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Night Sky Heat Sink For Electric Generation

Use night sky radiative cooling to cool down blocks of mud to very cold temperatures and use them as heat sinks for electricity generation
  [vote for,

Low grade heat is cheap. If you paint something black and leave it in sunlight, it can easily reach 40-60C temperatures. If you drill down a kilometre, the rocks are 40C. Not enough to boil water, but enough to have a bath or heat homes. Which takes up a significant fraction of our energy use in Britain, so that's quite something as it is.

However, we can't generate appreciable electricity from it. The temperature differences between the heat source and ambient are too low to get much power, and at a very low efficiency.

But what if we could instead use far colder heat sinks? Say, by radiating away excess heat to the night sky?

If it wasn't for our atmosphere (I am NOT advocating we remove the atmosphere), the night sky would make an excellent sink, at a temperature of only 3K above absolute zero. Unfortunately for radiative cooling, we have an atmosphere, and clouds, and these absorb heat and reradiate it at night. On cloudless nights when the temperature is low enough but above freezing, it is possible to produce ice, but getting below this without help is difficult.

Enter the help. In 2014, researchers at Stanford University demonstrated it was possible to achieve radiative cooling in the daytime with an appropriately doped radiator. If it can be made to emit infrared in the window the atmosphere is transparent to, 8-14 micrometres, and reflect enough of the other light hitting it, it is possible to radiate enough energy to reduce temperatures by *42 degrees celcius at midday*. In California.

So. What if we were to use this advance to improve nighttime radiative cooling, and use it to freeze a large heatsink, a block of mud perhaps? During the day this could then be used with an appropriate heat source, whether geo or solar thermal, to produce electricity. It wouldn't be small, but we're not trying to power a vehicle here (someone will suggest we try to power a vehicle).

If, say, we can create a heat sink temperature of 240K, and a heat source of 330K (achievable by simple flat plate solar collectors), the Carnot efficiency would be 21%. Real world heat engines achieve, afaict from searching the internet, about 75% of the theoretical maximum, so we might achieve 15% efficiency of converting the sunlight into electricity. Not as high as the 20% that is typical for solar PV, but this system would incorporate thermal storage by design, enabling it to deliver power consistently and when it is needed (not *right* when its needed, not like gas turbines, but the demand is relatively predictable). Perhaps further optimisations will give us colder sinks and hotter sources. We could also use goethermal, avoiding any reliance on sunlight entirely.

This wasn't something that we could have built nine years ago. I'm somewhat excited by it. Partly because it's unusual enough to flummox the usual crowd of people who don't want Britain to build any energy generation.

Selky, Jan 30 2023

Nighttime Radiative Cooling Paper http://gcep.stanfor...diative_Cooling.pdf
A paper detailing actual and theoretical cooling achievable. [Selky, Jan 30 2023]

Persian Ice House https://www.fieldst...ow-make-ice-desert/
How to make ice in the desert. [Selky, Jan 30 2023]

The classic Cosmic Background Refrigeration
//The desert is hot, but space is c-c-c-cold.// [pocmloc, Jan 30 2023]

radiative cooled water condenser
[xaviergisz, Feb 03 2023]

SkyCool Systems https://www.skycoolsystems.com/
You can buy these now [BunsenHoneydew, Feb 25 2023]


       We beat night cooling to death and fed it through the mincer and turned it into tesco value sausages on the linked idea.   

       But the idea of using the difference for energy generation is novel and good so [+]   

       Also, if you put wheels on this do you think you could use this system to power a vehicle?
pocmloc, Jan 30 2023

       Nice. There's another way to make ice in the desert which the ancients knew of. If you fill a reflective parabolic bowl with water and insulate the outside of the bowl then the water will freeze on a cloudless night even if ambient air temperature stayed above zero.   

       I've got an old 12 ft diameter satellite dish and a bunch of reflective mylar balloon material kicking around.
One of the experiments I want to try is seeing if I can get a five gallon bucket of water suspended at its focal point to freeze in the summer.


       So Halfbakery was already talking about selective radiative surfaces in 2006, eight years before the idea was baked in Stanford?   

       How many other things has this happened to I wonder...
Selky, Jan 30 2023

       Don't blame me, I didn't join until 2009!   

       (though I will confess to reading for years before signing up)
pocmloc, Jan 30 2023

       //How many other things has this happened to I wonder...//   

       Over the years many things have been posted here before any cited research.   


       don't tell anybody...   

       Boeing got a patent for something almost identical to one of my ideas, a couple of years after. I e-mailed the Patent Office to complain about their lack of prior-art search, but they were all "too late, you should have complained earlier". Idiots.
neutrinos_shadow, Feb 02 2023

       [n_s], they don't search halfbakery for prior art? That's not right. Sites like this, and various minor internet forums, would probably invalidate a good number of patents if they looked for prior art on them.
Selky, Feb 03 2023

       [n_s] you can request re-examination and they will reassess the patent. Unfortunately this costs a bit (e.g. $1,500 for a US patent). Although halfbakery ideas are occasionally cited as prior art during examination, the ideas here are usually not considered "enabling disclosures". That is, there is usually not enough detail in the ideas posted to allow an engineer to produce the invention.
xaviergisz, Feb 03 2023

       (I'll shift this discussion to the relevant post, my Fusion Beam.)
neutrinos_shadow, Feb 06 2023

       //reflective parabolic bowl//   

       Can someone explain why reflective is important? Shirley we're losing heat by IR emissivity? So we'd want a very black surface? Reflective surfaces emit very little, hence why the USAF is putting mirrored coatings on F22s to make them less detectable by FLIR.   

       //Boeing got a patent for something almost identical to one of my ideas,//   

       The US patent system is broken. I've had a few patentable ideas, I was put in touch with a couple of guys in my field who were further over into that area of things at MUCH bigger name universities. They both said, along the lines of: Don't bother. The patent will advertise the technology, if it can be sidestepped it will be and you'll be out of the loop. If it can't they'll contact you and say "we're going to infringe on your patent". It's then your job to defend it, which you will not be able to sustain. Universities, no matter the size, don't help in this regard in a meaningful way. Perhaps if higher-ups are personally involved, or the law dept. feels like a challenge. All that for 20 years. Semi-monopolized industries can just wait. Your only hope is the secret-sauce method.   

       I've been contacted by two organizations asking me to take ideas down. I haven't, to an extent out of principle, but mostly because they didn't even offer me a nice pen or anything.
bs0u0155, Feb 07 2023

       //I've been contacted by two organizations asking me to take ideas down// Do tell. I am jealous because I have never had such contact. Maybe because my ideas are too stupid. Also maybe because I never check the email address listed on this site.
pocmloc, Feb 07 2023

       //because I never check the email address listed on this site// I think we have a winner. One idea was the water heater with a eutectic/phase change wax chamber, so that the temperature of a hot water heater/tank output wouldn't change as you used it. Realistically, it means you could scale heater/tanks down dramatically. The other was mitochondrial gene therapy. Opposite ends of the scale really.
bs0u0155, Feb 07 2023


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