Nuclear Fusion and Renewable Energy Resources

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Nuclear Fusion and Renewable Energy Resources

• Lecture 17
• GLY 120

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Alternative energy sources - renewable and low
impact on the environment

• Nuclear Fusion
• Geothermal energy
• Solar power
• Hydroelectric power
• Biomass
• Wind energy
• Hydrogen fuel

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Nuclear Fusion

• Combine two isotopes to make a larger one and
  harness the resultant energy (similar in amount
  to nuclear fission).
• Main process in stars (our sun) and hydrogen bomb
  (uncontrolled reaction)
• The typical nuclear fusion reaction achievable on
  Earth is the combination of heavy Hydrogen
  isotopes to produce Helium
• 2H 3H (deuterium tritium) He neutron
  
• energy (17.6 million electron volts)

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However...

• There has only been limited success in achieving
  controlled nuclear fusion because
• Extremely high temperatures required
• gt100 million C
• Reactions can be maintained over only fractions
  of a second
• Reaction requires more energy than the amount
  released
• Future technology may find a way, but it is
  currently not useful

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• Advantages -
• enormous potential source of energy (essentially
  unlimited, the oceans have vast amounts of
  deuterium)
• low environmental costs
• no CO2 emissions
• non-hazardous, benign by-products Helium

• Disadvantages -
• technology currently not available...
• technology may NEVER exist...
• or may not ever be economical (e.g., requires
  more energy than it creates)

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Geothermal Energy

• Involves tapping heat generated deep in the
  earth, usually due to active or dormant volcanism
• A sustainable resource as long as it is not
  extracted faster than it is naturally
  replenished.
• Need the following geologic conditions for a
  potentially economic source of geothermal energy
• recent volcanic activity (magma body within 3-10
  km of the surface)
• permeable aquifer
• impermeable cap rock

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• Three types of power plants are used to generate
  power from geothermal energy
• Dry steam plants
• take steam out of fractures in the ground
• and use it to directly drive a turbine that spins
  a generator.
• Flash plants
• take hot water, usually at temperatures over
  200C, out of the ground
• and allows it to boil as it rises to the surface
• then separates the steam phase in steam/water
  separators
• and then runs the steam through a turbine.
• Binary plants
• the hot water flows through heat exchangers,
  boiling an organic fluid that spins the turbine.
• The condensed steam and remaining geothermal
  fluid from all three types of plants are injected
  back into the hot rock to pick up more heat

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• Disadvantages
• Wastewater disposal is a problem (often a saline
  brine - rich in toxic elements),
• Subsidence during groundwater extraction
  (reduced permeability in aquifer),
• Can produce earthquakes during forced injection
  (Rocky Mountain Arsenal)

• Advantages
• Vast potential energy resource
• Simple technology
• Easy to find sources of heat
• Clean resource
• little air pollution
• few CO2 emissions
• no solid waste

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• Rocky Mountain Arsenal
• From April 1962 to November 1965, several hundred
  earthquakes occurred in the Denver, CO, area
• The source of the earthquakes was traced to the
  Rocky Mountain Arsenal, which was manufacturing
  materials for chemical warfare
• Liquid waste from the manufacturing process was
  being pumped down a deep disposal well to a depth
  of about 3600 m

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• The rock receiving the waste was highly fractured
  metamorphic rock
• Injection of the new liquid increased the fluid
  pressure, causing slippage along fractures
• When the injection of the waste stopped, so did
  the earthquakes

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• Geothermal Heat Pumps
• Take advantage of the stable Earth temperature of
  45-58?F (7.2-14.4?C) just a few feet below the
  surface
• GHP's circulate water or other liquids through
  pipes buried in a continuous loop (either
  horizontally or vertically) next to a building.
• Depending on the weather, the system is used for
  heating or cooling.

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• Heating
• Earth's heat (the difference between the earth's
  temperature and the colder temperature of the
  air) is transferred through the buried pipes into
  the circulating liquid and then transferred again
  into the building.
• Cooling
• During hot weather, the continually circulating
  fluid in the pipes 'picks up' heat from the
  building - thus helping to cool it - and
  transfers it into the earth

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• GHP's use very little electricity and are very
  easy on the environment.
• In the U.S., the temperature inside over 300,000
  homes, schools and offices is kept comfortable by
  these energy saving systems, and hundreds of
  thousands more are used worldwide.
• The U.S. Environmental Protection Agency has
  rated GHP's as among the most efficient of
  heating and cooling technologies

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• GHPs can be used worldwide
• Unlike other kinds of geothermal heat, shallow
  ground temperatures are not dependent upon
  tectonic plate activity or other unique geologic
  processes.
• Thus geothermal heat pumps can be used to help
  heat and cool homes anywhere

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• How much geothermal energy is there?
• Thousands more megawatts of power than are
  currently being produced could be developed from
  already-identified hydrothermal resources.
• With improvements in technology, much more power
  will become available.
• Usable geothermal resources will not be limited
  to the "shallow" hydrothermal reservoirs at the
  crustal plate boundaries.
• Much of the world is underlain (3-6 miles down),
  by hot dry rock - no water, but lots of heat.
• Scientists have experimented with piping water
  into this deep hot rock to create more
  hydrothermal resources for use in geothermal
  power plants.
• As drilling technology improves, allowing us to
  drill much deeper, geothermal energy from hot dry
  rock could be available anywhere.
• At such time, we will be able to tap the true
  potential of the enormous heat resources of the
  earth's crust.

