So,

I've been thinking about this on and off for awhile now. It first started with the idea of a solar trap.

Solar trap being something like having a solar collector focusing light on a container of water, having an infra red barrier around the container, and a black body at the centre. Incoming solar energy passes by the IR reflector, absorbed by the black body and re-emitted as radiation which is reflected by the IR reflector.

I was pleasantly surprised some form of this technique is used in the high efficiency solar water heaters.

So what stops one doing this in reverse? having a visible reflector, IR transmitting layer.

Could this allow solar cooling during the day? It would of course depend on the net flux of radiation, perhaps looking at natural sunlight spectrum there maybe a band strongly absorbed by the atmosphere that is within the range put out by a black body.
-- lostmind, Jun 11 2012

black body radiation http://www.spectral...lator/blackbody.php
basic calculator for black body radiation [lostmind, Jun 12 2012]

solar radiation http://solar.energy.free.fr/sld018.htm
solar radiation spectrum [lostmind, Jun 12 2012]

cold mirror http://en.wikipedia.org/wiki/Cold_mirror
effectively what I was thinking of [lostmind, Jun 12 2012]

Night Sky Cooling http://cedarmountai...p?PageID=5_TrueID=5
Half-baked version which works only at night [goldbb, Jun 14 2012]

I'm thinking something like chrome tube going into a two-piece, thick ceramic container, with a black water tank. The light is reflected down the tune into the container.

The inside of the ceramic container surface would be many wedges, flash-deposited with aluminium, to maximise light bounces to make sure most of it hits the water tank and is not reflected straight back out again.

Or is that needlessly over-complicated?
-- not_morrison_rm, Jun 12 2012


How dare you ask such a question within these hallowed halls?! That kind of thinking flies in the face of Halfbakery tradition and values going back centuries!
-- Alterother, Jun 12 2012


It's not going to work well during the day, as the net radiation would not tend to be favorable. It should work as a heat dump during the night, allowing the cooling of a heat sink, which is then used during the day. It wouldn't be wonderfully efficient.

There is at least one short story that more or less uses this as a premise, by rejecting the local heat to space, they create a large(ish) low pressure system to pull in rain. It was published in Analog something over 8 years ago, so I can't remember any more detail.
-- MechE, Jun 12 2012


I think you could use it during the day, though it depends what the sky's radiation in the range of 1-10 micron (approx range of a black body at 300K) is. The solar spectrum in this region is minimal (see link) while the black body puts out up to 250W/m^2/um
-- lostmind, Jun 12 2012


If you can find a low cost filter that reflects below about 2 micron, then maybe. Below that point, the sun wins. Good luck on the low cost though, I've been looking for that sort of thing for professional reasons, without much luck.

Also remember that you won't have a perfect black body. You can get within a few percent if you're willing to spend money and don't need it to resist damage, but it's still going to be on the wrong side, as is the less than perfect filter, and the less than perfect reflection of every mirrored component in the system.

I'm not saying it's not possible, I'm saying the ROI is going to be poor.
-- MechE, Jun 12 2012


i wonder if silicon could do the deed. Useful Wavelength Range (Transmission) – 1.06μm to 6.7μm & 30μm to FIR

it's narrow though
-- lostmind, Jun 12 2012


well, i found what i was thinking of. a cold mirror
-- lostmind, Jun 12 2012


There is nothing new under the sun.
-- UnaBubba, Jun 12 2012


//Incoming solar energy passes by the IR reflector, absorbed by the black body and re-emitted as radiation which is reflected by the IR reflector.//

Isn't this more-or-less a greenhouse?
-- Wrongfellow, Jun 12 2012


//There is nothing new under the sun.

Yes, but the area under our sun must be quite small relatively speaking. Which would presumably include all the space that is far enough away to get none of our sun's light as our sun wasn't around then.

So, cosmically speaking there's a lot of area not under our sun, a very long way away. That doesn't really help us if that's where the really new things are being stored.

I must get out more often.
-- not_morrison_rm, Jun 12 2012


//     the area under our sun must be quite small relatively speaking. //

Au contraire, mon frere.

The Sun is a sphere; other than points arbitrarily designated as poles based on the planar orientation of the Solar System, it has no identifiable top and bottom. It is surrounded by literally everything in the Universe, and because it is omniradial, it likewise faces everything in the Universe. Therefore, depending on how one chooses to define one's own relative geometrical position, the Sun is either over, under, or beside everything.

So, from an heliocentric standpoint, this means that the area 'under' the Sun is actually a very, very large area, and that 'everything under the Sun' is, in fact, everything.
-- Alterother, Jun 12 2012


//other than points arbitrarily designated as poles based on the planar orientation of the Solar System, it has no identifiable top and bottom.//

Not so - the sun rotates, and hence has definite poles.
-- MaxwellBuchanan, Jun 12 2012


But... but... which way is up?
-- lurch, Jun 12 2012


A "Reverse solar collector" is called a light bulb.
-- sqeaketh the wheel, Jun 12 2012


I am elucidated. I think?

So, all the new stuff is currently being stored in the centre of the sun?

