Conventional vs Sustainable Energy - PowerPoint Presentation

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Conventional

vs

Sustainable Energy

ResourcesSlide2

This lecture will help you understand:

Reasons for seeking alternative fuels

Contributions to world energy by alternative fuelsNuclear energy The social debate over nuclear powerBioenergyHydroelectric powerSlide3

Central Case: Sweden’s search for alternative energy

In 1980, Sweden’s people voted to phase out nuclear energy

The government has promoted hydroelectric, biomass, and wind powerSweden will still use nuclear power instead of fossil fuelsPublic support for nuclear power has increasedSlide4

Alternatives to fossil fuels

Our global economy is powered by fossil fuels

These fuels also power ⅔ of electricity generation Fossil fuels are limited and pollute

We need to shift to resources that are less easily depleted and environmentally gentlerSlide5

Conventional alternatives

We have alternatives to fossil fuels

They are renewable and less polluting and harmful But they are more expensive in the short term when external costs are not included in market pricesThe most widely used “conventional alternatives” to fossil fuels:Nuclear, hydroelectric, and biomass energyThey exert less environmental impact

These are intermediates along a continuum of renewability Slide6

The U.S. relies on fossil fuels

The U.S. relies more on fossil fuels and nuclear power than other countries

Conventional alternatives play minor, yet substantial, roles

The use of conventional alternatives has been growing more slowly than fossil fuelsSlide7

Nuclear power

Nuclear energy occupies an odd and conflicted position in our debate over energy

It is free of air pollution produced by fossil fuelsYet it has been clouded by weaponry, waste disposal, and accidentsPublic safety concerns have led to limited developmentThe U.S. generates the most electricity from nuclear powerBut only 20% of U.S. electricity comes from nuclear

France gets 76% of its electricity from nuclear power

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Fission releases nuclear energy

Nuclear energy

= the energy that holds together protons and neutrons within the nucleus of an atom Nuclear fission = the splitting apart of atomic nucleiThe reaction that drives the release of nuclear energy in power plants

This chain reaction keeps a constant output of energy

Nuclei of large atoms are bombarded with neutrons, releasing energy and neutronsSlide9

Nuclear energy comes from uranium

Nuclear reactors

= facilities within nuclear power plants Nuclear fuel cycle = the process that begins when uranium is minedRadioisotopes = emit subatomic particles and high-energy radiation as they decay into lighter radioisotopesThey become stable isotopes

Uranium-235 decays into lead-207

Uranium is used for nuclear power because it is radioactiveSlide10

Nuclear reactors use uranium-235

Over 99% of uranium occurs as uranium-238 (

238U)It does not emit enough neutrons for a chain reactionSo we use 235U, with a half-life of 700 million years

235

U is enriched to 3% and formed into pellets (UO

2

)

Which are incorporated into fuel rods used in nuclear reactors

After several years in a reactor, uranium is depleted

The fuel no longer generates enough energy

Spent fuel can be reprocessed, but it is expensive

So it is disposed of as radioactive wasteSlide11

Fission in reactors generates electricity

A

moderator = a substance (water or graphite) that slows the neutrons bombarding uranium Allows fission to begin in a nuclear reactorExcess neutrons must be soaked up

Control rods

= a metallic alloy that absorbs neutrons

They are placed into the reactor among the water-bathed fuel rods

They are moved into and out of the water to control the rate of the reactionSlide12

A nuclear power plant

The reactor core is housed in a reactor vessel

The vessel, steam generator, and plumbing are located in a containment buildingContainment buildings are constructed to prevent leaks of radioactivity due to accidents or natural catastrophesNot all nations require containment buildingsSlide13

A typical light water reactorSlide14

Breeder reactors make better use of fuel

Breeder reactors

use 238U (normally a waste product)A neutron is added to 238U to form 239Pu (plutonium)

They make better use of fuel, generate more power, and produce less waste

But breeder reactors are more dangerous than conventional reactors

Its highly reactive coolant raises the risk of explosions

Plutonium can be used in nuclear weapons

They also are more expensive

Most of the world’s breeder reactors have been closedSlide15

Fusion remains a dream

Nuclear fusion

= forces together small nuclei of lightweight elements under extremely high temperature and pressureDrives the sun’s output of energy and hydrogen (thermonuclear) bombsIf we could control fusion, we could produce vast amounts of energy from water

