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Sustainable Energy

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Title: Understanding Our Environment Author: CCSN Last modified by: mourad Created Date: 1/16/2002 10:44:40 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: Sustainable Energy


1
Sustainable Energy
2
Outline
  • Conservation
  • Cogeneration
  • Tapping Solar Energy
  • Passive vs. Active
  • High Temperature Solar Energy
  • Photovoltaic Cells
  • Fuel Cells
  • Energy From Biomass
  • Energy From Earths Forces

3
CONSERVATION
  • Utilization Efficiencies
  • Todays average new home uses half the fuel
    required in a house built in 1974.
  • Reducing air infiltration is usually the
    cheapest, quickest, and most effective way of
    saving household energy.
  • According to new national standards
  • New washing machines will have to use 35 less
    water in 2007.
  • Will cut U.S. water use by 40 trillion liters
    annually.

4
Utilization Efficiencies
  • For even greater savings, new houses can be built
    with extra thick superinsulated walls, air-to-air
    heat exchangers, and double-walled sections.
  • Straw-bale construction
  • Home orientation

5
Energy Conversion Efficiencies
  • Energy Efficiency is a measure of energy produced
    compared to energy consumed.
  • Thermal conversion machines can turn no more than
    40 of energy in primary fuel into electricity or
    mechanical power due to waste heat.
  • Fuel cells can theoretically approach 80
    efficiency using hydrogen or methane.

6
Energy Conversion Efficiencies
  • Transportation
  • Most potential energy in fuel is lost as waste
    heat.
  • In response to 1970s oil prices, average U.S.
    automobile gas-mileage increased from 13.3 mpg in
    1973 to 25.9 mpg in 1988.
  • Falling fuel prices of the 1990s discouraged
    further conservation.

7
Energy Conversion Efficiencies
  • Transportation
  • By 2002, the average fuel economy of Americas
    passenger fleet had dropped to 20.4 mpg, the
    lowest since 1980.
  • Most decrease due to SUVs and light trucks.
  • Hybrid gasoline-electric vehicles have the
    highest efficiency rating and lowest emissions
    available in the United States.

8
Energy Conversion Efficiencies
  • Net Energy Yield - Based on total useful energy
    produced during the lifetime of an entire energy
    system minus the energy required to make useful
    energy available.
  • Expressed as ratio between output of useful
    energy and energy costs.

9
Negawatt Programs
  • It is much less expensive to finance conservation
    projects than to build new power plants.
  • Power companies investing in negawatts of demand
    avoidance.
  • Conservation costs on average 350/kw
  • Nuclear Power Plant 3,000 - 8,000/kw
  • Coal Power Plant 1,000/kw

10
Cogeneration
  • Cogeneration - Simultaneous production of both
    electricity and steam, or hot water, in the same
    plant.
  • Increases net energy yield from 30-35 to 80-90.
  • In 1900, half of electricity generated in U.S.
    came from plants also providing industrial steam
    or district heating.
  • By 1970s cogeneration had fallen to less than 5
    of our power supplies.

11
TAPPING SOLAR ENERGY
  • A Vast Resource
  • Average amount of solar energy arriving on top of
    the atmosphere is 1,330 watts per square meter.
  • Amount reaching the earths surface is 10,000
    times more than all commercial energy used
    annually.
  • Until recently, this energy source has been too
    diffuse and low intensity to capitalize for
    electricity.

12
Solar Energy
  • Passive Solar Heat - Using absorptive structures
    with no moving parts to gather and hold heat.
  • Greenhouse Design
  • Active Solar Heat - Generally pump heat-
    absorbing medium through a collector, rather than
    passively collecting heat in a stationary object.
  • Water heating consumes 15 of U.S. domestic
    energy budget.

13
HIGH TEMPERATURE SOLAR ENERGY
  • Parabolic mirrors are curved reflective surfaces
    that collect light and focus it onto a
    concentrated point. Two techniques
  • Long curved mirrors focused on a central tube
    containing a heat-absorbing fluid.
  • Small mirrors arranged in concentric rings around
    a tall central tower track the sun and focus
    light on a heat absorber on top of the tower
    where molten salt is heated to drive a
    steam-turbine electric generator.

