The Naked Scientists

The Naked Scientists Forum

Author Topic: Can heat be converted directly to electricity?  (Read 3520 times)

Pierre

  • Guest
Can heat be converted directly to electricity?
« on: 18/05/2010 09:30:03 »
Pierre  asked the Naked Scientists:
   
Hi,

Just listened your Feb-14 podcast and I heard Dave say that "heat cannot be directly converted into electricity"

That made me twitch, so I went on Google and found several results among which this:

http://web.mit.edu/newsoffice/2001/electricity-1205.html

Agreed, this is not on the market yet, but I think this could be coming
sooner or later.

Love your programme,

Pierre

What do you think?
« Last Edit: 18/05/2010 09:30:03 by _system »


 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
Can heat be converted directly to electricity?
« Reply #1 on: 18/05/2010 13:20:35 »
You are right; it can be.
We are still waiting for this to become a commercial reality though.

Also see:

Is there much milage in fitting 'Nanotube cuffs' on exhaust pipes?
http://www.thenakedscientists.com/forum/index.php?topic=29183.0
 

Offline techmind

  • Hero Member
  • *****
  • Posts: 934
  • Un-obfuscated
    • View Profile
    • techmind.org
Can heat be converted directly to electricity?
« Reply #2 on: 08/06/2010 23:49:44 »
You cannot convert heat, but the flow of heat into electricity. You can do it directly using the Thermoelectric Effect (or more specificially, the Seebeck effect). http://en.wikipedia.org/wiki/Thermoelectric_effect

The theoretical best efficiency is given by the Carnot efficiency (100%×(1-Tcold/Thot)   (with the temperatures measured in Kelvin, i.e. Celcius+273) isn't great, but gets better as the temperature gradient increases. Note however that mechanical technologies such as steam engines and steam turbines are also subject to the same limit.

Well-known Seebeck devices, usually based on bismuth telluride ( http://en.wikipedia.org/wiki/Thermoelectric_materials ), operate at (from memory) something like 10% of the theoretical Carnot efficiency.

So... some magical future technology might be able to do up to 10x better than we can at present, but you still have to let a lot of heat "go to waste" in order to extract comparable amounts of energy from it!



At present the thermoelectric effect is useful for getting modest amounts of power where other methods are inconvenient, eg for powering spacecraft or remote instruments - but it's not going to help with national power generation or solve our energy crisis any time soon (if ever!).
« Last Edit: 08/06/2010 23:54:33 by techmind »
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
Can heat be converted directly to electricity?
« Reply #3 on: 09/06/2010 00:31:14 »
It's probably pushing things a bit to say this, but the photoelectric effect might be considered a means of converting radiant thermal energy directly into electricity. It sort of depends on your definitions of "light" and "heat".

However, in terms of recovering useful amounts of energy from thermal energy that would otherwise be dissipated, it's a non-starter for now.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Can heat be converted directly to electricity?
« Reply #4 on: 12/06/2010 18:29:39 »
You cannot convert heat, but the flow of heat into electricity.
You usually make quite precise answers so I hope you don't mind if I'm a bit nitpicking here. Heat already is a flux of energy, by definition, so "flow of heat" is a bit nonsense.
 

The Naked Scientists Forum

Can heat be converted directly to electricity?
« Reply #4 on: 12/06/2010 18:29:39 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums