Renewable Sources of Energy

Unit 1: Part (a)

Conventional & Non-conventional Energy Sources (Ctd.)
• Today every country draws its energy needs from a variety of sources. We can broadly categorize these
sources as conventional and non-conventional.
• The conventional sources of energy (or) non-renewable sources of energy are the natural energy
resources which are present in a limited quantity and are being used for long time. Some of the
conventional sources of energy are fossil fuels, hydro-electric power, nuclear power etc.
• The commercial energy sources are those energy sources for which the consumer needs to pay the price
for the consumption. Some examples are coal, petroleum and electricity.
• In general, non-commercial energy sources are those energy sources that are freely available, and
consumer don’t need to pay the price for their consumption. Some examples are firewood, straw and
dried dung.
• In an industrialized countries, most of the energy requirements are met from commercial sources, while
in an industrially less developed countries, the use of commercial and non-commercial sources are about
equal.
• The non-conventional sources of energy (or) renewable sources of energy cant be exhausted easily and
can be generated at a constant rate for their use over and over again. Some of non-conventional sources
of energy are wind energy, tidal energy, solar energy etc.
Main sources of power generation
There are three main sources of power generation:

1. Thermal Power:

It is generated in India at various power stations with the help of coal and oil. It has been a major source of electric power. In
2004-05, its share in total installed capacity was 70 percent.

2. Hydro electric Power:

It is produced by constructing dams over overflowing rivers. For example Bhakra Nangal Project, Damodor Valley Project and
Hirakund Project etc. In 1950-51, installed capacity of hydro-electricity was 587.4 MW and in 2004-05, it was 19600 MW.

3. Nuclear Power:

India has also developed nuclear power. Nuclear Power plants use uranium as fuel. This fuel is cheaper than coal. India has
nuclear power plants at Tarapur, Kota (Rajasthan) Kalapakam (Chennai) Naroura (UP). Its supply accounts for only 3 percent
of the total installed capacity.
Source: Non- conventional energy resources by G.D. rai
Non - conventional energy sources
S. No Non - conventional energy sources Unit No.
1 Solar Energy 1
2 Wind Energy
2
3 Geothermal Energy
4 Energy from Bio-mass and Bio-gas 3
5 Fuel Cells
6 Hydrogen Energy 4
7 Ocean Thermal Energy Conversion
8 Tidal Energy 5
9 Magneto Hydro Dynamics (MHD) Generator

Reference: M. R. Islam et al. (eds.), Renewable Energy and the Environment, Renewable Energy
Sources & Energy Storage, https://doi.org/10.1007/978-981-10-7287-1_1
Source: Renewable energy sources and emerging technologies by
kotahri
 Prospects of renewable sources of energy in world

 The incoming solar energy absorbed by atmosphere in one year is equal to 3.8 *
10^24 J .
 This equal to 15-20 times the amount of energy stored in all of the world
reserves .
 Renewable sources already supply major part of worlds energy needs
 Biomass supplies about one seventh of all fuel consumed
 Hydro generates one quarter of world energy needs
 Renewables are very attractive because of the following reasons
They can be matched in scale to the need
They can be built in remote locations where energy is required
Rapid planning and construction
Diversity of systems available also increases flexibility and security.
 Prospects of renewable sources of energy in world - Solar energy (PV)

Annual installed photovoltaic

solar capacities in MW
projection from 2010 to 2015
in world

Many countries invest huge

Schematic diagram of Solar photovoltaic system amount of money for increasing
their photovoltaic solar capacity.
Among them China is the market
Reference: M. R. Islam et al. (eds.), Renewable Energy and the leader with generating capacity
Environment, Renewable Energy 43,050 MW in 2015
Sources & Energy Storage, https://doi.org/10.1007/978-981-10-7287-1_1
Prospects of renewable sources of energy in world - Solar energy (CSP)

Installed capacity of CSP of the top 5 countries

In tower based CSP plants, the tower is the central receiver. Solar
beams are directly concentrated by lenses or flat heliostats mirrors
using the principle of light reflection to accrue heat in liquid and to Reference: M. R. Islam et al. (eds.), Renewable Energy and the
turn them into steam, which is then used for electricity generation. Environment, Renewable Energy
Sources & Energy Storage, https://doi.org/10.1007/978-981-10-7287-1_1
Prospects of renewable sources of energy in world - Wind energy

According to Global Wind

Statistics 2016, the
world’s total capacity of
wind energy was 486,749
MW.

