Those sources of energy which are being produced continuously in nature and are inexhaustible, are called renewable source of energy. For example, wood is a renewable source of energy because if trees are cut from the forests for obtaining wood, than more trees will grow in the forest in due course of time. So, the loss of wood by cutting trees is made good by nature. The renewable source of energy are: Hydroenergy (Energy from flowing water): Wind energy and Ocean Thermal energy); Geothermal energy; Biomass energy (Energy from bio fuel such as Wood, Biogas and Alcohol), Hydrogen.
The renewable sources of energy are also called non- conventional sources of energy. A yet another name for renewal sources of energy is the alternative sources of energy.
According to the above classification wood (obtained by the cutting of trees) is a renewable source of energy. Now, a newly planted sapling usually takes more than 15 years to grow and mature into a tree. So, replenishment of cut down trees takes a very long time.
Another disadvantage is that the cutti down of trees on a large scale (for obtaining wood) causes depletion of the forests leading to an imbalance in nature. Due to these reasons, using wood as a source of energy is not ba wise decision (even through it is a renewable sources of energy).
Choice of a Fuel
The fuel which we choose for our domestic industrial use should have a high calorific value. The means that the fuel chosen should be such that it gives us more heat per unit mass.
The fuel should burn without giving any smoke or harmful gases. In other words, the combustion products by the burning of fuel should not be poisonous, and they should not pollute the environment.
Carbon dioxide and water vapour are the harmless products produced by the burning of fuels. But some fuels produce poisonous gases like carbon us. The fuel (CO) and sulphur dioxide (SO2), etc., Which should be well above the normal room temperature.
The fuel which we choose should be cheap and easily available. Another point which we have to keep in mind is that the fuel should be easy to handle, safe to transport and convenient to store.
The fuel should have low percentage of non- combustion materials. This means that the residue left behind after the burning of fuel should be as low as possible. For example, coal is a fuel which leaves behind a lot of Ash after burning. The removal and disposal of Ash poses a big problem in factories and power plants where large quantities of coal are burnt everyday.
The fuel should burn smoothly and at a steady rate. This is because if a fuel burns too fast, then most of the heat produced by it well be wasted. And if the fuel burn too slowly, then the heat produced may not serve our purpose.
The fuels should have a low rate of evaporation at room temperature. We will now write down the characteristics an ideal fuel (or good fuel) point- wise.
