Source: Ecologically man is only a part of energy flow in nature. Man requires energy for his daily needs. The major energy sources are fuel wood, fossil fuels such as coal, petroleum and natural gas. Apart from these, the other direct energy resources are sunlight, hydroelectric and wind power, tidal, geothermal and nuclear energy.
Energy Requirement: During early stages of human civilization, the daily per capita need for energy was just 2,000-4,000 kilo calories. During the agricultural stage, the muscular energy of domestic animals was used for work. The per capita energy consumption gradually increased. In nineteenth century, during the industrial stage of human civilization, the use of fossil fuel started and the per capita energy requirement increased to 70,000 kilo calories per day.
Today we need energy for agriculture, industry, transport, communication, comfort and defence. The per head energy consumption varies from country to country
Depletion of fossil fuels
Today the world's energy resources have reached critical stage. Most of the world's human population uses fossil fuels (coal, petroleum and natural gas). The fossil fuel resources are being rapidly depleted. As a result these resources may last only another few centuries. The dwindling stocks of fuels has led to the search of alternate sources of energy.
Sources of Energy
Some alternative sources of fuel are solar energy, hydro-electric energy, geo-thermal energy, wind power, tidal energy, energy from garbage, dung energy and nuclear energy. They are generally called renewable/ non- conventional sources of energy.
Sun is an inexhaustible and pollution free source of energy. Solar equipments have been developed to harness sun-rays to heat water, cook meals, light our houses and run certain machines.
It is generated by fusion of the atoms of certain elements such as Uranium - 235. The processes results in the release of enormous amount of energy. Fission of 1 amu (atomic mass unit) of Uranium - 235 can generate energy equivalent to that obtainable from burning of 15 metric tons of coal or about 14 barrels of crude oil. In our country atomic power stations have been set up in Tarapur (Bombay), Narora (Uttar Pradesh), Kota (Rajasthan) and Kalpakkam (Tamil Nadu).
It has been used for centuries to run the wind-mills for grinding grains and pump water in certain areas. But the wind does not blow with required intensity all the year round and in all areas. Therefore, wind power can be used only in certain areas and on certain days.
Cattle dung is widely used as fuel in rural areas of our country. This deprives our fields of valuable organic manure. Now cattle dung is used in Biogas or Gobar Gas Plant to produce an odourless, low pressure gas. This gas can be used for cooking and heating. The residue is used as manure.
The garbage of houses contains waste paper, plastics and several other materials. It can be used to produce electricity.
Tidal waves of the sea can be used to generate electricity.
In some places, the heated water comes to the earth's surface as hot springs. It can be used for heating water and building and for generating electricity.
It is produced from the kinetic energy of water falling from height. A number of power stations have been established on many rivers in our country.