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A Flexible Way To Convert Waste Heat To Electricity (asianscientist.com)
A research group in Japan has developed an inexpensive, large-scale and flexible thermoelectric generator (FlexTEG) that has high mechanical reliability and can convert heat into electricity efficiently. The findings are published in the journal Advanced Materials Technologies.
From a report: Thermoelectric conversion is one of the most attractive techniques for converting low-temperature (150C or lower) waste heat into electric power. However, widespread adoption of this technology has been hampered by a lack of suitable packaging techniques for thermoelectric generation modules that can operate in the 100-150C range. In addition, the production cost of modules for generating power at room temperature was prohibitive.
In the present study, scientists at Osaka University, Japan, have developed a method to manufacture thermoelectric generation modules in a cost-efficient manner while preserving the conversion efficiency of the modules. They mounted small thermoelectric semiconductor chips on a flexible substrate and were able to achieve reliable and stable adhesion of the electrical contacts between the chips and the flexible substrate. They called their invention FlexTEG.
In the present study, scientists at Osaka University, Japan, have developed a method to manufacture thermoelectric generation modules in a cost-efficient manner while preserving the conversion efficiency of the modules. They mounted small thermoelectric semiconductor chips on a flexible substrate and were able to achieve reliable and stable adhesion of the electrical contacts between the chips and the flexible substrate. They called their invention FlexTEG.
The industries I can see adopting this quickly:
Automotive industry: There is a continuing push to improve overall mileage of a car. If waste heat can be captured as electrical power, It will get adopted.
Power industry: These guys are already trying to up their efficiency and the competition is stiff. If the power industry can implement this it will get implemented real fast.
Industrial processes: These guys vent so much waste heat it isn't funny. But they do have space normally. I can see them intentionally re-tuning their discharge temperatures to take advantage of this. Many of these industries are (also) very competitive. If they can shave a couple tenths of a percent of their costs, they will do it.
I expect most people in the industries I mentioned will not immediately notice it. But one of those industries will see it and get it implemented. And then Ford or Chevy or Subaru will come out with a car that doesn't have an alternator in it. All of the electrical power is generated from a rebuilt radiator and exhaust system that recycles the power from the heat. A lot of alternators on a car can draw 1-2 hp. So that is now either top end power or additional MPG. Either way everyone else in the industry is now saying "how do we do that?"
I expect the same thing to occur in industrial process, only the average consumer will never hear of it. In metal refining their price per ton will drop by a penny or two consistently and everyone else will start asking how they managed to shave that much cost off without reducing anymore many power.
In either case, once this gets adopted in a particular industry, everyone in that industry will stampede to adopt it so they can stay competitive.
Architectural plans are like computer source code with a couple of differences: You only compile once.
Less than 2% if I read the article right. Which is almost 10x worse than other existing systems.
Sure it bends, but the efficiency is so crappy it's only useful for novelty applications.
> A lot of alternators on a car can draw 1-2 hp. So that is now either top end power or additional MPG.
You're correct there. The alternator needs to be able to produce about 1 HP of electricity. At 1.8% conversion efficiency, a TEG would need 56 horsepower (42,000 watts) of heat in order to generate enough electricity, in the lab. Do you think your engine wastes 56 HP as tailpipe heat while cruising around? Even at full throttle?
The car uses about 20 HP to maintain cruising speed. Is it wasting three times that amount as heat? Probably not. Let's say it's wasting 5 HP as tailpipe heat.
Obviously blowing the exhaust through "radiator" (heat exchanger) isn't going to make the exhaust cold. It'll be out almost as hot as it went in. Perhaps we can recover 1HP, on a brand new vehicle in the lab. We need 56HP, we only got 1HP. Oops.
Now go look in your tailpipe. See the soot? Notice all the rust and everything on the bottom of the car after a few years of driving? That'll probably cut efficiency in had again, so we end up getting about 1% of the power we need.
Thanks though.
If you read the actual paper, you will see that this process delivers a whopping 1.84% efficiency.
The Carnot efficiency of generating power from low grade heat is terrible, and then you slap a very inefficient Seebeck semiconductor thermoelectric generator on top of that, and about the best you can do is recharge your Apple Watch from the waste heat from your furnace.
This is not the solution to global warming.
They don't reduce emissions. They reduce the perception of emissions by the public.
The cars didn't reduce emissions the last 20 Years in real mileage, only on paper.
aaaaaaa
Another way, perhaps simpler than the math and making assumptions about waste heat, is to try this simple experiment:
Walk by your tailpipe with the car running. Does it feel like a 42,000 watt heater to you? In other words, did you get cooked when you walked by?
why would you try to sequester waist heat at the coolest part of the exhaust system on a ICE vehicle?
the exhaust manifold even at idle can reach hundreds of degrees F. Go down the pipe a little further and you have a heat mill called a catalytic converter
The average light off temperature at which the catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F. But as the amount of pollutants in the exhaust go up, so does the converter's operating temperature.
Seems to me to a pretty good place to put some of these to me.
1600F would be about 3033 kelvin/watt [K/W].
the exhaust manifold usually in the 700 to 1000 degree range depending on the load on the engine.
now you have another 1895 kelvin/watt [K/W]
so that's almost 5 K/W of wast heat that can be tapped for free.
just saying that you're just looking at the wrong places to look.
Could still be useful for many devices that don't need a lot of power. Sensors for example, where they only need to take occasional measurements (many things just don't change that fast).
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Because marketing and vendor lock-in.
Your assumptions on engine usage and efficiency are way way off. By your estimate: 20HP to the wheels and 5HP rejected as waste (you didn't mention the radiator so I am assuming you are including the radiator in this number), the engine of the car would be 80% efficient. Not only would you be upsetting known engine design and tip toeing up to (or over) the line on known modern physics and metallurgy, most engine manufacturers would be knocking on your door asking what the secret is.
