Chapter 5: Sources of Energy Notes

What is Energy? 

The capacity to do work or the overall power generated from our natural resources is referred to as energy. Energy comes in a variety of ways and can be transformed from one to another. Energy in usable form is dissipated as a less usable form into the environment.

Conventional Sources of Energy:

The traditional sources of energy are generally termed as conventional sources of energy, which are being used for a very long time. The primary conventional sources of energy are wood & fossil fuels like coal, petroleum, etc.  Also, the fuels derived from coal such as charcoal, coke are also called conventional sources of energy.

Sources of Energy

A source of energy is one that can consistently provide enough usable energy for a long period of time. Energy comes primarily from natural sources such as the sun, oceans, fossil fuels, wind, and so on, and is transformed into electrical energy that we use for our everyday needs and benefits.

A good source of energy should be:

  • It is both safe and easy to use. Nuclear technology, for example, can only be used by highly qualified engineers with the assistance of nuclear power plants. It is not suitable for our domestic use.
  • It is easy to transport Gas, petrol, diesel, LPG, and other fuels, for example, must be transported from the point of origin to the point of consumption.
  • It is simple to store. Huge storage tanks, for example, are needed to store petrol, diesel, LPG, etc.

Classification of Sources of Energy

  1. Renewable Sources of Energy: Renewable energy sources are inexhaustible, meaning they can be replaced and used to produce energy again and again after we use them. In nature, there is an infinite number of these, and they evolve in a relatively short period of time. e.g. Solar Energy, Wind Energy, etc. 
  2. Non-Renewable Source of Energy: Non-renewable energy sources are those that are exhaustible and cannot be replaced once used. These resources have accumulated over millions of years in nature. e.g. Fossil fuels, etc.

Let’s discuss the fossil fuels in detail as:

Fossil Fuels

A natural fuel formed by dead animals plants deep under the earth in the presence of high pressure, and the high temperature gets converted into fossil fuels over a long time. The plants and animals that are died millions of years ago are buried in the earth and get mixed with rocks, sand, mud over a long period of time in the absence of oxygen. Due to the unavailability of oxygen, the effects of high pressure, high temperature, and bacteria convert the buried remains of dead plants and animals into fossil fuels.

Fossil fuels are buried combustible geologic deposits of organic things, such as dead plants and animals, that have been accumulated underneath thousands of feet of sediment. Due to the intense heat and pressure within the earth’s crust, these deposits decomposed over time and were changed to natural gas, coal, and petroleum.

Coal, crude oil, natural gas are obtained from the earth’s crust in the form of fossil fuel. Fossil fuels are used for over a very long time in the home for cooking food. Also, fossil fuels are still being used for generating electricity from thermal power plants. 

Formation of Fossil Fuels

Looking back millions of years, the earth’s landmass was dominated by seas and wetlands. Huge trees and various green plants began to develop in these marshes. Furthermore, the ocean’s surface was coated with algae, which were little plants. After these plants and algae died, they fled to the bottom strata of the seas and wetlands.

With the passage of time, this layer of organic materials was covered by clay, sand, and other minerals. Later, as the weight of this layer of clay and sand rose, the moisture or water in the organic stuff was forced out, and ultimately fossil fuels were produced. This time is known as the Carboniferous epoch and is thought to have occurred roughly 300 million years ago.

Fossil fuels are produced by the compression of dead organic matter buried deep beneath the earth for millions of years. An entire organism or its sections are often buried in sand or mud during its development. Then they decompose and disappear, leaving no trace of their presence. In reality, after an organism’s death, the hardest parts of the organism settle down, are covered by sediments, and are exposed to intense pressure and temperature, or the Earth turns them into fossil fuels, a process known as fossilization

Advantages of Fossil Fuels

  • Fossil fuels have the ability to generate a large amount of electricity from a single source.
  • They are fairly easy to locate.
  • They are inexpensive.
  • Oil and gas can be transported quickly and easily using pipelines.
  • Over time, they’ve become safer.
  • Despite being a limited resource, there is plenty of it.

Disadvantages of Fossil Fuels

  • Fossils are non-renewable energy sources that cannot be restocked once used.
  • The combustion of fossil fuels pollutes the atmosphere.
  • The Earth’s fossil fuel reserves are finite and could be depleted too.

Types of Fossil Fuels

Fossil fuels are basically categorized into three main types of fuels, that are:

  1. Coal is mined and used to power 1/3 of the world’s electricity (the largest consumers are China, India, and the US).
  2. Petroleum oil is drawn up through the earth and refined into various oils that we use for fuel (like gasoline, diesel, kerosene, etc.).
  3. Natural gas primarily methane found near oil resources, which prompted the controversial fracking procedure.

Types of Fossil Fuels


Carbon, hydrogen, nitrogen, oxygen, and Sulphur make up this hard, black material. Anthracite, bituminous, and lignite are the three main forms of coal. The hardest variety of coal, anthracite, has a higher carbon content. The oxygen and hydrogen content in lignite is high, but the carbon content is low. Coal is processed in the industrial sector to produce products such as coke, coal tar, and coal gas.

Coal is a black substance with a rock-like feel. It consists of carbon, nitrogen, oxygen, hydrogen, and sulphur. It is important to understand that there are three varieties of coal: anthracite, lignite, and bituminous.

The formation of Coal is explained as:

  • Coalification is the term for the process of coal creation.
  • Millions of years ago, the lush forest in the low-lying wetland was buried by the ground.
  • Soil continued to accumulate on top of them, compressing them.
  • They encountered extreme temperatures and pressure as they moved deeper and deeper into the cave.
  • As a result, the chemicals were gradually transformed into coal.

Some of the main uses of Coal are:

  1. Initially, coal was used to generate steam in railway engines.
  2. It’s used to prepare food.
  3. Thermal power plants use it to generate energy.
  4. It is utilized as a fuel in industries.


