The Naked Scientists

The Naked Scientists Forum

Author Topic: What are thermoelectric generators (TEGs)? How do they work?  (Read 4774 times)

thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 337
    • View Profile
Almost 70% of the energy produced by a car engine is lost, mostly in the form of heat that exits along the exhaust pipe. But, by using some old fashioned physics and some new engineering, it's possible to capture and reuse some of this heat energy. Thermoelectric Generators (TEGs) convert wasted heat into electricity, without the need for complex moving parts. They've been used in the space industry for 40 years to power space probes and now the car industry is finally starting to catch up. Laurie Winkless finds out how...

 Read the article then tell us what you think...
« Last Edit: 10/02/2012 13:58:40 by chris »

peppercorn

  • Hero Member
  • *****
  • Posts: 1563
    • View Profile
    • solar
Our Naked Scientists have touched on this before:
http://www.thenakedscientists.com/HTML/podcasts/show/2008.07.27/

So are there any new articles to support:
"BMW, Chevrolet and Volkswagen are all developing TEG systems, so we may see them on cars very soon"  --  ???

I'd be interested to see this moving from the realms of university labs, etc to actually being applied commercially on new vehicles.

Geezer

  • Neilep Level Member
  • ******
  • Posts: 8416
  • "Vive la résistance!"
    • View Profile
I'm sure they are experimenting with TEGs, but whether they will be commercialized or not is a big question.
 
There are a couple of problems; one is that, at the moment, their efficiency is low, so, even if you could apply all of the waste heat to the TEG, you'll be lucky to convert 10% of it into work.
 
That does not sound all that bad until you realize that a lot of the waste heat is dissipated from the engine and the cooling system (I think at least 30%) and it is too cold for a TEG. Pretty soon you are down to 10% of 70% of 70% of the fuel energy, and that's before you convert it back into work!
 
I believe we really need something with a thermal efficiency of around 50% that can recover the "low grade" energy as well as the "high grade" energy to justify all the extra weight and expense.
 
BMW did put a steam engine in a car as an energy recovery system for a bit, but I suspect they have chucked it. When you do the calculations, you discover that the work that can be scavenged from the exhaust is rather pathetic.

peppercorn

  • Hero Member
  • *****
  • Posts: 1563
    • View Profile
    • solar
I'm sure they are experimenting with TEGs, but whether they will be commercialized or not is a big question.

My point exactly!
Saw this yesterday following on from this question.

There's clearly some interesting new materials coming to the fore, but nothing suggests that these devices are particularly close to graduating to mass-produced vehicles (let alone the family hatchback) any time soon.

This continued obsession with believing that bolting-on fixes to a technology (that is fundamentally more than a century old) is ever going to make more than minuscule improvements in F.E. is fantasy and a waste of resources. .... And time is running out!

Greg

  • Guest
None
« Reply #4 on: 23/03/2012 11:16:01 »
Worth pointing out that there are applications for TEGs in which their inefficiency is actually a bonus. For instance, if you're using a wood burning stove to heat an off-grid home (a boat or cabin, say), you don't want to convert anything close to 100% of that heat energy to electricity. But if you had a stove putting out 5kw of heat 24 hours a day, channelled 20% of that energy into a TEG, and converted 5% of *that* energy to electricity, you'd be getting 1.2kwh of free energy every day without noticing any difference in terms of heating. That's comparable to a 250W solar panel at the height of summer. So stovetop TEGs have huge potential to do the job in winter that solar panels do in summer.

Nizzle

  • Hero Member
  • *****
  • Posts: 964
  • Extropian by choice!
    • View Profile
    • Carnivorous Plants
So can we build this thing on the surface of the moon, which always has a hot side and a cold side (except during lunar eclipse maybe) and use it to power a lunar base?

We could start small, close to a pole, and make a bigger system closer to lunar equator later on?

peppercorn

  • Hero Member
  • *****
  • Posts: 1563
    • View Profile
    • solar
if you had a stove putting out 5kw of heat 24 hours a day, channelled 20% of that energy into a TEG, and converted 5% of *that* energy to electricity, you'd be getting 1.2kwh of free energy every day without noticing any difference in terms of heating. That's comparable to a 250W solar panel at the height of summer. So stovetop TEGs have huge potential to do the job in winter that solar panels do in summer.

That's fine if:
a) You can use 4.95kW of heat energy 24 hours a day every day for a season (ie. winter).
b) You can remove 0.95kW of heat from the cold side of the relatively small surface on the 'cold' side of the TEG fast enough to stop it overheating and energy free.
c) See a Return on Investment in a sensible timeframe to pay for the installation, and then guarantee the TEG devices will continue to work above ~97% efficiency making enough of a profit for a good time after.

Then ask yourself, how does this compare with the price of other more mature technologies to achieve the same thing?  There's Stirling engines, Organic Rankine cycle (ORC) engines or even Woodgas generators powering a old piston engine; alll these can be hooked up to an alternator, or whatever you like!
« Last Edit: 16/05/2012 10:53:34 by peppercorn »

bonaboots

  • Newbie
  • *
  • Posts: 3
    • View Profile
Quote
If you had a stove putting out 5kw of heat 24 hours a day, channelled 20% of that energy into a TEG, and converted 5% of *that* energy to electricity, you'd be getting 1.2kwh of free energy every day without noticing any difference in terms of heating. That's comparable to a 250W solar panel at the height of summer. So stovetop TEGs have huge potential to do the job in winter that solar panels do in summer.

Kind of like what this interesting new gadget is doing


http://biolitestove.com/homestove/homestove-technology/ It cooks beans and runs a mobile phone at the same time.  I found this company yesterday, and find it really exciting that they are developing a technology that will make a huge difference to people who cook on biofuels off-grid.  I just wonder how long that thermoelectric generator will last.

Laurie

  • Guest
None
« Reply #8 on: 08/02/2013 10:26:56 »
Just a quick update on this:

1. TEGs are already commercially available, though they are generally used as Peltiers, so to control temperature. In fact they're most often used to keep lasers at very well-defined temperatures.

2. Also interesting are the newer, thin film thermoelectric materials which can harvest very low grade heat - these guys have shown that they can even harvest the heat produced by a fingertip. Link here: http://pubs.rsc.org/en/content/articlelanding/2013/EE/C3EE23729J

3. BMW have built a prototype TEG assembly and fitted it on one of their cars and have already produced ~600W (when the car is at high speeds - on the motorway, for example). Link here: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/thermoelectrics_app_2012/wednesday/mazar.pdf

 

SMF 2.0 | SMF © 2011, Simple Machines