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Power Science

Body Heat Energy Generation 214

Posted by CmdrTaco
from the i'm-sweating-right-now dept.
BuzzSkyline writes "Researchers in Belgium have developed devices to harvest the waste heat our bodies throw off in order to convert it to electricity to run devices such as a wristband blood oxygen sensor and an electrocardiogram shirt. As a side benefit, the power sources help cool you down and keep you looking cool, all while running sundry micropower devices. In fact, the researchers mention that the energy harvesting head band works so well that it can get uncomfortably cold. In that case, they say, 'This problem is solved in exactly the same way as someone solves it on the body level in cold weather: a headgear should be worn on top of the system to limit the heat flow and make it comfortable.' But it would be such a shame to cover up the golden heat-harvesting headband with a hat."
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Body Heat Energy Generation

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  • What's next? A body-movement powered (or better, heat & movement hybrid power), fully functional stillsuit?

  • Screw that (Score:4, Insightful)

    by elrous0 (869638) * on Wednesday December 23, 2009 @10:59AM (#30535210)
    You're wasting the real potential of this thing. I live in an area that gets hot as hell in the summer. If it really does get "uncomfortably cold," I'd pay good money for a whole suit made of the stuff.
    • by dintech (998802)

      Good idea and hurry the hell up with that next shipment of Spice.

    • Re: (Score:3, Informative)

      by Thelasko (1196535)
      Unfortunately, the summary and the Physics Buzz article grossly misrepresent the research being done here. The device only becomes "uncomfortably cold" when ambient temperatures are below what are considered comfortable by most people. The AIP article also notes that it is unlikely that this device will ever be able to harvest enough energy to power current portable devices. They instead suggest that future devices be designed around the power output of this device.
      • Re: (Score:3, Insightful)

        by StikyPad (445176)

        Right, that's the problem.. you can't "harvest" heat unless you have a significant temperature differential, and a 20F difference (~95 to ~75) is laughable.

        Also, I question the idea of "waste" heat. The body heats itself enough to keep the extremities functional, and little beyond that. Making the body work harder could potentially result in hypothermia, although it could also result in a higher "resting" metabolic rate, so it really depends on whether or not the user has extra calories to spare.

        There are

        • by Xtravar (725372)

          Yeah, I find it kind of scary that there's a headband that will sap your brain of heat. That can't be good for your brain, can it?

          Still waiting for the devices that run off sugar in the blood stream so we can all stop being fat.

        • Re: (Score:2, Insightful)

          by interploy (1387145)

          Also, I question the idea of "waste" heat. Making the body work harder could potentially result in hypothermia, although it could also result in a higher "resting" metabolic rate, so it really depends on whether or not the user has extra calories to spare.

          I question your relative activity level. Have you ever shoveled a driveway clear of snow? I can go out in 10F in coat/gloves/hat/scarf and have to strip down to just a sweatshirt inside of thirty minutes. I give off so much heat that my clothes are literally steaming. You're talking as if the body has a finite amount of heat to give, but that's not the case. The heat output is equivalent to the amount of energy expended. If this thing can't power a gameboy, there's no way it can sap so much heat it risks gi

      • by timeOday (582209)
        Not even a wristwatch? Some run 10 years on a button battery.
        • by Thelasko (1196535)

          Not even a wristwatch? Some run 10 years on a button battery.

          The article notes that this technology out performs human mounted solar cells. Seeing as there are currently solar powered wrist watches, [citizenwatch.com] I believe this new device is capable of powering a wristwatch, but that's about it.

    • Turn on your TV during the "infomercials".
      Half of those are for some kind of device or chemical that will let you burn "all that fat" in days with minimal effort.

      These devices siphon the energy from your body in order to work.
      And you get that energy from food.
      See where I'm going with this?

