Waste Heat to Electricity?

Darwin_Frog writes: "Recent advances in thermionics at MIT lets waste heat generate electricity, thus pushing entropy one step further down the chain. These devices work at a temperature around 250 deg. C, instead of around 1000, so cars can augment the alternator by using the waste heat in the exhaust system to produce power for onboard electronics and A/C."

Comments

Matrix style

[King of Caffiene]

soon they'll be able to use excess heat from humans...matrix style.

Hmmm...

[caseydk]

I think it might make the EPA happy if companies had these in their smokestacks... maybe reduce their power draw a bit...

less power required= less pollution

Re:Hmmm...

[wass]

I used to work at an MIT laboratory that was sponsored with DARPA funding. I left 2 years ago to go back to school to get my PhD in physics. I'm not sure of the exact details, but here's the basic scoop as far as I see it.

DARPA essentially funds research laboratories to perform research projects that will further advance technology related to DARPA interests. In my case, the research was unclassified, and our group was able to colloborate with other groups and colleages, present our research at conferences, as well as publish our methods/systems/data in scientific journals.

The laboratories that DARPA funds are either university laboratories, FFRDCs (Federally-Funded Research and Development Centers), and commercial laboratories (ie, IBM or Motorola research labs, for instance). It is usually standard practice for employees of all the above labs, upon the beginning of employment, to sign contracts handing over patent rights to the employer (ie, the FFRDC or the company). Actually, I'm not sure about students, as I haven't signed any patent forms yet. But did when I was an employee of MIT. So did Richard Feynman when he worked for Los Alamos (FFRDC).

So, essentially, DARPA has certain technological goals it wants to achieve, and funds a variety of sources to help achieve them. Usually for each specific project, DARPA funds a variety of research labs, and has them compete for further funding. The research labs in turn present their results at least annually for funding renewal. Eventually, DARPA gets it's results (or lack of them), and gets what it needs in terms of advanced technology, and then cna use that technology within more advanced systems.

I do not know specifically what kind of strings come attached with DARPA funding. However, I would imagine that most likely the research labs themselves get some significant percentage of patent rights as a bonus for conducting DARPA research. Otherwise there is no incentive for, say, Boeing to research a new type of stealth aerofoil if DARPA holds on to all patent rights. I know my boss at MIT had his share of patents, but of course, MIT essentially owns said patents.

Note that DARPA's ultimate purpose is to get better technology into Defense-related projects. They advocate using COTS (Commercial Off-The-Shelf) hardware/devices whenever possible. That is, don't waste $$$ designing your own op-amp if Analog-Devices has one that's within your specifications. Of course, you must roll your own if the COTS op-amps don't meet your bandwidth/linearity/bias/power/etc requirements. So, DARPA doesn't care about who gets the patent rights for that op-amp, they want the research that makes use the op-amp. So, in this example, your tax dollars are already going to Analog Devices and helping their own patent processes.

Your concerns about tax dollars funding university patents are either too narrow or too broad. Realize DARPA funds commercial entities as well as FFRDS too, which have similar patent processes. However, DARPA's fundamental purpose is to fund advanced research projects to further American defense interests. That's what it does, and it will support commercial, government, or university research labs to achieve this goal. It's a government agency, so obviously it is funded with tax dollars. I don't think DARPA cares about patents, as long as it can utilize the fruits of the research.

Re:Hmmm...

[Knobby]

Agreed!

Now, for all the naysayers and trolls out there who can't see how this could possibly work I want you to stop and think for a second!!.. You're not going to glue these things onto the outside of your stock exhaust system. You're going to design a new exhaust system that incorporates this technology AND hopefully optimizes the waste heat recovery without increasing the accoustic and chemical emmissions or reducing performance. How would that be done?

Well you want to begin by increasing the surface roughness on the inside of the exhaust piping to increase the surface area and thin the boundary layer which will increase the convective heat transfer coefficient. Okay, so now we have a heat exchanger that should remove heat from the exhaust stream at a greater rate than previously, however, the penalty for this is an increased pressure drop and a non-optimal inlet temperature for the catalytic converter. So, you reduce the length of the piping prior to the catalytic converter and possible increase the diameter of the piping.. Better yet, because the typical catalytic converter sold by Corning produces a huge pressure drop, why not design a nice smooth diffuser with some internal fins that trades the separation induced pressure drop developed within Corning's catalytic converter for one that results in improved heat recovery.. The point to all this is that there are a lot of design changes that will probably need to be made, but there's no reason why recoverying waste heat to improve efficiency should be considered impossible or even difficult.. Given a particular TEG, the design optimization problem is something a senior mechanical engineering student should be able to sort out in a week or two..

