[HN Gopher] Mechanical power generation using Earth's ambient ra...
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Mechanical power generation using Earth's ambient radiation
Author : defrost
Score : 169 points
Date : 2025-12-07 21:55 UTC (1 days ago)
(HTM) web link (www.science.org)
(TXT) w3m dump (www.science.org)
| HPsquared wrote:
| Somewhat different, but this reminds me of an approach that uses
| temperature gradients in the ocean to power a heat engine.
|
| https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio...
| jasonpeacock wrote:
| OTECs are amazing, and step 1 of "The Millennial Project:
| Colonizing the galaxy in eight easy steps"[0]
|
| [0]: https://en.wikipedia.org/wiki/The_Millennial_Project
|
| There's a shore-based research OTEC in Hawaii, but the best is
| a floating, closed-loop OTEC in the ocean.
| andbberger wrote:
| wiki article states "Up to 10,000 TWh/yr of power could be
| generated from OTEC without affecting the ocean's thermal
| structure". which converts to about 500GW which... isn't that
| much
| pezezin wrote:
| 10 000 TWh/yr is one third of the current total electric
| energy generation of the whole planet, is not a small
| amount.
|
| Source, page 39 of the full report:
|
| https://www.iea.org/reports/global-energy-
| review-2025/electr...
| nine_k wrote:
| This can't be correct.
|
| 10,000 TWh/y = 1e+7 GWh/y, divide it by 365.25 days/y to
| produce daily output of 27,379 GWh/day, then by 24 h/day to
| get pure power of 1,141 GW. It's still more than a
| terawatt, three orders of magnitude larger than the largest
| nuclear reactors.
| andbberger wrote:
| oops. yes. still not that much though. i mean it's a lot
| but it's "one more large industrialized country" a lot
| not "kardashev 2" a lot
| WJW wrote:
| Kardashev 2 has a Dyson sphere. Of course anything on a
| single planet can never have that much.
| IAmBroom wrote:
| Those goalposts of yours are on a FTL ship...
| AstroNutt wrote:
| Interesting link. I would think step 7 would come before step
| 6 though. I thought about this for a few minutes and can't
| come with a reason otherwise.
| adastra22 wrote:
| The timelines are increasing powers of 2. It'll take much
| longer to colonize all asteroids than to settle Mars.
| AnimalMuppet wrote:
| 400 milliwatts per square meter? That's interesting that they can
| do it at all, but that level is completely impractical for real
| use.
| aetherspawn wrote:
| > the generation of >400 milliwatts per square meter of
| mechanical power with a potential for >6 watts per square
| meter.
|
| Keep in mind the power is fully mechanical so no electricity or
| control circuit is required. And based on the simplicity it
| seems like a good candidate to power something that you need to
| last 100 years with no maintenance for example.
| abeppu wrote:
| I think the "last 100 years with no maintenance" is not
| likely feasible with this approach. The top plate has a
| coating that supports high infrared emissivity -- and I think
| it would need to be regularly cleaned to work well. And you
| can't really prevent it from getting dirty by enclosing it
| b/c that both substantially changes the performance and moves
| the maintenance burden to cleaning the enclosure.
| AnimalMuppet wrote:
| Mechanical things don't usually work for 100 years with no
| maintenance. Bearings run dry, if nothing else.
| ufocia wrote:
| Air bearings always run dry without problems.
| contingencies wrote:
| Until they are replaced with dust, pollution, hair,
| animals, leaf litter, aggressive plants, seismic events,
| pollen, skin particles, birdshit, fallen logs, slime
| mold, etc.
| yetihehe wrote:
| Air bearings run dry until they get some moisture. Then
| they fail. Old joke about making radio enclosures: make
| it as watertight as possible, then drill a small hole on
| the bottom to let the water escape.
| IAmBroom wrote:
| No moving parts in open water last without maintenance. Life,
| uh, finds a way.
| foxglacier wrote:
| So what? It's research, not business. Surely you didn't expect
| they'd found a practical source of free energy that was ready
| to compete with solar but somehow nobody else bothered to try
| before?
| nrhrjrjrjtntbt wrote:
| It is interesting to know if it has potential (pun intended)
| for some use. Even if that is some very niche thing.
| 15155 wrote:
| This is plenty of power to run a microcontroller and a radio
| (sporadically) with an energy-harvesting setup.
| clickety_clack wrote:
| In one of the later Foundation series books, Isaac Asimov had a
| whole world run on this.
