Ch 20 Sustainable Energy

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• Ch 20 Sustainable Energy

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Ch 20 Outline

• 20.1 Conservation
• Cogeneration
• 20.2 Tapping Solar Energy
• Passive vs. Active
• 20.3 High Temperature Solar Energy
• Photovoltaic Cells
• 20.4 Fuel Cells
• 20.5 Energy From Biomass
• 20.6 Energy From Earths Forces

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Conservation

• Utilization Efficiencies
• Todays average new home uses half the fuel
  required in a house built in 1974.
• Reducing air infiltration is usually the most
  effective way of saving household energy.
• According to new national standards
• New washing machines will have to use 35 less
  water.
• Will U.S. cut water use by 40 trillion liters
  annually and save enough electricity every year
  to light all the homes in the U.S.?

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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 so have passive solar gains in
  winter and shade from trees in summer
• Turn off appliances on standby - TV, printer,
  computer

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Standby Energy Consumption
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Energy Conversion Efficiencies

• Energy Efficiency is a measure of energy produced
  compared to energy consumed.
• Thermal conversion machines such as steam
  turbines can turn no more than 40 of energy in
  primary fuel into electricity or mechanical power
  due to waste heat.
• We could be recapturing the heat and using it for
  space heating
• Fuel cells can theoretically approach 80
  efficiency using hydrogen or methane.

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Energy Conversion Efficiencies

• Transportation
• Raising average fuel efficiency in U.S. by 3
  miles per gallon would save more oil than the
  maximum expected production from drilling in
  Arctic Wildlife Refuge.
• There are now more vehicles in the U.S. than
  there are licensed drivers.
• In the 1970s, when oil prices rose, U.S. doubled
  auto gas mileages. Reached 25.9 mpg in 1988 but
  now down to 22.1 mpg.

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Energy Conversion Efficiencies

• Transportation
• For short trips, could walk or bicycle
• Could buy high efficiency mini car that gets 60
  mpg like the one shown in photo
• Could buy hybrid gasoline electric car

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Transportation Efficiencies

• Could buy plug in hybrid car which recharges
  batteries from household current at night
• Electricity costs the equivalent of 50 cents per
  gallon
• Need to generate more electricity but could
  capture pollutants at the plant
• Could buy diesel. A diesel sold in Europe
  currently gets 150 mpg.
• A diesel plug in hybrid could make the U.S.
  entirely independent from imported oil.

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Transportation Efficiencies

• Fuel-cell powered vehicles are being developed
  which use hydrogen gas as fuel.
• Produce water as their only waste product
• Will take at least twenty years to come to market
• Most hydrogen is currently created from natural
  gas, making it no cleaner or more efficient than
  burning the gas directly.
• Governments in U.S. and Europe are spending
  billions on this.

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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 power supplies.

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Cogeneration

• Interest is being renewed
• District heating systems are being rejuvenated.
• Plants that burn municipal waste are being
  studied.
• Combined cycle coal gasification plants may be
  used in urban locations.
• Apartment building-sized power generating units
  are being built that use methane, diesel or coal.

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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.

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Solar Energy

• Passive Solar Heat - using absorptive structures
  with no moving parts to gather and hold heat
• Greenhouse Design

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• Active Solar Heat - 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. A flat panel of 5 m2 can provide
  hot water for family of 4.

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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.

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Parabolic Mirrors
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Solar Energy

• Only solar power tower in U.S. is in Southern
  California. It generates enough electricity for
  5,000 homes at cost far below oil or nuclear
  power.
• If entire U.S. used solar towers, it would take
  up an area half the size of South Dakota (but
  less land than will be strip mined in next 30
  years to get coal).
• Parabolic mirrors or solar box cookers can also
  be used for home cooking in tropical countries.

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Solar Cooker

• An inexpensive insulated box with a black
  interior and a clear plastic lid can serve as a
  solar cooker. Helps reduce deforestation and
  avoids health risks from smoky cooking fires in
  tropical countries.

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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
• 2007 - 2.50 / watt
• 2009 - 1.00 / watt

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Photovoltaic Cells

• During the past 25 years, efficiency of energy
  capture by photovoltaic cells has increased from
  less than 1 of light to more than 15 in field
  conditions and over 75 in the laboratory.
• Invention of amorphous silicon collectors has
  allowed production of lightweight, cheaper cells.
• Roof tiles with photovoltaic cells can generate
  enough electricity for a home.
• At least 2 billion people now live without
  electricity. This could be a solution to their
  problems.

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Storing Electrical Energy

• Electrical energy storage is difficult and
  expensive.
• Lead-acid batteries are heavy (3-4 tons) 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.

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Fuel Cells

• Fuel Cells - use ongoing electrochemical
  reactions to produce electric current.
• Cathode () and anode (-) separated by
  electrolyte which allows ions to pass, but is
  impermeable to electrons
• Hydrogen passed over anode where a catalyst
  strips an electron
• Electrons pass through external circuit, and
  generate electrical current.
• Hydrogen ion passes to cathode where it is united
  with oxygen to form water.

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Fuel Cell
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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. Oxygen comes from air.
• Fuel cells run on pure oxygen and hydrogen, and
  produce no waste products except drinkable water
  and radiant heat.

