Can infrared photons also eject electrons in 'photoelectric effect'?

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  • #1
royp
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Hello,

I have this question whether it will be possible to generate electricity by heating up a suitable metal (conductor). We know from the photoelectric effect that high energy photons (of visible light; probably with frequency closer to that of violet) can knock off the outer electrons from some material in enough numbers to create a significant electric current - as is evident from solar panels.

Are there suitable metals/materials having outer electrons quite loosely bonded to the atoms in such a way that the electrons can be ejected from them by simply heating these materials sufficiently - so much so that it will produce useful electric current?

This question is prompted by a 'stove fan' I recently purchased. There is a motor at the back of the fan and it appears that the bottom of the fan, when placed above the stove and heated, supplies 'power' to the motor.

I will be grateful for your explanations. Thanks in advance.
 
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  • #2
sophiecentaur
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Summary:: My question is whether it will be possible to generate electricity by heating up a suitable metal by means of 'photoelectric effect'

Are there suitable metals/materials having outer electrons quite loosely bonded to the atoms in such a way that the electrons can be ejected from them by simply heating these materials sufficiently - so much so that it will produce useful electric current?
Thermionic emission is a common phenomenon. The hot filament in thermionic valves liberates electrons from its surface. They can be drawn off from the filament by a very low Potential Difference between this Cathode and a positive Anode. This doesn't 'generate electricity' though.
However, neither photo electrons nor thermionic electrons are a useful source of energy in themselves. The most effective way to get energy from photons is to use the energy gap across the gap in a semiconductor device (Photovoltaics) or with the Seebeck effect, which produces a current with two junctions - (hot and cold). It's the Seebeck effect that works a stove fan; hot junction in close contact with the stove top and cool(er) junction in contact with the heatsink (blown by the fan, once it gets going).
The
 
  • #3
royp
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Many thanks, sophiecentaur; for an absolutely spot on and clear explanation. With my limited knowledge of electronics, It helped enormously!
 
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  • #4
royp
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Many thanks for your reply, DaveE. I read the reply in my email but did not see in this thread.
In this connection, I would like to ask something related. I had a chat recently with a friend. They need to use a large fan (15 Kw motor) for circulation/cooling purposes and curious to know whether utilising waste heat generated at his work (industry) can help. They use a large furnace to generate heat.

I believe, the current/voltage produced with two junctions semiconductor device by Seebeck effect is minimal. As the heat generated in my friend's place is huge, is it possible to use many small similar devices each producing a small voltage; then using a step-up transformer (or something similar) to accumulate significant voltage to run the fan (15 Kw)? Is it feasible?

Thanks in advance
 
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DaveE
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Many thanks for your reply, DaveE. I read the reply in my email but did not see in this thread.
In this connection, I would like to ask something related. I had a chat recently with a friend. They need to use a large fan (15 Kw motor) for circulation/cooling purposes and curious to know whether utilising waste heat generated at his work (industry) can help. They use a large furnace to generate heat.

I believe, the current/voltage produced with two junctions semiconductor device by Seebeck effect is minimal. As the heat generated in my friend's place is huge, is it possible to use many small similar devices each producing a small voltage; then using a step-up transformer (or something similar) to accumulate significant voltage to run the fan (15 Kw)? Is it feasible?

Thanks in advance
I deleted that reply (about peltier devices, RTGs, solid-state refrigerators) since those devices really don't use IR photons. It's nearly always conducted heat. Of course photons can move heat too, but it just isn't efficient. So, I thought I was answering a question you didn't really ask.

While thermoelectric devices are interesting and are successful in niche applications, they just aren't very efficient or cheap, so you won't see them in many applications where more conventional technologies are used.

What you are referring to for your friends waste heat is called cogeneration and it is common in large facilities, but I don't think you'll ever see it done with Peltier devices, there are better ways.
 
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DaveE
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We designed systems with Peltier coolers (for big laser diodes) and my rough rule of thumb was that in a good design to provide 1W of cooling you would have to input 2W of electric power and then remove 3W of heat from the hot side. So you can see they are pretty lossy devices.

They are even less efficient when used to generate electricity. Here's a manufacturer of TEC's that claims 5% efficiency for power generation.
 
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