Tremendous energy is released when deuterium and tritium are fused to form heliumSlide16

Nuclear power delivers energy cleanly

Nuclear power helps us avoid emitting 600 million metric tons of carbon each year

Power plants pose fewer health risks from pollutionThey are safer for workers than coal-fired plantsUranium mining damages less land than coal miningDrawbacks of nuclear power:

Nuclear waste is radioactive

If an accident or sabotage occurs, the consequences can be catastrophic

The world has 436 operating nuclear plants in 30 nations Slide17

Coal versus nuclear powerSlide18

Nuclear power poses small risks, but…

It poses the possibility of catastrophic accidents

The most serious accident in the U.S. = Three Mile Island in Pennsylvania in 1979

Meltdown

= coolant water drained from the reactor

Temperatures rose inside the reactor core …

Melting the metal surrounding the fuel rods …

Releasing radiation

The emergency could have been far worse Slide19

Chernobyl was the worst accident yet

1986 explosion at the Chernobyl plant in Ukraine

The most severe nuclear plant accident ever seen It was due to human error and unsafe designFor 10 days, radiation escaped while crews tried to put out the fire

More than 100,000 residents were evacuated

The landscape for 19 miles still remains contaminated

The accident killed 31 people directly

Thousands more became sick or developed cancer

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The Chernobyl accident

The destroyed reactor was encased in a massive concrete sarcophagus, which is still leaking radioactive materialSlide21

Radioactivity from Chernobyl spread widely

Atmospheric currents carried radioactive fallout from Chernobyl across much of the Northern HemisphereSlide22

Smaller-scale accidents have occurred

Western reactors are safer than Chernobyl

But smaller accidents have occurredA 1999 accident in Japan killed two workers and exposed 400 others to radiationAging plants require more maintenance and are less safeRecent terrorist attacks raised fears that similar attacks could be carried out against nuclear plants

Or stolen radioactive material could be used in attacks

The U.S. “megatons to megawatts” program buys radioactive material from the former Soviet Union

Using it in power plantsSlide23

Waste disposal remains a problem

Spent fuel rods and all other waste must be put in a safe location

Where leaking radioactivity will not harm future generations Waste is held in temporary storage Spent rods are stored in water

U.S. plants are running out of room

Waste is now stored in thick barrels of steel, lead, and concreteSlide24

U.S. storage of high-level radioactive waste

Waste is held at 125 sites in 39 states

161 million citizens live within 75 miles of nuclear waste Slide25

Waste storage at Yucca Mountain, Nevada

It is safer to store all waste in a central repository

It can be heavily guarded Yucca Mountain, Nevada was chosen for this sitePresident Obama’s administration does not support itSo waste will remain at its current locationsSlide26

Yucca Mountain, NevadaSlide27

Benefits of storing waste at Yucca Mountain

It is remote and unpopulated

It has minimal risk of earthquakes that could damage the tunnels and release radioactivity Its dry climate reduces chances of groundwater contamination The water table is deep underground, making groundwater contamination less likely

It is on federal land that can be protected from sabotage Slide28

Concerns with Yucca Mountain as a site

Some argue that earthquakes and volcanoes could destabilize the site’s geology

Fissures in the rock could allow rainwater to seep into the caverns

Nuclear waste will need to be transported there

From current storage areas, and from future nuclear plants and military installations

Shipments by rail and truck over thousands of miles could cause a high risk of accident or sabotage Slide29

Dilemmas slow nuclear power’s growth

Concerns over waste disposal, safety, and costs have affected nuclear power’s growth

It is enormously expensive to build, maintain, operate, and ensure the safety of nuclear facilities Decommissioning plants can be more expensive than construction Power plants serve less than half their expected lifetimes

Electricity costs more than from coal and other sources

Governments must subsidize nuclear powerSlide30

The future of nuclear energy

75% of nuclear power plants in Western Europe will be retired by 2030

But some nations are rethinking this because of concerns over climate change Asian nations are increasing nuclear capacity 56 plants are under construction

