maximum            71                    5%
Polluted stream (?!)         55                    4%
Iowa cornfield               20                   1.5%
Pine Forest                   6                   0.5%
Wyoming Prairie              0.3                 0.02%
Nevada Desert                0.2                 0.015%




                                                                  20
                iClicker Question
•   The photosynthesis reaction
    – A     takes in sugar and water and produces
      carbon dioxide and energy
    – B     takes in sugar and sunlight and
      produces sugar and energy
    – C     takes in sunlight and water to produce
      sugar and oxygen
    – D     takes in sunlight, carbon dioxide and
      water to produce sugar and oxygen
    – E     takes in sunlight, oxygen and water to
      produce sugar and energy

                                                     21
                iClicker Question
•   The photosynthesis reaction
    – A     takes in sugar and water and produces
      carbon dioxide and energy
    – B     takes in sugar and sunlight and
      produces sugar and energy
    – C     takes in sunlight and water to produce
      sugar and oxygen
    – D     takes in sunlight, carbon dioxide and
      water to produce sugar and oxygen
    – E     takes in sunlight, oxygen and water to
      produce sugar and energy

                                                     22
                iClicker Question
•   Metabolic consumption of food is like
    photosynthesis in reverse in that
     – A     you use oxygen and water to produce
       energy and carbon dioxide
     – B     you use carbon dioxide and water to
       produce energy and oxygen
     – C     you use sugar and oxygen to produce
       energy and carbon dioxide
     – D     you use sugar and oxygen to produce
       carbon dioxide and water
     – E     you use sugar and carbon dioxide to
       produce energy and oxygen
                                                   23
                iClicker Question
•   Metabolic consumption of food is like
    photosynthesis in reverse in that
     – A     you use oxygen and water to produce
       energy and carbon dioxide
     – B     you use carbon dioxide and water to
       produce energy and oxygen
     – C     you use sugar and oxygen to produce
       energy and carbon dioxide
     – D     you use sugar and oxygen to produce
       carbon dioxide and water
     – E     you use sugar and carbon dioxide to
       produce energy and oxygen
                                                   24
        How much biomass is available?

•   Two estimates of plant production in book come up
    with comparable answers:
     – 10
          17 grams per year

     – 320 grams per m averaged over earth’s surface
                         2

     – consistent with 4010
                             12 W photosynthesis

•   U.S. annual harvested mass corresponds to 80 QBtu
     – comparable to 100 QBtu total consumption

•   U.S. actually has wood-fired plants: 6,650 MW-worth
     – in 2002, burned equivalent of 200,000 barrels of
       oil per day



                                                          25
             Ethanol from Corn




•   One can make ethanol (C2H5OH: a common
    alcohol) from corn
     – chop; mix with water

     – cook to convert starches to sugars

     – ferment into alcohol

     – distill to separate alcohol from the rest
                                                   26
      Does Ethanol as a Fuel Make Sense?
•   We put more energy into agriculture than we get out (in
    terms of Caloric content) by about a factor of two
     – at least in our modern, petrol-based mechano-farming

     – sure, we can do better by improving efficiencies

•   Estimates on energy return
     – controversial: some say you get out 0.7 times the
       energy out that you put in (a net loss); others claim
       it’s 1.4 times; often see numbers like 1.2
     – 1.2 means a net gain, but 83% of your total budget
       goes into production; only 17% of crop is exported as
       energy



                                                               27
                   Ethanol, continued
•   Right now, using tons of fossil fuels to get ethanol
     – and not clear we’re operating at a net gain

•   Why on Earth are we trying?
     – corn has worked its way into much of our foods

         high fructose corn syrup

         cow feed

         corn oil for cooking

     – powerful presence in the halls of Congress

         the corn lobby is partially responsible for

          pervasiveness of corn in our diet (soft drinks)



                                                            28
               iClicker Question

•   Fructose is bad for your health.
    – A    True
    – B    False
•   Sucrose is better for you than fructose.
    – A    True
    – B    False




                                               29
               Food For Thought
•   Differences
    between
    glucose,
    fructose,
    and sucrose



•   And then
    there is
    ethanol
                                  30
            Ethanol Issues, continued

•   Energy is a high-payoff business, especially when the
    government helps out with subsidies
     – thus the attraction for corn ethanol (which does get
       subsidies)
•   Can supplant actual food production, driving up price of food
     – there have been tortilla shortages in Mexico because corn
       ethanol is squeezing the market
     – after all, we only have a finite agricultural capacity
     – both land, and water are limited, especially water
•   Ethanol from sugar cane can be 8:1 favorable
     – Brazil doing very well this way: but corn is the wrong
       answer!
     – but lookout rain forests: can actually increase CO2 by
       removing CO2-absorbing jungle

                                                                    31
               iClicker Question

•   The basic chemical formula for both
    glucose and fructose is C6H1206
     – A    True
     – B    False




                                          32
               iClicker Question

•   The basic chemical formula for both
    glucose and fructose is C6H1206
     – A    True
     – B    False




