Module 1 energy 2023

MINISTRY OF EDUCATION AND TRAINING
NONG LAM UNIVERSITY
FACULTY OF FOOD SCIENCE AND TECHNOLOGY

Course: Physics 1
Module 1: Energy

Instructor: Dr. Nguyen Thanh Son

Academic year: 2022-2023


Contents
Module 1: Energy
1.1. Energy resources using traditional materials
1.1.1 Energy resources using traditional materials
1.1.2 Problems with these resources
1.1.3 Alternative energy sources
1.2. Thermionic engine/converter
1.2.1 Principle of thermionic emission
1.2.2 Thermionic engine
1.3. Electric energy
1.3.1 Electricity is a secondary energy source
1.3.2 Electricity generation
1.4. Nuclear energy
1.4.1 Einstein’s mass – energy relation
1.4.2 Nuclear reaction
1.4.3 Nuclear fission and nuclear fusion
1.5. Solar energy
1.5.1 Energy from the sun
1.5.2 Applications of solar technology

1.6. Other energy sources
1.6.1 Wind energy
1.6.2 Hydroelectric energy
1.6.3 Biomass energy
1.6.4 Fuel cells

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1.1. Energy resources using traditional materials
Energy is one of the most fundamental parts of our universe. It is a scalar physical quantity. In physics
textbooks, energy is often defined as the ability to do work or to generate heat.
While one form of energy may be transformed to another, the total energy remains the same. This
principle, the conservation of energy, was first postulated in the early 19th century, and applies to any
isolated system. In other words, energy is subject to the law of conservation of energy. According to this
law, energy can neither be created (produced) nor destroyed by itself and it can only be
transformed.
We use energy to do work. Energy lights our cities. Energy powers our vehicles, trains, planes and
rockets. Energy warms our homes, cooks our food, plays our music, and gives us pictures on television.
Energy powers machinery in factories and tractors on farms.
Energy from the sun gives us light during the day. It dries our clothes when they're hanging outside on a
clothe line. It helps plants grow. Energy stored in plants is consumed by animals, giving them energy;
and predator animals eat their prey, which gives the predator animal energy.
Everything we do is connected to energy in one form or another.
There are many sources of energy. Energy is present in the universe in various forms, including
mechanical, electromagnetic, chemical, and nuclear, etc. Furthermore, one form of energy can be
converted into another. For example, when an electric motor is connected to a battery, the chemical
energy in the battery is converted into electrical energy in the motor, which in turn is converted into

mechanical energy as the motor turns some device.
The transformation of energy from one form to another is an essential part of the study of physics,
engineering, chemistry, biology, geology, and astronomy. When energy is changed from one form to
another, the total amount present does not change. Conservation of energy means that although the form
of energy may change, if an object (or system) loses energy, that same amount of energy appears
in another object or in the object’s surroundings.

1.1.1 Energy resources using traditional materials
These traditional materials (or resources) include: coal, oil and natural gas (collectively called fossil
fuels). All three were formed many hundreds of millions of years ago before the time of the dinosaurs hence the name fossil fuels.
• Coal
Coal is a hard, black colored, rock-like substance. It is made up of carbon, hydrogen, oxygen,
nitrogen, and varying amounts of sulphur. There are three main types of coal - anthracite, bituminous
and lignite. Anthracite coal is the hardest and has more carbon, which gives it a higher energy content.
Lignite is the softest and is low in carbon but high in hydrogen and oxygen content. Bituminous is in
between. Today, the precursor to coal - peat - is still found in many countries and is also used as an
energy source.
Coal is mined out of the ground using various methods. Some coal mines are dug by sinking
vertical or horizontal shafts deep under ground, and coal miners travel by elevators or trains deep under
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ground to dig the coal. Other coal is mined in strip mines where huge steam shovels strip away the top
layers above the coal. The layers are then restored after the coal is taken away.
The coal is then shipped by trains and boats and even in pipelines. In pipelines, the coal is ground
up and mixed with water to make what is called a slurry. This is then pumped many miles through
pipelines. At the other end, the coal is used to fuel power plants and other factories.
Coal is used to generate electricity. Power plants burn coal to make steam. The steam turns

turbines which generate electricity.
`
A variety of industries use coal's heat and by-products. Separated ingredients of coal (such as
methanol and ethylene) are used in making plastics, tar, synthetic fibers, fertilizers, and medicines. The
concrete and paper industries also burn large amounts of coal.
Coal is baked in hot furnaces to make coke, which is used to smelt iron ore into iron needed for
making steel. It is the very high temperatures created from the use of coke that gives steel the strength
and flexibility for products such as
bridges, buildings, and automobiles.
• Oil or petroleum
Oil is another fossil fuel. It was
also formed more than 300 million years
ago. Some scientists say that tiny diatoms
are the source of oil. Diatoms (a kind of
algae) are sea creatures having the size of
a pin head. They do one thing just like
plants: converting sunlight directly
into stored energy.
In the Figure 1, as the diatoms died
they fell to the sea floor (1). Here they
were buried under sediments and other
Figure 1 Process of oil formation.
rocks (2). The rocks squeezed the diatoms,
and the energy in their bodies could not escape. Under great pressure and heat, oil and natural gas were
eventually generated. As the earth changed and moved and folded, pockets where oil and natural gas
can be found were formed (3).
Oil has been used for more than 5,000-6,000 years. The ancient Egyptians used liquid oil as a
medicine for wounds, and oil has been used in lamps to provide light. In North America, Native
Americans used oil as medicine and to make canoes water-proof. The demand for oil continued to
increase as a fuel for lamps. Petroleum oil began to replace whale oil in lamps because the price for

whale oil was very high.
As mentioned above, oil and natural gas are found under ground between folds of rock and in
areas of rock that are porous and contain the oils within the rock itself. To find oil and natural gas,
companies drill through the earth to the deposits deep below the surface. The oil and natural gas are
then pumped from below the ground by oil rigs. They then usually travel through pipelines or by ship.
The petroleum or crude oil must be changed or refined into other products before it can be used.

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Oil is stored in large tanks until it is sent to various places to be used. At oil refineries, crude oil
is split into various types of products by heating the thick black oil. Oil is made into many different
products - fertilizers for farms, the clothes you wear, the toothbrush you use, the plastic bottle that holds
your milk, the plastic pen that you write with. There are thousands of other products that come from oil.
Almost all plastic comes originally from oil. The oil products include gasoline, diesel fuel, aviation or
jet fuel, home heating oil, oil for ships and oil to burn in power plants to make electricity.
• Natural gas
Natural gas is lighter than air. Natural gas is mostly made up of a gas called methane. Methane
is a simple chemical compound that is made up of carbon and hydrogen atoms. Its chemical formula is
CH4 - one atom of carbon along with four atoms of hydrogen. This gas is highly flammable.
Natural gas is usually found near petroleum underground. It is pumped from below ground and travels
in pipelines to storage areas.
Natural gas usually has no odor, and we cannot see it. Before it is sent to the pipelines and
storage tanks, it is mixed with a chemical that gives a strong odor. The odor smells almost like rotten
eggs. The odor makes it easy to smell if there is a leak.
Natural gas is a major source of electricity generation through the use of gas turbines and steam
turbines. Natural gas is also used for heating and cooking. Natural gas is an essential raw material for
many common products, such as paints, fertilizers, plastics, antifreezes, dyes, photographic films,