| coder543 wrote:
| Which book? Which world? I don't remember this, but it has been
| a few years.
| monegator wrote:
| foundation and earth, if i recall correctly
| phyzome wrote:
| If anyone is interested in passive sub-ambient cooling (not for
| power generation, just for "free" cooling) I strongly recommend
| https://www.youtube.com/@Nighthawkinlight -- he has been doing a
| lot of experiments in this space and releasing recipes as he
| goes. Stuff you can do in your kitchen.
| gsf_emergency_6 wrote:
| Vid of the engine in action, from the team that made the paper
|
| https://www.youtube.com/watch?v=5VSmBl8Rv_o
|
| This one shows that it is not as unbelievable as it sounds :)
|
| https://youtube.com/shorts/9KuTdPGqhVo
| jcims wrote:
| DIY radiative cooling paint from YouTuber NightHawkInLight -
| https://www.youtube.com/watch?v=N3bJnKmeNJY&list=PL1a2HkcVbm...
|
| It has pretty impressive performance.
|
| Tech Ingredients did one or two vids as well -
| https://www.youtube.com/watch?v=dNs_kNilSjk
|
| Was thinking of whipping up a batch for my rv.
| kumarvvr wrote:
| This concept is used all over India to cool down homes that are
| on the top floors.
|
| https://www.amazon.in/EXCEL-CoolCoat%C2%AE-Reflective-Coatin...
|
| Basically, have a highly reflective white coat on your roof, to
| reduce temperatures by about 3 Degrees Celsius.
|
| Almost all homes in Urban India are made from concrete and
| bricks, which can hold a lot of heat.
|
| I myself have been in houses that use this to cover only some
| rooms of the house (mainly the bedroom), and the temperature
| difference is definitely noticeable. It also makes the room
| livable in the extreme hot summers in India.
| kragen wrote:
| This is the opposite. It says, "Refelects [sic] 90% of solar
| infrared rays," because of its "High IR reflective Pigments
| [sic]," so its emissivity in the infrared is 0.1, but the IR-
| selective paints we're talking about here are optimized for
| _high_ infrared emissivity, which means they absorb a lot of
| infrared.
|
| Maybe there's some wiggle room here because _solar_ infrared
| is mostly near IR and MWIR, and the place where we want high
| emissivity (absorptivity) is longwave IR, but to the extent
| that the advertisement makes any claims about infrared
| emissivity, it claims very _low_ infrared emissivity, not
| _high_.
|
| A paint with low emissivity across the spectrum will slow
| down the temperature rise when the sun is up, but also slow
| down the temperature drop when the sun is down. This can
| still make rooms livable, but it isn't the same as what you
| get with regular whitewash, where the temperature of the roof
| is actually _lower_ than the temperature of the air around
| it.
| jcims wrote:
| It kind of blew my mind when I first learned about this
| whole phenomenon (mostly from the YouTube series I posted).
| Not all white paints are equal and it's kind of interesting
| to think that something that looks mostly identical to our
| eyes has very different (passive) properties in the
| infrared.
|
| I think one of the things in the paints that Ben adds is a
| set of microspheres that reject incident incoming infrared
| beyond a certain angle but allow it to pass through when
| radiated. Something like that.
| kragen wrote:
| IIRC, the papers they're working from mention that lime works
| very nearly as well as the baryta they're using. Guess what
| people have been painting their houses white with for several
| thousand years?
| marcosdumay wrote:
| Not with the optimal mixture for maximum-packing of limestone
| nanospheres.
|
| That effect is almost not perceptible in normal milled
| limestone.
| rriley wrote:
| Great! Now I desperately need this Stirling engine for my morning
| coffee: https://a.co/d/6Ja2LeF
|
| Video of how it works:
| https://www.youtube.com/watch?v=Q5QEBqjkNjo
| kogasa240p wrote:
| Since we're talking about stirling engines, I've always wondered
| how using geothermal heat for a larger stirling engine would
| work.
|
| https://youtu.be/duuk_r--lqU?t=99
|
| Even though the video uses the sun to heat the oil, I would think
| it would be feasible to use geothermal heat instead.
| not_kurt_godel wrote:
| https://en.wikipedia.org/wiki/Organic_Rankine_cycle
| kogasa240p wrote:
| Very fascinating article.