The U.S. nuclear industry has stopped building plants

Expanding nuclear capacity would decrease reliance on fossil fuels and cut greenhouse gas emissions

Engineers are planning ways to make nuclear power plants safer and less expensiveSlide31

Bioenergy

Bioenergy (biomass

energy) = energy obtained from organic material that makes up organisms Wood, charcoal, agricultural crops, manureBioenergy has great potential for addressing our energy challenges

Over 1 billion people use wood for heat, cooking, and lightSlide32

Overharvesting and developing new sources

Biomass is only renewable if it is not overharvested

Overharvesting causes deforestation, erosion, and desertificationHeavily populated arid regions are most vulnerableCooking produces indoor air pollutionNew biomass sources are being developed

Biopower

= biomass sources are burned in power plants

Generating heat and electricity

Biofuels

= liquid fuels used to power automobiles Slide33

Biopower generates electricity

Waste products of industries or processes

Woody debris, crop residuesSpecifically grown crops (fast-growing willow trees, bamboo)Co-firing combines biomass and coalGasification turn biomass to steam

Pyrolysis

produces a liquid fuel

Many types of biomass are combusted to generate electricitySlide34

Scales of production

Farmers, ranchers, or villages use manure, wood waste, or biogas from digestion to generate electricity

Small household biodigesters work in remote areasThe U.S. has dozens of biomass-fueled power plantsBiomass power increases efficiency and recyclingIt reduces CO2 emissions and dependence on imported fossil fuelsIt is better for health and supports rural economies

But burning crops deprives the soil of nutrients

Relying only on bioenergy is not a sustainable optionSlide35

Ethanol can power automobiles

Ethanol

= a biofuel made by fermenting carbohydrate-rich cropsEthanol is added to U.S. gasoline to reduce emissionsIn 2009, 10 billion gallons were made in the U.S. from cornCongressional mandates will increase ethanol productionSlide36

Cars can run on ethanol

Flexible-fuel vehicles

run on E-85 85% ethanol, 15% gasoline8 million cars are in the U.S.Most gas stations do not yet offer this fuelBagasse = crushed sugarcane residue used to make ethanol

50% of new Brazilian cars are flexible-fuel vehiclesSlide37

Ethanol may not be sustainable

Environmental scientists don’t like corn-based ethanol

Growing corn impacts ecosystemsPesticides, fertilizers, irrigationTakes up land that could be left unfarmedEthanol competes with food and drives up food pricesAs farmers shifted to ethanol, corn for food droppedMexicans could not afford tortillas, and so they riotedGrowing corn requires energy for equipment, pesticides, and fertilizers

Its EROI ratio is about 1.5:1, so it is inefficientSlide38

Biodiesel powers engines

Biodiesel

= produced from vegetable oil, cooking grease, or animal fatsVehicles can run on 100% biodiesel

B20 = 20% biodiesel

Biodiesel reduces emissions

Its fuel economy is good

It costs a bit more than gasoline

Crops are specially grown

Using land, deforestationSlide39

Novel biofuels are being developed

Algae produce lipids that can be converted to biodiesel

Their carbohydrates can be fermented to make ethanolIt can be grown in ponds, tanks, or photobioreactorsAlgae grows fast and can be harvested every few daysIt can use wastewater, ocean or saline waterIt can capture CO2 emissions to speed its growthBiofuels from algae are currently expensive

Cellulosic ethanol

= produced from structural plant material (e.g., corn stalks) that has no food value

Switchgrass provides ethanol, habitat, and high EROISlide40

Two novel biofuels

Algae is a candidate for a next-generation biofuel

Switchgrass provides fuel now and may provide cellulosic ethanolSlide41

Is bioenergy carbon-neutral?

