Transcript Chapter 18: Renewable Energy Alternatives

Chapter 18: Renewable Energy
Alternatives
Lesson 1: Biomass and Geothermal
Energy
 The Reasons for Alternative Energy
 Alternative energy resources are needed to
replace fossil fuels, reduce air pollution, and
reduce the emission of greenhouse gases.
 Benefits of renewable energy
• Most of them are unlikely to run out
• If renewable energy resources replace fossil fuels,
they will help decrease air pollution and
greenhouse gas emissions
• Become less dependent on other nations to supply
us with fuel
• Will create jobs for people to design, build, and
maintain the needed technology
 Renewable energy today
• Fossil fuels supply 80% of our energy
• Use of renewable energy sources is generally
growing much faster than use of nonrenewable
energy
• Currently renewable energy sources cannot yet
produce enough power to replace fossil fuels
and nuclear energy
 Biomass Energy
 Energy derived from biomass is used for cooking,
heating, powering motor vehicles, and generating
electricity.
 Biomass is material that makes up living organisms
or comes from organisms.
 Biomass energy is energy that is produced from this
material
 More than 1 billion people still burn wood from
trees as their main energy source
 Wood, charcoal, and manure account for 35% of
energy use in developing nations
 Biomass energy can now power motor vehicles and
generate electricity
 Biofuels
• Liquid fuels from biomass sources are known as
biofuels
• Ethanol
oProduced by the fermentation of starches or
sugars
oUsed in gasoline engines
oIn the US it is mainly produced from corn
oA blend of gasoline and alcohol called
gasohol is widely used in the US because it
releases smaller amounts of many
pollutants
• Biodiesel
oProduced from vegetable oil
oCan be used in its pure form, but is usually
mixed with conventional petroleum-based
diesel fuel
oCuts down on emissions
 Biopower
• Electricity that is generated by the combustion of
biomass is called biopower.
• Many of the sources used for biopower are the
waste products of existing industries or processes
such as sawdust and cornstalks.
• The decomposition of biomass by microorganisms
produces gas that can be used to generate
electricity.
• The methane produced in landfills, called “landfill
gas,” is captured and sold as fuel.
 Benefits of biomass energy
• The carbon produced by the combustion of
biomass is the same amount of carbon that was
removed from the atmosphere by
photosynthesis to make the biomass in the first
place.
• Biomass is distributed worldwide
• Help reduce dependence on imported fuels
 Costs of biomass energy
• Biofuel crops take up land that might be used for
growing food or left in its natural condition
• Deforestation, soil erosion, and desertification can
result if wood is cut down too rapidly for fuel
• Can cause indoor air pollution and increases the
risk of respiratory system problems.
• Corn ethanol provides only a small amount more
energy than the energy needed to produce it.
 Geothermal Energy
 Steam and hot water produced by geothermal
energy can be used for generating electricity
and for heating
 Deep beneath the surface of Earth, high
pressure combined with the breakdown of
radioactive elements produces heat –
geothermal energy.
 Hot springs and geysers are the result of
geothermal energy
 Harnessing geothermal energy
• Steam from geysers at the surface is used to
supply energy
• Usually wells must be drilled down hundreds or
thousands of meters toward heated rocks and
water
 Generating electricity
1. Magma heats ground water
2. Wells tap underground heated water or
steam
3. Steam turns turbines and generates power
4. Steam is cooled and condensed
5. Water is returned back into the aquifer
• Some geothermal plants will pump cold water
deep underground where it reaches heated
rocks and turns into steam
 Hot groundwater can be used directly for
heating homes, offices, and greenhouses
 A ground source heat pump takes advantage of
the fact that the temperature of soil a few feet
underground stays the same all year.
• In the winter, the water in the pipes picks up heat
from the ground and transfers it to a building
• In the summer, the water in the pipes transfers
heat from the house to the ground.
