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posted by n1 on Tuesday September 30 2014, @04:37AM   Printer-friendly
from the dilitium-crystals-next dept.

New system aims to harness the full spectrum of available solar radiation.

The key to creating a material that would be ideal for converting solar energy to heat is tuning the material’s spectrum of absorption just right: It should absorb virtually all wavelengths of light that reach Earth’s surface from the sun — but not much of the rest of the spectrum, since that would increase the energy that is reradiated by the material, and thus lost to the conversion process.

Now researchers at MIT say they have accomplished the development of a material that comes very close to the “ideal” for solar absorption. The material is a two-dimensional metallic dielectric photonic crystal, and has the additional benefits of absorbing sunlight from a wide range of angles and withstanding extremely high temperatures. Perhaps most importantly, the material can also be made cheaply at large scales.

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  • (Score: 0) by Anonymous Coward on Tuesday September 30 2014, @09:36AM

    by Anonymous Coward on Tuesday September 30 2014, @09:36AM (#99926)

    Why complicate the description? First, the "solar absorber" is a light absorber. But we already have a name for the property of absorbing a very large fraction of light: Such substances are called "black".

    So what the researchers have done is to create an almost perfectly black substance. Yes, that doesn't sound as fancy as "solar absorber", but it accurately describes what it is, while being immediately clear to anyone who understands English.

    And BTW, by calling a black substance as what it is, you free your thinking from being restricted to the one application, converting sunlight to heat, and are free to think of other applications as well.

    • (Score: 4, Informative) by geb on Tuesday September 30 2014, @11:45AM

      by geb (529) on Tuesday September 30 2014, @11:45AM (#99941)

      You have failed to read/understand even the summary. The material is not perfectly black, although it would look that way to humans. The idea was to have a material with the inverse absorbtion spectrum as Earth's atmosphere - i.e. strongly absorbing in the visible wavelengths that air allows through, but weakly absorbing/emitting in the rest of the spectrum.

      Such a material is very highly specialised and fully deserves a distinct name. Anybody running a mirror array type solar farm would see a boost in efficiency above mere black material, through losing less heat to black body radiation.

      I'm not convinced that concentrating arrays like that have much future in electrical generation, since photovoltaic panels can make much better use of efficiency of scale in manufacturing, but still an interesting concept being described here.

      • (Score: 3, Interesting) by Anonymous Coward on Tuesday September 30 2014, @01:22PM

        by Anonymous Coward on Tuesday September 30 2014, @01:22PM (#99984)

        I'm not convinced that concentrating arrays

        It would make better use in large mirror array concentrators. The kind that heat up salt. If it doesnt reflect light back out as easily it could also remove some of the problems with those sorts of setups. Blinding of airline pilots and attraction of birds. As big mirrors are dead easy to make. Concentrators have a better 'overnight base load' than solar cells. The downside is the maintenance of the pumps as salt is massively corrosive.

        It seems to be made for exactly that sort of instillation.

        If you combine it with a solar cell that perfectly reflects everything it doesnt use. That could be interesting too. As the rest could go into the concentrator.

        Rooftop solar cells I think have a limited lifetime. As the power companies have realized they do not have the infrastructure for everyone to have one. No one wants to pay for it (especially the people buying the solar panels who have been sold the dream of 'free power'). The power companies will play regulatory games to really mess it up. They have the capital to do it too. I think the money party will soon end on them. You are already starting to see serious issues with it in Hawaii and Arizona. Which has nothing to do with the tech (which is only getting cheaper and better) but a money/political thing.

        I remember the promise of nuclear 'too cheap to meter'. Too cheap to meter means a 'flat rate' to build the grid. You will start to see consumption only plans (what you have now but with more law behind it). You can generate all you like but if you use any you pay for it. Meaning you may get the hours of 11 to 2 free but the rest of the time when you need power you pay for it. No credit. Basically they will not buy your power. They are already starting to get rid of the subsidies. They may take it one step further and say you can not 'game the system' and do a shunt switch with a battery bank. My state already has 'gaming rules' bought and paid for by the power companies. You will then see full 'off the grid' AC/heat/refrigeration systems. Then laws against that and more regulatory goo.

    • (Score: 2) by bob_super on Tuesday September 30 2014, @04:11PM

      by bob_super (1357) on Tuesday September 30 2014, @04:11PM (#100043)

      Forget that sham invisibility clock from yesterday, I only wear the New UltraBlack.

