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Power Hardware

MIT Unveils Sun-Free Photovoltaics 103

Posted by Soulskill
from the channeling-dark-power dept.
An anonymous reader writes "Researchers at MIT just unveiled a new solar power generator that doesn't need sunlight to function. The button-sized power generator can tap energy from heat, the sun's rays, a hydrocarbon fuel, or a decaying radioisotope, and it can run three times longer than a lithium-ion battery of the same weight. It is hoped that the technology may one day be used to generate power for spacecraft on long-term missions where sunlight may not be available."
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MIT Unveils Sun-Free Photovoltaics

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  • by elrous0 (869638) * on Friday July 29, 2011 @03:12PM (#36925580)

    We use this thing to run a space heater, which in turn heats up the generator and provides even more energy. Bingo, we've got an endless energy supply. String a bunch of these puppies together and goodbye fossil fuels!

    You're welcome, world.

  • I want one for my laptop. At last I'll be able to surf continuously.

    • by CastrTroy (595695)
      I've wondered about this. Laptops create quite a bit of heat. Wouldn't it be possible to capture some of that heat and charge the battery with it. Obviously you couldn't do this continuously, as per the laws of thermodynamics, but wouldn't it be possible to get some benefit from this? Also, you could probably save on running fans as well if you converted the waste heat back into electricity.
      • This would be the laptop equivalent of hybrid cars so yes technically it's possible.

        By capturing energy from the 'waste' heat, the heat produced by operating the computer would give it slightly longer battery life. Just like regenerative braking of hybrids charges a battery which then allows them to use the full weight of the vehicle for power generation while only carrying a small percentage of increased weight.
      • by wagnerrp (1305589)
        This acts like an insulator. Given a sufficiently large heatsink, you could potentially do this. Within the confines of a laptop, it will simply cause a CPU to run hotter. A hotter CPU requires a higher voltage to maintain stability, which in turn consumes more power and produces even more heat.
  • Can I put this on my walls in the summer and actually get energy from cooling my house down?
    • by Anonymous Coward

      Not as much as it takes to cool it, down but it might reduce the bill at least.

    • by trum4n (982031)
      In theory, yes.
  • by Baloroth (2370816) on Friday July 29, 2011 @03:21PM (#36925726)

    The button-sized power generator can tap energy from heat, the sun's rays, a hydrocarbon fuel, or a decaying radioisotope.

    Looking at TFA, it looks like it takes heat, converts it to light in very specific frequencies, and then uses that to generate electricity. So, any source of heat whatsoever should theoretically be able to power these. We already possess thermoelectric generators, but they tend to be effective only at very specific and fairly low temperatures. Potentially, this kind of technology could replace conventional turbines in most power plants (nuclear, coal, et al. Basically, any that directly generate heat). Anyone know what kind of efficiencies these could operate at vs. steam turbines? I know turbines are fairly efficient (but large, hence this new tech), but it seems like these could (maybe) exceed those.

    Also, if these things could be designed to require fairly low heat, then I imagine they could be used in basically any everyday device, generating low power from room-temperature heat. They don't seem to require the heat-differential of thermo-electric generators, so I wonder if they could supplement/ replace batteries in many daily electronic devices (pacemakers and hearing-aids come to mind, cell phones likely require way to much power). Anyone know if that kind of thing is at all practical?

    • They don't seem to require the heat-differential of thermo-electric generators

      In this house we obey the laws of thermodynamics! (sorry).

      Steam turbines are pretty good efficiency-wise (as a fraction of the theoretically optimum Carnot efficiency), given the constraints on operating temperature that they operate under due to corrosion considerations and so forth. If something could work with a higher temperature heat source, it could get higher efficiency.

      • Yes, in certain places, they are efficient. However, if you do not have a good enough cooling source(say a river on a very hot day, space, etc), then it does not work so well. This is to steam turbine electric generation what LEDs are to Incandescents. What is really interesting is that it could be possible to replace these every 10 years and gain more efficiency.
    • by thynk (653762)

      I think it's neat tech alright, but I'm not sure converting the heat energy to light energy to electricity is going to be more efficient than converting heat energy to electricity. Since TFA doesn't seem to give us any efficiency stats, it's hard to tell.

      • We don't ever convert from heat energy to electricity in standard power production. It's always heat to mechanical energy to electrical energy.

        Thermocouples do directly convert heat to electricity, but they're typically not for power generation (except in specialty scenarios like satellites), they're mostly for sensors.

