2. • This lecture was prepared considering the following references
• Solar Energy by Arno Laus Olindo Miro and Rene, chapter 1 to 3.
• Photovoltaics: fundamentals, technology and practice : mertens, Konrad, chapter 1
Dr. Eng. Mansour Alramlawi 2023 2
Lecture 1 : Energy
3. Lecture 1 : Energy
• Every law has its exceptions, except for this law
Conservation of Energy
In other words, energy cannot be created or destroyed; it can only
change forms or be transferred from one part of the system to another.
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4. • Definition of Energy
A definition of energy from Max Planck (founder of quantum physics)
Energy is the ability of a system to bring outside effects (e.g., heat, light) to bear.
• Energy is usually measured in the unit of joule (J), named after the English physicist James Prescott Joule. It
is defined as the amount of energy required to apply the force of 1 newton through the distance of 1 m, 1 J = 1
Nm.
𝐸 = න
𝑡𝑖
𝑡𝑓
𝑃(𝑡)𝑑𝑡
• Where P the amount of energy consumed per time unit.
• P is usually measured in the unit of watt (W), named after the Scottish engineer James Watt. 1 W is defined as
one joule per second, 1 W = 1 J/s and 1 J = 1 Ws.
Lecture 1 : Energy
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5. • In electrical engineering the unit of the kilowatt hour (kWh) is normally used which is
1 kWh=1000 Wh=1000W. 3600 s=3.6 . 106 Ws =3.6 MWs = 3.6 MJ
• Due to the fact that in the energy industry very large quantities are often dealt with, a listing of unit prefixes
into factors of 10 is used
Lecture 1 : Energy
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6. • Energy Types
1. Primary energy, which ‘is the energy embodied in natural resources prior to undergoing any human-
made conversions or transformations. Examples of primary energy resources include coal, crude oil,
sunlight, wind, running rivers, and uranium
2. Secondary energy is the converted form of the primary energy
3. End energy the used energy by the consumer after conversion and transportation looses is counted.
Depiction of the types of energy as an example of coal-fired power: Only about one third of the
applied primary energy arrives at the socket by the end customer
Lecture 1 : Energy
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7. • Problems with Today’s Energy Supply
Growing Energy Requirements
growth of the world population
rising standards of living
Tightening of Resources
our energy infrastructure heavily depends on fossil fuels
Increasing the prices because of high demand
Climate Change
Greenhouse gases such carbon dioxide (CO2)
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Lecture 1 : Energy
Distribution of worldwide primary energy
consumption in 2008 according to energy carriers
8. The reason is that CO2, besides the other gases (called trace gases) affects the temperature of the Earth through
the greenhouse effect.
For clarity, consider.
1. The light from the Sun arrives almost unhindered through the atmosphere,
2. the light absorbed by the ground,
3. this causes the surface to be warmed,
4. the ground will emits heat radiation,
5. this radiation is again absorbed by the trace gases,
6. released to the environment as heat.
• The heat energy thus remains in the atmosphere and only a small amount is returned back into Space, So the
trace gases acts as the glass of a greenhouse.
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Lecture 1 : Energy
9. Methods of energy conversion
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Lecture 1 : Energy
• Along all the process steps of making electricity out of fossil fuels, at least 50% of the initial available
chemical energy is lost in the various conversion steps.
• Chemical energy (from hydrogen) can be directly converted into electricity using a fuel cell. Typical
conversion efficiencies of fuel cells are 60%.
10. • Renewable energy carriers
are energy carriers that are replenished by natural processes at a rate comparable or faster
than their rate of consumption by humans.
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Lecture 1 : Energy
Various possibilities for the use of renewable energies
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Hydroelectric
Tidal Generator
Geothermal power station CSP-Solar thermal power station
Lecture 1 : Energy
12. Renewable energy
• Advantages
▪ They are practically inexhaustible,
▪ almost free of any emissions,
▪ their decentralized availability,
▪ there are practically no fuel costs. (The Sun shines for free, the wind blows irrespectively and the heat of
the Earth is an almost inexhaustible reservoir.)
• Disadvantages
▪ The energy densities in the renewable energies are small,
▪ the varying energy supply (especially, photovoltaics and wind power)
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Lecture 1 : Energy
13. • PV technology
• If this energy is converted into electricity directly using devices based on semiconductor materials, we
call it photovoltaics (PV).
• The term photovoltaic is a combination of the Greek word phós, photós (light, of the light) and the name
of the Italian physicist Alessandro Volta.
