Sources of Energy

"There is enough on Earth for everybody's needs, but not enough for everybody's greed." Mahatma Gandhi.

These standardised Class 10 Science notes cover what energy is, how we generate electricity, and the full range of conventional and non-conventional sources of energy, followed by why this topic matters more than ever today. You can find more free notes like these in our resources library.

What is energy?

Energy is the ability to do work, or the total power we draw from natural resources like the Sun, the oceans, fossil fuels and wind.

When energy is used in a usable form, some of it is always dissipated to the surroundings as heat in a less usable form. This means that any source of energy we use to do work is consumed, and that portion cannot be used again in the same way.

Law of conservation of energy

The law of conservation of energy states that energy can neither be created nor destroyed. It can only be converted from one form into another.

What makes a good source of energy?

A good source of energy, or a good fuel, is one that:

1. does a large amount of work per unit volume or mass,
2. is easily accessible,
3. is easy to store and transport, and
4. is economical.

How is electricity generated?

Most power stations generate electricity by spinning a turbine that is connected to a generator, also called a dynamo. The simplest turbines have one moving part: a rotor and blade assembly. A moving fluid such as steam pushes on the blades and makes them spin. This spins the shaft of the dynamo, which converts the movement into electricity.

Sources of energy can be divided into two broad groups: conventional sources of energy and non-conventional sources of energy.

Conventional sources of energy

Conventional sources of energy are those that have been in use for a very long time or are used widely across the world, for example coal and other fossil fuels.

Fossil fuels

• Fossil fuels form when dead organic matter is compressed over millions of years, buried deep under the Earth. Coal and natural gas are examples.
• Fossil fuels are non-renewable sources of energy because they have limited reserves. Finding alternative sources is therefore essential to avoid an energy crisis.

Thermal power plant

• A thermal power plant is a power station that burns fossil fuels such as coal and petroleum to produce electricity.
• These plants use the steam produced by burning fossil fuels, mainly coal, to move the turbines that generate electricity.
• Burning coal heats water and forms steam, which is used to run the turbine.
• Thermal power plants are usually located near coal or oil fields, because it is easier to transmit electricity than to transport coal.

Hydro power plant

• A hydro power plant converts the kinetic energy of flowing water, or the potential energy of water falling from a height, into electricity.
• Hydro power plants are usually built near dams or waterfalls.

Bio-mass

Cow dung, plant materials such as the residue left after harvesting crops, vegetable waste, sewage and animal products are all sources of bio-mass fuel. Because the main starting material is often cow dung, this fuel is popularly known as gobar gas.

Working of a bio-gas plant:

• The plant has a dome-like structure built with bricks. A slurry of cow dung and water is made in a mixing tank, from where it is fed into the digester.
• The digester is a sealed chamber with no oxygen, containing anaerobic micro-organisms that break down the complex compounds in the cow-dung slurry.
• Once decomposition is complete, gases such as methane, carbon dioxide, hydrogen and hydrogen sulphide are produced.
• The bio-gas is stored in the gas tank above the digester, from where it is drawn through pipes for use.

Features:

• Bio-gas is an excellent fuel because it contains up to 75 per cent methane. It burns without smoke and leaves no residue such as the ash left behind by wood, charcoal and coal.
• Its heating capacity is high, and it is also used for lighting.
• The slurry left behind is removed from time to time and used as manure, which is rich in nitrogen and phosphorus.

Wind energy

• Wind is a natural phenomenon caused by pressure differences due to the unequal heating of land and water on the Earth's surface. The kinetic energy of wind is harnessed to do mechanical work.
• For example, a windmill can be used to lift water from a well and also to generate electricity.
• Wind energy is harnessed by rotating structures known as windmills.
• Windmills have huge blades or fans fixed high on a rigid support. This support is attached to turbines that rotate at high wind speeds and generate electricity.

Advantages of wind energy:

• It is an environment-friendly and efficient source of energy.
• There are no recurring expenses for producing the electricity.

Disadvantages of wind energy:

• A wind energy farm can be set up only in places where wind blows for most of the year.
• The wind speed must be greater than 15 km per hour to rotate the turbine.
• Back-up storage facilities are needed for times when there is no wind.
• A large area is required to set up the farm.
• The set-up cost is high.