      Or drop it down the pool for maximum heating. (they can modify it to not absorb the wavelengths that don't make it past the surface, if that' cheaper)

  • (Score: 1, Interesting) by Anonymous Coward on Tuesday September 30 2014, @11:29AM

    by Anonymous Coward on Tuesday September 30 2014, @11:29AM (#99938)

    Areas that get a lot of sun, like the desert, also get very cold. This absorber will need to handle the temperature extremes, for many years, to be of practical use.

    • (Score: 3, Interesting) by VLM on Tuesday September 30 2014, @12:31PM

      by VLM (445) Subscriber Badge on Tuesday September 30 2014, @12:31PM (#99967)

      And be durable enough to have bird poop washed off. Speaking of washing off, the spectral characteristics will rapidly, like in a month or so, approach the characteristics of dust/dirt.

      This is why its a complete waste of time and money for actual generation purposes.

      What it could be VERY handy for is stuff like absolute calibration of thermal and color sensors and playing thermal games with absolute light level detectors (aka modern IR thermopile detectors). And lining the interior of optical things as an anti-reflection coating like real cameras or telescopes or microscopes etc.

      "the material can also be made cheaply at large scales"

      LOL yeah wake me when its cheaper than steel. That's the economic problem, unless land is very expensive its cheaper just to toss down twice as much black iron pipe than to toss down something only slightly cheaper than a solar panel.

      Passive solar is incredibly difficult to pull off economically. Greenwashing is cheap, and not trying to run a profit is cheap, and allowing for short lifetimes / high maint is cheap. But real deployable profitable systems with a net ecological gain are VERY hard to engineer.

      • (Score: 2) by edIII on Wednesday October 01 2014, @12:56AM

        by edIII (791) on Wednesday October 01 2014, @12:56AM (#100203)

        But real deployable profitable systems with a net ecological gain are VERY hard to engineer.

        You seem to have a good understanding of it then. What do you think is the best idea at the moment to do that?

        --
        Technically, lunchtime is at any moment. It's just a wave function.
        • (Score: 2) by VLM on Wednesday October 01 2014, @12:04PM

          by VLM (445) Subscriber Badge on Wednesday October 01 2014, @12:04PM (#100408)

          I tried all kinds of ideas and never got a net positive.

          Strangely enough the best solution although super high labor was what boils down to a black trash bag in a window with a fan blowing in it when the delta T between inside and outside is low. You'd think throwing away a bag every week or so would waste more oil than just burning it directly, but there was a precise sweet spot around 50F where it actually paid off. If your labor is free and the environmental damage of the labor is zero (LOL) etc.

          I had trouble thermal modeling passive air collectors, unless you get really optimistic about maint just burning the wood would be net ecologically cheaper.

          The problem is we have a really well engineered system for solar collection turned into thermal heating and its called chopping down trees and burning them in a stove. You have to net total system beat that, and its VERY hard to do.

          I'm not talking about "I'm not living in a windowless house, I'm gonna have windows, so lets optimize for the most BTU input per sq ft" thats just sound engineering. I was trying to design collectors... something I'd bolt on to my house. The engineering of the total lifetime system costs (economic and environmental) never worked. AFAIK other than fudged books for greenwashing no one else has ever pulled this off either on a very small scale.

          I mean, I can build a solar oven that slow cooks food. So "just move house air thru it", right? But on a total system cost basis, once you add the cost of moving the air and the value of the heat gained, you'd be better off just burning the wood used to make it.

          • (Score: 2) by VLM on Wednesday October 01 2014, @12:09PM

            by VLM (445) Subscriber Badge on Wednesday October 01 2014, @12:09PM (#100410)

            Edited to add one thing thats getting close is solar electric. LOL at that in 1995, but in 2014 I can get about a third of a watt-year for about a buck capital cost. The electric company sells me electricity for about a buck per watt-year. So hooking a heater up to a modern 2014 COTS shipped from amazon solar panel costs about three times as much as paying the electric company to burn coal for me. with the slight problem that most of the heat would be generated in late June and not so much in December given my lattitude. Whoops.

            Still, not long after its cheaper to install solar panels than to pay the electric company, figure maybe 5 years, then not long after it'll be cheaper to toss panels on the roof and hook up a heater.

            It boils down to copper cables of electricity being ridiculously efficient way to move energy compared to fans blowing air thru tubes or whatever.

  • (Score: 0) by Anonymous Coward on Wednesday October 01 2014, @06:18AM

    by Anonymous Coward on Wednesday October 01 2014, @06:18AM (#100320)

    Every 3 to 6 months we read of another super solar improvement - greatly efficient and cheap to mass produce. Yet on the market all you get is very inefficient and extremely expensive solar components. When are we going to see a real change?
    Granted the existing energy companies have a vested interest in keeping solar expensive .. maybe THAT is the key.