      How many heat-harvesting headband do you need to burn out a single twinkie?
      Who cares! I've seen them sell patches made out of "green tea extract" that should "burn calories" when you wear them.
      10 to 1 that you get to burn

    • Re:Screw that (Score:4, Informative)

      by Wardish (699865) on Wednesday December 23, 2009 @03:58PM (#30538220) Journal

      Sorry to say, since it's a heat engine, it moves heat from warmest to coolest. In hot weather YOU are the coolest. The device would warm you up.

  • by Hatta (162192)

    I don't understand how it can get cold. You can harvest energy from a temperature gradient, but once the headband is at ambient temperature, there's no more gradient. How does it get cold?

    • Re:Cold? (Score:4, Insightful)

      by oodaloop (1229816) on Wednesday December 23, 2009 @11:04AM (#30535244)
      It feels cold because it's sucking heat out and using it. So it's constantly leaching heat out. Hence it would feel cold. Simple, really.
      • by Thanshin (1188877)

        It feels cold because it's sucking heat out and using it. So it's constantly leaching heat out. Hence it would feel cold. Simple, really.

        Heat can't be turned directly into energy, only difference in heat.

      • Re:Cold? (Score:4, Insightful)

        by Hatta (162192) on Wednesday December 23, 2009 @11:29AM (#30535512) Journal

        It's not sucking heat out, that would actually require extra energy input. It's not a pump, it's more like a water wheel.

        But my question has been answered. It doesn't get below ambient temperature. We just don't feel ambient temperature as cold as it actually is, because air is a pretty good insulator.

        • by Thangodin (177516)

          Yeah, I was wondering the same thing. Either the ambient temperature has to be pretty cool, or the thing has to be fitted with liquid coolant--which makes it essentially a battery. Leaving this out of the explanation makes all the claims pretty underwhelming.

        • We just don't feel ambient temperature as cold as it actually is, because air is a pretty good insulator.

          Also, we are warm blooded so heat generation is constant like a treadmill. In order to prevent heat buildup and feel comfortable, the heat has to transfer from the body to the environment which requires a temperature difference, which is why 98.6F ambient temperature feels hot to us, but 72F feels comfortable because the air conducts away heat at a balanced rate of exchange. As you mentioned air is an

      • by Thelasko (1196535)

        It feels cold because it's sucking heat out and using it. So it's constantly leaching heat out. Hence it would feel cold. Simple, really.

        From TFA:

        at lower ambient temperatures, the heat flow rapidly exceeds the sensation of discomfort and the device turns into uncomfortably cold object. For example, at 19C, the TEG already produces 3.7 mW, but the sensation of cold becomes too annoying.

        At 19C you would start to become uncomfortable whether you were wearing this device or not.

    • by Thanshin (1188877)

      If it gets as cold as the ambient, it's as unconfortable as not wearing anything on that clothing slot. Which, beyond the polar circle, for example, can be between "quite" and "fucking".

    • Re: (Score:3, Insightful)

      by sakdoctor (1087155)

      Those of us who descended from the mammalian evolutionary tree, keep our bodies warmer than ambient temperatures.

      • Those of us who descended from the mammalian evolutionary tree, keep our bodies warmer than ambient temperatures.

        What about those of us who were brought to life from the primordial marinara soup by the touch of His Noodley Appendage, you insensitive clod!

      • by srobert (4099)

        That would include almost everyone on Slashdot.

      • by lewiscr (3314)
        You must live up north. In the Southern US, we try very hard to keep our bodies below ambient tempature. It avoids all that nasty dizziness, coma, and death business.
    • Re: (Score:3, Informative)

      by confused one (671304)

      It's better at conducting heat away from your skin than air; and, because it's extracting energy and using a small radiator as a heat sink, it remains colder than the skin. It only feels cold. It would never actually reach ambient because your body is keeping it above ambient, with the asumption that "ambient" is well below body temperature. From the article:

      "At 22C, it produces about 30W/cm2, i.e., close to the theoretical limit of power generation on people at this temperature in a compact device. There is, however, a drawback of such high power generation: at lower ambient temperatures, the heat flow rapidly exceeds the sensation of discomfort and the device turns into uncomfortably cold object. For example, at 19C, the TEG already produces 3.7 mW, but the sensation of cold becomes too annoying. "

      • Re: (Score:3, Funny)

        by vegiVamp (518171)
        So in warm countries (or during a heat wave), when ambient is *above* body temperature, do yo wear it inside-out ?
        • That might work with some modification but you could see how that might not be a good idea (hyperthermia bad). They did mention an increase in power production when the wearer moves from outdoors to an air conditioned indoor environment.
      • by ceoyoyo (59147)

        Your quote dropped a "micro" symbol. 30 W/cm2 is enough to power my laptop from a bit of skin about the size of my thumb nail.

    • Re:Cold? (Score:5, Informative)

      by Issarlk (1429361) on Wednesday December 23, 2009 @11:23AM (#30535466)
      The headband is at ambiant temperature, but your body is much warmer. Heat flow from your body to the headband and leaves a cold sensation on your skin. The material of the headband applied to the body is probably a good conductor of heat ; it's like with a piece of metal that feels cold to the touch and a piece of wood that doesn't while both are at room temperature.
      • by lazn (202878)

        How about those who live in a desert where the ambient temperature is HIGHER than body temp?

        • by RsG (809189)

          Broadly speaking, I'd expect those living in deserts to find other solutions. You don't wear the same clothes in two diametrically opposite climates - why would that change simply because the cloth is high tech?

          The obvious, not yet developed choice for people in a hot environment would be cloth with embedded solar collectors. If you want to hedge your bets, bring some of each, and dress for the climate as needed. Of course, all of this takes for granted the affordability of such solutions, but to be blun

      • by Thelasko (1196535)
        TFA states that the headband only becomes uncomfortable below 19 degrees Celsius, which is below common room temperatures. One could argue that a human would be uncomfortable below room temperature wheather they are wearing this device or not.

        However, you are correct. Humans are not good at judging temperature. We are good at judging heat transfer, which is why metal objects seem colder at the same temperature as nonmetals.
    • by carvalhao (774969)
      Although I can't name it, there was a movie in the 80's about a building that recycled human body heat for energy... until the computer went awry and started killing everyone for their body heat.
    • by mcgrew (92797) *

      Seventy degree air (21.11 C) is comfortable. Jump into a pool of eighty degree (26.66 C) water and it feels like it's freezing. Water that comes from your cold water tap in the summer is close to the ambient temperature, but soak a rag in it and wrap it around your neck and it will cool you off quickly (until the water in the rag raises its temperature to match yours).

    • by selven (1556643)

      As you said, the headband approaches ambient temperature. In the winter, ambient temperature is -4, ie. cold.

    • by ceoyoyo (59147)

      At a comfortable ambient temperature your body is usually a good deal warmer than the air. I'm sitting in a room with about a temperature of 22 degrees right now, and that's a little warmer than I'd like, but there's still a healthy temperature gradient between that and my 37ish degree core temperature.

      Try sitting in a bath where the water is at ambient air temperature and see if it feels cool or not.

  • by rolfwind (528248) on Wednesday December 23, 2009 @11:04AM (#30535252)

    If this is true:

    In fact, the researchers mention that the energy harvesting head band works so well that it can get uncomfortably cold.

    Wouldn't it be extremely marketable? Especially for the military with troops in hot places and with bulky body armor and probably all types of personal electronic equipment to keep charged?

    • Re: (Score:3, Interesting)

      by dvoecks (1000574)
      That only works if the air temp is lower than 98.6. This sort of thing works by harnessing the difference in energy between the "hot" side and the "cold" side. Sure, it would work well at room-temperature, but who needs cooling at room-temp? About the only time you really need cooling when the air is significantly below normal body temperature outside is when you've got a fever, or are heavily exerting yourself. I definitely could get behind a headband that powers an mp3 player when I'm on a jog. It co
      • Re: (Score:2, Funny)

        by Adhemar82 (958364)
        Time to invade Siberia!
      • by vegiVamp (518171)
        You'd still have a temperature gradient, just the other way round.
      • by mcgrew (92797) *

        Sure, it would work well at room-temperature, but who needs cooling at room-temp?