                                          33
               iClicker Question

•   Sucrose is a complex sugar made of
    glucose and fructose.
     – A    True
     – B    False




                                         34
               iClicker Question

•   Sucrose is a complex sugar made of
    glucose and fructose.
     – A    True
     – B    False




                                         35
                 Quantitative Ethanol
•   Let’s calculate how much land we need to replace oil
     – an Iowa cornfield is 1.5% efficient at turning incident sunlight
       into stored chemical energy
     – the conversion to ethanol is 17% efficient
          assuming 1.2:1 ratio, and using corn ethanol to power farm

           equipment and ethanol production itself
     – growing season is only part of year (say 50%)
     – net is 0.13% efficient (1.5%  17%  50%)
     – need 40% of 1020 J per year = 41019 J/yr to replace petroleum
     – this is 1.31012 W: thus need 1015 W input (at 0.13%)
     – at 200 W/m2 insolation, need 51012 m2, or (2,200 km)2 of land
     – that’s a square 2,200 km on a side




                                                                          36
What does this amount of land look like?




        We don’t have this much arable land!
         And where do we grow our food?

                                               37
             Take Home Points
•   Hopefully this illustrates the power of
    quantitative analysis
     – lots of ideas are floated/touted, but

       many don’t pass the quantitative test
     – a plan has to do a heck of a lot more

       than sound good!!!
     – by being quantitative in this course, I

       am hoping to instill some of this
       discriminatory capability in you

                                                 38
       Other Renewable Resources
•   Consult text and other books for more on the
    other renewable resources
•   Note that there are few likely major players
     – Restricted by location and development costs

•   When considering most abundant renewable
    resources
     – consider the approximate value of QBtu

       available annually
     – compare to our consumption of 100 QBtu per

       year

                                                      39
       Renewable Resources Review
•   Solar (photovoltaic, solar thermal)
     – get 100 QBtu/yr with < 2% coverage of U.S. land area

•   Wind
     – maybe 180 QBtu/yr worldwide, maybe 25 QBtu in

       U.S.
•   Biomass
     – if we divert 10% of the 40 TW global budget into

       energy, would net 4 TW, or 120 QBtu worldwide;
       maybe 7 QBtu in U.S., given about 6% of land area
•   Hydroelectric
     – 70 QBtu/yr feasible worldwide: twice current

       development
     – 5 QBtu/yr max potential in U.S.
                                                              40
                  Geothermal Energy
•   Geothermal: run
    heat engines off
    earth’s internal
    heat
     – could be as much
       as 1.5 QBtu/yr
       worldwide in 50    Binary-cycle
                          Binary-cycle power plants use moderate-
       years              temperature water (225 ºF–360 ºF, or 107
     – limited to a few   ºC–182 ºC) from the geothermal reservoir.
                          In binary systems, hot geothermal fluids
       rare sites         are passed through one side of a heat
                          exchanger to heat a working fluid in a
                          separate adjacent pipe. The working fluid,
                          usually an organic compound with a low
                          boiling point such as iso-butane or iso-
                          pentane, is vaporized and passed through a
                          turbine to generate electricity.

                                                                       41
                             Geothermal Energy
•   Dry steam
      –    Use very hot (>455 °F, or >235 °C)
           steam and little water from the
           geothermal reservoir.
      –    Steam goes directly through a pipe to a
           turbine to spin a generator that
           produces electricity.
      –    This type of geothermal power plant is
           the oldest, first being used at
           Lardarello, Italy, in 1904.
•   Flash steam
      –    Flash steam power plants use hot
           water (>360 ºF, or >182 ºC) from the
           geothermal reservoir.
      –    When the water is pumped to the
           generator, it is released from the
           pressure of the deep reservoir.
      –    The sudden drop in pressure causes
           some of the water to vaporize to steam,
           which spins a turbine to generate
           electricity.
•   Both dry steam and flash steam power
    plants emit small amounts of carbon dioxide,
    nitric oxide, and sulfur
      –    Generally 50 times less than traditional
           fossil-fuel power plants.
•   Hot water not flashed into steam is returned
    to the geothermal reservoir through injection
    wells.
                                                      42
                      Tidal Energy
•   Tidal: oscillating hydroelectric “dams”
     – a few rare sites are conducive to this (Bay of Fundy,
       for example)
     – can only generate when the tide is flowing in or out

         only for about 10 hours each day

     – up to 1 QBtu/yr practical worldwide




                                                                43
                                Tidal Energy System in France
         Ocean Thermal Energy Conversion
                    (OTEC)
•   Ocean Thermal Energy
    Conversion (OTEC)
     – use thermal gradient
       to drive heat engine
     – complex, at sea, small
       power outputs




                                           44
               iClicker Question

•   Are there any other alternative renewable
    energy resources?
     – A   Yes
     – B   No



•   Don’t forget that there is more to energy
    than meets the Earth

                                                45

				
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