Some of the conventional sources of energy have poor efficiency and produce a lot of smoke due to incomplete combustion. For example,
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Wood:
As is well-known, wood is burnt in traditional chelas. It has poor efficiency because only about 8% of the wood is utilized as fuel.
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Besides incomplete burning (combustion), it produces gases like carbon monoxide which are dangerous for health.
Animal dung:
Animal dung mixed filth mud and made in the form of cakes and dried are burnt in many parts of the country for use for domestic purposes.
As dung cakes are burnt inefficiently in the conventional manner, it produces a lot of smoke. Further as animal dung contains useful nutrients for soil, the burning of animal dung causes considerable wastage of useful elements, besides producing air pollution.
Agricultural wastes:
Agricultural wastes like sugarcane (from which juice has been extracted) are burnt for use in industries. This and other animal and plant wastes could more profitably be used in bio-gas plants.