Can a Reverse Solar Trap Enable Solar Cooling?

[lostminty]

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.

 

[Bobbywhy]

For many graphs of atmospheric transmission and absorption and further references, you may go here:
http://www.google.com/search?q=atmo...gW-hLiaDw&sqi=2&ved=0CGMQsAQ&biw=1286&bih=621

 

[lostminty]

found this

http://www.ispoptics.com/Images/MaterialChart.gif

Germanium seems a good candidate, for a better view

http://rmico.com/technical-notes/bk7-quartz-ge-si

in particular

based on this calculator
http://www.calctool.org/CALC/phys/p_thermo/wien

peak radiance of a 300 K object is 10 μm

there's some absorbance around that wavelength

 

[lostminty]

So, after a bt of googling. This turns out to exist.

A cold mirror

http://en.wikipedia.org/wiki/Cold_mirror

Although, they don't quite cover the spectrum that would be optimal, the limit currently for commerical mirrors is up to 2500nm,This is usually layered dialectric coatings.

really want that to be transmissive between 2500nm and 15000nm.

Germanium does a good job, although the ROI would be terrible, silicon, which does about 1600-7000nm would be ok, though I am guessing cost wise it wouldn't be much better.