Renewable Energy Resogvgbgvtbghbyurces.pdf

1
UNIT
CONTENTS
Part-l: Various Non Conventional
Energy Resources
Part-2 : Availability of Non Conventional
Energy Resources
Part-3 : Classification of Non
Introduction
and Solar Cells
Conventional Energy Resources
Part-4: Relative Merits and Demerits
Part-5 : Theory of Solar Cells,
Solar CellMaterials
Part-6 : Solar Cell Array
Part-7: Solar Cell Power Plant
Part-8 : Linitations
1-1M(0E-Sem-7)
1-2M to 1-9M
........1-9M to 1-11M
1-11M to 1-12M
1-12M to 1-13M
1-13M to 1-19M
1-19M to 1-20M
1-20M to 1-22M
1-22M to 1-24M

1-2 M(OE-Sem-7)
Answer
Que 1.1. What are the conventional and non conventional energy
sources ? Describe the fossil fuel as a conventional energy source.
a.
1
A. Conventional (Non Renewable) Energy Sources : These are the
sources ofenergy which are exhaustible i.e., cannot be replaced ifonce
they are used.
2
3
B. Non Conventional (Renewable) Energy Sources : These are the
sources of energy which are inexhaustible i.e.,can be used to produce
energy again and again.
4
5
Various Non Conventional Energy Resources.
Long Answer Type and Medium Answer Type Questions
C. Fossil Fuel as a Conventional Energy Source :Some of the fossil
fuels are discussed below :
6.
PART-1
Introduction and Solar Cells
Questions-Answers
Example:Coal,Petroleum products, Naturalgasete.
Coal Energy :
Example: Sun,Water, Animal dung, Agro-waste etc.
silt.
Coal is a convemtional energy source.
It is formed due todegradation oftreesand plants buried under layers of
Uses of coal:
It is composed of mainly carbon and hydrocarbons.
Coal is found in Jharkhand, U.P., M.P., Bihar etc. in India.
Coal is used to generate electricity. Power plants use coal for heating
the water to generatesteam, which runs the turbines to generate
electricity.
Various industries use heat obtained from coal in making plastics,
tar, synthetic fiber, etc.
Environmentalproblems :
Coal is heated in furnace to make coke, which is used to melt iron
for making steel.

b.
1
2.
3
4.
enewable Energy Resources
5
4
2
3.
i. Coal also produces sulphur dioxide which is a cause for acid rain.
Natural Gas :
Natural gas formed by decomposition ofdead animals and plants buried
under the earth.
It is mainly composed of methane (CH,) with small amount ofpropane
and ethane.
Natural gas is the cleanest fossil fuel.
Uses of natural gas :
Due to combustion of coal, carbon dioxide is produced which is
responsible for causing global warming.
i
energy.
ii.
It is also used in thermal power plants for generating electricity.
Advantages :
Que 1.2.
It is used as a domestic and industrial fuel.
1-3M (0E-Sem-7)
Natural gas has a high calorific value and it burns without any
smoke.
It can be easily transported through pipelines.
Discuss renewable forms of energy. Highlight their merits and
demerits.
Answer
Various Sources of RenewableEnergy:
A. Solar Energy :
ii.
Give a brief review of various sources of renewable
1. Solar energy is a clean, cheap and abundantly available renewable energy
and it is also the most important of the non conventional sources of
energy because it is non-polluting and, therefore helps in decreasing
the green house effect.
OR
Solar energy can be used as :
By direct conversion to afuel by photosynthesis.
By direct conversion to electricity by photovoltaic.
ii. By conversion to electricityvia thermo-electric power system.
The sun releases the enormous amount of energy due to continuous
fusion reaction taking place inside the sun.
The sun sends out the energy in the form of radiations at the rate of
3.7 x 1020 MW.

14M(OE-Sem-7)
b.
6
1.
2.
4.
a.
B. Biomass :
Solar
Biomass
|Biofuels
i
Geothermal
5. However, the energy intercepted by the earth is about 1.85 x 10!"MW.
Merits of Solar Energy :
Noiseless operation.
energy.
Sun
Hydro
Merits :
Earth
Wind
Fig. 1.2.1. Renewable sources of energy.
Ocean
Thisenergy available is several times more than alltheenergy produced
and consumed in the world.
Tidal
wave
Moon)
Occupies less space on floor as there isno need ofstorage vessels.
ii. Cheaper initial cost and no need ofcontainers to store the fuel.
Demerits:
1. Solar equipments fail to work in nights, cloudy days or rainy season.
Large space is required for the collection ofsolar energy at a useful
rate.
Green plants trap solar energy through the process of photosynthesis
and convert it into organic matter. This organic matter is known as
biomass.
Wood, charcoal, agriculturalwaste produces the bio-energyafter burning,
and cow dung,garbage are anaerobically decomposed to obtain the
Dried animal dung or cattle dung cakes are used directly as fuels in
rural area but it produces smoke and has low efficiency ofburning.
Cost ofobtaining bio-energy through plantations is lesserthan cost
ofobtaining energy from fossil fuels.

Renewable Energy Resources
b. Demerits:
1
2
3.
4
C. Hydro Energy :
5.
a.
i
b.
i.
1.
2.
Plants ensure acontinuous supply ofenergy due to their continuous
growth.
3.
iii. Growth of biomass consumes more C0, than is released during
combustion ofbiomassbesides producingthe atmosphere-purifying
oxygen asa by-product ofthephotosynthesis process.
4.
Accumulation of water in the pipe line and need to remove it at
periodic intervals.
i. Inefficient designing ofgas appliances.
1-5 M(OE-Sem-7)
üi. Seasonal variation in gas production due to lack of temperature
control and poor insulation of the plant.
It is a renewable energy source, which is used to generate electricity.
Hydropower is obtained from water flow or falling water from aheight.
Water stored behind dam and at aheight has alot of potential energy
which is converted into mechanical and electrical energy.
The water is released gradually and is allowed to fall under the
gravitational force and drive which rotate hydraulic turbines.
The generators attached with turbine produce the electricity.
Advantage :
D. Wind Energy :
Hydropower does not pollute the water or the air during operation and
nowaste products are formed.
Limitation :
The generation of electricity by hydroelectric power plants results in
pollution and ecologicaldisturbance like flooding situationand adverse
effects on flora and fauna.
Wind energy is a renewable source of non polluting energy and it has
tremendous potential which ifharnessed, can easily satisfy the energy
demands of a country.
Estimates reveal that 2 %of the total solar energy falling on earth is
converted to kinetic energy in the atmosphere.
30%ofthis kinetic energy occurs in the lowest 1000 mofelevation i.e.,
wind in the lowest kilometer has maximum kinetic energy which can be
converted intomechanica! energy which in turn can be utilized to
generate electricity or to perform some other useful work.
Since, the energy possessed by wind is by virtue of its motion, so the
device used to extract its energy should be capable ofslowing down the
wind.

1-6 M (0'3-Sem-7)
a.
b
1
2
3
4
5
6
a.
1
Merits :
ii.
E. Tidal Energy :
2
a.
ii. Non polluting and eco-friendly.
i.
Demerits:
E:
F:
Abundance availability for no price.
Useful at remote places also for electricity generation.
Less favourable in city locations as the wind is available at higher
locations.
i. Present day wind energy systems are a source of immense noise
pollution.
It is unreliable and intermittent.It is not available regularly.
Gravitational pull by sun and moon result in the tides.
This type ofenergy can be harnessed byconstructing the tidal barrage.
Energy can be harnessed from high as well as from low tides.
E:
F:
During high tides, the sea water flows into the reservoir ofthe barrage
and operates the turbine which in turn produces electricity, by rotating
generators.
During low tides, the water stored in the reservoir flows into the sea
and again operates the turbine.
In this way the energy can be harnessed from high and low tides.
Merits :
E:F
i. Very less area is required because they are on bays.
b. Demerits:
Itis free from pollution as it does not use any fuel.
It does not produce any unhealthy waste like gases, ash, refuse.
etc.
F. Ocean Thermal Energy :
i. Tidal power plants can be developed only if naturalsites are available.
The capital cost ofthe plant is high.
Utilization of tidal energy on smallscale has not yet proved
economical.
OTEC i.e., ocean thermalenergy conversion plants convert the heat of
theoceanintoelectricalenergy, with the help oftemperature difference.
The large temperature difference between warm surface sea water
(28- 30 "C)and cold deep sea water (5 - 12 °C) is used to generate
electricity, with the help of oceanthermal energy conversion system.
Merits :
The OTEC process exploits the temperature difference between
the warm surface and cold bottom water to produce electricity. In
India,the conditions for operation of OTEC plant are favourable
because of this temperature different that remains constant
throughout the year.

b. Demerits:
1
2
3
a.
b
G. Wave Energy :
1.
2
3
4
ii.
5
6.
i
a.
i.
Inexpensive transmission ofelectricity is possible provided the OTEC
plant is less than 30 km from the sea shore.
ii. OTEC technology is costly and difficult.
At greater distance (from plant to sea shore) the transmission cost
ofelectricity is increased.
OTEC technology is in infant stage.
The motion of the sea surface in the form of wind waves forms a source
of energy.
Floating propellers are placed in shallow waters, near the shores and
due tomotion of the waves,the propellers also get the motion and this
kinetic energy can be used to drive turbines.
ii.
This is cheap, clean and inexhaustible source of energy.
Merits :
H. Geothermal Energy :
Ocean wave energy source is renewable and free of cost: hence its
importance will increase with time.
Demerits:
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Waves are continuous. They come and go between 6 second.
Collector size of wavemachines is comparatively smaller than solar
devices.
Corrosion of materials used in plant.
i
Marine growth of algae in the plant.
Obstruction to ships.
The energy harnessed from the hot rocks present inside the earth is
called as geothermal energy.
There is an increase in the temperature of the earth with increasing
depth below the surface.
The fission of radioactive material naturally occurring in the rocks
increases the temperature of the earth as we move down from the
earth's surface.
Hot molten rocks called 'magma' are present in the core of the earth.
This causes sometimes volcanic action.
This hot steam is used to operate turbines to generate electricity.
Artificially it can also be harnessed with the help ofpipes by drilling the
hot rocks, which make the hot water to gush out through pipes which
turns the turbine ofthe generator to produce electricity.
Merits :
It is cheap and clean source ofenergy.
Geothermal plants require little land area.

1-8 M (OE-Sem-7)
b. Limitations:
1.
2
K. Hydrogen Energy :
3.
4.
5
6
7.
a.
b.
i
2
i. Noise pollution results from the drilling operations.
Air pollution results in case of release of gases like H,S, NH, present
in the steam waste.
Hydrogen is considered as an alternative future source of energy.
It is a non conventional energy resource.
1.
Hydrogenenergyhasatremendous potentialbecause it can be produced
from water which is available in abundance in nature.
In sun's core, hydrogen atoms combine to form helium atom which is
known as fusion reaction.
Itgives the radiant energy which sustains the life on the earth.
Hydrogen can be separated from water by means ofelectrical energy.
It can also be obtained from fossil fuels.
Advantages :
i.
ii. Its burning is non-polluting.
i
Disadvantages :
i.
Hydrogen energy has very high energy content.
Highly flammabie.
Que 1.3. Discuss the main features ofvarious types ofrenewable
and non-renewable energy sources. Also explain the importance of
non-conventional energy sources in the context of global warming.
AKTU2016-17, 2018-19; Marks 10
It is more expensive.
Answer
A. Types of Renewable Energy Sources : Refer Q. 1.2, Page 1-3M,
Unit-1.
B. Types of Non-renewable Energy Sources : Refer Q. 1.1,
Page 1-2M, Unit-2.
C. Importance of Non-conventional Energy Sources in the Context
of Global Warming:
Global warming is the phenomenon of rise in temperature of
environment due to the rise in concentration ofthe various gases like
CH,, C0,, aerosols, NO,, etc which is caused by the burning of
conventional fossil fuels in industries.
Non-conventional energy resources like solar energy, wind energy, ocean
thermal energy, etc are eco-friendly resources and do not produce any
kind ofpollutants or harmful gases like CO,.CH,, S0,, NO, etc.