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Solar Power

• Renewable resource many forms including
• Direct solar energy
• architectural designs use solar energy to heat
  and cool homes
• solar panels used to heat water to drive turbines
• heliostats
• mirrors move and track the sun
• focus rays on receiver (gt 1000 C)

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• parabolic reflectors
• cylindrical reflector focuses rays on heating
  element
• photovoltaic (solar) cells to generate
  electricity
• cells contain a material that becomes unstable
  when struck by light
• emits electricity as the crystalline lattice
  reorganizes itself
• low conversion efficiency 10-12 in silicon
  cells, 4-6 in cadmium/copper cells
• AND high cost per kwh

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• Indirect solar energy - heat from solar energy
  drives other Earth systems which can be harnessed
  
• Moving water - hydroelectric power
• Biomass
• Wind

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Hydroelectric Power

• Moving water
• tides - use energy of tidal forces to drive
  turbines
• focus water flow using locks, gates
• ocean currents and waves
• difficult to concentrate (funnels/horns) and
  utilize

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• rivers - dams trap the water in a reservoir,
  force water to flow past turbines
• constructed to increase height from which water
  drops
• provides a constant flow of water through
  turbines
• 80-90 efficient in converting energy to
  electricity
• 35-40 for fossil fuels
• 30 for nuclear fuels
• Harness energy of falling water
• Require dams to create reservoirs
• In addition to power generation, also control
  flooding and water supply

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Biomass

• Energy from organisms or their remains
• wood
• agriculture - burn or compost vegetation
• urban waste - methane gas from decay, collect and
  use as natural gas
• ethyl alcohol - derived from corn, added to
  gasoline

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Wind

• Harness wind energy using "wind farms" with huge
  windmills

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Wind-electric potential 48 contiguous U.S.
states ( of each states energy need). 12 states
could provide 90 of the total U.S. energy need
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• Advantages of Solar Power (both direct and
  indirect)
• free and renewable
• mostly pollution-free
• no CO2 emissions or other pollutants - except
  biomass

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• Disadvantages - direct solar energy
• expensive - difficult to store electricity
• cost per kilowatt hour (kwh) is 5-6 times that of
  other methods but costs may decrease in the
  future
• intermittent and localized
• construction of facilities involves semiconductor
  manufacture
• mining and manufacturing hazards and costs
• large arrays affect landscape aesthetics

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• Disadvantages indirect solar energy
• dams cause numerous environmental problems to
  river systems
• sediment pollution
• change stream velocity
• inhibit fish migrations
• large projects displace humans and animals
• Three Gorges Dam, China
• dam failures result in catastrophic floods

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• windmills are eyesores, noisy, and affect media
  reception
• wood is renewable but not necessarily sustainable
  as a resource
• deforestation
• desertification
• adds greenhouse gases and other forms of air
  pollution

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Three Gorges Dam Project

• Will be the worlds largest dam
• Goals
• Power generation
• Flood control
• Improved navigation

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Artists drawing of what the finished project
will look like
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Some facts about the Three Gorges project

• Project expected to take 17 years completion
  expected in 2009.
• The Three Gorges Reservoir will inundate 632
  square kilometers (395 square miles) of land.
• An estimated 1.2 million people will be resettled
  by the dam
• The project's 26 hydropower turbines are expected
  to produce 18.2 million kilowatts, up to
  one-ninth of China's output.
• Source Chinese government

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What will it cost?

• Chinese Government estimate 25 billion
• Forced resettlement (jobs, culture, housing)
• Loss of farmland, historical sites, tourism
• Environment
• sediment pollution and erosion
• sediment-filled reservoir no flood control
  capacity
• deforestation
• altered ecosystem

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Hydrogen Fuel

• Three attractive advantages
• Abundant resource
• mostly present in molecules combined with other
  elements (i.e., H2O, CH4)
• Combustion provides large quantities of heat
• Waste products just water

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• How is hydrogen separated?
• Pass electric current through water
• Collect pure oxygen (O2) and hydrogen (H2)
• Relatively infinite supply of water, but the
  process does require electricity (fossil fuel?
  hydro? solar?)
• Usually takes more energy to separate hydrogen
  than you receive from it as a fuel.
• More of an energy carrier

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• How could it be used as an energy resource (for
  example, in automobile engines)?
• combustion (like gasoline)
• fuel cells (hydrogen and oxygen vigorously react
  to produce electricity and heat)
• electric motor in cars

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• Disadvantages
• very dangerous, highly explosive
• needs to be highly pressurized or as a liquid
• difficult to safely store and transport
• simple technology could mean on-site manufacturing