One use case not being discussed here is that by using these types of devices, you can power a device/sensor out in the field without a really expensive installation. You can run these off of a motor housing, compressor discharge, steam line, etc. It is about being able to provide power where it is very costly to bring.
To install a sensor/instrument in a plant,refinery,etc., you have to set up scaffolding and/or use a cherry picker, run cable (usually armored) through cable trays, bend and install conduit, have all of the right junction boxes, glands, etc. You've already spent 10's of thousands just to get power out to your device.
Solar is not really an option in some places. Either you've got no sunlight because you're in a pipe rack and you've got to route a cable from a PV panel (go back to installation cost) or you're in a hazardous rated area of the plant where you have explosive atmospheres and need special Ex rated equipment.
This of course brings in its own failure modes which can often go undetected - sensor stopped reporting because the motor broke / was replaced with a cooler model / was used less by a production change / doesn't get as hot in winter / not enough diff in summer.
Yes, I was a bit hasty with undetected. The situation is complex.
I have a site which has sensors that go off for various reasons. I add heartbeats to detect this. Now I have a site with sensors that may go off for a number of reasons, and an alert panel telling me they are off all the time.
As the alerts aren't actionable (ie, I expect sensor Y to go off every day in the winter around midnight and come back again when it warms up) I add a filter to ignore the alert from it around midnight.
I now have to make sure I handle all the other edge cases - how long is it safe to have this sensor off? 50% of the sensors off? Every third sensor off? What if there is a really cold/hot snap lasting through the day or several days?
All of these questions are edge cases, and they require complexity to solve them. Complexity means bugs. The most common bug by far is that situation X was detected by the sensor, but didn't make its way to us for edge cases.
I have a Peltier-powered fan that I put on top of my wood stove. It spins extremely fast. I like it because I can tell how hot my stove is by looking at the fan, instead of walking over to the wood stove and looking at the thermometer: https://www.amazon.com/s?k=wood+stove+fan&sprefix=wood+st%2C...
I like the general idea, but it strikes me as a little poignant that so many of these sources of waste heat could just be wrapped with insulation instead? Certainly pipes and ducts - though in cases where the heat is truly waste (and is being intentionally dumped into a cooler environment, like from refrigeration or heat pumps) it does seem like converting it to electricity is a win, at least.
In the cases where you are dumping heat, I believe these devices can have the opposite problem of effectively insulating the heat source.
I think it might technically be possible to have a very conductive heat-engine. But it seems to me like most options are still less conductive than leaving them out.
Wastewater comes to mind. A lot of it is heated, either directly (from e.g. showers, cooking) or indirectly because it was stored in toilets.
Edit: But then again, capturing and re-using the heat energy directly and saving the energy cost for heating via e.g. an electric heater would probably be even more efficient than extracting some of the heat as electricity.
Do you have a way of utilising or storing electricity/heat? If so, either are more efficient than not doing so. For example, if it's cold where you live and the heating is usually running... just expelling the heat from your fridge into the house is efficient. If you are cooling, it's not. Electricity would be better... or at least piping the heat out.
This device exists, you replace a vertical section of your sewer pipe with a copper heat exchanger pipe. The HX heats up your incoming cold water when you take a shower. The HX must be vertical because in a vertical sewer pipe, surface tension makes the water spread out and wet the entire inner surface of the pipe for good heat transfer.
I looked into the economics at one point. Would be great for a laundromat or hotel, not so much for the average single family home.
The economics mostly depend on the temperature of the water coming into your house and the ease of install in your house. They are supposedly code on new construction in large parts of Canada now.
The economics were also better when copper prices were lower.
Some sources, you might want to move the heat away (ie, CPU), maybe these loads of pipes they have are the same. But yes, point taken, insulation first. Ockhams Razor: don't multiply entities beyond necessity.
On a High-End Desktop Chip? YES! Intel made such a cooler recently[1]. But on mobile/low power devices it might be worthwhile to have them run a little warmer (within spec) but take the heat energy back via a peltier element. Would be interesting to see such an element directly on die feeding back into the chip directly, sort of an electric rebreather for a chip.
