Environmental Science
Unit 7 – Energy
(STE 7th ed. Chapter ##)
In the long run, humanity has no choice but to rely on
renewable energy. No matter how abundant they
seem today, eventually coal & uranium will run out.
––Daniel Deudney & Christopher Flavin
Where are we going?
1. Energy Resources
sources, evaluation
2. Oil
what is it? supplies, environmental issues
3. Natural Gas
what is it? supplies, environmental issues
4. Coal
what is it? supplies, environmental issues
5. Nuclear Energy
what happened to nuclear power?
6. Renewable Energy
what is it? supplies, environmental issues
1. Energy Resources
U.S. has 4.6% of
world population
uses 24% of the
world’s commercial
energy
Changes in US Energy Use
Changes in US Energy Use
Experience shows
that it takes ~50 years
to phase in new
energy alternatives
Questions
• what was the basis of the energy economy until 1800?
• what was the basis of the energy economy during 1900?
• what was the basis of the energy economy during 1960?
• what is the projected basis of the energy economy by the year 2025?
• what is the projected basis of the energy economy by the year 2100?
How to Evaluate Resources
•
How much available?
– Oil will be depleted in 40-80 years
•
Net energy yield?
•
Cost to develop, phase in, & use?
•
Environmental effects of extraction, transport, & use?
– Water, air and soil pollution
– Land disruption
– Global Warming
•
Sustainability?
– General concensus is to improve energy efficiency
Net Energy
•
Suppose that for every 10 units of oil, we have to use and waste 8 units
to find, extract, process and transport the oil to users. There are only 2
of useful energy available.
– Net Energy = Useful energy produced / Energy used to produce it
– 10/8 = 1.25
– The higher the ratio, the higher the net yield
OIL
• Currently oil has a high net energy ratio since much of it comes from
large accessible deposits in the middle east
• when the sources deplete the ratio will decrease
Net Energy
has a low ratio, large amounts of energy
are needed to extract and process
uranium ore and to build and operate
power plants
Ratios < 1 = energy loss
Questions
• what are the noticeable patterns?
• how will these current patterns change based on future
trends predicted?
• what is the primary difference between Solar heating and
carbon based fuels?
2. Oil
•
•
fossil fuel, produced by the decomposition of deeply buried organic
matter from plants & animals – ‘biogenic theory’
crude oil: complex liquid mixture of hydrocarbons, with small amounts
of S, O, N impurities
– Only 35-50% can be economically recovered from a deposit.
– As prices rise, about 10-25% more can be recovered from
expensive secondary extraction techniques
– This lowers the net energy yield
Oil: Extraction and
Processing
•
•
•
Extraction:
– primary - drill & pump
– secondary - inject H2O
– tertiary - inject steam or CO2
refine to separate by boiling point:
– high: gasoline, aviation fuel
– medium: heating oil, diesel
– low: grease, wax, asphalt
transport by tanker, truck, pipeline
Oil: Sources
•
Organization of Petroleum Exporting Countries (OPEC) - 13 countries
have most of the world reserves:
– Algeria, Ecuador, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya,
Nigeria, Qatar, Saudi Arabia, United Arab Emirates, & Venezuela
•
other important producers:
Alaska, Siberia, & Mexico
Oil in US
• < 3% of world reserves
• uses nearly 30% of world
reserves;
• 65% for transportation;
• increasing dependence on
imports
Energy: A Definition
1979 Iranian Revolution
Oil Prices
1973 Oil embargo
2003 Iraq Invasion
1939-1945 WW2
9/11
1993 Gulf War
Oil
•
•
•
•
•
•
1968 – largest oil field in US discovered on Alaska’s North slope (Prudhole Bay)
10-20 x109 barrels
Difficult to move oil tankers from Atlantic ocean through NW passage
1977 - Trans-Alaska pipeline to nearest ice-free sea port
Production is decreasing
Look to Arctic National Wildlife Reserve’s 1002 area (ANWR)
Oil: Pros and Cons
• Pros
– still cheap
• Cons
– pollution & environmental
degradation – GH gases
CO2 Emissions
Cleaner burning FF
CO2 emissions per unit of energy produced for various energy resources.
