Biomass: Biomass is defined as living matter or its residues.  Biomass includes all new plant growth,  agricultural and forest residues,  biodegradable organic affluents from industries and carbonaceous wastes.  
BioEnergy: The energy obtained from the biomass is called bioenergy.  
Biogas: It is a mixture of gases produced by anaerobic degradation of biomass in the presence Of water but in absence of oxygen.  
Anaerobic Degradation: Anaerobic microorganisms decompose the biomass which contains carbon compounds through a series of reactions into a mixture of gases called biogas. 
Composition of Biogas: It is mainly composed of 75 % methane, 25 % carbon dioxide and traces of other gases.  
Working of a Biogas Plant: The cow dung and other wastes are mixed with water in equal proportions in the mixing tank to  Prepare the slurry. This slurry enters the digester upto the cylindrical level through inlet chamber. The slurry takes around 50  - 60 days to start function. During this period, the slurry undergoes anaerobic degradation in presence of water, but in absence of air due to the closed dome. Now, the biogas starts collecting in the dome. When more and more biogas is collected, it develops a pressure on the slurry in the dome forcing the spent slurry to move into overflow tank through the outlet chamber. From the overflow tank, the spent slurry is removed and used as manure. This is because the spent slurry is rich in nitrogen and phosphorus compounds. When the slurry began to function, more fresh slurry is added regularly to produce more biogas. This biogas formed is then supplied to village homes through a network of pipes for cooking purpose through the gas outlet. The large scale of using the bio-wastes and sewage materials for producing biogas can provide a safe and efficient method of waste disposal apart from supplying energy and manure.

a) It is eco-friendly.
b) It is found abundantly.
c) It converts visible as well as IR rays into electricity.

a) Use of mirror is to increase the concentration of solar energy.
b) The use of glass sheet is to trap heat radiation.

a) using smokeless devices.
b) Afforestation.

a) Tidal energy
b) Wave energy
c) Ocean thermal energy