3
Que 14.
1
2
Answer
3
4
Discuss the prospects of non conventional energy
sources in India.
5.
6
7
Thus, we can say that non-conventionalenergy resources are playing
an important role in context ofglobal warming by not producing harmful
gases which increases the temperature of environment.
8.
9
PART-2
Availability of NonConventional Energy Resources.
1-9 M(OE-Sem-7)
Questions-Answers
Prospects of Non Conventional Energy Sources in India:
more.
India is heavily dependent on fossil sources of energy for most of its
demand.
This has necessitated the country to start aggressively pursuing
alternative energy sources - solar, wind, biofuels, and small hydro and
India is the 4th largest country with regard to installed power generation
capacity in the field of renewable energy sources.
Wind, hydro, biomass and solar are main renewable energy sources.
India has tremendous potentialities to harness the much-needed energy
from renewable sources.
The country has an estimated renewable energy potential of around
90000 MW from commercially exploitable sources; wind,
48500 MW; small hydro, 15000 MW and biomass/bio-energy.
25000 MW.
Inaddition, India has the potential to generate 35 MW per square km
using solar photovoltaic and solar thermal energy.
India is among top 5 destinations worldwide for solar energy
development.
Government has launched JawaharlalNehru National Solar Mission
which aims to generate 20 GW by 2022.
10. Wind energy is the fastest growing renewable energy sector.
11. Wind energy, with an installed capacity of nearly 15 GW, accounts for
the bulk of installed renewable energy capacity in (ndia making it fifth

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12. Coastal areas ofGujarat, Tamil Nadu, AndhraPradesh, as well as vast
areasofMaharashtraand Madhya Pradeshprovide agoodpotential for
its development.
13. Globally, India is in the fourth position in generating power through
biomass and has the potential to become aworld leader in the utilisation
of biomass.
14. Biomasspower projectswith an aggregate capacityof773.3MVWthrough
over 100projects have been installed in the country.
top country in the world, after USA, China, Germany, and Spain in
terms ofinstalled capacity.
15. Forthe last 15 years, biomass power has become an industry attracting
annual investment of over 1000 billion, generating more than 9billion
unit of electricity per year.
16. More than 540 million tonnes oferop andplantationresidues are produced
every year in India and a large portion is either wasted, or used
inefficiently.
17. By using these surplus agriculturalresidues, by conservative estimates
more than 16000 MW ofgrid quality power could be generated through
biomass.
18. With numerous rivers and their tributaries in India, smallhydro RE
(< 25 MW) presents an excellent opportunity with an estimated potential
of 15000 MW with only 17 percent ofthis sector exploited so far.
19. Over 674 projects aggregating to about 2558.92 MWgenerating capacity
has been set up in the country as on 31.12.2009. Most of thepotential is
in Himalayan states as river-based projects and in other states on
irrigation canals.
it ?
Que 1.5.
Write short note on MNRE.
A.
2.
Answer
1.
MNRE:
What is MNRE ? What are the mission and function of
OR
3. Creation CASE and ministry:
AKTU2015-16, Marks 04
The Ministry of New and Renewable Energy (MNRE) is the nodal
ministry ofthe government ofIndia for all matters relating tonew and
renewable energy.
The broad aim of the ministry is todevelop and deploy new and
renewable energy for supplementing the energy requirements of the
country.

4.
5.
6.
7.
B.
1
2
3
a. Commission for Additional Sources ofEnergy (CASE) in 1981.
Department ofNon Conventional Energy sources (DNES) in 1982.
Ministry of Non Conventional EnergySources (MNES) in 1992.
d. Ministry of Non Conventional Energy Sources (MNES) renamed
as ministry of New and Renewable Energy (MNRE) in 2006.
b
C.
The role of new and renewable energy has been assuming increasing
significance in recent times with the growing concern for the country's
energy security.
Energy self-sufficiency was identified as the major driver for new and
renewable energy in the country in the wake ofthe two oil shocks ofthe
1970s.
The sudden increase in the price ofoil, uncertainties associatedwith its
supply and the adverse impact on the balance ofpayments position led
to the establishment ofthe commission for additional sources ofenergy
in the department ofscience and technology in March 1981.
The commission was charged with the responsibility of formulating
policies and their implementation, programmes for development ofnew
and renewable energy apart from coordinating and intensifyingR &D
in the sector.
MISSION:
1-11 M (OE-Sem-7)
The Jawaharlal Nehru national solar mission was launched on the 11th
January, 2010 by the Prime Minister.
The mission has set the ambitious target ofdeploying 20,000 MWofgrid
connected solar power by 2022 is aimed at reducing the cost of solar
power generation in the country through :
i Long termn policy,
Large scale deployment goals,
ii. Aggressive R&D, and
iv. Domestic production of critical raw materials, componerts and
products, as aresult to achieve grid tariffparity by 2022.
Mission will create an enablingpolicyframework to achieve this objective
and make India aglobal leader in solar energy.
PART-3
Classification of Non ConventionalEnergy Resources.
Questions-Answers

1-12M(OE-Sem-7)
Que 1.6. What are the conventional and non-conventional energy
sources ? Write short notes on classification of energy resources.
Answer
B.
A. Conventional and Non Conventional Energy Resources :
Refer Q. 1.1, Page 1-2M, Unit-1.
i.
1.
2
i.
ii.
Classification :
Primary Energy Resources:
These resources are obtained from the environment.
Example: Fossil fuels, solar energy, hydro energy and tidal energy.
These resources can further be classified as :
Conventional Energy Sources :
a.
Example :Thermal power.
b. Non Conventional Energy Sources :
Example :Wind energy, geothermal, ocean energy, solar energy
and tidal energy.
Renewable: These sources are being continuouslyproduced in
nature and are inexhaustible.
Example: Coal, petroleum etc.
Example: Wood, wind energy, biomass, biogas, solar energy etc.
b. Non Renewable :These are finite and exhaustible.
C. Secondary Energy Resources : These resources do not occur in
nature but are derived from primary energy resources.
PART-4
Example: Electrical energy from coal burning, H, obtained from
hydrolysis of H,0.
Relative Merits and Demerits.
Questions-Answvers
Que 1.7. What arethe advantages and limitations of non
conventional or renewable energy resources ?

Answer
A. Advantages :
1
2.
3
4
B.
1.
2
4
5
Renewable energy is an indigenous resource available in considerable
quantities to all developing nations and capable, of having asignificant
local, regional or national economic impact. The use ofrenewable energy
could helpto conserve foreign exchange and generate local employment
if conservation technologies are designed, manufactured, assembled
and installed locally.
Several renewable resources are financially and economically competitive
for certain applications, such as in remote locations, where the costs of
transmitting electrical power or transporting conventional fuels are
high, or in those well endowed with biomass, hydro or geothermal
resources.
1-13 M (OE-Sem-7)
Since conversion technology tends to be flexible and modular, it can
usually be rapid deployed. Other advantages ofmodular over very large
individual unit include easyin adding new capacity, less risk in comparison
with lumpy investments, lower interest on borrowed capital because of
shorter lead times and reduced transmission and distribution costs for
dispersed rural locations.
Rapid scientificand technological advantages are expected to expand
the economic range of renewable energy applications over the next 8-10
years, making it imperative for international decision makers and
planners tokeep awareness of these developments.
Limitations:
Inadequate documentation and evaluation of pastexperience, ascarcity
of validated field performance data and a lack of clear priorities for
future work.
3 Technical and economic uncertainties in many renewable energy
systems, high economic and financial costs for some systems in
comparison with conventional supply option and energy efficiency
measures.
Weak or non-existent institutions and policies to finance and
commercialize renewable energy systems.
Skeptical attitudes towards renewable energy systems on the part of
the energy planners and a lack of qualified personnel to design,
manufacture, market, operate and maintain such systems.
Inadequate donor coordination in renewable energy assistance activities,
with little or no information exchange on successful and unsuccessful
projects.
PART-5
Theory of SolarCells, Solar Cell Materials.

1-14 M (OE-Sem-7)
Answer
Que 1.8. Write short note on solar cells and its materials.
A. Solar Cells :
1
2
3.
4.
1
2
3
4
5
B. Solar Cell Materials :
Questions-Answers
B.
Photovoltaic energy is the conversion of sunlight into electrical energy
through aphotovoltaic cell, commonly calleda solar cell.
Solar cells are the solid state electronic device used to convert the
electromagnetic energy of solar radiation directly into direct current
electricity. This conversion takes place inside the cell.
When sunlight strikes the solar cell, electrons are knocked loose. They
move towards the treated front surface. An electron unbalance is created
between the front and back. When the twosurfaces are joined by a
connector, like awire, an electric current flows between the negative
and positive sides.
These individual solar cells arearranged together in an array.
The solar cell is made of different material and silicon and silicon is one
used for nearly 90 %applications.
cost.
The choice ofmaterial depends on the band energygap, efficiency and
The maximum efficiency of solar cell is achieved with the band gap
energy of 1.12 eV-2.3 eV.
The various materials like aluminum silicon, Si (1.12eV), Aluminium
antimonide, AlSb (1.27 eV), Cadmium telluride, CdTe (1.5 eV), Zink
telluride, ZaTe (2.1 eV), Cadmium sulphide,CaS (2.42 eV) etc. are the
materials suitable for solar cell.
Que 1.9. Write short note on :
Thesmaller theenergy gap, the large number ofphoton ofsolar spectrum
will be useful to produce the required energy for electrons to jump the
forbidden band gap.
A. Principle of solar photovoltaic, and
Photovoltaic effect.
Answer
A Principle of Solar Photovoltaic :

1.
2.
3.
4
1
Then, asemiconductor attains the property to conduct the current. This
is the basic principle on which the solar cell works and generates power.
B. Photovoltaic Effect :
2
3
1
cell.
2.
3
It is afield ofsolar energy utilization by which solar radiation is converted
into electrical energy using adevice called photovoltaic cell or solar cell.
Asolar cellis made up of a semiconductor material like silicon (Si) or
gallium arsenide GaAs.
4.
5.
In semiconductors, atoms carry four electrons in the outer valence
orbit, some of which can be dislodged to move freely in the materials, if
extra energy is supplied.
When asolar cellis illuminated, electron-hole pairs are generated and
the electric current I is obtained.
is the difference between the solar light generated current I, and the
diode dark current ,
Mathematically :
Answer
Where,
1-15 M (OE-Sem-7)
I=
1,-1,=I,-I, exp
I =
Saturation current,
e= Electronic charge,
T= Absolute temperature, and
K= Boltzmann's constant.
= 1.38 x 10-23 J/K.
Que 1.10. Explain the mechanism of photoconduction in a PV
AKTU2016-17, 2018-19; Marks 10
In p-n junction after the photons are absorbed, the free electrons of
the n-side will tend to flow to the p-side, and the holes of the
p-side will tend to flow to the n-side to compensate for their respective
deficiencies.
This diffusion willcreate an electric field E, from the n-region to the
p-region.
This ield will increase until it reaches equilibrium ofV,, the sum ofthe
diffusion potentials for holes and electrons.
If electrical contacts are made with the two semiconductor materials
and the contacts are connected through an external electrical conductor,
the free electrons will flow from the n-type material through the
conductor to the p-type material.
The flow of electrons through the external conductor constitutes an
electriccurrent which will continue as long as more free electrons and
holes are being formed by the solar radiation.

