Prof. Vilas shamrao Patil

1. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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1.3 CLASSIFICATION OF ENERGY SOURCES: The
classification of different energy sources is given in tree diagram
shown in Fig. 1.2. Primary energy is also called as raw energy.
It is the directly available form of energy.
Fig. 1.2 : Different energy resources
For example, solar energy is used for drying, cooking, wood,
water at higher level, coal etc. Thus primary energy is that
energy form available in nature which is used as it is without
changing its form. Many times it is necessary to have energy
such as electricity. Then primary energy needs to be transformed
to usable energy form which is called secondary energy. Thus,
secondary energy is the usable energy. Most commonly used
secondary energy is electricity because many applications are
based on it, electricity can be easily transported, distributed,
measured and controlled. Many times, it is not possible to
convert primary (raw) energy directly into secondary (usable)
energy. Some other forms of energy are formed while converting
primary energy into secondary energy. These different energy
forms obtained between primary and secondary sources are

2. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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called intermediate energy sources. Consider following
examples of energy transformations :
Renewable Energy Resources In example 1, when wood is
burnt, we get heat and light which can be used directly. It is
example of primary (raw) energy used directly. In example 2,
petrol is fossible fuel, converted to mechanical energy in
automobiles. Thus raw energy form is petrol and usable energy
is mechanical energy. This conversion involves no intermediate
energy form generated and intermediate energy source is absent.
In example 3, when coal is burnt, it gives heat which is used to
heat water to form steam, which is used by generators to finally
produce electricity. Here, coal is primary energy source, hot
water and steam form intermediate energy sources and electrical
energy (electricity) forms the secondary energy source. The
primary energy is of two types : conventional and non-
conventional. The energy sources which are in use from long
back, particularly before 1975, are called conventional. The
energy sources which are considered for its large scale use after
energy crisis (1973) are called alternative or non-conventional.
However, the demarcation between conventional and non-
conventional energy sources is not rigid. Today's non-
conventional energy sources become conventional after few
decades. The non-conventional sources are likely to have more
and more share of energy market in decades to come. The
conventional sources are further classified into recoverable and

3. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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non-recoverable. Some sources are recoverable, some are
partially recoverable and some are non-recoverable (coal at very
high depth). Non-conventional sources are divided into two
categories —renewable and non-renewable. Renewable sources
are also called as non-traditional energy sources. Renewable
energy sources are those which can be replenished even after
their use. For example, solar energy, wind energy, ocean tides,
ocean waves, biomass, etc. Non-renewable energy sources are
those which do not get replenished after their use. For example,
nuclear fission or nuclear fusion fuels. Non-renewable energy
sources are those which are formed very slowly in nature and
likely to be exhausted in few more decades or centuries. The
secondary energy is classified as commercial and non-
commercial depending upon the production and purpose of that
energy source. For example, electricity is commercial source of
energy, whereas heat in solar cooker is non-commercial source
of energy.
1.4 AGE OF RENEWABLES AND ALTERNATIVES:
In earlier section (1.3) we have seen the classification of energy
resources and the meaning of alternative and renewable energy
sources. Further Table 1.1 shows that most of the energy
demands of the world are fulfilled by conventional energy
sources such as coal, oil, natural gas, etc. These conventional
sources are on the verge of extinction. The situation of energy
available and its cost became worst in 1973 during energy crisis
which compelled the world to switch over from conventional
sources to non-conventional renewable energy sources. This was
the beginning of age of renewables and alternatives. Different
forms of alternative, renewable energy resources are being
searched all over the world. There is significant research and

4. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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technological development in the field of these renewable
energy sources. The percentage of share of these energy sources
has increased in recent years. Some of these energy sources are
as follows :
1.Solar energy : The power plant based on solar energy converts
solar energy to thermal one and then to electrical or solar energy
to electrical energy directly by photovoltaic route. This is
discussed in detail in chapter
2. Wind energy : The power plant involves conversion of wind
energy to electrical energy using wind turbine.
3. Geothermal energy : In this case heat inside the earth is
extracted in the form of dry steam/wet steam/hot brine through
hot deep well (1.5 to 3 km). The steam is used for turbine which
gives electrical energy.
4. Ocean thermal energy : Here, heat in upper layer of ocean
water is used for driving steam turbine/gas turbine on shore in
floating plant and cold water from bottom is used as condenser.
5. Ocean wave energy : High ocean waves (2 to 4 m) drive
hydroturbine in cyclic manner to generate electricity.
6. Ocean tide energy : During high tide water is stored in high
reservoir and is released during low tide which drives turbine to
produce electricity.
7. Waste incineration : In this case, combustible waste (paper,
rags, wood, residence-waste etc.) is burnt to obtain steam which
drives the steam turbine.
8. Bio fuels : Wood, rice and wheat husk, biogas and other
biomass is burnt and the generated heat is used for steam-turbine
generator.
9. Fuel-cell : Chemicals can be used as fuels to produce
electricity upto few kW to MW.

5. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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10. Nuclear energy : There are two ways of using nuclear
energy -nuclear fission and nuclear fusion. In nuclear fission,
heavy nuclei of radioactive atoms such as uranium and
plutonium fissile material are bombarded with slow neutrons to
form (fragments) two lighter nuclei with enormous amount of
release of heat energy and 2 to 3 neutrons. Some fertile materials
can be converted into fissile materials and then used for fission.
When the fission is controlled, then it is effectively used for
energy production. This is done in nuclear reactor. Further, fast
breeder reactors are more suitable.
In nuclear fusion, two lighter nuclei (hydrogen) combine at very
high temperature to form heavy nucleus (helium) which gives
very high amount of energy released. Compared to nuclear
fission, nuclear fusion gives very large amount of energy
released.
This energy is likely to serve as major energy source in future.
11. Magneto-Hydro Dynamics (MHD) : Here, hot gases are
seeded to form ionised gases which are passed through magnetic
field perpendicular to the current. This is direct conversion of
heat to electricity.
It has been mentioned before that there is an ever growing rate
of demands for secondary usable energy all over the world.the
main source of the energy are conventional (like hydroelectric
power , petrolium oil, natural gas,coal etc.) But natural reserve
of the primary energy resources of these are limited and likely
to be exhausted soon in few decades or centuries to come and
the problem will be grave.
Another difficulty is that the price of the resoursc are hiking
very fast. The world awoke in the respect after 1973 petrolium
price rise.Many of the countries have short supply of the reserves

6. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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of the resources, hence they are compelled to import them at
high price and their economy is threatened.
Therefore all over the world serious attempts are made to
find new alternative sources of energy and more attention is
focussed on obtaining energy from renewable sources (like solar
radiation, tide waves, wind etc.) at low cost. Technologies are
being developed and improved. But renewable energy resources
are as a rule electrical energy routes i.e. the energy from these
resources has to be first transformed into electrical energy, then
it could be transported, distributed and used. Therefore, it is very
costly.
Another difficulty is the low efficiency of conversion into
electrical energy. But most of the renewable energy available is
very cheap. Another alternative is nuclear energy. Though
enormous amount of energy could be derived (as heat) in nuclear
plants, care has to be taken to protect from hazardous gamma
radiations and get away with radioactive ash. Biomass energy
also is a good alternative. It can be used for generation of fuel
gas and electrical energy.
The following table gives a brief account of alternative and
renewable resources in use or likely to be used on large scale in
near future.
Table 1.2 : Alternative and Renewable Power Plants
No. Source Power Plant
1 Solar energy (i)Solar-thermal steam power plant. (ii)
Solar-photovoltaic cell power plant.
2 Wind Wind-turbine generator plant.
3 Geothermal
energy
Geothermal steam power plant.

7. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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4 Ocean thermal
energy
Ocean thermal energy power plant.
5 Ocean wave
(high waves)
Ocean waves driving hydro-turbine
generators.
6 Ocean tide Hydro-turbine generators are operated
by water reservoirs by high and low
tides.
7 Waste
incineration
Combustible waste is burnt and used as
fuel generate steam for electric power
generator.
8 Bio-fuels Wood, husk of rice and wheat is burnt,
bio-gases are burnt to operate steam
operated electric power generators.
9 Fuel cells power Chemical energy is converted into
electrical energy.
10 Nuclear energy Nuclear fission and fusion power
plants.
11 Magneto-hydro
energy
Hot gases and strong magnetic field
used energy in the power plant.
All these resources are used to generate electric power first.
India's plans : New and Renewable Sources of Energy (NRSE)
schemes under the Ministry of Non-conventional Energy, India
has planned to harness energy in the 9th plan (1998-2003) as :
Small hydro -20 MW Solar systems,
Solar system,PV, Thermal -100 MW
Biomass - 250 MW
Wind farms -2000 MW
Agricultural waste -250 MW
1.5 ENERGY DEMANDS:

8. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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Real history of civilization of mankind starts from the
caveman (Before 10 lac years). With civilization, the
population of the world also has grown enormously. It has
grown from a few lac to around 400 crores. Discoveries,
inventions in the field of science have evolved tremendous
development in technologies and it has brought about
industrialisation and needs of man are growing limitlessly with
the availability of luxuries. (A number of luxuries have now
become necessities ). The life style of man has changed and is
changing every day. A common man always requires
secondary (usable) energy in the form of fuels (coal, diesel,
petrol, kerosene, natural gas, chemicals, firewood....), electrical
power, chemicals (for processes, cleaning, washing,
charging....), renewables (solar heat, biogas, wind, ....). He has
to purchase most of it. (only solar heat, wind energy are free
of cost).
Energy is required to grow food i.e. for agriculture. For
agriculture electric power, fuel, chemicals etc. are required.
Energy is required for social purposes (as electric power, fuel),
for municipalities (for supplying water by pipelines and electric
pumps, fuel (diesel, petrol etc.), for industries which transform
primary energy into usable one, for transportation; for military
(defense), research laboratories. Energy consumed in urban area
is much more than in rural area. Increased field of
communication by transport, by roads, air, water, by railways,
cars, aero planes, even rockets (for launching communication
satellites) requires large amount of energy. So is true for growing
industries of iron, steel, plastics, oil processing, clothing, fabrics,
cement, chemicals, food products, building material, medicines,
luxury items. Industries require mainly electric power, fuels and
water.

9. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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Therefore there is ever-growing demand for energy. Some
figures make the things clear. In the age of cave man per head
(capita) energy consumption was about 3 kWh. per day. In the
beginning of the 21st
century it has grown to 410 kWh per day.
The world's primary energy demand per year in 1972 was 270 x
1018J while in 2020 it is expected to grow to 840 x 1018
J. per
year.
[Of course, per capita consumption of energy in developed
countries is much more (about 200 x 109
J) than in developing
countries (about 50 x 109
J). India's share is only 8.5 x 109
J per
head].
Presently energy is being produced from both conventional and
non-conventional sources. Energy sources such as coal and
lignite, oil, natural gas, nuclear, solar, wind, biomass, etc. are
used to produce secondary energy. The energy produced is used
all over the world and so also in India in different sectors and in
different forms.
But the demand of energy is higher than production. For
instance, Table 1.3 gives sector-wise consumption of electricity
in India during 2013-14. The demand for energy is increasing
rapidly due to growing population, industrialization,
transportation, commercialization. The increase in energy
demand after 1950 is shown in Fig. 1.2.

10. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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Fig. 1.2 : Increasing energy demand of primary sources .
From Fig. 1.2 it is seen that there is growing demand of
energy in last few decades. The energy demand of the world has
continued to increase at an annual growth rate of 3 to 4%. This
seems to increase further in future. The reasons for this can be
stated as follows :
1. Increasing per capita consumption with increasing standard of
living. Further, this consumption is higher in developed
countries than in developing and underdeveloped countries.
Also, this consumption is higher in urban areas than in rural
areas.
2. Increasing population — Rapidly increasing population takes
away the increased production of energy.
3. Transportation, commercialization and mechanization are
also responsible for increased energy demand.
This trend of increased demand will continue and production
will decrease. There are estimates about fossil fuels which are as
follows :

11. V.S. Patil/B.SC.III/Physics/2021-22/Notes
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(i) The rate of oil production in the world will reach its peak in
2015, then it will decline gradually. Most of the oil reserves are
likely to be consumed by the end of this century. The oil
provides 30% of world's need for energy. It is the fuel used in
world's transportation system.
(ii) The peak in natural gas production will come in 2025, about
10 years after peak in oil production.
(iii) As oil and natural gas become scarcer after 2025, a greater
burden will fall on coal. It is estimated that production of coal
will touch a maximum in 2050. This shows that in future one has
to switchover from fossil fuels to other non-conventional
renewable energy sources. Also the nuclear energy is one of the
options for energy in future.