Energy is the capacity to do work, and its availability determines the progress of any society. Every activity, from cooking and lighting to running industries and vehicles, requires energy. Most of the energy we use today comes from conventional sources such as fossil fuels (coal, petroleum and natural gas), firewood, and hydroelectricity. However, the growing demand for energy, the limited reserves of fossil fuels, and the environmental damage they cause have made it essential to develop alternative and renewable sources of energy.
Energy sources are broadly classified into conventional sources and non-conventional sources. Conventional sources, like coal, petroleum, natural gas, firewood and hydropower, have been in use for a long time. Non-conventional sources, like solar energy, wind energy, tidal energy, geothermal energy and nuclear energy, are newer and are being increasingly exploited. Sources are also classified as renewable (can be replenished, such as solar and wind) and non-renewable (cannot be replenished, such as coal and petroleum).
In this chapter, we will study the characteristics of a good source of energy, the different conventional and non-conventional sources of energy, the advantages and disadvantages of each, and the principles of producing and using energy in an environmentally responsible way.
A good source of energy should have the following characteristics:
A fuel is a source of heat energy. The amount of heat energy produced on complete combustion of a unit mass of fuel is called its calorific value, measured in kilojoules per kilogram (kJ/kg).
Fossil fuels, such as coal, petroleum and natural gas, were formed from the remains of plants and animals that lived millions of years ago. They are non-renewable sources of energy.
The burning of fossil fuels releases carbon dioxide, sulphur dioxide, nitrogen oxides and smoke, which cause air pollution, global warming and acid rain. Moreover, fossil fuels are limited and will get exhausted one day. Therefore, they must be conserved.
Thermal power plants burn fossil fuels to heat water and produce steam, which drives turbines to generate electricity. They cause a lot of air pollution.
In a hydro power plant, the potential energy of water stored at a height is converted into kinetic energy as it falls, which rotates the turbines and generates electricity. Hydropower is a renewable source of energy. However, building large dams has disadvantages: it disturbs the environment, submerges forests and land, and requires relocation of people. Hydroelectric power is generated where rivers exist and dams can be built.
Biomass is the organic matter produced by plants and animals, for example wood, animal dung, crop waste and plant residues. Wood and cow dung are traditional sources of energy used in rural areas. Biogas is produced by the anaerobic decomposition of biomass in a biogas plant. Biogas, which is mainly methane, is an excellent fuel used for cooking and lighting, and the residue is used as manure.
Solar energy is the energy obtained from the sun. The sun's energy can be converted into heat energy (solar cookers, solar water heaters) and into electricity (solar cells).
Advantages of solar energy: renewable, pollution-free and available in abundant amounts in tropical countries. Disadvantages: not available at night and on cloudy days, and solar cells are expensive.
The kinetic energy of moving air (wind) can be used to generate electricity. A windmill has large blades that rotate when wind blows; the rotation drives a generator. A group of windmills placed in a suitable location is called a wind farm. Wind energy is clean and renewable, but windmills can be built only in places where the wind speed is sufficient and steady. Wind farms occupy large areas, and the wind may not blow at all times.
Geothermal energy is the heat energy from inside the earth. In volcanic regions, hot rocks heat the underground water, producing steam. This steam can be used to run turbines and generate electricity. Geothermal energy is used in places like Iceland and in the hot springs of some regions.
Nuclear energy is released during nuclear reactions such as fission and fusion.
Nuclear energy has a very high energy density: a small amount of nuclear fuel produces a huge amount of energy. However, the disposal of radioactive waste and the risk of accidents are serious concerns.
Every source of energy has environmental effects. Burning fossil fuels causes air pollution and global warming. Large dams affect ecosystems and displace people. Nuclear power produces radioactive waste. Therefore, we must:
The choice of an energy source depends on its availability, cost, environmental impact and the ease of use.
| Source | Renewable/Non-renewable | Example | Main Use |
|---|---|---|---|
| Coal | Non-renewable | Coal | Thermal power, industry |
| Petroleum | Non-renewable | Petrol, diesel | Transport |
| Natural gas | Non-renewable | CNG | Clean vehicle fuel |
| Hydropower | Renewable | Hydro dam | Electricity |
| Biomass/biogas | Renewable | Cow dung, crop waste | Cooking, electricity |
| Solar energy | Renewable | Sunlight | Heating, electricity |
| Wind energy | Renewable | Windmills | Electricity |
| Nuclear energy | Non-renewable (in practice) | Uranium | Electricity |
| Geothermal energy | Renewable | Earth's heat | Electricity |
| Source | Advantages | Disadvantages |
|---|---|---|
| Fossil fuels | High calorific value, easy transport | Non-renewable, cause pollution |
| Hydropower | Renewable, cheap electricity | Dam construction affects environment |
| Solar energy | Renewable, pollution-free | Not available at night, costly panels |
| Wind energy | Clean, renewable | Needs steady wind, large area required |
| Nuclear energy | Huge energy from small fuel | Radioactive waste disposal, accidents |
Energy powers every aspect of modern life, and the choice of an energy source is a question of balance between availability, cost and environmental impact. Conventional sources such as fossil fuels have powered our civilisation but are finite and cause pollution and climate change. Renewable and non-conventional sources, including solar, wind, tidal, geothermal and biomass energy, offer cleaner and sustainable alternatives, although each has its own limitations. Nuclear energy provides enormous power from a tiny amount of fuel but raises concerns about radioactive waste and safety. The future of energy lies in a mix of sources, improved efficiency and conscious conservation. This chapter equips you not only for the examination but also for understanding the energy debates and choices that will shape our planet's future.