Unit 7. Energy: Resources and Consumption
Energy is a key component of modern human society. It is used to power our daily lives and the
world’s growing population demands considerable increases as non-western
economies grow. We’ll look fundamental
aspects of energy and today’s primary sources, as well as the role of
alternative fuels.
What are the basic forms of energy?
Energy is the ability to do work or the potential to cause change, and the amount of work (w) is equivalent to the force (f) exerted on an object, times the distance (d) that the object moves.
Work: W = F . d.
There are two main categories of energy, potential and kinetic energy, and within these two categories there are several types of energy. Potential energy is the stored energy associated with a position in a gravitational field. For example, when you are standing on your snowboard at the top of a mountain, you have a large amount of gravitational potential energy. The gravitational potential energy (Ep) of a body is equal to the mass (m) of the object, multiplied by gravity (g), times the elevation (h) of the object:
Potential Energy: Ep= m . g . h.
When you push off the top of the mountain to snowboard down to the valley you are applying a force against gravity to move your body; you are doing work. As you move down the mountain you are converting your potential energy to kinetic energy, which is the energy of motion. The amount of kinetic energy (Ek) in a system is measured by ˝ the objects mass (m) times the velocity (v) squared. The amount of work (W) done by kinetic energy is dependent on the change in kinetic energy (rEk) plus the change in velocity (rv) of the object.
Kinetic energy: Ek = ˝ m . v2
Work:
W = rEk
+ rv
As your snowboard glides over the snow, you are creating friction and converting kinetic energy to internal (heat) energy, which is energy that is associated with the speed of atoms and molecules (Figure 7.1). While going down the slope you may also feel the sun burning your face. This heat is caused by radiant energy or the energy of photons carried by electromagnetic radiation. When you arrive at the bottom of the hill after a long ride, you may be hungry from expending so much energy, so you go to the lodge to eat a burger, otherwise known as chemical energy, so your body can do more work. Chemical energy is energy contained within molecular bonds holding the elements of chemical substances together.
The main source of energy that
we use is the Sun. Solar energy (or radiant energy) warms the planet and allows
photosynthetic plants to grow; it makes up 99% of the energy budget of our
planet. The food we eat stores chemical energy that primary producers or plants
have captured from the sun through metabolic pathways. This chemical energy is
either consumed directly, or indirectly from secondary
consumption of an animal, then subsequently used to power the cellular
functions in our bodies. To move your body, as in pushing off from the top of
the mountain in the snowboard example, you must convert chemical energy to kinetic
energy.
The firewood warming the ski lodge at the bottom of the slope is another source of chemical energy that can be readily converted to heat energy for warmth or for cooking. Fossil fuels, such as oil and coal, are other examples of chemical energy that are extracted from the Earth to power our lives. For example, it is converted to electrical energy that is transported into our homes to power appliances or into the battery of the music player you were listening to as you snowboarded down the mountain slope.
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Figure
7.1 Internal
heat generated from atomic speed increases with greater friction, so that
greater speed means higher heat http://earth.ast.smith.edu/‑james/a111/lectures/figs/04-03.jpg |
What are the laws that govern energy?
When eaming the law that govern energy, we enter the field of
thermodynamics, which describes energy as it changes from one form to another. The
first law of thermodynamics (also known as the law of conservation of energy)
states that energy can be neither created or destroyed, but can be changed from
one form to another. Another way to put this is the total input of energy into
a system must equal the total output of energy from the system. In the
snowboard example, as we went down the mountain, energy was transformed from
gravitational potential energy to the kinetic energy of motion. In this process
energy was not created or destroyed, it was just
transformed from one type of energy to another (Figure 7.2).
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Figure
7.2 Energy
transformations. http://www.ngdir.ir/SiteLinks/Kids/Image/energy_image_en/forms%20of%20energy2.gif |
However in practice, the energy
available for work in a system is not perfectly conserved as energy changes
from potential to kinetic energy. The second law of thermodynamics states that
perfectly efficient energy transformations are not possible. This means that
there are unavoidable losses in useable energy when we transform it from
one type to another. For example as our snowboarder was moving down the
mountain, the transfer of gravitational potential to kinetic energy was not
perfectly efficient, meaning that 100% of the potential energy was not
transformed to 100% of the kinetic energy. We lost useable energy for
work in the form of heat energy from the friction of the snowboard on the hill,
as well as from our bodies moving through the air, itself creating heat from
the friction of the collision with molecules in the air.
