Thermoelectricity through infrared emissions: a new, vast energy source?

We know a thermoelectric generator produces electricity from temperature differences, and we know the earth is warm compared to outer space – does that mean we have a vast, untapped energy source? Physicists at the Harvard School of Engineering and Applied Sciences (SEAS) think so, and have proposed two different ways we could generate DC power by emitting infrared light into space.

For the layman, this isn’t entirely easy to understand. Instead of absorbing light to win energy, this solution would emit infrared light:

“It’s not at all obvious, at first, how you would generate DC power by emitting infrared light in free space toward the cold,” says principal investigator Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS. “To generate power by emitting, not by absorbing light, that’s weird. It makes sense physically once you think about it, but it’s highly counterintuitive. We’re talking about the use of physics at the nanoscale for a completely new application.”

One device would have a “hot” plate on the bottom, and a “cold” plate on top. The cold plate would remain cool by radiating heat to the sky.

Based on measurements of infrared emissions in Lamont, Oklahoma (as a case study), the researchers calculate that the heat difference between the plates could generate a few watts per square meter, day and night. Keeping the “cold” plate cooler than the ambient temperature would be difficult, but this device illustrates the general principle: differences in temperature generate work.

The second device would utilize the temperature differences between nanoscale electronic components. Some of the technology used to work at a nanoscale level has its origin in 1968 documents by inventor J.B. Gunn. Gunn invented a diode used in police radars, and his circuit diagrams detail the behavior of the diode when a temperature difference is present:

Simply put, components in an electrical circuit can spontaneously push current in either direction; this is called electrical noise. Gunn’s diagrams show that if a valve-like electrical component called a diode is at a higher temperature than a resistor, it will push current in a single direction, producing a positive voltage. Capasso’s group suggests that the role of the resistor could be played by a microscopic antenna that very efficiently emits the Earth’s infrared radiation toward the sky, cooling the electrons in only that part of the circuit.

In principle, if you covered a device with lots of these tiny circuits and aimed it at the sky, you could generate power. It won’t be ready tomorrow, but recent advances in nano-fabrication and other technologies are bringing these infrared applications into the realm of possibility.

Read more at: Science Daily.