Non-conventional (alternative) sources of energy

Non-conventional sources of energy are also known as renewable sources of energy. Examples include solar energy, tidal energy, wave energy and geothermal energy.

Solar energy

The light energy and heat energy that reach us from the Sun are together known as solar energy.

Solar cooker, and how it works:

• Black surfaces absorb more energy than other surfaces. Solar cookers and solar water heaters use this property by coating their insides black.
• Reflecting surfaces such as mirrors are used to focus the Sun's rays.
• The device is covered with a glass plate, which traps heat inside the cooker through the greenhouse effect.

Solar cell, and how it works:

• A device that converts solar energy directly into electricity is known as a solar cell.
• A typical solar cell produces a voltage of about 0.5 to 1 V and around 0.7 W of electrical power. A large number of such cells joined together form a solar panel, which can generate enough power for practical use.

Advantages: there are no moving parts, they need very little maintenance, and they can be set up in remote areas without the trouble and cost of transmission lines.

Disadvantages: they require a special grade of silicon that is not easily available, and the use of silver for the interconnections makes them expensive.

Uses: traffic signals, calculators, artificial satellites and space probes.

Energy from the sea

Tidal energy

• Because of the gravitational pull of the Moon on the revolving Earth, the level of water in the sea rises and falls. This is called high and low tides, and the difference in sea levels gives us tidal energy.
• Tidal energy is harnessed by building a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy into electricity.

Wave energy

• Waves are produced by strong winds blowing across the sea. These waves carry huge kinetic energy, which can be trapped by a variety of devices to rotate a turbine and generate electricity.

Ocean thermal energy

• The difference between the surface temperature of ocean water and the temperature of water at a certain depth is used to harness this form of energy.
• The temperature difference must be at least 20 degrees Celsius between the surface and water down to a depth of about 2 km.
• Warm surface water is used to boil a volatile liquid such as ammonia to form vapour that moves the turbine. Cold water from the depths is then used to condense the vapour back into liquid.

Geothermal energy

• Due to geological changes, molten rocks formed in the deeper, hotter regions of the Earth's crust are pushed upward and become trapped in certain regions called hot spots.
• When underground water comes into contact with these hot spots, steam is generated that finds an outlet at the surface, known as a hot spring.
• The steam trapped in the rocks is routed through a pipe to a turbine and used to generate electricity.

Nuclear energy

• In a process called nuclear fission, the nucleus of a heavy atom such as uranium, plutonium or thorium is bombarded with low-energy neutrons and splits apart into lighter nuclei, releasing a tremendous amount of energy.
• This energy can be used to produce steam, which in turn generates electricity.

Difference between nuclear fission and nuclear fusion:

• In fission, a heavy nucleus divides into two fragments along with a few neutrons. In fusion, lighter nuclei join together to produce a heavier nucleus.
• Fission reactions can take place even at room temperature. Fusion reactions take place only at very high temperatures, such as 10 million kelvin.
• Fission needs the bombardment of external neutrons. Fusion does not need external neutrons.
• The energy released per unit mass in fission is less. The energy released per unit mass in fusion is high, nearly seven times that of a fission reaction.
• Neutrons are liberated during fission. Positrons are liberated during fusion.
• A fission reaction can be controlled, for example inside a nuclear reactor. A fusion reaction cannot be controlled.
• The atom bomb works on the principle of fission. The hydrogen bomb works on the principle of fusion.

Some well-known nuclear power plants in India:

• Tarapur nuclear power plant, Maharashtra
• Rana Pratap Sagar power plant, Rajasthan
• Kalpakkam, Tamil Nadu
• Narora, Uttar Pradesh
• Kakrapar, Gujarat
• Kaiga, Karnataka

Conventional and non-conventional sources: a quick comparison

• Conventional sources have been in use since early times. Non-conventional sources have generally been identified in the recent past.
• Conventional sources are exhaustible. Non-conventional sources are inexhaustible.
• Conventional sources cause pollution when used, as they emit smoke and ash. Non-conventional sources are generally pollution free.
• Conventional sources involve huge expenditure to generate and use. Non-conventional sources need lower expenditure.
• Examples of conventional sources are coal, natural gas and firewood. Examples of non-conventional sources are geothermal, solar and wind energy.