        If you live in a dry climate, over a hundred degrees F isn't bad unless you're in the sun. In a humid climate eighty five is uncomfortably hot, as your sweat won't evaporate as well. It probably wouldn't work well in Arizona in the summer, but it would be great in a place like St Louis or (moreso) Thailand.

        It would have worked well in Viet Nam, probably wouldn't work at all in Iraq.

      • by dintlu (1171159)

        While human core temperature is generally 98.6, our skin temperature is typically between 85-95 F, depending on environment and where on the body the temperature is measured.

    • by Thelasko (1196535) on Wednesday December 23, 2009 @11:39AM (#30535616) Journal

      Wouldn't it be extremely marketable? Especially for the military with troops in hot places and with bulky body armor and probably all types of personal electronic equipment to keep charged?

      This also defies the laws of thermodynamics. Allow me to explain:

      1. In Iraq, the surroundings are hotter than the human body. Therefore, it is impossible to harvest energy from human waste heat because heat is flowing to the human, not away from it.

      2. The temperature gradient between a humans body and it's surroundings is not large enough to generate significant amounts of electricity. If it was, internal combustion engines would be a hell of a lot more efficient than they are today.

      3. If the temperature gradient between a human body and it's surroundings were large enough to generate significant amounts of electricity, you might want that energy to keep warm!

  • by v1 (525388) on Wednesday December 23, 2009 @11:05AM (#30535256) Homepage Journal

    As a side benefit, the power sources help cool you down

    Typically if you take something that's trying to dump waste heat, and install something that recovers power from that heat, it creates an insulating effect, reducing the cooling the object was receiving. Heat can't be turned directly into energy, only difference in heat. Adding a heat reclamation system doesn't help cool something down because the power it's getting is from the temperature difference, not the heat itself. Instead it takes power from the temperature gradient, and as such reduces the temperature gradient, thus reducing cooling efficiency.

    • Re: (Score:2, Informative)

      by maxwell demon (590494)

      Well, unless they built a perpetual motion machine of the second kind. :-)

      But actually, it may be due to the fact that normally you don't really feel the real temperature, but when it's cold, the temperature of the air directly at your skin is still higher than the surrounding air (unless there is wind, which is why you feel cold faster when there's wind). If this device has better heat transport to the surrounding air (e.g. because the surface to air is larger than the surface to you skin), you may feel co

      • Well, there are wrist watches that wind from simple body motion.

        If you combined the device this article covers with something that "winds" from simple body motion, the combination of the two might be more practical, either generating energy from motion or from temperature differential.

        Of course, carrying around the batteries to keep a good store of the energy on hand might be a pain too.

    • Typically if you take something that's trying to dump waste heat, and install something that recovers power from that heat, it creates an insulating effect, reducing the cooling the object was receiving. Heat can't be turned directly into energy, only difference in heat. Adding a heat reclamation system doesn't help cool something down because the power it's getting is from the temperature difference, not the heat itself. Instead it takes power from the temperature gradient, and as such reduces the temperature gradient, thus reducing cooling efficiency.

      This would be the reason why fremen stilsuits would be impossible, right? Even as a kid it struck me that someone was trying to have a free lunch.

      • Re: (Score:3, Interesting)

        by vlm (69642)

        This would be the reason why fremen stilsuits would be impossible, right? Even as a kid it struck me that someone was trying to have a free lunch.

        The part that kills the stillsuit is there is an inherent minimum energy requirement to separate drinkable water from uh, bodily output, and there is also an inherent minimum energy requirement to condense water out of the air. Unfortunately, to generate that energy, the human body requires MORE water than would be produced by either process... Healthy human kidneys already do a pretty near optimal job of "recycling water".

