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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

• #### New source of power ? (Score:5, Insightful)

by Anonymous Coward on Saturday February 17, 2007 @08:35PM (#18055908)
How is this "a new source of power" ? it's just improving efficiency by reducing loss.
• #### Re:New source of power ? (Score:4, Insightful)

on Saturday February 17, 2007 @08:48PM (#18056006) Journal
But the result would be the same as doubling the number of power plants available, once this technology (supposing it works as advertised) is installed - you'd suddenly be able to halve the number of running generators.
• #### Re: (Score:3, Insightful)

That's if, and only if, the efficiency gain is 100% over nominal. They don't say it is.
• #### Re: (Score:2, Informative)

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]
• #### I wouldn't worry about the computers.... (Score:5, Insightful)

on Saturday February 17, 2007 @09:41PM (#18056360) Journal
Computers still are, and probably always will be, a fairly small fraction of electrical consumption. Yeah, data centers are all the way up to 1%... But 1% is 1%. Not a big component... Hell, I'd be more concerned about this [slashdot.org] - if we replace fossil fuel cars with electric in the next fifty years, electric power used to recharge vehicles will probably become one of the biggest fractions of the total load.
• #### Re: (Score:2)

Also it's takes more a LOT more energy to deliver all that spam as snail mail.
• #### Re: (Score:2)

Most devices are becoming more energy efficient. Even for what you are talking about (servers), the amount of energy used per unit of work isn't going up.
• #### Re:New source of power ? (Score:5, Interesting)

<fordimanNO@SPAMgmail.com> on Saturday February 17, 2007 @08:50PM (#18056030) Homepage Journal
You're exactly right. But the common man doesn't understand 'efficiency gains' as something significant. Perceptually, people don't get how much energy is lost to waste heat.

I mean, hell. If this works well, it could be used as a component in hybrid vehicles; they only have 25% efficiency on the gasoline engine, and if they're parallel types, the heat generated by the gasoline engine could be used to keep the electrical engine in juice.

It might even be possible to recapture a bit of energy off the moderate heat generated in the electrical motor.

Of course, there will be the thermodynamical morons in here, trying to say that this little device is next in the step towards the latest self-powering promise, drawing energy from the zero point or whatever other perpetual motion bollocks is being flouted these days.

Here's a hint guys: you can't win and you can't break even. You can only take your income (solar energy) and savings (batteries, fuels, and nuclear fuels) and spend it (burning fuel or running electrical equipment). If you can boost your output per unit input, great stuff - but please don't assume it means you've hit a lotto (perpetual motion) that doesn't exist.
• #### Re:New source of power ? (Score:5, Funny)

on Saturday February 17, 2007 @08:56PM (#18056078)
Dude, this is like the next step to a self powering device. It would run forever.
• #### Obligatory (Score:2)

"Lisa, in this house we obey the laws of thermodynamics!"

• #### Re:The point of the robot... (Score:5, Insightful)

on Saturday February 17, 2007 @11:34PM (#18056906)
"But the common man doesn't understand 'efficiency gains' as something significant."

Yeah, they insulate their houses to save on energy bills just 'cause.
• #### Re: (Score:2, Insightful)

I think he means there is a difference between understanding it's a waste when the heat you are paying for is going out the window, there is a very direct cost. It's less likely for people to think that the heat coming out of the back of their vacuum cleaner is also wasted energy. Electrical appliances get hot when they run, right? Nothing unusual about that.
• #### Re: (Score:2, Interesting)

Nine times out of ten, the "thermodynamical morons" are the ones shouting down the proponents of the "free" power source. The claims are not about whether perpetual motion is possible (it isn't), but whether or not we can get out more energy than we put in by tapping other power sources (anything from naturally occurring temperature differences to some sort of unknown cosmic energy).

The people who always bring up the impossibility of perpetual motion lose the argument before it even begins, since they fa
• #### Re: (Score:2)

>hybrid vehicles; they only have 25% efficiency on the gasoline engine,

Toyota claims 45% for the Prius. I don't believe them, but one of the advantages of a hybrid is that it can keep the gas engine in the most efficient part of its working range. On top of that the availability of low-end torque from the electric system frees designers to use low-torque designs like the Atkinson (or Miller) cycle which are more efficient.
• #### Re: (Score:2)

Uh, Zero Point energy (or the Casimir effect or whatever you want to call it) is still an income, as you put it. Small amounts of energy have already been apparently extracted from it, albeit nothing sustainable.