Energy tends to change from a higher quality, that is a more usable type of energy, to a lower quality, that is a less usable type of energy. This property is described by the entropy, which dictates that systems tend to drift from a high energy to a lower energy state (i.e., a more disorganized form). For example, energy moves from kinetic energy to heat or thermal energy, which easily dissipates and is thus more difficult to harness and used for work. It is not possible to recapture the heat energy that we lost as we moved down the mountain; therefore, potential energy was useable energy in our example that was then lost from the system. In another example, when burning gasoline in our cars we are converting chemical energy from the gasoline to the energy of motion or kinetic energy. In the process, we are losing large amounts of thermal energy through friction of the engine parts rubbing together, as well as from the resistance of the tires on the road and the resistance of the car moving through the wind. Because we cannot transfer 100% of the available energy to useable energy, these processes have energy transfer rates that are not 100% efficient.
Energy efficiency refers to the
ratio between energy output (services such as light, heat and mobility) and
input (primary energy like gasoline or food). In general, the greater the number of energy transformations,
the larger the fraction of energy wasted in the form of avoidable and
unavoidable energy losses. Approximately 50% of all of useable energy from
primary inputs are lost today from inefficient energy transformations. These
losses can be decreased or avoided with the right technology. For example, some avoidable useable energy
losses include poorly designed appliances, low efficiency incandescent lights
and poorly insulated homes, which allow useable energy to escape the system,
often as heat energy (Figure 7.3).
Simple strategies to save energy include converting incandescent lights
to fluorescent lights for an efficiency gain from 5% to 22%. Similarly,
designing more efficient combustion engines for cars will have profound impacts
on energy demands. A powerful way for achieving sustainable development in the
near future depends on our ability to improve energy efficiency. This would
both reduce the amount of energy that we consume, and it would decrease the
greenhouse gas emissions and pollution waste into the atmosphere from burning
fossil fuels.
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Figure 7.3 Heat energy lost around the house that can be reduced by more
efficient insulation. http://www.salford.gov.uk/energy_efficiency_home-2.jpg |
What are the major sources of today’s
energy?
Energy used for human
applications can be broken down into two broad categories: non-renewable energy
sources (fossil fuels and nuclear) and renewable energy sources (biomass,
hydrologic, solar, wind, and geothermal). Fossil fuels preserve solar energy
that was stored in organic compounds millions of years ago. Coal, oil and
natural gas are today the dominant forms of fossil fuels used around the world
accounting for 80% of all energy used globally (Figure 7.4). Coal accounts for
~24% of the energy used around the world, which is harvested from rock layers
that originate from ancient swamps. Oil (~34%) and natural gas (~21%) account
for more than half of all energy used around the world, and is trapped in rocks
that form natural containment vessels.
Because fossil fuels were formed tens to hundred of millions of years
ago, they and cannot be replenished, so these energy resources are finite.
Nuclear fuel accounts for ~7% of
global energy use and is also considered a non-renewable form of energy because
the uranium needed to create nuclear fuel is a finite, mined resource. Nuclear
fuel goes through many steps before it can be used in a nuclear power plant to
generate electricity, but is involves more efficient energy transformations
than other fossil fuels. Whereas no
significant greenhouse gases are emitted, radioactive waste products greatly
complicate the use of nuclear power plants as a energy
source.
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Figure 7.4 Primary energy supply by fuel type http://www.iea.org/textbase/papers/2006/renewable_factsheet.pdf |
In 2003, renewable energy resources accounted for ~13% of
the total global energy supply. Of that,
combustible renewables or biomass burning accounted for the greatest proportion
of energy. Combustible renewables are distinct from fossil fuels
because they are a renewable resource. Combustible renewables and renewable
waste are organic material and waste from plants, trees and crops that are
traditionally used as firewood for cooking and heating in many developing
countries. However, modern uses include combustion to produce energy in the
form of electricity, steam and biofuels. Hydroelectric energy accounts for the second
largest proportion of renewable energy with ~2% of global energy use.