Introducing...

[Iamthefallen]

Introducing Athlon XP 5000 - Now self powered!

Re:Introducing...

[mother_superius]

In this universe, we obey the laws of thermodynamics!

Nice but not the end of entropy

[SysKoll]

According to the article, this "breakthrough" is a reverse Peltier junction with about twice the efficiency of current semiconductor thermoconverters. Nice, but nothing revolutionary.

I think it's quite excessive to claim this will reduce entropy. Although I agree that if it's economically deployed in, say, cars, it will supplement the alternator.

Could this new junction actually replace the alternator for producing electricity in a car? Let's see: assume a car has a 100 HP internal combustion engine. That's 75 kW. Two third of this is wasted in heat. Typically, the radiator gets about half of this heat (the other half is dissipated away in radiant heat or through the exhaust. Assume further that 20 percent of this can be recovered and converted to electricity (for a really efficient semicon pile). That's 75 * 2/3 * 0.50 * 0.20, or 5 kW. That's more than a good SUV alternator. So this could actually work, provided it's reliable and not too expensive.

You'll need a battery for the short runs, though.

--SysKoll

Re:Nice but not the end of entropy

[GMwrench]

I don't think so. First your 100 HP engine will only produce 25-35 HP most of the time. Peak power is only produced during hard accerlation during cruse it's much lower and at iddle almost nonexistant. This is 99% of the time. Also an alternator only produses 1-1.5 KW. And the battery cannot be replaced it's needed to start the engine and supply power at low speed when your charging device is insufficent.

Re:Nice but not the end of entropy

[ZxCv]

Even at 25-35 HP, according to his math, that still makes 1.6-2.3 KW. More than an alternator, according to you.

Also, there was no mention of replacing the battery. In fact, I believe it was: You'll need a battery for the short runs, though.

Maybe read the post a little harder next time before responding in a such a know-it-all tone?

Re:Neat Idea, but not terribly useful...

[cascino]

It's true, the applications for automobiles seem rather limited, but thermionics could stand to revolutionize the nature of power plants.
IANAS, but I believe that today's newest and most efficient coal, oil, and even nuclear power plants can at some point be looked at as a simple heat -> steam -> turbine system, the same concept that's powered locomotives for over one-hundred years! As you'd imagine, such a system is terribly inefficient.
Thermionics, as I understand it, eliminates the "middleman" of the equation by translating heat directly to electricity. It certainly will be interesting to see how this develops on a commerical and thus much larger scale.

Use on Hybrid cars?

[BlueJay465]

My question is how much more gas mileage could this technology squeeze forth given an array of these attached to the heat producers of a vehicle, like the engine or the brake pads.

Another thing is how do these "thermal diodes" compare to a Peltier Element in heat conversion to electricity?

Re:Use on Hybrid cars?

[Graff]

It doesn't do this by converting the heat into electricity however. What it does is effectively act as an alternator, converting the kinetic energy into electricity. The loss of kinetic energy slows the vehicle to a stop while charging a series of batteries. Thus, no heat from brake pads in the first place.

Relevant quote from that article on techtv:

When decelerating or braking, the electric motor turns into a generator to charge the batteries automatically. It's a unique hybrid feature called regenerative braking. Normally when you brake, all that energy is converted into heat into the brakes. Toyota's Prius actually recaptures about 30 percent of that energy to recharge the nickel-medal-hydride batteries in the back

Anyonw know how much they cost.

[argoff]

It'd be great if we could use this for cheap solar cells. Regular solar cells are pretty expensive. (I'm almost convinced that other industries are screwing with the market to make them cost so much). Anyhow, does anyone know how much this new stuff would cost? PS: nuclear's my favorite, but it's too easy for the govt to regulate.

thermodynamics, and entropy, and all that

[StandardDeviant]

here's the layman's formulation of the things that give chemistry students the cold sweats, the rules of the game as it were:

1. You can't win.
2. You can't break even.
3. You have no choice about playing.

Any closed system ends up in the state of most disorder, and all systems are closed if you look at the boundaries carefully. No matter how hard you try, no matter what ingenous things you do, in the end, the dealer wins and everything is dust. Cold dust, at that. The more energy you expend enforcing order, the more chaos you cause. There are no wins in technology, only a prolonging of the inevitable loss. So while I'm sure this new doohickey is neat, somewhere, Carnot is laughing and his cycle is tapping you on the shoulder snickering to itself.

