Heated Exchange

German researchers have found a way to generate electricity directly from heat, solving what had been a persistent problem when the energy created by such systems also effectively created its own insulation, stopping the energy flow.

These "thermionic generators" create electricity based on the temperature difference between two metallic plates that are separated by a vacuum. When one plate is heated, electrons "evaporate" from its surface just as molecules of a liquid evaporate when the liquid is heated above a certain temperature. These free-floating electrons then condense on the surface of the cooler plate, the way that water vapor condenses on a surface that is cooler than the surrounding air. Since the two plates now have a charge differential because of the transfer of electrons, an electric current will flow between them.

The problem has been that when the plates are separated by more than three to five micrometers, too many electrons can build up between them. Electrons, you may remember from science class, carry a negative charge and the "electron cloud" that forms between the plates blocks the current transmission. Like charges repel each other, and a cloud of negatively-charged electrons repel the evaporating negatively-charged electrons, meaning they can't condense on the cooler plate and create a charge differential and a current. Since a micrometer is one millionth of a meter, that means if the plates separate by as much as a spiderweb's strand of width the electron cloud is too thick. But if they touch, they lose the temperature differential and electrons don't transfer from one plate to another. This is called the "space-charge problem," and it has kept scientists from using thermionic generators even though they've been known for more than 60 years.

Researcher Jochen Mannhart figured out how to create an electric field between the two plates, which allows the electrons themselves to keep moving instead of building up in a cloud. It allows for a much better current transmission and power generation.

Mannhart and others want to continue to develop the process to increase the generator efficiency. Thermionic generators are obviously much simpler than turbines, which are the usual way that power plants generate electricity now -- and they could be much more efficient. They might also be able to generate electricity from much lower-temperature sources, such as solar heating or even the waste heat from car engines.

A practical thermionic generator would also mean the world finally has a use for Rush Limbaugh or Lawrence O'Donnell -- although both men do almost nothing but generate hot air, the lower temperatures such a generator would require might be well within the range they and others produce on a consistent basis. This is good news, as the oxygen such folks have previously wasted to inflict their opinions on us might now be considered an acceptable expense in the generation of electricity. I was going to suggest that electricity be used to shock them into silence when they said something stupid, but that would sort of block the power generation aspect of my idea.