1-16 M (OE-Sem-7)
6
7.
8.
1
B.
Current Collection
Grid
2.
3.
(Metal Fingers)
4.
0.2 um
5
300 um
Answer
Sun light
n-region
p- region
Base material
Metal conductor
Negative
contact
Fig. 1.10.1.
A Principle: Refer Q.1.9, Page 1-14M, Unit-1.
Limitations :
Que 1.11. Deseribe principle of solar photovoltaie conversion.
Discuss the limitations of solar photovoltaic energy conversion.
Holes
Diffused layer
This is the basis of photovoltaic conversion, that is, the conversion of
solar energy into electrical energy.
Load
The combination of n-type and p-type semiconductors thus constitutes
a photovoltaic (PV) cell or solar cell.
+ ve
-contact
All such cells generate direct current which can be converted into
alternating current ifdesired.
When photons oflight energy from the sun strike the cell, some ofthem
(30 %) are reflected (since reflectance from semiconductors is high).
Photons ofquantum energy hu<Eg cannot contribute to photoelectric
current production (h is the Planck's constant and vthe frequency.
Photovoltaiccells are exposed directly to the sun. As the temperature
rises, leakage across the cell increases. Consequently,thereis reduction
in power output relative to input ofsolar energy.
Incident active photons produce electron-hole pairs with high quantum
efficiency. Better celldesign is required to ensure 95 %absorption.
Thesemiconductorwith optimum band gap should be usedfor maximum
efficiency.

Que 1.12. Classify solar cells. Derive an expression for maximum
power output and efficiency of a solar cell.
Answer
1
C.
b. Polycrystalline silicon cells (band gap 1.12 eV), and
a.
1
2
3.
4
b.
2.
3.
1.
4.
C.
1
2
3
According to type of crystal, the solar cells are of three types:
Monocrystalline silicon cells (band gap 1.12 eV),
1.
Amorphous silicon cells (band gap 1.75 eV).
Monocrystalline Silicon Cell :
1-17 M(OE-Sem-7)
In monocrystalline silicon cells, silicon is doped with boron to produce p
type semiconductor.
Monocrystalline rods are extracted from silicon and then sawed into
thin plates or wafers.
The upper layer of the wafers is doped with phosphorous to produce n
type semiconductor. This becomes p-n junction.
Maximum efficiency is 24 %.
Polycrystalline Silicon Cell :
In polycrystalline cells, liquid silicon is poured into blocks that are sawed
into plates.
During solidification of the material, crystal structures of varying sizes
are formed.
The size ofcrystallites mainly depends upon the cooling condition. If the
molten silicon is cooled very slowly, the crystallites of larger size are
obtained.
The silicon solar cells made from polycrystalline silicon are low cost but
low efficiency (maximum efficiency is 17.8 %).
Amorphous Silicon Cell :
Ifa silicon film isdeposited on glass or another substrate material, this
is socalled amorphousor thin layer cel.
The layer thickness is less than l um, so production costs are lower due
to the low material costs.
A. Efficieney of SolarCell:
However, the efficiency of amorphous cells is much lower than that of
the other cells. Because of this, they are primarily used in low power
equipment such as watches, pocket calculators etc. Maximum efficiency
is 13 %.
The electrical characteristics of asolar cell are expressed by the voltage
current (V-Dcurvesplotted under agivenillumination and temperature
conditions as shown in Fig. 1.12.1.

1-18 M (OE-Sem-7)
3
4
5
6.
2. In Fig. 1.12.1, the maximum useful power ofthe cell is represented by
A
1.
Voltage
3
Fig. 1.12.1.Voltage-current (V-) characteristic ofasolar cel.
the rectangle with the largest area.
V
Where,
When the cellyields maximum power, the current and voltage are
represented by the symbols I and Vrespectively.
Leakage across the cell increases with temperature which reduces
voltage and maximum power.
Mathematically:
Where,
sketch.
Cell quality is maximumwhen the value offill factor' approaches unity,
where the fill factor (FF) is expressed as
Answer
Current
FF =
V
7. Maximum power output,
Maximum efficiency of a solar cell is defined as the ratio of maximum
electric power output to the incident solar radiation.
max
=
Open circuit voltage, and
I =Short circuit current.
I,V,
max
m
sc
1m
I,A,
A= Cells area.
I-Incident solarflux, and
= Vmax P x max P
Que 1.13. Describe solar photovoltaic (SPV) module with neat
Solar Photovoltaic System :
|AKTU
2018-19, Marks 10
It refers to awide variety ofsolar electricity systems.
2 This system use solar array made of silicon to convert sunlight into
electricity.
Components other than PV array are collectively known as balance of
system (BOS)which includes storage batteries, an electronic charge
controller and an inverter.

4 Storage batterieswith charge regulators are provided for back-up power
supply during periods ofcloudy day and during nights.
5
6.
7.
8
9
Batteries are charged during the day and supply power to loads as
shown in Fig. 1.13.1.
PVarray
Charge
regulator
Battery
1-19 M (OE-Sem-7)
InverterACload
Fig. 1.13.1. Block diagram of solar photovoltaic system.
The capacity ofabattery is expressed in ampere-hours and each cell of
the lead-acid battery is of2 volts.
Batteries are installed with a microprocessor based charge regulator to
monitor the voltage and temperature.
It also regulates the input and the output current to eliminate
overcharging and excessive discharge respectively.
Answer
DC load
An inverter is provided for converting DCpower from battery or PV
array to ACpower.
10. Itneeds to have an automatic switch-offin case the output voltage from
the array is too low or too high.
PART-6
Solar Cell Array.
11. The inverter is also protected against over loading and short circuit.
Questions-Answers
Que 1.14. Write a short note on solar cell array.
AKTU2016-17,2018-19; Marks 05
2. They may be tracking arrays or fixed arrays.
1 Solar cells are strung in series and thus form a solar module or array.

1-20 M (OE-Sem-7)
4
5.
3
6.
a.
1.
2.
b.
2.
1.
i.
1
Atracking array is defined as one which is always kept mechanically
perpendicular to the sun-array line so that all times it intercepts the
maximum isolation.
2
Sucharrays must be physicallymovable byasuitableprime-mover and
are considerably more complex than fixed arrays.
Afixed array is usually oriented east-west and tilted up at an angle
approximately equal to the latitude ofthe site.
Fixed arrays are mechanically simpler than tracking arrays. Thus the
array designs fall into two broad classes:
Flat-Plate Arrays :
Wherein solar cells are attached with asuitable adhesive to some kind
ofsubstratestructure usually semi-rigid to prevent cells beingcracked.
This technologysprings from the space-related photovoltaic technology,
and many such arrays have been built in various power sizes.
Concentrating Arrays :
Whereinsuitable optics, e.g., Fresnellenses, paraboliemirrors, compound
parabolic concentrators (CPC), and others, are combined with
photovoltaic cells in array fashion.
This technology is relatively new tophotovoltaic in terms ofhardware
development, and comparatively fewer such arrays have actually been
built.
PART-7
Answer
Que 1.15. With the aid of blockdiagrams explain :
i. Autonomous solar power plant, and
Solar Cell Power Plant.
ii. Combined solar power plant.
Questions-Answers
Autonomous Solar Power Plant :
This plant also known as grid independent or stand alone PVsystem for
supplying the current having no connection with grid.
It is located at the load centre and dedicated to meet all the electrical
loads ofavillage or community or aspecific set ofloads.

3.
4
5
6
7.
8.
9.
Energy storage is generally essential.
It is most relevant and successful in remote and rural areas having no
access to grid supply.
Indicative capacity ofsuch a system is 10W- 100 kW.
The main components ofa general stand-alone solar PV system are
shown in Fig.1.15.1.
Solar array
PWM
switching
regualtor
1
Duty
ratio
Feedback
signals
MPPT
controller
1-21 M (OE-Sem-7)
Battery
charger
Mode
controller
1, AA
DC to AC
inverter
Batteries Dumpload!
Loads
Fig. 1.15.1.Ageneral stand-alone or autonomous solar PV system.
The MPPT senses the voltage and current outputsof the array and
adjusts the operating point to extract maximum power under the given
climatic conditions.
The output ofthe array after converting to AC is fed to loads.
The array output in excess of load requirement is used to charge the
battery.
10. Ifexcess power is still available after fully charging the battery, it may
be shunted to dump heaters.
11. When the sun isnot available, the battery supplies the load through an
inverter.
12. The battery discharge diode D prevents the battery from being
overcharged after the charger is opened.
13. The array diode D, is toisolate the array from the battery to prevent
battery discharge through array during nights.
14. Amode controller is a central controller for the entire system.
15. It collects the system signals and keeps track of charge or discharge
state of the battery, matches the generated power and load and
commands the charger and dump heater on-off operation.
ii. Combined Solar Power Plant or Hybrid PV System :
Ahybrid PV system is essentially a system that employs at least one
more source, other than the PV, to meet the electrical power demand of
the loads.

1-22 M (OE-Semn-7)
2
a.
3. The hybrid PVsystem can be classified depending on the type ofsource
it uses,e.g., PV-wind hybrid system, PV-diesel hybrid system and PV.
fuel cell hybrid system.
The other sources that are generally used in conjunction with the PV
source are diesel generators, wind generators,micro-turbines, fuelcells,
etc.
A
1
PV-Wind Hybrid System :
2
i. Inthe case ofthe PV-wind hybrid system, thevariationinthe wind
velocity results into large changes in the frequency and output
power of the generator.
As a result, it is advisable to convert the AC output to the DC and
then convert it back to AC through the inverter.
iii. The PVand the rectified outputofthe windgeneratorare connected
in parallel forming a DC link.
iv. However, the drawback ofthis system is that PVand wind both are
the unreliable, sources and hence, in absence of the sun and wind,
alarge battery bank is required to meet the load demand.
Wind
generator
systen ?
Answer
PV
array
AC-DC
converter
DC-DC
Advantages :
converter
Inverter
PART-8
Low cost of maintenance.
Fig. 1.15.2. PV-wind hybrid system.
Limitations.
Battery
Que l.16. What are the advantages and limitations of solar energy
AC
loads
Questions-Answers
DC loads
Noiseless andcheap energy conversion syste.
Inverter

3.
4.
6
5. Having long life.
7.
8.
B.
1.
2.
3
4.
5.
Highly reliable.
10. System modularity allows users to start with small system for single
application and add on to their systems as their needs increase.
Environment friendly.
Suitable for mobile loads such as cars, buses etc.
No fuel is required.
1.
These systems are suitable for rural, remote and isolated areas.
Modularity in operation.
1.
Limitations :
Higher initial cost.
Irregular supply of solar energy and do not generate power during
cloudy season.
Require storage batteries for supply power during night.
Efficiency is low.
Large area required for plant.
Que 1.17. What are the applications of photovoltaicsystems ?
Answer
Write about the solar cells, its material and applications.
A. Solar Street Light :
1-23M(OE-Sem-7)
OR
Solar Cell and Material :Refer Q. 1.8, Page 1-14M, Unit-1.
Application:Theapplicationsofphotovoltaic systemsaregivenbelow:
PVarrays
B. Home Lighting System :
AKTU 2015-16, Marks 7.5
It comprises ofacompact fluorescent lamp, two 35 watt solar arrays and
an 80 ampere-hour tubular cell battery as shown in Fig. 1.17.1.
Street light
Battery box
Fig. 1.17.1. Solar street light.
These are the most popular solar PV units,typically designed to work
with two light points and one TV point.

