Mechanical power generation using Earth's ambient radiation

Posted by defrost 4 days ago

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Comment by cameldrv 4 days ago

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)

Comment by wombatpm 4 days ago

Now you just need a couple of droids and you could go into the moisture farming business

Comment by sigmoid10 3 days ago

What I really need is a droid that understands the binary language of moisture vaporators.

Comment by timdiggerm 3 days ago

But can he speak Italian lawn games?

Comment by nmeagent 3 days ago

I was going to look into this once, but instead I opted to go into Tosche station to pick up some power converters and unfortunately never quite got around to it.

Comment by 3 days ago

Comment by jeffrallen 4 days ago

Nah, those are not the droids he's looking for.

Comment by viraj_shah 4 days ago

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?

Comment by gsf_emergency_6 4 days ago

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

Comment by cameldrv 3 days ago

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.

Comment by nickdothutton 3 days ago

I think I read something similar in a "Boys survival book, desert chapter" in the early 80s.

Comment by burnt-resistor 3 days ago

Neat. Reminds me that Applied Science made an acoustic radiometer video recently. https://youtu.be/lAeJvZfVLbE

Comment by kragen 3 days ago

Wow, that's awesome, and a much bigger temperature difference than I would have guessed. Did you get frost?

Comment by phyzome 4 days ago

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.

Comment by jcims 4 days ago

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.

Comment by kumarvvr 4 days ago

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.

Comment by kragen 3 days ago

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.

Comment by schiffern 2 days ago

To be fair it does say "reflects solar infrared rays," which I would interpret as "the IR from the Sun" (aka NIR).

The product datasheet[0] claims a thermal emittance (aka LWIR) of 0.82. Having such a high value is typical for non-metallic surfaces.[1]

[0] https://5.imimg.com/data5/CA/RO/MY-653008/excel-cool-coat.pd...

[1] https://ntrs.nasa.gov/api/citations/19840015630/downloads/19...

Comment by jcims 3 days ago

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.

Comment by kragen 3 days ago

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?

Comment by marcosdumay 3 days ago

Not with the optimal mixture for maximum-packing of limestone nanospheres.

That effect is almost not perceptible in normal milled limestone.

Comment by gsf_emergency_6 4 days ago

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

Comment by HPsquared 4 days ago

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...

Comment by jasonpeacock 4 days ago

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.

Comment by AstroNutt 4 days ago

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.

Comment by adastra22 4 days ago

The timelines are increasing powers of 2. It’ll take much longer to colonize all asteroids than to settle Mars.

Comment by andbberger 4 days ago

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

Comment by pezezin 4 days ago

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...

Comment by nine_k 4 days ago

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.

Comment by andbberger 4 days ago

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

Comment by IAmBroom 3 days ago

Those goalposts of yours are on a FTL ship...

Comment by WJW 3 days ago

Kardashev 2 has a Dyson sphere. Of course anything on a single planet can never have that much.

Comment by 4 days ago

Comment by throwaway34564 3 days ago

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

Comment by cindyllm 1 day ago

[dead]

Comment by Animats 4 days ago

> 400 milliwatts per square meter

About two orders of magnitude weaker than solar panels, even over 24 hours.

E = (T2-T1) / T2

Comment by kragen 3 days ago

Yes, but it works at night!

Not sure if you can get the MTBF on Stirling engines higher than on LFP batteries, though.

Comment by gsf_emergency_6 3 days ago

And in the day time, if transparent and applied to solar panels, the "efficiency" gain (~10W psqm) itself will dwarf other considerations.( Remembering that bulk of radiative cooling shouldn't happen below ~1300nm) And then there's beating the efficacy of carbon capture at mitigating warming by orders of magnitudes

Nothing to sneeze at. Just be careful of midbrow high-effort dismissals from the old and wise:)

These guys are applying them to solar panels:

https://www.i2cool.com/tideflow/uwJVdixI.html

  "Case Study 2: Solar Farm in Dubai
  Problem: Solar panels lost 15–20% efficiency at 55°C+ temperatures.
  Solution: Coated panels with i2Cool’s film.
  Results:
  Panel surface temperature: ▼25.7°C (from 58°C to 32.3°C)
  Power output: ▲8% (equivalent to adding 2,400 new panels to a 30MW farm)"

Comment by burnt-resistor 3 days ago

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.

Comment by scoopertrooper 3 days ago

>400 milliwatts per square meter of mechanical power with a potential for >6 watts per square meter.

Comment by Animats 3 days ago

What miracle gets a Stirling engine to be 15x more efficient? Stirling engines have been around for over a century.

Comment by kogasa240p 4 days ago

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.

Comment by not_kurt_godel 4 days ago

https://en.wikipedia.org/wiki/Organic_Rankine_cycle

Comment by kogasa240p 3 days ago

Very fascinating article.

Comment by fooker 4 days ago

You boil water :)

Comment by clickety_clack 4 days ago

In one of the later Foundation series books, Isaac Asimov had a whole world run on this.

Comment by coder543 4 days ago

Which book? Which world? I don't remember this, but it has been a few years.

Comment by monegator 4 days ago

foundation and earth, if i recall correctly

Comment by AnimalMuppet 4 days ago

400 milliwatts per square meter? That's interesting that they can do it at all, but that level is completely impractical for real use.

Comment by 15155 4 days ago

This is plenty of power to run a microcontroller and a radio (sporadically) with an energy-harvesting setup.

Comment by aetherspawn 4 days ago

> 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.

Comment by abeppu 4 days ago

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.

Comment by AnimalMuppet 4 days ago

Mechanical things don't usually work for 100 years with no maintenance. Bearings run dry, if nothing else.

Comment by ufocia 4 days ago

Air bearings always run dry without problems.

Comment by yetihehe 3 days ago

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.

Comment by contingencies 4 days ago

Until they are replaced with dust, pollution, hair, animals, leaf litter, aggressive plants, seismic events, pollen, skin particles, birdshit, fallen logs, slime mold, etc.

Comment by IAmBroom 3 days ago

No moving parts in open water last without maintenance. Life, uh, finds a way.

Comment by foxglacier 4 days ago

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?

Comment by nrhrjrjrjtntbt 4 days ago

It is interesting to know if it has potential (pun intended) for some use. Even if that is some very niche thing.

Comment by burnt-resistor 3 days ago

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.

Comment by blacksmith_tb 3 days ago

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.

Comment by bilsbie 3 days ago

I wonder if you could harness different temperatures at different water depths.

Comment by thijson 3 days ago

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.

Comment by carabiner 3 days ago

Cost to build, maintain this machine? $/watt?

Comment by rriley 4 days ago

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