Transcript Sustainable Energy 1

Sustainable Energy
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Outline
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Conservation
 Cogeneration
Tapping Solar Energy
 Passive vs. Active
High Temperature Solar Energy
 Photovoltaic Cells
Fuel Cells
Energy From Biomass
Energy From Earth’s Forces
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CONSERVATION
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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 U.S. water use by 40 trillion
liters annually.
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Utilization Efficiencies
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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
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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
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Transportation
 Most potential energy in fuel is lost as
waste heat.
- In response to 1970’s 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 1990’s
discouraged further conservation.
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Energy Conversion Efficiencies
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Transportation
 By 2002, the average fuel economy of
America’s 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
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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
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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
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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 1970’s cogeneration had fallen to
less than 5% of our power supplies.
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TAPPING SOLAR ENERGY
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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.
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Solar Energy
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Passive Solar Heat - Using absorptive
structures with no moving parts to gather and
hold heat.
 Greenhouse Design
Active Solar Heat - Generally pump heatabsorbing 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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 up three-quarters of
that supply.
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Burning Biomass
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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
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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
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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
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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
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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
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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 EARTH’S FORCES
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Hydropower
 By 1925, falling water generated 40% of
world’s 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
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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
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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
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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
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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
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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
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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.
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Tidal and Wave Energy
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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
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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
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Conservation
 Cogeneration
Tapping Solar Energy
 Passive vs. Active
High Temperature Solar Energy
 Photovoltaic Cells
Fuel Cells
Energy From Biomass
Energy From Earth’s Forces
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