The generation capacity

varies from place to place
due to their environmental
condition. Asia has the
Energy conversion in a typical wind turbine maximum proportion in
this sector as there is a
Reference: M. R. Islam et al. (eds.), Renewable Energy and the plenty of availability of
Environment, Renewable Energy wind in Asian sub-
Sources & Energy Storage, https://doi.org/10.1007/978-981-10-7287-1_1
continent
Prospects of renewable sources of energy in world - Bio energy

Formation of bio-mass and fuel

 The latest data depict that “Bio energy” supplies 10% of global Share of sources in bio-mass production
energy. From the forests, woody bio-mass and wastes supply 56
EJ (1 EJ = Exajoule = 1018 J). Latin American and Caribbean
zones are using bio energy mostly.  The worldwide bio-mass plant capacity is increased
from 66 to 72 GW in 2012. The average growth rate of
it in 2012 was 5%. In long run, the bio-mass
Reference: M. R. Islam et al. (eds.), Renewable Energy and the generation as well as waste power generation could be
Environment, Renewable Energy
Sources & Energy Storage, https://doi.org/10.1007/978-981-10-7287-1_1
270 GW by the end of 2030
Prospects of renewable sources of energy in world - Geothermal energy

Country wise generation of electricity from geothermal energy in 2015

Schematic diagram of geothermal system

Reference: M. R. Islam et al. (eds.), Renewable Energy and the
Environment, Renewable Energy
Sources & Energy Storage, https://doi.org/10.1007/978-981-10-7287-1_1
Usage of geothermal energy for various purposes
Prospects of renewable sources of energy in India
 India is implementing one of the world’s largest programs in renewable energy. The country
ranks second in the world in biogas utilization and fifth in wind power and photovoltaic
production.

 Renewable sources contribute to about 5% of the total power generating capacity in the
country

Renewable energy potential and installed capacity in India (December, 2009)

 At present renewable sources contribute only 4% of power generation while India has set a
target of generating 10% of electricity from renewable sources by 2012.

 It is planned to cover electrification of all those remote villages which are not approachable
by grid power supply.

Source: Renewable energy sources and emerging technologies by kotahri

Prospects of renewable sources of energy in India

Energy consumption (in Peta Joules) in India

Reference: Shibani K. Jha, Harish Puppala, Prospects of Renewable Energy Sources in India: Prioritization of
Alternative Sources in Terms of Energy Index, Energy (2017), doi:10.1016/j.energy.2017.03.110
 Prospects of renewable sources of energy in India

Breakup of primary commercial energy resources in India Growth of Renewable energy over the decades

Image Source: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FGrowth-of-Renewable-Energy-in-India-FY-07-

14_fig2_306347415&psig=AOvVaw2pCiS0jZSgqgTrmHJ6vA2y&ust=1631593381936000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCODk6JeN-_ICFQAAAAAdAAAAABAP
Prospects of renewable sources of energy in India (Ctd.)

Energy Potential of Wind source across the country Energy Potential of Solar source across the country

Reference: Shibani K. Jha, Harish Puppala, Prospects of Renewable Energy Sources in India: Prioritization of
Alternative Sources in Terms of Energy Index, Energy (2017), doi:10.1016/j.energy.2017.03.110
Prospects of renewable sources of energy in India (Ctd.)

Energy Potential of Biomass source across the country Geothermal provinces across the country

Reference: Shibani K. Jha, Harish Puppala, Prospects of Renewable Energy Sources in India: Prioritization of
Alternative Sources in Terms of Energy Index, Energy (2017), doi:10.1016/j.energy.2017.03.110
Prospects of renewable sources of energy in India (Ctd.)

Environmental & techno-economic aspects of renewable sources studies

Reference: Shibani K. Jha, Harish Puppala, Prospects of Renewable Energy Sources in India: Prioritization of
Alternative Sources in Terms of Energy Index, Energy (2017), doi:10.1016/j.energy.2017.03.110
SOLAR ENERGY - Extra terrestrial radiation
 Solar energy received in the form of radiation can be converted directly
(photovoltaic cells) or indirectly (concentrating solar power) into other
forms of energy such as heat and electricity which can be utilized.

 Sun is expected to radiate at an essentially constant rate for a few billion

years. So, it may be regarded an renewable source of energy.

 Major drawbacks for extensive application of solar energy are variable

manner in which it arrives at the earths surface and requirement of large area
to collect energy.

 Energy radiated by the sun as electromagnetic waves of which 99% have

wavelengths (w) in the range of 0.2 to 4.0 micrometers (1 mm = 10^(-6) m).

 Solar energy reaching the top of the earth atmosphere consists of 7%

ultraviolet radiation (w < 0.39 mm), 47% visible light (0.39 < w < 0.78)
and 45% infrared radiation (4mm < w > 0.78 mm).

Source: Renewable energy sources and emerging technologies by kotahri

 SOLAR ENERGY - Solar radiation on earth
 Solar radiation that penetrates the earth atmosphere and reaches the
surface differs in amount and character from the radiation at the
top of the atmosphere.