medicines, and explosives as well. Another use is powering natural gas vehicles in many countries such
as Argentina, Brazil, Pakistan, Italy, Iran, and the United States.
1.1.2 Problems with these resources
• Someday they will run out
Fossil fuels are generally such fuels as coal, natural petroleum (oil) and coal. These materials
were derived from the fossilized remains of plants and animals. Much of the world has relied upon these
fuels for decades and more. As the years go on, the sources of these fuels have become less and less.
The problem with fossil fuels is that they will someday run out. It takes time for these energy sources to
develop within the crust of the earth. At the current rate of consumption, there is no way that these fuels
can develop naturally and not be used up. Currently there are ways being developed to sustain these
fuels.
More efficient uses of these energies are being produced. Cars with better gas mileage are being
manufactured. Hybrid cars which use electricity as well as gas are just one of many products which
have been developed to sustain the use of fossil fuels. Still these fuels are being depleted.
Fossils fuels cannot last forever at the current rate of consumption. Alternatives are being
developed to sustain the lifestyles that we have become accustomed to.
• They have adverse impacts on the environment
Another problem with the use of fossil fuels is no matter how safely and efficiently these fuels
are being used, they still have adverse impacts on the environment. The combustion of these fuels
contributes pollutants to the atmosphere and contributes to the greenhouse effect. This effect increases
global warming and the melting of the polar ice caps.

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♦ Environmental problems with coal, oil, and gas
• We consider the wide variety of environmental problems in burning fossil fuels - coal, oil, and gas.
They probably exceed those of any other human activities. The ones that have received the most

publicity in recent years have been the "greenhouse effect," which is changing the earth's climate; acid
rain, which is destroying forests and killing fish; and air pollution, which is killing tens of thousands of
people every year, while making tens of millions ill and degrading our quality of life in other ways.
• Coal, oil, and gas consist largely of carbon and hydrogen. The process that we call "burning" actually
is chemical reactions with oxygen in the air. For the most part, the carbon combines with oxygen to
form carbon dioxide (CO2), and the hydrogen combines with oxygen to form water vapor (H2O). In
these chemical reactions, a substantial amount of energy is released as heat. Since heat is what is needed
to instigate these chemical reactions, we have a chain reaction: reactions cause heat, which causes
reactions, which cause heat, and so on.
• The carbon dioxide that is released is the cause of the greenhouse effect. A large coal-burning plant
typically burns 3 million tons of coal and produces 11 million tons of carbon dioxide every year. The
water vapor release presents no problems, since the amount of water vapor in the atmosphere is
determined by evaporation from the oceans - if more is produced by burning, that much less will be
evaporated from the seas.
The greenhouse effect and global warming
• Electromagnetic radiation is an exceedingly important physical phenomenon that takes various forms
depending on its wavelength. Every object in the universe constantly emits electromagnetic radiation,
and absorbs (or reflects) that which impinges on it. According to the laws of physics, the wavelength of
the emitted radiation decreases inversely as the temperature increases. Conversely, the rate at which an
object emits radiation energy increases very rapidly with increasing temperature (doubling the absolute
temperature increases the radiation 16-fold). Now let us consider a bare object out in space, such as our
moon. It receives and absorbs radiation from the sun, which increases its temperature, and this increased
temperature causes it to emit more radiation. Through this process it comes to an equilibrium
temperature, where the amount of radiation it emits is just equal to the amount it receives from the sun.
That determines the average temperature of the moon. If this were the whole story, our earth would be
54 degrees cooler than it actually is, and nearly all land would be covered by ice.
• The reason for the difference is that the earth's atmosphere contains molecules that absorb infrared
radiation. They do not absorb the visible radiation coming in from the sun, so the earth gets its full share
of the visible radiation. But a fraction of the infrared radiation emitted by the earth is absorbed by those
molecules which then reemit it, frequently back to the earth. That is what provides the extra heating.

This is also the process that warms the plants in a greenhouse - the glass roof does not absorb the visible
light coming in from the sun, but the infrared radiation emitted from the plants is absorbed by the glass
and much of it is radiated back to the plants. That is how the process got its name - greenhouse effect. It
is also the cause of automobiles getting hot when parked in the sun light; the incoming visible radiation
passes through the glass windows, while the infrared emitted from the car's interior is absorbed by the
glass and much of it is emitted back into the interior.
• Molecules in the atmosphere that absorb infrared radiation and thereby increase the earth's
temperature are called greenhouse gases. Carbon dioxide is an efficient greenhouse gas. Our problem is
that burning coal, oil, and gas produces carbon dioxide, which adds to the supply already in the
atmosphere, increasing the greenhouse effect and thereby increasing the temperature of the earth. The
average temperature of the earth has been about 1 degree warmer in the 20th century than in the 19th
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century, which is close to what is expected from this carbon dioxide increase. As the rate of burning
coal, oil, and gas escalates, so too does the rate of increase of carbon dioxide in the atmosphere.
• Two side effects will accentuate this temperature rise. One is that the increased temperature causes
more water to evaporate from the oceans, which adds to the number of water molecules in the
atmosphere; water vapor is also a greenhouse gas. The other side effect is that there would be less ice
and snow.
Acid rain
• In addition to combining carbon and hydrogen from the fuel with oxygen from the air to produce
carbon dioxide and water vapor, burning fossil fuels involves other processes. Coal and oil contain
small amounts of sulfur, typically 0.5% to 3% by weight. In the combustion process, sulfur combines
with oxygen in the air to produce sulfur dioxide (SO2), which is the most important contributor to acid
rain. Air consists of a mixture of oxygen (20%) and nitrogen (79%), and at very high temperatures,
molecules of these can combine to produce nitrogen oxides (NO), another important cause of acid rain.
Sulfur dioxide and nitrogen oxides undergo chemical reactions in the atmosphere to become sulfuric
acid and nitric acid, respectively, dissolved in water droplets that may eventually fall to the ground as