It seems like the devices would insulate the server-farm. That might not be worth it, because you'd need extra cooling to offset the higher insulation.
DoE says they breakeven is 2.5 - 7 years. That's in the US, imagine how much of a slam dunk it is in countries with carbon prices and higher energy prices.
These devices actually require a similar amount of water to be moving through the drain pipe/heat exchanger and the cold water line that's refilling the water heater. So they're really only effective during showers.
This would be worse for efficiency than uninsulated pipes. It would be wrapping them in a conductor to more efficiently take away the heat that is supposed to stay inside.
Of course in the limited cases where the application requires the heat to be transferred to the destination, you wouldn't use this method. Those pipes are likely heavily insulated.
But most cases, moving hot waste, the loss of heat is a side effect (the waste material just happens to be hot), and may in fact be an undesirable side-effect that squanders energy. Now, they don't need to squander that energy.
Easy example is a chimney - they're only trying to get rid of the exhaust gasses we don't want inside, and DGAF if it is cold or hot. In fact, heat exchangers are often installed to attempt to capture some of the lost heat and minimize losses.
Same for waste liquids going for treatment, or actual product exiting a hot process and going into a cold/ambient temp process -- they've got to dump the heat, far better to grab some energy on the way out.
> Easy example is a chimney - they're only trying to get rid of the exhaust gasses we don't want inside, and DGAF if it is cold or hot. In fact, heat exchangers are often installed to attempt to capture some of the lost heat and minimize losses.
Good example, except that you need a certain amount of heat to carry away the water (steam). I believe the rule of thumb for old-style furnaces is 80% efficiency with the 20% carrying away the water vapor.
Yup, and there's the same issue with using these on internal combustion automobile or truck exhausts - the density change of increased cooling could might change the back pressure/suction at the exhaust port and reduce the engine efficiency. It would surely be a consideration on highly tuned race motors, but I have no idea if the magnitude of the effect would be even noticeable on street cars & trucks. It is certainly fairly small, as you can drive through a puddle that soaks the exhaust and billows out clouds of steam, sucking out far more heat vs this thermoelectric system, and the engine doesn't even notice.
So, sure if you did it naively, without checking & compensating for secondary effects, you might have a net problem. But I'd be highly confidant that a bit of R&D and engineering design changes would easily take care of it.
There are many industrial processes that produce large amounts of waste heat. Capturing some of that can make sense. But I guess unless you're retrofitting existing installations you get better efficiency with different solutions than wrapping stuff around a pipe.
I think most industrial waste heat is indeed wasted. You don't tend to build for example chemical factories close to where you would have offices or homes.
An air conditioner is a heat pump. It uses energy to pump heat from one end to another. One of these thermoelectric generator devices is basically the reverse, it generates energy when heat is pumped through it. There is perhaps an analogy here to a water pump, pumping water from one place to another, and a water wheel, generating energy when water is pumped through it.
Take an ordinary house. The default, low-energy state is the one it tends to if we don't mess with it. The inside and outside of the house come to about the same temperature as energy leaks in through the insulation and holes in it, though slowly.
Now we put in a heat pump. This changes the system. With a little energy input, we capture the energy in the inside of the house, and we move it to the outside. The energy state of the system changes, it begins to gain energy as we put some in to create the heat differential.
Then we attempt to capture this heat differential. We place a heat engine, which one of these devices is, across our temperature differential. Assuming total efficiency for both processes, which we do not in reality have, our heat engine undoes the heat differential and produces for us the exact amount of energy we ourselves put in to create that heat differential. The inside and outside now come to some resting state, possibly with a constant heat differential upheld by the pump and actively sabotaged by the engine. Theoretically, we get net 0 energy and dysfunctional air conditioning, but in practice, we get a net loss of energy to inefficiencies.
The same applies to the water analogy. Imagine two tanks of water connected by a porous wall. The state it reaches naturally is that both tanks are at the same level through water seepage, though it is slow. If we place in a pump, we get a pressure differential across the tanks: one tank becomes higher and another lower. Then we place a wheel across the differential to take advantage of that pressure. Energy is generated, and at the same time the height difference is lost. Again net 0, though in reality you will experience a lot of inefficiencies.