 Part of the radiation is reflected back into the space especially by

clouds. Radiation entering the atmosphere is partly absorbed by
molecules in air. Part of solar radiation is scattered by droplets in
clouds and by atmospheric molecules.

 Solar radiation that has not been absorbed or scattered and reaches
the ground directly from the sun is called Beam radiation.

 Solar radiation received from the sun after its direction has been
changed by reflection or scattering by the atmosphere is called
Diffuse radiation.

 Isolation is defined as the total solar radiation energy received on a

horizontal surface of unit area (1 sq. m) on the ground in unit time (1
day). (Isolation = Beam radiation + Diffuse radiation).
 Extraterrestrial radiation is the measure of solar radiation that would be received in the absence of atmosphere.

 A typical spectral distribution of extraterrestrial radiation is shown in Figure below.

 The curve rises sharply with the wavelength and reaches the maximum value of 2074 W/m2/µm at a
wavelength of 0.48 μm.
 It then decreases asymptotically to zero, showing that 99% of the sun’s radiation is obtained up to a
wavelength of 4 µm.
Source: Renewable energy sources and emerging technologies by kotahri
 The distance between the sun and the earth varies due to the elliptical motion of the earth.

 Accordingly, the extraterrestrial flux also varies, which can be calculated (on any day) by the equation

Where, n is the day of the year counted from the first day of January

 Solar radiation reaching the earth is essentially equivalent to blackbody radiation.

 Using the Stefan–Boltzmann law, the equivalent blackbody temperature is 5779 K for a solar constant of 1367
W/m2.

Beam radiation (Ib): Solar radiation received on the earth’s surface without change in direction, is called beam
or direct radiation

Diffuse radiation (Id): The radiation received on a terrestrial surface (scattered by aerosols and dust) from all
parts of the sky dome, is known as diffuse radiation
SOLAR ENERGY - Solar radiation geometry

 Sun at zenith: Position of sun directly over head.

 Air mass (m): It is the ratio of the suns rays through the atmosphere to the length
of path when the sun is at zenith.

 At sea level AM = 1, when the sun is at zenith or directly overhead; AM = 2 when

the angle subtended by zenith and line of sight of the sun is 60°; AM = 0 just
above the earth’s atmosphere

 Latitude (φ) of a location on earths surface is the angle made by the radial line
joining the specified location to the center of earth with the projection of this line
on the equatorial plane. The latitude at equator is zero and 90 degrees at poles.

 Declination (δ) is the angle between a line extending from the center of the sun to
the center of the earth and the projection of this line on equatorial plane.

Source: Renewable energy sources and emerging technologies by kotahri

SOLAR ENERGY - Solar radiation geometry (Ctd.)

Source: Renewable energy sources and emerging technologies by kotahri

SOLAR ENERGY - Solar radiation geometry (Ctd.)
 Incident angle (θ): The angle of incidence for any surface is defined as the angle formed between the direction of the suns rays
and the line normal to the surface.

 Slope angle: The angle between the inclined slope and the horizontal plane.

 Solar azimuth angle (γ): It is the angle in the horizontal plane between the line due south and the horizontal projection of
normal to inclined plane.

 Slope ( β): It is an angle made by the plane surface with the horizontal surface. The angle is taken as positive for a surface
sloping towards south, and negative for a surface sloping north

Source: Renewable energy sources and emerging technologies by kotahri

Local apparent time (LAT)
 The time used for calculating the hour angle ω is the ‘local apparent time’ which is not the same as
the ‘local clock time’.

 It can be obtained from the local time observed on a clock by applying two corrections.

 The first correction arises due to the difference between the longitude of a location and the
meridian on which the standard time is determined.

 This correction has a magnitude of 4 minute for each degree difference in longitude.

 The other correction is known as the ‘equation of time correction’ which is required due to the fact
that the earth’s orbit and the rate of rotation are subject to certain fluctuations

The positive sign in the first correction is for the western hemisphere while the negative sign is
applicable for the eastern hemisphere.
Solar energy - Solar radiation measurements (Ctd.)
Pyranometer

 The pyranometer designed by the Eppley laboratories, USA, operates on the principle of
thermopile.

 It consists of a black surface which heats up when exposed to solar radiation. Its
temperature rises until the rate of heat gain from solar radiation equals the heat loss by
conduction, convection and radiation.

 On the black surface the hot junctions of a thermopile are attached, while the cold
junctions are placed in a position such that they do not receive the radiation.

 An electrical output voltage (0 to 10 mV range) generated by the temperature difference

between the black and the white surfaces indicates the intensity of solar radiation.