Reality: An ICE engine is roughly 25% efficient (with variations per manufacturer and their patented goodies), and an ICE car has a tank to wheel efficiency around 17%-19% (to account for other losses- transmission, parasitic losses, wheel contact losses, etc). I'll use the 25% for this exercise.
Using the 20HP to maintain highway speeds. The engine produces 20HP at the shaft and this goes to the wheels. So the thermal input to the engine is 80 HP: 20HP goes to the shaft and 60HP gets rejected through the radiator, direct radiation from the engine or down the tailpipe. The majority of the heat rejection is through the radiator: This is a controlled point of heat rejection. The only heat lost at the tail pipe is the heat carried by the ejected mass of that is left over from the products of combustion (CO2, H20 and some un-combusted hydrocarbons that made it into the exhaust pipe). So if this new heat-to-electricity generator is 1.84% efficient. It draws power off the rejected heat. In this case the car is rejecting 60HP in heat and would be getting 1.1HP in electrical power out of it. This is assuming the waste heat could be channeled into a useful shape. But automotive engineers are clever, I think they could work something out.
So this would be an at a glance improvement of 1%. It is actually more though. By removing the alternator, some of the parasitic losses (that contribute to the total of 17-19%) are removed. So the car gets more power at the wheel and a higher fuel efficiency. Even if the automotive industry doesn't jump on this, you can bet the trucking industry will leap on a 1% engine efficiency improvement. And this savings will be bigger for the refrigerator trailers that draw electricity off the trucks. For them, every shipping dollar counts.
Architectural plans are like computer source code with a couple of differences: You only compile once.
So you have pushed the problem upstream to the power generation plants.
You say that like its a bad thing. Power generation plants are far more efficient right out of the gate than even the best car engine.
And I'm ignoring the fact that you can put solar panels out and cut the power plant out of the loop altogether.
(solar power doesn't have the efficiency yet to drive cars around full power on solar cells).
What are you talking about? There already are people powering EVs with 100% solar power. That's not even a question. A typical large roof can provide more than enough energy to power an EV for typical driving needs. Larger solar farms can do even better.
The power plants currently generate lots of waste heat
Power plants are FAR more efficient than the engines in cars. It's not even close. Yes they generate waste heat which can be recaptured but what do you think is easier or more sensible? Capturing waste heat from millions of inefficient cars or capturing waste heat from a few thousand already more efficient power plants?
Both Power generation and trucking are highly competitive with low profit margins and anything they can do to improve their bottom line will be done.
You think power generation is a low margin business? You might want to look closer because their margins are pretty solid on average. Gross margins of around 60% and Operating margins of around 10-15% on average. In the US most power generation is a regulated monopoly. Not software company margins but I wouldn't describe them as a low margin business either. And again, most trucking would benefit FAR more from utilization of EVs (or hybrids) than some marginal gains in thermal recapture from inefficient ICEs. You're proposing stepping over a dollar to pick up a few pennies.
Auto companies, for decades, have been playing around with thermoelectric recovery of power from internal combustion exhaust heat as a replacement or supplement for the alternator. They'd LOVE to replace that pack of moving parts, wearing bearings and slip rings, and fan-belt wear, with a quiet, solid state, black box that pulls the necessary power "for free" from otherwise wasted heat, rather than sucking down a horsepower or two (when the battery needs its starting and pre-start energy consumption replaced) and lasts the life of the car - or at least the muffler or catalytic converter.
But this won't do it. It's less efficient than the peliter cells they've already tried, and its big advantage is that it is thin and can flex, which isn't needed in a car.
The last two improvements in electric generation for cars were the result of semiconductor technology: The replacement of the double-wound, commutator-rectified generator with the diode-rectified alternator, an the relay-and-buzzer electromechanical regulator with a semiconductor regulator (currently built into the alternator).
The main advantage, which got these deployed as soon as the semiconductors were up to it, was that the alternator could generate enough at idle to immediately pick up the operating load and start replacing the battery power used to start the engine. Generators needed the higher RPMs of driving to replace the starting power. This drastically reduced the depth of discharge on the battery, lengthening its life, and also avoided the scenario of running the battery down if you have an in-city driving cycle composed of just short trips. (The other advantage was that commutators and relay-regulators wore out, requiring regulator replacement and generator rebuilds occasionally during the life of the vehicle, while slip rings on an alternator can last until the bearings also fail.)
A waste-heat scavenger doesn't generate substantial power until the exhaust system is up to temperature, or close to it. That would put you back to the lots-of-short-trips-kills-the-battery scenario if you replaced the alternator with a heat scavenger. It would be even worse, because you'd still be powering the running loads off the battery even as you drive away. So you still need the alternator.
By the time the scavenger is putting out, the alternator would typically have replaced the starting power and any pre-starting energy use, and be just running the operating loads. 3/4 horsepower is close enough to a kilowatt as not to bother with the difference, and your typical vehicle's run power is well below that, so (even with its slight inefficiencies) it's not putting enough running load on the engine to make much difference So far, peltier cells (apparently better than this invention) haven't been attractive enough as a fuel-saver to justify their expense.
There are other issues too. (Like increased complexity and opportunity for failure, whether they can stand the heat levels needed to scavenge significant power, and the vibration to last the life of the car without an expensive repair.) But the above lack of improvement on an alternator seems to me to be enough of a killer in itself.
Having "free" energy available doesn't mean the value of the-amount you can collect and put to good use will exceed the direct and reliability risk costs of collecting it.
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