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Solar Cells
Theory of solar cells
Solar cell materials
Solar cell array
Solar cell power plant
Limitations
Short Answer Questions
University asked Questions
MCQs

1
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Energy is the major input to drive the life cycle and improve it
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In future, improvement in
the living standard of the mankind, industrialization of the developing countries and the global
demand for energy will increase with ever-growing population
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The power
sector is one of the major significant constituents of infrastructure
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Classification

Crude Oil, Hard Coal,
Natural Gas Liquids,
Natural Gas,
Nuclear Energy, etc
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Waste

Electricity and Heat

Wind, Geothermal,
Biomass,
Hydroelectricity,
Wave and Tidal
Energy, etc
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Coal

Fire wood

Petroleum
Electricity

Straw
Dried dung

Bio energy
Solar energy
Wind energy
Tidal energy
Energy from-

urban waste

Energy

Renewable
Energy Resources

Solar

Hydro Energy

Tldal Energy

Wind

Biomass

Non-Rene«°able
Energy Resources

Petroleum

Natuml Gas

Nuclear

Availability of Renewable Energy Resources
In India, 71% of the installed power capacity is thermal, about 12% is hydro power, 15% is other
renewable sources and about 2% is Nuclear power
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It provides energy by the process of nuclear fusion
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Solar thermal route (solar energy is converted to thermal energy with the help of
devices such as solar water heaters and solar cookers etc)

ii
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The kinetic energy of the wind is converted into electrical energy using wind turbines
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Gross Wind power potential in India is about 45,000 MW
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Asia’s largest wind form is located at Mupandal in Tamil Nadu
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It is a form of hydropower that converts energy of tides into electricity
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A barrage or dam is typically used to convert tidal energy into electricity by forcing the water

through turbines activating a generator
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India is seeking technical assistance from France which is a world leader in harnessing tidal

energy and has also successfully established a 240MW tidal energy plant at a place called La
Rance
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This temperature gradient is of the range of about 10°C is sufficient to vaporize volatile substances

like ammonia, propane etc
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The best location for establishing OTEC plants are situated along the coast of Tamil Nadu, Andaman

Nicobar Islands and Lakshadweep
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The sea solar power corporation of USA has entered into commercial agreement with Tamil Nadu

Government establishment
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❖ GEOTHERMAL ENERGY
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It is found trapped in Earth’s crust at a depth of 10 km in the form of hot springs, geysers etc
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National Aerospace Laboratory Bangalore has set up a pilot project in Manikaran for R&D and for

collecting operational data to design larger geothermal power plant
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(Biomass

refers to the organic biodegradable waste of animal and plant origin)
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It is mainly rich in carbohydrates like starch & cellulose and also contains varying amount of

nitrogen and phosphorous
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Bio gas is mainly Methane (55- 65%) & CO2 (35% – 40%)
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The organic waste extracted from biogas plant is said to be rich in phosphorous and potassium and

can be very effectively used as manure
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•

Bio energy in the form of biogas is expected to become one of the key energy resources for global

sustainable development
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What is energy?
A: The word “energy” comes from the Greek word (energeia) which means “activity, operations”
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It can also be defined as the load
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Q2
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It is
endless and quickly replaced, while the non-renewable energy resources like oil, coal and natural gas
(fossil fuels) and uranium (nuclear fuel) are limited, consumed very fast and it’s not possible to replace
them within human timescales
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Q3
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It is the most abundant
renewable energy resource
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Solar panels rarely exceed 50%
efficiency over a year
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Why is solar energy really a form of nuclear energy?
A – Because the solar energy which arrives on earth is part of a spectrum of radiation types emitted by
thermonuclear fusion (not fission) reactions which take place on the sun
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Of
course, a tiny amount of light and heat also arrives from other stars than the sun
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So, to say all light is solar energy, or hat all of the power of a solar panel comes from our sun is
not strictly true
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For example (a) solar water heater converts solar radiation energy into heat
energy, from one form into another, then it stores the heat in a hot water store and delivers it to your taps;
(b) a solar PV panel converts solar radiation energy into electrical energy, from one form into another,
then delivers it to your electricity supply, often without storing it
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University asked Questions
Q1
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How can renewable energies be compared?
Q4
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Are fossil fuels renewable?
Q6
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MCQs
Q1
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Positive
B
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No charge
D
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The amount of energy used by devices in your home in a month is measured in:

A
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Kilowatts (kW)
C
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Volts (V)
Q3
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The ability to do work
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The energy of moving electrons
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The energy of electricity
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The force of moving atoms
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What energy production method produces the most air pollution?
A
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Nuclear energy
C
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Coal energy
Q5
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It creates air pollution
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It creates water pollution
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It creates radioactive waste
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It destroys ecosystems
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What is a drawback or risk of wind energy production?
A
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B
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C
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D
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Q7
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It is renewable
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It doesn’t create pollutants
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It has relatively low maintenance costs
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All of the above
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What is a drawback of solar energy production?
A
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B
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C
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D
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Q9
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A
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Heat
C
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Nervous
Q10
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A
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False
Q11
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A barrage
B
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A photovoltaic panel
D
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Which of these is a disadvantage of hydroelectric power?
A
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Dams destroy the habitats of estuary species
C
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None of the above

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They are also commonly called ‘photovoltaic cells’ after this phenomenon, and also to differentiate
them from solar thermal devices
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•

At the most basic level, the semiconductor absorbs a photon, exciting an electron which can then
be extracted into an electrical circuit by built-in and applied electric fields
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This
process is known as ‘excitation’
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This
is known as a ‘hole’ and behaves like a particle analogous to an electron in the conduction band
(albeit with positive charge)
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This exciton must be split (also known as ‘dissociation’) before the charge carriers can be collected
and used
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This describes the level of screening between charges in a semiconducting material and affects the
binding energy of the exciton
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a) A photon is absorbed by the semiconductor, b) an electron is promoted from the valence band to
the conduction band, leaving a hole in the valence band
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We then apply a few finer electrodes on the top of the p-type semiconductor layer
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Just below the p-type layer
there is a p-n junction
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The entire assembly is encapsulated by thin glass to protect the solar cell from any mechanical
shock
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The light energy, in the form of photons, supplies sufficient energy to the junction to create a
number of electron-hole pairs
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The free electrons in the depletion region can quickly come to the n-type side of the junction
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Once, the newly created free electrons come to the n-type side, cannot further cross the junction
because of barrier potential of the junction
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As the concentration of electrons becomes higher in one side, i
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n-type side of the junction and
concentration of holes becomes more in another side, i
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the p-type side of the junction, the p-n
junction will behave like a small battery cell
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If we connect a small load across the
junction, there will be a tiny current flowing through it
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➢ The first generation (known as conventional devices) are based upon crystalline silicon, a well-studied
inorganic semiconductor
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➢ The third generation are the emerging photovoltaics – technologies which are still undergoing research
to reach commercialization
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These materials are all inorganic
semiconductors, and generally work in the most direct manner: a photon is absorbed – creating an
exciton, which is thermally dissociated (inorganic semiconductors typically have high dielectric
constants) and subsequently transported to the electrodes via an electric field
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1%) and was the first material to reach the commercial market
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The band gap of silicon is 1
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However, this is
lower than the optimum band gap (1
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In addition, the band gap is indirect – reducing the absorption efficiency and thus requiring
relatively thick layers to efficiently harvest sunlight
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7 – allowing for the thermal separation of charge-carriers after
generation
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Gallium arsenide (GaAs)
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It boasts the highest performance of any photovoltaic material, reaching 29
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This is because GaAs has a direct and more favorable band gap of 1
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Additionally, GaAs has superior electron-transport properties to silicon
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b
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1%
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44 eV, giving it the same advantages as
seen in GaAs – good absorption in thin films and low photon energy losses
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Despite these advantages, there are some issues – cadmium is highly toxic and
tellurium is very rare, making the long-term viability of this technology uncertain
for now
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Copper Indium Gallium Selenide (CIGS)
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Copper indium gallium selenide (CIGS) has achieved similar performances to CdTe
devices, with a peak of 23
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The compound has the chemical formula CuInxGa(1-x)Se2 where x can take a value
between 0 and 1
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0 eV (x = 1, pure copper indium selenide) and 1
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• However, like GaAs cells, CIGS are expensive to fabricate and result in solar panels
that cannot compete with the current commercial technologies
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Third Generation Solar Cells
The third generation of photovoltaics – also known as the emerging photovoltaic technologies – includes
dye-sensitized, organic, and perovskite solar cells
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Photons are absorbed by the dye, and the generated electron and hole transfer
to the oxide scaffold and electrolyte respectively, where they are transported to the appropriate electrodes
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These dyes are coated onto an oxide scaffold (typically titanium oxide) which are immersed in a
liquid electrolyte
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The charge carriers can then be collected at the electrodes
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However, issues still exist with use of a liquid electrolyte due to temperature stability (can
potentially freeze or expand), the use of expensive materials, and volatile organic compounds
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To date, efficiencies of 18
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These cells work similarly
to inorganic devices
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Instead, the exciton must be transported to an
interface with a material that has an energy level offset greater than the binding energy of the
photon
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As excitons can typically only diffuse approximately 10 nm before the electron and hole
recombine, this limits the thickness, structure, and ultimately – the performance of an organic
photovoltaic cell
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Currently, organic materials
suffer from stability issues arising from photochemical degradation
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Perovskites were introduced to the field relatively recently, with the