 The output can be obtained on a strip chart or on a digital printout over a period of time.
This is a measure of global radiation
SOLAR ENERGY - Solar radiation measurements
Pyrheliometer

 This is an instrument which measures beam radiation falling on a

surface normal to the sun’s rays.

 In contrast to a pyranometer, the black absorber plate (with hot

junctions of a thermopile attached to it) is located at the base of a
collimating tube.

 The tube is aligned with the direction of the sun’s rays with the help
of tracking mechanism and alignment indicator.

 The black plate receives only beam radiation and a small amount of
diffuse radiation falling within the acceptance angle. Image source:
https://www.google.com/url?sa=i&url=https%3A%2F%2Fcircuitdigest.com%2Ft
utorial%2Fsolar-radiation-measurement-methods-using-pyrheliometer-and-

 Problems with pyrheliometer are aperture angle, finite dimensions pyranometer&psig=AOvVaw30gAW9vuCJmNaqoPvyJuxI&ust=163194156100000

0&source=images&cd=vfe&ved=0CAsQjRxqFwoTCPCIuJyehfMCFQAAAAAdAAAA
ABAO

and imprecision in tracking system.

 Solar energy - Solar radiation data for India

Tropical: This type of climate has every month of the year with an
average temperature of 18 °C (64.4 °F) or higher, with significant
precipitation (rain or snow that falls to or condenses on ground).

Arid, desert, hot: This type of climate is defined by little

precipitation.

Temperate: This type of climate has the coldest month averaging

between 0 °C (32 °F) and 18 °C (64.4 °F) and at least one month
averaging above 10 °C (50 °F).

Cold: This type of climate has at least one month averaging below
0 °C (32 °F) and at least one month averaging above 10 °C (50 °F).

Köppen-Geiger climate classification in India and surface Polar: This type of climate has every month of the year with an
global horizontal irradiance (GHI) observation stations average temperature below 10 °C (50 °F).
Reference: Harsh G. Kamath, J. Srinivasan, Validation of global irradiance derived from INSAT-3D over India, Solar Energy,
https://doi.org/10.1016/j.solener.2020.03.084
Solar energy - Solar radiation data for India

 India lies within the latitudes of 7° N and 37° N, with annual

intensity of solar radiation between 400 and 700 cal/cm2/day.

 Most parts of India receive 4–7 kWh/m2/day of solar

radiation with 250–300 sunny days in a year.

 The annual average daily global solar radiation in India (in

kWh/ m2/day) is shown in Figure.

 A similar map can also be drawn for average daily diffuse

radiation.

 The highest annual radiation energy is received in the

western Rajasthan while the northeastern region receives the
lowest annual radiation.

Source: Renewable energy sources and emerging technologies by kotahri

Annual solar radiation pattern
 India is divided into five regions as shown, with changing solar
radiation pattern between January and December.

 It gives the annual average of global solar energy received on a

horizontal plane.

 The daily record of global radiation data is useful for industry as

India lies in the sunny regions of the world.

 Other countries having a rich solar flux belt are Saudi Arabia,
Central Australia and South Africa.

 The peak values are measured from March to May, when the
western Rajasthan and Gujarat receive over 600 cal/cm2/day
(25,100 kJ/m2/day).

 During monsoon and winter months the daily solar radiation

decreases to 400 cal/cm2/min (16,700 kJ/m2/min).

Source: Renewable energy sources and emerging technologies by kotahri

Solar energy - Solar radiation data for India (Ctd.)

Error statistics of half-hourly satellite derived GHI data for the chosen validation sites:
om is mean daytime GHI at the station, MBE is mean bias error, RMSE is root mean square error, rMBE is relative mean bias error, rRMSE is the
relative root mean squared error and R2 is the coefficient of determination.

Reference: Harsh G. Kamath, J. Srinivasan, Validation of global irradiance derived from INSAT-3D over India, Solar Energy,
https://doi.org/10.1016/j.solener.2020.03.084
Solar collectors
Flat plate collectors
Concentrating collectors
Types of energy storage systems
Solar collectors
A solar thermal energy collector is an equipment in which solar energy is collected by absorbing radiation in an
absorber and then transferring to a fluid. In general, there are two types of collectors:
1. Flat-plate solar collector
2. Concentrating-type solar collector

FLAT-PLATE COLLECTOR
It consists of five major parts as mentioned below:
(i) A metallic flat absorber plate of high thermal conductivity made of copper, steel, or aluminium, and having
black surface. The thickness of the metal sheet ranges from 0.5 mm to 1 mm.

