Collecting Solar Power, the Black Hole Way

Not pictured: A convenient terrestrial solar panel. Image from thebadastronomer Flickr stream, via CC.

Light can't escape a black hole. Some people look at this fact and get the shudders. Others think, "Hey, that would make a really effective solar panel!"

Or, rather, it might if not for that whole "massive, crushing force of gravity" problem. MIT's Technology Review has a neat piece about scientists trying get around that minor hiccup. They're working with light-distorting metamaterials, the stuff you frequently see written up in stories about the coming of futuristic cloaking devices, alongside references to Harry Potter's invisibility cloak. But instead of bending light around the metamaterial, these researchers are focusing on a weirder--and, in my opinion, much cooler--goal.

...a metamaterial that distorts space so severely that light entering it (in this case microwaves) cannot escape.Their black hole consists of 60 layers of printed circuit board arranged in concentric circles (see picture below). The printed circuit boards are coated in a thin layer of copper from which Qiang and Tie have etched two types of pattern that either resonate at microwave frequency or do not. They've measured microwaves at 18 GHz going in and none coming out. And the circular symmetry of their metamaterial means that the microwaves are absorbed in all directions at once.

There you have it: The light-capturing power of a black hole, without the teeny inconvenience of being smooshed. Incorporate the material in solar collectors, and you could end up with a much more efficient way of harnessing the sun for energy.


    1. A fresnel lens focuses rays. This completely absorbs them, changing the energy of the microwaves into heat.

      It’s more equivalent to a completely black surface.

  1. It is really annoying that both journalists and as far as I can tell physicists are referring to these creations as “black holes”, which has an established meaning.

    Wouldn’t the standard physics term for this be “black body”?

  2. I’m failing to understand how this significantly differs from a piece of black felt that absorbs light in the visible spectrum and emits it as heat. Is it just that no known materials exist that do this in the 18GHz range? Does it really qualify as a black hole?

  3. Hmmm. From what I read the microwaves are absorbed and heat (i.e. IR radiation) is thrown off. Maybe an evaporating black hole??

  4. No black holes were created for this story. Here on Earth we’ve developed something called a rectenna that converts microwave radiation directly to electricity without converting it to heat first. Big woo.

    1. Something about hearing the words “black hole” and “rectenna” used in the same post makes me think about some kind of unpleasant medical procedure.

  5. The Russians say ‘singularity’, because ‘black hole’ in Russian is definately where the sun don’t shine. And the article didn’t mention light, just microwave radiation.

  6. And the article didn’t mention light, just microwave radiation.

    Light and microwave radiation are both forms of electromagnetic radiation. The only difference is the wavelength, and corresponding frequency, of the wave.

  7. “Light and microwave radiation are both forms of electromagnetic radiation. The only difference is the wavelength, and corresponding frequency, of the wave.” True, but we already have ways of turning light into heat. It’s turning heat into electricity that’s the problem. When you change one form of energy into another there’s almost always losses. That’s why there’s only one electrical machine that I know of that is 100% efficent.

    1. fortunately for the scientists, they don’t purport to have even begun to think about that problem, in the article, that I read.

  8. This seems like pretty ridiculous science reporting. It’s true that light can’t escape from a black hole, but that’s not what a black hole is. A black hole is a gravitational singularity. And this thing does not “bend space.” What does “at least as far as light is concerned” even mean? As far as I can tell, we’re just talking about something that is black to microwaves, which achieves that by interesting (though not clear from the article) means. Alright. So say that.

  9. Well, it’s obviously not a black hole. It’s a waveguide. And much like other “super absorbing” materials, like carbon nanotubes (, these materials have only solved half — in retrospect, make that LESS than half of the solar energy problem. The material must also contain some sort of “built in” potential field so that created electron/hole carriers can actually produce power. Furthermore, the electron/hole carriers must be able to move efficiently through the material so that they can exit the material without becoming “trapped” or recombining – and thus be used to create electrical power. These last two items are absolutely as important as the first: simply absorbing light.

  10. Interesting idea, and how well it would work and what you could do with it would depend on a lot of things. One, the basic idea of a specific wavelength EM “black hole” isn’t that it just absorbs it as a perfect black body. It actually bends all the light in a non-scattering, non-absorbing way, without so much as Brillouin scattering at interfaces, until the light (or microwaves, or whatever) reaches the center and then it could be absorbed, or it could be used, in the case of visible light, as a concentrated source for a high efficiency PV cell. Or, the absorbed light could drive a thermionic emitter, or run the hot side of a heat engine, etc. There are lots of ways such a system could be used to make solar power, and if the cost of such a visible light “black hole” is lower than the cost of large optics, such as Fresnel lenses commonly used in concentrated PV applications or large dish mirrors used in Stirling engine systems, then it’s essentially a cheaper concentrator, and one with a very wide acceptance angle such that it doesn’t require tracking, which would lower costs even more. The big gap between this sort of idea and reality, however, would be that these sorts of metamaterial stacks are usually only good at a single wavelength or a small set of frequencies. Of course, this is also true of most PV cells, so if you have the absorption spectrum of your metamaterial concentrator well matched to the absorption spectrum of your PV cell, then all you’re doing is missing the light that would be converted to heat and have to be shed somehow, so it would lower cooling requirements when compared to conventional optics. Still, it strikes me as a big maybe in several ways. I’m not sure if it could be done with visible light, and if you look at the rather comparable research in making 1, 2, and 3-d photonic crystal type metamaterials, and getting those from IR up into the visible spectrum, it can take decades of work to achieve results, and then, once achieved, the materials and manufacturing processes used typically aren’t cheap.

    Plus, with the trend towards multiple junctions in PV cells to increase efficiency, the design of such a metamaterial concentrator would get much, much more complex.

    So, I don’t think it’s a likely approach to solar, honestly, but developing such devices in various wavelengths could have a lot of applications in other photonic and optoelectronic applications.

  11. ‘Light can’t escape a black hole. Some people look at this fact and get the shudders. Others think, “Hey, that would make a really effective solar panel!”‘

    Others read this and think, “Hey, this has nothing to do with black holes or solar panels!”

    Bad reporting- to be fair to the repost, the tech review was already bad. Near perfect absorption does not merit the title of black hole, nor perfect solar panel, etc. Can’t a result carry its own interest without the absurd comparisons/hyperbole?

  12. Why does a reporter who barely understands the topic they are covering use ‘black hole’? Because it gets their article published around the world and onto Boing Boing. Success.

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