1-24 M (OE-Sem-7)
2. When necessary, a small DC fan can also be run from this system.
C. Water Pumping System:
1.
2.
3
4
1.
2
It is another important application ofphotovoltaic systems.
These systems are mainly, employed in rural areas for agricultural
applications, where power is not available easily and economically.
D. Solar Vehicles:
PV arrays
Fig. 1.17.2. Solar water pumping system.
Farmers use an 1800 watt PV array to operate a 2 hp DC motor pump
set.
now.
It can give water discharge of 140,000 litres per day from a depth up to
7meters which is sufficient to irrigate 5-8 acres of land holding several
crops.
Battery box
Pump
Solar photovoltaic systems are also used in solar vehicles like solar cars,
tractors etc. But solar vehicles are not used on commercial level until
Research and development is continuously trying to increase the
efficiency of solar vehicles and tomake it commercially workable.
VERY IMPORTANT QUESTIONS
Following questions are very important. These questions
maybe asked in your SESSIONALS as well as
UNIVERSITY EXAMINATION.
Ans. Refer Q. 1.3, Unit-1.
9.1. Discuss the main features of various types of renewable
and non-renewable energy sources. Also explain the
importance of non-conventional energy sources in the
context of global warming.
resources.
Q. 2. What are the conventional and non-conventional energy
sources ? Write short notes on classification of energy

2
UNIT
Part-1 :
Part-3 :
Part-2 : Flat Plate Collectors
Part-5 :
Solar Thermal Energy
CONTENTS
Part-4: Application of Flat
Plate Collectors
Part-9:
Solar Radiation
Part-11:
Material for Flat Plate Collectors
Part-6 : Focusing of Collectors.
Part-12 :
Performance of Flat
Plate Collectors
Part-7 :
Part-8: Ápplication of Collectors
Materials for Collectors
Part-10: Solar Thermal Power Plants
Performance of Collectors
Thermal Energy Storage
for Heating
Thermal Energy Storage
for Cooling
Part-13 : Limitations of Solar
Power Plants
2-1 M (OE-Sem-7)
.2-2Mto 2-9M
.2-9M to 2-11M
.2-11M to 2-11M
2-11M to 2-12M
2-12M to 2-15M
2-15M to 2-19M
2-19M to 2-20M
2-20M to 2-21M
2-21M to 2-22M
2-22M to 2-25M
2-25M to 2-31M
2-31M to 2-33M
2-33M to 2-34M

2-2 M(OE-Sem-7)
Answer
1
2
3.
Que 2.1. Write a short note on solar radiation.
a.
PART- 1
Solar Radiation.
Questions-Answers
1
The solar radiations received by the earth's surface vary with the location.
However radiation received outside the earth's atmosphere is different
than what we receive on the earth surface because of absorption,
reflection, scattering and attenuation by particulates and clouds present
in the atmosphere.
The solar radiation is grouped in the following two categories:
Extraterrestrial Solar Radiation :
2
2
The intensity of the sun's radiation outside the earth's atmosphere
is called extraterrestrial and has no diffuse components.
OR
b. Terrestrial Solar Radiation :
Extraterrestrial radiation is the measure of solar radiation that
would be received in the absence of atmosphere.
1. The radiation we receive on the earth surface is called terrestrial
radiation and is nearly 70% of extraterrestrialradiation.
A Spectral Distribution of Solar Radiation :
Solar radiations pass through the earth's atmosphere and are
subjected to scattering and atmospheric absorption and apart of
scattered radiations are reflected back into space.
1 Solar radiation spectral distribution shows the distribution pattern
ofextraterrestrialand terrestrial radiation ofdifferent wavelengths.
The maximum values of radiation are reaching in the range of
0.4 um to 2.3 um, with maximum value occurring at 0.48 um.

2500
2000
Spectral 1500
irradiance,
W/mum 1000
500
0
0.5
Terrestrial
region
Extraterrestrial radiation
1 1.5
Terrestrial radiation
B. Terms used in Solar Radiations :
tospace
2 2.5 3 3.5 4
Wavelength, um
Fig. 2.1.1. Spectral distribution of extraterrestrial and terrestrial radiation.
Reflected back
by surface
Reflected back radiation
Extraterrestrial
2-3 M(OE-Sem-7)
Diffuse
Scattering
Diffuse
+radiation
Surface of earth
Atmospheric
absorption
Direct
radiation
4.5
Fig. 2.1.2. Direct diffuse and total solar radiation.
Beam Radiation I)) : Solar radiation received on the earth's
surface without change in direction is known as beam or direct
radiation.
ii. Diffuse Radiation I,) :The radiation received on a terrestrial
surface (scattered by aerosols and dust) from all parts of the sky
dome is known as diffuse radiation.
iüi. Total Radiation (I,) :The sum of beamand diffuse radiation (i.e.,
I, +14)interceptedat the earth's surface per unit area of locationis
known as total radiation and it is also known as insolation. The
radiations received byacollectorsurface are always global radiations.
iv. Air Mass (m):Itis the ratio of the path length of beamradiation
through the atmosphere, to the length of path when sun is at over
head or zenith.

24 M(OE-Sem-7)
Que 2.2. Describethe differencebetween the direct radiationand
diffuse radiation.
Answer
S.No.
1
2
3.
4.
S.No.
Que 2.3.
radiation.
1.
Solar radiation received on the
earth's surface without
change in direction is known
as direct radiation.
Answer
2
Direct Radiation
It has a unique path.
3
Direct solar radiation is
generally most intense at any
one spot on the surface ofthe
earth at solar noon.
It has the least amount of the
atmosphere to travel through.
Global Radiation
A. Differences between Global Radiation and Diffuse Radiation:
Globalsolar radiation is the
total amount of solarenergy
falling on a horizontal
surface.
Typicalvaluesfor dailyglobal
solar radiation range from 1
to 35 MJ/m?.
|AKTU2017-18, Marks 10
Diffuse Radiation
Distinguish between global radiation and diffuse
The values are usually
highest in clear
conditions during the
summer and lowest during
winter or very cloudy days.
The radiation received on a
terrestrial surface (scattered by
aerosols and dust) from all parts
of the sky dome is known as
diffuse radiation.
It does not have a unique path.
It does not happen in diffuse
radiation.
It has the more amount of the
atmosphere to travel through.
Diffuse Radiation
Diffuse solar radiation is the total
amount of solar energy falling on
a horizontal surface from all parts
of the sky apart from the direct sun.
Typical valuesfor daily diffusesolar
radiation range from 1 to
20 MJ/m2.
The values are usually highest
sun during the cloudy conditions and
lowest during clear sky days.

1.
2.
2
3.
4
a,
Que 2.4. What do you mean by solar constant ?
Answer
b.
C
d
e,
The solar constant is the energy received from the sun on a unit area
perpendicular to sun's rays at the mean distance from the sun, outside
the atmosphere.
Que 2.5.
The standard value of the solar constant based on experimental
measurements is 1367 W/m with an accuracy of +1.5 %.
The value of solar constant remains constant throughout the year.
However, this value changes with location because earth to sun distance
changes seasonally with time.
The extraterrestrial radiation observed on different days is known as
apparent extraterrestrial solar irradiance and can be calculated on any
day of the year using the following equation :
Where,
Definethe terms:
Altitude angle,
Incident angle,
Zenith angle,
1,=I1+0.033cos
Hour angle.
Answer
Note: According to above equation, the apparent solar irradiance will
be maximum during December last or first week of January, as the
earth's centre is nearest to the sun during these days.
2-5 M(OE-Sem-7)
I =1367 W/m?.
I,= Apparent extraterrestrial solar irradiance
(W/m),
Explain solar radiation geometry.
Latitude angle, and
360n
n =
Number of days of the year counting January
las the first day of the year,and
365
OR
Iy =I cos 0,
1 The solar radiation comes from the sun on the earth's surface with
arbitrary orientation and can be found out by knowing the beam radiation
falling either on horizontal or perpendicular surface to sun's radiation.
The amount of incident beam flux on an inclined surface per unit time
and per unit area is given as

2-6 M (OE-Sem-7)
3
a.
b.
C.
Where,
The various angles which are useful for conversion of beam radiation
on the arbitrary surface are :
Incident Angle (0) :
1. It is defined as the angle between the incident beam radiation and
the normal to aplane surface.
Latitude Angle(¢):
2
1. The latitude of a place is the angle subtended by the radialline
joining the place to the centre of the earth, with the projection of
the line on the equatorial plane.
1
2
3.
Declination Angle (6):
1
2.
Note: The latitude is taken as positive for any location towards the
northern hemisphere and negative towards the southern
hemisphere i.e., the latitude at equator is 0 while at north and
south poles are +90° and- 90° respectively.
The declination is the angle made by the line joining the centres of
the sun and'the earth with its projection on the equatorial plane.
The declination angle varies from a maximum value of +23.5° on
June 21 to a minimum of -23.5° on December 21.
Declination,
ò
I= Incident flux of beamradiation, and
0, =Angle ofincident ofbeam radiation.
The declination (in degrees), for any given day may be calculated
from the approximate equation of"Cooper".
(degrees)
+30
8= 23.45 sin (284+ n)
365
where, n is the number of days in the year.
+20
+10
0
-10
-20
-30
d. Hour Angle (o):
Sep. 22d Dec. 22
360
-23.5
Mar. 22
Time of the year ’
Jun, 22
Fig. 2.5.1, Variation of declination angle.
+23.5°|
Sep. 22
It is the angle through whichthe earthmust be rotated to bring the
meridian ofapoint directly in line with the sun's ray.
In other words,it is the angular displacement ofthe sun, east or
west of the local meridian, due to the rotation of the earth on its
axis at an angle of 15° per hour.

e.
f
i.
3
4
Where,
Altitude Angle (a) :
The hour angle is zero at solar noon, negative in the morning and
positive in the afternoon for the northern hemisphere (India) and
vice-versa for southern hemisphere (Australia).
Mathematically hour angle can be expressed as
1 It is a vertical angle between the projection of the sun's rays on the
horizontal plane and the direction of the sun's rays.
Zenith Angle (0,) :
Mathematically:
1.
2
1
) = 15(LST - 12)
LST = Local solar time.
Surface Azimuth Angle (y):
2.
Equator
h. Slope (p):
1 It is the vertical angle between the sun's rays and line perpendicular
to the horizontal plane through the point.
Fig. 2.5.2. Latitude , hour angle oand sun's declination 8.
2-7 M(OE-Sem-7)
N
P
Sun rays
It is the angle in the horizontal plane, between the line due south
and the horizontal projection of the normal to the inclined plane
surface.
Solar Azimuth Angle (y,) :
By convention, the angle will be taken negative for northern
hemisphere (India) and vice-versa for southern hemisphere
(Australia).
1. It is the angle between the plane surface, under consideration, and
with the horizontal.
It is taken to be positive for surface sloping towards south and
negative for surfaces sloping towards north.
It is the angle in ahorizontal plane, between the line due south and
the projection of beam radiation on the horizontal plane.

