Energy generated by using wind, solar, small hydro, tides, geothermal heat and biomass is known a non-conventional energy. All these sources are renewable process of energy generation and do not cause environmental pollution.
NON CONVENTIONAL ENERGY SOURCES AND STORAGE DEVICES
In 1939, Otto Hahn studied the effect of bombardment of
fast neutron on uranium.
The fission of U-235 nucleus by slow neutrons released enormous
amount of energy. The energy released is called nuclear energy or fission
energy.
Nuclear fission is defined as the process of splitting of
heavier nucleus into two or more smaller nuclei with simultaneous liberation of
large amount of energy.
NUCLEAR ENERGY
When U-235 is bombarded by slow moving neutron, unstable U-236
is formed.
This nucleus disintegrates into two equal nuclei with the release
of huge amount of energy and few neutrons.
MECHANISM OF NUCLEAR FISSION
Heavy nucleus splits into two or more nuclei.
Two or more neutrons are produced by fission of each
nucleus.
Large quantity of energy is produced .
All the fission fragments are radioactive , giving off gamma
radiations
The fission products fall into two groups- one between
mass no.80-100 and other 120-150
CHARACTERISTICS OF NUCLEAR
FISSION REACTION
All the fission reaction are self propagating chain
reaction because fission products contains neutrons which further cause fission
in other nuclei.
The nuclear reactions can be controlled ,by absorbing the
neutrons using Cd, B or Hf.
Every secondary neutron released in the fission reaction
does not strike a nucleus , some escape into air. Hence a chain reaction cannot
be maintained.
The number of neutrons resulting from a single fission is
known as multiplication factor. When it is less than 1 , no chain reaction take
place. The process of combination of lighter nuclei to form heavier nuclei,
with simultaneous liberation of huge amount of energy.
Example : Fusion reaction in sun
NUCLEAR FUSION
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S.No
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Nuclear fission
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Nuclear fusion
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|
1.
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It is a process of breaking a heavy nucleus with
projectiles into two or more light fragments with liberation of large amount
of energy
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It is a
process of fusion of lighter
nuclei to form heavier nuclei, with
simultaneous liberation of huge amount of energy.
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|
2.
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This process occurs with the emission of radioactive rays.
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It does not emit any radioactive rays.
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3.
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It takes place simultaneously at ordinary temperature.
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It takes place at very high temperature(106K)
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4
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It gives rise to chain reaction
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No chain reaction
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5
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Neutrons are emitted
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Positrons are emitted
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6
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It can be controlled.
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It cannot be controlled.
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DIFFERENCES BETWEEN NUCLEAR FISSION AND NUCLEAR FUSION
In the nuclear fission reaction , the secondary neutrons
emitted from the fission of uranium may hit another uranium nuclei and cause
fission producing more neutrons and so on. Thus a chain of self sustaining
nuclear reaction is set up . This type of reaction is known as nuclear chain reaction.
The secondary neutrons released may escape to the air and
will result in the breaking of the chain and the amount of energy released will
be less.
For the chain reaction to continue, sufficient amount of
U-235 must be present to capture the neutrons.
The minimum amount of fissionable material requited to
continue the nuclear chain reaction is called Critical mass. The critical mass
of U-235 is between 1 to 100Kg.
If the mass of the fissionable material is more than the
critical mass, it is called super critical mass. And if it is lesser, it is called sub critical mass.
The super and sub critical mass may hinder the propagation
of the chain reaction.
NUCLEAR CHAIN REACTION EXAMPLE OF NUCLEAR CHAIN REACTION
When U-235 is bombarded by thermal neutrons, it undergoes
fission and releases three neutrons. These 3 neutrons strike another U-235 nucleus
causing 3x3=9 neutrons. These nine further give rise to 27 reactions. This process
is known as nuclear fission chain reaction.