Petroleum is an oily, transparent liquid that’s frequently green or black in colour. It smells weird and is made up of petroleum gas, diesel, paraffin wax, petrol, lubricating oil, and other substances. Because of its extensive range of applications in a variety of industries, it is also known as Black Gold.

Petroleum is a naturally occurring liquid found in rock formations. This is a complicated combination of hydrocarbons with varying molecular weights, as well as other organic molecules. Some chemical compounds derived from petroleum are also derived from other fossil fuels.

The formation of Petroleum is explained as:

  • Sea animals and plants died, and their bodies sank to the ocean’s depths.
  • The layers of sand and clay squeezed them.
  • When they come into contact with high temperatures and pressure, they turn into petroleum.
  • In a refinery, a series of operations remove the petroleum from the crude oil. Petroleum refining is the term for this process.

Some of the main uses of Petroleum are: 

  1. In the form of gasoline, it is utilised to power internal combustion engines.
  2. It’s utilised in roofing, road pavements, and as a water repellent, among other things.
  3. It’s used to make detergents, plastics, fibers, and polythene, among other things.

Natural gas

Natural gas is a non-toxic and non-polluting fossil fuel. It’s odorless and colorless, and it’s easy to transport through pipelines. It is compressed and stored under high pressure as compressed natural gas (CNG). It is a fossil fuel that is both less polluting and less expensive. The most important natural gas is methane.

Natural gas is found deep beneath the earth’s crust, either alone or in conjunction with oil above the petroleum reserves. Natural gas is created underneath the soil by the decomposition of organic matter that has been submerged in water. In the absence of oxygen, this breakdown is carried out by anaerobic bacteria.

The formation of natural gas is explained as:

  • Sink in the ocean’s bottom combine with organic debris to generate mud that is rich in organic matter.
  • The mud purifies when it is buried behind further strata, forming an organic shale. This keeps it from being exposed to oxygen. This is done to prevent microorganisms from decomposing the organic materials.
  • As the pressure and temperature rise, the shale transforms into a waxy substance called kerosene.
  • Kerosene is converted to natural gas at temperatures of 90-160 °C.

Some of the main uses of Natural gas are:  

  1. Compressed Natural Gas (CNG) is utilised to generate electricity.
  2. It is used in autos as fuel.
  3. It can be utilised in the kitchen at home.
  4. Chemicals and fertilizers use it as a starting material.

Sample Problems

Problem 1: What are the disadvantages of burning fossil fuels?


The disadvantages of burning fossil fuels are:

  • The combustion of fossil fuels often produces byproducts, which pollute the air.
  • Coal and petroleum combustion emit toxic carbon, nitrogen, and sulfur dioxides, which pollute the environment and contribute to acid rain and the greenhouse effect.
  • The biggest contributor to global warming is gases released by the burning of fossil fuels.

Problem 2: Compare fossil fuels and the sun as direct sources of energy.


Fossil fuels are derived from the remains of dead plants and animals in the earth’s crust. They are similar to coal and petroleum in that they are readily accessible. There are non-renewable energy sources that cannot be replaced.

Solar energy or the sun as direct sources of energy, on the other hand, is plentiful in nature and can be replenished.

Problem 3: What is fossilization?


Fossil fuels are produced by the compression of dead organic matter buried deep beneath the earth for millions of years. An entire organism or its sections are often buried in sand or mud during its development. Then they decompose and disappear, leaving no trace of their presence. 

In reality, after an organism’s death, the hardest parts of the organism settle down, are covered by sediments, and are exposed to intense pressure and temperature, or the Earth turns them into fossil fuels, a process known as fossilization.

Problem 4: Why Fossil Fuels are non-renewable?


While natural processes create fossil fuels on a continuous basis, they are classified as non-renewable resources because they take millions of years to form and known viable reserves are exhausted much faster than new ones are created.

Problem 5: Discuss what is LPG?


Liquefied petroleum gas (LPG) is made up mostly of propane, butane, propylene, butylene, and isobutane. LPG is a highly combustible combination of various hydrocarbon gases that is frequently used as a fuel in domestic cooking. It’s also utilised as a fuel in some cars. Propane and butane are the primary active components of LPG.


Coal is a blackish or brownish-black sedimentary rock that develops from coal seams, which are a type of start rock. This is thought to have formed from the algae plants’ waste. Coal is mostly composed of carbon, with trace amounts of other organic elements such as hydrogen, sulfur, oxygen, and nitrogen. When dead and rotted plant and animal debris is exposed to the heat and pressure of deep burial for millions of years, it transforms into peat and then coal. Because wetlands are where coal is mined, the region is also known as coal woods. The majority of today’s coal has been discovered to be significantly younger than the times described.


As a fuel, coal rock is always preferable. Despite being utilized for thousands of years, coal was only used in modest quantities until the industrial revolution. Since the invention of the steam engine, the consumption of coal has grown rapidly. Some industrial operations, such as iron and steel manufacture, require the usage of coal. Coal production and use cause irreversible mortality and sickness. Because coal is a human source of carbon dioxide, which contributes significantly to climate change, its expanding use has serious environmental consequences. Coal combustion will emit around 14.5 billion tonnes of CO2 globally in 2020.

Formation of Coal

Coalification is a long-term process that converts dead materials such as plants and flowers into coal. During geological eras, the Earth was once covered in lush woodlands, particularly in wetland areas. In these areas, acidic water and dirt now prevent the decomposition and oxidation of dead plants. Peat is formed as a result of this process. The coalification process began when bogs accumulating peats held significant amounts of carbon, which was later completely buried by sediments.

Now, millions of years of pressure and heat have caused water, carbon dioxide, and methane to escape, leaving the matter with carbon content. The amount of heat and pressure used to turn dead stuff into coal determines the coal’s gradation. Sub-bituminous, bituminous, and anthracite coals are generated under high temperature and pressure, whilst Lignite is formed under relatively mild conditions. 