2-8 M(OE-Sem-7)
Que 2.6.
A.
2.
1.
W
Answer
2.
A. Day Length
3.
Thus it gives the direction of the shadow cast in the horizontal
plane by avertical rod.
b.
4.
Zenith/horizontal plane at Z
N
B. LocalApparent Time (LAT).
I;
cos0,
Normal to the
Write short note on local apparent time (LAT).
Write short note on :
Day Length :
Fig.2.5.3. Various sun-earth angle on tilted surface.
a. At solar noon,
Sun
IE
cos
/
On tilted surface,
OR
The time ofsunrise, sunset and the duration ofthe day length depend
upon the latitude ofthe location and the month in the year.
At sunrise and sunset, the sunlight is parallel to the ground surface with
azenith angle of90°.
9, = 0 and o = 0,
coS ), =-tanotan
Normal tothe
inclined plane at O
The hour angle pertaining to sunrise or sunset (o)isgiven below:
N=
Projection ofsun's ray
in a horizontal plane
Projection ofnormal
to inclined plane in
a horizontal plane
2
15
AKTU 2015-16, Marks 03
= cos- [(-tan (-B) tanô)
The corresponding day length (in hours) is given by
cos-tan(-p)tanß

B. Local ApparentTime (LAT):
1
2.
1.
The time used for calculating the hour angle o is the local apparent
time.
It is given by
classified?
2
Answer
3.
Que 2.7. What are solar collectors ? How solar collectors are
Solar Collectors :
a.
1
LAT = Standard time + Equation of time
correction + 4 (Standard time longitude
- longitude oflocation)
Solar collectors are used to collect the solar energy and convert this
energy into the thermal energy by absorbing them.
2.
PART-2
This thermal energyis further used for heatingacollector fluid such as
water, oil or air.
Solarcollector surface is designed for high absorption and low emission.
4. Solar collectors are classified in two types :
b.
1
Flat Plate Collectors.
2
Questions-Answers
2-9 M (OE-Sem-7)
Non-Concentrating Collector :
Que 2.8.
It is also known as flat plate solar collector.
In these collectors, the area ofcollector to grasp the solar radiation
is equal to the absorber plate and has concentration ratio of1.
Concentrating Collector :
It is also known as focusing type solar collector.
In these collectors, the area ofthe collector is kept less than the
aperture through which the radiation passes, to concentrate the
solar flux and has high concentration ratio.
Explain the principle ofconversion ofsolar energy into
heat. Explain a flat plate solar collector.

2-10 M (OE-Sem-7)
advantages ?
Classify different types of solar thermal collector and show the
constructional details of a flat plate collector. What are its main
Answer
A. Principle:
C. Flat Plate Collector :
1
1 When solar radiation from the sun comes in the form of light (a short
wave radiation) to the earth, visible sunlight is absorbed onthe ground
and transformed into heat energy ; the material becomes warm and
stores the heat, conducts it tosurrounding materials (air, water other
solids or liquids) or reradiates it to other material oflower temperature.
B. Classification: Refer Q. 2.7, Page 2-9M, Unit-2.
2
Flat plate collector is simplest indesign and it is mostimportantpartof
anysolar thermal energy system.
ii.
In this collector both direct and diffuse radiations are absorbed and
converted into useful heat.
D. Components of FlatPlate Collector:
1
Absorber plate,
2
Transparent covers,
iv Box.
Insulation, and
OR
Absorber Plate:
i. Transparent Covers :
Absorber plate is used to grasp and absorbsolar radiation.
The plateis usuallymetallic(copper, aluminum orsteel), sometimes
plastics have been used in some low temperature applications.
1 These are one or more sheets made of glass for trapping the heat
received by the absorber plate.
2. Ithelpsin reducingthe convectiveand radiativeheat losses.
position.
iii. Insulation :It minimizes the heat losses by conduction.
Thermal
insulation
iv. Box : It contains the above components and keep them into desired
Transparent cover
Absorber plate
-Seriesoftubes
Housing
Fig. 2.8.1. Schematicdiagram ofa flat plate solar collector.

E. Advantages of FlatPlate Collector:
1.
2
3
1.
Que 2.9.
2
collectors.
3
4
5
It absorbs both direct and diffuse radiations.
There is no need of tracking.
Answer
6
7
It has low cost and requires less maintenance.
PART-3
LongAnswer Type and MediumAnswer Type Questions
b.
Material for Flat Plate Collectors.
Questions-Answers
2-11 M(OE-Sem-7)
Write a short note on materials used for flat plate
The properties of the materials used for collectors can be classified as:
Thermophysical properties such as thermal conductivity, heat
capacity etc.
Physicalpropertieslikedensity,tensilestrength,meltingpoint ete.,
and environmental properties like moisture penetration, corrosion
resistance and degradation due to pollutants in atmosphere.
The materialfor absorber plate shouldhave high thermal conductivity,
adequate tensile strength and good corrosion resistance.
The most common material used for absorber plate is Copper because of
high conductivity and resistance to corrosion.
Other materials which are used for absorber plate are Aluminium, Iron,
Brass,Silver, Tin and Zinc.
The material for insulation should have low thermal conductivity, should
be stable at high temperature.
Some commonly used materials are crown white wool, glass wool, calcium
silicate, cellular foam etc.
For cover plate, tempered glass is most common material. Transparent
plastic materials such as acrylic polycarbonate plastic, polyvinyl fluoride
are used for cover plate.
PART-4
Application ofFlat Plate Collectors.

2-12M (OE-Sem-7)
collector.
Que 2.10. Explain the disadvantages and application offlat plate
Answer
A. Disadvantages of Flat Plate Collector :
2
1. Low temperature is achieved.
3
LongAnswer Type and Medium Answer Type Questions
1.
Questions-Answers
2
3
B. Applications of Flat Plate Collector :
There is a large heat loss by conduction due to large area.
These are heavy in weight.
a.
It is used in solar water heating.
It is used inspace heating and cooling.
It is used in low temperature power generation.
Answer
PART-5
Performance of FlatPlate Collectors.
Questions-Answers
Que 2.11. What do you understand by performance analysis of
flat plate collector ?
A. Performance Analysis of Flat Plate Collector :
The performance ofsolar collector depends on the following factors:
Mathematically, F, =
Fin Efficiency Factor (F) :It is defined as the ratio of actual rate of
heat transferred to the heat that would be transferred, if entire fins
(plate area) are at base temperature.
Ractual
A,la,t4,-U,(T, -T,))

b.
C.
Where,
Mathematically,
Where,
Mathematically,
or,
Qoctual Actual rate of heat transferred to the tube
Where,
Mathematically,
A,= Collector area,
Collector Efficiency Factor (F):It is defined as the ratio of useful
heat removed by flowing fluid in the tubes to the rate ofheat transferred
to the fluid, ifthe fin is at local fluid temperature.
or
I,= Incident total radiations,
base,
U, = Overall heat loss coefficient,
T,= Plate temperature,
T, = Ambient temperature,
a, =Absorptivity, and
I,= Transmitivity.
F, =
C
Collector Heat Removal Factor (F) :It is defined as the ratio of
actual useful energy gain by fluid to the rate ofheat transferred to the
fluid, if the fin is at inlet fluid temperature.
A,la,t,-U,(T, -T,))
Q, = Useful heat removed by flowing fluid in the
tubes, and
T,= Local fluid temperature.
A,la,r,4, -U,(T;-T,))
n, =
2-13 M(OE-Sem-7)
n,=
mC,(T, -T;)
A,la,r,4, -U,(T,-T,))
m= Mass flow rate offluid per unit area ofcollector,
Cf= Specific heat of fluid,
T = Outlet fluid temperature, and
T, =Inlet fluid temperature.
d. Collector Eficiency (n): It is defined as the ratio of useful energy
absorbed by collector to the incident solar energy over it.
A,!,
FrA,la,r,1, -U,(T,-T,))
Al,
(:e, =Fp4,(a,r,!,-U(T,-T,)

2-14 M (OE-Sem-7)
Or
or
flat plate collector?
C.
Where,
Answer
d
and,
e
f.
are:
a. Incident Solar Radiation:
b. Number of Cover Plate:
1. Thedifferent factors which affect the performance offlat plate collector
1
Que 2.12. What are the factors which affect the performance of
2
n, = m + c
1
m=-FUL
Collector Tilt :
2
1 The efficiency of collector is directly related with solar radiation
falling on it and increases with rise in temperature.
(T;-T,)
1.
c= FRato
2.
3.
1
I,
Selective Surface:
Spacing between Absorber Plates and Glass Cover:
1. The more space between the absorber and the cover plate, the less
is the internal heat losses.
FU,(T;-T,)
(It is a linear equation)
(Effective heat loss coefficient)
Increase in number ofcover plate reduces the internal convective
heat losses but also prevents the transmission of radiation inside
the collector.
(Efective opticalefficiency)
Therefore, the increase in cover plates will reduce the heat absorbed
by the absorber.
It should not oxidise.
Toachieve better performance, flat plate collector should be tilted
at angle oflatitude of the location.
Fluid Inlet Temperature :
The collectoris placed with south facingatnorthernhemisphere to
receive maximumn radiation throughout the day.
It should be corrosion resistant.
It should be able to withstand high temperatures.
On increasing the inlet temperature ofthe fluid there is an increase
in operating temperature of the collector and this lead to decrease
in efficiency.

g. Dust on Cover Plate:
1 The efficiency of collector decreases as dust particles increases on
the cover plate.
2. Frequent cleaning is required to get the maximum efficiency of
collector.
PART-6
1.
Focusing ofCollectors.
Answer
Questions-Answers
Que 2.13. Explain the concentrating solar collector. Also, discuss
its working.
Discussthe principleofaconcentratingsolarcollector. Howitdifers
with flat plate collector ? How collector coating can be used to
improve the performance ofcollectorwith referencetotheflat plate
collector ?What is the concentrating ratio for focusing collector ?
OR
A Concentrating Solar Collector :
2-15 M(OE-Sem-7)
Rays/
Concentratingsolar collector is adevice to collectsolar energywith high
intensity of solar radiation on the absorbing surface by the help of
reflector or refractor.
OR
AKTU2017-18, Marks10
Aconcentratingsolar collectoris amodifiedform offlat-plate collector
by introducing a reflecting or refracting surface between the solar
radiation and absorber.
Focal Receiver
-Cylindrical trough
Fig. 2.13.1. Concentrating type ofcollector.

2-16M (OE-Sem-7)
B. Principle:
1.
1.
C. Working of Concentrating Solar Collector :
2
3
4
1
2
These systems have high collector efficiency, since the losses are much
less as compared to non-concentrating type ofcollectors.
D. Difference between Flat and Focusing Collectors:
3
4.
Concentrating solar collector uses reflective surface to concentrate
sunlight to asmallarea, where it absorbed andconverted to heat.
5.
6
This collector system comprises ofaconcentrator and an absorber.
In these collectors radiation from sun falls on a relatively large area
which is focused through concentratoron to an absorberofconsiderably
smaller area.
S. No. Concentrating Collectors
2
3
1.
As a result of energy concentration, fluid can be heated up to a
temperature of500 °C or more.
4.
5
6.
It requires less absorber area.
It has high collection efficiency.
Suitable for large power
generation.
Heat storage cost is lower.
It has high initial and
maintenance cost.
Flat-Plate Collectors
E. Use of Collector Coating to Improve the Performance of
Collector :
It requires more absorber area.
It has low collection efficiency.
Suitable for small power
generation.
Heat storage cost is higher.
It has low initial and
maintenance cost.
No need of anti-freeze solutions. It needs anti-freeze solutions.
Most solar collectors employ a transparent cover plate often made of
glass. These materials reflect around 8% ofthe incident solar radiation,.
which leads to the reduction in the collector heat output.
The use of an antireflection coating could therefore improve the
performance of such system by increasing the transmitted energy
through the glass cover.
Recently, a silica low-reflection coating via a dip-coating process has
been developed.
The refractive index of the thin film is well controlled.
The exact value of the filmn refractive index that leads to a minimum of
reflection on the surface of the glass cover can be achieved.
A comparison has been made between an uncoated flat-plate solar
collectorglass cover and one with aporous sol-gel anti-reflection coating.
Using the porous sol-gel coatingwith the index ofrefraction ofn =1.23

F. Concentration Ratio (C): It is defined as the ratio of the effective
aperture ratio to the absorber tube area.
1
a.
i.
Answer
ii.
on the glass cover of the solar collector increases the useful energy by a
factor ofapproximately 1.05.
1.
Mathematically,
3.
Where,
C=
Que 2.14. Enumerate the different types of concentratingcollector.
Effective aperture ratio
Absorber tube area
W-D,
TD,
W= Aperture, and
D, = Outer diameter of absorber tube.
2-17 M(OE-Sem-7)
The different types of concentratingcollector are as follows:
Parabolic Trough Collector:
Principle:The principle of parabolictrough collector is, whenthesolar
radiations falls on the area of parabolic reflector are concentrated at the
focus of parabola.
Vertex
Focus
Sun rays
tParabolicreflector
Fig. 2.14.1.Cross section ofparabolie trough collector.
Working :
In the parabolic trough collector mostly cylindrical parabolic
concentrators are used in which the absorber is placed along the focus
axis where collectorpipe is used as an absorberwithaselective coating.
2 The solar radiation coming from particular direction is collected over
the area of collector and then focused to the collector pipe which is
placed along the focus line to heat up the fluid.
The orientationofthe parabolic trough collector is kept in the east-west
or north-south directions.