<starts preparing for trip to centre of the sun, ponders - now a layer of sunblock 1m metre thick needs how many bottles...>
-- not_morrison_rm, Jun 12 2012


Okay, it has poles... If I'd been thinking, I would have realized that it would just fly apart if it were apolar. Lack of EM field integrity and all that.

But I stand by my claim that, from the heliocentric perspective, every direction is down. Or up. There's not really any difference on the cosmic scale.
-- Alterother, Jun 13 2012


Thinking there must be some neutral zone, either inside the sun, or perhaps equidistant from another sun, so both their unders cancel each other out?
-- not_morrison_rm, Jun 13 2012


Seeing 'under' is a definition relying on gravity, you could pick some distance where the sun's gravity is no longer detectable by our best existing equipment although this would vary as equipment and techniques got better. A less controversial method would be to define anything being outside a sphere 4.5 billion light years in radius as not "being under the sun" as that is the approximate age of Sol so gravity waves (or anything else) could not reach there yet.
-- AusCan531, Jun 13 2012


Oddly, the sun rotates faster (about once every 25 Earth days) at its equator than it does nearer its poles, where a rotation takes about 38 Earth days.

I would suggest anything within the sun's light zone is "under the sun", if you can see it from 4.5 billion light years.
-- UnaBubba, Jun 13 2012


Choose any table in any room in your house ('room' here being defined as any space delineated by a floor, a ceiling, and any number of walls). Place a book on top of the table. The book is under the ceiling, yes? Now place the book under the table. Is the book not still under the ceiling?

By extension, just because the Sun's rays do not fall upon a particular object or area does not mean that said object or area is exempt from being under the Sun, presuming the observation is being made from the perspective of the Sun (which is implied in the syntax of the saying).

And likewise, I don't see how gravity has anything to do with what is 'under' or 'over' anything else. It all has to do with relativistic spatial orientation. Under or over is defined by the observer's point of view. If I stand on my head, I can make a valid argument that the floor is above the ceiling and that the book sitting on the floor is over the table.
-- Alterother, Jun 13 2012


//If I stand on my head, I can make a valid argument// - ah - but can you drink a cup of tea at the same time? or paint the pincers of an earwig whilst completing a soduko with your toes? These are demanding times, and new skills are needed.
-- xenzag, Jun 13 2012


// but can you drink a cup of tea at the same time? //

If you give me a straw.

// or paint the pincers of an earwig //

One of my hobbies is painting very small things, so yes. I even have my own brushes.

// whilst completing a soduko with your toes? //

If it's an easy one, printed very large, and you give me all afternoon. I really suck at soduko. I rock the NYT crossword, though.

So do you see what I mean now?
-- Alterother, Jun 13 2012


No-one *really* sees what you mean, [Alter]. I think you need to properly define or redefine "see" and to use more words to describe your past experiences, current predicaments and future intentions and aspirations... regale us with a lot more of your homilies and apparent humility, as it were.

After all, seeing is believing.
-- UnaBubba, Jun 13 2012


// If I stand on my head, I can make a valid argument that the floor is above the ceiling// I hope you can make a valid argument whilst holding your breath, as according to your definition you're under the Atlantic Ocean.

I think that the better definition of "under" is between one object and the centre of the local, dominant gravitational (or pseudo-gravitational) pull ie the Earth's when we're on the planet and the Sun's when we're toodling around the Solar System. Everything is relative of course, but as a practical working definition, this one works best.
-- AusCan531, Jun 14 2012


// Oddly, the sun rotates faster (about once every 25 Earth days) at its equator than it does nearer its poles, where a rotation takes about 38 Earth days. //
So, the Sun is all twisted up, like an old phone cable?
-- AbsintheWithoutLeave, Jun 14 2012


I guess it must be. Can you imagine how much farther its light and heat would reach, if someone were to untwist it?
-- UnaBubba, Jun 14 2012


I'm still reeling from "The Sun has got poles"...I mean, where did they stick the flag?
-- Ling, Jun 14 2012


//Can you imagine how much farther its light and heat would reach, if someone were to untwist it?//
But I took a rubber band and twisted it for just a few minutes (it's a slack afternoon) and it snapped.
I know the Sun is a bit bigger, but it's been doing this for 4 billion years - when that goes, I don't want to be around.
-- AbsintheWithoutLeave, Jun 14 2012


Under and over are terms relative to the observer's gravitational direction. If I am under a table, turning the table upside down does not make me over the table. During the day, I am under the sun. At night, the sun is under my feet. Therefore, one can only have new ideas at night.

If the sun is considered to be the observer, down is the centre of the galaxy, which would mean that one could only have good ideas for 6 months of the year. (Any astronomy nerd know which 6 months?)
-- marklar, Jun 14 2012


//     use more words to describe your past experiences, current predicaments and future intentions and aspirations... regale us with a lot more of your homilies and apparent humility, as it were.   //

Your wish, sir, is my command.
-- Alterother, Jun 15 2012


ironically, I do seem to have come up with something entirely new, the mock-butt toaster, but would prefer that not to be my lasting contribution to western civilisation...
-- not_morrison_rm, Jun 16 2012



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