Properties of Coal

Physical Properties

  • The relative density for the specific gravity of coal is determined by the degree of mineral impurity and the coal’s rank. It is critical to have a conceptual understanding of the density of each coal in order to determine the qualities of the composites and blend. The density of the coal seam is required for the conversion of resources into reserves. The relative density is determined by the sample’s weight loss in water.
  • The particle size distribution of the coal is determined by its rank, which in turn defines its brittleness, as well as the handling, crushing, and milling it has undergone. Because a specific size of coal is required for the furnace and the coke oven, its crush ability must be evaluated and its behavior quantified.

Chemical Properties

  • Because all coals are mined in humid environments, the moisture content is critical. Adventitious moisture is defined as groundwater and other extraneous moisture that evaporates quickly. The moisture contained within the coals is referred to as intrinsic moisture, and it may be quantified.
  • The volatile matter in coal is the component of the coal other than moisture that is freed at high temperatures in the absence of air. It’s commonly made up of a mix of long and short-chain hydrocarbons, as well as aromatic hydrocarbons and sulfur.
  • Ash is the non-combustible residue that remains after coal has been burned. The bulk substance that remains after the carbon, oxygen, sulfur, and water have been pushed off during conversion is represented by ash. The calculation of the ash percentage is straightforward. When the coal is thoroughly bonded, it is assessed and expressed as a percentage of the original weight. It also gives a good understanding of what coal is like.
  • Fixed carbon can be defined as the carbon that remains after all volatile materials have been removed. Because some carbon is lost in hydrocarbons with the volatiles, this differs from coal’s ultimate carbon concentration.

Types of Coal

Anthracite, bituminous, sub-bituminous, and lignite coal are the four basic forms of coal. The amount and kind of carbon in the coal, as well as its ability to generate heat when burned, are used to rank it.

  1. Anthracite: Because it contains around 86–97 percent carbon, it has the highest heating value of all the other coal kinds. Anthracite coal mines are extensively employed in the metal industry.
  2. Bituminous: Bituminous coal has a carbon concentration of 45–86 percent. It is the most common form of coal found in the United States. Bituminous coal is utilized to create power since it is an important fuel and raw material for generating coking coal.
  3. Sub-Bituminous: Sub-bituminous coal contains 35–45 percent carbon and has a lower heating value than bituminous coal.
  4. Lignite: Lignite coal contains roughly 25–35 percent carbon and has the lowest energy content of any known coal variety. Because of its high moisture content, lignite has a low heating value.

Uses of Coal

  • It is used for electricity and power generation in numerous nations due to its low cost.
  • Typically, powdered coal is used to generate steam, which then provides high-pressure electricity.
  • Coal is also utilized as a raw material in the production of steel and iron, both of which we use every day.
  • Coal is readily available in nations such as India and China, and many households, particularly in rural regions, utilize it for activities such as cooking.
  • Thermal power generation, which aids in the generation of energy, is a common usage of coal. Powdered coal is burned at a high temperature, which converts water to steam. This steam is utilized to turn turbines at high speeds under a strong magnetic field. Electricity is generated only after that.
  • Steel is made indirectly from coal in the steel industry. In this process, coal is cooked in furnaces to make coal coke. Manufacturers use coal coke to smelt iron ore into iron, which is then used to create steel. Meanwhile, ammonia gas from coke ovens is recovered and used to generate nitric acid, ammonia salts, and fertilizers.


Black Gold is another name for petroleum. The mother of all goods,’ as it is also known. This is primarily owing to the fact that crude oil is used to make gasoline, plastics, pharmaceuticals, synthetic fabrics, and a variety of other items. Petroleum is commonly found as a liquid that forms naturally during the creation of rocks. It is composed of a complicated mixture of hydrocarbon molecules and other chemical compounds. Some chemical compounds derived from petroleum are also derived from fossil fuels.

When petroleum is extracted directly from the ground, it is referred to as crude oil. Despite the fact that humans have been on the planet for over 4000 years, crude oil was first extracted from the ground in China roughly 2500 years ago. Also, after coal, petroleum or mineral oil is the most abundant energy source in India. Petroleum is utilized in the manufacturing industry to provide heat, lighting power, machine lubricants, and raw materials for a variety of other products.

Petroleum Refining


Petroleum refineries are massive industrial complexes that require a large number of processing units as well as auxiliary structures such as storage tanks and utility units. Petroleum refineries have their own unique set of structures and processes that are required for refining. The location of the refinery, economic circumstances, and the goal products all have a significant impact on this process.

An oil refinery, also known as a petroleum refinery, is a type of industrial manufacturing plant. This is the location where crude oil is extracted and refined into higher-value goods like gasoline, jet fuel, petroleum naphtha, heating oil, asphalt foundation, liquefied gas, and petroleum kerosene.

Formation of Petroleum

Petroleum is made up of the remains of animals and plants that have died. This occurs when a plant or animal dies and sinks to the ocean floor. After that, it takes millions of years for the organic matter, which is combined with silt and salt, to disintegrate. Different microorganisms also contribute to the breakdown of organic substances. It causes a number of significant chemical changes. Hydrogen and bigger carbon atoms are typically left behind throughout the refining process.

Furthermore, when it arrives at the ocean’s depths, the stuff is not sufficiently degraded. This is caused by a shortage of oxygen. It is covered by numerous layers of slip and sand and stays on the seafloor. Millions of years of tremendous pressure and temperature are required for the complete refining process.

Uses of Petroleum

  • LPG, or liquefied petroleum gas, is utilized in the home and in the workplace every day.
  • Vehicle fuels include gasoline and diesel. When it comes to big trucks, diesel is the favored fuel.
  • In the dry cleaning process, gasoline is used as a solvent. Diesel, on the other hand, can be used as a power generator.
  • Kerosene is used to power jet jets and stoves.
  • Lubricants help reduce machine wear and tear as well as corrosion.

Product of Petroleum

Some products obtain from the refining of petroleum:

  1. Diesel Oil
  2. Gasoline
  3. Kerosene
  4. Tar
  5. Lubricants
  6. Paraffin Wax

FAQs on Coal and Petroleum

Question 1: Can coal be reused or recycled?