2-18 M (OE-Sem-7)
b.
1
2,
3.
C.
1
2
Mirror strips
Absorber tube
Shield
Stay rods.
Mirror-Strip Reflector :
Fig. 2.14.2. Atypical cylindrical parabolic system.
Mirror
strips
Jack shaft
Class shield on
absorber tube
It has a number of planes or slightly curved or concave mirror strips
which are mounted on a base.
Chain drive
These individual mirrors are placed at such angles that the reflected
solar radiations fall on the same focal line where the absorber pipe is
placed.
Fresnel Lens Collector :
In this system, collector pipe is rotated so that the reflected rays on the
absorber remain focused with respect to changes in sun's elevation.
Focus
Sun rays
Fig. 2.14.3. Mirror-strip solar collector.
In thiscollector, a Fresnel lens is used in which linear grooves are
present on one side and flat surface on the other side.
The solar radiations which fall normal to the lens are refracted by the
lens and are focused on the absorber (tube) as shown in Fig. 2.14.4.

1.
2.
3
d Compound Parabolic Concentrator (CPC):
i.
Absorber pipe
It is also known as Winston collector.
Advantages :
1.
2
It is atrough like arrangement oftwo facing parabolic mirrors which
are attached toan absorber.
3
In thissystem, solar radiations from all directions are reflected towards
the absorber kept at the bottom, which collects both direct and difused
solar radiations to heat up the fluid.
Fig. 2.14.4. Fresnel lens collector.
It has high concentration ratio.
There is no need of tracking.
Solar radiations
Optical axis
Parabolic
mirror-A
Fresnel lens
2-19 M(OE-Sem-7)
The efficiency for accepting diffuse radiationis high.
Solar radiations
PART-7
Parabolic
mirror-B
Flat receiver (absorber)
Fig. 2.14.5. Compound parabolicconcentrator (CPC).
Materialsfor Collectors.
Questions-Answers
Que 2.15. Write a short note on materials used for concentrators.

2-20M(OE-Sem-7)
1.
Answer
2
4
3. Acrylic is found to be a good material for Fresnel lenses. Polymethyl
6.
3
Glass and transparentplastic films aregenerally used as cover material
for receivers. Glass should have low iron content to reduce absorption.
5. Coatings are required to have strong solar absorptiity, weather
resistance, stabilityat high temperature. Black paints are good. Black
chrome is also suitable. It can be electroplated on steel, copper,
aluminium etc.
3
4
2.
4
5.
The reflector of a concentrator should have high reflectivity therefore
mirror glass or front surface mirrors can be used.
2.
Glass is the most durable with low iron content and is used as a
transmitting material. Now-a-days plastics are also in use.
1.
methacrylate is generally used.
Que 2.16. Write advantages and disadvantages of concentrating
collector over flat plate solar, collectors and applications of
concentrating collectors.
Answer
A. Advantages of Concentrating Collector :
1. It gives high concentration ratio.
Other metal oxide coatings are black copper oxides, black nickel etc.
Insulation isrequired to reduce heatlosses. Fiberglasswithandwithout
binder, urethane foams and mineral fibre blankets are commonly used
for insulation.
Application ofCollectors.
PART-8
LongAnswer +ype and Medium Answer Type Questions
Questions-Answers
B. Disadvantages of Concentrating Collector :
In expensive process.
High fluid temperature can be achieved (up to 500°C).
Thermal heat loss is less.
Efficiency ofthis system increases at high temperature.
These collectors are best suited for places having more number ofclear
days in a year.
It has non-uniform flux on absorber.
It has high initial cost.
It needs costly tracking device.

5
C. Applications :
2.
1. They are used for which need high amount of heat such as power
generation.
3
It needs maintenance in order to retain the quality ofreflecting surface
against dirt and oxidation.
a.
They used in solar power plant.
b.
C.
They used to collected large solar energy which is used to convert water
into steam.
Answer
concentrator collector ?
Performance of Collectors.
Que 2.17. What do you understand by performance analysis of
A. Performance Analysis : The performance of concentrator collector
depends on the following factors:
Questions-Answers
Where,
C=
PART-9
Concentration Ratio (C): It is defined as the ratio oftheeffective
aperture ratio to the absorber tube area.
Mathematically,
Effective aperture ratio
W-D,
Absorber tube area
Mathematically, y=
2-21 M(OE-Sem-7)
rD,
W= Aperture, and
D, = Outer diameter ofabsorber tube.
Intercept Factor (y): It is defined as the ratio of radiationintercepted
by absorber tube to the total reflected radiation.
Radiation intercepted by absorber tube
F, =
Total reflected radiation
Collector EfficiencyFactor (F):Collectorefficiencyfactor isgiven
by the relation :
1
D,
|U, Dh,

2-22 M (OE-Sem-7)
1
d. Instantaneous Collector Efficiency (n,) :Instantaneous collector
efficiency is given by the relation:
2
3.
a.
1
Where,
Answer
2
4
Where,
3.
U,= Overall heat loss coefficient,
D, and D, = Outer and inner diameter, and
h,= Heat transfer coefficient of thetube.
4, = Useful heat gain,
Que 2.18. Explain the different types of solar thermal power plants.
A. Solar Thermal Power Plant :
I,,= Beam radiationnormallyincidenton aperture,
I= Diffuse radiation, and
L= Length of concentrator.
PART- 10
Solar Thermal Power Plants.
Questions-Answers
Solar thermal power generation involves the collection of solar heat
which is utilized to increase the temperature of a fluid in a turbine
operating on a cycle such as Rankine or Brayton.
Solar thermal power plants can be classified as low, medium and high
temperature cycles.
Low temperature cycles operate at about 100 °C, medium temperature
cycles up to 400 °C, while high temperature cycles work above 500 °C.
Low Temperature Solar Power Plant:
Alow temperature solar power plant uses flat-plate collector arrays
shown in Fig. 2.18.1.
Hot (above 90 °C) water is collected in an air insulated tank. It flows
through aheat exchanger, through which the working fluid of the
energy conversion cycle is also circulated.
The working fluid is either methyl chloride or butane having a low
boiling temperature up to 90 °C.
Vapours so formed operate aregular Rankine cycle by flowing through
aturbine, a condenser and aliquid pump.

5.
6. Finally, the organicfluid is pumped back to the evaporatorfor repeating
the whole cycle.
Generator
7.
As the temperature difference between the turbine outlet and the
condensed liquid flowingout is small, i.e., about 50 °C, the overall efficiency
of the generating system is about 2 %(8 %pumped cycle efficiency
x25 %collector system efficiency).
Condenser
b.
1.
Butane turbine Heat exchanger
Oil
circuit
Pump
Parabolic
Oilpump
Pump
solar collector
field
Medium Temperature Solar Power Plant :
Steam
Fig. 2.18.1. Low temperature solar power plant.
Such plants up to 150 kW capacities are operative in Israel for the last
25 years.
6
Hot
water
Solar thermal power plants operating on medium temperatures up to
400 °C use the line focusing parabolic collector for heating synthetic oil
flowing in the absorber tube as shown in Fig.2.18.2. Aschematic diagram
ofatypical plant isshown in Fig. 2.18.2.
Steam
tank
Steam
lcircuit
Water circuit -
2-23 M(OE-Sem-7)
Pump
1. Generator
2. HP turbine
3. LP turbine
4. Condenser
5. Cooling tower
6. Preheater
7. Boiler
8. Superheater
9. Reheater
pump
Cooling|
water
Array ofsolar
collectcors
-
pump
Fig. 2.18.2. Medium temperature solar power plant.
Power
supply
5

2-24 M (OE-Sem-7)
2
3
4
5
C.
1.
2.
d.
1.
2
3
4.
5
6.
7.
Asuitable sun-tracking arrangementis made to ensure that maximum
quantity ofsolarradiation is focused onthe absorber pipeline.
Preheater and superheater are used to increase the inlet steam
temperature for the high pressure (HP) turbine.
Reheaters are used toraise the steam temperature for low pressure
(LP) turbine.
The system generates superheated high pressure steam to operate a
Rankine cycle with maximum efficiency.
High Temperature Solar Thermal Power Generator :
Forefficient conversionofsolar heat into electrical energy, the working
fluid needs to be delivered intoturbineat ahigh temperature.
There are two possible systems-the paraboloidal dish' and the 'central
receiver to achieve high temperatures.
Central Receiver Power Plants :
In these power plants, solar radiations are reflected from arrays of
mirrors (called heliostats) installedin circulararcs around provided with
atracking tower.
Reflected radiations concentrate on to the receiver.
The array is providedwith atrackingcontrolsystem that focuses beam
radiation towardsthe receiver as shown in Fig. 2.18.3.
Incident Central receiver
solar energy
Array ofheliostats
Tower
Turbine
Pump
Generator
Condenser
To cooling tower
Fig. 2.18.3. Central receiver power plant.
Water is converted into steam in the receiver itself that operates a
turbine coupled with agenerator.
Alternatively, the receiver may be utilized to heat amolten salt and this
fluid is allowed to flow through a heat exchanger where steam is
generated to operate the power cycle.
The 'central receiver' is an important part ofthe collection equipment.
Typically, two receiver designs are in use external type and cavity type.
The external receiver is cylindrical in shape; the solar flux reaches the
outer surface and heat is absorbed by the receiver fluid flowing through
the tubes on the inner surface.

8. In a cavity receiver', the solar flux enters through several apertures,
where the radiant energy is transferred to the receiver fluid.
Que 2.19.
Answer
1.
storage system for solar thermal energy.
Thermal Energy Storage for Heating.
Explain sensible heat storage, latent heat storage and
thermochemical storage of solar energy.
Classifyvariousenergy storage systems. Describe steam
PART- 11
A Energy Storage System :It stores the excess amount of energythan
requirement ofthe demand and supplies stored energy when the demand
exceeds the supply of energy of the system.
Thermal Energy Storage :
Questions-Answers
Thermal
storage
Solids
SensibleLatent he
It is the storage ofenergy by heating, melting or vaporization ofmaterial
and the energy becomes available as heat.
2. Thermal energy storage is of two types :
at storage
Liquids
OR
Thermo
chemical
Solar
ponds
Classification of energy
storage methods
Battery
2-25 M(OE-Sem-7)
Electrical
Absorbents
Fig. 2.19.1.
Electromag
netic
Electro
static
Pumped
hydro
Mechanical
Compres
sed air

2-26M (OE-Sem-7)
i.
1.
2.
3.
ii.
1
b
1
2
C.
1
Sensible Heat Storage:
The energy stored in this system is due to rise in temperature of the
storage medium (solid or liquid).
When the phase does not change on heating solid or liquid, then this
type ofstorage iscalled sensibleheat storage.
The sensible energy (E) is given by the relation :
Where, m = Mass,
Collector
E- mC,.dT
T, =Finaltemperature.
Latent Heat Storage :
T
=Specificheat at constant pressure,
T,=Initial temperature, and
The energystored inthis systemis in the form oflatent heat caused by
phase change during heating either from solid to liquid or liquid to
vapour.
Pump
T2
Electric Storage :
Storage
tank at T;
To collector
Thermo-Chemical Energy Storage :
For example: A + B.
Fig.2.19.2. Latent heat storage.
To Load
In this process, the heat of a chemical reaction is used to store thermal
energy.
Return from load
This systemis suitablefor mediumand hightemperature applications.
Solar heat absorbed
+C+D
In this process, the capacitor stores large amount of electrical energy for
long periods.