The energy released by the nuclear fission is called
nuclear fission energy or nuclear energy. cause of the release of energy. The
enormous amount of energy released during the nuclear fission isdue to the loss
in some mass, when the reaction takes place. During nuclear fission, the sum of
masses of the products formed is slightly less than thesum of masses of target
species and bombarding neutron. The loss in mass get converted into energy
according to Einstein equation. where c= velocity; m = loss in mass and E=
energy
Total masses of reactants = 235.12 + 1.009 = 236.129 amu
Total masses of products = 140.91 +91.91 +3x1.009 + 235.847
amu
Loss in mass = 0.282 amu
The loss of 0.282 amu of U-235 liberates = 0.282x931.47 =
262.676meV
NUCLEAR ENERGY
NUCLEAR REACTOR OR PILE
The arrangement or equipment used to carry out fission
reaction under controlled conditions is called nuclear reactor.
The energy released by the fission reaction in the nuclear
reactor can be used to produce steam which can turn turbines and produce
electricity.
COMPONENTS OF A NUCLEAR REACTOR
1. Fuel rods
2. Moderator
3. Control rods
4. Coolant
5. Protective screen
6. Heat exchanger / pressure vessel
7. Turbine
FUEL RODS: The fissionable material used in the nuclear reactor
is enriched U-235. It is used in the form of rods or strips. It produces heat
energy and neutrons , thus iniating nuclear chain reaction.
MODERATOR: It slows down fast fission neutrons . Ex.,
ordinary water, Heavy water , graphite, beryllium. The kinetic energy of fast
neutron is reduced to slow neutrons(0.25 eV)
CONTROL RODS: To control the rate of fission of U-235 , these
rods absorb the excess neutrons . So the fission reaction proceeds at steady
rate. Movable rods made of Cd or B are suspended between fuel rods. These rods
are lowered and raised as of need. If the rods are deeply inserted inside the
reactor, they will absorb more neutrons and the reaction become very slow. If
the rods are pushed outwards, they will absorb less neutrons and the reaction
will be very fast. It controls the nuclear chain reaction and avoids the damage
to the reactor.
COOLANT: Substance which cools the fuel core by removing
heat produced by fission. The coolant liquid is circulated in the reactor core.
It enters the base and leaves at the top. The heat carried by outgoing liquid
is used to produce steam. Ex., Water ( act as coolant and moderator) Heavy water
, liquid metal ( Na or K) , Air, organic compounds like poly phenyls.
PROTECTIVE SCREEN/ SHIELD: The moderator , control rods and
fuel element are enclosed in a chamber which has a thick concrete shield(10m
thick). These walls stop the nuclear radiations from moving out of the reactor.
The environment and the operating persons are protected from destruction in
case of leakage of radiation.
HEAT EXCHANGER : It transfers the heat liberated from the reactor
core to boil water and produce steam at about 400Kg/cm2.
PRESSURE VESSEL : It encloses the core and also provides the
entrance and as exit passages for coolant. It withstand the pressure as high as
200 atm.
TURBINE : The steam generated in the heat exchanger is used
to operate a steam turbine, which drives a generator to produce electricity.
The exhaust steam is condensed and sent back to the heat exchanger.
NUCLEAR REACTOR
LIGHT WATER NUCLEAR POWER PLANT
It is the one in which U-235 fuel rods are submerged in
water. Here water acts as coolant and moderator.
WORKING
The fission reaction is controlled by inserting or
removing the control rods of B-10 automatically from the spaces in between the
fuel rods. The heat emitted is absorbed by the coolant (light water) .The
heated coolant then goes to the heat exchanger containing sea water, which is
converted to steam. The steam drives the turbines , generating electricity.
BREEDER REACTOR
Breeder reactor is the one which converts non-fissionable
material (U-238, Th-232 ) into fissionable material (U-235, Pu-239).
In breeder reactor, of the three neutrons emitted in the
fission of U-235, only one is used in propagating the fission of U-235.The
other two are allowed to react with U-238. Thus two fissionableatoms Pu-239 are
produced for each atom of U-235 consumed. The breeder reactor produces more fissionable
material than it uses.