Re:thermodynamics, and entropy, and all that

[Phanatic1a]

While that's all very true, it's not tremendously *relevant* here. While you can't break even, you *can* get arbitrarily close to breaking even. Nobody's claiming that thermionics allows you to build an over-unity device, or violate the 2nd law.

What this does do is allow us to design more efficient processes than before. That's a cost savings, a resources savings, and quite allowed by Carnot.

Re:thermodynamics, and entropy, and all that

[dragons_flight]

I am a physicist and have studied entropy, though it is not my specialty.

At a fundemental level, entropy is a measure of the number of accesible states of a system for a given energy distribution. Presumably you know that temperature is really just a statistical measure of average kinetic energy in a substance. In the simple case of a uniform temperature gas, it's possible to compute the entropy directly, by (a process analogous to) counting the possible ways to arrange the molecules and distribute their kinetic energy such that you still have the same temperature. (Okay it's not really counting cause there is [usually] a continuum of positions and energy values, but the idea is there, only with more integrals.)

Roughly speaking a system is "ordered" or "disordered" based on how much freedom it has in distributing the energy in it's heat. For instance, in highly complicated and stable configurations (e.g. DNA) you can infer that the heat gets distributed only in ways that don't break down the basic structure. Of course with enough heat it will no longer be stable, but that's a different case.

While the number of accesible internal configurations for the heat energy is the basis for entropy, very few people actually use this. What is actually used is a set of laws mathematically derived from this which can be directly applied to macroscopicly measurable quantities. Chemists know more about these areas than I do, but I'll cover a few of the basics.

The most important is known as the Second Law of Thermodynamics, stated simply "Entropy always increases (or stays the same)." Whenever you do anything that moves energy (such as heat) around, the net entropy will increase (except in those rare cases when it stays the same). It is possible to locally decrease the entropy of one system, but you are guaranteed to increase the entropy of everything else by at least the difference.

There is another important trick about entropy. It tells you that it's impossible to transfer energy from heat to any other form with 100% efficiency. Not only that but you can't even do it with arbitrarily close of 100% efficiency unless you have something who's initial temprature is arbitrarily close to 0 degrees Kelvin. Heat engines, any device that changes heat into other forms of energy, depend on having a difference in temperatures available (for instance, cool river water versus hot steam pipe). If you just have a box sitting at room temperature, it can't work.

There is an interesting caveat here. The Second "Law" and most of how we typically apply entropy are based upon something called the Fundemental Assumption of Thermodynamics. Roughly stated: "All possible energy configurations are equally likely". As it turns out this is rarely ever exactly true, but it is so nearly true in almost every concievable macroscopic situation that it makes no difference. Entropy always increases is a mathematically certain law derived from the fundemental assumption and mathematical definitions of temperature, etc, but it is still concievable that their might be systems where the fundemental assumption doesn't apply and entropy might decrease. Over the years there have been a few suggestions for how to build such a thing (mostly at a quantum mechanical level), but no one has ever succeeded.

If someone does build a box that sits on a desk and converts ambient heat into energy output, then they are almost certainly guaranteed a Nobel prize. On the other hand there may be something better than the fundemental assumption, which is exactly true and excludes all possibility of such a wonderful, energy giving black box.

Re:thermodynamics, and entropy, and all that

[dragons_flight]

I reread your original post and several others, and I think I may have misinterpreted what you really wanted to know, so I'll try to clarify.

There is energy in everything that has heat. To extract that energy you have to do one of two things: make it colder or decrease it's entropy.

Thermodynamics and conservation of energy guarantee that any mechanical process that makes it colder will cost more energy to perform than the difference between the energy contents in the cold and hot states. Thus you can't have any net gain of energy through a mechanical cooling.

What you can do is bring it into contact with something cooler. Heat energy is transfered from the hot thing to the cool one and in the process you can extract some energy. This is what the devices in the original story do. In fact, ultimately this is what all thermal power sources do, though the details may be obscured by changes in pressure, volume, etc. If you have a convenient hot source, such as "waste" heat, or geothermal power then you can bring it into contact with ambient temperatures and extract power while it cools.