2.
3
d.
e.
1.
2
3
i.
The total energy stored is given by
Where,
i.
These are oftwotypes:
T.E. =
V= Volume ofthe dielectric,
E= Dielectric constant, and
E- Electricfieldstrength.
iü. ElectrostaticEnergy Storage: It is the energy stored in the
large capacity capacitors. The total energy stored is given by:
Where,
Battery Storage :A rechargeable storage battery (called secondary
battery) receives electrical energy as direct current which is stored
in the form of chemical energy by a reversible electro-chemical
reaction.
Where,
1
H=
2.
1
[= Dielectric constant,
Electromagnetic Energy Storage : In this process, the energy is
stored in the magnetic field of a superconducting coil, carrying direct
current. The energy stored is given by :
V=Volume of thedielectric, and
E - Electric field strength.
E=
[.V.E2
1
2
These are of twotypes:
LI
L= Inductance, and
Mechanical Energy Storage :
2-27 M(OE-Sem-7)
I=Current.
In this process, the energy canbe stored in the form ofkinetic energy or
poteutial energy.
So, in thisprocess the storage ofsolar energyfirstly convertsinto these
two forms ofenergy before utilization.
Pumped Hydro Storage :
Pumped hydro storage system consists oftwo reservoirs i.e., upper
and lower reservoir.
Apump-turbine combination is installed between these reservoirs
which can work as a pump or turbine and the energyto be stored is
developed by asolar enginewhich is further used to drive the pump
to raise the water from lower reservoir to upper reservoir.

2-28M(OE-Sem-7)
3.
4.
5.
Lower reservoir
ii.
Lake or river
Motor
generator
b. Compressed Air Storage :
Compressor
Pump
turbine
Air
Clutch
Fig. 2.19.3. Pumped hydro storage.
Therefore, the energy stored in upper reservoir ispotential energy.
When water flows down from upper reservoir to the lower reservoir,
the pump and turbine combination acts as a turbine to convert
potential energy into the mechanical energy.
This mechanical energy can be further converted into electrical
energy by agenerator which is coupled to the turbine.
a n d
a
Cooler
T o
t u r b i n e
Compressed air energy storage has similar principles as pumped
storage system.
Valve
The excess electrical energy generated by turbine during low loads
can be stored by compressing the air in large vessels at high
pressures.
Compressed
Upper reservoir
Storage|
dgenerato
air storage
HHMotor(GeneratorHE
From
motor
and
pumn
Clutch
Fuel
Valve
Exhaust
Gas turbine
Combustor
Fig. 2.19.4. Compressed air energy storage.
Que 2.20. How many ways we can store solar energy ?Explain in
brief about thermal energy storage and mechanical storage.

Answer
1.
a.
C.
d.
b. Solar Pumping: Solar water pump work with the help of solar cell,
which convert solar energy into electrical energy.
A.
A.
These are different ways through which we can store solar energy:
1.
Solar Pond:It is a
natural or artificialbody of waterfor collecting and
absorbing solar radiation energy and storing it as heat.
2.
Que 2.21. Define solar air heater with neat sketch and also write
its application.
3.
Solar Cooker:Asolar cooker is a device which uses sunlight as its
energy source and these sun rays are absorbed by a blackened metal
tray which kept inside the solar box. Solar cooking is done by the help of
solar cooker.
Answer
Solar Still :The process used to convert saline water intO pure water
by using solar energy is called solar distillation and the device used is
called solar still.
Thermal Energy Storage and Mechanical Energy Storage :
Refer Q. 2.19, Page 2-25M, Unit-2.
Solar Air Heater:
Solar air heater is a technology in which the energy from the solar
insolation is captured by an absorbing medium and used to heat air.
Solar air heaters use roof, wall or window mounted solar collectors to
heat the air that passes through them.
Transparent
COver
2-29 M(OE-Sem-7)
Reflection loss
Airin
Air passage
Solar radiation
Ambient air
Insulation
Conduction loss
Absorber plate
Fig. 2.21.1.
Convection
loss
Radiation loss
Air out
Bottom ofcollector
Aconventionalsolar airheater is essentially aflat plate collector with
an absorber plate.

2-30 M (OE-Sem-7)
4
5. The whole assembly is enclosed in asheet metal container.
B. Applications of Solar AirHeater:
1.
2. Solar air heater serves as weather cladding.
A
Que 2.22. Explain thermal energy storage for solar heating.
Answer
1.
It is atransparent cover system at the top and insulation at the bottom
and on the sides.
2.
3.
Solar air heater provides ventilation and process air heating.
a.
Thermal Energy Storage for Space Heating:
The solar energy is utilized for space heating in winter or in colder
countries.
The different methods adapted for space heating by utilizing the solar
energy are passive and active method.
Solar space heating reduces the considerable heating load on air
conditioningapparatus during winter.
Active Space Heating:
1. The active method of space heating utilizes perforated collectors
(air heater) through which the cold air is circulated, gets heated
andsupplied to the livingspace directly.
Radiation
C o l l e c t o r
Fan
’ Hot air
Pebble
Storage tank
-Coolair
Fig. 2.22.1. Schematic diagram ofactive space heating by air collector.
2 In other arrangement to utilize this available heat in the night, hot
air is first circulated through the tank packed with rocks,gravel or
pebbles that serve as athermal storage.
3 When there is no sunshine or during night the cold air from rooms
flow through this pack and after heating get distributed in the
living rooms as shown in Fig. 2.22.1.

4.
5
6.
7
8.
In other arrangement the water heating arrangement is provided
through the collectors placed at top of the roof as shown in
Fig. 2.22.2.
The hot water stored in astorage tank is circulated through the
tubes attached to black absorber surface ofcollector.
The heat is delivered to livingspace byafan blowingthe room air
through aheating coil in the heat exchanger, through which hot
water from storage tank is circulatedin the coils.
The heat is extracted by re-circulated air through the exchanger
and transferred to the room.
The water storage system is more compact than pebble packed
system due to higher specific heat capacity of water, but costly
because of pump and secondary heat exchanger.
Pump
R a d i a t i o n
C o l l e c t o r
2-31 M (OE-Sem-7)
Pump
Storage
tank
Heater
PART- 12
Hot
Questions-Answers
air
Cold
air
Fig. 2.22.2. Schematicofactive space heating by water collector.
Heat exchager
Thermal EnergyStorage for Cooling.
Que 2.23. Deseribesolarabsorptionrefrigerationsystemfor space
cooling.

2-32 M (OE-Sem-7)
Define solar air conditioning and refrigeration system.
Answer
A. Solar Air Conditioning System :
1.
2
3
4.
B.
1.
2.
3.
a.
1
2
4
3
4.
6
8
7.
9.
OR
Asolar air conditioningsystemis simplyasystem ofcoolingand heating
that utilises solarpower, rather than electricity.
|AKTU 2018-19, Marks10
Thiscan be done through passive solar,solar thermal energyconversion
and photovoltaic conversion.
It is eco-friendly as well as energy efficient.
It can be operated with green resources of heat as backup resources
when solar radiation is unavailable.
Solar Absorption Refrigeration System for Space Cooling :
Solar energy can be used for cooling the buildings and preserving food
by refrigeration.
The cycle used for cooling with utilization of solar energy is vapour
absorption cycle.
b.
The performance of vapour absorption system depends upon the
working fluids pair i.e., refrigerant and absorbent.
C.
On the basis ofthis,the absorption systems are classified as:
Ammonia or water absorption system,
Ammonia or water or hydrogen electrolux refrigeration system,
and
Lithium bromide (LiBr) or water absorption system.
Ammoniaor Water Absorption System :
The most commonly used refrigerant in absorption system is
ammonia.
5 The main components ofthissystem are shown in Fig. 2.23.1.
It is cheap, readily available and has great affinity with water.
It is used as absorbent and absorbs NH, very fast.
The ammonia-water absorption system is used for cooling- 50 °C.
The heat requircd in generator is supplied by water heated in flat plate
collector.
The hot water transfers the heat to the mixture of absorbent and
refrigerant pair, rich ofrefrigerant.
The refrigerant in vapour form enters in the condenser andweak solution
returns back in the absorber.
In some designs the absorbents are used in the bed ofcollector.

10. On heating they liberate the water vapour stored in the insulated tank
and used for heating the generator during sunshine and off sunshine
hours.
Solar
radiation,
Weak
solution
Collector
Answer
Pump
Generator
Recupe
rator
valve
Absorber
Throatling Expansion valve
Low pressure
CondenserHeat
2- 33M(OE-Sem-7)
vapour
PART- 13
Heat rejected Cold air out
Evaporator - Warm
Fig. 2.23.1. Absorption cooling system.
rejected
Limitations ofSolar Power Plants.
Questions-Answers
air
Que 2.24. Explain thermal energy storage for solar heating and
cooling. What are limitations of solar plants ?
A. Thermal Energy Storage for Solar Heating:Refer Q. 2.22,
Page 2-30M, Unit-2.
B. Thermal Energy Storage for Solar Cooling : Refer Q.2.23,
Page 2-31M, Unit-2.

234 M(OE-Sem-7)
C. Limitations :
1
2
3
5
6.
7
4 Energy not available during night and during clouds.
8
Large area required for collecting solar thermal energy.
Low energy density 0.1 to 1kW/m?.
Direction ofrays changes continuously with time.
Energy storage is essential.
High initial cost.
Requires hybrid plant withstorage facility for supplyingenergy during
night.
Solar central power plants in MW range are not economical.
VERY IMPORTANT QUESTIONS
Following questions are very important. These questions
may be asked in your SESSIONALS as well as
UNIVERSITY EXAMINATION.
Q. 1. Describe the difference between the direct radiation and
diffuse radiation.
Q.2. Classify different types of solar thermal collector and show
the constructional details ofaflat platecollector. What are
its main advantages ?
Q.3. Define solar air heater with neat sketch and also write its
application.
Q.4. Explain therm al energy storage for solar heating and
cooling. What are limitations of solar plants ?