3. Natural Gas
• fossil fuel
• mixture of 50–90% methane
(CH4), smaller amounts of
ethane (C2H6), propane
(C3H8), & butane (C4H10),
and hydrogen sulfide (H2S)
• propane & butane removed
as liquefied petroleum gas
(LPG);
• typically transported by
pipelines
• much burned or pumped
back into ground
NG: Sources
• Russia & Kazakhstan: almost 40% world's supply
• Iran (15%), Qatar (5%), Saudi Arabia (4%), Algeria (4%), United
States (3%), Nigeria (3%), Venezuela (3%)
• Natural gas is versatile and clean-burning fuel, but it releases
the greenhouse gases carbon dioxide (when burned) and
methane (from leaks) into the troposphere
NG: Pros and Cons
• Pros
– reserves 65–80 yrs for U.S.,
125 years for world at
current consumption rates;
– burns cleaner, & produces
less carbon dioxide than
other fossil fuels
• Cons
– pollution & environmental
degradation
4. Coal
Coal is a solid fossil fuel that is formed in several
stages as the buried remains of land plants that lived
300-400 million years ago
Coal: Sources
Due to air pollution laws,
search for cleaner coal,
thicker seams
•
Coal reserves in the United
States, Russia, and China could
last hundreds to over a thousand
years
•
The U.S. has 27% of the world’s
proven coal reserves, followed by
Russia (17%), and China (13%)
•
In 2005, China and the U.S.
accounted for 53% of the global
coal consumption
Since 1940’s production shifted
west, from underground to
surface mines
Coal
•
•
Coal seams vary in thickness from a few inches to hundreds of feet
60% coal produced by strip mining – ripping tops off mountains
Aerial view of a Montana strip mine.
Dragline used in strip mine to remove coal.
The Washington Post 032008
Coal: Pros and Cons
• Pros
– most abundant fossil fuel;
– high net energy yield;
• Cons
– dirtiest fuel, highest carbon
dioxide
– major environmental
degradation
– major threat to health
5. Nuclear Energy
•
Nuclear fission is the splitting of
a large nucleus into smaller nuclei
•
Energy is released because the
sum of the masses of these
fragments is less than the
original mass
•
Heat produced drives a turbine to
produce electricity
Power from Nuclear Fission
Critical Mass
•
•
Self-propagating
chain reaction
Excess neutrons
•
With small mass,
1 n are lost
0
•
Past 15 kg,
reaction is
sustained
http://www.kscience.co.uk/animations/chain_reaction.swf
Power from Nuclear Fission
Types of Fission Reactor
•
Commerical nuclear power is produced using thermal neutrons
Fuel rods contain fissile material (natural, enriched, or mixed)
Moderator slows down neutrons, increases chances of fission
Control rods made from boron absorb 10n
Coolant water or gas
Steam turbine or generator converts heat into electricity
•
Different reactors use different
coolants, fuel and moderators
Small amounts of
radioactive gases
Uranium fuel
Control rods
input (reactor
Containment shell
core)
Heat exchanger
Steam
Turbine
Generator
Waste heat
Hot
water
output
Coolant
Cool
water
input
Moderator
Shielding
Coolant
Pressure
passage
vessel
Periodic removal and
storage of radioactive
wastes and spent fuel
assemblies
Water
Periodic removal
and storage of
radioactive liquid
wastes
Electric
power
Useful energy
25%–30%
Waste heat
Condenser
Water source (river,
lake, ocean)
Power from Nuclear Fission
Water remains liquid
due to high pressure
Types of Fission Reactor: PWR
Expansion of water as T
rises reduces number of
slow moving n
Water = coolant, moderator
and n absorber
Popular design due to safety
record, more economic to run
After three or four years in a
reactor, spent fuel rods are
removed and stored in a
deep pool of water contained
in a steel-lined concrete
container
After spent fuel rods are
cooled, they are moved to
dry-storage containers made
of steel or concrete
Decommissioning
of reactor
Fuel assemblies
Enrichment
of UF6
Conversion of
U3O8 to UF6
Reactor
Fuel fabrication
(conversion of enriched UF6
to UO2 and fabrication of
fuel assemblies)
Uranium-235 as UF6
Plutonium-239 as PuO2
Spent fuel
reprocessing
Temporary storage of
spent fuel assemblies
underwater or in dry
casks
Low-level radiation
with long half-life
Open fuel cycle today
“Closed” end fuel cycle
Geologic disposal
of moderate &
high-level
radioactive
wastes
What Happened to Nuclear Power?