Once burned, coal cannot be reused or recycled. When coal is burned, coal ash is created. This coal ash contains a variety of minerals that can be used, including calcium and aluminium. Each year, around 40% of the coal ash produced is efficiently reused to fill abandoned coal mines. Coal ash is occasionally used as a top layer on highways and high-rise construction foundations. Recycling coal ash also helps to reduce greenhouse gas emissions by putting carbon to use.

Question 2: Is coal a natural resource?


Yes, coal is a natural resource since it is made up of dead and rotting vegetation and plants that have been buried for millions of years at high temperatures and pressures.

Question 3: Describe the Process of Petroleum Refinement.


The refining of oil is a highly mechanized process. Throughout this process, crude oil is removed from the soil and converted into a range of valuable goods. Among the products are cooking oil, heating oil, jet fuel, diesel, kerosene, and asphalt foundation. This is the method by which petroleum is produced.

Question 4: What does a petroleum refinery do?


Petroleum refineries turn crude oil into petroleum products for use as transportation fuel, cooking fuel, road paving fuel, and electricity-generating fuel, as well as chemical feedstocks. The refining process separates crude oil into its constituent parts, which are subsequently reassembled into new products.

Question 5: Where is petroleum found?


Petroleum is now found in large subsurface reservoirs where ancient seas once existed. Petroleum deposits can be found both on land and underwater. They use massive drilling machinery to obtain crude oil.

Biogas Plant

The biogas plant is a dome-shaped building. Organic material, such as waste food waste, lipids, sludge, cow dung, and so on, is combined with water and fed into the digester via the entrance depicted in the image. The digester is a sealed room where organic matter is decomposed anaerobically.

After a few days, the organic matter decomposes entirely, releasing gases such as methane, carbon dioxide, hydrogen, and hydrogen sulfide. These gases are then pulled through pipes from the storage tank above the digester and sent to surrounding centers for usage via decentralization pathways.

Construction of a Biogas Plant:

The biogas plant is a brick and cement structure having the following parts:

  • Digester: The digester is a closed chamber that has no oxygen and hence inside the chamber the digester anaerobic oxidation takes place.
  • Gas Tank: After anaerobic oxidation in the digester the gases are released into the gas tank.
  • Mixing Tank: Cow dung and farm waste are mixed by adding some water to the mixing tank.

Working of a Biogas Plant:

To extract biogases and manure from the biogas plant following steps takes place as discussed below using multiple figures:

Step 1: 

To make a biogas plant firstly, a hole is drilled into the soil and such a type of arrangement will be formed. 

Step 2: 

Now some part of cow dung and farm waste is taken and three parts of water mixed to this part. They are mixed very well in the mixing tank and the slurry of the mixture fed into the mouth of the digester.

Step 3: 

When the mixture of cow dung and water is known as slurry moves into the digester, the microorganisms get an environment of non-oxygen so they start decomposing the organic matter into simpler substances.

Step 4: 

The decomposition process takes some days of time. After decomposition gases like methane, carbon dioxide, hydrogen, and hydrogen sulfide on a whole called Bio-gas are sent to the gas tank.

Step 5: 

Biogas is highly rich in methane constituting around 75 % of biogas. As this process continues after some days the slurry which gets left out after the decomposition is very rich in nitrogen and phosphorous.

Step 6: 

This slurry is taken out then it is supplied to the farm as “manure”.

It can that by setting up a biogas plant and feeding the cow dung and farm-based to this plant we are getting a very good source of fuel i.ebiogas. Additionally, we also get the source of manure which is very rich in nitrogen and phosphorous.

Advantages of Biogas

  • Since India has a very high rural population, the fuel will be easily available.
  • This fuel burns without the smoke.
  • The slurry residue is used as manure on the farm.
  • It is Environment friendly.
  • Excellent fuel quality with reasonable heating efficiency.
  • Many countries like India subsidized the biogas plants too.

Disadvantages of Biogas

  • The fuel has less heating capacity compares to other resources.
  • As biogas consists of carbon dioxide, methane, hydrogen, and hydrogen sulfide, it can corrode the parts of the biogas plant.
  • it can’t be constructed easily because cow dung is mostly available in villages only.

Sample Problems

Problem 1: Why charcoal is better than fuel and wood?


There are several reasons where we can say charcoal is better than charcoal. They are:

  • Charcoal has a very high calorific value than wood i.e the amount of heat produced by charcoal is much higher than wood.
  • Charcoal doesn’t produce smoke, whereas wood and fuel produce smoke and cause pollution.
  • Charcoal is much convenient to use than wood.

Problem 2: List two advantages and two disadvantages of using cow dung?



  • Cow dung gives clean fuel which is called Biogas.
  • Used dung can be used as manure for the farms.


  • Cow dung produces a lot of smokes which can lead to pollution.
  • Cow dung contains important elements like nitrogen and phosphorous, which is getting wasted after burning them.

Problem 3: What are the ways to make biofuels?


Ethanol and Biodiesel are two types of biofuels. By fermentation process ethanol is produced on Biomass and used in producing biological crops. Whereas Biodiesel is used in combination with gasoline for machines.

Problem 4: What are the inputs and outputs of the Biogas Plant?


A biogas plant is used mainly to produce biogas which is a very pure form of gas. Now let’s look into the inputs and outputs of the biogas plant:

Inputs: Cow dung and farm waste.

Outputs: Biogas and manure.

Problem 5: List some uses of Biogas?


The uses of Biogas are listed below:

  • Biogas is comparatively very cheaper than other common fuels.
  • There is no storage problem of gas because it is directly supplied from the plant through pipelines.
  • In biogas, even the residue is very useful because it used as manure in farms
  • It is used for lighting and for generating electricity.
  • At last, biogas burns without smoke. Hence, it doesn’t cause any air pollution.   

Problem 6: What are all the elements present in the produced biogas?


