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## Creating Power From Wasted Heat186

Roland Piquepaille writes "Today, about 90 percent of the world's electricity is created through an indirect and inefficient conversion of heat. It is estimated that two thirds of the heat used by thermoelectric converters are wasted and released. But now, researchers from the University of California at Berkeley have found a new way to convert this wasted heat into electricity by trapping organic molecules between metal nanoparticles. So far, this method of creating electricity creation is in its very early stage, but if it can scale up to mass production it may lead to a new and inexpensive source of energy."
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## Creating Power From Wasted Heat

• #### Not by trapping molecules actually... (Score:5, Informative)

on Saturday February 17, 2007 @08:53PM (#18056058) Homepage

The researchers coated two gold electrodes with molecules of benzenedithiol, dibezenedithiol or tribenzenedithiol, then heated one side to create a temperature differential. For each degree Celsius of difference, the researchers measured 8.7 microvolts of electricity for benzenedithiol, 12.9 microvolts for dibezenedithiol, and 14.2 microvolts for tribenzenedithiol. The maximum temperature differential tested was 30 degrees Celsius (54 degrees Fahrenheit).
So the device is a thermocouple. You give is a temperature difference and it generates a small voltage. Notice that the current generated is not mentioned, so we can not even tell how much power is generated. If there is something new here it is that we have an organic Seebeck junction instead of the typical solid state junction. The article mentions your car's radiator as an example of wasted heat - no doubt - but to use that heat you need to provide, and maintain a heat differential across your 'recapture device'. Likely the device will just act as an insulator, and your radiator will no longer function. If not you will find that you need some huge fan to blow even more air past the radiator, and now the amount of energy you recover is less than that needed to drive your fan. I also think that the 30% efficiency mentioned for electricity generation is a bit on the low side. Don't hold your breath.
• #### Re:New source of power ? (Score:2, Informative)

on Saturday February 17, 2007 @08:57PM (#18056096)
It's a nice idea but the power hungry devices of today are just getting more and more power hungry so doubling the output of a standard power plant will just serve to keep the new power hungry devices running.

Just look at at this previous SlashDot article: http://hardware.slashdot.org/article.pl?sid=07/02/ 16/196235 [slashdot.org]
• #### Um hello. Not new. (Score:3, Informative)

on Saturday February 17, 2007 @09:03PM (#18056144)
http://en.wikipedia.org/wiki/Thermoelectric_Effect [wikipedia.org]

Invented almost 200 years ago. I have a huge box full of Peltier "chips" sitting in my store room..
• #### Re:2nd Law? Try the 3rd law (Score:3, Informative)

on Saturday February 17, 2007 @09:52PM (#18056432)
I think the 3rd law is more appropriate here, since they are basically talking about using the waste heat of an earlier process, and converting part of it to usable energy.

The 2nd law just basically states that any energy conversion process cannot be 100% efficient, AKA "entropy".

In effect, this is adding a secondary process to the first (or possibly list of processes), of which we already know some amount of energy will escape due the 2nd law.

This additional process just makes the overall process more efficient, and does not really add to it above the original process's input energy. However, the 3rd law just states you can't achieve 0 entropy in a process with a finite number of steps. Basically, you can never have a process that is 100% energy conversion efficient.

Probably the more important question is does the increase of enthalopy merit the proposed decrease in entropy? AKA, does the cost of implementing this solution outway the benefit.
• #### Re:Not by trapping molecules actually... (Score:5, Informative)

on Saturday February 17, 2007 @10:28PM (#18056598) Homepage

Why do you have to use the radiator?
I inferred from the article that one might add these devices to the radiator to recapture lost heat, and that it would be done for cars already in use. But your question is quite valid. The actual reason for a radiator in a car engine that has one, is to keep the temperature of the engine low enough so that the moving parts continue to move, that the oil lubricates, and that parts don't actually melt. If one had materials that could take the heat, say piston liners that were excellent insulators and still allowed the piston to move, and all of the excess heat simple exited the cylinder you would not need a radiator. Or if you owned a Beetle, a 2CV, or some other vehicle with an air cooled engine you would not need a radiator.
But fundamental to thermodynamics is that you can not have a cycle more efficient than the Carnot Cycle http://en.wikipedia.org/wiki/Thermodynamic_cycle [wikipedia.org]. This give a max efficiency = 1-(TEMPlow/TEMPhigh), so you always want that low temp to be as low as possible - for a car engine that would be the ambient air. If you have your device, then the hot side is on the engine, and the low side is in the air. But the device itself will get hot, an you will have to blow a lot of air on the cold side to keep it cold. It you let the whole device rise to the same temperature you get no conversion.
• #### Re:Way to save energy.. (Score:3, Informative)

on Saturday February 17, 2007 @11:33PM (#18056900)
They don't have to be efficient. The wasted heat is used in the building so there is effectively no waste. Any electricity generated is just an added bonus.

