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Power Hardware

Capturing Solar Power With Antennae 190

Posted by CmdrTaco
from the those-bugs-are-gonna-get-headaches dept.
necro81 writes "Researchers at the University of Missouri and the Idaho National Laboratory have demonstrated a new method of capturing solar power. Rather than using semiconductors to capture photons of sunlight, they fabricated small coiled antennae (several um square) that resonate with the wave nature of light. The antennae are tuned towards midrange infrared light (5-10 um), which is abundant on our cozy-warm Earth — even at night. They also demonstrated a way to imprint these coils on a substrate, like how CDs or vinyl records are produced, but could be scaled to roll-to-roll mass production. The usual caveat applies: it may be 5-10 years until this could hit the market."
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Capturing Solar Power With Antennae

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  • by elrous0 (869638) * on Tuesday May 17, 2011 @04:16PM (#36158280)

    It will still be 5-10 years away.

  • Antennas (Score:5, Informative)

    by LearnToSpell (694184) on Tuesday May 17, 2011 @04:16PM (#36158282) Homepage
    Antennae are for bugs.
  • by GameboyRMH (1153867) <gameboyrmh@@@gmail...com> on Tuesday May 17, 2011 @04:18PM (#36158310) Journal

    The summary fails to mention the most important advancement here: 90%+ efficiency. That's a game-changer for solar power.

    • by joe_frisch (1366229) on Tuesday May 17, 2011 @04:23PM (#36158370)

      What are they using to rectify the signal to convert to DC? The antenna is neat - but not at all surprising, its size should just scale with wavelength. You could make a 125nm long antenna that would resonate with visible light (well withing the resolution of existing lithography). The problem is how to convert the 100THz signal you get to a DC signal. You need a fantastically fast diode.

      If they have managed this, that would be an impressive achievement. The fastest diodes I am aware of are around 1THz, but its well outside my field and there might be something faster out there

      BTW: the efficiency isn't all the impressive. For single frequency light, conventional solar cells can be quite efficient (~80%???), but they don't do will with broad thermal light (like sunlight). The photons that are less than a band-gap don't do anything, and the ones above a bandgap waste any excess energy.

      • by Brett Buck (811747) on Tuesday May 17, 2011 @04:31PM (#36158486)

        I think you see the problem - I *am* in a related field and I certainly don't know of any practical or efficient way to rectify it. I can think of absurdly inefficient ways, but we already have a bunch of those.

        • by mldi (1598123)
          I would imagine this is why we aren't powering space stations on the dark side of earth with giant laser beams? Because that idea tickles me.
        • by pz (113803)

          Might there be an efficient way to frequency scale the signal and bring it down to usable levels? Or does the fact that we're talking about light-scale dimensions mean most of what we think about in terms of EE is not applicable?

        • I'm totally out of my depth on this (so please forgive my ignorance...) but perhaps if I'm understanding properly we've already got a start [manchester.ac.uk] on rectifying THz radiation [library.ethz.ch].
      • by dbc (135354)

        Yes, antennas tend to be very narrow band. Rectification is the key here... I remember hearing about somebody using nano-antennas to capture solar energy in the early 80's... back then, though, they figured they were 5-10 years away from having something ready for the market.

      • Alas, the authors mention this indirectly. Emphasis mine:

        More extensive research needs to be performed on energy conversion methods to derive overall system electricity generation efficiency. ... This research is at an intermediate stage and may take years to bring to fruition and into the market. The advances made by our research team have shown that some of the early barriers of this alternative PV concept have been crossed and this concept has the potential to be a disruptive and enabling technology.

        At least they made actual progress in this paper with real models. That's more than can be said for the hundreds of theoretical models.

      • Unobtainum diodes (Score:5, Informative)

        by Animats (122034) on Tuesday May 17, 2011 @04:59PM (#36158830) Homepage

        What are they using to rectify the signal to convert to DC?

        Unobtainum diodes. They don't actually know how to do that.

        Terahertz diodes do exist [vadiodes.com]. Low-cost, high-efficiency, integrated terahertz diodes, no. But as work proceeds on terahertz electronics, someone may solve that problem. Each nanoantenna needs its own nanodiode, so the diodes have to be fabricated on the substrate with the antenna, which complicates the fab problem. The enthusiasm about roll-to-roll low cost fabrication in the article is premature. We'll probably see this working first on a wafer, and it may not be cheap.

        Even if it's expensive, there's an initial market for satellite power panels. The performance improvement would be worth it.

        • Re:Unobtainum diodes (Score:5, Informative)

          by joe_frisch (1366229) on Tuesday May 17, 2011 @05:08PM (#36158908)

          I've bought some 300Ghz diodes from Virginia Diodes. Worked great, but $7K each as I remember......