rain. This rain is therefore acidic.
• After the rain falls, water percolates through the ground, dissolving materials out of the soil. This
alters the soil’s pH and introduces other materials into the water. If the soil is alkaline, the water's
acidity will be neutralized, but if it is acid, the acidity of the water may increase. This water is used by
plants and trees for their sustenance, and eventually flows into rivers and lakes. There have been various
reports indicating that streams and lakes have been getting more acidic in recent years.
Air pollution and health effects
• The greenhouse effect and acid rain have received more media attention and hence more public
concern than general air pollution. This is difficult to understand, because the greenhouse effect causes
only economic disruption, and acid rain kills only fish and trees, whereas air pollution kills people and
causes human suffering through illness.
• We have already described the processes that produce sulfur dioxide and nitrogen oxides, which are
important components of air pollution as well as the cause of acid rain. But many other processes are
also involved in burning fossil fuels. When carbon combines with oxygen, sometimes carbon monoxide
(CO), a dangerous gas, is produced instead of carbon dioxide. Thousands of other compounds of
carbon, hydrogen, and oxygen, classified as hydrocarbons or volatile organic compounds, are also
produced in the burning of fossil fuels. During combustion, some of the carbon remains unburned, and
some other materials in coal and oil are not combustible; these come off as very small solid particles,
called particulates, which are typically less than one ten thousandth of an inch in diameter, and float
around in the air for many days. Smoke is a common term used for particulates large enough to be
visible. Some of the organic compounds formed in the combustion process attach to these particulates,
including some that are known to cause cancer. Coal contains trace amounts of nearly every element,
including toxic metals such as beryllium, arsenic, cadmium, selenium, and lead, and these are released
in various forms as the coal burns.
• All of the above pollutants are formed and released directly in the combustion process. Some time
after their release, nitrogen oxides may combine with hydrocarbons in the presence of sunlight to form
ozone, one of the most harmful pollutants.
• Let us summarize some of the known health effects of these pollutants:
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Sulfur dioxide is associated with many types of respiratory diseases, including coughs and colds,
asthma, bronchitis, and emphysema. Studies have found increased death rates from high sulfur dioxide
levels among people with heart and lung diseases.
Nitrogen oxides can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to
respiratory infections such as influenza; at higher levels it can cause pulmonary edema.
Carbon monoxide bonds chemically to hemoglobin, the substance in the blood that carries
oxygen to the cells, and thus reduces the amount of oxygen available to the body tissues. Carbon
monoxide also weakens heart contractions, which further reduces oxygen supplies and can be fatal to
people with heart disease. Even at low concentrations, it can affect mental functioning, visual acuity,
and alertness.
Particulates, when inhaled, can scratch or otherwise damage the respiratory system, causing
acute and/or chronic respiratory illnesses. Depending on their chemical composition, they can contribute
to other adverse health effects. For example, benzo-a-pyrene, well recognized as a cancer-causing agent
from its effects in cigarette smoking, sticks to surfaces of particulates and enters the body when they are
inhaled.
Hydrocarbons cause smog and are important in the formation of ozone.
Ozone irritates the eyes and the mucous membranes of the respiratory tract. It affects lung
function, reduces ability to exercise, causes chest pains, coughing, and pulmonary congestion, and
damages the immune system.
Volatile organic compounds include many substances that are known or suspected to cause
cancer. Prominent among these is a group called polycyclic aromatic, which includes benzo-a-pyrene
mentioned above.
Toxic metals have a variety of harmful effects. Cadmium, arsenic, nickel, chromium, and
beryllium can cause cancer, and each of these has additional harmful effects of its own. Lead causes
neurological disorders such as seizures, mental retardation, and behavioral disorders, and it also
contributes to high blood pressure and heart disease. Selenium and tellurium affect the respiratory
system, causing death at higher concentrations.
• It is well recognized that toxic substances acting in combination can have much more serious effects

than each acting separately, but little is known in detail about this matter. Information on the quantities
of air pollutants required to cause various effects is also very limited. There can however be little doubt
that air pollution is a killer.
1.1.3 Alternative energy sources
• Alternative energy is an
umbrella term that refers to
any source of usable energy
intended to supplement or
replace fuel sources without
the undesired consequences
of the replaced fuels.
• The sources of alternative
energy are nuclear, solar,
wind, geothermal and other
energies; each of them having
Figure 2 Left: Normal earth. Right: What the earth would be if we
its own advantages and
are not using alternative energy sources.
disadvantages. Alternative
energy sources hold the key towards the future; without them, our planet will eventually head into a
blackout, or back to the Middle Ages, as shown in Figure 2.
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• Oil fuels the modern world. No other substance can have the enormous impact which the use of oil
has had on so many people, so rapidly, in so many ways, and in so many places around the world.
• Alternative energy sources must be compared with oil in all these various attributes when their
substitution for oil is considered. None appears to completely equal oil.

• But oil, like other fossil fuels, is a finite resource. There will always be oil in the earth, but eventually
the cost to recover what remains will be beyond the value of the oil. Also, a time will be reached when
the amount of energy needed to recover the oil equals or exceeds the energy in the recovered oil. At that
point oil production becomes a net energy loss.
• Oil being the most important of our fuels today, the term "alternative energy" is commonly taken to
mean all other energy sources and is used here in that context. Realizing that oil is finite in practical
terms, there is increasing attention given to what alternative energy sources are available to replace oil.
The table below mentions many alternative energy sources that have been developed so far.
Alternative energy sources
Hydro-power electricity
Solar energy
Wind energy
Wood/other biomass
Tidal power
Wave energy
Nuclear fission
Nuclear fusion
Geothermal energy
Ocean thermal energy
Ethanol
Biofuel

1.2. Thermionic engine
Also known as thermionic generator or thermionic converter, thermionic engine is a device in
which heat energy is directly converted into electrical energy; it has two electrodes, one of which is
raised to a sufficiently high temperature to become a thermionic electron emitter, while the other,
serving as an electron collector, is operated at a significantly lower temperature. It utilizes the same
principles as the thermionic vacuum
tube, an electronic device in which
electrons are driven from a cathode to

an anode by the application of a high
potential bias.
1.2.1 Principle of thermionic
emission
♦ Principles of thermionic emission
• A thermionic converter can be
viewed as an electronic diode that
converts heat into electrical energy
via thermionic emission. It can also be
regarded in terms of thermodynamics
as a heat engine that utilizes an
electron-rich gas as its working fluid.
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Figure 3 Schematic of a basic thermionic converter.


• A thermionic converter is a diode of which one electrode is heated to a sufficient high temperature
(~1700 K) so that electrons are thermionically emitted. The electrons are collected on a cooled counter
electrode (~900 K), converting heat into electricity.
• A major problem in developing practical thermionic power converters has been the limit imposed on
the maximum current density because of the space-charge effect. As electrons are emitted between the
electrodes, their negative charges repel one another and disrupt the current. Two solutions to this
problem have been pursued. One involves reducing the spacing between the electrodes to the order of
micrometers, while the other entails the introduction of positive ions into the cloud of negatively
charged electrons in front of the emitter. The latter method has proved to be the most feasible from
many standpoints, especially manufacturing. It has resulted in the development of both cesium and
auxiliary discharge thermionic power converters.
• Emission of electrons is fundamental to thermionic power conversion. The energy required to remove

an electron from the surface of an emitter is known as the electronic work function (ϕ). Its value is
characteristic of the emitter material and is typically one to five electron volts (eV). Some electrons
within the emitter have an energy greater than the work function and can escape. The proportion
depends on the temperature. The current density J0, in amperes per square meter, or the rate at which
electron is emitted from the surface of the emitter, is given by the Richardson–Dushman equation
J0 = RT 2 exp( −eϕ / kT)

(1)

where T is the absolute temperature, in kelvins, of the emitter, e is the electronic charge in coulombs,
and k is Boltzmann’s gas constant, in joules per kelvin. The parameter R in the above equation is also
characteristic of the emitter material.
• Note that the rate of emission increases rapidly with emitter temperature T and decreases
exponentially with the work function ϕ. It is therefore desirable to choose an emitter material that has a
small work function and that operates reliably at high temperatures.
• Electrons that escape the emitter surface have gained energy equal to the work function, plus some
excess kinetic energy. Upon striking the collector, a part of the energy is available to force current to
flow through the external load, such as a bulb or a resistor, thereby giving the desired conversion from
thermal to electrical energy. Part of this energy is converted into heat that must be removed to maintain
the collector at a suitably low temperature. The collector material should have a small work function.
1.2.2 Thermionic engine (thermionic converter)
• Thermionic converters are designed for use in domestic heating systems. They are also used in
regulation of current in electric circuits.
• In a thermionic converter, the electrons received at the anode flow back to the cathode through an
external resistance. However, because the cathode is hotter than the anode and the work function of the
anode is lower than that of the cathode, the rate of electron emission at the cathode is greater than that
required at the anode to complete the circuit. The surplus electron flow may then be drawn off from the
anode as additional electrical energy, effectively converting the heat energy from the cathode into
electrical energy at the anode. Such devices currently show efficiencies of up to 20% for the energy
conversion.

