New highly efficient thermoelectronic generator

December 3, 2013, American Institute of Physics
This is a view into the test generator, looking at the emitter (~ 3 cm diameter). Credit: J.Mannhart

Through a process known as thermionic conversion, heat energy—such as light from the sun or heat from burned fossil fuels—can be converted into electricity with very high efficiency. Because of its promise, researchers have been trying for more than half a century to develop a practical thermionic generator, with little luck. That luck may soon change, thanks to a new design—dubbed a thermoelectronic generator—described in AIP Publishing's Journal of Renewable and Sustainable Energy (JRSE).

Thermionic use the temperature difference between a hot and a cold metallic plate to create electricity. "Electrons are evaporated or kicked out by light from the hot plate, then driven to the cold plate, where they condense," explained experimental solid-state physicist Jochen Mannhart of the Max Planck Institute for Solid State Research in Stuttgart, Germany, the lead author of the JRSE paper. 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. 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 to fly to the cold plate.

This is a photo of the hot test generator in action. Credit: J.Mannhart
"Practical thermionic generators have reached efficiencies of about 10 percent. The theoretical predictions for our thermoelectronic generators reach about 40 percent, although this is theory only," noted Mannhart. "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."

This is a micrograph of the W-grid used as gate in the test generator. The holes have a diameter of ~0.6 mm. Credit: J.Mannhart

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More information: The article, "Highly-Efficient Thermoelectronic Conversion of Solar Energy and Heat into Electric Power" by S. Meir, C. Stephanos, T.H. Geballe, and J. Mannhart appears in the Journal of Renewable and Sustainable Energy:

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3 / 5 (2) Dec 03, 2013
"Practical thermionic generators have reached efficiencies of about 10 percent. The theoretical predictions for our thermoelectronic generators reach about 40 percent

Woha. Talk about improved efficiency. All kinds of uses for this in energy harvesting schemes.
4.7 / 5 (3) Dec 03, 2013
I think there will be immediate interest from the oil/coal power plant sector:
Typical thermal efficiency for utility-scale electrical generators is around 33% for coal and oil-fired plants...

source: http://en.wikiped..._station

It might be possible to get more power out of the waste heat than the initial turbine...

Though, I suppose cost to implement is a factor.
1 / 5 (4) Dec 03, 2013
I highly doubt this will be more efficient than a turbine. If that were to be the case though it would dramatically lower the cost of electric production. These are solid state, way simpler than a turbine.

What is more likely though is having these scrounge up any energy post-turbine, and there is quite a lot of it. This is especially true for nuclear plants. If we could get more electrical energy out of the waste heat, then perhaps many of the cooling problems could be partially alleviated.
2.1 / 5 (7) Dec 03, 2013
This is wonderful technology. So much of the energy we produce is lost with Waste Heat. While it could replace turbines, it would not have to at first, because we could gather heat after the turbines have done their job. Forget big cooling towers, or water cooling your computer, or Radiators in your car, all gone with the introduction of reliable and efficient Thermoelectric devices! You could even produce electricity from hot air in the tropical regions, and combat global warming directly, LOL. You could integrate them directly into solar cells and cool them while also generating electricity from their heat, and increasing their lifespan.

This, as far as Im concerned, is the holy grail of energy research, along with cold fusion, if that ever works out.
2.3 / 5 (9) Dec 03, 2013
The hard part is maintaining a high temperature gradient from the hot side to the cold side, which always requires some form of significant heat sinking, and makes practical applications few and difficult. Thermoelectrics is great, though. Just tough to get that double digit efficiency in a real scenario.
5 / 5 (1) Dec 03, 2013
It has already been used in two Russian satellites as a nuclear power generator, it was called Topaz. Today it's the only viable generator for deep space missions, as I know.
1.8 / 5 (5) Dec 03, 2013
What is more likely though is having these scrounge up any energy post-turbine

If the device has to glow orange to work, it's not going to extract any waste heat after the turbine, because the steam is below 100 C.
2 / 5 (4) Dec 03, 2013
eikka, very true...not enough is known about it at this point.

Quixote hit the big point though, its the gradient that's going to be tough to maintain. Thus these plants will still require cooling towers, and unfortunately krundolo, that means you cannot just pull electricity out of the warm air.
Dec 03, 2013
This comment has been removed by a moderator.
3 / 5 (4) Dec 03, 2013
What is more likely though is having these scrounge up any energy post-turbine

If the device has to glow orange to work, it's not going to extract any waste heat after the turbine, because the steam is below 100 C.

Indeed, and agreed. However It seems like (and I'm probably missing something here) this could be put in close proximity to the core of a traditional fission reactor and bypass the steam process completely.

I can't see a fundamental problem with this, but I can't design a new kind of nuclear reactor either.
1 / 5 (1) Dec 03, 2013
What about what Italba suggested a few posts up. Coupled with an RTG, surely this device would produce far more power than current RTG's. If this is the case, then the future of deep space missions looks bright (if we can get the radioisotope fuel that is!!!). But I don't know enough about this device, to know if it can be used with radioactive decay as the heat source.
5 / 5 (1) Dec 04, 2013
If I'm not mistaken, this is a more efficient vacuum tube. Make a hi-fi tube amp! But in all seriousness, if you can make a triode with this, could have some RF amplifier applications at the very least...
5 / 5 (1) Dec 05, 2013
How about putting these behind concentrated light solar panels to increase the overall efficiency by capturing some of the energy that gets converted to heat.

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