14
Parabolic Mirrors
15
Promoting Renewable Energy
  • Proposed Energy Conservation Policies
  • Distributional Surcharges
  • Small fee levied on all utility customers.
  • Renewable Portfolio
  • Suppliers must get minimum percentage of power
    from renewable sources.
  • Green Pricing
  • Allows utilities to profit from conservation
    programs and charge premium prices for renewable
    energy.

16
Photovoltaic Solar Energy
  • Photovoltaic cells capture solar energy and
    convert it directly to electrical current by
    separating electrons from parent atoms and
    accelerating them across a one-way electrostatic
    barrier.
  • Bell Laboratories - 1954
  • 1958 - 2,000 / watt
  • 1970 - 100 / watt
  • 2003 - 5 / watt

17
Photovoltaic Cells
  • During the past 25 years, efficiency of energy
    capture by photovoltaic cells has increased from
    less than 1 of incident light to more than 10
    in field conditions, and over 75 in the
    laboratory.
  • Invention of amorphous silicon collectors has
    allowed production of lightweight, cheaper cells.
  • Currently 700 million annual market.

18
Storing Electrical Energy
  • Electrical energy storage is difficult and
    expensive.
  • Lead-acid batteries are heavy and have low energy
    density.
  • Metal-gas batteries are inexpensive and have high
    energy densities, but short lives.
  • Alkali-metal batteries have high storage
    capacity, but are more expensive.
  • Lithium batteries have very long lives, and store
    large amounts of energy, but are very expensive.

19
FUEL CELLS
  • Fuel Cells - Use on-going electrochemical
    reactions to produce electric current.
  • Positive electrode (cathode) and negative
    electrode (anode) separated by electrolyte which
    allows charged atoms to pass, but is impermeable
    to electrons.
  • Electrons pass through external circuit, and
    generate electrical current.

20
Fuel Cells
  • Fuel cells provide direct-current electricity as
    long as supplied with hydrogen and oxygen.
  • Hydrogen can be supplied as pure gas, or a
    reformer can be used to strip hydrogen from other
    fuels.
  • Fuel cells run on pure oxygen and hydrogen
    produce no waste products except drinkable water
    and radiant heat.
  • Reformer releases some pollutants, but far below
    conventional fuel levels.

21
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22
Fuel Cells
  • Typical fuel cell efficiency is 40-45.
  • Current is proportional to the size of the
    electrodes, while voltage is limited to about
    1.23 volts/cell.
  • Fuel cells can be stacked together until the
    desired power level is achieved.

23
Fuel Cell Types
  • Proton Exchange Membrane - Design being developed
    for use in automobiles.
  • Lightweight and operate at low temps.
  • Efficiency typically less than 40.
  • Phosphoric Acid - Most common fuel design for
    stationary electrical generation.

24
Fuel Cell Types
  • Carbonite - Uses inexpensive nickel catalyst, and
    operates at 650o C.
  • Good heat cogeneration, but difficult to operate
    due to the extreme heat.
  • Solid Oxide - Uses coated zirconium ceramic as
    electrolyte.
  • High operating temperatures, but highest
    efficiency of any design.
  • Still in experimental stage.

25
ENERGY FROM BIOMASS
  • Plants capture about 0.1 of all solar energy
    that reaches the earths surface.
  • About half the energy used in metabolism.
  • Useful biomass production estimated at 15 - 20
    times the amount currently obtained from all
    commercial energy sources.
  • Renewable energy resources account for 18 of
    total world energy use, and biomass makes up
    three-quarters of that supply.

26
Burning Biomass
  • Wood provides less than 1 of US energy, but
    provides up to 95 in poorer countries.
  • 1,500 million cubic meters of fuelwood collected
    in the world annually.
  • Inefficient burning of wood produces smoke laden
    with fine ash and soot and hazardous amounts of
    carbon monoxide (CO) and hydrocarbons.
  • Produces few sulfur gases, and burns at lower
    temperature than coal.

27
Fuelwood Crisis
  • About 40 of world population depends on firewood
    and charcoal as their primary energy source.
  • Of these, three-quarters do not have an adequate
    supply.
  • Problem intensifies as less developed countries
    continue to grow.
  • For urban dwellers, the opportunity to scavenge
    wood is generally nonexistent.