    • Problem, thermodynamics?
      • All devices like this do not convert heat into electricity. They convert a heat gradient into electricity. The original heat is still there.
    • by timeOday (582209)

      Also, if these things could be designed to require fairly low heat, then I imagine they could be used in basically any everyday device, generating low power from room-temperature heat.

      According to the article:

      a slab of tungsten, engineering billions of tiny pits on its surface. When the slab heats up, it generates bright light with an altered emission spectrum because each pit acts as a resonator, capable of giving off radiation at only certain wavelengths.

      Is that black body radiation?

      Radiating visib

      • by Baloroth (2370816)
        That was my though exactly. TFA and the summary both say this works in sunlight, so I assume it has a fairly low threshold of heat to start "glowing". It seems like it might be possible to make them "glow" at room temperature. The law of thermodynamics wouldn't be violated AFAIK (the device would get colder, requiring new heat to be added... but there is plenty of that in our environment). The efficiency would be probably be... well, very, very low. Like I said, it'd be for low power devices. Essentially a
    • by adolf (21054)

      Why not just skip the energy conversion from heat to light that makes this new widget special, and just use the correct mix of fuel/air/catalyst/whatever to make coal/oil/gas burn -bright- (instead of merely hot), and use a photovoltaic without any new wizardry?

      Of course, it'd be blindingly inefficient compared to running a steam turbine with the same fuel. But then, so is this other gadget...

      I think there's a lot of new applications which open up with a contained method for converting heat into electricit

  • by Marble68 (746305) on Friday July 29, 2011 @03:22PM (#36925742) Homepage

    So, Can I combine it with a battery and then use it as a heat sink for the CPU in my phone?

    I only need juice until it gets hot, right?

    • by Arlet (29997)

      In order for the device to extract energy from heat, it needs to be cold itself.

      • by bar-agent (698856)

        In order for the device to extract energy from heat, it needs to be cold itself.

        Couldn't it work the other way? The device is hot and the surroundings are cold?

        • TFA indicates that the heat from any source is converted to specific light frequencies, then to electricity.

          As far as I understand the process (from TFA), heat is required but not cold.

          Both linked articles are short, you should read them.

  • Comparing this device to a battery is like comparing a gas tank to a an electric motor. A battery stores energy, while this converts it to another form.
    How much more power does it produce than a solar panel of the same weight?
    • by dhj (110274) * on Friday July 29, 2011 @03:40PM (#36925962)

      Good point... The summary left off an important bit of information from TFA:

      "Based on that technology, MIT researchers have made a button-sized power generator fueled by butane that can run three times longer than a lithium-ion battery of the same weight; the device can then be recharged instantly, just by snapping in a tiny cartridge of fresh fuel"

      So... using this to convert butane to electrical energy it lasts three times longer than a lithium-ion battery of the same weight.

      But if you look at energy density of the two fuel sources: http://en.wikipedia.org/wiki/Energy_density [wikipedia.org]

      You find that butane/propane/gas/diesel is about 45 megajoules / kg and Li-ion batteries store about 0.75 megajoule / kg. Converted energy 2.25 megajoules (3x Li-Ion) out of stored energy 45 megajoules = 5% efficiency rate converting butane heat to electrical energy using this device.

      --David

      • by Thelasko (1196535)

        You find that butane/propane/gas/diesel is about 45 megajoules / kg and Li-ion batteries store about 0.75 megajoule / kg. Converted energy 2.25 megajoules (3x Li-Ion) out of stored energy 45 megajoules = 5% efficiency rate converting butane heat to electrical energy using this device.

        You neglected to include the mass of the oxygen consumed in that butane reaction. Don't worry, everyone does. At 13 oxygen atoms per butane molecule, and ~16 grams per mole that's 208 grams of oxygen per 58 grams of butane for a stoichiometric reaction.

        Forgive me, my thermochemistry is rusty.

        • by Thelasko (1196535)

          You neglected to include the mass of the oxygen consumed in that butane reaction. Don't worry, everyone does. At 13 oxygen atoms per butane molecule, and ~16 grams per mole that's 208 grams of oxygen per 58 grams of butane for a stoichiometric reaction.

          Sorry, my point is that the lithium ion battery is heavier, in part, due to its need to carry both reactants with it. Butane can react with the oxygen in the atmosphere. However, if you didn't have the convenience of abundant oxygen, like in space, you would have to carry the oxygen with you making the whole thing 4.5 times heavier.