You want to extract heat from the air. Doing it this way, and supposing there is (optimistically) an average differance of 3 degrees C between the ground and the air above it, you could get at most 1% of the energy transfered between the two. This is the thermodynamic ideal. No system will ever do better over so scant a temp difference near room temperature. Air doesn't have that much energy, nor is it a very good conductor of heat, so it doesn't seem like this would ever be worthwhile.

So, yes, you could get energy from the air that way, but that doesn't seem to be what you want. As I said, no mechanical process will give you positive energy gain, and you don't have a cool spot to compare it to, so what else. The other option is to decrease entropy. I don't know how to break the Second Law, so I want to take the entropy and shove it somewhere else. I decrease the entropy of my stuff, which means I get energy out. Unfortunately I increased the entropy of that other stuff, which means I had to put energy in! Thermodynamics tells us that the only time you win in this situation is if that other stuff was colder than the stuff you started with. Yet again you need to have a temperature difference to get any benefit.

So no, you can't extract energy from the room all by itself. You need a temperature difference if you hope to have a net output of energy. Unless of course you know how to build the magic black boxes that lead to a net decrease in the entropy of the universe, in which your Nobel prize and billions await.

Hmmm...

[jimhill]

I couldn't help noticing that within a few paragraphs the writeup mentioned that (1) the research was partly sponsored by DARPA and (2) patents have been applied for with one already issued. Color me bitter, but as one of the taxpayers who funded the research I can't say I'm overjoyed at the prospect of paying licensing fees to MIT through the eventual commercial implementors.

I'm all in favor of government-sponsored research. They have the resources to investigate stuff with great benefits but staggering R&D costs. I'm all in favor of universities conducting the sponsored research. Grad students are cheap (I know, I was one for many years) and the brainpower is not less than one finds in industry. However, when the government pays a university to do something new, the university's benefits should be the equipment bought for the research and the prestige that comes from doing it first/best/cheapest.

is it more efficient than turbines?

[Pyromage]

this truly is the fundamental question: can this be made to be more efficient than a turbine/generator combo?

If this can be more efficient than a turbine, we can have solid-state power plants. Nukes are nothing more than a complex method of boiling water to push a turbine: if we can replace the water, we have an order of magnitude less waste! Not to mention that the core stuff is much easier to deal with than heavy water. Plus, with no pumps or pipes to break, it becomes even safer than it already is.

Or other things, say laptops? PDAs? Naturally all these kinds of applications are XYZ years off, but just imagine what would happen when we get the effiency of these things up? I'd bet that boiling water to turn a turbine is real low efficiency: if we cut out the turbine step alone, that should increase effiency by a whole lot.

This is truly cool shit.

Re:is it more efficient than turbines?

[leucadiadude]

You are confusing reactor waste with waste heat.

The waste comes from the approximately 65% of the original heat pumped into the primary circuit being lost to the river. You have to condense the steam coming out of the turbine so you can pump it. It takes a *lot* of energy to condense this steam back to water. You may not be raising a particular gallon of river(or ocean) water by more than a few degrees (usually less than 5-8F) but you are moving a whole pisspot full of cooling water through your condenser. So the total energy rejected to the environment is quite large. Real world example, the plant where I work is 34.2% efficient, which is actually pretty good for a large steam cycle power plant. The reactor core pumps about 3400MW of heat into the primary circuit and we get about 1175MW of electricity out of the turbine generator, the vast majority of the rest (2225MW) is transferred to the 1,000,000 GPM of ocean water used to cool that pesky steam back into water so it can be pumped.

Now if you could design an economical steam pump (or better yet a two phase pump - steam in and water at higher pressure out) your billions of $'s would be waiting for you. You would be able to knock the stuffing out of the Rankine Cycle and increase plant efficiency into the 50-60% range overnight.

use waste heat as -- heat

[vscjoe]

That's nice, but it seems like a lot of effort for something that, in many cases, has a much simpler solution: use waste heat for heating. A lot of waste heat could be used for heating homes and water for domestic use, and this is largely untapped in the US. (A lot of low-level waste heat could also be avoided entirely if people gave up on their inefficient water heaters and insulated their pipes.)

