An engine that uses garbage, farm and ranch waste and derivatives of oil, coal and ethanol, is the latest invention of Embrapa, the Brazilian agricultural research agency, to bring low-cost energy to poor rural and isolated communities. The motor operates by balancing waves of heat and cold, which drive the pistons with external combustion, leaving the energy sources outside. “So any energy providing source can be used,” said agronomist Luis Guilherme Wadt, one of the project's researchers.

The engine cannot propel vehicles but it can generate electricity and operate water pumps and ventilation systems. The power depends on the source and the size of the engine, which they hope to have perfected in 2009.

The greatest benefit is environmental. “We use the waste that would otherwise pollute to generate energy and work,” Wadt told Tierramérica.