| fooker wrote:
| You boil water :)
| cameldrv wrote:
| Not an engine, but some friends of mine got a mylar sheet that's
| black on one side and reflective on the other. We tried it out in
| the desert tied onto trees/vehicles. You put the shiny side down,
| so the hot IR radiation of the earth is reflected away, and the
| black side sees the extremely cold (in IR) desert sky. If you put
| a little hole in the middle and put a bucket under it, you get a
| fair bit of water, because the mylar sheet gets about 20 degrees
| C below ambient and a lot of water condenses on it. (even in the
| desert)
| wombatpm wrote:
| Now you just need a couple of droids and you could go into the
| moisture farming business
| jeffrallen wrote:
| Nah, those are not the droids he's looking for.
| sigmoid10 wrote:
| What I really need is a droid that understands the binary
| language of moisture vaporators.
| timdiggerm wrote:
| But can he speak Italian lawn games?
| viraj_shah wrote:
| Fascinating 20 degrees C is huge. What's a fair bit of water?
| At what time of day and how long did you collect water?
| gsf_emergency_6 wrote:
| These guys claim >40degC, and are deploying in Dubai..
|
| https://www.i2cool.com/tideflow/uwJVdixI.html
|
| https://baitykool.com/radiativeskycooling.html
|
| Peak performance, I think. Considering that they got the
| black white sides flipped
| cameldrv wrote:
| I didn't do the measurment and it's been a while so it's
| possible I misremembered the temperature delta, or maybe it
| was degrees F. It was about a 2-3 square meter sheet and it
| made about a liter of water overnight.
| kragen wrote:
| Wow, that's awesome, and a much bigger temperature difference
| than I would have guessed. Did you get frost?
| nickdothutton wrote:
| I think I read something similar in a "Boys survival book,
| desert chapter" in the early 80s.
| burnt-resistor wrote:
| Neat. Reminds me that Applied Science made an acoustic
| radiometer video recently. https://youtu.be/lAeJvZfVLbE
| Animats wrote:
| > 400 milliwatts per square meter
|
| About two orders of magnitude weaker than solar panels, even over
| 24 hours.
|
| E = (T2-T1) / T2
| kragen wrote:
| Yes, but it works at night!
|
| Not sure if you can get the MTBF on Stirling engines higher
| than on LFP batteries, though.
| scoopertrooper wrote:
| >400 milliwatts per square meter of mechanical power with a
| potential for >6 watts per square meter.
| Animats wrote:
| What miracle gets a Stirling engine to be 15x more efficient?
| Stirling engines have been around for over a century.
| burnt-resistor wrote:
| RF energy harvesting in urban areas results in about 0.5-5
| mW/m^2. I would guess it would be about 1-2 orders of magnitude
| less in rural areas.
|
| This is like shaving nickels to make money.
|
| Certainly, there are better energy sources like the fusion
| reactor in the sky and building a fusion reactor (that's
| perpetually 30 years away).
|
| TIL: Active nuclear reactors of all types around the world are
| mappable using antineutrino detectors. It would probably also
| expose the location of every stationary nuclear-powered ship
| and submarine too.
| carabiner wrote:
| Cost to build, maintain this machine? $/watt?
| bilsbie wrote:
| I wonder if you could harness different temperatures at different
| water depths.
| thijson wrote:
| You can, it's called OTEC:
|
| https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio...
|
| Just like this scheme, it's not very economically efficient.
|
| Carnot efficiency is proportional to the temperature ratio
| between the hot end and the cold end in degrees Kelvin. If both
| temperatures are in the 200's, then efficiency will be low.
|
| OTEC does provide lots of potable water though, so that's one
| advantage.
| throwaway34564 wrote:
| Slightly off-topic - I was momentarily excited this was a
| replication of
| https://journals.aps.org/prapplied/abstract/10.1103/PhysRevA...
| (Electric Power Generation from Earth's Rotation through its Own
| Magnetic Field)
|
| I've been stalking the citations for this paper for a while now.
| Surely people would be scrambling to replicate these results. It
| could truly be transformative for the world if it works and is
| scale-able.
|
| The science looks good to me
| burnt-resistor wrote:
| Davis is so frickin windy, wind power would be my first choice.
|
| Secondarily, using a deep ground source heat pump to power a
| Stirling cycle engine would probably be much more powerful than
| harvesting a few mW from ambient temperature gradient between
| surface and air.
|
| That's my 2 centidollars.
| blacksmith_tb wrote:
| Stirling engines are of course fun, but I wonder if the same
| approach but with the specially-coated radiator on a Peltier
| instead would net much - it'd avoid the moving-parts problem, at
| least.
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