The fissionable nucleides such as U-235 and Pu-239 are
called fissile nucleides. The nonfissionable nucleides such as U-238 &
Th-232 are called fertile nucleides. The most common breeding reaction is that of
plutonium-239 from non-fissionable uranium-238. The term "fast
breeder" refers to the types of configurations which can actually produce
more fissionable fuel than they use, such as the LMFBR. This scenario is possible
because the non-fissionable uranium-238 is 140 times more abundant than the
fissionable U-235 and can be efficiently converted into Pu-239 by the neutrons
from a fission chain reaction.
SOLAR ENERGY CONVERSION
It is the process of conversion of direct sunlight into more
useful forms. It occurs by the following two mechanism.
(i) Thermal conversion (ii) Photo conversion
THERMAL CONVERSION
It involves absorption of thermal energy in the form of Ir
radiation. Solar energy is an important source for low temperature heat which
is useful for heating buildings, water and refrigeration.
Methods of thermal conversion
1. Solar heat collectors : It consists of natural materials
like stones, bricks or materials like glass, which can absorb heat during day
time and release it slowly at night. Used in cold places, where houses are kept
in hot condition using heat collectors.
2. Solar water heater : It consists of an insulated box
inside of which is painted with black paint. It is also provided with a glass
lid to receive and store solar heat. The black painted copper coil allows the
cold water in and heats it up and flows out into a storage tank.
PHOTO CONVERSION
It involves conversion of light energy directly in to
electrical energy. Ex. Photo galvanic cell or solar cell
PHOTOGALVANIC CELL
It is the one which converts the solar energy directly into
electrical energy.
PRINCIPLE : The basic principle is based on the photovoltaic
effect. When solar rays fall on a two layer of semiconductor devices, a
potential difference between two layer is produced. This potential difference
causes flow of electrons and produces electricity.
CONSTRUCTION : Solar cells consists of a p- type semiconductor
( Si doped with B) and n-type semiconductor(Si doped with P ) .
WORKING : When solar rays fall on p-type semiconductor, the
electrons from the valence band get promoted to the conduction band and cross
the p-n junction into n-type semiconductor. Thereby potential difference is
produced which causes flow of electrons and hence current is generated.
APPLICATIONS OF SOLAR CELLS :
1. Lighting purpose
2. Solar pumps can be run by solar battery
3. Used in calculators, electronic watches, radios and TV.
4. Used to drive vehicles
5. Used in space craft and satellites
WIND ENERGY
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o Energy recovered from the force of the wind is called wind
energy. The wind energy is harnessed by making use of wind mills.
o WIND MILLS : The strike of blowing wind on the blades of the
wind mill make it rotating continuously. The rotational motion of the blade
drives a number of machines like waterpump, flour mills and electric generators.
o WIND FARMS : When a number of wind mills areinstalled and
joined together in a definite pattern it forms a wind farm. The wind farm
produce alarge amount of electricity. The minimum speed required for satisfactory
working of a wind generator is 15Km/hr.
Advantage: (i) no pollution (ii) cheap (iii) renewable
FUEL CELL
A fuel cell is a device that converts a fuel and air
directly into electricity, heat and water by means of electrochemical
reactions.
In a fuel cell, the electricity can be generated as long
as the fuel and oxygen are supplied into the cell.
It consists of an electrolyte and two electrodes.
In a fuel cell , a fuel is sent through the anode and the
oxygen is supplied through the cathode. The electrolyte carries the charged particles
from anode and to cathode and vice versa.
A catalyst such as Pt, Pd, Mg or Ni is often used to
initiate and speed up the reactions at the electrodes.
A fuel cell will also have a fuel reformer which can use
hydrogen fuel from any hydrocarbon fuel like natural gas, methanol or even gasoline.
A single fuel cell can generate a tiny number of direct
current but a large number of such fuel cells in the form “stack” can provide the
power output from few watt to mega watts. The cell consists of two porous
carbon electrodes impregnated with a finely
divided platinum or nickel as catalyst with an electrolyte of 25-40% KOH
.
The cell develops an emf of 1.23V.
The efficiency of hydrogen-oxygen fuel cell is 70% .
The operating temperature is 60-70C .