If the point is to do air conditioning, you cannot recapture energy from the heat. Just running the air conditioner at a lower power achieves the same result more efficiently. Similarly with the water pump, it will in reality be more efficient to just not pump as much water up, and you will reach the same result.
Not really : Peltier-based devices like this add (some) resistance to the heat flow. This added resistance means the air conditioner (or any heat pump, e.g. a fridge) gets less efficient.
I think the energy captured by the device will always be lower than the extra energy needed for the heat pump.
A device like this is not useful in a system where you are actively pumping heat around.
Often these kinds of things collide with the laws of thermodynamics and end up decreasing the energy the system provides to its endpoint by the same amount that is extracted. Not always, just often.
A classical example would be putting some thing to collect the energy generated by turning a rotating door to power lights in a lobby, it is probable that this will end up causing the people using the rotating door to expend the exact amount of extra energy that is captured by the system (probably because the easiest way to collect the energy is to put some extra resistance on turning the door)
So why do it? Well in the case of the rotating door it is easy to see why, because by having everyone give just a little extra of their personal energy (like two extra spoonfuls of cereal in the morning, and a sip of orange juice) the company manages to externalize the cost of lighting their fancy lobby and nobody even notices that the energy was taken from someone else to do it.
Put a notice about how the lobby is powered by green energy, that's really the icing on the cake.
Complete aside: Has anyone actually implemented this classical example?
I've heard it mentioned a few times but always assumed the people floating it hadn't thought about orders of magnitude enough: a "sip" of orange juice is indeed a lot of energy, about 80 kJ [1], and if you could extract that much energy from one person every 10 seconds you'd get 8 kW, which could power a decent sized lobby if the lighting is efficient.
But to extract 80 kJ over 1 m... you have to push with 80 kN, or 17 thousand pounds (or 1.4 TRex bites worth of force [2]). More realistically, if we have everyone push with an annoying but manageable 50 N (about 10 pounds), we'd get 5 W, which might power a single (dim) LED bulb.
As I said, this is a bit off topic for the original post, but the common theme is that people tend to confuse "extracting some energy" with "extracting a useful amount of energy in a cost effective way" (they also tend to overestimate mechanical energy). This on top of the thermodynamic constraints you mention to start with.
Some of them have been implemented at small scale. I believe the "floor that turns foot traffic into power" has been implemented a couple of times. Certainly the "lift a rock to power a light" has been implemented several times. I believe someone even stuffed a soccer ball or three with things that generate power when the ball is kicked.
In fact it's a perennial design winner in various design contests that are judged by designers and not engineers or scientists. It looks awesome when you design some cool little gadget that "harvests" enough energy to power a small town from a soccer ball or something. The fact that it doesn't work is not a disqualifier in those contests. It't totally what I'd enter at this point if I were going to enter such a contest, it's an obviously winning play.
But the floor that converts foot traffic to energy doesn't generate much energy, and is very unpleasant to walk on. The soccer ball that extracts energy from the kick means that it has extracted energy from the kick, so it doesn't go flying away like a soccer ball should but is more likely playing with a ball of damp laundry. Guess what kids don't want to play with? The "lift a rock to power a light" does work, but it provides a lot less light for a lot less time than people think, and the rock ends up being pretty heavy. (But it does have at least some legitimate use cases, just not as many as you might hope.) The bike that extracts energy from the biker is so insanely unmarketable that what's winning in the market right now is the exact opposite, the electric bikes that supplement the biker's power.
(Also I will add as honorable mention the "solar powered X" that is spec'ed with one or two orders of magnitude too few solar panels. Putting panels on the top of your electric car may even be theoretically worthwhile in the long run, but only as a small supplement to the car. The idea that you'll be toodling down the highway at 75mph on 10ish square feet of solar panels is risible. Multiply that by some large two-digit numbers.)