          Here they need more like 100 THz. Might be possible with some sort of nonlinear optical material, but the fields are probably much too low.

          Even if this whole scheme does work, its not clear it is any better than a conventional solar cell - they are quite efficient for narrow-band radiation right above their bandgap. You can stack different band-gap solar cells to get a quite efficient stack, but it doesn't make economic sense - sunlight is free, its the solar cells that cost money......

          • its not clear it is any better than a conventional solar cell

            Working at night is a decent beneift.

            • by ultranova (717540)

              Working at night is a decent beneift.

              Yeah, it does so by converting ambient infrared radiation - in other words, ambient heat - into work. Any waste heat released through said work is then re-absorbed by the antenna, to be used again.

              In other words, this sounds like a second-order perpetual motion machine to me.

          • by wierd_w (1375923)

            An odd idea just occured to me...

            Perhaps you dont need to switch at that frequency.

            If you have two antennas of very close lengths, but sufficiently different in length to resonate at different discrete frequencies, you could combine them to produce a very reliable "Beat" wave of a much lower frequency that would have partial wave reinforcement from both antennas, that would be within the capabilities of current transisto technology.

            Naturally this would sacrifice a huge amount of the potential energy of the

            • Unfortunately unless you combine in a nonlinear device, the beat just has the original frequency components. If you were to combine the 2 signals in a linear circuit and then low pass filter, you wouldn't see anything. A nonlinear combination would produce a low frequency signal - this technique is called "mixing" and is very widely used in radio systems. The mixer that does the nonlinear combination is typically constructed from a set of diodes - so you wind up back with the original problem.

          • Antenna would probably work at a much higher temperature than semiconductors so it might be possible to focus the light on a small area.

      • by LWATCDR (28044)

        What about doing the reverse? Use this to produce light? Maybe for a monitor or screen. Yes no the problem is to make a lot of really cheap transmitters. Maybe really tiny magnetrons?

      • by i_b_don (1049110)

        What? Best in class photovoltaic solar cells, in university settings under optimal conditions are around 43%-44%. That's the top efficiency of some very complex structures that are not mass producible using a light source that's 80x normal. 80% is unheard of. In fact, as I was thought in school 15 years ago, the theoretical maximum efficiency of the transistor solar cell method is 50%, thus the reason that 43% is considered really damn good. 80% is god-like.

        d

      • by Grog6 (85859)

        You just need a really high frequency step-up transformer.

        One for each antenna... :)

      • by c0lo (1497653)

        What are they using to rectify the signal to convert to DC? The antenna is neat - but not at all surprising, its size should just scale with wavelength. You could make a 125nm long antenna that would resonate with visible light (well withing the resolution of existing lithography). The problem is how to convert the 100THz signal you get to a DC signal. You need a fantastically fast diode.

        If they have managed this, that would be an impressive achievement.

        The PDF [inl.gov] mentions (on page 2):

        One possible embodiment is metalinsulator-insulator-metal (MIIM) tunneling-diodes.

        Is it possible? Does it make sense?

    • by drerwk (695572)
      The P fails to notice that they are not yet able to rectify the current, and hence can not yet get power out, and so the 90% number is only for antenna coupling, not conversion to DC current.

      More extensive research needs to be performed on energy conversion methods to derive overall system electricity generation efficiency.

      It is like saying current solar cells are 90% efficient because 90% of photons are absorbed; it says nothing about the quantum efficiency of conversion. I am willing to bet that the QM Efficiency of the necessary rectifier will be the big loss; though it may only be 50%.

    • by lupine (100665) * on Tuesday May 17, 2011 @04:33PM (#36158510) Journal
      From TFA:
      The individual nantennas can absorb close to 90 percent of the available in-band energy.

      So the total system efficiency depends on how wide that band is in relation to total solar energy available and whether nantennas can be stacked and designed to capture energy over a range of bands.
      • by skids (119237) on Tuesday May 17, 2011 @04:58PM (#36158816) Homepage

        Such a system would be yet another layer in the panel to deal with a specific frequency range. Perhaps several layers with different wavelengths in each. It's journalists that make the mistake of promoting this as a whole solar panel.

        That said, the rectification issue is a deal killer. Not only are we talking THz, but IIRC from the last media go-round with this technology, voltages way below practical diode thresholds.

        • by xded (1046894)

          You don't necessarily have to stack'em up. You could linearly change the single antenna lengths along the array, to let them resonate over different frequencies. This way you would obtain in a single layer a very wide bandwidth antenna. Or you could use other well-known RF tricks (assuming you're able to replicate them litographically).

          This would probably be one of the advantages over multi-junction solar cells. Of course assuming you're able to turn that HF energy into DC...

      • The individual nantennas can absorb close to 90 percent of the available in-band energy.

