[HN Gopher] Lasers etch a 'perfect' solar energy absorber
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Lasers etch a 'perfect' solar energy absorber
Author : clouddrover
Score : 126 points
Date : 2020-02-06 10:29 UTC (12 hours ago)
(HTM) web link (www.rochester.edu)
(TXT) w3m dump (www.rochester.edu)
| logfromblammo wrote:
| > _"...etching a full-color photograph of a family into the
| refrigerator door; or proposing with a gold engagement ring that
| matches the color of your fiancee's blue eyes. "_
|
| Yeah... they should have stopped at car colors.
| vorpalhex wrote:
| Can we get a title update? Article reads `Lasers etch a 'perfect'
| solar energy absorber`.
| adrianN wrote:
| This is of course a neat tech demo, but I don't really see the
| application. Thermal electrical generation seems to be crap
| compared to photovoltaics and for just heating stuff up, black
| paint must be orders of magnitude cheaper, even if it might not
| be a "perfect" absorber of sunlight.
| mrfusion wrote:
| If it could work on plastic this would be amazing for rooftop
| pool solar heaters.
| Gravityloss wrote:
| In mediterranean countries hot water is regularly heated with
| rooftop tanks / heaters. This could mean higher temperatures
| achieved with that relatively easily.
| logfromblammo wrote:
| Materials that are perfectly black in visible and near-infrared
| light, and mirrors in thermal infrared would be naturally warm.
| Materials that are mirrors in visible light and perfectly black
| in far infrared would be naturally cool.
|
| If you paired those materials, you could collect solar energy
| on the hot end, and radiate thermal energy into empty space on
| the cool end, and put a Stirling engine between them. Then you
| have a heat engine that does not dump its waste heat into the
| atmosphere. At the theoretical limit, that means your
| passively-radiating cool end can approach 3 K, instead of 300
| K.
|
| So you take a huge polished stainless steel dome, and etch the
| outside to be black at visible and near-infrared wavelengths,
| from 200 nm to 8000 nm, and you take some smaller domes, etch
| them to be black between 8000 nm and 14000 nm, and put them at
| the focal points of some parabolic reflectors, all in the
| shadow of the first dome, aimed at empty space. (8000 nm to
| 14000 nm is the "infrared window", where the atmosphere is
| mostly transparent to those wavelengths.)
| BlueTemplar wrote:
| Yeah they should team up with the guys that made the "anti-
| solar panel" :
|
| https://www.sciencenews.org/article/device-harnesses-cold-
| ni...
|
| (They just painted aluminium black...)
|
| ----
|
| EDIT: No, wait, that's a different team that the one I had in
| mind ? I seem to remember them using a complex material that
| _specifically_ took advantage of this "infrared window" ??
|
| ----
|
| EDIT2 : Ok, same guy(s), slightly different device :
|
| https://www.asme.org/topics-resources/content/new-solar-
| ener...
|
| > A thin wafer of germanium had the right properties: It is
| fairly opaque at visible wavelengths, absorbing most incoming
| sunlight, while being generally transparent at the mid-
| infrared.
|
| > Because most of the energy in the solar spectrum is in the
| visible and near-IR range, Fan said, germanium could capture
| solar energy for use in thermal or photovoltaic applications,
| while allowing mid-IR energy to escape for radiative cooling.
|
| > The Stanford team tested the concept with an experimental
| device that placed a germanium wafer in front of a mid-
| infrared emitter.
|
| > As reported in a recent paper in the journal Joule, the
| wafer absorbed enough sunlight to warm up by 24 degrees
| Celsius, while the emitter sent enough radiation through the
| infrared "window" to cool itself by 29 degrees Celsius below
| ambient temperature.
| logfromblammo wrote:
| That's what I was thinking of. They laminated a reflective
| material under a thin sheet that had a particular
| absorption spectrum, with a thermally conductive bond, and
| put fused silica on top of it to protect against weather.
|
| Laser-etching of normally reflective metals makes the
| material less complex. For one, you don't have to match
| thermal expansion coefficients any more.
|
| The night-sky radiative cooling concept is thousands of
| years old-- https://en.wikipedia.org/wiki/Yakhchal --but we
| have better materials now. India and Persia made ice by
| filling shallow trays with water, insulating them
| underneath with straw, and exposing the water to a calm,
| clear, night sky.
| VBprogrammer wrote:
| I guess concentrating solar collectors might be a useful
| application?
| wiggler00m wrote:
| Various potential applications in biomedical, environmental,
| and energy fields.[1] Could improve the efficiency of solar
| thermal power stations:
|
| "Control over the absorption spectral range of surfaces is of
| major importance for a wide range of applications, such as
| selective solar absorbers, thermal emitters, structural
| colouring water condensation and daytime and night-time
| radiative cooling. In particular, for a solar-thermal energy
| absorber operating at high temperature, the absorber should
| be an SSA since the main cooling mechanism is thermal
| radiation... an ideal solar light absorber has nearly 100%
| absorbance within the solar spectrum and negligible thermal
| emittance within the blackbody radiation spectral range at
| mid-to-high temperatures (100-500 degC), i.e., an SSA. SSAs
| can thus maximise the temperature of solar absorbers and
| increase the efficiency of a heat engine driven by solar
| radiation."
