Lecture 9 energy_sources

Environmental Science
A Study of Interrelationships
Eleventh Edition

Enger & Smith

Chapter 9
Energy Sources

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Outline

 Energy Sources
 Resources and Reserves
 Fossil-Fuel Formation
 Issues Related to the Use of Fossil Fuels
 Renewable Sources of Energy
 Energy Conservation
 Are Fuel Cells and a Hydrogen Economy in the
Future?

Energy Sources

 Nonrenewable energy sources are those whose
resources are being used faster than can be
replenished.
– Coal, oil, and natural gas
 Renewable energy sources replenish themselves
or are continuously present as a feature of the
environment.
– Solar, geothermal, tidal, etc.
– Some forms are referred to as perpetual energy.

Energy Sources

All energy sources

Resources and Reserves
 A resource is a naturally occurring substance of
use to humans that can potentially be extracted
using current technology.
 A reserve is a known deposit that can be
economically extracted using current technology,
under certain economic conditions.
 Reserves are smaller than resources.
 Reserve levels change as technology advances,
new discoveries are made, and economic
conditions vary.

Fossil Fuel Formation

 Coal
• 300 million years ago, plant material began collecting
underwater, initiating decay, forming a spongy mass
of organic material.
• Due to geological changes, some of these deposits
were covered by seas, and covered with sediment.
• Pressure and heat over time transformed the organic
matter into coal.


Recoverable coal reserves of the world 2004


 Oil and natural gas probably originated from
microscopic marine organisms that accumulated on
the ocean floor and were covered by sediments.
• Muddy rock gradually formed shale containing dispersed
oil.
• Natural gas often forms on top of oil.


Crude oil and natural gas pool

Issues Related to the Use of Fossil Fuels

 Fossil fuels supply 80% of world’s commercial
energy.
• Oil 35%
• Coal 24%
• Natural Gas 21%


 Coal is most abundant fossil fuel.
• Primarily used for generating electricity.
 There are three categories of coal:
• Lignite
– Is least desirable because of its high moisture content.
• Bituminous
– Most widely used because it is most abundant and easiest to
mine.
• Anthracite
– Has the highest energy content and is cleanest burning, but
is hard to obtain.


 There are two extraction methods:
• Surface mining (strip mining), which is the process of
removing material on top of a vein, is efficient but
destructive.
• Underground mining minimizes surface disturbance,
but is costly and dangerous.
– Many miners suffer from black lung disease, a respiratory
condition that results from the accumulation of fine coal-
dust particles in the miners’ lungs.


 Coal is bulky and causes some transport problems.
 Mining creates dust pollution.
 Burning coal releases pollutants (carbon and
sulfur).
• Millions of tons of material are released into atmosphere
annually.
• Sulfur leads to acid mine drainage and acid deposition.
• Increased amounts of atmospheric carbon dioxide are
implicated in global warming.


Underground mining


Surface-mine reclamation


Acid mine drainage


 Oil is more concentrated than coal, burns cleaner,
and is easily transported through pipelines.
• These qualities make it ideal for automobile use.
• It is difficult to find.
• It causes less environmental damage than coal mining.


 Present technology only removes 1/3 of an oil
deposit.
 Secondary recovery methods are used to
recover more oil, such as forcing water or gas into
wells to drive the oil out.
 As oil prices increase, more expensive and
aggressive secondary recovery methods will need
to be used.


Offshore drilling


 Processing
• As it comes from the ground, oil is not in a form suitable
for use, and must be refined.
• Multiple products can be produced from a single barrel of
crude oil.
 Oil Spills
• Accidental spills only account for about 1/3 of oil pollution
resulting from shipping.
• 60% comes from routine shipping operations.


Processing crude oil


 The drilling operations to obtain natural gas are
similar to those used for oil.
 It is hard to transport and in many places is burned
off at oil fields, but new transportation methods are
being developed.
• Liquefaction at -126o F (1/600 volume of gas)
 It is the least environmentally damaging fossil fuel.
• It causes almost no air pollution.

Renewable Sources of Energy
 Currently, alternative energy sources supply almost
13.5% of the world’s total energy.
• Some studies suggest these sources could provide half
of the world’s energy needs by 2050.
• Renewable sources will become much more important as
fossil fuel supplies become more expensive.
– Hydroelectric power
– Tidal power
– Geothermal power
– Wind power
– Solar energy
– Biomass conversion


Renewable energy as a share of total energy consumption (world 2003)


 Hydroelectric power is created when flowing
water is captured and turned into electricity.
• Damming a river and storing water in a reservoir is the
most common method.
• Pumped storage plants use two reservoirs separated by
a significant elevation difference.
• The potential for developing hydroelectric power is best
in mountainous regions and large river valleys.
• The World Energy Council estimates that it would be
technically possible to triple the electricity produced by
hydropower with current technology.


