geoengineering with sterling engines

[farmerben]

Proposal:  A solar powered sterling cycle shaped approximately like a tree or mushroom is deployed in vast numbers to counter global warming.   Instead of an engine, we run it as a heat pump with input electricity.   It radiates heat into the atmosphere and has a cooling effect below the ground level.   It also shades the ground.  It can be deployed in arctic, or hot desert conditions.  It could condense dew and collect rainwater.  It can help preserve sea ice.

If the future brings cheap silicon, aluminum, nearly free electricity, and productivity growth we stipulate that they would be affordable.  I'd prefer one to write my name on one and it leave behind, than a gravestone or a statue.

Does the basic concept work?

[AckSed]

Do you mean Stirling engines?

Anyway, this would need a lot more work to realise. For one, how tall are these? Cooling the Earth by radiating heat into the atmosphere is the equivalent of tidying up by rearranging junk in your house from one room to the next - you still have the same amount of junk.

My analogy breaks down because some would be radiated up and out into space, but much more would be convected into the gas of the atmosphere and we're right back where we started. If you wanted to use massed Stirling heat-pumps to cool the world, you'd need to make sure it couldn't come back, and my first instinct is to make them either very tall so they're outside most of the atmosphere, or tune all the radiators so that the specific wavelength of IR they emit isn't absorbed by the atmosphere.

You were on the right track when you mentioned shading. I'm going to presume that you're not talking about high-atmosphere or orbital infrastructure. You want cheap, simple and ground-based.

There is indeed a wavelength of IR in which most of it simply escapes into space, and there are several metamaterials that, when silvered, reflect the majority back into space at that wavelength. The nuance is that that 'window' mostly works in hot, arid environments. In hot, tropical environments, that window changes because of the increased humidity. It's still useful in that case, mind: passive cooling by definition does not use any power, and in general the less power the world uses, the less heat and greenhouse gasses our civilisation creates.

Here's an overview of these Passive Radiative Daytime Cooling materials and one that is supposed to work in all environments: https://www.nature.com/articles/s41467-020-20646-7

[Shpaget]

Wouldn't a simple mirror be more efficient?

[darthgently]

2 hours ago, farmerben said:

Proposal:  A solar powered sterling cycle shaped approximately like a tree or mushroom is deployed in vast numbers to counter global warming.   Instead of an engine, we run it as a heat pump with input electricity.   It radiates heat into the atmosphere and has a cooling effect below the ground level.   It also shades the ground.  It can be deployed in arctic, or hot desert conditions.  It could condense dew and collect rainwater.  It can help preserve sea ice.

If the future brings cheap silicon, aluminum, nearly free electricity, and productivity growth we stipulate that they would be affordable.  I'd prefer one to write my name on one and it leave behind, than a gravestone or a statue.

Does the basic concept work?

Well trees create shade, transpire heat away, and capture carbon, and tree coverage of the planet is blossoming as CO2 increases.  Just saying

Also, as warming increases, so does cloud formation.  Albedo is central to heat throughput, moreso than water vapor of clouds increasing retention

Edited May 6 by darthgently

[AckSed]

24 minutes ago, Shpaget said:

Wouldn't a simple mirror be more efficient?

Maybe so. However, these materials allow other wavelengths of light through, being transparent to translucent to visible light, so you could grow shade-tolerant plants underneath, or have solar panels.

The paper describes a metamaterial that was consistently capable of 5 deg. C of cooling below ambient in Shanghai when it was ~28-30 deg. C and 40% humidity. It was also able to be treated to be hyperhydrophobic, and tough enough to be deemed weather-resistant.

Now, if we wanted to get into active cooling using the IR window, we have to get weirder. Quantum. (I'm climbing out on a brittle limb, so all this is less about, "Why?" and more, "Why not?")

Fortunately, it uses things we can already make: LEDs.

Through physics I don't quite understand, LEDs at higher efficiency take in heat to produce light:

Quote

The scientists claim that highly efficient LEDs should become cold as they emit light. They examined the practical efficiency limits of present optoelectronic technology for cooling applications by optimizing gallium arsenide/indium gallium phosphide (GaAs/GaInP) double heterostructure LEDs. In a practical design, based on presently available optoelectronic materials, they predict their design is capable of reaching an external LED efficiency in excess of 97 percent. Any efficiency above 80 percent produces net cooling.

After optimizing the LED for efficiency, the designed device is projected to emit photons whose energy exceeds the applied voltage, reducing the number of photons wasted as heat. Heat in the form of lattice vibrations makes up for this energy shortfall, leading to a refrigeration effect.