Hydroelectric power plants use the kinetic energy of falling water to generate
electricity. A turbine and a generator convert this energy into mechanical and
then electrical energy.
Modern renewable forms of energy account for less than 1%
of global energy used today. However, their use is on the increase as the
impact of fossil fuels burning is become clearer and this resource is becoming
scarcer or politically more difficult to secure. Modern renewables are generated from solar,
wind, water and geothermal energy, and are produced
on local scales; therefore, their use would result in renewable energy
development, changes in infrastructure, and job creation in many regions of the
world.
Solar panels use photovoltaic
cells that convert light energy into electricity at the atomic level.
Photovoltaic systems can be constructed to any size based on individual energy
requirements, and are low-maintenance. They are ideal for supplying power to
homes far from utility power lines in remote areas, especially when their
efficiency is further improved. Electricity generating wind turbines are used
to harness the kinetic energy from wind created
by the uneven heating of Earth lower atmosphere (or troposphere). Renewable energy can also be generated from wave
and tidal movement at coastal areas or it can be captured from Earth's internal
heat. Typically, geothermal energy is used where access to hot rocks and water
is available.
What are some of the costs and benefits associated with today’s sources
of energy?
Fossil fuel burning accounts for
more than 70% of all electricity generated in the
The combustion of coal, oil, and
natural gas to generate electricity and power our vehicles contributes to
global warming through increasing the concentration of carbon dioxide (CO2)
in the atmosphere (Figure 7.5). Furthermore, the secondary emissions associated
with fossil fuel burning, such as sulfur oxides (SOx),
nitrogen oxides (NOx), hydrocarbons, soot,
dust, smoke and other suspended particulate matter cause persistent health
problems like cancer and asthma. Atmospheric emissions from power plants alone
are responsible for roughly two-thirds of SOx
emissions, one-third of NOx emissions, and
one-third of all CO2 emissions in the
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Figure 7.5 Global fossil carbon emissions over time http://upload.wikimedia.org/wikipedia/en/5/56/Global_Carbon_Emission_by_Type.png |
In some ways, nuclear fuel is cleaner than fossil fuels, because nuclear power plants emit no significant greenhouse gases or generate particulate air pollution. However, the radioactive nature of nuclear fuel creates risks of nuclear accidents, like the 1986 disaster at Chernobyl in the former USSR (now Ukraine). Nuclear accidents can have disastrous consequences for the population and the environment through radiation poisoning and contamination of land and water resources. There is also no simple way to dispose of the spent nuclear waste that is left after the nuclear fuel has been used in the reactors. Finally, nuclear fuel can be used to create nuclear weapons, which are a major concern for escalating regional conflicts.
Presently, renewable energy resources
only account for ~13% of total energy needs.
Biomass burning, mostly in developing countries, and hydroelectric power
are currently the most widely used sources of renewable energy. However,
biomass burning is a major cause of deforestation and threatens biodiversity
around the world. In addition, hydroelectric dams can be damaging to local
people, riparian ecosystems, native species and migrating coldwater fish
populations. Hydroelectric dams also release methane from decaying organic
matter trapped within dam reservoirs, contributing to global warming. The huge Three Gorges Dam project in China is
one of the most controversial dam projects in the world, with large scale
environmental costs for short-term economic benefit. Less ecologically invasive
renewables such as wind, solar, geothermal and wave energy may be able to
mostly avoid undesirable atmospheric emissions, waste and negative impacts on
land and water resources.
What drives our need for energy?
Energy is a key requirement for
economic and social development. Throughout human history, development has been
tied to energy resources, whether that was through human or animal muscle
energy for work, or from more modern types of energy such as machines that use
fossil fuel or electric energy to do work. The industrial revolution radically
altered the relationship between humans and energy, allowing for the rapid
expansion of the human population and economic development in many regions of
the world. However, about three quarters of the people on earth currently still
do not have access to the benefits from advanced energy resources and still
rely on human or animal muscle power to do the majority of their work.
