Classifying the sources of energy

How Sources of Energy are Classified?

Classification of the Various Sources of Energy

Have you heard of renewable and non-renewable sources of energy? There is a good chance you have. They are the most common way of classifying energy sources. But there are other classifications too.

Classification of the Various Sources of Energy

The various sources of energy can be classified into:

  • Primary and secondary sources of energy
  • Renewable and non-renewable sources of energy
  • Commercial and non-commercial sources of energy
  • Conventional and non-conventional source of energy

Primary and Secondary Sources of Energy

The sun and Wind provides solar and wind energy respectively

Primary sources of energy: These are energy sources that exist naturally and whose energy can be used directly. The energy from primary sources always needs further processing for more utilization.

Examples of primary sources of energy: sun(solar), Wind, hydro(water), fossil fuel, wood, geothermal, nuclear, etc.

The sun produces solar energy naturally (i.e. without any human effort). And this solar energy can be used directly to dry clothes and aid photosynthesis. But we get more from it when it is further processed. Further processing could result in the generation of electricity, heating and more.

The primary sources of energy are the main sources of energy because they beget secondary sources of energy.


Secondary sources of energy: This source is derived from the primary sources of energy through the energy conversion process. They do not occur naturally.

Examples of secondary sources of energy are electrical energy generated from power stations, hydrogen extracted from natural gas, petrol, diesel, and other products derived from crude oil, etc.

Electrical energy is the most common secondary source of energy. It can be generated from water, solar, geothermal, coal, nuclear, wind, and other primary sources of energy.

In a hydropower station, the potential energy of water (water at a height) is used to drive a turbine (creating mechanical energy), and in turn, drive a generator to produce electrical energy.

Also, solar panels are used for converting solar energy into electrical energy. Hydrogen, as a secondary source of energy, can be made from natural gas (a primary source).

So, the primary sources of energy go through conversion processes to produce secondary sources of energy.


Difference between Primary and Secondary Sources of Energy

They occur naturallyIt doesn’t occur naturally
They are the main source of other forms of energyThey are generated from primary sources
Examples: Coal, crude oil, wind, biomass, nuclear, geothermal, ocean waves and tides, etc.Examples: Electrical energy, hydrogen gas, diesel, petrol, heat, biofuel etc.

Renewable and Non-renewable Sources of Energy.


Renewable (Non-depletable) sources of energy: These energy sources are ones that are not limited and can naturally replenish itself constantly within a short time.

Examples of renewable sources of energy are the Sun(solar), wind, biofuels, hydro(water), geothermal, ocean, etc. Read more on renewable energy

Non-renewable(depletable) sources of energy: These energy sources have limited supply and can’t replenish itself in a short time.  They are the ones that will eventually finish and will take millions of years to replenish. Examples are Nuclear (Uranium), Coal, natural gas, Petroleum, and more.

Difference Between Renewable and Non-renewable Sources of Energy.

Renewable Non-renewable
These sources are not limitedThese sources are limited
They can be replenished within a short time.They take too long time time to replenish
They cause less pollutionThey cause far more pollution
These sources are mostly inexhaustibleThey are mostly exhaustible
Examples: Water, sun, wind, biomass, geothermal, etc.Examples: Coal, Nuclear, crude oil, etc.

Commercial and Non-commercial Source of Energy


Commercial source of energy: This source of energy is one that is majorly used for commercial purpose, and are available at a stipulated price. It is not free. Example: Coal, fossil fuel, nuclear, etc.

Non-commercial source of energy: This is one that is used primarily for home consumption, and it is available either for free or almost free. Examples are firewood, cow dung, charcoal and so on.

Difference Between Commercial and Non-commercial Sources of Energy.

These sources are sold in the marketplace for a stipulated price These sources are cheap in price or can be gotten for free
They are less abundant in natureThey are more abundant in nature
They cause less pollutionThey cause more pollution to the environment
Higher pollutant of the environmentLess pollutant of the environment
Examples: Nuclear, coal, crude oil, natural gas, etc.Examples: Wood, charcoal, wastes from animals and plants, etc.

Conventional and Non-conventional Sources of Energy

Conventional source of energy: This is the major energy source that is commonly used and was discovered so many years ago. They are mostly non-renewable sources of energy. Examples are Fossil fuel, firewood, water(hydro), coal and so on.


Non-Conventional source of energy: This energy source is one that was discovered recently and has been in use in just recent years. i.e. newly discovered and not largely utilised. They are mostly classified as Renewable sources of energy. Examples: Sun(solar), biomass, wind, tides, etc.

Difference Between Conventional and Non-conventional Sources of Energy

These sources have been discovered and been in use for a long timeTheir use was discovered a few years ago.
More of a pollutant to the environmentLess of a pollutant to the environment
Most of these sources are non-renewableMost of these sources are renewable
Examples: Coal, Hydro(water), oil and gas, etcExamples: wind, solar, biomass, tides, waves, geothermal, etc.


Sources of energy can be classified as primary or secondary, conventional or non-conventional, commercial or non-commercial, and renewable or non-renewable.

The most common classification of ‘sources of energy’ is renewable and non-renewable.

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Frequently Asked Questions

What is the greatest source of energy?

The greatest source of energy is the sun. It is an indirect source of most of the other sources of energy: wind, biomass, crude oil, etc. It is available in abundance and has varieties of uses.

What is the earth’s main source of energy?

The sun is the earth’s main source of energy. This is because most energies on earth(if not all) are said to come(directly or indirectly) from the sun.

What are the two main sources of earth’s energy?

The sun and geothermal. Geothermal is the thermal energy formed from inside the earth’s crust while the sun provides energy from outside the earth.

What is the oldest source of energy?

The sun(solar energy) is mostly believed to be the oldest source of energy. It is what has been sustaining living things on earth. It has been aiding photosynthesis in plants, used for heating and doing other domestic purposes, and now used for generating electrical energy.

Is electricity a source of energy?

Yes, electricity is a source of energy. It is a secondary source of energy. This is because it is mostly derived from primary sources of energy (e.g hydro, sun, coal, etc)

What is the primary source of all energy?

The primary source of all energy is the sun. Without the sun, most of other sources of energy might not have come to be. Other sources of energy (wind, coal, crude oil, etc) is directly or indirectly a result of the sun

Which energy sources are non-renewable?

Non-renewable energy sources are Coal, Nuclear, crude oil, natural gas, etc.

What are your thoughts?