So my thinking is, somehow further optimise the ultra-efficient LED to emit in the 8–13 μm atmospheric window, focus it so that the majority of the IR is directed upwards and you can in fact take the heat, and push it somewhere else. The authors of the paper proper state that at ambient temperature, with the light emitted captured by a PV cell, it has a coefficent of performance of 1.7, better than a thermoelectric cooler. At lower, cryogenic temperatures it's even better.

[insert_name]

This is thermodynamically equivalent to running a freezer with the door open,  due to the second law of thermodynamics it will just generate more heat than doing nothing would

[mikegarrison]

2 hours ago, insert_name said:

This is thermodynamically equivalent to running a freezer with the door open,  due to the second law of thermodynamics it will just generate more heat than doing nothing would

Consider a spacecraft cooling system. It moves heat from inside the spacecraft to the radiators, and due to the Second Law, you end up with more heat in the radiators than you removed. Sounds like a net loss, right? Except having hot radiators is actually good, because then the heat radiates out into the rest of the universe.

That seems to be the idea the OP is going for, except the issue is that it would be as if your radiators were covered by insulating blankets. In that case all you would be doing is getting the radiators hot to no good effect. (The atmosphere is the insulating blanket.)

[kerbiloid]

The warmed atmosphere trnsfers the heat to the ocean.

[darthgently]

4 minutes ago, kerbiloid said:

The warmed atmosphere trnsfers the heat to the ocean.

The oceans are also heated geothermally

[kerbiloid]

25 minutes ago, darthgently said:

The oceans are also heated geothermally

Any excessive heat will add a little more to the ocean temperature.

[darthgently]

40 minutes ago, kerbiloid said:

Any excessive heat will add a little more to the ocean temperature.

Life on earth likely started at undersea geothermal vents.  So, they've been consistent for some time while the surface of the planet went through incredible extremes.   Musk should probably put a human backup colony on the sea floor among the deep ones also

[farmerben]

There is no excessive heat.  We have a heat pump that cools the ground or the ocean directly using solar and wind energy.  It can't compete with trees as a climate balancing system, but it can exist in places where trees can't.

[magnemoe]

5 hours ago, kerbiloid said:

Any excessive heat will add a little more to the ocean temperature.

Only the top layer of the ocean is above 4 centigrade. Its an effect you know from swimming in places with winters, especially lakes as the top one meter is significantly warmer, doing scuba its get colder 20 meter down even in Egypt or Florida so an wet suit is standard. 
It has been ideas of using the temperature difference between the deep ocean and the top to generate power but the height difference require to much power. 

[Terwin]

1 hour ago, farmerben said:

There is no excessive heat.  We have a heat pump that cools the ground or the ocean directly using solar and wind energy.  It can't compete with trees as a climate balancing system, but it can exist in places where trees can't.

The heat must go somewhere and any time you move energy up a gradient (ie moving heat from cool to warm) you generate waste heat.

As the atmosphere acts as a thick blanket, how do you plan to remove more heat from the planet(including the air) than you generate in waste heat?

 

Also, as we are already in an ice age(polar ice caps are NOT normal for the earth nor are glaciers), is further cooling even a good idea?

[insert_name]

10 hours ago, mikegarrison said:

Consider a spacecraft cooling system. It moves heat from inside the spacecraft to the radiators, and due to the Second Law, you end up with more heat in the radiators than you removed. Sounds like a net loss, right? Except having hot radiators is actually good, because then the heat radiates out into the rest of the universe.

That seems to be the idea the OP is going for, except the issue is that it would be as if your radiators were covered by insulating blankets. In that case all you would be doing is getting the radiators hot to no good effect. (The atmosphere is the insulating blanket.)

He said he wanted to heat the atmosphere and use that to cool the ground, going off the spacecraft analogy, this would be like putting the radiator inside of the spacecraft.

[magnemoe]

27 minutes ago, Terwin said:

The heat must go somewhere and any time you move energy up a gradient (ie moving heat from cool to warm) you generate waste heat.

As the atmosphere acts as a thick blanket, how do you plan to remove more heat from the planet(including the air) than you generate in waste heat?

Also, as we are already in an ice age(polar ice caps are NOT normal for the earth nor are glaciers), is further cooling even a good idea?

Well if civilization / industrialization was 10.000 year earlier we would have an climate crisis even without global warming, because the end of the ice age, but it would be an added factor. 
And they would have sea level rises who is not an serious climate change issue, but it would still be slow back then as in hundreds of years before effects except special cases. 
Switching from charcoal to fossil coal in the 19't century was an huge environmental benefit as it stopped deforestation, same as switching from coal to gas in the US. 

But the obvious solution is to build more nuclear plants, yes they have problems but they are pretty local and something you can build around. 