It's nice when people come up with better technology, but the inefficient use of energy in the US right now is not a technological problem, it's a political problem. Let's hope that we'll eventually be doing well enough that it will really become a technological problem.

Re:Heatsinks for Power

[Legion303]

Especially in laptops, this could be great, and hypothetically could power the device indefinetely, assuming an initial charge to start everything up.

You *might* extend battery life for a small length of time (measured in tens of minutes at the most) by recycling some of the waste heat, but entropy still rules. You cannot recycle all of the waste heat, so you will be unable to run your device for anything close to indefinitely.

-Legion

More info

[Raven42rac]

The Toyota Prius actually *does* reclaim heat. It does so while braking, converting the energy that normally would be transferred to the brake pads, to aid in charging up the half of the engine that is electric. So this theory is useful, and is currently in practice. I saw a report on TechTV about it. The car employs a process called "regenerative braking, which reclaims up to 30% of this waste heat, and helps charge up the batteries of the car. www.techtv.com/freshgear/story/0,23158,3357682,00. html

Re:More info

[beable]

Dude, it doesn't "reclaim heat". It uses a generator as a brake, thus avoiding using brake pads to convert kinetic energy into heat. From the link you posted:

* When decelerating or braking, the electric motor turns into a generator to charge the batteries automatically. It's a unique hybrid feature called regenerative braking. Normally when you brake, all that energy is converted into heat into the brakes. Toyota's Prius actually recaptures about 30 percent of that energy to recharge the nickel-medal-hydride batteries in the back.

To stop the car, it needs to remove kinetic energy from the car. In normal braking, the energy is absorbed by the brakes, which radiate the energy away later. Regenerative braking instead uses a generator to convert the kinetic energy into electricity (and heat), storing it in the car's batteries. Electric trains have been doing this for years.

EXTREMELY Useful

[fireboy1919]

When dealing with vehicles of any kind, the primary problem is that the energy source has to be portable. Therefore, you need a source with a high energy density. In other words, something that you can get a lot of energy from while it takes a small amount of space. Even more importantly, you want the energy in a form that you're going to use it in, or as close as possible to such a form, because conversion of energy causes a loss of energy.

To date, combustion based systems have the highest energy density of any portable energy source (barring fission reactions). Therefore, there will always be a use for it.

Perhaps automobiles won't necessarily need them - we can afford to carry additional weight - the fuel/weight ratio for automobiles is evidence of this - you can carry a LOT with a small amount of fuel for a car - and you can then drive for a long time.

But what about flying vehicles? Fuel/weight ratio is EXTREMELY important. The more efficiency that we can get the better. The best part about this is that it might remove the need for an alternator, which drains the power and adds weight to any flying device (which is significant for the small vehicles, such as the automonous surveyor helicopters used by the U.S. military). Improvements in fuel usage can mean a big deal for the aircraft industry.

Of course that's not the only industry that will benefit. Heat-differential technology is used as a power source for some areas...have you heard of geothermal and solar power plants? Know how those work? What if they could double their output? That would be significant.

Not enough information yet

[Animats]

Not too much info yet. In particular, there's no indication of how much such devices will cost per watt. This is a basic problem with things like Peltier-effect devices and solar cells; they work fine, but you need an awful lot of them to get serious power levels. If this requires something like a wafer fab to make, it will be a niche device for years to come.

Cold Fusion Redux

[Baldrson]

Peter L. Hagelstein was the guy at MIT who had MIT's lawyers churning out cold fusion patents like there was no tomorrow at the same time that MIT's official position was that cold fusion was an illusion -- and making official recommendations against its funding.

You'll still have a net loss...

[MarkusQ]

This has the same problem as the things that generate electricity from your body heat/motion/whatever. By adding such a device to the system you make the original system harder to cool (because your gizzmo acts as an insulator) or harder to move (because your gizzmo has mass) or whatever (details vary depending on how you're trying to get energy out of the system) and in the end you will reduce the efficiency by an amount that will require you to put more fuel/power/food/whatever into the original system. If your parasitic gizzmo were 100% efficient you still wouldn't gain anything, and in any real case you'll face a net loss.

Example: You put a heat-based gizzmo on your car's exhaust pipe. The temerature (and thus pressure) in the exhaust system goes up, making the engine less efficient and making you use more fuel to go the same distance.

Example: You put one on your CPU. Same deal, except your cooling system now has to work harder to keep it at a reasonable temperature, and thus uses more power.