28
Fuelwood Crisis
  • By 2025, worldwide demand for fuelwood is
    expected to be twice current harvest rates while
    supplies will have remained relatively static.

29
Dung
  • Where other fuel is in short supply, people often
    dry and burn animal dung.
  • Not returning animal dung to land as fertilizer
    reduces crop production and food supplies.
  • When burned in open fires, 90 of potential heat
    and most of the nutrients are lost.

30
Methane
  • Methane is main component of natural gas.
  • Produced by anaerobic decomposition.
  • Burning methane produced from manure provides
    more heat than burning dung itself, and left-over
    sludge from bacterial digestion is a
    nutrient-rich fertilizer.
  • Methane is clean, efficient fuel.
  • Municipal landfills contribute as much as 20 of
    annual output of methane to the atmosphere.

31
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32
Alcohol from Biomass
  • Ethanol and methanol are produced by anaerobic
    digestion of plant materials with high sugar
    content.
  • Gasohol - mixture of gasoline and ethanol.
  • Ethanol in gasohol raises octane ratings and acts
    as a substitute for lead antiknock agents.
  • Ethanol production could be a solution to grain
    surpluses and bring a higher price for grain
    crops.

33
ENERGY FROM EARTHS FORCES
  • Hydropower
  • By 1925, falling water generated 40 of worlds
    electric power.
  • Hydroelectric production capacity has grown
    15-fold.
  • Fossil fuel use has risen so rapidly that
    currently, hydroelectric only supplies
    one-quarter of electrical generation.

34
Hydropower
  • Total world hydropower potential estimated about
    3,000 terrawatt hours.
  • Only 20 of total electrical generation.
  • Much of recent hydropower development has been in
    very large dams.

35
Dam Drawbacks
  • Human Displacement
  • Ecosystem Destruction
  • Wildlife Losses
  • Large-Scale Flooding Due to Dam Failures
  • Sedimentation
  • Herbicide Contamination
  • Evaporative Losses
  • Nutrient Flow Retardation

36
Dam Alternatives
  • Low-Head Hydropower - Extract energy from small
    headwater dams.
  • Run-of-River Flow - Submerged directly in stream
    and usually do not require dam or diversion
    structure.
  • Micro-Hyrdo Generators - Small versions designed
    to supply power to single homes.

37
Wind Energy
  • Estimated 20 million MW of wind power could be
    commercially tapped worldwide.
  • Ten times total current global electrical
    generating capacity.
  • Typically operate at 35 efficiency under field
    conditions.
  • When conditions are favorable electric prices
    typically run as low as 3 cents / KWH.

38
Wind Energy
  • Wind Farms - Large concentrations of wind
    generators producing commercial electricity.
  • Negative Impacts
  • Interrupt view in remote places.
  • Destroy sense of isolation.
  • Potential bird kills.

39
Geothermal Energy
  • High-pressure, high-temperature steam fields
    exist below the earths surface.
  • Recently, geothermal energy has been used in
    electric power production, industrial processing,
    space heating, agriculture, and aquaculture.
  • Have long life span, no mining needs, and little
    waste disposal.
  • Potential danger of noxious gases and noise
    problems from steam valves.

40
Tidal and Wave Energy
  • Ocean tides and waves contain enormous amounts of
    energy that can be harnessed.
  • Tidal Station - Tide flows through turbines,
    creating electricity.
  • Requires a high tide / low-tide differential of
    several meters.
  • Main worries are saltwater flooding behind the
    dam and heavy siltation.
  • Stormy coasts with strongest waves are often far
    from major population centers.

41
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42
Ocean Thermal Electric Conversion
  • Heat from sun-warmed upper ocean layers is used
    to evaporate a working fluid, such as ammonia,
    which has a low boiling point.
  • Gas pressure spins electrical turbines.
  • Need temperature differential of about 20o C
    between warm upper layers and cooling water.

43
WHATS OUR ENERGY FUTURE ?
44
Summary
  • Conservation
  • Cogeneration
  • Tapping Solar Energy
  • Passive vs. Active
  • High Temperature Solar Energy
  • Photovoltaic Cells
  • Fuel Cells
  • Energy From Biomass
  • Energy From Earths Forces

45
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