In principle, biomass energy releases no net carbon

Photosynthesis removes carbon that is released when biomass is burnedBurning biomass is not carbon-neutral:If forests are destroyed to plant bioenergy cropsIf we use fossil fuel energy (tractors, fertilizers, etc.)The Kyoto Protocol gives incentives to destroy forests for biofuel cropsOnly emissions from energy use (not land-use changes) are “counted” toward controlling emissionsSlide42

Hydroelectric power (hydropower)

Hydropower

= uses the kinetic energy of moving water to turn turbines to generate electricityStorage technique = water stored in reservoirs behind dams passes through the dam and turns turbinesRun-of-river approach generates electricity without disrupting the river’s flow

Flow water over a small dam that does not impede fish passage

Useful in areas away from electric gridsSlide43

A typical damSlide44

A run-of-river systemSlide45

Hydroelectric power is widely used

Hydropower accounts for 2.2% of the world’s energy supply

And 15.6% of the world’s electricity productionNations with large rivers and economic resources have used damsHowever, many countries have dammed their large riversPeople want some rivers left undammedThe U.S. government built dams to employ people and help end the economic depression of the 1930s

Engineers exported their dam-building techniquesSlide46

Hydropower is clean and renewable

Hydropower has two clear advantages over fossil fuels for producing electricity:

It is renewable: as long as precipitation fills rivers we can use water to turn turbinesIt is clean: no carbon dioxide is emittedHydropower is efficientIt has an EROI of 10:1As high as any modern-day energy sourceSlide47

Hydropower has negative impacts

Damming rivers destroys wildlife habitats

Upstream areas are submergedDownstream areas are starved of waterNatural flooding cycles are disruptedDownstream floodplains don’t get nutrientsDownstream water is shallower and warmer

Periodic flushes of cold reservoir water can kill fish

Dams block passage of fish, fragmenting the river and reducing biodiversity

Large dams can cause earthquakes or collapseSlide48

Hydropower may not expand much more

China’s Three Gorges Dam is the world’s largest dam

It displaced 1 million peopleGenerates as much electricity as dozens of coal-fired or nuclear plantsMost of the world’s large rivers have already been dammedPeople have grown aware of the ecological impact of dams and resist more construction

Developing nations with rivers will increase hydropowerSlide49

Conclusion

With limited fossil fuel supplies, nations are trying to diversify their energy portfolios

Nuclear power showed promiseBut high costs and public fears stalled its growthBiomass energy sources include wood and newer biofuelsThey can be carbon-neutral but are not strictly renewableHydropower is a renewable, pollution-free alternative

But it is nearing maximal use and can involve substantial ecological impactsSlide50

QUESTION: Review

Conventional alternative fuels:

Exert less environmental impact than fossil fuels but are currently not feasible

Are intermediate sources of fuel that can help us on

our path towards sustainability

Are final sources of fuel that will give us energy independence

Are no longer available for widespread useSlide51

QUESTION: Review

The reaction that drives the release of energy in today’s nuclear power plants is:

Nuclear fission

Nuclear fusion

Control rods

Nuclear emergenciesSlide52

QUESTION: Review

Why have nuclear power plants not been popular in the United States?

Fears about accidents or sabotage

Storage of nuclear waste is still not solved

High costs of building and maintaining plants

All are issues regarding nuclear energySlide53

QUESTION: Review

Ethanol in the United States is made mainly from ______, and is used to ______.

Soybeans, heat homes

Sugarcane, drive cars

Corn, drive cars

Willow trees, make electricitySlide54

QUESTION: Review

Which of the following is an interesting future biofuel?

Corn

Algae

Nuclear

Shale oilSlide55

QUESTION: Review

Which of the following forms of hydropower is least environmentally destructive?

The storage approach

Run-of-river approach

Bend-of-river approach

All of these are destructive forms and none should be used.Slide56

QUESTION: Weighing the Issues

Given the choice of living next to a coal-burning power plant or nuclear plant, which would you choose?

The nuclear plant, because it’s cleaner.

The coal plant, because it won’t be as likely a target for terrorists.

Neither one; I’d move to another place.

Either one; I don’t care.Slide57

QUESTION: Interpreting Graphs and Data

If ethanol in the United States continues to be produced from corn, a drawback suggested from this graph could be:

a) More corn is available for ethanol.

b) More competition between food and fuel.

c) Less land planted in corn.

d) None of these.