        • No, I'm pretty sure he got it right. The 45MJ number is based on a stoichiometric reaction of 1kg of butane with the necessary additional mass of oxygen for complete combustion. You should be getting about 60x the life of a Li-Ion cell, but you're only getting 3x, so you're operating at 5% "efficiency". The battery doesn't store the O2, nor in the O2 included in the 45MJ/kg, so it's straight algebra.

        • And you've neglected to account for the actual mass of the butane/Li-Ion reactants vs the mass of the reaction chamber and TPV. The Li-ion battery needs only a casing, all the other mass is the anode and cathode. The TPV needs a container for the butane, a reaction chamber, ducting for air to enter the reaction chamber, and the separate TPV cell.

          Then, we need to look at volumetric energy density comparisons too, as devising a container strong enough to hold a mass of butane with comparable energy in a simil

          • by adolf (21054)

            Stated like that, it sounds almost as useless as the fluff about small-scale butane-powered fuel cells and tiny little gas turbines that I saw on these very pages a decade or so ago, none of which seem to have actually materialized.

        • by wagnerrp (1305589)
          Unless you're talking about going into space, you don't have to carry your own oxygen.
          • Does it consume enough oxygen that an enclosed, non-space environment is a problem, such as an office building or airplane?
  • I am simply stunned that nobody has mentioned body heat. Think about it, all you would need to do to charge your cell-phone is put it in your pocket! Spelunking? Attach a patch to your arm and your light lasts even if you (idiotically) run out of batteries. The applications for this tech are endless, and quite frankly, the article criminally neglects this fact.
    • by ThorGod (456163)

      The problem there is biological organisms are very efficient. Off the top of my head, 500 calories will get a biker 5+ miles down the road, whereas 500 calories might get a car ~300 feet down the road. (Obviously wrong statistic, but you get the idea.)

  • I've clicked on everything I can see, and I don't see the actual efficiency rating they keep alluding to.

  • Those clever Germans have already mastered solar power without the sun.
    http://bishophill.squarespace.com/blog/2010/4/13/its-true.html [squarespace.com]

    • by rbrausse (1319883)

      Those clever Spaniards have already mastered solar power without the sun.

      ftfy, the German mentioned in the blog was the language of the Swiss news report about an article in the Spanish paper El Mundo.

      If you are unhappy about all the nations mentioned just read this [theecologist.org]

  • are in a square foot?
  • I had this idea like 5 years ago. But, being a mathematician, I merely discovered the existence of the idea. These engineers have only supplied an example implementation of the idea.

    Trivial, trivial.

    (sarcasm)

  • How old are thermocouples? Seriously folks, that someone took heat energy and created a current flow is no reason to go ga ga. Look at efficiency. Carnot heat engine is quite abstract and no matter what, there is an absolute maximum efficiency given the temperature of the source and the sink. Unless you have a bottomless pit of of sink at absolute zero degree kelvin, this sucker too would look very much like a thermocouple. Curious, interesting, might find some application in some weird situations. But in general, if ain't gonna replace either the IC engine or the battery any time soon.
    • I think the point of this thing is that it's a major improvement in conversion efficiency over thermocouples. One of the target applications is RTGs on spacecraft. So maybe you can get 3x the electricity out of the same chunk of plutonium. That's a major improvement. However, using it as a replacement for laptop batteries probably isn't going to fly.

  • Nice little gizmo I admit. Hope it turns out to actually be useful (or lead to something that is) For those who want to make a free energy device: You know people, science concluded a long time ago that you can not make more energy from nothing. If it was that simple it would have been done a long time ago. You imply that if I had lightbulb 1 and solar panel 1 in a room, then there was a wire running to another room running lightbulb 2 which shined on panel 2.. which in turn had a wire back to 1 that the en
  • It's unlikely to replace current electricity generators but it could be a good supplement. Something that converts ambient heat to electricity could be used to...

    - extract that bit more electricity from the exhaust of steam turbines and engines (ex. electric hybrid cars).

    - extend battery life of devices that get hot (ex. laptops (though good laptops run fairly cool anyway)).

    - be used to cool things down for "free" (if we can make them efficient enough). Uses: fridge walls, aircons, solar panel coolers, et

  • Seems to me that if you're on a spacecraft and you don't have some sort of nuclear power plant, you're in trouble. Or should I be thinking "probes" here?

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