Source: Renewable energy sources and emerging technologies by kotahri

(ii) Tubes or channels are soldered to the absorber plate. Water flowing
through these tubes takes away the heat from the absorber plate. The
diameter of tubes is around 1.25 cm, while that of the header pipe which
leads water in and out of the collector and distributes it to absorber tubes,
is 2.5 cm.

iii) A transparent toughened glass sheet of 5 mm thickness is provided as

the cover plate. It reduces convection losses through a stagnant air layer
between the absorber plate and the glass. Radiation losses are also reduced
as the spectral transmissivity of glass is such that it is transparent to short
wave radiation and nearly opaque to long wave thermal radiation emitted
by interior collector walls and absorbing plate.

(iv) Fibre glass insulation of thickness 2.5 cm to 8 cm is provided at the

bottom and on the sides in order to minimize heat loss.

(v) A container encloses the whole assembly in a box made of metallic sheet
or fibre glass.
Source:
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.alternative-
energy-tutorials.com%2Fsolar-hot-water%2Fflat-plate-
collector.html&psig=AOvVaw06yRuMJfOqtvB0GsTa12pn&ust=16322037654920
00&source=images&cd=vfe&ved=0CAsQjRxqFwoTCJCw84fvjPMCFQAAAAAdAA
AAABAD
 The commercially available collectors have a face area of 2 m2.
 The whole assembly is fixed on a supporting structure that is installed in a tilted position at a suitable angle
facing south in the northern hemisphere.
 For the whole year, the optimum tilt angle of collectors is equal to the latitude of its location.
 During winter, the tilt angle is kept 10–15° more than the latitude of the location while in summer it should be
10–15° less than the latitude

Disadvantages
 It has no optical concentrator.
 Here, the collector area and the absorber area
are numerically the same, the efficiency is low,
and temperatures of the working fluid can be
raised only up to 100°C.

Source: Renewable energy sources and emerging technologies by kotahri

CONCENTRATING COLLECTOR

 Here the area receiving the solar radiation is several times greater than the absorber area and the efficiency is
high.

 Mirrors and lenses are used to concentrate the sun’s rays on the absorber, and the fluid temperature can be
raised up to 500°C.

 For better performance, the collector is mounted on a tracking equipment to face the sun always with its
changing position.

 An optical system of mirrors or lenses projects the radiation on to an absorber of smaller area.

 This process compensates the reflection or absorption losses in mirrors or lenses and losses on account of
geometrical imperfections in the optical system.

 A term called ‘optical efficiency’ takes care of all such losses.

 For higher collection efficiency, concentrating collectors are supported by a tracking arrangement that tracks
the sun all the time, so that beam radiation is on to the absorber surface.

 As collectors provide a high degree of concentration, a continuous adjustment of collector orientation is

required.
Plane receiver with plane collectors
 It is a simple concentrating collector, having up to four adjustable reflectors all around, with a single
collector as shown.
 The CR varies from 1 to 4 and the non-imaging operating temperature can go up to 140°C.

Source: Renewable energy sources and emerging technologies by kotahri

Compound parabolic collector with plane receiver

 Reflectors are curved segments that are parts of two parabolas .

 The CR varies from 3 to 10. For a CR of 10, the acceptance angle is 11.5° and tracking adjustment is
required after a few days to ensure collection of 8 hours a day.

Source: Renewable energy sources and emerging technologies by kotahri

Cylindrical parabolic collector
The reflector is in the form of trough with a parabolic cross section in which the image is formed on the focus of the
parabola along a line as shown in Figure.
The basic parts are:
(i) an absorber tube with a selective coating located at the focal axis through which the liquid to be heated flows,
(ii) a parabolic concentrator, and
(iii) a concentric transparent cover. The aperture area ranges from 1 m2 to 6 m2, where the length is more than the
aperture width. The CR range is from 10 to 30.

Source: Renewable energy sources and emerging technologies by kotahri https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.yourelectricalguide.com%2F2018%2F07%2Fconcentrating-

solar-collector-types-power-plants-advantages-
disadvantages.html&psig=AOvVaw1Lzgm2xLovpbSg6CgO4ArR&ust=1632203944567000&source=images&cd=vfe&ved=0CA
sQjRxqFwoTCIC1l9TvjPMCFQAAAAAdAAAAABAU
Collector with a fixed circular concentrator and a moving
receiver
 The fixed circular concentrator consists of an array of long, narrow, flat
mirror strips fixed over a cylindrical surface as shown in Figure.
 The mirror strips create a narrow line image that follows a circular path
as the sun moves across the sky.
 The CR varies from 10 to 100.

Fresnel lens collector

 Fresnel lens refraction type focusing collector is made of an acrylic
plastic sheet, flat on one side, with fine longitudinal grooves on the
other as shown in Figure.
 The angles of grooves are designed to bring radiation to a line focus.

 The CR ranges between 10 and 80 with temperature varying between

150°C and 400°C.

