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MIT Combines Carbon Foam and Graphite Flakes For Efficient Solar Steam Generati 110

Posted by timothy from the science-fiction-future-awaits dept.
rtoz (2530056) writes Researchers at MIT have developed a new spongelike material structure which can use 85% of incoming solar energy for converting water into steam. This spongelike structure has a layer of graphite flakes and an underlying carbon foam. This structure has many small pores. It can float on the water, and it will act as an insulator for preventing heat from escaping to the underlying liquid. As sunlight hits the structure, it creates a hotspot in the graphite layer, generating a pressure gradient that draws water up through the carbon foam. As water seeps into the graphite layer, the heat concentrated in the graphite turns the water into steam. This structure works much like a sponge. It is a significant improvement over recent approaches to solar-powered steam generation. And, this setup loses very little heat in the process, and can produce steam at relatively low solar intensity. If scaled up, this setup will not require complex, costly systems to highly concentrate sunlight.
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MIT Combines Carbon Foam and Graphite Flakes For Efficient Solar Steam Generati More

MIT Combines Carbon Foam and Graphite Flakes For Efficient Solar Steam Generati

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  • Sponge-like? (Score:5, Funny)

    by ArcadeMan ( 2766669 ) on Tuesday July 22, 2014 @08:27AM (#47507183)

    SpongeBob Square Solarpanel?

  • Finally (Score:1, Informative)

    by Triklyn ( 2455072 )

    now here's a renewable i could get behind.

    • Re:Finally (Score:4, Informative)

      by Mr D from 63 ( 3395377 ) on Tuesday July 22, 2014 @08:42AM (#47507287)
      “There is still a lot of research that can be done on implementing this in larger systems.”

      Translated;

      “There is still a lot of research that MUST be done TO IMPLEMENT this in larger systems.”

    • Do you realize that the #1 Greenhouse Gas is water vapor?

      http://www.skepticalscience.co... [skepticalscience.com]

      • :) was not aware, but i think you should propose a water sequestration program. it'll be real effective for you know... governing water loss from the oceans.

      • Re: (Score:1)

        by Anonymous Coward
        If we take all of human's current power usage, rounded up to 20 TW, and applied that toward water vapor production, just using enthalpy of vaporization and no heating, we could produce ~300 gigatonnes of water vapor, which in five hundred years will catch up to the ~1400000 gigatonnes of water vapor evaporating from the oceans each year, assuming there is no mechanism for removing water vapor from the sky. Of course, if you put some of that energy into actually pumping the water vapor beyond the tropospher

      • Re: (Score:2)

        by geekoid ( 135745 )

        Did you know that's becasue of increased CO2?

  • De-salination? (Score:5, Interesting)

    by Squidlips ( 1206004 ) on Tuesday July 22, 2014 @08:36AM (#47507237)
    Could it be used for de-salination
    • Possibly, but there is no indication if this material will see fouling or depositing from such a process.

    • Re:De-salination? (Score:5, Funny)

      by ArcadeMan ( 2766669 ) on Tuesday July 22, 2014 @08:46AM (#47507331)

      Faster CPUs, better solar panels, radiation shielding and drinkable water for all the world.

      Graphite. Is there anything it can't do?

    • This is exactly what I was thinking about. I am betting all along the Middle East and African coastlines this would be a killer technology to both drive steam turbines and produce potable water concurrently. I would bet the issue would be salts and other particulates clogging the water passages though. Might work as a final stage distillation in a plant that is completely solar powered though.

      The other issue for using it as an electric (or rather mechanical) generation source is the fact that it needs di
      • This foam looks pretty fragile to me. I would guess with any flow rate approaching what would be required to run a steam turbine, the foam would be torn apart. I think that is one reason the researchers didn't point this out as a likely use.

    • Re:De-salination? (Score:4, Insightful)

      by Immerman ( 2627577 ) on Tuesday July 22, 2014 @08:56AM (#47507401)

      Oh, now *there's* an idea. I suspect you'd have issues using saltwater though - when the water is boiled the salt would be left behind within the foam. In a closed-loop system that might not be an issue as the distilled water would be reintroduced to the reservoir preventing excessive concentration of salts, but otherwise you'd almost certainly end up with salt crystals completely coating the foam, Which would either render it immediately ineffective or eventually build up to such a level that it dies as a solid block of salt with an embedded carbon lattice.

      Of course desalination isn't cheap, so it might be cost-effective to replace the foam regularly. You might even be able to rinse the crystals away with filtered seawater in order to reuse the foam.

      • Re:De-salination? (Score:5, Insightful)

        by Chris Mattern ( 191822 ) on Tuesday July 22, 2014 @09:37AM (#47507689)

        You wouldn't boil the saltwater in foam, genius. Use properly prepared and recycled water as a heat transfer fluid and use that heat to distill seawater in tanks built for that process.

        • Brilliant.