The Holy Laws of Thermodynamics aren't being violated, the source of energy is just different.

• #### Re: (Score:2)

But the common man doesn't understand 'efficiency gains' as something significant. Perceptually, people don't get how much energy is lost to waste heat.

Just about anyone who buys gasoline and knows that the hood of the car gets hot can understand that if that heat were used to help move the car, s/he'd need to buy less gasoline.

• #### Re: (Score:2)

Not only that, but the concept of just being able to "use" waste heat with no penalties is a bit misleading. Power plants work on a heat *differential*, not simply heat. If you slow down the transfer of your waste heat to the environment, you're lowering the heat differential utilized by the plant, and thus lowering your efficiency.

Wake me up when someone beats Carnot :P (okay, okay, bypassing it altogether is a much better option ;) )
• #### Re: (Score:2, Insightful)

It's not a more efficient thermal cycle or a more efficient dynamo. It is a new source of power - waste heat. OK, waste heat has been used before, usually for direct heating, but not for this kind of electricity production in utility power plants.
• #### Re: (Score:2)

It's not a more efficient thermal cycle or a more efficient dynamo. It is a new source of power - waste heat. OK, waste heat has been used before, usually for direct heating, but not for this kind of electricity production in utility power plants.

Not true. It's called Combined Cycle Power Generation.

The waste flue gas from the gas turbines heats water that then powers steam turbines.

• #### Open that fridge! (Score:5, Funny)

on Saturday February 17, 2007 @08:38PM (#18055930)
So now instead of yelling at my kids for leaving the fridge door open I'll have to get them to leave it open every now and then in order to keep the electricity bill down.

I could really dig have a lower electricty bill in the summer rather than a higher one. When can I build a house with this stuff?
• #### Re:Open that fridge! (Score:5, Funny)

on Saturday February 17, 2007 @08:46PM (#18055982)
In this house, we obey the laws of thermodynamics!
• #### Re: (Score:2)

Hey, maybe you can use the head differential between the air conditioned inside and the out outdoors to generate eletricity!

Seriously though, I wonder what the limits are to this. Like, could you use this on solar panels (behind the solar cells) to suppliment the normal solar electricity generation? The cells only convert, what, 5% of the light to electricity. I'm sure the panels get hot. Hot enough to drive this new tech?

-matthew
• #### generation vs consumption (Score:3, Insightful)

on Saturday February 17, 2007 @08:53PM (#18056054) Homepage
we've seen a lot of "new energy" stories on /. today, and there's been a lot of talk in the media lately, too. but NO ONE is talking about conserving energy. of course, this is an american perspective, and self-constraint is unamerican as it gets.

who cares if we figure out, say, how to meet 10% of our energy needs with new tech when our consumption rises 10% (or more).

a lot of "new energy" isn't really energy. as others have pointed out, hydrogen, is really just a way to transport energy.

it occurred to me recently, that, collectively, humans are like any other organism. we cannot control ourselves from the inside (something to do with goedels theorem maybe), and thus we will overrun the planet until we choke on ourselves -- or run out of energy. so i don't worry about it too much.

oh. whoops. depressing cold day here in st louis today.

mr c
• #### Re: (Score:2)

You're right, of course. Conservation in the home is step one. Of course, conservation in the production industry is another very good step.

Why not conserve that additional 10%?

Low powered CPU cores, higher efficiency appliances, LED light bulbs, and similar efficiency improvements could see that personal conservation isn't needed for several years.

I dunno. Are you one of the sorts who oppose things like thorium-based reactors for political reasons rather than on their merits?
• #### Re:generation vs consumption (Score:5, Insightful)

on Saturday February 17, 2007 @10:30PM (#18056610) Homepage Journal
LED light bulbs are overrated. Compact florescent bulbs are much more efficient, but they aren't a sexy as LED's. Here's some ways to conserve, but no one will do this:

1. No more incandescent bulbs.
2. Live 10 minutes away from work in a condo/apartment instead of the suburbs in a giant house
3. Stop leaving your computer on all day

Actually, #2 is about the only one that really saves the most money. Smaller places cost less to heat/cool, and not driving as much saves a huge amount of energy.