Source: Renewable energy sources and emerging technologies by kotahri

Paraboloid dish collector

 To achieve high CRs and temperature, it is required to build a

point-focusing collector.

 A paraboloid dish collector is of point-focusing type as the

receiver is placed at the focus of the paraboloid reflector.

 As a typical case, a dish of 6 m in diameter is constructed from

200 curved mirror segments forming a paraboloid surface.

 The absorber has a cavity shape made of zirconium–copper alloy,

with a selective coating of black chrome. The CR ranges from 100
to a few thousands with maximum temperature up to 2000°C.

 For this, two-axis tracking is required so that the sun may remain
in line with the focus and vertex of the paraboloid.

Source: Renewable energy sources and emerging technologies by kotahri

Central receiver with heliostat

 To collect large amounts of heat energy at one point, the ‘Central Receiver Concept’ is followed.
 Solar radiation is reflected from a field of heliostats (an array of mirrors) to a centrally located receiver on
a tower .
 Heliostats follow the sun to harness maximum solar heat.
 Water flowing through the receiver absorbs heat to produce steam which operates a Rankine cycle turbo
generator to generate electrical energy.
 With a central receiver optical system, a large number of small mirrors are installed, each steerable to
have an image at the absorber on the central receiver.
 A curvature is provided to the mirrors so as to focus the sunlight in addition to directing it to the tower.

Source: Renewable energy sources and emerging technologies by kotahri

Solar Thermal Storage
Sensible heat storage
Latent heat storage
SOLAR THERMAL ENERGY STORAGE
 Solar energy is available only during the sunshine hours.
 Consumer energy demands follow their own time pattern and the solar energy does not fully match the
demand.
 As a result, energy storage is a must to meet the consumer requirement.
 There are three important methods for storing solar thermal energy.
 These are discussed in subsections below.

Sensible Heat Storage

Liquids

Solids
 For sensible heat storage, rocks or gravel packed in an insulated vessel are used with solar heaters and it provides a
large and inexpensive heat transfer surface.
 A typical size of rock piece varies from 1 to 5 cm.
 This system operates efficiently as the heat transfer coefficient between the air and the solid is high.
 As a thumb rule, 300 kg to 500 kg of rock per square metre of collector area is sufficient for space heating
applications.
 Refractory materials like magnesium oxide bricks, silicon oxide and aluminium oxide, are used in storage devices to
operate up to 600°C.
Latent Heat Storage (Phase Change Heat Storage)

 In this system, heat is stored in a material when it melts, and heat is extracted from the material when it
freezes.
 Heat can also be stored when a liquid changes to gaseous state, but as the volume change is large, such a
system is not economical.
 A few such materials which melt on heating have been experimented for their suitability for solar energy
applications.
 These are organic materials like paraffin wax and fatty acids; hydrated salts such as calcium chloride hexo
hydrate (CaCl2. 6H2O) and sodium sulphate deca hydrate (Na2SO4.10H2O); and inorganic materials like ice
(H2O), sodium nitrate (NaNO3) and sodium hydroxide (NaOH).
 Phase change materials such as sodium sulphate decahydrate (Glauber’s salt) melt at 32°C, with a heat of
fusion of 241 kJ per kg.

 Paraffin wax possesses a high heat of fusion (209 kJ/kg), and is known to freeze without supercooling.
 The inorganic material ice is quite suitable if energy is to be stored/extracted at 0°C.
 Sodium nitrate having a melting point of 310°C is suitable for high temperature applications.
Thermochemical Storage
 With a thermochemical storage system, solar heat energy can start an endothermic chemical reaction and new
products of reactions remain intact.
 To extract energy, a reverse exothermic reaction is allowed to take place.
 Actually, the thermochemical thermal energy is the binding energy of reversible chemical reactions.
 A schematic representation of thermochemical storage reaction is shown in Figure.
 Chemicals A and B react with solar heat and through forward reaction are converted into products C and D. The
new products are stored at ambient temperature.

 When energy is required, the reverse reaction is allowed to take place at a lower temperature where products C
and D react to form A and B. During the reaction, heat is released and utilized
Photovoltaic systems
Photovoltaic effect
 The photovoltaic effect is the generation of voltage and electric current in a material upon exposure
to light.
 It is a physical and chemical phenomenon.
 Photovoltaic power generation is a method of producing electricity using solar cells.
 A solar cell converts solar optical energy directly into electrical energy.
 A solar cell is essentially a semiconductor device fabricated in a manner which generates a voltage when
solar radiation falls on it.
 In semiconductors, atoms carry four electrons in the outer valence shell, some of which can be dislodged to
move freely in the materials if extra energy is supplied.
 Then, a semiconductor attains the property to conduct the current.
 This is the basic principle on which the solar cell works and generates power.
SEMICONDUCTOR MATERIALS AND DOPING
 A few semiconductor materials such as silicon (Si), cadmium sulphide (CdS) and gallium arsenide (GaAs) can be
used to fabricate solar cells.
 Semiconductors are divided into two categories—intrinsic (pure) and extrinsic.
 An intrinsic semiconductor has negligible conductivity, which is of little use.
 To increase the conductivity of an intrinsic semiconductor, a controlled quantity of selected impurity atoms is
added to it to obtain an extrinsic semiconductor.
 The process of adding the impurity atoms is called doping.