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• There are some advantages for using thermionic converters:
Heat sources such as solar energy, which is a renewable resource, may be used. Heat energy
which would otherwise be a wasted side-effect of an industrial process may be partially and usefully
recycled using such devices.
Devices may be manufactured using micro-electronic fabrication techniques, for very small
converters, where conventional converters are impractical.
When compared to conventional devices, such devices are likely to be smaller, weigh less, and
cause little or no pollution.
• Typically, the space between cathode and anode in such devices must be very small, and there are
difficulties in constructing such devices. Vacuum diodes may require spacing of less than 0.001 inch.
The spacing can be increased by the use of low pressure diodes with the space filled with a suitable
plasma, such as cesium gas. This advantage, however, brings with it further disadvantages, due to the
complexity of analyzing the behavior of gases in such an environment and the heat exchange reactions
within the plasma during the operation of the device, which tend to render it less efficient. In order to
encourage the release of electrons from cathode, surfaces of very low work functions must be
constructed. Such surfaces have in the past been characterized by the use of very small points, or tips,
which have the effect of increasing the potential gradient by concentrating it at the tips, to render
electron emission easier.
1.3. Electric energy
1.3.1 Electricity is a secondary energy source
• Electricity is a form of energy which can produce light, heat, magnetism, and chemical changes, and
which can be generated by friction, induction, or chemical changes. Electricity is a basic part of nature,
and it is one of our most widely used forms of energy. Electricity is usually produced using fossils,
hydraulic power or nuclear reactions, etc. Electricity is a controllable and convenient form of energy
used in the applications of heat, light and power.

• Electricity is a secondary energy source which means that we get it from the conversion of other
sources of energy, such as coal, natural gas, oil, nuclear power and other natural sources, which are
called primary sources. In most cases a primary source of energy is used to drive a turbine; the turbine
in turn drives a generator, and the electric power from the generator passes through a transformer to
power lines.
• In the late-1800s, Nikola Tesla pioneered the generation, transmission, and use of alternating current
(AC) electricity, which can be transmitted over much greater distances than direct current. Tesla's
inventions used electricity to bring indoor lighting to our homes and to power industrial machines.

1.3.2 Electricity generation
• A generator is a device that converts mechanical energy into electrical energy. The process is based
on the relationship between magnetism and electricity (electromagnetic induction). In 1831, Faraday
discovered that when a magnet is moved inside a coil of wire, electrical current flows in the wire.

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• A typical generator at a power plant uses an
electromagnet - a magnet produced by electricity - not a
traditional magnet. The generator has a series of
insulated coils of wire that form a stationary cylinder.
This cylinder surrounds a rotary electromagnetic shaft.
When the shaft rotates, it induces a small electric current
in each section of the wire. Each section of the wire
becomes a small, separate electric conductor. The small
currents of individual sections are added together to form
one large current, as shown in Figure 4. This current
carries the electric power that is transmitted from the

power plant to the consumers.
• Steam turbines, internal-combustion engines, gas
combustion turbines, water turbines, and wind turbines
are the most common methods to generate electricity.
Most power plants are about 35 percent efficient. That
means that for every 100 units of energy that go into a
plant, only 35 units are converted into usable electrical
energy.
• The electricity produced by a generator travels along
cables to a transformer, which changes electricity from
low voltage to high voltage. Electricity can travel over
long distances more efficiently using high voltage.

Figure 4 Diagram of a turbine generator
of alternating current electricity.

• Transmission lines are used to carry the electricity to a substation. Substations have transformers that
change the high voltage electricity into lower voltage electricity. From the substation, distribution lines
carry the electricity to homes, offices, and factories, which require low voltage electricity. Figure 5
depicts electrical power generation, transmission, and distribution.

Figure 5 A graphic depictions of electrical power generation, transmission, and distribution.

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1.4. Nuclear energy
1.4.1 Einstein’s mass – Energy relation

• In physics, mass-energy equivalence is the concept that any mass has an associated energy and vice
versa. In special relativity, this relationship is expressed using the mass-energy equivalence formula
E = mc2

(2)

where m is the mass of the object of interest, c is the speed of light in a vacuum, c = 3x108 m/s, and E is
the energy equivalent of the mass.
• Because the speed of light squared is a very large number when expressed in appropriate units, a small
amount of mass corresponds to a huge amount of energy. Thus, the conversion of mass into energy
could account for the enormous energy output of the stars, but it is necessary to find a physical
mechanism by which that can take place.
Example: A stick of wood is burned, and it releases 1000 joules of heat energy. How much mass
was "converted into energy?" (Ans. 1.1 x 10-14 kg)
• Two definitions of mass in special relativity may be validly used with this formula. If the mass in the
formula is the rest mass, the energy in the formula is called the rest energy. If the mass is the relativistic
mass, then the energy is the total energy.
• Formula (2) does not depend on a specific system of units. In the International System of Units (SI),
the unit for energy is the joule, for mass the kilogram, and for speed the meter per second. Note that
1 joule equals 1 kg·m2/s2. In the SI unit system, E (in joules) = m (in kilograms) multiplied by
(3x108 m/s)2.
• The concept of mass-energy equivalence unites the concepts of conservation of mass and conservation
of energy, allowing rest mass to be converted to forms of active energy (such as kinetic energy, heat, or
light). Conversely, active energy in the form of kinetic energy or radiation can be converted into
particles which have rest mass. The total amount of mass/energy in a closed system (as seen by a single
observer) remains constant because energy cannot be created or destroyed, and in all of its forms,
trapped energy exhibits mass. In relativity, mass and energy are two forms of the same thing, and
neither one appears without the other.
• The energy equivalent of one atomic mass unit (1 u):
1 uc2 = (1.66054 × 10-27 kg) × (2.99792 × 10 8 m/s)2 = 1.49242 × 10-10 kg (m/s)2 = 1.49242 × 10 -10 J

× (1 MeV/1.60218 × 10 -13 J) = 931.49 MeV, so 1 uc2 = 931.49 MeV.
• From (2) we have