But, oh environmentalists are more concerned about prohibiting housing developments or zoning that actually makes sense.
• #### Environmentalists? (Score:4, Interesting)

on Sunday February 18, 2007 @01:11AM (#18057326) Homepage
What's your sample to say what "oh environmentalists" are concerned with? Consider Portland, OR, where environmentalists put in zoning to pack housing into the center of town and prohibit it from sprawling farther out. (True, the anti-environmentalists lately threw a wrench into that with a misleading statewide referendum.) Or on the other side of the country, environmentalists in Vermont are also encouraging more housing in and close to traditional town centers rather than sprawling across the countryside. What is your sample set of "environmentalists" who prefer that we'd all live in suburbs in giant houses? I'd suggest that whoever you can find fitting that description just flies a flag of convenience - the evil often cloak themselves in the names of the good.
• #### Re: (Score:2)

Well, Livermore, CA. Sierra club and company vs. a home builder on a ballot issue to allow development. Yeah, it was another suburban development, but you know what happens instead? Yep, people build houses another 20 miles further out from the city. So thanks to them we have the most expensive, worthless cow pasture in the world in the middle of a city. This is a huge country, and if people in cities love looking at cows, they should you know, not think they are the center of the world and head out of the
• #### Re: (Score:3, Informative)

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 bett
• #### Re: (Score:2)

if you really, really don't want to change the light often ... bulb over my stairs).

CF are great for that.

• #### Re: (Score:2)

Wohoo I've done all 3 of the above! Do I get a prize?

• #### Re: (Score:2)

If you live in places where heating costs most (those in which the winter reaches unlivable temperature), #2 is no can do. The reason a large house is needed (or recommended) is because being trapped in a small apartment for the winter will make most people extremely nervous. Instead, what can be done is to buy a thermostat that can change its temperature based on the time of day, and to make sure that the house is cold when you're at work.
• #### Re: (Score:2)

I don't follow. Why would living in an apartment make one nervous? Heating breakdown? That can happen in a house as well. Worse, if you're in your house, you're on your own and possible out of reach - in a city condo, if worst comes to worst you're close to help. Also, if you're really nervous, invest in a small electrical heater (like... a stack of computers), so that two central infrastructures have to break down for you to get cold.
• #### Re: (Score:2)

It's called going stir crazy, or getting cabin fever. People don't do well psychologically when confined to a small space for an extended period of time.
• #### Re: (Score:2)

Live ten minutes away from work, in a corporate society that actively works against job security. It would technically be far more energy inefficient as you would have to work harder to generate more income to pay for the regular costs of relocation and property transfers. That's about as good as charging a carbon tax which makes the poorest amongst us pay the most.

Better batteries are where the money should be going. Really good long life rechargeable batteries make all the alternate energy sources far m

• #### Re: (Score:2)

a lot of "new energy" isn't really energy. as others have pointed out, hydrogen, is really just a way to transport energy.

So is oil, when you get down to it.

Doesn't make hydrogen any more or less viable.
• #### Re: (Score:2)

Depending upon what you believe, there is no new energy. The big bang released all the energy there is and ever would be.

who cares if we figure out, say, how to meet 10% of our energy needs with new tech when our consumption rises 10% (or more).

It a heck of a lot better than having our consumption rise and not having a better way to deal with it...

Who cares if we find a cure for cancer when people are just going to die in car accidents?

• #### Technically... (Score:2)

this is a "conservation" story. We're converting stored fuel into heat energy to generate electricity. We waste much of this heat. The story is about wasting less heat. That's efficiency in the same way that CF bulbs throw off less heat (waste) and insulation in your house allows less heat to escape (waste).

We're not lowering our demand of consumer electricity, we're lowering the demand of fuel source for the amount of supply generated.
• #### 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: (Score:3, Interesting)

. 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 el

• #### 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: (Score:2)

There are engines which use ceramic lubricant that has much higher heat tolerance. This permits the engine to run at much higher temperature and also greater thermodynamic efficiency.
• #### You don't want insulators (Score:2)

If one had materials that could take the heat, say piston liners that were excellent insulators

Then you burn the fuel hotter and need more cooling - but there is a point where it is very useful and I've seen ceramic cylinder liners (partially stabilised zirconia) for truck engines around ten years ago. You can't take it too far - the all ceramic engine project was a failure for Mercedes due to the expected high cost of each engine and the extra weight for the larger cooling system. A mix of ceramic and

• #### Re: (Score:2)

Well, if you stick it on the engine block you lose the air cooling, meaning the radiator has to work
harder and the engine fries faster when the radiator fails. Plus you are possibly reducing the carnot efficiency of the engine. But if you splice it into the hose between the engine and the radiator, you get something. The exhaust manifold does offer a significant temperature differential, though it would probably fry the device and overheat the manifold (due to the insulating effect).