I vaguely recall back in one of my engineering classes we did the math on turning all of the stationary bikes at the gym into power generating units.
I believe the result was that the value of power generated was so utterly dwarfed by the costs in copper, inverters, etc. - not to mention additional maintenance costs - that it was at least an order of magnitude outside of making sense.
Some of those economics certainly have changed over the last 15 years but many (I’m looking at you, copper) are rather fixed and won’t go down over time.
Also
> 1.4 TRex bites worth of force
I have never seen T Rex bites as a unit of measurement before and I love it.
> I vaguely recall back in one of my engineering classes we did the math on turning all of the stationary bikes at the gym into power generating units.
I’ve heard the story (myth?) that Edison’s house had a gate that was relatively hard to push, and which visitors asked him to fix but he refused - and it eventually turned out it was providing energy to his locally dug well, pulling some water out with every opening @ closing of the gate.
> a "sip" of orange juice is indeed a lot of energy, about 80 kJ [1], and if you could extract that much energy from one person every 10 seconds you'd get 8 kW, which could power a decent sized lobby if the lighting is efficient.
What's the total energy expended to produce those 80 kJ worth of orange juice, though? You need to power agricultural machines, food trucks, etc. etc.
I see it every few years as well, and I'm glad I finally did the math (it's not that hard actually)! It's probably a good freshman physics example, to make people think about orders of magnitude and energy. Or a good "Fermi question" if you're one of those places that still interviews with those.
A shortcut for this is that a horsepower is about 750 watts (745.7 or so), and that you can extract one horsepower from a fit human for a very limited amount of time before they stop humaning. You can sustain about half this, or a little less, with the correct human. These super-approximate numbers come in useful for, e.g., human-powered airplane design. (The equivalent horsepower numbers for a horse are about 15 hp peak, 2 hp sustained. Naming is hard.)
So, if you're proposing a system that extracts energy from N humans at a time, and you're hoping to get more than N hp out of it... you're probably off by a bit. If you're hoping to do this without the humans noticing, you're probably off by an order of magnitude.
The goal is to harvest heat that is already being wasted by escaping to the environment. They aren't putting an additional load on the system unless they are foregoing insulating the pipes but there are a lot of cases where pipes are not insulated and these devices would be applicable.
Consider the hot pipe example. Sounds like free energy, right? Hot pipes leak heat energy, it’s what they do. However, pipes are also usually suspended in the air, and air is a really good insulator. You put this device on a pipe, you might start wicking heat away from the pipe faster, making your boiler or whatever need to expend more energy to keep the pipe hot.
Using a wheel to harness the power of people has been around for a while but often does not end well (see Arnold in the opening sequence of Conan). There was also a soccer ball generator. Kids had to be forced to "play" with that one too.
How much electricity does this contraption need to generate, before it's accounted for its own embodied energy (that is, the power needed to manufacture it)? Probably more than anyone would ever actually use one.
It reminds me of solar panels on cars. It sounds great if you don't think too hard about it, but a highschool physics course can easily prove how completely useless it would be in practice.
Ideas like these end up being nothing but virtue signaling, whether people know it or not.
Practically all of our "green" solutions rely on the fact that their energy-intensive manufacturing is done somewhere with lots of cheap (and polluting) energy sources.
Show me a wind-powered lithium battery factory and I'll change my mind.
It can make sense to combine stoves used for heating with peltier elements. When the heat is used at lower temperature than the combustion, you can get electricity on the exchange. So you run your boiler at 105% normal capacity and extract 5% electricity. This generates electricity at the price of gas. Of course, your boiler must have the extra capacity, and the additional components are an investment.
It's not always so straight forward. You would want your return to be lower than about 55C for a condensing boiler otherwise they're a lot less efficient.
It still should radiate into the house, helping to bring the temperature up to the thermostat point. If you're capturing any of that heat and converting it for any reason, your boiler's simply going to have to work harder to do its job.
It's the first law of thermodynamics, isn't it? I'm not a physicist.
It depends on what the converted energy is used for. If you use it to power a device in the house then it's quite likely most of that energy will end up as heat in the house again.