 Hydroelectric power currently supplies 16% of
world’s electricity.
• In South and Central America, 65% of electricity used
comes from hydroelectric power.
• Norway gets 99% of its electricity and 60% of all its
energy from hydroelectric power.
• Construction of “minihydro” (less than 10 megawatts) and
“microhydro” (less than 1 megawatt) plants is increasing;
these plants can be built in remote places and supply
electricity to small areas.


 Reservoir construction causes significant
environmental and social damage.
• Loss of farmland or forest land due to flooding.
• Community relocation.
• Prevention of fish migrations.
• Trapping of silt fills in reservoir and stops flow of
nutrients downstream.
• Mercury accumulation.


Hydroelectric power plant.


 Tidal Power
• Tides, the daily rise and fall of ocean levels relative to
coastlines, are a result of gravitational forces and the
revolution of the earth.
• As water flows from a higher level to a lower level, it can
be used to spin an electricity-generating turbine.
• Since tidal changes of roughly 16 feet are needed to
produce practical amounts of power, suitable sites are
limited.
• Little is understood about how altering the tides can
affect complex aquatic and shoreline ecosystems.


 Geothermal Power
• Geothermal energy is linked to geologically active areas
where heat from the Earth can reach the surface
through thinner crust.
• Wells are drilled to obtain steam trapped underground,
and the steam powers electrical generators.
• The U.S. has about half of the world’s geothermal
electrical generating capacity. California produces 40%
of world’s geothermal electricity.
• It can cause unpleasant odors and high mineral content
leads to high maintenance (corroded pipes and
equipment).


Geothermal power plant


 Wind Power
• As warm air becomes less dense and rises, cooler,
denser, air flows in to take its place. This flow of air is
wind.
• U.S. Department of Energy has stated the Great
Plains could supply the 48 contiguous states with
75% of their electricity.
• Wind power is considered competitive with new coal
and natural gas plants and cheaper than nuclear
plants.


 The European Wind Energy Association recently
increased its target from 40,000 to 60,000
megawatts by 2010.
 A push for energy deregulation and concerns
about smog, acid rain, and global warming are
driving policy makers to require utilities to sell
electricity from renewable sources.
 Eight states (Texas, Wisconsin, Massachusetts,
Connecticut, New Jersey, Minnesota, Nevada,
and Pennsylvania) require utilities to provide
some “green” electricity.


 There are some negative effects from wind
generators:
• The moving blades produce noise and some consider
the windmills visual pollution.
• Moving blades are hazardous to birds, although newer
windmills have slower-moving rotors that many birds
find easier to avoid.
• Vibrations from generators can cause structural
damage.


 Daily energy from the sun is 600 times greater
than energy produced each day by all other
energy sources combined.
• The major problems with solar energy are its
intermittent and diffuse nature.
 Solar energy is utilized in three ways:
• In passive heating, the sun’s energy is converted
directly to heat and used at collection site.
• In an active heating system, the sun’s energy is
converted into heat, but transported elsewhere to be
used.
• Solar energy is also transformed into electrical energy.


Passive solar heating


Solar heating designs.


 In a passive solar system, light energy is
transformed to heat energy when it is absorbed
by a surface.
 Buildings designed for passive solar heating in
the Northern Hemisphere usually have large,
south-facing windows.
 Floors and walls, made of materials that absorb
and store the sun’s heat during the day, slowly
release heat at night when it is needed most.
This feature is called direct gain.


 An active solar system requires a solar collector,
a pump, and a system of pipes to transfer the
heat from the site of production to the area to be
heated.
 Water heating for domestic use is generally the
most economical application of active solar
systems.
 A major consideration in the use of an active
solar system is the initial cost of installation.


 A photovoltaic cell (PV) is a solid-state
semiconductor that converts sunlight directly into
electricity.
 The amount of PV power installed worldwide has
increased from 100 megawatts in 1992 to 1,200
megawatts in 2002.
 Thin-film technology has made it possible to build
solar cells into roof shingles and tiles, building
facades, and the glazing for skylights and atria.


 Improving solar cell efficiency while holding
down the cost per cell is an important goal of the
growing PV industry, and significant progress
has been made in this area.
 Photovoltaics are probably the most benign
method of power generation known.
 They are silent, produce no emissions, and use
no fuel other than sunlight.


 Many of the developing countries of the world
will introduce electricity to villages through the
use of photovoltaics rather than the use of
generators that require fuel and distribution
lines.


Photovoltaic shingles


Solar generation of electricity


 Biomass Conversion
• All biomass is produced by green plants that convert
sunlight into plant material through photosynthesis.
• Biomass is still the predominant form of energy used by
people in less-developed countries.
• It accounts for 14% of world energy use.


 There are four distinct sources of biomass
energy:
• Fuelwood
• Municipal and industrial wastes
• Agricultural crop residues and animal wastes
• Energy plantations


 In less-developed countries, fuelwood has been a
major energy source for centuries.
 Fuelwood is the primary energy source for nearly
half the world’s population.
 Due to intense population growth, an estimated 1.3
billion people cannot get enough fuelwood, or are
using it faster than rate of regeneration.
 It is a source of air pollution and particulate matter.