After the process of anaerobic oxidation, the biogas is produced and taken through pipes. The biogas majorly consists of methane element constituting 75% and thereafter carbon dioxide, hydrogen and hydrogen sulphide with minimal contributions.  

Non-Conventional Sources of Energy

The Sun is the ultimate source of energy on our planet and all other examples that are mentioned above are obtained either directly or indirectly from the sun. For example, the wind energy that we obtain from the winds and the winds are produced by the unequal heating of two different regions of the surface of the earth. Thus, we can use these sources of energy till our earth receives light from the sun, which is there for the next millions of years. This is also the reason why non-conventional sources of energy are also called renewable sources of energy as every day these energies are getting renewed in nature.

Non-conventional sources of energy, often known as renewable sources of energy, are energy sources that are continually renewed by natural processes. Non-conventional energy sources are not quickly depleted and may be created at a consistent pace for repeated usage.

Tidal, Wind, Solar, Nuclear, Biomass, and other natural resources geothermal energy, are referred to as “non-conventional resources.” Because they are pollution-free, we can use them to generate clean energy with minimal waste.

Furthermore, these energy sources are less expensive and do not contaminate the environment or natural surroundings. They are also known as renewable energy sources since they may be created or created through natural processes at a rate greater than or equal to the rate at which they are used.

Lets discuss each example of non-conventional sources of energy with their examples, advantages, disadvantages as:

Tidal Energy

Before knowing what is tidal energy, let’s first understand what are tides? Tides is the periodic movement of the ocean waters due to the gravitational force of the moon and the sun. Tides are of two types – high tides i.e the rise of water and low tides i.e the fall in the level of water. Since it is caused due to the sun and the moon’s gravitational effect, tidal energy is called renewable energy.

Tidal energy is the energy possessed by the rise and fall of water during high and low tides. The tidal energy can be processed to electricity by building dams across the narrow openings of the sea.

The tidal energy from tides are obtained and used to generate electricity using a machine called Tidal Energy Generator. Tidal barrages or dams are built over a limited sea entrance. When the sea level rises, water pours into the dam. This causes the turbine blades, which are connected at the dam’s entrance, to shift. As a consequence, power is generated.

Tidal Energy obtained by Tidal energy generator

Advantages of Tidal Energy

Some advantages of tidal energy are:

  1. Tidal energy is a renewable energy source, which implies that it does not deteriorate as it is consumed.
  2. Tidal power plants, in addition to being a sustainable energy source, do not release greenhouse gases during electricity generation.
  3. The tidal currents are quite predictable. Low and high tides follow predictable patterns, making it easy to predict when electricity will be generated throughout the day.
  4. Tidal power plants are capable of producing large amounts of electricity. One of the key reasons for this is because water is extremely dense – over 800 times denser than air.
  5. Also, the system established to obtain tidal energy has low operational and maintenance costs.

Disadvantages of Tidal Energy

Some disadvantages of tidal energy are:

  1. The possible installation location must fulfill extremely precise conditions in order for a tidal power plant to be developed. Because they must be positioned on a coastline, possible station locations are limited to coastal states.
  2. Because of the high density of water, tidal energy turbines must be substantially more robust than wind turbines. The cost of building a tidal power producing facility varies based on the technology used.
  3. The fact that tidal energy is renewable does not imply that it is fully ecologically benign. The development of tidal energy power plants can have a significant influence on the surrounding ecology.
  4. While tidal power generates predictable power, it does not produce steady power. We can predict when the tidal power plant will create electricity, but that output may not match the demand for energy.

Wind Energy  

The energy obtained from the wind is called wind energy. The wind contains kinetic energy which can used to harness energy by converting it to mechanical energy by the use of windmill. Although, wind energy has been used by us for a long time, it was used in propelling the sails of the ship in the ancient times.

Advantages :

i. Like solar energy , it is also a renewable form of energy.

ii. It does not cause any air pollution and global warming by releasing harmful gases.

iii. It is space efficient and requires very little space on the land surface and the land between two windmills can be used for agriculture and other different purposes.


i. It is very location specific as wind mills cannot be setup in all places. It can only be installed at places where there is strong winds

ii. It is very costly to setup and difficult for repair.

iii. Storms and cyclones cause great damage to windmills.

Now having understood the advantages and disadvantages of wind energy, let’s understand the working of a wind mill and how it produces energy.

A windmill is tall tower like structure having blades (mostly three). Under the influence of winds , these blades rotate and these rotate the coil connected to the blades. This coil is placed between North and south pole of the magnet which acts as electric generator and produces electricity.

Solar Energy

The sun is the biggest source of energy that we have, it’s radiating very high energy constantly for very long time and will continue to do so. The energy we obtain from the sun is called solar energy.  

Solar energy can be harnessed using several devices like solar cooker and solar panel.

Solar Cooker

We all know that a black surface absorbs most of the energy that fall on it and reflects back very less amount of it. This principle used by solar cooker and solar water heaters. In addition to it, some solar cooker use heater to focus the sun rays at a particular point for more heating. Also the cookers are covered with a glass plate, can you guess why? It’s because of the green-house effect as the glass plates traps the sun’s heat inside the cooker.

Disadvantage of solar cooker: The solar cooker can only function when there is sun’ heat , it cannot store the solar energy for reuse.

Solar Panel

The disadvantage of solar cooker is overcome by the use of solar panel. A solar panel is a collection of solar cells. A single cell can produce a voltage of about 0.5-0.9 V and can produce a energy of 1.5 W.  


i. They need no maintenance and last for about  25 years.

ii. They can store solar energy in the form of electricity and can be reused in several ways.

iii. They are very important source of energy for space missions as all the orbiters , satellites use solar energy.


i. The solar cells are made up of silicon. Though , it is available in abundant quantity but high-grade silicon is very expensive, therefore the cost on setting up becomes very expensive.

The solar energy is also crucial for our survival. This is because without solar energy plant cannot do photosynthesis and thus there would be no food left.