first use in a photovoltaic device reported in 2006 (where it was the dye in a DSSC achieving
2
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However, 2012 is considered the birth of the field, due to the publication of a landmark paper in
which an efficiency of 10
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Since then, the peak efficiency has risen to 25
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These materials have remarkable properties, including strong tuneable absorption characteristics
and ambipolar charge transport
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A perovskite solar cell
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There are still issues with stability and the use of toxic materials (such as lead) preventing the
technology from being commercialized, but the field is still relatively young and very active

Solar Cell array
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A solar array comprises a collection of linked solar modules made up of multiple solar panels
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The number and size of solar panels in a solar array varies in line with the intensity of sunlight
present at the place where it is installed
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are other important factors of consideration for the purchase of a solar array
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•

Solar panels present in a solar array are made of silicon cells, a glass casing and a metallic
frame
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These silicon cells have conductive properties that are useful for absorbing and transforming the
sun’s rays into electricity
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This, in turn, initiates electric current f flow through a process termed as the
“photovoltaic effect”
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❖ The direct current (DC) electricity so produced is passed to a solar inverter by the wires present
in the solar array
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Features of a Solar Array
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A solar array comprises extremely lightweight and extra thin solar lighting modules
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This protection comes in handy in rough environments
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Solar arrays have a distinctive cell layout as well as modular shap for matching the space
restraints of specific mounting areas
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Applications of a Solar Array
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A solar array harnesses solar power that can be used for solar heating, electrical power generation,
lighting of spaces, etc
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When used with solar thermal collectors or hot water panels, solar arrays are useful for generating
hot water that can be used in light industrial applications and domestic spaces
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This is possible in case of passive and active solar designs alike
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A solar cell is the basic building block of a solar module
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A solar module designed for charging a 12 volt battery will typically have 36 solar cells while the
typical residential grid connected system uses solar modules with 60 solar cells
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By increasing the number of solar cells the module voltage and wattage increases
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Small custom solar modules will
contain solar cells that are cut to smaller sizes
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The solar cells are set into a frame
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6 V DC
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This gives a nominal output voltage of 24 V DC
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A solar array (also known as a PV cell array) is set of solar panels connected in a grid
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A solar panel is made up of solar cells connected in series to give a desired dc voltage