Any effeciency numbers? Mindful how ineffeceint peltiers are and this reads like it is nothing new beyond adding liquid metal heat-pipes and an array of lots of them so you can wrap around a non-flat surface more easily.
Also - not aware of many hot pipes of waste heat. beyond some power stations and then they already use that heat for things like heating green houses and other initiatives.
Heck even my fridge and freezer's waste heat (probably best source in a home) is only waste in the summer, otherwise is passively warms my home. Then you have heat exchanges.
So really would love to see the numbers and the waste heat they are on about and compared to existing less technical solutions - like using it to heat a greenhouse.
> That version exhibited a total power output of 56.6 watts when placed on the hot surface, the scientists said.
> “Think about an industrial power plant with pipes hundreds of feet long,” Priya said. “If you can wrap these devices around an area that large, you could generate kilowatts of energy from wasted heat that’s normally just being thrown away. You could convert discarded heat into something useful.”
Whole kilowatts! And it would only cost a few hundred thousand pounds in expensive peltier materials!
Though not directly related, this does remind me of an idea I once had.
I live in the Caribbean. My house effectively has a few heat pumps running most of the time (split air conditioning units) as well as a dryer and a water heater. Why can't the heat moved by those units be used to heat water or to dry clothes? By using the heat directly, there wouldn't be a need to use a Peltier unit or deal with the associated losses.
A combination of interface (how do you get the water heater to use the excess heat?), quality (a/c waste heat isn't that hot), and matching generation with demand.
There are power plants that use excess heat for heating. The term is cogeneration or combined heat and power.
In the Caribbean you get unlimited free energy from the sun, considering that solar panels are very cheap you could just rig the system to dump all excess power to the water heater, but considering you already get unlimited solar power you could just place the water tank in the sun to heat water. If that is not enough a home made aluminum can heat pipe plus water pump or just a long black hose with a water pump would nearly boil your water during the day.
Using solar panels to generate electricity is nominally illegal here actually. I know other Caribbean islands use solar water heating pretty extensively, but it's never been a thing here. I suspect it's a matter of lack of Government and business incentives as we've always been a fossil fuel based economy with relatively affordable electricity.
My father in-law once asked me if one could charge a phone using body heat. I did some calculations but the thing is that if the heat difference is small, the conversion efficiency goes down too. As others suggest, insinuating the source is much smarter if you want to save energy losses, and with much simpler (cheaper) technology.
Insulation is great if your goal is to keep the heat from escaping. With this solution, the goal is usually the exact opposite.
For example, you don't wrap your laptop in a blanket to keep it nice and cozy. Likewise you don't wrap insulation around the motor block in an ICE vehicle. And if you pump coolant around through pipes, the whole point is to radiate out the heat so that it cools down. That heat is actually a problem that you are trying to get rid off.
The example of a heating pipe in the article is a bit unfortunate of course. Isolating those would be a good idea. Unless they are interior pipes in which case the heating system heating the house would not be that big of a deal.
> Likewise you don't wrap insulation around the motor block in an ICE vehicle.
Well... for every rule there is an exception I guess, there was a Mercedes demonstration vehicle that used a modified diesel engine without a coolant loop and insulated head to keep the heat in the engine. It never made it to production due to cost but the thing was ridiculously efficient.
you still need to radiate the heat you produce; the device cold side heats up during operation, up to the point where the conversio stop, so you're going to have to cool it.
besides, water in a ice engine need to be cooled down fast, at the rate these device extract temperature from the sources, you're going to have to need a huge surface area being extracted, or two set of radiators - one to control the circuit temperature, the other to cool the generators.
these device application are a lot narrower than one might expect.
I had this exact idea of using peltiers to reclaim energy from waste pipes. Think about big industrial systems. I knew from reading the specs that existing peltiers wouldn't cut it. So I decided to let it go until progress in material science (maybe graphene) made it more efficient. There is a theoretical design that is radically more efficient. It uses an S shape design, but it's not possible at the moment. This looks to be using ordinary peltier designs but sliced up. This could be used like a stove-top heat pump that uses a peltier, and the heat from a stove to power a fan that helps circulated the warm air more efficiently. Of course this would add some insulation around the pipe too, so it may not be the free lunch it seems.