Advantages of solar energy:

i. Solar energy is available to us in infinite amount. Since, sun will be there and will continuously emit energy for the next few hundred million years.

ii. Solar energy can protect the nature and reduce global warming. Solar energy is a green form of energy which can be converted to electricity and used in different energy and this process of creating electricity is much cleaner than from burning coal which emits harmful gases into our atmosphere.

iii. Solar devices (like solar panels and solar cookers) though expensive now are one time investment and saves a good amount money in long term.

iv. Proper harnessing of solar energy is also a very crucial aspect of our space exploration as the artificial satellites and other orbiters that we sent on outer space and different planets operate using solar energy.

Wind Energy  

The energy obtained from the wind is called wind energy. The wind contains kinetic energy which can used to harness energy by converting it to mechanical energy by the use of wind mill. Although, wind energy has been used by us for a long time ,  it was used in propelling the sails of the ship in the ancient times.

Advantages :

i. Like solar energy , it is also a renewable form of energy.

ii. It does not cause any air pollution and global warming by releasing harmful gases.

iii. It is space efficient and requires very little space on the land surface and the land between two windmills can be used for agriculture and other different purposes.


i. It is very location specific as wind mills cannot be setup in all places. It can only be installed at places where there is strong winds

ii. It is very costly to setup and difficult for repair.

iii. Storms and cyclones cause great damage to windmills.

Now having understood the advantages and disadvantages of wind energy, let’s understand the working of a wind mill and how it produces energy.

A windmill is tall tower like structure having blades (mostly three). Under the influence of winds , these blades rotate and these rotate the coil connected to the blades. This coil is placed between North and south pole of the magnet which acts as electric generator and produces electricity.


Geo-thermal Energy

Geo-thermal energy is the heat energy possessed by the rocks inside the earth. The places where the rocks inside the hot is very hot are called hotspot.  

Now, the heat of these rocks heats up the underground water and turns it into steam. This steam is extracted by drilling hole into the ground and connecting pipeline to rotate the turbine with the help of the steam and produce electricity for use.  

In India, only one place is Madhya Pradesh has a hotspot . But in US there are a no. of geo-thermal power plants. The Pacific ring of fire is also a suitable spot for geo-thermal energy sites.


i. They are renewable and completely environment friendly.

ii. They are also energy of future and new research to harness geothermal energy more efficiently is going on in different parts of the world.

Biomass Energy

First understand what is Biomass? The waste and the dead remains of living animals , plants  is called  bio-mass. They contain carbon compounds. The chemical energy stored in them is called bio-mass energy. This form of energy being used by humans from the very early age. Humans burn wood and cattle dung for cooking for a very long time and is continuing till this date. But this method is not very beneficial as it releases harmful gases into the atmosphere.

A much more advanced and efficient use of biomass is the production of bio-gas from biomass. The bio-gas is produced by the decomposition of biomass in the absence of oxygen. Bio-gas contains nearly 60% methane and rest is carbon dioxide , hydrogen and hydrogen sulfide.  

Bio-gas is produced in a large dome shaped plant also called bio-gas plant. In India, however, these plants are called Gobar Gas plant because the main item form which the bio-gas is produced here is cow dung( also called gobar in native language).  


i. It is an efficient technology which produces fuels from our wastes.

ii. It reduces our dependencies on fossil fuels as bio-gas produced from biomass plants can be directly used as fuel

iii. It is very cost effective and cheap.

iv. It is carbon neutral. Carbon dioxide is released on burning bio-waste but no carbon is released into the atmosphere on burning bio-fuels like bio-gas etc.


i. It releases methane in the environment which causes greenhouse effect and global warming.

ii. It is not as effective as fossil fuels.

iii. Building of bio-gas plant requires a lot of space.

Nuclear Energy

Nuclear energy is the energy produce when one heavy nucleus splits into two light nuclei or two light nuclei fuses to one heavy nucleus producing enormous amount energy in form of heat and light.  

Nuclear reaction are of two types :

i. Nuclear Fission  

ii. Nuclear Fusion

Nuclear Fission- The process in which one heavy nucleus (e.g uranium , polonium) splits into two light nuclei producing large amount of energy and neutrons along with it.

Nuclear Fusion- The process in which two light nuclei fuses into one heavy nucleus at a very high temperature and pressure, producing large amount of energy.

In both the reaction, the origin of energy is loss in mass, the sum of the products is less than the sum of the products. The loss in mass in converted into energy according to Einstein’s mass-energy equation, E=mc2.

Though, nuclear reactions produces large amount of energy, but they are uncontrolled and can cause explosions.

But we humans, till now can only control the fission reaction. Inside the nuclear reactor, fission reaction occurs under controlled condition which produces heat which is used to produce steam to rotate the turbine to produce electricity.

Nuclear Fission Reaction

We have seen the definition of nuclear fission which says that in fission reaction, one heavy nucleus splits into two light nuclei and produces high amount energy and neutrons along with it. These neutrons goes and hit the other atoms of Uranium (or plutonium) and thus the chain reaction continues and each of this reaction emits a huge amount of energy in form of heat and light. This is the reason why nuclear reactions are uncontrollable. Now , let’s understand how electricity is being produced by the nuclear power plant.

Advantages of nuclear energy:

i. Nuclear energy is a green source of energy which does not produces any harmful gases .

ii. The amount of energy obtained from a single nuclear reaction is very high.


i. Nuclear reactions are very hard to control, as they are chain reactions and even a slight mistake can cause huge risks.

ii. The elements used in the reaction are radioactive and the radiation can cause severe health issues like cancer and other genetical deformation.

iii. Unfortunately, this is also used in nuclear weapons. An atomic bomb is based on nuclear fission reaction where the reaction is uncontrollable. It was used two times in World War2 and cause the deaths of millions of people.

To date, we cannot control fusion reactions.  

Nuclear fusion occurs inside the sun where two hydrogen atoms are combined to form one helium atom which in process produces huge amount of energy.

Sample Problems 

Problem 1: What are the conditions for a source of energy to be good source of energy?