          Of course then you're no longer using the foam for desalination, as I interpreted the question, but only indirectly as a replacement for some other heat source. If this foam (plus the sealed, transparent, insulated tanks containing it and the water) can truly be produced more cheaply than an energy-equivalent solar concentrator then that could indeed be a viable option. It seems like it would be a *lot* less fault tolerant than a sheet of polished metal bent into a parabolic trough on a stationar

      • But you could burn away the carbon and have an unlimited supply of sea salt.

      • Or have a closed loop exchange heat with an open loop, depending on the relative tempratures. If you have a liquid that significantly exceeds the boiling point of water in the closed loop there should be enough room to operate. Your going to loose effiency, there is a ton of Sun and open area in many dry places.

    • They speak of micropores in the sponge material. This would likely foul with particulate in the water. The water in the system would need to be fairly pure to start.

      That being said, if it is an efficient steam generator, perhaps, it could be used to provide the heat source for desalination systems such as what are used onboard navy ships for the production of fresh water?

    • Re: (Score:2)

      by HiThere ( 15173 )

      Not directly. If you fed salt water into the system is would get blocked up with salt crystals. Indirectly, yes. The output is steam, and you could use that to heat the salt water to the point where it started rapidly evaporating. (You'd want to recycle the "working fluid" water, so you don't just bubble it through the salt water, but instead you use the salt water to cool the steam until it condenses and then feed it back into the heater.)

  • I hadn't previously heard of this MIT' before. I hope we see good things from them.

    • Re:The next generation of MIT? (Score:4, Funny)

      by ArcadeMan ( 2766669 ) on Tuesday July 22, 2014 @08:44AM (#47507303)

      It's MIT Prime, a.k.a. MIT: The Next Generation.

    • There's another MIT headline further down the front-page: "MIT's Ted Postol Presents More Evidence On Iron Dome Failures"

      I'm guessing timothy copy-pasted that headline then deleted everything except the first few characters, but forgot to zap the apostrophe. All to save himself the arduous task of typing "MIT".

      Well, I'm just speculating, of course.

      • Are you suggesting that Timothy (or any slashdot "editor") uses a keyboard? I thought those were too old-fashioned for them and they did all their entry using 12th-generation iPad femtos with tactile inputs that are derived from Minority Report

  • But (Score:2)

    by rossdee ( 243626 )

    You've still got to convert that steam into electricity, presumably with a turbine. so what is the overall efficiency?
    And do you get bits of graphite and carbon foam gumming up your turbine?

    • that's what I came to post.
      the inefficiencies of steam-powered power-plants are in the moving parts of the rankine cycle. this device helps create the steam (one of the four major parts of the rankine cycle), but we can't harness it to do work.

      • I was imagining a great big terrarium.

      • > the inefficiencies of steam-powered power-plants are in the moving parts of the rankine cycle

        No, the inefficiencies of the Rankine cycle come from fundamental laws of thermodynamics and are inherent to all heat engines.

    • Re: (Score:3)

      by pavon ( 30274 )

      The quickest numbers I could find [mpoweruk.com] say that at the scales of large power-plants, the generator is very efficient, but the turbine not so much, around 50%. This would put the system as a whole at around 40% efficency sunlight -> electricity. That's competitive with the best solar voltaic systems tested in the lab, and 50-100% better than practical systems on the market. Assuming their system really does scale up to power plant sizes, of course.

    • Re: (Score:2)

      by LoRdTAW ( 99712 )

      I would worry more about condensation of the cool steam in the turbine itself. The only way this would be good for a turbine is if the steam can be further heated via a solar super heater.

      This is why power plant boilers have a superheater which passes the steam from the boilers steam drum through a heat exchanger in the hot exhaust stream of the boiler. This brings the steam temperature up well past the boiling point of water and prevents steam from condensing in the turbine. Imagine a turbine spinning at 3

    • Re: (Score:2)

      by LWATCDR ( 28044 )

      Simple, low.
      The greater the heat differential the greater the efficiency. To use low temperature aka low pressure would require massive turbines. BTW temperature and pressure in a gas are very related. So much so that you can almost treat them as the same thing.

    • Re: (Score:2)

      by geekoid ( 135745 )

      It needs 1/10 the solar energy then previous methods.
      That means mirror don't have to be as precise, uses less area, cheaper, can make smaller plants.
      I still don't know what data centers aren't put in sunny area and power from Industrial Solar Thermal.

      • Re: (Score:2)

        by spitzak ( 4019 )

        I don't think it produces 10x as much steam for a given amount of solar energy. What it does is produce steam at a solar intensity 1/10 of the level at which other things produce steam (the other thing is producing zero steam at the temperature this one is producing steam at).

        I think the real result is you need the same amount of reflector as for other schemes, however it can concentrate the solar energy on an area 10 times as large, which may be much less expensive (due to it not requiring as much accuracy

    • A turbine is the wrong technology. I think that this would work better with a Sterling Engine [wikipedia.org]. The steam temperature is (obviously) 100C, and the cold side could either be ambient air temperature or water.

      The Sterling crank output could drive a generator, and there are some existing Sterling designs that use the linear motion of the pistons as magnets with a coil for electrical generation. The boiling water is a closed loop that is the hot side of the Sterling engine.