Example: You wear a swatch. It takes a little bit more energy each time you move your arm. If you want to power a computer the same way, you'll soon be too tired to type.

The key point is in every case you will have to put more energy in than you get back out. That's why perpetual motion machines do not and can not work.

-- MarkusQ

Re:You'll still have a net loss...

[MsWillow]

Example: You put a heat-based gizzmo on your car's exhaust pipe. The temerature (and thus pressure) in the exhaust system goes up, making the engine less efficient and making you use more fuel to go the same distance.

Um, the catalytic convert is already there, and it gets rather hot. Bolting a few of these gadgets there, and on the engine block and in the radiator, won't make the temperature go up any, nor will it impede the flow of exhaust.

Mind you, I doubt it'd fully replace an alternator, but it'd help. The alternator robs horsepower, too, and if these gadgets are "free" (as in do not take more work to run), the net effect should be to increase fuel economy.

This says nothing about the cost and complexity, however. I'm not sure that making these cheap, robust and able to run along with an alternator will be a trivial exercise.

Re:Desert?

[killthiskid]

Ok, I want to point something out to all those who don't get this:

Using something like this requires a temperature GRADIANT... i.e., you could be in a desert that is 5000 degrees, and could NOT use that temperature (i.e. ambient air energy) to generate energy with a junction like this without some form of lower temperature location.

You must have two areas with a temp. gradiate difference bewtween the two that you can place this device across... in this case, the gradient can be lower (250 degrees) and is more efficient. This gradient comes from the difference in termperature between the exhaust and the surronding air.

It's all based upon the tech of peltier junctions.

Re:Hmmm... - might ruin smokestack effect

[victim]

Sapping heat from the smokestack contents will probably cause it to not work correctly.

The goal of a smokestack is to get the harmful exhaust away from the ground long enough that it disperses sufficiently before touching down.

This is done with convection. The hot gas in the tall stack creates the draw that powers it and blows the plume up after it leaves the stack, the hot plume continues to lift itself until it bleeds off too much heat, then it starts coming back down, but presumably dispersed enough to not be too noxious.

The smoke stack was designed with a known gas temperature and dispersal requirement and a desire to minimize masonry. If you take away heat from the gas you will reduce your plume altitude and cause it to come down in a more concentrated region.

I doubt you can use the thermo-generated electricty to run blowers to compensate. The `no free lunch' law of thermodynamics will probably forbid that. (Unless blowers are much more efficient than convection.)

Now, if you are just bleeding off waste steam then it would work, but most of the energy in steam is the expansion from water to steam, there is relatively little left in the puffy clouds.

Mostly unrelated note: I used to live in Pittsburg in a community where all the houses were required to have slate roofs, stone or brick exteriors and no wood trim. Even the window frames were metal. It was a fire-proof community from the days when the steel mills spewed lots of solids including hot cinders. The plume was powerful enough to carry those large distances fast enough that they were still hot enough to start a fire.

Thermodynamic efficiency limits

[Animats]

The law of thermodynamics that's relevant here is that the maximum efficiency of any heat engine is

• (T1 - T2)/T2

where T1 is the temperature at the hot side, and T2 is the temperature at the cold side. Both of these temperatures are measured from absolute zero.

This is why extracting energy from something that's just a little warmer than its environment is very inefficient. With the hot side at 100C and the cold side at 20C, you're limited to about 20% efficiency in theory, and will be lucky to get half that. Power plants generate steam at upwards of 600C, not just above the boiling point, for exactly this reason. Gas turbines run even hotter. Solar plants for power production typically focus enough energy on a target to reach the 600C level, as Solar Two in Mojave does.

You just can't extract much power from things that are merely warm. They have to be really hot.

Re:Meteor?

[dattaway]

How many kilowatts can we reclaim from this meteor?

Four smaller ones? Imagine reclaiming the heat from a cluster of these...

Cheaper and more efficient solar power?

[Ogerman]

By careful selection of materials, ENECO scientists are creating highly efficient, solid state conversion devices, called "thermal diodes," that will operate from 200 to 450 Celsius -- typical temperatures for waste heat and for concentrated solar radiation.