        Human powered camping filters only work because only a small fraction of the water

      • Re: (Score:3, Funny)

        by dintech (998802)

        Drinking your own pee has always been free.

      • by drinkypoo (153816)

        Actually, there's no reason stillsuits have to be impossible. I've been thinking a lot about this and the only conclusion I've come to about them is that if they're black, there must be some kind of magic insulating layer in between that and the wearer. That, or that you would never ever wear them outside without some covering. The black, presumably, is for protection from UV. But there are other possibilities; you could cover it in solar cells, and do electrolysis of water (or operate a desalination system

    • by JerryLove (1158461) on Wednesday December 23, 2009 @11:49AM (#30535698)

      Yes. Power is generated when heat is moved from an area of high concentration (your head) to an area of low concentration (the air).

      If the device facilitates that transfer in order to get more energy from it; then it would indeed cool you down. It requires only tha the headband be more effective at radiating heat than your skin is.

    • by Shotgun (30919)

      As a side benefit, the power sources help cool you down

      Typically if you take something that's trying to dump waste heat, and install something that recovers power from that heat, it creates an insulating effect, reducing the cooling the object was receiving.

      Unless, the device dumping the waste heat originally had a very inefficient path for dumping the heat. You can come in, install a more efficient "heat dumping" path and then bleed off some of the difference in the form of useful energy.

  • Welcome to the desert of the real...
  • Free Energy? (Score:3, Insightful)

    by lobiusmoop (305328) on Wednesday December 23, 2009 @11:11AM (#30535338) Homepage

    FTFA:
    "Imagine portable electronics that run on a free, reliable energy source."

    Um, I'm already practically there. I can get a KWh out of the wall for 5p (10c), charge up an iPhone from dead to full for a quarter (5KWh battery capacity there) and can get as many cheap chargers as I like. On my list of concerns right now, body-heat chargers are pretty far down.

    • by Shikaku (1129753)

      Brown energy is the new green! The brown energy is the product of human heat generation. This brown energy can be used to fertilize crops.

    • Re: (Score:3, Insightful)

      by Anonymous Coward

      http://en.wikipedia.org/wiki/Battery_(electricity)#Rechargeable_battery_chemistries [wikipedia.org]

      I'd love to know where you get 5 kWh from an iPhone battery. Li-Ion batteries have an energy density of 128 Wh/kg, so your iPhone battery must weigh 39 kg.

      Granted, a 5 kWh Li-Ion battery will cost a fortune, so for something of that capacity, you're more likely to use a lead-acid battery of car/alarm/emergency light fame. That battery would weigh 129 kg. My brother-in-law has an iPhone; I'll ask him if it came with a dolly fo

    • Um, I'm already practically there. I can get a KWh out of the wall for 5p (10c), charge up an iPhone from dead to full for a quarter (5KWh battery capacity there) and can get as many cheap chargers as I like.

      Um, I think you're off by at least three orders of magnitude there.

      On my list of concerns right now, body-heat chargers are pretty far down.

      Well, as long as you spend your whole life no more than a few hours away from a power outlet, that makes sense.

      I'm still not buying the body-heat solution, though. Let's get something that runs off blood sugar instead.

    • by oodaloop (1229816)
      And once your phone never needs to be re-charged again, you'll wonder how you ever lived with something as archaic as plugging it in when it was low. Also, it may be cheap to you, but that doesn't mean it's cheap to, say, the environment. Having the population of the UK charge their devices off of coal-fired power plants instead of human generated heat isn't exactly optimal.
      • by vlm (69642)

        Also, it may be cheap to you, but that doesn't mean it's cheap to, say, the environment. Having the population of the UK charge their devices off of coal-fired power plants instead of human generated heat isn't exactly optimal.

