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Sustainable Energy. Chapter 22. Outline:. Conservation Cogeneration Tapping Solar Energy Passive vs. Active High Temperature Solar Energy Photovoltaic Cells Fuel Cells Energy From Biomass Energy From Earth’s Forces. CONSERVATION. Utilization Efficiencies

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sustainable energy

Sustainable Energy

Chapter 22

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

outline
Outline:
  • Conservation
    • Cogeneration
  • Tapping Solar Energy
    • Passive vs. Active
  • High Temperature Solar Energy
    • Photovoltaic Cells
  • Fuel Cells
  • Energy From Biomass
  • Energy From Earth’s Forces

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

conservation
CONSERVATION
  • Utilization Efficiencies
    • Most potential energy in fuel is lost as waste heat.
      • In response to 1970’s oil prices, average US automobile gas-mileage increased from 13 mpg in 1975 to 28.8 mpg in 1988.
        • Falling fuel prices of the 1980’s discouraged further conservation.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

utilization efficiencies
Utilization Efficiencies
  • Today’s 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 US water use by 40 trillion liters annually.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

energy conversion efficiencies
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

energy conversion efficiencies1
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

negawatt programs
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

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

cogeneration
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 US came from plants also providing industrial steam or district heating.
        • By 1970’s cogeneration had fallen to less than 5% of power supplies.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

tapping solar energy
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 earth’s 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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

average daily solar radiation
Average Daily Solar Radiation

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

solar energy
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 US domestic energy budget.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

solar energy1
Solar Energy
  • Eutectic Chemicals are also used to store large amounts of energy in a small volume.
    • Heating melts the chemicals and cooling returns them to a solid state.
      • Most do not swell when they solidify and undergo phase changes at higher temperatures than water and ice.
        • More convenient for heat storage.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

high temperature solar energy
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

promoting renewable energy
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

photovoltaic solar energy
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
      • 2001 - $5 / watt

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

energy costs
Energy Costs

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

photovoltaic cells
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.
    • Invention of amorphous silicon collectors has allowed production of lightweight, cheaper cells.
      • Currently $100 million annual market.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

storing electrical energy
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuel cells
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuel cells1
Fuel Cells

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuel cells2
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuel cells3
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuel cell types
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuel cell types1
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

energy from biomass
ENERGY FROM BIOMASS
  • Plants capture about 0.1% of all solar energy that reaches the earth’s 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 of three-quarters of that supply.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

burning biomass
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuelwood crisis
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

fuelwood crisis1
Fuelwood Crisis
  • Currently, about half of worldwide annual wood harvest is used as fuel.
    • Eighty-five percent of fuelwood harvested in developing countries.
      • By 2025, worldwide demand for fuelwood is expected to be twice current harvest rates while supplies will have remained relatively static.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

wood harvest
Wood Harvest

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

slide30
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

methane
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

anaerobic fermentation
Anaerobic Fermentation

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

wind energy
Wind Energy
  • Estimated 20 million MW of wind power could be commercially tapped worldwide.
    • Fifty times current nuclear generation.
      • Typically operate at 35% efficiency under field conditions.
        • When conditions are favorable (min. 24 km/hr) electric prices typically run as low as 3 cents / KWH.
          • Standard modern turbine uses only two or three blades in order to operate better at high wind speeds.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

wind energy1
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

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

geothermal energy
Geothermal Energy
  • High-pressure, high-temperature steam fields exist below the earth’s 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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

tidal and wave energy
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

tidal power
Tidal Power

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

ocean thermal electric conversion
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.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

summary
Summary:
  • Conservation
    • Cogeneration
  • Tapping Solar Energy
    • Passive vs. Active
  • High Temperature Solar Energy
    • Photovoltaic Cells
  • Fuel Cells
  • Energy From Biomass
  • Energy From Earth’s Forces

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.