•
After more than 50 years of development and enormous government
subsidies, nuclear power has not lived up to its promise because:
– Multi billion-dollar construction costs.
– Higher operation costs and more malfunctions than expected.
– Poor management.
– Public concerns about safety and stricter government safety
regulations
•
some countries (France, Japan) investing increasingly
•
U.S. currently ~7% of energy nuclear;
•
no new U.S. power plants ordered since 1978; 40% of 105 commercial
nuclear power expected to be retired by 2015 & all by 2030;
•
France 78% energy nuclear
TMI
•
March 29, 1979, number 2
reactor near Harrisburg,
Pennsylvania lost coolant &
core suffered partial meltdown
•
Majority contained
•
50,000 people evacuated &
another 50,000 fled area;
•
unknown amounts of radioactive
materials released
•
partial cleanup & damages cost
$1.2 billion so far
•
released radiation increased
cancer rates
Movie
CNN 2002
Chernobyl
•
April 26, 1986, reactor
explosion (Ukraine) flung
radioactive debris into
atmosphere
•
Flawed design
•
Major world-wide release of
radioisotopes due to no
secondary containment
•
56 immediate + 4000
expected deaths
•
Encased in concrete
Movie
CNN 2002
Nuclear: Pros and
Cons
•
Pros
– U.S. has major reserves of
uranium
•
Cons
– risk of radioactive
contaminant leaks
– radioactive wastes (short– &
long–term)
A 1,000 megawatt
nuclear plant is
refueled once a
year, whereas a coal
plant requires 80 rail
cars a day
Nuclear Waste Solutions
•
Scientists disagree about the best methods for long-term storage of
high-level radioactive waste:
– Bury it deep underground.
– Shoot it into space.
– Bury it in the Antarctic ice sheet.
– Bury it in the deep-ocean floor that is geologically stable.
– Change it into harmless or less harmful isotopes.
What’s next?
•
•
General consensus?
– To improve energy efficiency
Disagreement about the next best option
Option 1 – turn to renewable energy resources
Option 2 – burn more coal
Option 3 – turn to natural gas (cleaner)
Option 4 – Nuclear power
6. Renewables
1. Energy efficiency
2. Solar energy
3. Hydropower
4. Wind Power
5. Biomass
6. Solar–hydrogen revolution
7. Geothermal
8. Sustainability
Energy
Waste
•
Flow of
commercial
energy through
the U.S. economy
•
84% is wasted
•
41% due to
thermodynamics
•
43 % due to
efficiency
Efficiency
Reducing Waste by Improving Efficiency
•
•
•
•
•
•
allows nonrenewable fuels to last longer
gives time to phase in renewable energy
decreases dependence on oil imports
reduces environmental damage
slows global warming
saves money
Improving Energy Efficiency
• cogeneration
• efficient lighting & appliances
• increases in vehicle fuel
efficiency; use of alternative
fuels
• better insulation
~86 %
wasted
Solutions
Reducing Energy Waste
Prolongs fossil fuel supplies
Reduces oil imports
Very high net energy
Low cost
Reduces pollution and
environmental degradation
Buys time to phase
in renewable energy
Less need for military
protection of Middle East oil
resources
Creates local jobs
Fundamental Sources of Energy
FUSION
(SOLAR)
FISSION
Fossil fuels
Nuclear energy
Wind
(man-made)
Waves
Geothermal
Biomass
(natural)
Hydro
Direct solar
GRAVITATIONAL
PE/KE earthmoon-sun)
Tides
Renewable Energy Sources (RES)
•
RES
–
–
–
–
–
–
–
solar
wind
waves
hydro
biomass
geothermal
tidal
Solar derived
Capture energy from ongoing
natural processes
Replaced at a rate equal to or
faster than consumption
Why Are We Still Wasting So Much
Energy?
