Compare and contrast biomass and hydroelectricity as sources of energy.
(i) Biomass is a renewable source of energy and hydroelectricity is also a renewable source of energy.
(ii) The use of biomass by burning causes air pollution but the use of hydroelectricity does not cause any pollution.
(iii) Biomass energy can be obtained without using any special device but hydroelectricity can be produced only by establishing hydro-power plants.