Transcript Chapter 18 Renewable Energy 18

Chapter 18 Renewable Energy
18-1 Renewable Energy Today
Renewable Energy: from sources that are
constantly being formed (ex. solar, wind, moving
water, Earth’s heat)
I. Solar Energy – Power from the Sun
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Passive Solar Heating: uses the sun’s energy to
heat something directly
– Passive Solar Homes
– Large south-facing windows
– Well insulated
– Overhanging roof
 -summer = sun’s path is high in the sky
(roof provides shade)
 -winter – sun’s path is lower in the sky
(sunlight can shine into the home)
Passive Solar Home
Active Solar Heating: energy from
the sun is gathered by collectors and
used to heat water or to heat a building
Photovoltaic Cells
Photovoltaic Cells: solar cells –
convert sun’s energy into electricity
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Produces a very small electrical current
A small city would need hundreds of acres of
solar panels
Require extended periods of sunshine
Energy has to be stored in batteries or fed
back into the grid (net-metering)
Becoming increasingly efficient & less
expensive
Great potential in developed countries, where
energy consumption is minimal
Wind Farm
II. Wind Power – Cheap &
Abundant
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Wind moves a turbine to generate electricity
Fastest growing energy source in the world
Wind Turbines are cost effective and can be built in 3
months
Wind Farms: large arrays of wind turbines
Turbines take little space
– Some farmers add wind turbines to their land and sell
the electricity
An underdeveloped resource – scientists estimate
that the windiest spots on Earth could generate more
than 10 times the energy used worldwide
Problem = transporting electricity from rural areas
where it is generated to urban centers
III. Biomass – power from living
things
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Biomass fuel: any organic matter that is used as an
energy source (plant material, manure, etc.)
Fossil fuels don’t count because they are
nonrenewable
Wood & Dung are major sources of energy in
developing countries
Although wood is renewable – it can result in habitat
loss, deforestation, and soil erosion if trees are cut
down faster than they can grow
Burning wood & dung can release harmful air pollution
Biofuels
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Methane: produced when bacteria decompose
organic wastes
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Burn it to make heat / electricity
China ferments manure to make gas for heating & cooking
Britain opened a dung-fired power plant in 2002
Some landfills generate electricity w/ methane made from
decomposing trash
Alcohol
Ethanol – made by fermenting fruit or agricultural
waste
Corn is a major source in the US
Gasohol: gasoline + ethanol
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produces 28% less emissions than fossil fuels, but
produces 38% less energy
DAM
IV. Hydroelectricity – Power
from Moving Water
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Hydroelectric Energy: produced from moving
water
– Dam is built across a river to hold back a reservoir
of water
– Water is released to turn a turbine
– Turbine spins a generator to produce electricity
DAM
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Benefits:
– Expensive to build, but inexpensive to operate & last longer
than fossil-fuel powered plants
– No air pollutants
– Flood control
– Water for drinking, agriculture, industry, recreation
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Disadvantages:
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Changes a river’s flow
Reservoir floods large areas of habitat above the dam
People are often displaced
Water flow below the dam is reduced – disrupting
ecosystems downstream
– Prevents salmon from swimming upriver to spawn
– As river slows, it deposits sediment behind the dam instead
of enriching the land farther downstream
– Plant matter decaying in reservoirs can release large
amounts of greenhouse gasses
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Modern Trends - Micro-hydropower
– Electricity produced in a small stream w/out a
big dam
– Turbine may even float and not block the river
at all!
V. Geothermal Energy – Power from
the Earth
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Energy from heat in the Earth’s crust
In some areas, deposits of water in the Earth’s
crust are heated by energy within the Earth
Geothermal Power Plants pump heated
water or steam from rock formations and use
the water or steam to power a turbine – the
water is usually returned to the crust
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Geothermal Heat Pumps: Energy
for Homes
– Temp. of the ground is nearly constant
year-round
– Geothermal heat pump – uses stable
underground temp. to warm and cool
homes
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Simply a loop of piping that circulates a fluid
underground
18-2 Alternative Energy and Conservation
Alternative Energy: energy sources that are
still in development
 Must be
– Cost effective
– Acceptable environmental effects
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Government investment is often the only way
to research some of these possibilities.
Tidal Power
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Works like a hydroelectric dam
Tide rises, water flows behind a dam
 Sea level falls trapping water behind the dam
 Reservoir is released to turn a turbine
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Used in France, Russia, and Canada
Pros: renewable, non-polluting
Cons: high cost of building and maintaining,
few locations are suitable
Ocean Thermal Energy Conversion (OTEC)
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Warm surface water used to
boil sea water (boils at low
temp. at low pressure in a
vacuum chamber)
Steam turns turbine
Deep, cold ocean water cools
the steam to make reusable
water
not cost effective (so far)
environmental effects
unknown
Hydrogen – A Future Fuel Source?
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The most abundant element in the universe
Can be burned as a fuel
Does not release pollutants associated w/ burning fossil fuels and biomass
When hydrogen is burned, it combines with oxygen to produce water vapor
and small amounts of nitrogen oxides
Can be produced by using electricity to split molecules of water
The Challenge of Hydrogen:
 Takes a lot of energy to produce
 1 alternative: use electricity from solar cells or wind power to split water
molecules to produce hydrogen then store it in pressurized tanks and
transport it in pipelines
Fuel Cells: produces electricity chemically (like a battery)
 Combines hydrogen fuel w/ oxygen from the air
 Electricity is produced
 Water is the only byproduct
 Can be fueled by anything that contains plenty of hydrogen (natural gas,
alcohol, gasoline)
 Soon portable electronics (phones, games) may be powered by micro-fuel
cells (fueled w/ alcohol)  no charging or changing batteries 
Energy Efficiency: the percentage of energy
put into a system that does useful work
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Energy efficiency (in %) = energy out/energy in X 100
Efficient Transportation
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Developing efficient engines
Increasing the use of public
transportation systems
Hybrid Cars
Energy-efficient vehicles currently in use
 Use a small, efficient gasoline engine most of the time
 Also use an electric motor when extra power is needed (i.e.
accelerating)
 Converts some of the energy of braking into electricity (stored
in battery)
 Sometime shut off the gasoline engine (i.e. when stopped at a
red light)
 Cost less to refuel
 Produce less harmful
Emissions
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VIDEO
Cogeneration: the production of 2 useful forms of
energy from the same fuel source
 i.e. waste heat from an industrial furnace can power a
steam turbine that produces electricity
Energy Conservation: saving energy
 Using energy-efficient devices, wasting less energy
 Using less of any resource usually translates into
saving energy
 Most of the energy lost from homes is lost through
poorly insulated windows, doors, walls, and the roof
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Replace old windows w/ new high efficiency windows
Seal gaps around doors and windows with caulking or weather
stripping
Ways to Save Energy Around The House