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 Resourcessources, evaluation

2. Oilwhat is it? supplies, environmental issues

3. Natural Gaswhat is it? supplies, environmental issues

4. Coalwhat is it? supplies, environmental issues

5. Nuclear Energywhat happened to nuclear power?

6. Renewable Energywhat is it? supplies, environmental issues

1. Energy Resources

U.S. has 4.6% of world populationuses 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

Ratios < 1 = energy loss

has a low ratio, large amounts of energy are needed to extract and process uranium ore and to build and operate power plants

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

1973 Oil embargo

1979 Iranian Revolution

2003 Iraq Invasion

1993 Gulf War

Oil Prices

9/11

1939-1945 WW2

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

• ProsPros– still cheap

• ConsCons– 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

• ProsPros– 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

• ConsCons– 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 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

Coal: Sources

Since 1940’s production shifted west, from underground to surface mines

Due to air pollution laws, search for cleaner coal, thicker seams

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

• ProsPros– most abundant fossil fuel;– high net energy yield;

• ConsCons– 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, 10n are lost

• 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 gasSteam turbine or generator converts heat into electricity

• Different reactors use different coolants, fuel and moderators

Small amounts of radioactive gases

Uranium fuel input (reactor core)

Control rodsContainment shell

Heat exchanger

Steam Turbine Generator

Waste heat

Electric power

Hot coolant

Useful energy 25%–30%Hot

water outputPumpPump

Coolant Pump Pump

Moderator

Cool water input

Waste heat

Shielding Pressure vessel

Coolant passage

Water CondenserPeriodic removal and storage of radioactive wastes and spent fuel assemblies

Periodic removal and storage of radioactive liquid wastes

Water source (river, lake, ocean)

Power from Nuclear Fission Types of Fission Reactor: PWR

Water = coolant, moderator and n absorber

Popular design due to safety record, more economic to run

Water remains liquid due to high pressure

Expansion of water as T rises reduces number of slow moving n

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 reactorFuel assemblies

ReactorEnrichment of UF6 Fuel fabricationFuel fabrication

(conversion of enriched UF(conversion of enriched UF66

to UOto UO22 and fabrication of and fabrication of

fuel assemblies)fuel assemblies) Temporary storage of Temporary storage of spent fuel assemblies spent fuel assemblies underwater or in dry underwater or in dry caskscasks

Conversion of U3O8 to UF6

Uranium-235 as UFUranium-235 as UF66

Plutonium-239 as PuOPlutonium-239 as PuO22

Spent fuel Spent fuel reprocessingreprocessing

Low-level radiation Low-level radiation with long half-lifewith long half-life

Geologic disposal of moderate &

high-level radioactive

wastesOpen fuel cycle today

“Closed” end fuel cycle

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

• ProsPros– U.S. has major reserves of

uranium

• ConsCons– 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 GRAVITATIONALPE/KE earth-moon-sun)

Fossil fuels

Wind

Waves

Biomass

Hydro

Direct solar

Nuclear energy

(man-made)

Geothermal

(natural)

Tides

Renewable Energy Sources (RES)

Solar derived• RES

– solar– wind– waves– hydro– biomass– geothermal– tidal

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

Solar: Pros and Cons

Passive or Active Solar Heating

Advantages Disadvantages

Energy is free Need access to sun 60% of time

Net energy is moderate (active) to high (passive)

Sun blocked by other structures

Need heat storage system

Quick installation

No CO2 emissions

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 High-Temperature Heat and Electricity

Solar Thermal Systems:

(i) Heliostats (power towers)

(ii) Concentrators

Large arrays of solar collectors in sunny deserts can produce high-temperature 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 Disadvantages

Fairly high net energy Need access to sun

Work on cloudy daysLow efficiency

Quick installation

Need electricity storage system or backup

Easily expanded or moved

No CO2 emissions

High land use (solar-cell power plants) could disrupt desert areas

Low environmental impact

Last 20–40 years

Low land use (if on roof or built into walls or windows)

High costs (but should be competitive in 5–15 years)

Reduces dependence on fossil fuels DC current must be converted

to AC

Producing Electricity from Moving WaterHydropower 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

Large untapped potential

High environmental impact from flooding land to form a reservoir

High efficiency (80%)

High CO2 emissions from biomass decay in shallow tropical reservoirs

Low-cost electricity

Long life span

No CO2 emissions during operation in temperate areas

Floods natural areas behind dam

May provide flood control below dam

Converts land habitat to lake habitat

Danger of collapse

Provides water for year-round irrigation of cropland

Uproots people

Decreases fish harvest below dam

Reservoir is useful for fishing and recreation

Decreases flow of natural fertilizer (silt) to land below dam

Wind

Abundant, inexhaustible, widely distributed, cheap, clean, and emits no greenhouse gases

World’s most abundant energy source

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 costsModerate to high environmental impact

No net CO2 increase if harvested and burned sustainably

CO2 emissions if harvested and burned unsustainably

Low photosynthetic efficiencyPlantation can be located on semiarid land not needed for crops

Soil erosion, water pollution, and loss of wildlife habitat

Plantation can help restore degraded lands

Plantations could compete with cropland

Often burned in inefficient and polluting open fires and stoves

Can make use of agricultural, timber, and urban wastes

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 Disadvantages

High octane Large fuel tank needed

Some reduction in CO2 emissions

Lower driving range

Low net energy (corn)

High net energy (bagasse and switchgrass)

Much higher cost

Corn supply limited

Reduced CO emissions

May compete with growing food on cropland

Can be sold as gasohol

Higher NO emissions

Corrosive

Potentially renewable 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 Moderate to high

local air pollutionLow cost at favorable sites

CO2 emissions

Noise and odor (H2S)Low land use

Low land disturbance Cost too high

except at the most concentrated and accessible sources

Moderate environmental impact

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 Disadvantages

Not found in nature

Energy is needed to produce fuel

Negative net energyRenewable if from renewable resources CO2 emissions if produced from

carbon-containing compoundsNo CO2 emissions if produced from water Nonrenewable if generated by fossil

fuels or nuclear powerGood substitute for oil

Competitive price if environmental & social costs are included in cost comparisons

High costs (but may eventually come down)

Will take 25 to 50 years to phase in

Easier to store than electricity Short driving range for current fuel-cell cars

Safer than gasoline and natural gasNo fuel distribution system in place

Nontoxic

High efficiency (45–65%) in fuel cells

Excessive H2 leaks may deplete ozone in the atmosphere

Can be produced from plentiful water

Low environmental impact

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