A source of energy is considered to be good source of energy if,

  • Easily accessible
  • Easy to store and transport
  • Economical

Problem 2: Can any source of energy be completely pollution free? Why and why not?


No, any source of energy cannot be totally pollution free. This is because the process of producing energy may not cause pollution, but the production of devices required may cause pollution. Like solar energy is green but the making of solar cells cause pollution. Likewise, nuclear energy may not cause pollution but the e-waste generated after the fission reactions are harmful and cause health hazards. Still, they are much cleaner than non-renewable energy sources like fossil fuels, coal etc.

Problem 3: Name and define the process used for producing electricity using nuclear energy.


The process used for producing electricity from nuclear energy is Nuclear Fission.

Nuclear Fission: Nuclear Fission is the process in which one heavy nucleus splits into two light nuclei of almost equal mass and producing enormous amount of energy in the form of heat and light.

Problem 4: State two advantages and limitations of producing electricity from solar energy.


Advantages of solar energy:

  • It is a green source of energy as it causes no pollution to the environment.
  • It is widely available and will lasts for millions of years, and therefore it is more reliable form of energy rather than fossil fuels and coal.

Disadvantages of solar energy:

  • The cost of solar panel is too high, so all cannot afford it.
  • Installation of solar panels requires a lot of open space which receives good sunlight. Thus, it cannot be set up anywhere.

Problem 5: Why is the wood as a fuel not advisable, although wood is considered to be a renewable source of energy?  


The use of wood as fuel is not advisable because:

  • Forests once lost in the extraction of wood takes about 15-20 years to restore, which is quite a long period of time. Thus, the wood once lost cannot be renewed immediately.
  • The burning of wood releases several greenhouse gases like carbon dioxide and methane which causes greenhouse effect and the smoke causes air pollution.

Problem 6: How all the living beings on our planet are dependent directly or indirectly on our sun for survival?


Sun is called the ultimate source of energy in our planet because plants require sunlight to produce food using photosynthesis. Now, this process has two crucial importance, first, it provides all the animals in this planet including us food, secondly, it releases oxygen which is the life –supporting gas for the survival of all living beings. Sun also heats our planet which is creates a suitable temperature in our planet for living. Sun’s heating is the cause of winds and waves in our planet. Sun’s gravitational pull causes tides which is an important part of our ecosystem and also an important renewable source of energy. Thus, it is very clear that we all depend on sun directly or indirectly for our survival.  

Nuclear Fission  

Otto Hahn and Strassman found that Uranium-235 bombarded by a neutron splits up into two comparatively lighter nuclei. This process is known as nuclear fission. The neutrons used in the fission of the Uranium nucleus have low energy and are known as thermal neutrons. During the fission of uranium, two or three neutrons are also emitted along with the release of a large amount of energy besides the products of the fission.

Thus, the process of splitting a heavy nucleus into two comparatively lighter nuclei along with the release of a large amount of energy when bombarded with a thermal neutron is called nuclear fission

Nuclear fission of 92U235 when bombarded with a slow neutron (known as thermal neutron) is given below: 

92U235 0n→ 56Ba141 36Kr92+ 3 0n1 + Energy 

The energy released per fission of 92U235 (an isotope of uranium) is about 200 MeV. This fission is represented in the figure below: 

Nuclear fission of 92U235.

Note: It may be noted that nuclear energy produced by the fission of 1 kg of uranium – 235 is equal to the energy produced by the burning of 25,00,000.

Pollution from Nuclear fission

Nuclear fission causes more serious pollution problems than fossil fuels. During nuclear fission, nuclear radiation namely alpha particles (u-particles), beta particles (B-particles) and gamma rays (y-rays) are emitted. This radiation is very harmful to living organisms. The long and constant exposure of living organisms to these radiations cause many diseases or disorder in the human body like: 

  1. Nuclear radiation can change or damage the structure of cells in the human body
  2. They cause diseases like cancer, leukemia, and blindness.
  3. They cause genetic disorders in the human body.
  4. They cause sterility in the young generation.

Advantages and Disadvantages of Nuclear fission

The advantages of using nuclear fission energy are:

  • A small quantity of nuclear fuel (U-235) gives a large amount of energy by the process of nuclear fission while to produce a large amount of heat large quantity of fossil fuel is required. e.g. 1 kg of Uranium 235 releases energy equivalent to the energy released by the burning of 25,00,000 kg coal.
  • In a nuclear power plant, the nuclear fuel is inserted once to get energy over a long period of time. On the other hand, in a thermal power plant, fossil fuel is to be supplied constantly to get the energy.

The disadvantages of using nuclear fission energy are:

  • Nuclear fission causes more serious pollution problems than the burning of fossil fuels. During nuclear fission, radiation is emitted which is very harmful. They cause dangerous diseases like cancer, leukemia, and sterility.
  • The biggest problem of using nuclear fission energy is the safe disposal of nuclear waste. Nuclear waste continues to emit harmful nuclear radiation. Their complete elimination of nuclear waste is impossible while fossil fuel waste can be completely eliminated. e.g. if we burn coal it will give rise to ash which can be thrown in the fields.

Nuclear Fusion 

The fusion of nuclei does not take place so easily as it seems to be. In fact, nuclei are positively charged and hence they repel each other when coming closer to each other. These nuclei can be fused together if they move at a very high speed to overcome the force of repulsion between them. This can happen if the temperature is very high (about 10 K). At this temperature, the electron of the hydrogen atom is completely detached and hence we get a bare nucleus (i.e., naked nucleus) and a free electron. 

The collection of bare nuclei moving with very high speed and free electrons is known as plasma. Since the number of bare nuclei (positively charged) is equal to the number of electrons (negatively charged), hence net charge on Plasma is zero. These bare nuclei of hydrogen move with very high speed (because speed is proportional to the temperature) and hence fuse together to form helium nuclei. During the fusion of hydrogen nuclei, a large amount of energy is released. 