What do you do wit
• #### Indeed- it's only a smallish breakthrough... (Score:2)

I believe I saw what might pass for Zt values given for the stuff in another [greencarcongress.com] article:

benzenedithiol: 8.7 microvolts/K
dibezenedithiol: 12.9 microvolts/K
tribenzenedithiol: 14.2 microvolts/K

To put this in perspective with what we already have in the way of commonly used thermoelectric materials, Bismuth Telluride weighs in at -287 microvolts per degree Kelvin for N-doped material and 87 microvolts per degree Kelvin for P-doped material.

What we're reading about is roughly 1/5th as efficient at doing thermoelect
• #### Heh... This is what I get for posting late... (Score:2)

Needs must have SOME sleep before posting- but then, this IS Slashdot, right? >:-)
• #### Just ignore the post... (Score:2)

Heh... I'm so freaking tired and out of it, I didn't even notice that you'd already quoted the values, etc.

Not enough caffene, not enough sleep. Time to go to bed.
• #### Re: (Score:2)

Yep. But the newfangled device supposedly uses cheap organic materials instead of expensive metals.
Of course, looking at their picture you see hundreds of atoms of gold for every organic molecule.
But maybe they can make the device cheaper by using cheaper metals and only cut the efficiency
from something like 2% to 1%. And the thing probably melts a lot quicker than the old fashioned
thermoelectric modules. Not to mention that "nanotechnology" tends to be a short way of saying
not remotely economically
• #### 2nd Law (Score:2, Interesting)

I hope no one here will forget about the 2nd law of thermodynamics...
• #### Re: (Score:2)

I think Roland P already did.
• #### Re:2nd Law? Try the 3rd law (Score:3, Informative)

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
• #### Re: (Score:3, Informative)

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.
• #### 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..
• #### Awesome! (Score:5, Funny)

<nacturation AT gmail DOT com> on Saturday February 17, 2007 @09:21PM (#18056248) Journal
So this means global warming is a good thing. With all the electricity we'll be able to make, it's no problem to just run enough air conditions to solve the problem.

• #### Re: (Score:2)

Actually, AC units just transfer the heat from one spot to another. You actually add heat to the mix from the electric motors in the units as well, making things even worse for those "outside".
• #### Re:Awesome! (Score:4, Funny)

<nacturation AT gmail DOT com> on Saturday February 17, 2007 @10:39PM (#18056648) Journal
Air conditioners also sometimes make a nice "whooooosh!" sound, similar to the one just heard.

• #### Re: (Score:2)

Excellent point. I forgot about the noise pollution too!
• #### Kurt's Law (Score:2)

I've come up with a new law: The odds of an announcement regarding an "inexpensive source of energy" having a disclaimer that "this method of creating electricicty creation [sic] is in its very early stage" approaches one as the amount of energy in the proposed invention increases, and/or as the cost decreases.
• #### And yet... (Score:3, Interesting)

on Saturday February 17, 2007 @10:00PM (#18056466) Homepage
Cogeneration only wastes about 1/3 of the energy. That's not too far off from
the Carnot efficiency of 86% for a combustion temperature of 2000 centigrade.
And even the reamining "waste" heat could be used if better planning happened:
district steam, drying and other industrial uses.
• #### Cogeneration (Score:2)

Foreword: I am an American who dropped out of college in the US, moved to Sweden, and ended up doing an entire power engineering degree there.

After my lecture classes, while I was in American doing my thesis at a coal-fired power plant, I told my coworkers about the district heating systems which exist in almost every city back in Sweden. One of them joking said, "Sounds like a bunch of Communism to me." You know what? It is.