Solar cell power plant

1
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Solar panels consists a number of solar cells
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The energy produced by each solar cell is very small, but combining the energy
of 35 of them we have got enough energy to charge a 12 volt battery
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Solar Cells
It is the energy generating unit, made up of p-type and n-type silicon semiconductor
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3
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4
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C
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C
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5
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Sometimes the unused energy
generated during daytime is used to pump water to some height, so that it could be used to generate
electricity using its potential energy when required or mainly at night time
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Electron and hole pair
will get separated after absorbing the energy of photon
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Further the diode is reversed biased to increase
this electric field
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We combine the
current of all the solar cells of a solar panel, to get a significant output
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The
electrical energy coming from the combined effort of solar panels is stored in the Lithium-ion batteries to
be supplied at nighttime, when there is no sunlight
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In production of electric panels the
chemicals used are sodium hydroxide, hydrofluoric acid and carbon tetra oxide
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Its is real danger to the
workers producing the panels but if preventive measures and proper equipments are being used then the
production of panels is said to be safe
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Disadvantages of Solar Power Plant
•
•
•
•
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It requires a lot of land to be captured forever
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The energy storage options are not efficient and moreover costly if efficient
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There is a problem if it is cloudy for few days
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Applications
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Solar power plant is powering cities in most efficient manner
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Limitations
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They are a renewable energy resource
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Solar energy is free and solar panels have a long life
...
) Therefore,
they are a good long term investment
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And as they
last for up to 50 years, they soon more than compensate for the greenhouse gases emitted in making
them, especially if they replace polluting forms of lighting such as kerosene lamps
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They can be used in remote areas, where there is no access to an electricity grid
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Disadvantages of solar panels
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Variable light intensity due to: Cycle between day and night, The path of the Sun across the sky
Clouds, Shadows

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Changing angle of the incoming sunlight to the face of the panel, due to the changing position of
the Sun in the sky

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Dirt or other obstructions

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They do not produce electrical power at night, the time when most electrical power is needed in
homes
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Silicon-based solar panels contain some toxic materials, and energy is required to extract and
transport the raw materials, and to manufacture, transport and install the panels, which means
that greenhouse gases and various pollutants are produced at these stages
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Short Answer Questions
University asked Questions
Q1
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Write about the solar cells, their materials and applications
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Explain the mechanism of photoconduction in a PV cell
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Write short notes on “Solar Cell Arrays” & “ Solar Thermal Plant”
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How many types of solar cells?
A
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2
C
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4
Q2
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25 %
B
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48%
D
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The source of energy used for satellite is
A
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Edison Cells
C
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Cryogenic Cells
Q4
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P-type semiconductor
B
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Intrinsic semiconductor
D
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Which of the following materials cannot be used as solar cells materials?
A
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GaAs
C
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PbS
Q6
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Front contact
B
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Si-wafer
D
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What should be the band gap of the semiconductors to be used as solar cell materials?
A
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5 eV

B
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1
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1
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The efficiency of a solar cell may be in the range
A
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10 to 15%
C
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70 to 80%
Q9
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B
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D
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A module in a solar panel refers to
A
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C
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series arrangement of solar cells
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series and parallel arrangement of solar cells
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Solar cells are made of
A
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C
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silicon
germanium
silver
aluminium
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The voltage of solar cells is:
A
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C
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0
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The output of solar cells is of the order of
A
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5 watts
B
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0 watts
C
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0 watts
D
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A solar cell is a p - n Junction operating in


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B
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D
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Which of the following area is preferred for solar power plants
A
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C
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Coastal areas
Hot arid zones
Mountain tops
High rainfall zones

Q14
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B
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D
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Most of the solar radiation received on the earth surface is within the range of
A
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25 to 0
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0
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8 microns
C
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6 to 0
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0
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25 microns
Q16
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2
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1
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500 W/m²
D

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