Laser Etches Solar Absorbing Material

Having a laser cutter these days isn’t a big deal. But [Chunlei Guo], a professor at the University of Rochester, has a powerful femto-second pulse laser and used it to create what might be the perfect solar absorber. You can see a video about the work, below.

It stands to reason that white materials reflect most light and therefore absorb less energy than black materials — this is part of what makes a radiometer work. Tungsten, in particular, is a good metal for absorbing solar power, but this new laser treatment — which builds nanostructures on the surface of the metal — increases efficiency by 130% compared to untreated tungsten.

The team has previously used a similar technology to make metals either hydrophilic or hydrophobic. The process gives the metal a black color which is where much of the efficiency comes from. According to reports, there’s still a 15% increase using the laser-treated surface over a piece of plain black tungsten.

We’d like some of this for our solar pool heater. We doubt that is using tungsten to start with, so maybe that’s the first retrofit. There are plenty of non-tungsten designs. We are more likely to find tungsten in our light bulbs or our metal-shaping tools.

19 thoughts on “Laser Etches Solar Absorbing Material

  1. That’s interesting.
    Quite a few years ago I was looking in to materials for a solar hot water heating system and the best option to capture the suns rays and transfer it in to either oil then to the water or direct to the water. After about 60 various tests I found that using a similar process to black anodizing the aluminium would greatly outperform copper treated in a similar way. And both treated copper and alu would capture heat around 30% better than no treated samples. Initially we put this down to the etching process was increasing the surface area of the sample but maybe there was more to it.

    1. It may be that this greatly increases the surface area and roughness, so at least some reflected photons hit somewhere else on the surface and have a second chance at being absorbed.

      1. It’s one thing to have a good way of collecting heat. But they will also need a good way to remove it from the other side of the peltier device.
        A while back I was toying with the concept of a sheet of miniature THz Tesla coils to directly convert light into electricity. Perhaps nano technology will progress enough to manage it one day.

    2. Anodized aluminum has a very interesting nano structure on its surface. Perhaps that, combined with the black pigment, makes it a good light absorber. I’ll need to try it out, too.

  2. Sure it absorbs 99% of the visible light and perhaps also a lot of the infrared light (just because it’s black doesn’t mean it also absorbs infrared), turning all the energy of the sun into heat. But then you need to convert the heat into electric energy to make it useable. It looks like they are using a peltier device, which are horribly inefficient.

    Turning heat into useable energy is pretty hard to do efficient, things like large scale steam generators are about the best we can do at the moment. This requires enough power to turn a lot of water into steam, which is very hard with just the power of the sun. Hence we have to concentrate a lot of sunlight in solar farms onto a central tower to convert the energy efficiently.

    For small scale (think roof of your house scale) turning the energy directly into electrical energy makes more sense.

    1. Efficiency doesn’t matter because empty land in the desert is cheap and the sun is free. What matters is the installed cost per kW. The best you’ll do with turbines these days is ~$1000/kW. If you can beat that, then it makes lots of sense, even if you have 1% efficiency.

    1. Basically yes, but actually no. It is TUNED to absorb radiation, but black things are also better than white at radiating energy. This particular coating is tuned so that it absorbs light in visible spectrum, but is bad at absorbing (and radiating) in deep infrared. Just no one reporting is emphasizing that one particular development.

  3. Tungsten (wolfgram) mining, extraction, and or reclamation may have made significant strides in the past decades, but I recall reading a number of years ago that we’ll “run out of tungsten in 30 years”.
    What I read may have been related to incandescent lights.

  4. Until it gets dirty and nearly impossible to clean without destroying it. That’s the problem with all of these surface treatments. You’re better off with a rugged coating that can handle being abused.

  5. Light falling on a surface, close to parallel to the normal, which is covered in pyramids will hit it at least twice before being reflected, but what happens if you put pyramids on the pyramids? 😎

  6. guess those guys havent hear of vantablack and other CNT based blackest substances? tuning the material absorbance wavelength seems to be interesting but as a solar absorbtion more is better so other things are for sure better. also 130% more power from a peltier is a very bad metric to measure the performance of their etchings. peltiers are non linear devices at best

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