• Low-priced fossil
fuels and few
government tax
breaks or other
financial incentives
for saving energy
promote energy
waste
Heating Buildings and Water with Solar
Energy
We can heat buildings by orienting them toward the
sun or by pumping a liquid such as water through
rooftop collectors
Passive or Active Solar Heating
Disadvantages
Solar: Pros and
Cons
Advantages
Energy is free
Net energy is
moderate
(active) to high
(passive)
Quick installation
No CO2 emissions
Need access to sun
60% of time
Sun blocked by
other structures
Need heat storage
system
Very low air and
water pollution
High cost (active)
Very low land
disturbance
(built into roof
or window)
Active system
needs maintenance
and repair
Moderate cost
(passive)
Active collectors
unattractive
Using Solar Energy to Generate HighTemperature Heat and Electricity
Solar Thermal Systems:
(i) Heliostats (power towers)
(ii) Concentrators
Large arrays of solar collectors in
sunny deserts can produce hightemperature heat to spin turbines
for electricity, but costs are high
Solar Thermal Electric Facilities
Figure 12.23: Solar Electric Generating System (SEGS), Kramer Junction,
California, provides 165 MW from concentrating collectors shown here.
Movie
ABC 2006
Producing Electricity with Solar Cells
Photovoltaic (PV) cells can provide electricity for a house of
building using solar-cell roof shingles.
Trade-Offs
Solar Cells
Advantages
Fairly high net energy
Disadvantages
Need access to sun
Work on cloudy days
Low efficiency
Quick installation
Easily expanded or moved
Need electricity storage
system or backup
No CO2 emissions
Low environmental impact
High land use (solar-cell
power plants) could disrupt
desert areas
Last 20–40 years
Low land use (if on roof
or built into walls or
windows)
Reduces dependence on
fossil fuels
High costs (but should
be competitive in 5–15
years)
DC current must be converted
to AC
Producing Electricity from Moving Water
Hydropower etc.
• hydroelectric dams
• tides & waves
• ocean thermal energy conversion & solar ponds
Trade-Offs
Large-Scale Hydropower
Advantages
Disadvantages
Moderate to high net energy
High construction costs
High efficiency (80%)
High environmental impact
from flooding land to form a
reservoir
Large untapped potential
Low-cost electricity
Long life span
High CO2 emissions from
biomass decay in shallow
tropical reservoirs
Floods natural areas behind dam
No CO2 emissions during
operation in temperate areas
Converts land habitat to lake
habitat
May provide flood control below
dam
Danger of collapse
Provides water for year-round
irrigation of cropland
Decreases fish harvest below dam
Reservoir is useful for fishing
and recreation
Uproots people
Decreases flow of natural fertilizer
(silt) to land below dam
Wind
World’s most
abundant energy
source
Abundant, inexhaustible, widely
distributed, cheap, clean, and
emits no greenhouse gases
Movie
CNN 1999
Biomass
Plant materials and animal
wastes can be burned to provide
heat or electricity or converted
into gaseous or liquid biofuels
Trade-Offs
Solid Biomass
Advantages
Disadvantages
Large potential supply in some
areas
Nonrenewable if harvested
unsustainably
Moderate costs
Moderate to high environmental
impact
No net CO2 increase if harvested
and burned sustainably
CO2 emissions if harvested
and burned unsustainably
Plantation can be located on
semiarid land not needed for
crops
Low photosynthetic efficiency
Soil erosion, water pollution,
and loss of wildlife habitat
Plantation can help restore
degraded lands
Plantations could compete
with cropland
Can make use of agricultural,
timber, and urban wastes
Often burned in inefficient
and polluting open fires and
stoves
Converting Plants and Plant Wastes to
Liquid Biofuels: An Overview
•
•
Motor vehicles can run on
ethanol, biodiesel, and
methanol produced from plants
and plant wastes
The major advantages of
biofuels are:
– Crops used for production
can be grown almost
anywhere
– There is no net increase in
CO2 emissions.