• The working principle of solar cells is based on the photovoltaic effect, i.e. the generation of a potential
difference at the junction of two different materials in response to electromagnetic radiation.
• The photovoltaic effect is closely related to the photoelectric effect that explained by Albert Einstein,
assuming that the light consists of well defined energy quanta, called photons. The energy of such a
photon is given by
𝐸 = ℎ𝑣
where ℎ is Planck’s constant and 𝜈 is the frequency of the light.
• From Einstein relation we can say that the energy of a photon is directly proportional to its frequency
and inversely proportional to its wavelength.
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Lecture 1 : Energy
14. The photovoltaic effect, continue….
• Absorption of a photon in a material means that its energy is used to excite an electron from an initial energy
level 𝐸𝑖 to a higher energy level 𝐸𝑓,
• In an ideal semiconductor electrons can have energy levels below the so-called valence band edge, 𝐸𝑣, and
above the so-called conduction band edge, 𝐸𝑐. Between those two bands no allowed energy states exist which
could be handled by electrons. Hence, this energy difference is called the bandgap, 𝐸𝑔 = 𝐸c − 𝐸v.
• If the photon energy is higher than the bandgap energy of the semiconductor, it is sufficient to break bonds
and to excite a valence electron into the conduction band, leaving a hole behind in the valance band; hence
electron-hole pairs are created.
• If a photon with an energy smaller than 𝐸𝑔 reaches an ideal semiconductor, it will not be absorbed but will
traverse the material without interaction.
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Lecture 1 : Energy
15. Dr. Eng. Mansour Alramlawi 2023 15
Photon energy is lower than
the bandgap. The photon will
not be absorbed.
Photon energy is equal to
bandgap. The electron will
move to conduction band
Photon energy is higher than the
bandgap. The photon will be
absorbed and the electron will
move to the higher energy level
in conduction band but after a
while the electron will relax to a
lower energy level in conduction
band
Lecture 1 : Energy
16. The following steps summarize the photon effect on a semiconductor material
1. The absorption of a photon therefore leads to the creation of an electron-hole pair.
2. Usually, the electrons and holes will recombine.
3. With using the right semiconductor material (n- and p type materials) the electron-hole pair can be separated.
4. The separated electrons can be used to drive an electric circuit.
5. After the electrons have passed through the circuit, they will recombine with holes.
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Lecture 1 : Energy
17. Basic structure of PV cell:
▪ P-N Junction:
This junction is formed by doping one side of the silicon
with a material that introduces positive charge carriers (p-
type) and the other side with a material that introduces
negative charge carriers (n-type).
▪ Metal Contacts:
Metal contacts are applied to the front and back surfaces of
the cell. The front contacts are usually thin, grid-like
structures that allow light to pass through. The rear contacts
are typically larger and cover most of the back surface.
▪ Anti-Reflective Coating:
A thin anti-reflective coating is often applied to the front
surface of the PV cell to reduce the reflection of sunlight
and improve light absorption.
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Lecture 1 : Energy
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Lecture 1 : Energy
N-type material
Silicon doped with phosphorus.
The result is extra free electrons and fixed positive charges
P-type material
Silicon doped with boron.
The results extra free holes and fixed negative charged
19. • When combining the PN material the holes and electrons will be combined and create the depletion region or
space charge region that is charge free area.
• The exist of the positive and negative charge will create an eclectic filed in the depletion region.
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Lecture 1 : Energy
20. • When the photons in sun light has the enough energy higher then the 𝐸𝑔 energy and this photon is able to
reach the depletion region the generated electron hole pair will be generated.
• The existed electric filed will force the ions to move form the depletion region which will make the current.
• Soler cell operation
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Lecture 1 : Energy
21. For your information
• The generated power from the PV cell is very small that why the cells connected in series and parallel to
make the solar panel and then the solar panels combined to make the solar array.
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Lecture 1 : Energy
22. For your information
▪ The power of a solar module is measured according to the Standard-Test-Conditions (STC) and defined by
three limiting conditions:
1. Full Sun radiation (radiation strength E = 𝐸𝑠𝑡𝑐 =1000 W/m2)
2. Temperature of the solar module = 25 °C
3. Standard light spectrum AM 1.5 (to be explained later)
▪ The capacity of the solar module under these conditions is the rated power (or nominal power) of the module.
It is given in Watt-Peak (Wp) as it actually describes the peak power of the module under optimal conditions
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Lecture 1 : Energy
23. THANKS FOR YOUR ATTENTION
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