3
UNIT
Part-l :
Part-2 :
Part-4 :
Geothermal Energy,
MHD and Fuel Cells
Part-5 :
CONTENTS
Geothermal Energy
and its Resources
Part-3 : Environmental Consideration
Thermodynamics of Geothermal
Energy Conversion, Electrical
Conversion, Non Electrical
Conversion
Principle of Working of MHD
Power Plant
Performance and Limitations
of Geothermal Energy
Part-6 : Principle of Working of Various
Types of Fuel Cells
Part-7 : Performance and Limitations
of Fuel Cells
3-1 M (OE-Sem-7)
.3-2M to 3-5M
3-5M to 3-9M
.3-9M to 3-10M
3-10M to 3-14M
3-14M to 3-15M
3-15M to 3-22M
3-23M to 3-25M

3-2 M(OE-Sem-7)
1
2
Que 3.1. What is geothermal energy ? Give the classification of
geothermal energy resources.
Answer
3.
4
Describe the various types of identified geothermal energy resources
and mention its application at different temperatures.
5
6
7
A
1.
Geothermal Energy, MHD &Fuel Cells
PART-1
Geothermal Energy and its Resources.
Questions-Answers
LongAnswer Type and Medium AnswerType Questions
Geothermal Energy :
OR
The enormous amount ofenergy available inside the earth in the form
ofheat is known as geothermal energy. Geothermal energyis aform of
renewable energy and independent ofsun, having the source ofnatural
heat inside the earth.
Surface manifestation of this heat energy is indicated by hot water
springs and geysers discovered at several places.
Heat can be experienced from the temperature rise ofthe earth's crust
with increasing depth below the surface.
Radial temperature gradient increases proportionally to depth at arate
ofabout 30°C per km. At adepth of3-4 km, water bubbles up, while at
adepth of 10-15 km the earth's interior is as hot as 1000° to 1200C.
The core ofthe earth consists ofaliquid rock known as 'Magma' having
a temperature of about 4000°C.
This geothermal heat is transferred to the underground reservoir of
water which also circulates under the earth's erust. Its heat dissipates
into the atmosphere as warm water and the steamvents up through the
fissures in the ground as hot springs and geysers.
Limitless heat content in magma plus the heat generated by radioactive
decayofunstable elements suchasK, Thg,andUzgwhichare abundant
in earth's crust are forms of geothermal energy and considered as a
renewable energy resource.
Classification :Geothermal resources are of following types :
Hydrothermal Resources :
These are the depositsofhot water andsteam atlesser depths and these
can be extracted by means ofproduction well.

2
3.
a.
1
4. Examples of Hydrothermal Resource sites :
2.
b.
1
2.
3.
4
5.
High temperature water and steam (300° F to 700° F) is used for the
generation of electricity, otherwise it is used for space heating.
It may be seen that only apart ofthe rock is permeable constituting the
geo-fluid reservoir, so the field is able to produce commercially aviable
resource.
Nheroductionwell
Solid
rocks
Cold
water
Magma
Hot Water Fields:
Hot spring
3-3M(OE-Sem-7)
Porous
rocks
Solid rocks
Fig.3.1.1. Schematicview of hydro-geothermal energy resources.
conduct heat
At these locations hot water below 100 °C emit out as hot spring and the
geothermal aquifers being covered by confining layers to keep the hot
water under pressure.
Examples ofhot water fields are Sahestradhara near Dehradun, Sacred
kund at Badrinath in Uttarakhand, Manikaranin Kulluvalley (Himachal
Pradesh) and Internationally known fields are Pannonian basin
(Hungary), Poriver valley (Italy)and Klamath Falls Oregon (USA).
Wet Steam Fields:
B. Vapour-Dominated Resources :
The pressurizedwater is at more than l00 °C and contains small quantities
of steam and vapour in the geothermal reservoir (at 370 °C).
Sites where the steam escapes through cracks in the surface are called
fumaroles.
An impermeable cap-rock prevents the fluid from escaping into
atmosphere and drilling is carried out to bring the fluid to the surface.
The fluid is used to produce steam and boiling water in predominant
phase.
Examples of wet steam fields : Los Azufre (Mexico), Puna (Hawaii.
USA), Deing (Indonesia), Azores (Portugal) and Latera (Italy).
1. Vapour dominated reservoirs produce dry saturated steam ofpressure
above atmosphericpressure and at high temperature about 350 °C.
2. Water and steam coexist, but steam is in dominant phase and regulates
pressure in the reservoir.

34M(0E-Sem-7)
3 Steam obtained from such ageothermal field directly drives aturbine.
4. Examples : Malsukawa (Japan), The Geysers California (USA),
Kamojang (Indonesia) etc.
C. Hot Dry Rock Resources:
1.
2.
C.
D.
1.
2
1.
2.
3
This is ageological formation with high temperature rocks at 650 °C,
heated by conductive heat flow from magma but contains no water.
Totrap itsenergy the impermeable rockisfractured andwateris injected
to create an artificial reservoir.
1
Water circulates and hot fluids return tothe surface through the other
drilled well as steam and hot water, which are used to generate
electricity.
Geopressured Resources:
2.
3
These resources contains moderate temperature brines (160 °C)
containing dissolved methane and these are trapped under high pressure
in adeepsedimentaryformation sealedbetweenimpermeablelayers of
shale and clay at depths.
E. Magma :
When trapped by boring wells, three sources ofenergy are available :
b
C.
Thermal,
Mechanical as pressure, and
Chemical as methane.
Magma is a molten rock at temperature ranging from 900 °C to
1600 °C. This hot viscous liquid comes out from active volcanic vents and
solidifies.
Que 3.2.
It may form reservoirs at some depth from the earth's surface and
magma chambers represent ahuge energy source.
The existing technology does not allow recovery of heat from these
resources.
geothermal system ?
Answer
A. Hot Water Fields :
What is meant by dry steam, wet steam and hot water
|AKTU2015-16,2017-18; Marks 10
Hot water field, containing a water reservoir at temperature ranging
50-100 °C.
Such fields without much steam content can be useful for house heating
and agricultural purposes the temperature gradient in this feld is less.
The reservoir contains water in the liquid phase below the boiling point
of water under pressure.

4.
5 The geyser plant ofUSA is the largest plant in the world today.
B. Wet Steam Field:
1
2
3
4.
5.
6
C.
1
2.
3
4
5.
On the surface, there are often thermal springs whose temperature is
near the boiling point of water.These fields occur at depth less than
2 km.
3-5 M(0E-Sem-7)
The wet steam fields contain pressurized water in reservoir at
temperature higher than 100 °C.
When hot water at high pressure is brought to the surface, its pressure
is sufficiently reduced and some water will get flashed into steam and
remaining in the form ofboiling water.
The resulting mixture is a mixture of water and steam. Such fields are
suitable for power generation.
When the well is drilled at such locations, the pressurized water rises
into well because of less pressure above the well.
The vapour is used directly for producing power while the hot water
gets separated in the separator and is used for thermal applications.
The percentage of steam generated depends upon the available
geothermal fields and more than 90 % of hydrothermal reservoirs
exploited on industrial scales are this type.
Dry Steam Field:
These fields are similar to wet, steam fields but heat transfer from the
depth is much higher.
These reservoirs produce superheated steam at pressure above
atmosphere.
The permeability of these fields is lower than wet fields.
When the well is drilled up to the reservoir and extraction offluid starts,
adepressed zone is formed at the bottom of the well that enhances the
boiling of water surrounding the rocks.
The steam flows through the dry bottom area and starts expanding and
gets cool. But the heat added by surroundingrocks at high temperature
keeps the steam at superheated state. The degree ofsuperheating may
reach up to 100 °C.
PART-2
Thermodynamics of Geothermal Energy Conversion, Electrical
Conversion, Non Elecirical Conversion.
Questions-Answers

3-6 M(OE-Sem-7)
Que 3.3. What is geothermal energy ? Discuss different systems
used for generating the power using geothermal energy.
Explain geothermal power plants. Write the application of
geothermal energy.
Answer
A. Geothermal Energy: Refer Q. 3.1, Page 3-2M, Unit-3.
B. Different Systems used for GeneratingthePower:
a.
1.
2
3
4
5.
6
1.
Geothermal Energy,MHD &Fuel Cells
Vapour-Dominated Power Plant:
In a
vapour-dominated power plant, steam is extracted from geothermal
wells, passed through a separator to remove particulate contents and
flows directly toa steam turbine.
Centrifugal
separator
Valve
Production well
Dry steam
Steam
turbine
Direct contact
condenser
Generator
y
Condensate
pump
Reinjection
well
3
phase
tower
supply
|Cooling(
b. Liquid-Dominated Power Plants:
Cooling
water
pump
Fig. 3.3.1. Vapour-dominated power plant.
Steam then operates the turbine coupled with the generator is at a
temperature of about 245 °Cand pressure 7 bar which are less than
those in conventional steam cycle plants.
Thus, the efficiency of geothermal plants is low, i.e., about 20 %.
Exhaust steam from the turbine passes through a condenser and the
water so formedcirculates through the cooling tower.
It improves the efficiency of the turbine and controls environmental
pollution associated with the direct release ofsteam into the atmosphere.
Waste water from the cooling tower sump is re-injected into the
geothermal well to ensure continuous supply.
These plants are also called wet steam plants because they give wet
steam i.e., amixture ofhot water and steam under high pressure.
OR

2
i.
There are twotypes of liquid-dominatedpower plants:
ii. Binary cycle system.
Flashed Steam System :
1.
2.
3
4
1.
Flashed steam system,and
2.
3
4
Flashed system is preferred for high temperature mixture of
geothermal brine and steam, with low dissolved impurities.
Geothermal fluid (mixture of brine and steam) passes through a
flash chamber where alarge part of the fluid is converted to steam.
Dry saturated steam passes through the turbine coupled with the
generator to produce electric power.
Hot brine from the flash chamber and the turbine discharge from
the condenser are re-injected into the ground and reinjection of
the spent brine ensures a continuous supply of geothermal fluid
from the well.
Flash
chanmber
Production
well
Steam Turbine Generator
Condenser
ii. Binary Cycle System :
Hot brine
Geothermalfluid
3-7 M (OE-Sem-7)
Condensate pump
Pump
Cooling
tower
Cooling water
pump
Reinjection
well
Blow down
Fig. 3.3.2. Flashed steam geothermal power plant.
Abinary cycle is used where geothermal fluid is hot water with
temperature less than 100 °C.
This plant operates with alow boilingpoint working fluid (Isobutene
or Freon) in a thermodynamic closed Rankine cycle.
Hot brine from underground reservoir circulates through aheat
exchanger and is pumped back to the ground.
In heat exchanger, hot brine transfers its heat to the organic fluid
thusconvertingit to asuperheated vapour that is used inastandard
closed Rankine cycle.

3-8 M (0E-Sem-7)
4
Vapour flow
5
Heat
exchanger
6
Valve
7
Production Reinjection
well
2 Industrial process heat.
1 Generation of electric power.
well
3 Space heating for buildings.
C. Applications of Geothermal Energy:
Turbine
energy.
Production of salt from sea.
Textile industry.
Fig.3.3.3. Schematicview ofbinary cycle system.
Extraction manufacturing.
Sewage heat treatment.
Condenser
Pump
Generator
Cooling
tower
Geothermal water is utilized for greenhouse cultivationusing discharge
water from a geothermal drill hole.
Que 3.4. Discuss thedifferencebetweenageothermalpowerplant
and thermal power plant. Categorize resources of geothermal
OR
Write the difference between ageothermal power plant and thermal
power plant. AKTU 2015-16, Marks 10

Answer
A. Differences :
S. No.Geothermal Power Plant
1.
2
3.
4.
5.
6.
7.
It uses inexhaustible source of
energy.
Itis more environmentfriendly
These power plants in some
dangerous cases can cause
earthquakes.
Answer
It is mainly used for power
generations process.
Setup cost is high.
Byproducts of these plants are
not used.
These plants are less flexible.
8 Specified area is required.
PART-3
Thermal Power Plant
3-9 M(OE-Sem-7)
It uses exhaustible source of
energy.
It is less environment friendly.
There is no such problem.
It can be used for various
industrial processes.
Setup cost is low.
Byproducts ofthese plants can
be used.
B. Resources of GeothermalEnergy: Refer Q. 3.1, Page 3-2M, Unit-3.
These plants are more flexible.
No such restriction.
Environmental Consideration.
Questions-Answers
Que 3.5. Describe the various operational and environmental
problems encountered in obtaining the geothermal energy.
AKTU 2015-16, Marks 7.5
Operational and Environmental Problems of Geothermal
Energy Sources:
1. Geothermal energyis not completely pollution free energy.

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