 Benefits and costs of geothermal energy
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Can help replace the use of fossil fuels
Causes less air pollution
Releases smaller quantities of greenhouse gases
Sources may not always be truly sustainable
The water of many hot springs contains chemicals
that damage equipment and add to pollution
• Some geothermal energy projects may trigger
earthquakes
• Limited to areas where heated groundwater is
easily accessible
Lesson 2: Hydropower and Ocean
Energy
Generating Electricity with Hydropower
 The movement of river water can be used
to generate electricity
 In hydropower, or hydroelectric power, we
use the kinetic energy of moving water to
turn turbines and generate electricity.
 In the US 6% of the electricity is generated
by hydropower
 Using water stored behind dams
• A dam blocks a river and water is stored in a
reservoir behind the dam
• As the river water passes through the dam, the
water turns the blades of a turbine which cause
generators to produce electricity
• Most hydropower is generated by dams
 Using the natural flow of a river
• Called the run-of-the-river approach
• Some of the river water is diverted through a
pipe, which carries the water to the turbines.
• This method does not disturb natural habitats
as much
• When the river is low, little electricity is
produced
Benefits and Costs of Hydropower
 Hydropower is nonpolluting and relatively
inexpensive, but dams can harm
ecosystems and disrupt people’s lives.
 Most of the rivers that offer the best
opportunity for hydropower are already
dammed.
 Benefits
• Renewable resource
• Considered “clean” because nothing is burned
• Does not pollute the atmosphere or release
greenhouse gases
• Relatively inexpensive
• Dams can also control floods
 Costs
• Drastically change ecosystems
• Interrupts the natural flow of water
• Negative impact on fish populations
• Dam construction can cause damages to the
landscape, erosion, and landslides
• Dams can prevent important sediments and
nutrients from getting downstream
 Three Gorges Dam
• On China’s Yangtze River
• Completed in 2008
• Generates enough hydropower to replace dozens of
large coal and nuclear plants
• Controls floods and enables boats to travel farther
upstream
• Cost $26 billion to build
• Flooded many cities, destroyed the homes of 1.3
million people, and flooded 10,000 year-old
archeological sites.
• Rising water has destroyed farmlands and wildlife
habitats.
Energy From the Ocean
 The movement of tides and ocean thermal
energy can be used to generate electricity
 Tidal Energy
• The term tidal energy refers to using the
movement of tidal water to generate electricity
• Twice a day, as ocean tides rise and fall, large
amounts of water move upward and then draw
back
• In one method, a dam is built across a bay or tidal
river
oAs the tide rises, water moves through the dam
and enters the bay and as the water from the
receding tide passes through the dam it is
channeled through a system of turbines.
• Harnessing tidal energy works best in long, narrow
bays such as Alaska’s Cook Inlet or the Bay of Fundy
in Canada because the differences in height
between high and low tides are especially great.
• Tidal electricity stations have the benefit of
releasing few or no pollutants
• Can harm the ecology of the bay or river
• There are few places where tidal energy can be
harnessed effectively
 Thermal energy from the ocean
• Each day, ocean water near the equator
absorbs radiation from the sun
• Ocean thermal energy conversion (OTEC) is a
process that converts the thermal energy in
ocean water to electrical energy that people
can use.
• The natural temperature gradient in ocean water is
used to generate electricity
oWarm surface water circulates around pipes
that contain substances that boil at
temperatures that are lower than the boiling
point of water.
oThe heat from the water makes the substance
evaporate and the gas spins turbines to
generate electricity.
oCold water piped in from the ocean depths then
condenses the gas so it can be used again.
• Costs remain high
Lesson 3: Solar and Wind Energy
 Harnessing Solar Energy
 The sun’s energy can be used to heat buildings
and generate electricity
 The sun provides energy for almost all life
processes on Earth
 Using sunlight directly, without involving
mechanical or electrical devices is called
passive solar heating
• Involves designing a building to collect, store, and
distribute the sun’s energy naturally
• Greenhouses and homes that are designed with
windows that face south and east to capture
sunlight in winter are using passive solar heating
 An active solar heating system uses
technology to collect, move, and store heat
derived from the sun.