 In a pure semiconductor, electrons can stay in one of

the two energy bands—the conduction band and the
valence band.
 The conduction band has electrons at a higher energy
level and is not fully occupied, while the valence
band possesses electrons at a lower energy level but
is fully occupied

Source: Renewable energy sources and emerging technologies by kotahri

 The energy level of the electrons differs between the two bands and this difference is called the band gap energy,
Eg. Photons of solar radiation possessing energy E higher than the band gap energy Eg, when absorbed by a
semiconductor material, dislodge some of the electrons.

 These electrons possess enough energy to jump over the band gap from the valence band into the conduction
band.

 In this process, vacant electron positions or holes are left behind in valence band.

 These holes act as positive charges and can move if a neighboring electron leaves its position to fill the hole site.

 Mobile electrons and holes can thus enable a current flow through an external circuit if a potential gradient
exists in the cell material.
EFFICIENCY OF SOLAR CELLS
PHOTOVOLTAIC EFFECT
When a solar cell (p-n junction) is illuminated, electron–hole pairs are generated and the electric
current obtained I is the difference between the solar light generated current IL and the diode dark
current Ij, i.e.,

EFFICIENCY OF SOLAR CELLS

Source: Renewable energy sources and emerging technologies by kotahri

SEMICONDUCTOR MATERIALS
FOR SOLAR CELLS
• Single Crystal Silicon
• Polycrystalline Silicon Cells
• Bifacial crystalline cell over multi-
crystalline substrate
• Amorphous Silicon Cells

Source: Renewable energy sources and emerging technologies by kotahri

SOLAR PHOTOVOLTAIC SYSTEM
(SPS)
 A PV module produces dc power. To operate electrical appliances used in households, inverters are
used to convert dc power into 220 V, 50 Hz, ac power.

 Components other than PV module are collectively known as Balance of System (BOS) which
includes storage batteries, an electronic charge controller, and an inverter.

 Storage batteries with charge regulators are provided for back-up power supply during periods of
cloudy day and during nights. Batteries are charged during the day and supply power to loads.

 The capacity of a battery is expressed in ampere-hours (Ah) and each cell of the lead-acid type
battery is of 2 volts.

 Batteries are installed with a microprocessor-based charge regulator to monitor the voltage and
temperature and to regulate the input and the output currents to obviate overcharging and excessive
discharge.
Source: Renewable energy sources and emerging technologies by kotahri
APPLICATION OF PV SYSTEMS

 Solar PV power systems may be categorized into four classes—standalone, PV hybrid, grid connected and
solar power satellite.

 The standalone systems are self-sufficient, unreachable by state grid but have a battery system for
continuous supply.

 A PV hybrid system is installed with a back-up system of diesel generator.

 Such system are used in remote military installations, BSF border outposts, health centers, and tourist
bungalows.

 In grid-connected systems, a major part of the load during the day is supplied from the PV array, and then
from the grid when the sunlight is not sufficient.
Solar street light

 Solar street light as shown in Figure describes a standalone PV power generating device. It comprises a
compact fluorescent lamp, two 35 watt solar modules, and an 80 Ah tubular cell battery
Home lighting system
 Home lighting systems are the most popular solar PV units, typically designed to work with two light
points and one TV point. When necessary, a small dc fan can also be run from this system.

Source: Renewable energy sources and emerging technologies by kotahri

SPV Water Pumping System

 Individual farmers typically use an 1800 watt PV array to operate a 2 hp dc motor pumpset as shown in
Figure .
 It can give water discharge of 140,000 litres per day from a depth up to 7 metres, sufficient to irrigate 5–8
acres of land holding several crops

Source: Renewable energy sources and emerging technologies by kotahri

SPV Cell for Communication Equipment in Snow-bound Areas
 For a telecommunication network, PV modules of 4.5 kWp are sufficient to feed a battery bank of 48 V *1200 A
with a charge controller

Source: Renewable energy sources and emerging technologies by kotahri

GRID INTERACTIVE SOLAR PV POWER SYSTEM

 A grid-connected photovoltaic power system is connected with the state electric grid.
 The system operates to supplement the grid power during the daytime when a substantial quantum of
solar energy is extracted from the sunlight.
 During night the grid power alone feeds the load.
 This system also supplies emergency power during any short period of grid failure.
 This system requires additional equipment to control voltage, frequency and waveform so as to conform
to conditions for feeding the power into the grid.