Environmental consequences

• Non-renewable resources such as coal and petroleum cause more harm to the environment than renewable resources, in the form of air and water pollution and toxic wastes.
• Even renewable resources are not completely eco-friendly. Generating energy from wind, the Sun and tides also creates some environmental impacts and can affect biodiversity.

The main impacts of different sources are:

• Thermoelectricity: emissions of greenhouse gases, particulate matter and oxides of sulphur.
• Hydroelectricity: flooding of land to build dams, changes to downstream river flow, silting upstream of dams, a barrier to fish migration, growth of algae, and the loss of historical, archaeological and tourism sites, sometimes forcing local people to move.
• Bioelectricity: loss of biodiversity, air pollution, fish deaths, and contamination of groundwater and aquifers.
• Wind energy: noise pollution and the death of birds.
• Solar energy: the build-up of toxic residue in the environment.
• Nuclear energy: the risk of accidents, uncertainty in managing radioactive residue, and the danger of the spread of atomic weapons.

Sources of energy can also be grouped in another way, as renewable sources of energy and non-renewable sources of energy.

Why it still matters

The neat split in your textbook between conventional and non-conventional sources is, right now, one of the biggest stories in India's economy. In June 2025 India reached a landmark: half of its total installed electricity capacity, about 242 GW out of roughly 485 GW, now comes from non-fossil sources such as solar, wind, large hydro and nuclear. India reached this 50 per cent target a full five years ahead of the 2030 goal it had promised the world under the Paris Agreement.

The pace is quickening. In the financial year 2025 to 2026 India added around 55 GW of non-fossil capacity, its highest ever in a single year, pushing the non-fossil total towards 283 GW. The next target is 500 GW of non-fossil capacity by 2030. In plain terms, the wind farms, solar cells, hydro plants and nuclear reactors described in these notes are no longer just diagrams in a chapter. They are being built at record speed to replace the coal-fired thermal plants that still supply most of our electricity today.

This is exactly the shift that geographers and economists call the energy transition, and it raises real questions that scientists and policymakers are debating now: how do we keep the grid reliable when the wind drops or the Sun sets, how do we store surplus power, and who pays for the change. If this interests you, explore it further on the Learnacy Hub, especially the subject page on renewable energy, and see how the diagrams in these notes connect to the choices India is making right now.

Sources

1. Press Information Bureau, Government of India: non-fossil fuel share in total installed power capacity (Ministry of New and Renewable Energy)
2. Enerdata: India added 55.3 GW of non-fossil power capacity in FY 2025 to 2026
3. S&P Global: India hits 50 per cent non-fossil power capacity

Key takeaways

• Energy is the capacity to do work and is derived from natural resources like the Sun, oceans, fossil fuels, and wind.
• The law of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another.
• A good source of energy must perform significant work per unit volume or mass, be easily accessible, storable, transportable, and economical.
• Electricity is generated by spinning a turbine connected to a generator, where a moving fluid like steam pushes the turbine blades.
• Conventional energy sources, such as fossil fuels and hydro power, have been widely used for a long time, while non-conventional sources like wind and bio-mass are increasingly important.

Test yourself

What happens to energy when it is used in a usable form?

When energy is used, some of it is always dissipated as heat in a less usable form, meaning the portion used cannot be reused in the same way.

What defines a good source of energy?

A good source of energy does a large amount of work per unit volume or mass, is easily accessible, easy to store and transport, and economical.

How do thermal power plants generate electricity?

Thermal power plants burn fossil fuels like coal to heat water and produce steam, which spins turbines connected to generators to produce electricity.

What is bio-gas, and how is it produced?

Bio-gas is a fuel produced from the decomposition of cow dung and other organic waste in a sealed digester by anaerobic micro-organisms, yielding gases like methane.

How is wind energy harnessed?

Wind energy is harnessed using windmills with huge blades fixed high on a rigid support to capture the kinetic energy of wind and convert it into mechanical work or electricity.