A Max Planck Institute for Solid State Research in Stuttgart, Germany has a group that can claim high efficiency thermionic conversion of heat energy.  The heat source could be light from the sun, heat from burned fossil fuels, nuclear or any of the fuel sources that yield energy with heat.

Because of its thermionic energy’s promise, researchers have been trying for more than half a century to develop a practical generator, with little progress.  The progress might leap forward thanks to a new design called a “thermoelectronic” generator.  The new design has been described in AIP Publishing’s Journal of Renewable and Sustainable Energy.

Thermionic generators use the temperature difference between a hot and a cold metallic plate to create electricity.

Jochen Mannhart, an experimental solid-state physicist and the lead author of the JRSE paper, explains, “Electrons are evaporated or kicked out by light from the hot plate, then driven to the cold plate, where they condense.” The resulting charge difference between the two plates yields a voltage that, in turn, drives an electric current, “without moving mechanical parts,” he said.

Previous models of thermionic generators have proven ineffectual because of what is known as the “space-charge problem,” in which the negative charges of the cloud of electrons leaving the hot plate repel other electrons from leaving it too, effectively killing the current.

Max Planck Team's Thermoelectronic Generator Details.  Click image for more info.

Max Planck Team’s Thermoelectronic Generator Details. Click image for more info.

Mannhart, along with his former students Stefan Meir and Cyril Stephanos, and colleague Theodore Geballe of Stanford University, circumvented this problem using an electric field to pull the charge cloud away from the hot plate, which allowed electrons to fly to the cold plate.

Now for the encouragement, Mannhart explains, “Practical thermionic generators have reached efficiencies of about 10%. The theoretical predictions for our thermoelectronic generators reach about 40%, although this is theory only. We would be much surprised if there was a commercial application in the marketplace within the next five years, but if companies that are hungry for power recognize the potential of the generators, the development might be faster.”

Mannhart might be a little glum with his commercial prediction.  With the developed countries economies in such doldrums and the willingness to invest in new ideas very slow, he could be right.

On the other hand the race to 40% efficiency would be a serious game changer.  Depending on the economics of working units at industrial scale production – 40% is very competitive indeed.  Used as a secondary recovery after a primary use the efficiency gains and fuel savings would be very impressive.

Your humble writer would encourage the Mannhart and Max Planck team to stay the course; the results could be very useful and beneficial across the entire world economy.


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