 Solid waste is a major source of biomass and other
burnable materials produced by society.
 The burning of solid waste only makes economic
sense when the cost of waste disposal is taken into
account.
 Using municipal waste as a source of energy:
• Reduces landfill volume.
• Requires large volume and dependable supply, and must
be sorted.
• Produces air pollution, including pollutants not found in
other forms of biomass.


 Crop residues and animal wastes:
• Materials left over following the harvest of a crop
(e.g., straw and stalks) can be used as biomass fuel.
• Animal dung is dried and burned or processed in
anaerobic digesters to provide a burnable gas.


 Energy plantations:
• Many crops, including sugar beets, sugar cane, corn,
grains, and kelp, can be grown for the express
purpose of energy production.
• Two factors determine whether a crop is suitable for
energy use:
– Good energy crops have a very high yield of dry
material per unit of land.
– The amount of energy that can be produced from a
biomass crop must be more than the amount of energy
required to grow a crop.


 There are several technologies capable of converting
biomass into energy.
• Direct combustion and cogeneration
• Ethanol production
• Anaerobic digestion
• Pyrolysis
 Costs to generate electricity depend on the type of
technology used, size of the power plant, and the
cost of biomass supply.
• Currently as low as 9 cents per kilowatt hour.


Methane digester

Energy Conservation

 Conservation is not a way of generating electricity,
but a way of reducing need for additional energy
production/consumption and saving money for the
consumer.
 Much of the energy we consume is wasted.
• The amount of energy wasted through poorly insulated
windows and doors alone is about as much energy as the
U.S. receives from the Alaskan pipeline each year.
 Electrical utilities have recently become part of the
energy conservation picture.

Energy Conservation

 Many conservation techniques are relatively simple
and highly cost-effective.
• Highly efficient fluorescent light bulbs give the same
amount of light as incandescent bulbs for 25% of the
energy, and produce less heat.
• Lighting and air conditioning (removing the heat from
inefficient incandescent lighting) account for 25% of U.S.
electricity consumption.
• Automatic dimming or light-shutoff devices are being used
in new construction.

Are Fuel Cells and a
Hydrogen Economy in the Future?
 Hydrogen is abundant and generates heat and
pure water when it reacts with air.
 Hydrogen fuel cells are beginning to rise in
popularity due to their high efficiency and low
emissions.
• They do not need to be recharged, unlike batteries.
• They run continuously if provided with adequate fuel
input—anything from which hydrogen can be
extracted.

 The most common form is the proton exchange
membrane (PEM) fuel cell.
• Pressurized hydrogen gas enters the fuel cell and
contacts a catalyst that causes the hydrogen molecules
to split into hydrogen ions and electrons.
• A proton exchange membrane allows the hydrogen
ions, but not electrons, to flow through it.
• The electrons flow through an electric circuit to do work,
such as powering motors or generating lights.
• They hydrogen ions flow through the membrane and
recombine with electrons that have passed through the
circuit and with oxygen to form water.

 Obstacles delaying the development of fuel cells
include:
• Hydrogen used to power the cell is difficult to obtain in
a pure state.
• Hydrogen gas is highly flammable, difficult to store,
and not available to consumers as readily as oil-
derived fuels.
• Fuel reformation results in impure hydrogen,
decreasing fuel cell efficiency; it also releases carbon
dioxide, nitrous oxide, and particulate matter.

 Advantages of fuel cells include:
• Low operating temperature and minimal noise
generation make them safe to install in semi-exposed
areas.
• Cells are self-sustaining, making them ideal for
remote locations.
• They operate separately from power lines associated
with electrical distribution systems, so weather-related
power outages are diminished.
• They are nonpolluting.


Simple fuel cell

Summary

 Resources are naturally occurring substances of
use to humans.
 Reserves are known deposits from which
materials can be extracted profitably with
existing technology under present economic
conditions.
 Coal is the world’s most abundant fossil fuel.
 The supply of oil is limited.
 Natural gas is another major source of fossil-fuel
energy, but transport of natural gas to
consumers is problematic.

Summary

 Fossil fuels are nonrenewable.
 Hydroelectric power can be increased
significantly but may displace people.
 Geothermal and tidal applications are limited by
geographic locations.
 Wind power may be used to generate electricity
but requires wide, open areas and a large
number of wind generators.
 Solar energy can be collected and used in either
passive or active systems and can also generate
electricity.

Summary

 Fuelwood is the major source of energy in less-
developed countries.
 Biomass can be burned to provide heat or
electricity, or can be converted to alcohol or
used to generate methane.
 Energy conservation can reduce energy
demands without noticeably changing standards
of living.

Lecture 9 energy_sources

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