      This lends itself to a modular design

  • details (Score:4, Informative)

    by Anonymous Coward on Tuesday July 22, 2014 @08:46AM (#47507325)

    They found they were able to convert 85 percent of solar energy into steam at a solar intensity 10 times that of a typical sunny day.

    • i didn't get this sentence when i first read it, but now it makes sense.
      basically you'd need a magnifying glass on top of this thing.

  • costly concentration (Score:5, Insightful)

    by Immerman ( 2627577 ) on Tuesday July 22, 2014 @08:46AM (#47507327)

    > if scaled up, this setup will not require complex, costly systems to highly concentrate sunlight.

    So, mirrors are costly now - does that imply that this carbon foam stuff is cheaper to produce than a sheet of polished stainless steel? If so that *is* promising.

    • I was looking a cds the other day and found that printed cardboard sleeves were a few cents more expensive than the cheap slim line plastic cases with a paper insert. I wasn't expecting that so who knows it might be cheaper.

    • Re: (Score:2)

      by tomhath ( 637240 )
      This process still requires some mirrors; it starts to work at about 10x maximum solar light. But that's still a couple of orders of magnitude better than any other system using mirrors.

    • Mirrors are cheap. Water to wash a few hundred acres worth of mirrors is relatively expensive. Especially in the middle of the desert where we like to park solar installations.

      • And what makes you think it would be any more water-efficient to wash the glass/plastic covering an equal area of foam-solar reactors?

    • So, mirrors are costly now -

      Mirrors are cheap, it's the several acres of tracking mechanisms which the mirrors are mounted to that are expensive.

      The idea is, if the steam generator requires less concentrated light, you can save money on the solar tracking mechanisms, which lowers the final cost of each solar array.

      • I had more in mind a simple solar-trough design -admittedly less efficient than a tracking mechanism per unit area, but much less to go wrong. And if you have people go out a few times a year to adjust the orientation for seasonal variances you can still capture much of the energy you would from a tracking system. For desert situations where the environment is harsh and the land is essentially useless for anything else it can make a lot of sense.

  • I don't normally bitch about editing on summaries but, good heavens, does anyone even read this shit? The same "85% of solar energy..." line is used twice. The final line begins with "i-e" which means "that is," but it doesn't reference anything relevant to scaling. What's the appropriate tag here? !sensical? !edited? !proofed?

    I'm probably just burning through karma here, but I like to think that if it's a "legitimate" rage, that the body had a way of rejecting the negative effects.

  • Made of carbon? Damn! We're lucky we've been producing all this carbon with our cars or we'd never have a chance to solve this climate change problem!

  • No concentrators. Really? (Score:4, Interesting)

    by necro81 ( 917438 ) on Tuesday July 22, 2014 @09:02AM (#47507447) Journal
    The summary states "if scaled up, this setup will not require complex, costly systems to highly concentrate sunlight". But the video itself says that all of their testing was done with light at 10x normal solar intensity. In other words - you still need concentrated sunlight, you won't be able to set this beaker out in the bright sunshine and expect it to start boiling. The authors contrast it with solar power towers that concentrate sunlight to 100x or 1000x, but it still sounds like you'd need concentration of some sort.
    • If there were a viable system, you would still likely WANT to use mirrors just because they are low cost and make better use of the higher cost heat transfer elements.

      • I thought the mirrors in solar-powered towers were specially made for reflection (and thus more expensive) and had huge problems with keeping them clean. Don't quote me on this though.

    • Re: (Score:2)

      by dbIII ( 701233 )

      "if scaled up, this setup will not require complex, costly systems to highly concentrate sunlight"

      A parabolic mirror trough is an example of something that is not complex or costly.

    • Re: (Score:1)

      by cp5i6 ( 544080 )
      see fresnel lenses
  • This is all neat, but it's very far from practical application. What they've created is essentially just a very dark lump of porous carbon that can draw in water and exchange heat with it. Interesting, but not revolutionary by any means. Most important questions still remain:
    • What's the production cost of this material?
    • What are the scaling properties? (Presumably, since we're talking about surface heating here, pretty limited.)
    • What's the longevity of the material under non-stop usage?
    • What's the steam outle

    • Re: (Score:1)

      by kanweg ( 771128 )

      "Interesting, but not revolutionary by any means."

      To the contrary, it is fucking brilliant.
      1) Instead of having to heat up bulk of water (like what you do if you use a boiler), they only heat up the water that is actually going to be converted into steam. So, the start-up time is greatly improved.
      2) The steam generated passes through the foam up, where the foam is even hotter. The steam gets heated to a higher temperature, making it more useful to generate power. Another way of looking at the foam, is recog

      • 1) You're confusing your home water heating with a power steam generator. 2) Exactly, the foam is nothing but a heat exchanger. What exactly does this do that a heat exchanger doesn't? Look, fundamentally what they've got here is just a highly porous black body. They use the blackness to absorb lots of solar radiation energy and use its porousness to transfer heat to a working fluid. Neat, but not really such a revolution. As for hexane as a working fluid: not sure a highly flammable gas with a flash point

  • What, can't be bothered to review the headline before posting, Tim?

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