That sounds great! Can you share anything about the materials and/or performance?
I am only an armchair inventor. I once got as far as registering a company, and filing a business plan, but I noped out of it.
I just like to follow the science and noodle with the equations, hoping for something interesting.
The main problem for this application, I think, is maintaining a temperature gradient. So you add a heat sink to the cold side, but that only gets you so far. And then you have the extra cost and CO2 burden of manufacturing a heat sink (and aluminium is particularly dirty).
My plan was to look for places with a sustained temperature gradient. So, I sandwiched a peltier between the hot and cold pipes in my old house, to power some LEDs. As long as the house was occupied, there was always cold running water on one side, and hot tap water on the other.
So, if I was building, say, a power station, where cold water is being pumped in. I would arange the cold pipes close to the hot in one spot, insulate the outer surfaces, and stick a peltier generator in between. You can also use heat pipes (like on CPU fans) with coolant, to wrap the source hot/cold pipes, without needing a flexible peltier.
Gosh this is cool - yeah, it's basically BiTe pressed wafers in S form. Test results never were validated so I can't put faith in the results unfortunately, they were pretty good though.
Redesigning for temperature gradient is quite brilliant. My thinking was along the lines of an aerogel heat sync. In theory it could maintain a gradient much longer than current tech... at astronomical cost!
Reach out if you'd like to continue the discussion, I miss this project.
What’s the theoretical limit of heat -> electricity + hydrolysis?
It seems if we could capture electricity from a space shuttle reentry and make hydrogen/methane during descent, this would enable less energy intensive launches.
I’d imagine this would be done if it were possible, but the extreme burst of energy likely isn’t conducive to being absorbed by hydrolysis.
Thermodynamics requires temperature gradients, unless the object you're taking energy from is much hotter than it's surroundings then any energy extracted will be minimal and could be offset by the extra energy needed to run the collecting device.
This is true and so the solution isn’t really like some magic free power system, it’s more a tool we can use a niche applications where it might be more straightforward to just wrap something around a hot pipe and get a few watts of power than to run electrical wiring.
Would an approach like this generate a useful amount of electricity if used in a power plant setting? I.e. From the steam/condensed-but-still-hot water after it leaves the turbine?
Gas turbines in power plants can get very complicated when it comes to recovering waste heat. Some of them can hit something over 60% efficiency (vs cars where I think a typical ICE gets somewhere over 20%?). I think it’s mainly comes down to being worth the additinoal cost and complexity in a large power plant but not so much in an office building or road vehicle.
it is hilarious to me that this is coming out in the same year that Formula 1, who has tried to pioneer this technology for the last decade, has given up on its potential and removed it from the regulations.
The MGU-H that is being removed from F1 is based on entirely different technology, and has a much higher grade of waste heat to work with (being that it works with ICE exhaust gases. It's being removed mostly because of cost, though I would be unsurprised to find that it returns in a few years, if F1 stays ICE powered, simply because it is a really good thing for a hybrid car (minimized turbo lag, and it can recover extra electrical power).
Well... maybe. If your pipe is carrying waste heat to a radiator of some sort (cooling tower or whatever), insulation doesn't matter, because the heat is going to escape to the environment anyway.
absolutely not; that would make them unable to dissipate heat. Trying to use a peltier element to them to recover energy is just futile, it'd be better to have an peltier that cools it off by wasting energy instead.
To install a sensor/instrument in a plant,refinery,etc., you have to set up scaffolding and/or use a cherry picker, run cable (usually armored) through cable trays, bend and install conduit, have all of the right junction boxes, glands, etc. You've already spent 10's of thousands just to get power out to your device.
Solar is not really an option in some places. Either you've got no sunlight because you're in a pipe rack and you've got to route a cable from a PV panel (go back to installation cost) or you're in a hazardous rated area of the plant where you have explosive atmospheres and need special Ex rated equipment.