Rajesh Kumar Singh / AP

An Indian villager collects cow dung cakes, after they are sun dried on the banks of the River Ganges in Allahabad, India. Cow dung cakes are a major source of domestic fuel for rural households and an environmentally-friendly alternative to firewood.

In many parts of the developing world, caked and dried cow dung is used as fuel. Dung may also be collected and used to produce biogas to generate electricity and heat. The gas is rich in methane and is used in rural areas of India/Pakistan and elsewhere to provide a renewable and stable source of electricity.

Ajay Verma / Reuters

A villager makes cow dung cakes used as cooking fuel at Maloya village on the outskirts of the northern Indian city of Chandigarh on January 31, 2011.

Ajay Verma / Reuters

A villager makes cow dung cakes used as cooking fuel at Maloya village on the outskirts of the northern Indian city of Chandigarh on January 31, 2011.