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Figure 7.6 Population growth and energy use over time Adapted from:
http://www.biopolitics.gr/HTML/PUBS/VOL5/html/sot1_gre.htm |
Access to energy is directly
related to the quality of human life, social welfare and social
development. A society’s quality of life
or standard of living can be measured by the amount of total per capita energy
used (Figure 7.6). Societies with high levels of energy infrastructure and
availability are better able to meet the basic needs of their population. The
availability of energy also contributes to social development by improving
access to education and public health. Agricultural productivity and food
security is coupled with energy availability, with reliable energy sources
substantially improving the livelihoods of people living in rural communities.
Energy is the driver of economic
growth and economic development, as its availability supports the expansion of
businesses, schools and other aspects of the social infrastructure. In
addition, energy supports the transportation of goods, supplies and working
people, which are necessary for businesses and economies to flourish. Energy
and petroleum products are also key ingredient for the development of products,
such as medicines and electronics.
Economic activity and energy use
is expected to expand rapidly in the next twenty years, especially in emerging
economies such as
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Figure
7.7 World
marketed energy use by region 1970-2025 www.eia.doe.gov/iea |
Recognizing the key role of
energy in today’s human society is well illustrated by the strong positive
relationship between wealth [measured in gross national product, GNP, or gross domestic product, GDP) and
energy use (Figure 7.8). In the wealthier
nations, energy availability stimulates economic development,
which in turn creates more energy infrastructure, services and economic growth.
Many people in impoverished nations have little access to energy resources or
infrastructure, which limits social and economic development.
Energy availability is also
critically tied to the environment and sustainable development. Our use on
fossil fuels is fundamentally changing the composition of the Earth’s atmosphere,
which has major environmental and social consequences. Sustainable development
of energy depends on society to provide reliable sources of clean energy to the
growing number of people in emerging economies, as well as altering the energy
infrastructure to cleaner and perhaps distributed technologies.
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Figure
7.8 Energy
consumption versus GNP |
What does the
future hold for our global energy needs?
Global
demand for energy is expected to increase by more than 50% by the year 2030, based
on economic predictions. Although western nations are still the dominant users
of energy, other parts of the world are on a track to surpass North America as
the largest user, as Western Europe and
On
our current path, by the year 2030, fossil fuels are expected to meet 85% of
the new demand for energy, with oil supplying much of that need due to its
importance in the transportation and industrial sectors. Sixty two percent of
electricity generation needs are expected to occur from coal and natural gas,
with consumption of natural gas expected to increase two-fold by 2030. (Figure 7.9).
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Figure 7.9 World marketed energy use
by energy type 1970-2025 www.eia.doe.gov/iea |
Although fossil fuels are expected to supply the majority of global energy needs in 2030, total renewable energy use is also expected to increase significantly to meet the greater and longer-term demand for power (Figure 7.10). It is predicted that this increase may just keep pace with demand, rather than exceed it. Overall, renewable energy resources are expected to account for 20% of world electricity generation in 2030, which is only a 2% increase from today. Ninety percent of the electricity generated from renewable energy resources today comes from hydroelectric power plants with combustible renewables accounting for 6% of electricity generation, and other modern renewables such as wind, solar, and geothermal, accounting for the rest.
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Figure 7.10 Renewable supply by energy source 2003-2030 http://www.iea.org/textbase/papers/2006/renewable_factsheet.pdf |
In developing countries, heating and cooking currently account for the majority of renewable energy consumption, with traditional biomass burning contributing the largest portion, and this trend is expected to continue into the near future. Of the renewable resources, hydroelectricity is still expected to supply the greatest amount of electricity, with wind power the second-largest renewable energy source. Biomass and geothermal energy used for electricity generation are both expected to increase three-fold by 2030, while solar, wave and tidal energy are projected to increase substantially after 2025.
The
current level of renewable energy development represents only a small
proportion of what can be developed with technological investment. The cost of
many of these technologies has already decline significantly, and it is
estimated that use of renewable energy sources could meet 50-80% of the
Last updated: 8/25/2006 12:12 PM