• A flat-plate solar collector generally consists of
a black, heat-absorbing metal plate in a flat
box with a glass cover and has a long tube
running through it
oSunlight passes through the glass and heats
the metal plate and the fluid in the tube
absorbs heat from the metal plate
• In a photovoltaic (PV) cell, solar energy is
converted directly into electricity.
oContain two plates typically made of silicon
oOne plate is rich in electrons and when sunlight
strikes this plate it knocks some electrons loose
which are then attracted to the other plate
oThe flow of electrons creates an electric current
oPV cells can be arranged in panels or contained
in special roofing tiles
• Concentrating solar power (CSP) is a technology
that uses mirrors to focus sunlight in order to
generate electricity.
oA “power tower” has hundreds of mirrors
positioned in a large area surrounding a tall
tower that houses a receiver.
o Heated fluid in the receiver is used to produce steam
which turns the blades of a turbine and powers a
generator.
Benefits and Costs of Solar Power
 Solar power has many benefits, such as its
limitless supply, but it depends on weather
and is currently expensive
 Benefits
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Endless source
Technology uses no fuel
Quiet and safe technology
No greenhouse gases released
Requires little maintenance
Reduces dependence on power plants
Possible to sell excess solar electricity to power
companies
• Creating many new jobs
 Costs
• Manufacturing solar-energy devices creates
some pollution
• Some regions are not sunny enough to provide
much solar power
• Solar equipment is expensive
 Harnessing Wind Power
 Wind turbines convert wind’s kinetic energy
into electrical energy
 People have used wind power for thousands of
years with windmills
 A wind turbine is a device that converts the
wind’s kinetic energy into electrical energy
• Wind blowing into a turbine turns blades that
connect to a gearbox which connects to a
generator that produces electricity.
 Wind turbines are often built in groups
called wind farms
 Average wind speeds are approximately
20% greater over water than over land
 Offshore wind turbines are becoming more
common even though costs to erect and
maintain wind turbines in water are higher.
Benefits and Costs of Wind Power
 Wind power is nonpolluting and efficient,
but its supply is unpredictable and it may
damage the landscape and wildlife.
 Benefits
• Does not cause pollution
• Highly efficient
• Wind farms are less expensive than fossil fuel
power plants once they are up and running
 Costs
• Wind farm startup costs are generally higher than
those of fossil fuel power plants
• We have no control over when wind will occur –
unpredictable
• Some areas are windier than others
• When wind farms are proposed near communities,
the people living in the area often oppose them
oClutter the landscape
oToo noisy
• Birds and bats can be killed
Lesson 4: Energy From Hydrogen
 Producing Hydrogen Fuel
 Hydrogen fuel can be produced from the
breakdown of water or other hydrogencontaining compounds
 In electrolysis, water molecules are broken
down into oxygen gas (O2) and hydrogen gas
(H2) by an electric current that runs through
the water
• 2H2O → 2H2 + O2
• Does not emit greenhouse gases or pollutants
• A costly process
 Hydrogen can be extracted from the
breakdown of methane in natural gas.
• CH4 + H2O → 4H2 + CO2
• Less expensive
• Produces a greenhouse gas
 Scientists are investigating other ways to
obtain hydrogen
• The heat given off by a nuclear reactor may be
used to split water into hydrogen and oxygen
• Algae may be used to produce hydrogen
 Benefits
• Hydrogen is the most abundant element in the
universe
• Produces few greenhouse gases or pollutants
• Water and heat may be the only waste
products generated
• Can be stored and transported
 Costs
• Can catch fire if not stored properly
• Requires energy inputs
• Expensive to produce
• To be useful in a motor vehicle, hydrogen needs
to be compressed
Fuel Cells
 Fuel cells are used to generate electricity
 Hydrogen gas can be used to produce
electricity within fuel cells
 A fuel cell has a positive electrode and a
negative electrode and reactions in a fuel
cell result in an electric current
• Uses the reverse of the reaction for electrolysis
o2H2 + O2 → 2H2O
• Hydrogen gas enters the side of the cell with
the negative electrode and each molecule then
splits into two positively charged hydrogen ions
(H+)
• Oxygen gas enters the cell on the side with the
positive electrode
• A series of reactions cause an electric current
to flow from the negative terminal to the
positive terminal and while this happens the
oxygen and hydrogen ions combine to form
molecules of water
 A fuel cell can be used in many ways such as
powering vehicles and producing electricity.