∆E = (∆m)c2

(3)

where ∆E designates a change in the energy of the system and ∆m designates a change in the mass of
the system.
• This formula also gives the amount of mass lost from a body when energy is removed. In a chemical
or nuclear reaction, when heat and light are removed, the mass is decreased. So ∆E in the formula is the
energy released or removed, corresponding to a mass lost, ∆m. In those cases, the energy released and
removed is equal in quantity to the mass lost, times c2. Similarly, when energy of any kind is added to a
resting body, the increase in the mass is equal to the energy added, divided by c2.
Physics 1 Module 1: Energy
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• The rest mass of a system, however, is not the sum of the rest masses of its parts taken one-by-one,
free from the system. The difference between the rest mass of a system and the total rest mass of the
(free) component parts in the system is called the mass difference of the system, ∆m; the corresponding
energy is called the binding energy of the system. It is the energy which has been emitted in the
formation of the system.
• Nuclei are found to be made out of two constituents: protons and neutrons. We label a nucleus by its
atomic number Z which is the number of protons it contains, and by its mass number A = Z + N where
N is the number of neutrons the nucleus contains. The letter A (number of nucleons in the nucleus)
denotes the sum of Z and N.
The symbol used to identify a nucleus is ZA X where X is the name of the chemical element. For
example the carbon-14 nucleus, which contains 8 neutrons and 6 protons, is denoted by 146 C . Since the
element’s name specifies the number of electrons, and hence the atomic number Z, and since A = N + Z,

we can fully specify the nucleus by just the symbol for the chemical and the mass number.
• Nuclear binding energy, denoted by BE, is the minimum energy that would be required to
disassemble the nucleus of an atom into its component parts. To calculate the binding energy we use the
formula
BE = (∆m)c2 = [Zmp + Nmn − mnucleus]c2

(3’)

where Z denotes the number of protons and N number of neutrons in the nucleus, respectively and
mnucleus the rest mass of the nucleus of interest. We can take mpc2 = 938.2723 MeV and mnc2 = 939.5656
MeV.
Example: A deuteron 12 D , which is the nucleus of a deuterium atom, contains one proton and
one neutron and has a rest mass of 2.013 553 u. This total deuteron mass is not equal to the sum of the
masses of the proton and neutron. Calculate the mass difference and determine its energy equivalence,
which is called the binding energy of the nucleus.
Solution: Using atomic mass units (u), we have mp = mass of proton = 1.007 276 u,
mn = mass of neutron = 1.008 665 u, mp + mn = 2.015 941 u. The mass difference is therefore
∆m = 2.015 941 u − 2.013 553 u = 0.002 388 u. By definition 1 u = 1.66 x 10 -27 kg, thus
∆m = 3.96 x 10 -30 kg. Using ∆E = (∆m)c2, we found the binding energy of the deuteron is
BE = (3.96 x 10 -30 kg)(3.00 x 108 m/s)2 = 3.56 x 1013 J = 2.23 MeV.
As a result, the minimum energy required to separate the proton from the neutron of the
deuterium nucleus (the binding energy) is 2.23 MeV.
• Nature contains nuclei of many different sizes. In hydrogen they contain just one proton, in heavy
hydrogen ("deuterium") a proton and a neutron; in helium, two protons and two neutrons; and in carbon,
nitrogen and oxygen - 6, 7 and 8 protons of each particle, respectively. The weights of all these nuclei
have been measured, and an interesting fact was noted: a helium nucleus weighed less than the total
weight of its components. The same held even more for carbon, nitrogen and oxygen - the carbon
nucleus, for instance, was found to be slightly lighter than three helium nuclei. By measuring the mass
of different atomic nuclei and subtracting from that number the total mass of the protons and neutrons
as they would weigh separately, one gets the exact binding energy available in an atomic nucleus. This

is used to calculate the energy released in any nuclear reaction, as the difference in the total mass of the
nuclei that enter and exit the reaction.

Physics 1 Module 1: Energy

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1.4.2 Nuclear reaction
• In nuclear physics, a nuclear reaction is the process in which two nuclei or nuclear particles collide
to produce products that are different from the initial particles. While the transformation is spontaneous
in the case of radioactive decay, it is initiated by a particle in the case of a nuclear reaction. For
example:
6
3

Li +

2
1

H ==> 2 42 He + ∆E

If the particles collide and separate without changing, the process is called a collision rather than
a reaction.
• Energy conservation
Energy may be released during the course of a reaction (exothermic reaction) or energy may
have to be supplied for the reaction to take place (endothermic reaction). This can be calculated by
reference to a table of very accurate particle rest masses. According to the reference table, the Li
nucleus ( 63 Li ) has a mass of 6.015 atomic mass units (abbreviated u), the deuteron ( 12 H ) has 2.014 u,

and the helium-4 nucleus ( 42 He ) has 4.0026 u. Thus:
Total rest mass on left side = 6.015 + 2.014 = 8.029 u,
Total rest mass on right side = 2 × 4.0026 = 8.0052 u,
Missing rest mass = 8.029 − 8.0052 = 0.0238 u.
In any nuclear reaction, the total (relativistic) energy is conserved. The "missing" rest mass is
∆m = 0.0238 u and must therefore reappear as energy ∆E released in the reaction; its source is the
nuclear binding energy. Using ∆E = (∆m)c2, the amount of energy released can be determined. Hence,
the energy released is 0.0238 x 931.5 MeV = 22.17 MeV.
• The energy released in a nuclear reaction can appear mainly in one of three ways:
kinetic energy of the product particles,
emission of very high energy photons, called gamma rays,
some energy may remain in the nucleus, as a metastable energy level.
• When a product nucleus is metastable, it is indicated by placing an asterisk ("*") next to its atomic
number. The corresponding energy is eventually released through nuclear decay.
• In physical theories prior to special relativity, mass and energy were viewed as distinct entities.
Furthermore, the energy of a body at rest could be assigned an arbitrary value. In special relativity,
however, the energy of a body at rest is determined to be mc2. Thus, any body of rest mass m possesses
mc2 of “rest energy,” which is potentially available for conversion into other forms of energy. The massenergy relation, moreover, implies that if energy is released from the body as a result of such a
conversion, then the rest mass of the body will decrease. Such a conversion of rest energy into other
forms of energy occurs in ordinary chemical reactions, but much larger conversions occur in nuclear
reactions. This is particularly true in the case of nuclear-fusion reactions that transform hydrogen into
helium, in which 0.7 percent of the original rest energy of the hydrogen is converted into other forms of
energy.
• To calculate the energy released ∆E in a nuclear reaction, we use the formula
Physics 1 Module 1: Energy

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∆E = [ ∑ mreac tan ts − ∑ m products ]c2

where

∑m

reac tan ts

is the total rest mass of reactant nuclei (before the reaction) and

(3’’)

∑m

products

the total

rest mass of products (after the reaction).
If ∆E > 0 the nuclear reaction is exothermic and if ∆E < 0 the nuclear reaction is endothermic.
Example: Consider two deuterium nuclei fusing to form a helium nucleus: D + D ==> He + ∆E
(D consists of a proton and a neutron; He consists of two of each.) Each D has rest mass 2.01410 u and
He has rest mass 4.00260 u (1 u = 1.660566 x 10 -27 kg). Calculate ∆E. (Ans. 3.8 x 10-12 J)
1.4.3 Nuclear fission and
nuclear fusion
♦ Nuclear fission
• In nuclear physics,
nuclear fission is a
nuclear reaction in which
the nucleus of an atom
splits (breaks) into
smaller parts, often

producing free neutrons
and lighter nuclei
(fragments) and photons
(in the form of gamma
rays), as shown in Figure
6.

