Sustainable Energy

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Sustainable Energy
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Outline

• Conservation
• Cogeneration
• Tapping Solar Energy
• Passive vs. Active
• High Temperature Solar Energy
• Photovoltaic Cells
• Fuel Cells
• Energy From Biomass
• 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
  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.

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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

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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.

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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.

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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.

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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.

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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

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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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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
• 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.

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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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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.

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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
• 2003 - 5 / 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 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.

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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.

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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.

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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.
• 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.

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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 to about
  1.23 volts/cell.
• Fuel cells can be stacked together until the
  desired power level is achieved.

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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.

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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.

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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.
• Renewable energy resources account for 18 of
  total world energy use, and biomass makes up
  three-quarters of that supply.

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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.

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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.
• Problem intensifies as less developed countries
  continue to grow.
• For urban dwellers, the opportunity to scavenge
  wood is generally nonexistent.

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Fuelwood Crisis

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

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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.

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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.

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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.

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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.

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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.

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Dam Drawbacks

• 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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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.

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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.

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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.

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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.

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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.
• Main worries are saltwater flooding behind the
  dam and heavy siltation.
• Stormy coasts with strongest waves are often far
  from major population centers.

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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.
• Need temperature differential of about 20o C
  between warm upper layers and cooling water.

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WHATS OUR ENERGY FUTURE ?
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Summary

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

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