While it saves incredible amounts of money on fuel (which doesn't come from the
• #### Re: (Score:2)

Ermm no, see. You can say that the short-term self-interest which passes for capitalism does not generally arise in efficient system such as this, but that does not mean that the systems can only exist within a socialist regime. See also Industrial Ecology (yes, many of the best known instances are in Europe, but there are several in the US as well). Furthermore, public utility ownership in the US has been far more prevalent then you probably realize. I can think of a half a dozen systems off the top of my
• #### Community ownership (Score:2)

Many (most?) of the district heating systems in Denmark are community owned. I witnessed it once, someone took initiative to a local heat/power plants, and got a sufficiently large fraction of the community to sign up for it.

For US, it sounds like a perfect fit for the "designed" communities.

• #### Way to save energy.. (Score:2)

Producing electricity from a heat source (gas, coal, nuclear) is wasteful - typically only ~40% efficient. So in order to maximize our use of resources we should make use of that wasted heat. Pumping the heat (via water) to neighboring houses and greenhouses is just one example that is commonly used in Europe.

But this brings up another idea. Why not do away with burning fuels for heat. Large building could instead burn fuels to generate electricity and use the waste heat as their heat source. Extra ele
• #### Re: (Score:2)

Good idea ... see http://www.climate-energy.com/products.asp [climate-energy.com]
• #### Energy from waste heat (Score:2)

Isn't that called cogeneration?
• #### Good to see (Score:2)

Good to see that some professors can both do research and teach without lacking in one or the other. Professor Majumdar's a nice guy, his heat transfer class was very well taught, really helped get me interested in heat transfer as something to elaborate on for MechE.
• #### Waste heat density same as solar heat (Score:2)

The main problem in recovering energy from a diffused source with a small temperature diff over the surroundings is the little thing called Carnot limit efficiency. If the alleged technology is really succesful there is no need to limit it to waste heat. We could apply it equally well to solar energy collection too. But sadly, looks like the alleged device is a very low efficiency thermocouple.
• #### Sounds like a job for... (Score:2)

...a traditional heat engine like a Stirling Engine. I just trust something I can take a wrench to more than a convoluted biological solution that has biosystem requirements.
• #### If this works (Score:2)

we can generate power for the entire nation by fitting out the halls of Congress. Finally -- a good use for all that hot air!
• #### 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.
• #### Re: (Score:2, Insightful)

Thank you for a post that actually talks about some thermodynamic principles. Tapping into "waste" heat does seem like an attractive idea to people who do not have an understanding of thermodynamics. My understanding is that if you try to simply strap on another heat engine like a thermocouple, you're working with a very low temperature differential which means low efficiency.

One question though. Isn't a gas turbine just another heat engine that that is governmed by the limits of any thermodynamic c
• #### "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:"Wasted" heat is not available for this device. (Score:4, Interesting)

<bob.rohatensky@sasktel.net> on Sunday February 18, 2007 @07:39AM (#18058836) Homepage Journal
The analogy that helped me understand the 2nd Law of Thermodynamics was the hydroelectric dam.

In a hydroelectric dam, you can convert a portion of the potential energy of water flowing downhill into work. You can only convert the energy when the water is flowing downhill and you cannot convert all of the energy because that would stop the water from flowing. The maximum efficiency is the head difference (high and low water points). Unless the low point of the dam is at sea level, you are not getting all of the potential energy out of the water.

The 2nd Law of Thermodynamics and Carnot Efficiency have the same major points. You can only convert some of the heat to other work while it is moving from hot to cold and the maximum efficiency is the difference in the high and low temperatures relative to absolute zero.

As the parent post pointed out, power stations attempt to exhaust condensation heat as close as possible to ambient temperatures and there isn't much "waste" heat to recover. If there was an efficient thermocouple device like the article, its use would be in all the industrial waste heat from sources that are currently too small to justify existing heat recovery systems.

• #### Do the math, Carnot cycle, economics, etc.... (Score:2)

I hate to be repetitive, but for any new "energy source", one has to do one's homework.

This means "do the math". Figure out how much energy is captured, at what cost, over what period of time. You also need to figure out the true opportunity costs-- what are you giving up if you go down this path. Not to mention calculating the risks and uncertainties.

With most if not all schemes for capturing energy from small temperature differrences, the efficiency is soooo small, that the schemes can never even

• #### 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.
• #### Anyone have a spare first year thermo textbook (Score:2)

Please send it to this Roland guy or Zonk. We're seeing a lot of these articles, and they would be a bit more coherent with a bit more basic understanding.

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