        Its a "well known fact" that it takes about 10 kcal of petroleum products to make about 1 kcal of food, on average. Natgas turned into fertilizer, diesel powered everything, processing plants, shipping, etc. And the efficiency of the conversion device is probably not too good. And the efficiency of the human body at turning food into heat is not too good.

        So, ignoring capital costs, unless the UK power system is substantially below 1% efficient, you'll end up environmentally ahead using wall outlet power.

        • by Skater (41976)
          Flaw in your argument: people already exist and eat that food anyway. This idea is to take heat that already exists and is being wasted (sometimes) and make it do useful work for us.
          • Of course, if this device is pulling heat faster than the surrounding air, you will need to burn more calories than before to continue powering it.

            If you're in a situation where your body is already dumping heat as fast as it can (ie, you're sweating) it's recapturing waste energy. If you're in a cooler environment, though, the heat will need to be replenished by burning calories to maintain temperature. Users would either lose weight or eat more.

            Of course, all of this is a fair amount of bullshit since the

    • by mcgrew (92797) *

      It's only "free" in the sense that an empty potato chip bag is free. You paid for the bag when you bought the chips, and you also paid for the waste heat when you bought the chips.

  • by Anonymous Coward

    If your head gets too hot with the hat on, simply put another heat absorber around your hat. If your head gets too cold again, put on another hat.

  • Canada (Score:3, Funny)

    by Galestar (1473827) on Wednesday December 23, 2009 @11:25AM (#30535482)
    I live in Canada... I need all of my body heat as it is.
  • I was a student at this university, some 5 years ago all students who visited IMEC had to do an experiment for them, namely wear a watch with this technology and then it'd generate a few microwatts out of the difference between the outside and body temperature. They even gave a funny speech related to The Matrix before the experiment. It seems they've improved a lot in the meantime, though it's a shame the article doesn't mention how much power it currently generates.

    • Ummm, yeah it did. The pulseox meter required 62 uW. A watch sized device could theoretically generate between 100 and 600 uW per the article. The headband was generating 30uW/cm^2 for 3.7mW at 19C during their testing. The shirt required 0.5mW, was generating 0.8 to 5.5mW. All depending on the users activity level and the ambient conditions.
  • While that's pretty interesting, I'd like to see a non-invasive wristband blood glucose sensor. Now that would be something.

    • Re: (Score:3, Informative)

      If you need continuous monitoring, you probably need more accuracy than non-invasive means will get you.

      As of 2003 (when I spent a summer internship at Sensys Medical), the best non-invasive method (near-infrared spectroscopy) would get you within 20% of the actual value - and that's with an initial blood sample for calibration. IIRC, most consumer devices are accurate to 10-15%, with cheaper clinical devices being accurate to 5%.

      Knowing the hardware necessary for even that degree of accuracy as well as th

      • by wcrowe (94389)

        Hey, thanks for the post. I've never talked with anyone who has worked in the field before, so it was interesting.

  • I'd really be interested in seeing if this could safely be used inside the body somehow. You could use it to power pacemakers. More relevant to my own interests, it could possibly power an internal assembly for a cochlear implant processor. It would be nice to get rid of all of the external bits so I could run, jump, swim, and wear hats normally.
    • You have to have a heat sink as well as a source. Some component would have to remain outside to act as a radiator.
    • by TubeSteak (669689)

      I'd really be interested in seeing if this could safely be used inside the body somehow.

      Probably not very useful internally because you need a temperature differential.
      Unless you're willing to poke a permanent hole in the skin for a radiator,
      existing (rechargeable) battery technology is much better for internal use.

  • How many watts would this kind of thing provide? Would it be enough to power a basic computer? I suppose it depends a lot on ambient temperature, wind speed (which constantly renews the temperature differential) and body heat (higher when you're physically active).

  • If they can make an appliance that gets electricity from body heat and can be "uncomfortably cold", could they turn it into an air-conditioning device that run on its own, or even generate electricity while cooling? _That_ would be an invention.

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