The very best commercial solar cells today are about 18-20% efficient. The best (research) cell on record, was 32% efficient. It's really too bad they don't give any more specifics on this semi-conductor based device, because it wouldn't be too hard to figure a rough solar cell efficiency equivalent (based on the area of a concentrating lens or mirror)

Now perhaps a more interesting use of such a device would be to increase the efficiency of fuel cells, which themselves are not so efficient and produce lots of waste heat. In a residential setting, this heat can be used for hot water and during winter months. But in a vehicle, I can't think of much use otherwise. Powering headlights, A/C, etc. would be great. Especially if they were white LED headlights of course.. (-;

For your reading pleasure:
http://www.nrel.gov/hot-stuff/press/5399world.ht ml
http://acre.murdoch.edu.au/refiles/pv/text.html

Re:This would be useless in automotive..

[NevarMore]

I beg to differ. Being an ex-geek, now a car guy, I'd love to use the heat my engine throws off.

If the heat is being converted to electricity then there will be less heat. Lower heat in the exhaust alone means lower engine temperatures because the exhaust sytem radiates the most heat near the engine at the headers (the part where the exhaust comes off of each cylinder for you non-car types). Since thats where the exhaust is hottest thats where the devices would be mounted. A lower exhaust temperature means a lower overall engine temperature.

Secondly, the big step is going from 1000 degrees down to 250 degrees. Taking that 250 down to 180 or 160 would likely allow these devices to draw heat from the engine itself. Having these devices draw energy would reduce the work a typical liquid cooling system needs to do, allowing it to be reduced in size.

Newer cars and performance cars are replacing belt driven components with ones powered electrically, most notably fans and water/coolant pumps. Elimiating belts allows the engine to put more power to the wheels rather than turning an accesory. The catch is that these devices need more power from the battery and alternator. Alternators are presently limited to about 150-200 amps, enough for a stripped race machine to run its accesories, but not enough for a street driven car with lights, music systems, and long continuous driving. These thermocouples would add more electrical power to the system and use more of the energy produced by the combustion.

The automotive example is a bit advanced for the time, but in todays science community a potential commercial use is the best way to get money for new ideas.

Sorry if that went on too long, or was too automotive for you slashdot geeks. ;-)

Replacing or augmenting cooling towers

[JordanH]

I've always been struck with how much energy is thrown away in cooling towers at turbine-based electric generating plants.

Just a little background for people who don't understand the function of a cooling tower. A turbine plant turns it's turbines by converting a liquid (typically water) to a gas (steam). Once you have the steam, you have to cool it down if you want to use it again or if you want to efficiently discard it. Some plants are designed to cool it down to the point where very little additional heat will boil it again, but this can be tricky. Some plants have been designed such that the waste steam is cooled in heating buildings through steam radiators, but it can be problematic finding customers for this steam, especially year round.

If we have an efficient way to convert this steam to energy as we cool it, then the efficiency of these plants could go way up.

On a related note, I wish the politicians were seriously working towards about energy efficiency, alternate fuels and new oil exploration now. I only hear half measures and partisan wrangling. It's like the politicians seem to believe that we can't have BOTH more energy efficiency and new energy sources. I'd like to be less dependent on some of the foreign oil now. Some of those areas just aren't looking too stable these days.

Thermal diode := Peltier Element

[wowbagger]

A thermal diode IS a Peltier element. This has been covered in EE Times among other trade journals. All they've done is take the standard BiTe diode, which is very thick, and thinned it down by creating the layers with standard chipmaking techniques. So, instead of one diode junction being about 1mm thick, they make a device that is 0.1mm thick consisting of many tens of layers.

You forget, it runs on waste heat

[Spamalamadingdong]

First your 100 HP engine will only produce 25-35 HP most of the time. Peak power is only produced during hard accerlation during cruse it's much lower and at iddle almost nonexistant.

Which doesn't make much difference, because the engine's waste-heat output doesn't change nearly as fast with throttle opening as the crankshaft output does. Even at idle (zero power) you are still burning fuel and still pumping heat out the exhaust pipe. If you can force that waste heat to do some work for you instead of just being diluted to uselessness in the atmosphere, you've accomplished something.

A hybrid vehicle would probably shut down the engine at idle and eliminate that waste-heat stream, so the thermal converter would be more useful as a way to increase the general efficiency level of the powertrain. If you can get an extra 10% off the 40% of the heat which is rejected through the exhaust, that's 4% of your fuel value; added to a 30% engine thermal efficiency, you've gained 13%. That's nothing to sneeze at.