The cell power output is 300 watts to 5 kilowatts
The cell may be represented as C, Pt or Ni / KOH / C, Pt or Ni
WORKING :
At anode,
At cathode,
The net reaction is
HYDROGEN – OXYGEN FUEL CELL
It is an electrochemical cell or many electrochemical
cells connected in series, to be used as a source of direct current to at a
constant voltage.
Batteries are the store houses of electrical energy on
demand.
Batteries are classified as
1. Primary battery – It is the device in which the cell
reaction is non reversible and it cannot be recharged. Ex. Leclanche cell,
alkaline cell, button cell ( silver and mercury cell )_
2. Secondary battery – These cells are rechargeable and
reusable. Its electrode reaction can proceed in either direction. During
charging, electrical work is done on the cell to provide the free energy needed
to force the reaction in the non-spontaneous reaction. Example – Lead acid cell
, Nickel cadmium cell
3. Fuel cell – It is similar to a battery and produce
electricity using chemicals. They do not run down like batteries. Ex.
Hydrogen-oxygen cell, methanol fuel cell.
BATTERIES
Alkaline battery is a more modern version of dry cell. It
is introduced in 1949.
It consists of KOH electrolyte and Zn powder act as anode.
The carbon rod and manganese dioxide act as cathode.
The cell may be represented as
At anode 
At cathode 
The overall net reaction is
The alkaline cell gives a voltage of 1 volt to 1.5 volt.
ADVANTAGES :
1. It can deliver higher current without severe voltage
drop.
2. The shelf life of alkaline battery is 5-8 times more than
leclanche cell.
3. Zn does not dissolve in alkaline medium readily.
USES : It is used in shavers, radios, tape recorders and
electronic photographic flash units.
ALKALINE BATTERIES
SECONDARY BATTERIES
LEAD ACID STORAGE BATTERY OR ACCUMULATOR
It was invented by Gaston Plante in 1859. It acts both as
voltaic cell and electrolytic cell. On supplying electrical energy, this acts
as a voltaic cell . On recharging, the cell acts as an electrolytic cell.
CONSTRUCTION
1. The cell consists of a polypropylene container containing
six lead-acid electrochemical cells connected in series.
2. The voltage of cell is always multiple of 2 V, it can be
increased by dividing each cell with microporous polyethylene dividers.
3. All the cathode and anode plates within a single cell are
linked together, the anode of one cell being linked with the anode of the next
cell and the cathodes are also linked like wise.
4. The anodes are made of lead. Cathodes are made of solid
lead (IV) oxide or Lead dioxide, mounted on a lead base.
5. Both poles of the battery are also made of lead.
6. The electrolyte is 80% solution of sulphuric acid
saturated with Lead sulphate.
7. The cell is represented by
The electrode reactions are
Discharging : During discharge the lead plates (anode) act
as voltaic cell, and the cell reaction are
At anode – At the negative pole (anode) oxidation of lead
takes place 
Then the lead ions combine with sulphate ions to produce
lead sulphate 
Net reaction
At cathode – The electrons released at anode flow to the
cathode, where reduction reaction takes place
Net reaction 
The overall cell reaction during discharging
When current is drawn , lead – acid battery becomes less
efficient . So the battery has to be recharged.
RECHARGING
Charging is done by continuous application of potential from
an outside power source. As long as the current is passed, Pb ions are reduced
to lead metal while, at the lead dioxide electode, lead ions are oxidized . During
charging, reverse reaction takes place
LIMITATIONS
a. These batteries tend to slowly self discharge, so a car
left idle for several weeks might be unable to start.
b. The sulphuric acid becomes viscous when the temperature
is low, this inhibits the flow of ions between the plates and reducing the
current. This makes it very difficult to start a car in cold weather.
USES
a. The lead storage cells are mainly used in motor vehicle.
b. They also find applications in telephone exchanges ,
hospital , power stations, railway stations etc.,
NICKEL CADMIUM BATTERIES
LITHIUM BATTERY
OTHER TYPES OF SECONDARY LITHIUM BATTERIES
THE END