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Fuel Cells

• Typical fuel cell efficiency is 40-45.
• Current is proportional to the size of the
  electrodes, while voltage is limited (1.23
  volts/cell).
• Fuel cells can be stacked until the desired power
  level is achieved. A fuel cell stack that could
  provide all the electricity for a home would be
  about the size of a refrigerator.

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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.
• Biomass resources include wood, wood chips, bark,
  leaves and starchy roots.

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Burning Biomass

• Wood provides less than 1 of U.S. 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.
• Clean burning woodstoves are available but
  expensive, produces fewer sulfur gases than coal.
  

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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.
• Gathering wood is work of women and children and
  in some places it now takes 8 hours to get to
  supply and even longer to walk back with wood
  that will last only a few days.

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Fuelwood Crisis

• In cities, people must pay high prices for wood,
  as much as 25 of household income.
• By 2025, if current trends continue, the demand
  is expected to be twice current harvest rates
  while supply will stay steady.
• In some African nations, demand is already ten
  times the sustainable yield.

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Dung

• Where other fuel is in short supply, people often
  dry and burn animal dung.
• Downside not returning animal dung to land as
  fertilizer reduces crop production and food
  supplies.

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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. This
  could be burned for electricity.

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Anaerobic Production of Methane
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Methane

• Cattle feedlots and chicken farms are a
  tremendous potential fuel source since wastes
  contain more energy than all the nations farmers
  use.
• Haubenschild dairy farm uses manure to generate
  all their electricity. In January 2001, the farm
  saved 35 tons of coal, 1,200 gallons of propane,
  and made 4,380 selling electricity.

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Alcohol from Biomass

• Ethanol or methanol made from plant materials or
  diesel made from vegetable oils or animal fats
• Gasohol - mixture of gasoline and ethanol
• Ethanol in gasohol makes gasoline burn cleaner
  and most states require that 5 to 10 be added
  to gasoline.
• Most ethanol now made from grain but can be made
  from any cellulosic material such as wood chips
  or straw.

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Alcohol from Biomass

• Brazil is worlds leader in alcohol from biomass,
  mostly sugarcane waste.
• Ethanol production growing rapidly in the U.S.
  but use of corn for fuel has increased corn
  prices by 50. Since corn is used as animal
  feed, meat, milk and egg prices have risen.
• U.S. has 5 million flex fuel vehicles now
• Increasing fuel economy by 12 would reduce oil
  consumption just as much as use of ethanol and
  save 10 billion in subsidies.

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Alcohol from Biomass

• Energy crops - such as switch grass, cattails and
  hybrid poplars could be grown on marginal lands
  specifically as energy source.
• Low-input high-diversity fuels - mix of native
  prairie perennial species which grow well in dry,
  low nitrogen conditions and which could be
  harvested for fuel

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Fuel from Biomass

• Water is a worry when using ethanol as a biofuel.
• It takes 3 to 6 liters of water to produce a
  liter of ethanol and in many of plains states
  there is not enough water to produce both food
  and fuel.
• Biodiesel can be made from almost anything
  organic such as fat from meat or vegetable oil.
  European Union already consumes 1 billion gallons
  of biodiesel.

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Energy from Earths Forces

• Hydropower
• In 1925, falling water generated 40 of worlds
  electric power.
• Hydroelectric production capacity has grown
  15-fold but fossil fuel use has risen so rapidly
  that hydroelectric only supplies 20 of
  electrical generation.
• Untapped potential for hydropower in Latin and
  Central America, Africa, India and China

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Dams

• Much of hydropower in recent years has been from
  enormous dams
• Human Displacement
• Ecosystem Destruction
• Wildlife Losses
• Large-Scale Flooding due to Dam Failures
• Sedimentation
• Herbicide Contamination
• Evaporative Losses
• Nutrient Flow Retardation

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Dams

• Rotting of submerged vegetation kills fish,
  acidifies water, produces greenhouse gases
• Schistosomiasis - human disease caused by
  parasitic fluke that lives in snails, which like
  the slow moving water behind dams
• Indigenous peoples lose their lands

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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-Hydro Generators - small versions designed
  to supply power to single homes
• Government subsidies for small scale hydropower
  resulted in abuse of water resources e.g.
  diverting small streams

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Wind Energy

• Estimated 80 million MW of wind power could be
  commercially tapped worldwide.
• Five 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.

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Wind Power

• no fuel costs or emissions
• generates income for farmers who rent land for
  turbines or sell electricity BUT
• intermittent source
• not enough wind everywhere
• bird mortality
• power lines needed to transmit the electricity

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Wind Resources in the U.S.
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Geothermal Energy

• Geothermal Energy - tap energy from hot springs,
  geysers
• Few places have geothermal steam, but can use
  Earths warmth everywhere by pumping water
  through buried pipes using heat pumps
• Deep wells for community geothermal systems are
  being developed.
• Heat from Earths crust is never exhausted

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Geothermal Energy
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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
• Pelamis wave power generator - snakelike machine
  points into waves and undulates up and down,
  which pumps fluid to hydraulic motors that drive
  electrical generators. Cables carry power to
  shore.

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• The world's first commercial-scale and
  grid-connected tidal stream generator SeaGen
  in Strangford Lough.8 The strong wake shows the
  power in the tidal current

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Pelamis Wave Converter
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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.
• Cold water is then pumped from the depths to
  condense the ammonia again.
• Need temperature differential of about 20o C
  between warm upper layers and cooling water.

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Ideal Scenario for World Energy Consumption 2100