        Which is good for communications, where you want to exclude all but the target band. It could even work for power, providing the light source is a laser. But resonance methods aren't very good for capturing energy from broad spectrum sources like the sun.

        I predict that this technique will never gain traction for solar energy. However, it might replace photodiodes for fiber optic communications.

      • It's pretty easy to convert visible light into infrared- ie black paint. I doubt it would be hard to find a material to do it in a narrow range....

    • by blair1q (305137)

      Solar efficiency is measured as usable power output vs. total incident power across the full incident spectrum.

      This thing's efficiency is measured as usable power output vs. power across the very small bandwidth it detects. Which is to say, its solar efficiency is probably in the micro-percents.

    • Not 90% efficiency over whole light energy spectrum, but in a certain frequency band the antenna is tunned to, that means 90% efficiency in a narrow band of light energy.
    • I do not think the 90+ efficiency is the greatest game changer. Since they claim it could be produced like a CD/DVD/BR the possibility to create very large surfaces with low costs is far more important IMHO. We have surface area enough, PV is just very expensive per watt. Of course, assuming the cost per m^2 stays the same, increasing the efficiency will help decreasing the cost per watt.
      The micro-antenna part seems feasible, but I do not know enough of quantum mechanics to asses the feasibility of the tu
  • Anybody else read this and immediately think that it might potentially solve the problem of biologically powering medical implants that was mentioned in a story on Slashdot about a week ago?

  • ... to etch an antenna at the wavelength of 0.000001 meter? Well, OK, it's not trivial. But we do have things like lasers that can etch chemicals at that size and smaller. Then we need a way to transfer that etch to conductive metal, add rectification to make it usable and collectible, and have our own little power sources. A flat panel might do if the current level doesn't burn up the collection tap point.

    • by CCarrot (1562079)

      ... to etch an antenna at the wavelength of 0.000001 meter? Well, OK, it's not trivial. But we do have things like lasers that can etch chemicals at that size and smaller. Then we need a way to transfer that etch to conductive metal, add rectification to make it usable and collectible, and have our own little power sources. A flat panel might do if the current level doesn't burn up the collection tap point.

      They can 'print' them.
      https://inlportal.inl.gov/portal/server.pt?open=514&objID=1269&mode=2&featurestory=DA_101047 [inl.gov]

      This seems a bit well-aged for 'breaking' news, unless they've found some way to rectify the high frequency power...then it would be newsworthy indeed! I'll have to RTFA...

      • by chemicaldave (1776600) on Tuesday May 17, 2011 @04:55PM (#36158786)
        The newsworthiness is that instead of only 250 million nantennas on one small square like in that INL page, these guys replicated a design onto an "8 inch round silicon wafer" with 10 billion antenna elements. And they did it with high detail and little loss between the "master print" and the copy.
        • by CCarrot (1562079)

          Wow, that is quite impressive! I missed that in my skimming, thanks.

          Too bad we still can't do anything with all those antennas unless we can rectify the output...it seems like saying "look at how densely we can pack data into these drive platters!" before anybody has invented the read-write head. But it is good to know they're still trying to develop this idea.

        • The newsworthiness is that instead of only 250 million nantennas on one small square like in that INL page, these guys replicated a design onto an "8 inch round silicon wafer" with 10 billion antenna elements. And they did it with high detail and little loss between the "master print" and the copy.

          The newsworthiness would HAVE to be in the fabrication and design details. "Optical rectennas" as a form of solar cell have been discussed since AT LEAST the late 1980s (when I heard them described by other peopl

  • so, does this mean they are making vibrators? i thought vibrators used electricity.

    • by ceoyoyo (59147)

      A vibrator uses an electric motor to convert electricity to motion. If instead, you impose motion, then the electric motor becomes a generator and produces electricity.

      Yes. Think that one through carefully. ;)

  • by Maximum Prophet (716608) on Tuesday May 17, 2011 @04:32PM (#36158504)
    Don Lancaster described this process years ago. The trick is the tiny diode at the bottom of the antenna to turn the AC into DC. It has to handle 400 - 800 THz. Plausible, but difficult. 5-10 years really means they have no idea when they'd be able to produce this in industrial quantities.
  • by Anonymous Coward

    This is, of course, utterly useless for harvesting power from ambient thermal radiation. Even if you can make a diode that's remotely capable of rectifying current at high enough frequencies, the diode has to be kept colder than the source of the radiation. It's the electrical analog of a Brownian ratchet.

    Picking up a bit of the IR tail that conventional photovoltaics don't catch? Maybe, but there isn't very much power down there even if you got the efficiency usefully high. Turning ambient heat into us

  • This is the problem with solar power, it's mostly home owners who are buying them and the systems cost so much it takes decades to break even (if purely doing it for cost reasons, not CO2).