Hence, it is so said that the process in which two or more light nuclei fuse together (or combine) to form a heavy nucleus along with the release of energy is called nuclear fusion. According to Hans Bethe in the source of energy of the Sun and other stars is thermo-nuclear or nuclear fusion reactions.

When Tritium (1H3) fuse with deuterium (1H2), the following products are formed: 

1H3 + 1H2 → 2He4 + 0n1 + 17.6 MeV

This fusion is shown in the figure below: 

Nuclear fusion of 1H3.

Advantages and Disadvantages of Nuclear Fusion 

The advantages of using nuclear fusion are:

  • The energy released in nuclear fusion is much more than the energy released in a nuclear fission reaction.
  • In a nuclear fusion, hydrogen nuclei fuse together to form a helium nucleus which is stable. The helium nucleus does not emit any type of harmful radiation. So, we can dispose of it easily. On the other hand, by-products of nuclear fission reaction emit harmful radiation. Hence, the disposal of this product is a big problem.

The disadvantage of using nuclear fusion is that, in the experimental stage to have controlled nuclear fusion to produce electricity. The main problem found is to contain the ingredients of nuclear fusion at an extremely high temperature which is difficult to do.

Atomic Power Plants and Research Centres in India 

  • Bhabha Atomic Research Centre at Trombay near Mumbai, this centre has been established to carry out research work to use nuclear energy for peaceful purposes.
  • Tarapur Atomic Power Station (Maharashtra), was the first atomic power station established in India.
  • Rajasthan Atomic Power Station at Rana Pratap Sagar near Kota.
  • Narora Atomic Power Station at Narora in Uttar Pradesh.
  • Madras Atomic Power Station (now known as Indira Gandhi Centre for Atomic Research) at Kalpakkam in Tamil Nadu.

India gets most of the Uranium from the Jaduguda mines in Bihar. The uranium obtained from these mines is taken to Nuclear Fuel complex situated at Hyderabad for processing. At this complex, after enriching the uranium the fuel elements are formed. These fuel elements are then sent to different Nuclear power plants.

Difference Between Nuclear Fission and Nuclear Fusion

Nuclear FissionNuclear Fusion
1. In nuclear fission, a heavy nucleus splits up into lighter nuclei.1. In a nuclear fusion, light nuclei combine together to form a heavy nucleus.
 2 In nuclear fission, harmful nuclear radiation is emitted.2. In a nuclear fusion, no harmful radiation ae emitted
3. A nuclear fission starts when a slow neutron3. A nuclear fusion starts when light nuclei are heated at an extremely high temperature, bombards the heavy nucleus (like Uranium-235).
4. Nuclear fission is a chain reaction i.e. it multiplies very fast 4. Nuclear fusion is not a chain reaction
5. Nuclear fission reactions can be controlled to produce electricity.5. Nuclear fusion reactions are still uncontrolled and cannot be used to produce electricity. 
6. Nuclear fission reactions produce a large amount of energy  6. Nuclear fusion reactions produce nuclear fission much more energy.
7. Temperature plays no role to start a nuclear fission reaction7. Temperature of the order of 10 K is required to start a nuclear fusion reaction.
8. By-products of nuclear fission are radioactive and emit harmful radiation. 8. By-products of nuclear fusion are not radioactive and hence do not emit harmful radiation.
9. Nuclear fission causes more pollution9. Nuclear fusion causes no pollution.
 10. In nuclear fission, the disposal of nuclear waste is a big problem.10. In a nuclear fusion, no such problem is there.

Sample Problems

Problem 1: Which device is used to control the chain reaction?


Nuclear reactor is a device used to carry out the controlled chain reaction.

Problem 2: The mass number of three elements A, B, and C are 2,180 and 235 respectively. Which one of these is suitable for making a hydrogen bomb?


As it is known that a hydrogen bomb is based on nuclear fusion reaction. 

So element A is suitable for making hydrogen bomb.

Problem 3: What is the amount of energy produced from nuclear power plants in India?


About 3% of total energy is produced from nuclear power plants in India.

Problem 4: If 200 MeV energy is released in the fission of a single nucleus of 92U235, how much fission must occur per second to produce a power of 1 kW?


Given that,

The energy released per fission is 200 MeV or 200 × 1.6 × 10-13 J i.e. 3.2 × 10-11 J.

The energy required per second is 1 kW or 1000 W or 1000 Js-1 i.e. 103 Js-1


The number of fission per second is given as:

⇒ Energy required per second / Energy released per fission =103 Js-1 / 3.2 × 10-11 J

                                                                                            = 3.125 × 1013 s-1

Problem 5: Differentiate between nuclear fission and nuclear fusion in detail.


The detailed differentiation between the two types of nuclear reactions are as follows:

 Nuclear FissionNuclear Fusion
1.In a nuclear fission, a heavy nucleus splits up into lighter nuclei.In a nuclear fusion, light nuclei combine together to form a heavy nucleus.
2. Harmful nuclear radiation are emitted.No harmful radiation ae emitted.
3.A nuclear fission starts with a slow neutron.A nuclear fusion starts when light nuclei are heated at a extremely high temperature, bombards the heavy nucleus (like Uranium-235).
4.Nuclear fission is a chain reaction i.e. it multiplies very fast.Nuclear fusion is not a chain reaction.
5.Nuclear fission reactions can be controlled to produce electricity.Nuclear fusion reactions are still uncontrolled and cannot be used to produce electricity. 
6.Nuclear fission reactions produce a large amount of energy.Nuclear fusion reactions produce than the nuclear fission much more energy.
7.Temperature plays no role to start nuclear fission reaction.Temperature of the order of 10 K is required to start nuclear fusion reaction.
8.By products of nuclear fission are radioactive and emit harmful radiation.By-products of nuclear fusion are not radioactive and hence do not emit harmful radiation.
9.Nuclear fission causes more pollution.Nuclear fusion causes no pollution.
10. In a nuclear fission, the disposal of nuclear waste is a big problem.In a nuclear fusion, no such problem is there.

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