Energy is essential for working and survival of all the organisms on this planet. In fact, it is the energy which enables organisms to perform their biological functions.
Energy may be defined as the capacity of doing works. Energy cannot be created, neither can it be destroyed. It can only be converted from one form to the other form. This fact is known as the law of conservation of energy.
All the fossil fuels like Coal, Petroleum, Natural Gas etc. and the biomass serve as basic sources of energy for human beings. Fuel is a substance in solid, liquid or gas state that can be burnt to produce energy. Now, there are different types of fuels like Renewable and non- renewable.
Renewable fuel is the fuel which can be renewed in nature automatically. For example, if wood can be renewed by planting trees, it may rightly be called as a renewable fuel. But, petrol; Natural gas and coal that are fossil fuels, cannot be renewed if exhausted completely. Hence, these are called as non- renewable sources of energy.
Further, there are liquid fuels like gasoline, diesel, kerosene, etc. Coal and wood are solid fuels. But what is a fossil fuel?
Any substance in either of the solid, liquid or gaseous state, found buried deep inside the earth, formed over millions of years from the remains of animals or plants and which can be burnt to give off energy- is called as a fossil fuel.
A man needs about 2000 k Cal of energy for his living and this much of energy can be derived by him from the food he eats. Early men needed energy only for their survival processes like cooking, lighting, heating etc., but with the development of civilization and growth of human population the demand and consumption of energy started rising up and the industrial revolution brought in an era of concentrated use of large amounts of energy.
Since, the sources of energy available to man are limited in amount and the demand for energy is unlimited due to growing population and the greed for development, a vast gap is existing between the demand and supply of energy and some type of energy crisis has encircled the whole world, especially the developing world.