    So once a better technology comes along you have to junk the old tech and you may never break even.

    • This is the problem with solar power, it's mostly home owners who are buying them and the systems cost so much it takes decades to break even (if purely doing it for cost reasons, not CO2).

      So once a better technology comes along you have to junk the old tech and you may never break even.

      Hello 1978, welcome to 2011 where panels pay for themselves within 4 years, have a lifespan of 20+ years, and are significantly cheaper to produce and use less-rare components.

      • panels pay for themselves within 4 years

        You forgot to mention the tax credits and subsidies that make that four year timetable possible.

        Which means that as long as only a very few people install them, they're cheap. If EVERYONE installed them, well, the tax credits would basically reduce to "you pay for your neighbor's solar panels, and he'll pay for your solar panels"....

      • by ptbarnett (159784)

        Hello 1978, welcome to 2011 where panels pay for themselves within 4 years, have a lifespan of 20+ years, and are significantly cheaper to produce and use less-rare components.

        Maybe where you live. But, where I live, I'm paying 9.5 cents per kWh, and averaging about 1000 kWh per month. The present value (at a 4.5% discount rate) of my electric bill over 20 years at that price and consumption rate is about $15,000. Of course, I can't count on my electric rate remaining at 9.5 cents per kWh. I was paying almost twice that a few years ago.

        A quick search of the net finds a calculator that says the average sun-hours per day in my area is 5.43, and I'd need 7.4 kW of solar panels

        • Maybe where you live. But, where I live, I'm paying 9.5 cents per kWh, ... To break even in 4 years as you claim, the cost would have to drop to a bit more than $4,000, or about 57 cents/watt, installed. Where do I find these solar panels?

          Panel prices have been dropping but they're not quite that low yet. There's a company in Florida that sells UL approved panels for about $2/watt and non-approved for about $1. (It changes from time to time. I get the impression they're selling cosmetic rejects from majo

          • Two other factors

            * If you don't shoot for complete replacement, you can generate about $50 per month of power with a $4000 system (~250kwh/month). Then- in the summer, when you hit the penalty power rates, you are generating $75 per month of power. So about $700 per year.

            Where in the market can you invest $4000 and get a safe $700 payout?

            But that's $700 *savings*. Which means it's tax free. Which means it's like earning $1000 from investments (or $1250 more in salary).

            And power rates have roughly double

  • by wcrowe (94389)

    Yeah, I'm still waiting on the amazing solar innovations that were breathlessly announced five years ago to hit the market.

    • by demonbug (309515)

      Yeah, I'm still waiting on the amazing solar innovations that were breathlessly announced five years ago to hit the market.

      I was going to try looking up some solar power articles from five years ago, but there doesn't seem to be an easy way to restrict a search to a particular time period. Is there an advanced Slashdot search hidden away somewhere? Even Google only lets me restrict my search to "past day" or "past year", etc. I could have sworn you used to be able to actually input a date range, but it isn't there any more.

  • Is this 5-10 flying car years? Similar to dog years but in the other direction. 1 flying car year equals 1 normal human lifespan, apparently...

  • Is it possible that a widespread use of such antennas will lower the average temperature since it is tuned to mid range infra-red? They can sell it being super eco friendly :-)

  • Summary: They designed nano-scale devices that behave as antennas at infrared frequencies, meaning that infrared light induces a THz current in the antenna. They then proceeded to manufacture a few one-off test pieces that performed well and are now using a master pattern to roll/stamp the devices onto a film (though the full results of that weren't shown or aren't known yet).

    We don't typically think of stuff like light as being susceptible to this sort of thing because we haven't been able to make the ante

  • From the summary "The antennae are tuned towards midrange infrared light (5-10 um), which is abundant on our cozy-warm Earth â" even at night."

    But you can't extract work from a system which is in thermal equilibrium. This can't work unless the 'solar panels' are colder than the ambient night time radiation, which seems unlikely.

    I couldn't read TFA (slashdotted?), I skim read the fine paper, but didn't find any reference to this idea. So has someone incorrectly introduced this idea somewhere between the

  • This is basically a reprisal of the optical rectenna [nrel.gov], and it's already been pointed out that the hardest part isn't rectifying THz radiation, which requires only nanolithiography-sized antennae, but creating the diode fast enough to turn it into DC.

    The above link details the status of optical rectennas as of roughly 2002; They managed to get an efficiency of 1% in the near-infrared (100THz) - the diode just didn't exhibit the asymmetry and nonlinearity needed. I'd bet that to make anything happen efficie
  • Collecting solar energy with antennas - LLL seems to have done this in 2007.

    https://inlportal.inl.gov/portal/server.pt?open=514&objID=1269&mode=2&featurestory=DA_101047 [inl.gov]

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