– Widely available and easy
to store and transport
Trade-Offs
Ethanol Fuel
Advantages
High octane
Disadvantages
Large fuel tank needed
Lower driving range
Some reduction in CO2
emissions
High net energy (bagasse
and switchgrass)
Reduced CO
emissions
Low net energy (corn)
Much higher cost
Corn supply limited
May compete with growing
food on cropland
Higher NO emissions
Can be sold as gasohol
Potentially renewable
Corrosive
Hard to start in cold weather
This is actually backwards
Geothermal
•
•
Geothermal energy consists of
heat stored in soil, underground
rocks, and fluids in the earth’s
mantle.
We can use geothermal energy
stored in the earth’s mantle to
heat and cool buildings and to
produce electricity.
Trade-Offs
Geothermal Energy
Advantages
Disadvantages
Very high
efficiency
Scarcity of suitable
sites
Moderate net
energy at
accessible sites
Depleted if used
too rapidly
Lower CO2
emissions than
fossil fuels
Low cost at
favorable sites
Low land use
Low land
disturbance
Moderate
environmental impact
CO2 emissions
Moderate to high
local air pollution
Noise and odor
(H2S)
Cost too high
except at the most
concentrated and
accessible sources
Hydrogen
•
•
•
•
Environmentally Friendly
Extraction
Storage
Fuel Cells
Environmentally Friendly Hydrogen
Solar/Hydrogen Revolution
•
Some energy experts view hydrogen gas as the best fuel to replace oil
during the last half of the century, but there are several hurdles to
overcome:
– Hydrogen is chemically locked up in water an organic compounds
– It takes energy and money to produce it (net energy is low)
– Fuel cells are expensive
– Hydrogen may be produced by using fossil fuels
Movie
ABC 2006
Converting to a Hydrogen Economy
• Iceland plans to run its economy mostly on hydrogen (produced
via hydropower, geothermal, and wind energy), but doing this in
industrialized nations is more difficult.
– Must convert economy to energy farming (e.g. solar, wind)
from energy hunter-gatherers seeking new fossil fuels
– No infrastructure for hydrogen-fueling stations (12,000
needed at $1 million apiece)
– High cost of fuel cells
Trade-Offs
Hydrogen
Advantages
Can be produced from plentiful
water
Low environmental impact
Renewable if from renewable
resources
No CO2 emissions if produced
from water
Good substitute for oil
Competitive price if environmental
& social costs are included in cost
comparisons
Easier to store than electricity
Safer than gasoline and natural gas
Nontoxic
High efficiency (45–65%) in
fuel cells
Disadvantages
Not found in nature
Energy is needed to produce fuel
Negative net energy
CO2 emissions if produced from
carbon-containing compounds
Nonrenewable if generated by fossil
fuels or nuclear power
High costs (but may eventually
come down)
Will take 25 to 50 years to phase in
Short driving range for current
fuel-cell cars
No fuel distribution system in place
Excessive H2 leaks may deplete
ozone in the atmosphere
A Sustainable Energy Strategy
• What do we mean by sustainable?
A Sustainable Energy Strategy
• More sustainable energy strategy
– improve energy efficiency
– rely more on renewable energy
– reduce the harmful effects of using
fossil fuels and nuclear energy
shift from large, centralized macropower systems to
smaller, decentralized micropower systems
Solutions: A Sustainable Strategy
Fuels for the Future?
http://news.bbc.co.uk/2/hi/science/nature/7241909.stm