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New generator design promises increased efficiency

by Lindsay Jolivet Dec 20 / 13

A design for a powerful new generator has come closer to untangling an energy riddle that’s puzzled researchers for half a century.

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This is a photo of the hot test generator in action. (Photo: J.Mannhart/MPG.de).

Jochen Mannhart, a physicist at the Max Planck Institute for Solid State Research in Germany and member of the the Quantum Materials Advisory Committee, developed with his team a device they call a thermoelectronic generator, which converts heat energy directly into electricity.

“This work is basic research which shows a possible road to huge energy savings that needs to be explored,” Mannhart says.

Thermionic generators are already used in some situations, such as to power satellites. They create electricity between two metallic plates by heating one to drive electrons to the other, cold plate and generating an electric current.

About 80 per cent of the world’s electricity comes from heat such as the sun, or from burning fossil fuels such as coal, which is typically used to turn water into steam that turns a turbine. The method is inefficient, and researchers have been working for decades to develop generator that uses thermionic conversion to produce electricity directly.

However, past thermionic generators have struggled with a problem caused by electrons pushing back as they travelled from one plate to the other.

Electrons from the hot plate head toward the cold plate, but their negative charge repels the electrons that should follow, sending them evaporating back into the hot plate and killing the current. There are solutions such as adding ions, but they diminish the efficiency.

Mannhart’s design avoids the problem by using an electric field that draws away the troublesome charge cloud, helping the electrons travel freely. He says the researchers dubbed it “thermoelectronic” because it doesn’t need any ions. Mannhart says generators like this one could make coal combustion plants burn more efficiently, reducing the emission of gases such as CO2 by about 10 to 15 per cent.

“This percentage numbers may not seem large, yet because so much coal is burned, the absolute saving in CO2 emission could be enormous,” Mannhart says.

“We also imagine the use of the generators in vehicles or aircraft. They could efficiently convert gasoline into electric power, and are small, lightweight and silent.”

Mannhart says much work remains before we could see these devices propelling cars or lifting airplanes, but the possibilities are promising.

The generator design was published in the Journal of Renewable and Sustainable Energy.