Figure 6 Depicting of a nuclear fission with U-235.

• Fission of heavy elements is an exothermic reaction which can release large amounts of energy both
as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where the
fission takes place).
• Nuclear fission produces energy for nuclear power and for driving the explosion of nuclear weapons.
Both uses are made possible because certain substances, called nuclear fuels, undergo fission when
struck by free neutrons and in turn generate neutrons when they break apart.
• Nuclear fission can be harnessed and controlled via a self-sustaining chain reaction. A chain reaction
refers to a process in which neutrons released in a fission produce an additional fission in at least one
further nucleus. This nucleus in turn produces neutrons, and the process repeats, as shown in Figure 7.
The process may be controlled (nuclear power) or uncontrolled (nuclear weapons). If each fission
releases two more neutrons, then the number of fissions doubles each generation. In this case, in 10
generations there are 1,024 fissions and in 80 generations about 6 x 10 23 fissions.
• The amount of free energy contained in nuclear fuel is millions of times the amount of free energy
contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting
source of energy; however, the products of nuclear fission are radioactive and remain so for significant
amounts of time, giving rise to a nuclear waste problem.
Physics 1 Module 1: Energy
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Figure 7 Depicting of a chain reaction with U-235.

• The most common nuclear fuels are 235U (the isotope of uranium with an atomic mass of 235 and of
use in nuclear reactors) and 239Pu (the isotope of plutonium with an atomic mass of 239). These fuels
break apart into elements (fragments) with atomic masses centering near 95 and 135 u. In a nuclear
reactor or nuclear weapon, most fission events are induced by bombardment with another particle such
as a neutron.
• The following two equations are examples of the different products that can be produced when a U235 nucleus breaks apart:
235
U + n ==> 141
Ba + 92
Kr + 3n + 170 MeV,
92
56
36
235
92

U + n ==>

94
40

Zr +

139
52

Te + 3n + 197 MeV.

In the first equation, the number of nucleons (protons and neutrons) is conserved, e.g. 235 + 1 =
141 + 92 + 3, but a small loss in mass can be shown to be equivalent to the energy released. Similarity

is found for the second equation.
• If a massive nucleus like uranium-235 breaks apart, then there will be a net yield of energy because
the sum of the rest masses of the fragments and generated neutrons is less than the total rest mass of the
uranium nucleus and the initial neutron. The decrease in mass comes off in the form of energy
according to Einstein’s relation. The total energy released in fission varies with the precise break up, but
averages about 200 MeV or 3.2 x 10 -11 J for U-235 and about 210 MeV for Pu-239 per fission. This
contrasts with 4 eV or 6.5 x 10-19 J per molecule of carbon dioxide released in the combustion of carbon
in fossil fuels.

Physics 1 Module 1: Energy

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• Natural uranium is composed of 0.72% U-235 (the fissionable isotope), 99.27% U-238, and a trace
quantity 0.0055% U-234. The 0.72% U-235 is not sufficient to produce a self-sustaining critical chain
reaction in light-water reactors. For light-water reactors, the fuel must be enriched to 2.5-3.5% U-235.
♦ Nuclear fusion
• Fusion power is power generated by nuclear fusion reactions. In nuclear fusion, two light atomic
nuclei fuse together
(join) to form a
heavier nucleus and
in doing so, release
energy. In a more
general sense, the
term can also refer
to the production of
net usable power
from a fusion
source. Most design

studies for fusion
power plants
involve using fusion
reactions to create
heat, which is then
used to operate a
steam turbine, similar
to most coal-fired
Figure 8 Left is a diagram of the He-He reaction.
power stations as well
Right is a diagram of the D-T reaction.
as fission-driven
nuclear power stations.
• One example of nuclear fusion reactions is 32 He + 32 He ==> 42 He + 11 H + 11 H + ∆E and shown
graphically in the left panel of Figure 8. When two of 3He hit each other, the 2 neutrons and 4 protons
rearrange themselves into one nucleus ( 42 He ) and two free protons, releasing an amount of energy, ∆E.
• The easiest and most immediately promising nuclear reaction to be used for fusion power is
2
1

D + 13 T ==> 42 He + n + 17.6 MeV

This is the fusion of deuterium with tritium creating helium-4, freeing a neutron, and releasing
17.6 MeV of energy, as shown in the right panel of Figure 8. The neutron carries 14.1 MeV and the
helium-4 nucleus ( 42 He ) has the remaining 3.5 MeV.
Conservation of energy gives (2.014102+3.016050)uc2 = (4.002603+1.008665) uc2 + ∆E,
where ∆E is the energy released in the reaction.
As a result, ∆E = 0.01884 uc2 = 0.01884 x 931.5 MeV = 17.6 MeV; 14.1 MeV is given to the
neutron and 3.5 MeV to He-4. This means that the D-T fusion reaction is very highly exothermic,
making it a powerful energy source.

• Deuterium is a naturally occurring isotope of hydrogen, and as such is universally available. The large
mass ratio of the hydrogen isotopes makes the separation rather easy compared to the difficult uranium
Physics 1 Module 1: Energy

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enrichment process. Tritium is also an isotope of hydrogen, but it occurs naturally in only negligible
amounts due to its radioactive half-life of 12.32 years. Consequently, the deuterium-tritium fuel cycle
requires the breeding of tritium from lithium using one of the following reactions:
n + 63 Li ==> 13 T + 24 He,
n + 73 Li ==> 13 T + 42 He + n.
The reactant neutron is supplied by the D-T fusion reaction mentioned earlier, the one which
also produces the useful energy. The reaction with 63 Li is exothermic, providing a small energy gain for
the reactor. The reaction with 73 Li is endothermic but does not consume the neutron. At least some 73 Li
reactions are required to replace the neutrons lost by reactions with other elements. Most reactor designs
use the naturally occurring mix of lithium isotopes. The supply of lithium is more limited than that of
deuterium, but still large enough to supply the world's energy demand for thousands of years.
• The basic concept behind any fusion reaction is to bring two or more atoms close enough together so
that the strong nuclear force in their nuclei will pull them together into one larger atom. If two light
nuclei fuse, they will generally form a single nucleus with a slightly smaller mass than the sum of their
original masses. The difference in mass corresponds to an energy released according to the formula
∆E = ∆mc2.
• Nuclear fusion occurs naturally in stars. Nuclear fusion is the energy source which causes stars to
shine and hydrogen bombs to explode. The sun is a natural fusion reactor.
• The energy released in most nuclear reactions is much larger than that in chemical reactions because
the binding energy that glues nucleons in a nucleus together is far greater than the energy that holds
electrons to a nucleus. For example, the ionization energy gained by adding an electron to hydrogen ion
(H+) is 13.6 electron volts - less than one-millionth of that it takes to force nuclei to fuse, even those of
the least massive element, hydrogen. On the other hand, the fusion of lighter nuclei, which creates a

