The makers of the '$100 laptop' are toying with a novel source of power for its low-cost XO laptops: cows.

"We plan to drive a dynamo (taken from an old Fiat) through a system of belts and pulleys using cows/cattle," wrote One Laptop Per Child's Arjun Sarwal, in an email dated 21 October and posted to one of the group's discussion lists.

Sarwal and others are now finalising the design of the cow-powered generator.

The goal is to develop a low-cost energy source that can be used in Indian villages. Working in a village close to Mumbai, Sarwal said the group considered using solar energy but sunlight near Mumbai was not "consistently strong". There was not enough wind or running water nearby to use these as sources of power, and the cost of running a gas-powered motor was too high.

"But the village had an abundance of cattle that were being used in the fields. So we decided to design something around that," Sarwal wrote in a subsequent email.

The dynamo used in the system was taken from a Fiat car commonly used for taxis in Mumbai and therefore both cheap and readily available.

OLPC is close to putting its XO laptop into production, but has been beset by delays and rising costs. Originally intended to cost $100 each, the cost has since risen to nearly $200. And production is also moving slowly.

How OLPC built the $100 laptop

After a trial production run in August, OLPC had hoped to start mass production in late September or early October. That date has now slipped to 12 November, according to a Reuters report that quoted the group's chief technology officer, Mary Lou Jepsen.