[mikegarrison]

1 minute ago, insert_name said:

He said he wanted to heat the atmosphere and use that to cool the ground, going off the spacecraft analogy, this would be like putting the radiator inside of the spacecraft.

Sort of. The real problem here is not the Second Law. The real problem here is that cooling the Earth below the ground is not the goal.

The issue is that the atmosphere and oceans (which are thermally connected) are too warm and only getting warmer. Bringing more heat from underground into the atmosphere would not help at all. Yes, it would increase radiation into space, but increasing radiation into space is not the real goal. That would be like heating up metal to be red hot in order to cool it, because you know that red hot metal radiates more heat away from itself. But for obvious reasons this would not actually cool the metal, but instead make it warmer.

If we could pump the heat outside of the atmosphere, then the idea would have some possible merit (theoretically, not practically, because of the scales involved). But pumping the heat *inside* the greenhouse will only make the greenhouse hotter.

[Terwin]

27 minutes ago, magnemoe said:

Well if civilization / industrialization was 10.000 year earlier we would have an climate crisis even without global warming, because the end of the ice age, but it would be an added factor. 

Glacial period 

Ice age: somewhere on the planet has year-round Ice (covers the last 2.6my)

Glacial period: glaciers are advancing and covering more of the earth.  last one was 110ky-11.7ky ago

Interglacial period: glaciers are retreating and cover less of the earth .  Includes the last 11.7ky

 

We are still in an ice age.  You can tell by the poles being frozen wastelands.

 

People trying to encourage the next glacial period to start sooner to 'save the planet' make me worry about the goals of modern educational systems.

[darthgently]

42 minutes ago, mikegarrison said:

Sort of. The real problem here is not the Second Law. The real problem here is that cooling the Earth below the ground is not the goal.

The issue is that the atmosphere and oceans (which are thermally connected) are too warm and only getting warmer. Bringing more heat from underground into the atmosphere would not help at all. Yes, it would increase radiation into space, but increasing radiation into space is not the real goal. That would be like heating up metal to be red hot in order to cool it, because you know that red hot metal radiates more heat away from itself. But for obvious reasons this would not actually cool the metal, but instead make it warmer.

If we could pump the heat outside of the atmosphere, then the idea would have some possible merit (theoretically, not practically, because of the scales involved). But pumping the heat *inside* the greenhouse will only make the greenhouse hotter.

As noted in previous replies the atmosphere is nearly transparent to a specific band of IR.  So if one can radiate in that band, the heat is sent to space at just below the speed of light. 

Maybe with zero moving parts or active parts: 

 

Edited May 7 by darthgently

[Nuke]

im wary of renewable energy that requires vast amounts of land to be converted to energy farms.  just build nuclear reactors and let the critters have their habitats.

[magnemoe]

46 minutes ago, Terwin said:

Glacial period 

Ice age: somewhere on the planet has year-round Ice (covers the last 2.6my)

Glacial period: glaciers are advancing and covering more of the earth.  last one was 110ky-11.7ky ago

Interglacial period: glaciers are retreating and cover less of the earth .  Includes the last 11.7ky

We are still in an ice age.  You can tell by the poles being frozen wastelands.

People trying to encourage the next glacial period to start sooner to 'save the planet' make me worry about the goals of modern educational systems.

Its changes current status  who is probably bad for your even if an hotter earth with more oxygen have an much richer ecosystem.
Return of the dog sized spiders and ants is one effect. 

[StrandedonEarth]

18 minutes ago, Nuke said:

im wary of renewable energy that requires vast amounts of land to be converted to energy farms.  just build nuclear reactors and let the critters have their habitats.

PV can be co-located with crops, which benefits certain crops, and adds habitat for pollinators and animal. Win-win-win. Search “Agrivoltaics”

[Nuke]

10 minutes ago, StrandedonEarth said:

PV can be co-located with crops, which benefits certain crops, and adds habitat for pollinators and animal. Win-win-win. Search “Agrivoltaics”

not to say there arent lots of places where you can put solar panels which would otherwise be unused space. over canals, pools, parking lots, roads, roofs. if you are cutting down trees to install solar you are doing it wrong.

[darthgently]

47 minutes ago, Nuke said:

not to say there arent lots of places where you can put solar panels which would otherwise be unused space. over canals, pools, parking lots, roads, roofs. if you are cutting down trees to install solar you are doing it wrong.

Just remember that wherever you put them, you'll need to run and maintain wiring to them.  Don't underestimate the "maintain" part

[Nuke]

3 hours ago, darthgently said:

Just remember that wherever you put them, you'll need to run and maintain wiring to them.  Don't underestimate the "maintain" part

i live in a fishing town, i know. had more than one wiring harnesses that just became one big wire over time.

Edited May 8 by Nuke