Large thermoelectric plants are ~40% efficient. A burner heats water, the steam passes over a turbine (connected to a generator), the steam is then condensed (where all the energy is lost) and pumped back into the water tank so it can be heated again.

My suggested idea would, most likely, use an internal combustion engine at ~25% efficiency. But even at a lower efficiency it is still more efficient then just burning gas at 0%. (Note that the efficiency ratings are for electricity production.)

Willy
• #### Not a big deal (Score:4, Informative)

on Sunday February 18, 2007 @12:40AM (#18057156)
Unfortunately, thermoelectric converters based on the Seebeck effect are not going to help with efficiency by a large amount.

Firstly, there is a theoretical limit (Carnot Cycle [wikipedia.org]) to the efficiency of any pure heat engine based on the Second Law of Thermodynamics.

If a quantity of heat Q is taken from a high-temperature reservoir at temperature T2, partially converted into useful work W, and the remainder (Q - W) is deposited into a low-temperature reservoir at temperature T1, then the net increase in entropy is at least

\delta S = (Q-W)/T1 - Q/T2 >= 0.

So the efficiency (useful work generated per unit energy input)

e = W/Q < (T2 - T1)/T2

The waste heat is ultimately deposited into the environment, so T1 can't be much smaller than say 300K.

In a steam engine T2 has to be greater than the boiling point of water (at whatever pressure it is operated), but it is limited by what the materials of which it is composed can withstand. Temperatures of order 1000K are typical. That gives a maximum theoretical efficiency of around 70%. The best steam engines barely reach about half that efficiency.

However, modern power plants (which are not pure heat engines) use a Combined Cycle [wikipedia.org] that can do better by first generating electricity from their fuel with a combustion turbine and then using the waste heat from the combustion turbine to make steam to generate additional electricity via a steam turbine. Their efficiency can reach about 60% of the net calorific value of the fuel.

So you can see that one might be able to shave a few more percentage points off the waste, but it will not at all be the godsend we really need...

IMHO only nuclear power can fulfill that role today.
• #### "Wasted" heat is not available for this device. (Score:5, Informative)

on Sunday February 18, 2007 @01:03AM (#18057288)
The "wasted" heat that thermal power plants reject to the surroundings is rejected at a temperature only slightly above ambient. A steam turbine generator has an exhaust steam condenser which operates at a vacuum, where the steam condenses at only a few degrees Fahrenheit above the ambient temperature. There is no significant temperature difference available for the new device to operate with. While thermal power plants do reject over half the fuel energy consumed to the surroundings, it is a myth that this rejected heat can be effectively used. The rejected heat is available at a low temperature, only slightly above ambient, therefore little effective use can be made of it. This is the penalty that the laws of thermodynamics impose on the conversion of heat into work.
• #### Re:generation vs consumption (Score:3, Informative)

on Sunday February 18, 2007 @03:16AM (#18057984) Homepage Journal
Compact fluorescents, 50-70 lumens per watt off the shelf.

White LEDs, 30-45 lumens per watt off the shelf, 131 in the lab. And way more expensive.

http://www.netl.doe.gov/ssl/faqs.htm [doe.gov]
http://www.cree.com/press/press_detail.asp?i=11508 34953712 [cree.com]
http://members.misty.com/don/lede.html [misty.com]

Right now the reason to use LEDs is if the environment is harsh (vibrations, impacts, etc.) or if you really, really don't want to change the light often (traffic lights, or that %^#@!! bulb over my stairs). LEDs also scale down better than anything else.
• #### Re:2nd Law? Try the 3rd law (Score:3, Informative)

on Sunday February 18, 2007 @09:32AM (#18059160)
I haven't seen anyone point out the efficency of an carnot engine (car, your fridge, etc) depends on the output end being hot (the temperature difference).

If you cool the radiator to gain energy using this device, then you'll decrease the efficiency of the primary device.

e.g. if you connect this to the radiator at the back of your fridge, then your fridge will be less efficient.

I don't know whether the net gain is positive or negative though.
• #### The real story here... (Score:3, Informative)

<mparke' at' `gmail.com'> on Sunday February 18, 2007 @05:30PM (#18062108) Homepage Journal
...is that our buddy Roland Piquepaille finally posted a story that directly summarizes and links to the information instead of telling us to come to his blog for the real story.

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