Sustainable Energy 1
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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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