heavier nucleus and a free neutron, will generally release even more energy than it took to force them
together - an exothermic process that can produce self-sustaining reactions.
1.5. Solar energy
1.5.1 Energy from the sun
• Solar energy is the energy obtained from the sun.
• We know today that the sun is simply our nearest star. Without it, life would not exist on our planet.
We use the sun's energy every day in many different ways. The sun provides energy in two forms –
light and heat. The sun’s energy or solar energy can be used to heat water in our homes and businesses.
It can also be used to produce electricity. Energy produced by the sun is called solar power.
• Sunlight is the earth's primary source of energy. This energy can be harnessed via a variety of natural
and synthetic processes - photosynthesis by plants captures the energy of sunlight and converts it into
chemical form (oxygen and reduced carbon compounds), while direct heating or electrical conversion
by solar cells are used by solar power equipment to generate electricity or to do other useful work. The
energy stored in petroleum and other fossil fuels was originally converted from sunlight by
photosynthesis in the distant past.
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• The earth receives on average about 174 petawatts (1 petawatt = 1 PW = 1015 watts) of incoming solar
radiation at the upper atmosphere. Approximately 30% is reflected back to space while the rest is
absorbed by clouds, oceans, and land masses. The spectrum of sunlight at the earth's surface is mostly
spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.
• Solar energy refers primarily to the use of solar radiation for practical ends. Solar technologies are
broadly characterized as either passive or active depending on the way they capture, convert and
distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight
into useful outputs. Passive solar techniques include selecting materials with favorable thermal
properties, designing spaces that naturally circulate air, and referencing the position of a building to the
sun. Active solar technologies increase the supply of energy, while passive solar technologies reduce the

need for alternate resources.
♦ Solar energy storage methods
• The storage of solar energy is an important issue in the development of solar energy because modern
energy systems usually assume continuous availability of energy. Solar energy is not available at night,
and the performance of solar power systems is affected by unpredictable weather patterns; therefore,
storage media or back-up power systems must be used.
Thermal mass systems can store solar energy in the form of heat at domestically useful
temperatures for daily or seasonal durations. Thermal storage systems generally use readily available
materials with high specific heat capacities such as water, earth, and stone.
Phase change materials such as paraffin wax and Glauber's salt are other thermal storage media.
These materials are inexpensive, readily available, and can deliver heat at domestically useful
temperatures (approximately 64°C).
Solar energy can be stored at high temperatures using molten salts. Salts are an effective storage
medium because they are low-cost, have a high specific heat capacity and can deliver heat at
temperatures compatible with conventional power systems.
Off-grid systems have traditionally used rechargeable batteries to store excess electricity. With
grid-tied systems, excess electricity can be sent to the transmission grid. Net metering programs give
these systems a credit for the electricity they deliver to the grid. This credit offsets electricity provided
from the grid when the system cannot meet demand, effectively using the grid as a storage mechanism.
Pumped-storage hydroelectricity systems store energy in the form of water pumped from a lower
elevation reservoir to a higher elevation one when energy is available. The energy is recovered when
demand is high by releasing the water to run through a hydroelectric power generator.
• Solar energy is used commonly for heating, cooking, and even in the desalination of seawater, in
works by trapping the sun's rays into solar cells where this sunlight is then converted into electricity.
Other methods include using sunlight that hits parabolic mirrors to heat water (producing steam), or
simply opening a rooms blinds or window shades to allow entering sunlight to passively heat a room.
.1.5.2 Applications of solar technology
Four-fifths of the sun’s energy falls on the oceans and drives the water cycle. Evaporation from
the sea causes rain to fall on the land, resulting in the global hydropower resource. The remaining fifth
of the sun’s energy falls on the land and is still about 2,000 times greater than the total world energy

demand. The main technologies that have been developed to capture the solar energy are Passive Solar,
Solar Thermal, Photovoltaic modules, and Concentrating Solar Power (CSP) systems.
• Passive Solar refers to the way in which buildings are designed consciously to heat space. This
method can provide up to 70% of the building’s energy requirements simply by using design and solar
Physics 1 Module 1: Energy

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orientation. By installing large glass windows on right surfaces, one gains large amounts of solar
energy.
To avoid excessive heat, either overhanging balconies are installed or trees are planted nearby.
(The benefit of trees is that they reduce sunlight in the summer, but in the winter, when the leaves have
fallen and the sun is lower, they allow the light to come in.)
• Solar Thermal refers to the use of solar energy to heat water. A solar water heater is simply water
pipes that are painted black to improve heat absorption. The pipes are small in diameter, ensuring that
there is a large surface area of water exposed to the sun. Then, the pipes are placed in a small
greenhouse, which acts to keep them insulated. Solar water heaters are facing the sun to maximize gain.
• The Photovoltaic Effect refers to the generation of electricity from sunlight in a solid-state device with
photovoltaic cells
as its basic
building blocks. A
photovoltaic cell,
commonly called
a solar cell or PV
cell, is a device
used to convert
solar energy
directly into
electrical power.

As
mentioned above,
photovoltaic cells
are the basic
building blocks of
a photovoltaic
Figure 9 A diagrams illustrating the operation of a basic photovoltaic (PV) cell.
system. Individual
cells can vary in size from about 1 centimeter (1/2 inch) to about 10 centimeters (4 inches)
across. However, one cell produces only 1 or 2 watts, which is not enough for most applications. To
increase power output, cells are electrically connected into a packaged weather-tight module. Modules
can be further connected to form an array. The term array refers to the entire generating plant, whether it
is made up of one or several thousand modules. The number of modules connected together in an array
depends on the amount of power output needed. Most current technology photovoltaic modules are
about 10 percent efficient in converting sunlight. Further research is being conducted to raise this
efficiency to 20 percent.
• Photovoltaic cells, like batteries, generate direct current (DC) which is generally used for small loads
(electronic equipment) such as watches, calculators, and lighted road signs. When DC power from
photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid,
it must be converted into alternating current (AC) using inverters, solid state devices that convert DC
power into AC power.
• Figure 9 illustrates the operation of a basic photovoltaic (PV) cell made of semiconductor materials,
such as silicon, used in the microelectronics industry. When sunlight strikes the solar cell, electrons are
knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the
positive and negative sides of this material, forming an electrical circuit, the electrons can be captured in
the form of an electric current - that is, electricity. This electricity can then be used to power a load such
as a light bulb (here) or a small electric device. It is this kind of electricity that powers space satellites.
Physics 1 Module 1: Energy