Source: Renewable energy sources and emerging technologies by kotahri

SOLAR POWER PLANT USING A SATELLITE

Source: Renewable energy sources and emerging technologies by kotahri

Applications of solar energy
 Applications of
solar energy

Direct Thermal Solar Electric Photo voltaic

Solar Thermal
applications applications methods

Solar water
Heating

Space cooling
and Heating

Solar
distillation

Solar Pumping

Solar cooking

Solar green
house
Solar water Heating systems

Solar water heating systems primarily contains Some typical designs of solar heaters are
 Flat plate collectors 1. Natural circulation solar water heaters (pressurized)
 Storage tank 2. Natural circulation solar water heaters (non-pressurized)
 Circulation systems and auxiliary heating systems 3. Forced circulation solar water heater
 Control of the system

Natural circulation solar water heaters (pressurized)

Source: Non-conventional energy resources by G.D. rai

Natural circulation solar water heaters (non-pressurized)

Source: Non-conventional energy resources by G.D. rai

Forced circulation solar water heaters

Source: Non-conventional energy resources by G.D. rai

Space Heating

50-75% of annual
Passive system heating
requirement

Active system

Image Source:
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.solarreviews.com%2Fblog
%2Factive-passive-home-solar-heating-
system&psig=AOvVaw0OTm5q0AxsXFooOOFTXCtS&ust=1633164456324000&source=ima
ges&cd=vfe&ved=0CAsQjRxqFwoTCIDT4PLpqPMCFQAAAAAdAAAAABAD

Source: Non-conventional energy resources by G.D. rai

Passive Heating

Roof storage

Source: Non-conventional energy resources by G.D. rai

Convective loop

Source: Non-conventional energy resources by G.D. rai

Solar cooling
 The whole system consists of four units: generator,
condenser, evaporator, and absorber.

 The generator contains a solution mixture of absorbent and

refrigerant, and this mixture gets heated with solar energy.

 Refrigerant vapour is boiled off at a high pressure and flows

into condenser, where it gets condensed rejecting heat and
becomes liquid at high pressure.

 Refrigerant then passes through the expansion valve and

evaporates in the evaporator.

 The refrigerant vapour is then absorbed into a solution

mixture taken from the generator in which the refrigerant
concentration is quite low.

 The rich solution thus prepared is pumped back to the

generator at a high pressure to complete the cycle.

 A heat exchanger is provided to transfer heat between

solutions flowing between the absorber and the generator
Solar pumping
Solar pumping utilizes the mechanical power generated by the solar radiation to run the water pump.
Solar energy offers several beneficial features
i) The need for pump arises mostly during summer where solar radiation is intense.
ii) Pumping can be carried out intermittently without any problem.
iii) These solar pumps are inexpensive and maintenance cost are lower.
iv) The requirement of water decreases during periods of low radiation when solar pumping decreases.
v) Evaporation losses reduce during cloudy days. Rainwater is also available during rainy days.
Solar Stills

Source: Non-conventional energy resources by G.D. rai

Source: https://www.turbinegenerator.org/wp-content/uploads/2012/11/How-
a-solar-still-works1.jpg

Source: https://prd-wret.s3.us-west-
2.amazonaws.com/assets/palladium/production/s3fs-
public/thumbnails/image/wss-desalination-solar-still.jpg
Solar Cooking

Multi reflector Parabolic dish

Flat box type
type concentrator
Solar Green house

Image Source: https://www.pv-magazine.com/wp-content/uploads/2021/03/OConnor-greenhouse-2021-HEADER-1200x675.jpg

Image source: https://www.backyardgardenlover.com/wp-content/uploads/2020/11/how-does-a-greenhouse-work2.jpg
Image Source: https://goingsolar.com/wp-content/uploads/2019/03/Solar-greenhouse.jpg

Image Source:
https://assets.newatlas.com/dims4/default/5bcd7c0/2147483647/strip/true/crop/1997x1331+2+0/resize/1200x800!/quality/90/?url=http
%3A%2F%2Fnewatlas-brightspot.s3.amazonaws.com%2Fc6%2Ff1%2Ff6a414ad4bc7afe6118da7632895%2Fdepositphotos-21047035-l-
2015.jpg
Image Sourcehttps://sierragreenhouse.b-cdn.net/wp-content/uploads/2021/02/Types-of-
Greenhouses_1000px.jpg