|
| [1] https://www.nature.com/articles/s41377-020-0242-y (full
| text paper)
| jvanderbot wrote:
| Yes, any application requiring direct heat avoids electric
| heater losses. Alternatively, using this to generate
| electricity runs up against thermal electric losses.
| mikro2nd wrote:
| I'd hazard that this would be an obvious "first application"
| for this technique. If they can improve the absorption
| efficiency by 130%, that translates to reducing the number of
| mirrors by something like 25%, so a fairly significant cost
| saving. Alternately, if you can capture and store that energy
| without increasing costs too much you end up with a more
| efficient power plant per unit-area of land. Sounds good to
| me!
| jacobush wrote:
| Sometimes you want the higher temperature, like in a kiln?
| adrianN wrote:
| Ah yes, that might be something. Tungsten might even retain
| those nanostructures at higher temperatures. Good point.
| jiofih wrote:
| I was ready to debunk your comment, but then remembered that
| existing solar thermal panels are at ~90% efficient already. Is
| it somehow easier / more efficient to build a thermoelectric
| generator from a metal, vs existing flat-plate + liquid
| collectors?
| mnw21cam wrote:
| Solar thermal panels might be wonderful for heating up water
| or buildings, where the target temperature is fairly low.
| However, as the target temperature goes up, the target starts
| radiating that heat energy back out, which is where this
| innovation could be useful.
|
| So, it's useful for applications where you want a higher
| temperature than most solar heating applications now.
| mrfusion wrote:
| T^4 right?
| ww520 wrote:
| This sounds like magic. Very exciting. Is there a diagram or
| video showing what the geometry looks like?
| pjc50 wrote:
| So the interesting thing is
|
| > reduces heat dissipation at other wavelengths
|
| Most of the time we use the "blackbody" approximation; and we're
| familiar with the idea that black objects radiate and absorb heat
| well, while white or shiny ones do not. This lets us make
| something that absorbs like a black object and emits like a white
| one. In effect its own surface is like a tiny greenhouse effect.
| logfromblammo wrote:
| Or absorbs at visible light frequencies and reflects at lower
| thermal infrared frequencies.
|
| Until the object starts to glow red-hot, it will have low
| radiative losses. Once it gets that hot--maybe 3000K--it will
| radiate very well, until cooling enough to radiate mostly at
| the longer reflective wavelengths.
| wiggler00m wrote:
| Various potential applications in biomedical, environmental, and
| energy fields.[1]
|
| Could improve the efficiency of solar thermal power stations:
|
| _" Control over the absorption spectral range of surfaces is of
| major importance for a wide range of applications, such as
| selective solar absorbers, thermal emitters, structural colouring
| water condensation and daytime and night-time radiative cooling.
| In particular, for a solar-thermal energy absorber operating at
| high temperature, the absorber should be an SSA since the main
| cooling mechanism is thermal radiation... an ideal solar light
| absorber has nearly 100% absorbance within the solar spectrum and
| negligible thermal emittance within the blackbody radiation
| spectral range at mid-to-high temperatures (100-500 degC), i.e.,
| an SSA. SSAs can thus maximise the temperature of solar absorbers
| and increase the efficiency of a heat engine driven by solar
| radiation."_
|
| [1] https://www.nature.com/articles/s41377-020-0242-y (full text
| paper)
| griffman99h wrote:
| The Article also talks about hydrophilic and hydrophobic patterns
| using the same setup. I would be interested in seeing the
| properties of a channel or via through the tungsten etched with
| these patterns. It might change the thermal absorption rate of
| water passing through the hole or some other neat behavior like a
| change to the capillary effect. This could improve concentrated
| solar applications even further.
| BlueTemplar wrote:
| Just like the jellycat turbines ?
|
| https://www.youtube.com/watch?v=mB5nztzXo24
| icedistilled wrote:
| Or maybe they catch use the tech to launch a competitor to the
| holographic chocolate. http://www.morphotonix.com/chocolate/
|
| Edit: Oh sad day, it seems the chocolate may have just been a
| demo of the etching and molding technology.
| BlueTemplar wrote:
| :'(
| scotty79 wrote:
| > This improved the efficiency of thermal electrical generation
| by 130 percent compared to untreated tungsten.
|
| I wish they would include comparison to tungsten painted black.
| jandrese wrote:
| Maybe this is for applications where paint would be baked off
| by the intense concentrated thermal radiation?
| jerf wrote:
| Embedded video says "15% more than previous black metal
| samples", though that's still a bit non-specific.
| mark-r wrote:
| Is there any way to create a paint with the same properties,
| absorbing visible wavelengths but reflecting infrared?
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