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• The most common photovoltaic (PV) cell is made mostly from silicon, the earth’s second most
abundant element. Special panels of photovoltaic cells capture light from the sun and convert it directly
into electricity. PV generators operate with no moving parts, noise, or pollution. This makes them a
very appropriate renewable energy source for urban areas. Over the past few years, there has been rapid
progress in the development of PV cells, increasing their efficiency while decreasing their cost and
weight. Worldwide sales of PV modules have increased dramatically over the past few years, from 35
peak megawatts/year (35 MW/year) in 1988 to 83 MW/year in 1995. PV cells played an essential part
in the success of early commercial satellites and they remain vital to the telecommunication
infrastructure today.
• Concentrating Solar Power (CSP) systems
use lenses or mirrors and tracking systems to
focus a large area of sunlight into a small
beam. The concentrated light is then used as
a heat source for a conventional power plant.
A wide range of concentrating technologies
exists; the most developed are the solar
trough, parabolic dish, and solar power
tower. These methods vary in the way they
track the sun and focus light. In all these
systems, a working fluid is heated by the
concentrated sunlight, and is then used for
power generation or energy storage.
A solar trough consists of a linear
parabolic reflector that concentrates light
Figure 10 Solar troughs are the most widely
onto a receiver positioned along the
deployed and cost-effective CSP technology.
reflector's focal line. The reflector is made to

follow the sun during the daylight hours by
tracking along a single axis. Trough systems provide the best land-use factor of any solar technology.
An example of solar troughs is given in Figure 10.
A parabolic dish system consists of a stand-alone parabolic reflector that concentrates light onto
a receiver positioned at the reflector's focal point. The reflector tracks the sun along two axes. Parabolic
dish systems give the highest efficiency among CSP technologies. The Stirling solar dish combines a
parabolic concentrating dish with a Stirling heat engine which normally drives an electric generator.
The advantages of Stirling solar technology over photovoltaic cells are higher efficiency of converting
sunlight into electricity and longer lifetime. A Stirling engine has an approximate mean time before
failure (MTBF) of 25 years.
A solar power tower uses an array of tracking reflectors to concentrate light on a central receiver
atop a tower. Power towers are less advanced than trough systems but offer higher efficiency and better
energy storage capability.
• Beside those mentioned above, other devices and equipment using solar energy have been recently
developed. They include solar vehicles (cars, boats, etc.), solar distillation systems which are used to
make saline or brackish water potable, and solar cookers that use sunlight for cooking, drying and
pasteurization, etc.

Physics 1 Module 1: Energy

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`1.6. Other energy sources
1.6.1 Wind energy
• Wind energy is the energy obtained from wind. People harness the power of the wind to propel the
blades of wind turbines. The rotation of turbine blades is converted into electrical current by means of
an electrical generator. In the older windmills, wind energy was used to turn mechanical machinery to
do physical work, like crushing grain or pumping water. Wind towers are usually built together on wind
farms. Today, electrical currents are harnessed by large scale wind farms that are used by electrical

grids as well as by small individual turbines for providing electricity to isolated locations or individual
homes. In 2005, the worldwide capacity of wind-powered generators was 58,982 megawatts, and their
production made up less than 1% of world-wide electricity use.
• Wind power plants, or wind farms, are clusters of wind machines used to produce electricity. A wind
farm usually has dozens of wind machines scattered over a large area. Large scale wind farms are
typically connected to the local electric power transmission network, while smaller ones are used to
provide electricity to isolated locations.
• Wind power has advantages and disadvantages as shown below:
Advantages
Wind power produces no pollutions that
can contaminate the environment. Since no
chemical processes take place, like in the burning
of fossil fuels; in wind power generation, there
are no harmful by-products left over.
Farming and grazing can still take place
on land occupied by wind turbines.
Wind farms can be built off-shore.
Wind, used as a fuel, is free and nonpolluting and produces no emissions or chemical
wastes.
Wind energy as a power source is favored
by many environmentalists as an alternative to
fossil fuels, as it is plentiful, renewable, widely
distributed, clean, and produces lower
greenhouse gas emissions.
Disadvantages
Wind power is intermittent. Consistent
wind is needed for continuous power generation.
If wind speed decreases, the turbine lingers and
less electricity is generated.
Large wind farms can have a negative

effect on the scenery.

Figure 11 A diagram of a wind machine for electricity
generating (a wind generator).

• Currently, more than 20,000 wind turbines
are used for generating electricity around the
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world and over a million for pumping water. Countries such as Denmark, Germany, Britain, and Spain
have installed numerous wind systems in order to help meet some of their energy requirements.
• A wind turbine is a rotating machine which converts the kinetic energy in wind into mechanical
energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the
machine is usually called a windmill. If the mechanical energy is then converted into electricity, the
machine is called a wind generator. Figure 11 shows a diagram of a modern wind generator.
• The blades of the turbine are attached to a hub that is mounted on a turning shaft. The shaft goes
through a gear transmission box where the turning speed is increased. The transmission is attached to a
high speed shaft which turns a generator that makes electricity.
• In order for a wind turbine to work efficiently, wind speeds usually must be above 12 to 14 miles per
hour. Wind has to have this speed to turn turbines fast enough to generate electricity. The turbines
usually produce about 50 to 300 kilowatts of electricity each.
• If the wind speed gets too high, the turbine has a brake that will keep the blades from turning too fast
and being damaged.
• Operating a wind power plant is not as simple as just building a windmill in a windy place. Wind plant
owners must carefully plan where to locate their machines. One important thing to consider is how fast
and how much the wind blows. As a rule, wind speed increases with altitude and over open areas with
no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or

shorelines, and mountain gaps.
1.6.2 Hydroelectric energy
• Hydro means "water". So, hydroelectric energy is electrical energy generated using water power. In a
hydroelectric power plant, potential energy (or the "stored" energy in a reservoir) becomes kinetic
energy. This mechanical energy is then turned into electrical energy. Hydroelectric energy is a
renewable resource. Figure 12 shows a diagram of a hydroelectric power plant.

Physics 1 Module 1: Energy

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Figure 12 A diagram of a typical hydroelectric power plant.
From the figure: water is stored behind a dam in a reservoir. There is a water intake. This is a
narrow opening to a tunnel which is called the penstock.
Water pressure (from the weight of the water and gravity) forces the water through the penstock
and onto the blades of a turbine. The moving water pushes the blades and turns the turbine.
The turbine spins due to the force of the water. The turbine is connected to an electrical generator
inside the powerhouse. The generator produces electricity which travels over long-distance power lines
to homes and businesses.
• Therefore, we see that hydroelectric energy comes from the falling water; the force of falling water is
used to drive turbine-generators to produce electricity. Hydroelectric power plants produce more
electricity than any other alternative energy sources.
• Hydroelectric energy source offers many advantages over other energy sources. It is, however, facing
unique environmental challenges.
Advantages
Hydroelectric energy is fueled by water, therefore it is a clean fuel source. Hydroelectric power
plants do not pollute the air like power plants that burn fossil fuels, such as coal or natural gas.
Generally, hydroelectric energy is a domestic source of energy.
Hydroelectric energy relies on the water cycle, which is driven by the sun, thus it is a renewable

power source.
Hydroelectric energy is generally available as needed; people can control the flow of water
through the turbines to produce electricity on demand.
Hydroelectric power plants provide benefits in addition to clean electricity. Impoundment
hydroelectric power plants create reservoirs that offer a variety of recreational opportunities, notably
fishing, swimming, and boating. Most hydroelectric power plant installations are required to provide
some public access to the reservoir to allow the public to take advantage of these opportunities. Other
benefits may include water supply and flood control.
Physics 1 Module 1: Energy
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